pro Powerstep

Transcrição

pro Powerstep

Ano 11 Revista nº 41
ABR/MAI/JUN - 2009
Por que não o equilíbrio?
Balance: why not?
Conexão de PCHs com mais luz
ACF Maria Carneiro
SHP connection with more light
Comitê Diretor do CERPCH
Director Committee
Geraldo Lúcio Tiago Filho
Secretário Executivo
[email protected]
Gilberto Moura Valle Filho
CEMIG
[email protected]
Patrícia Cristina P. Silva
FAPEPE
[email protected]
Célio Bermann
IEE/USP
[email protected]
Cláudio G. Branco da Motta
FURNAS
[email protected]
José Carlos César Amorim
Editorial
Editorial
IME
[email protected]
Antonio Marcos Rennó Azevedo
[email protected]
Eletrobrás
Jamil Abid
ANEEL
[email protected]
Hamiltom Mossh
Legislação
MME
[email protected]
Legislation
Comitê Editorial
Editorial Committee
Presidente - President
Geraldo Lúcio Tiago Filho - CERPCH UNIFEI
Editores Associados - Associated Publishers
Adair Matins - UNCOMA - Argentina
Alexander Gajic – University of Serbia
Alexandre Kepler Soares - UFMT
Ângelo Rezek - ISEE UNIFEI
Antônio Brasil Jr. - UNB
Artur de Souza Moret - UNIR
Augusto Nelson Carvalho Viana - IRN UNIFEI
Bernhard Pelikan - Bodenkultur Wien – Áustria
Carlos Barreira Martines - UFMG
Célio Bermann - IEE USP
Edmar Luiz Fagundes de Almeira - UFRJ
Fernando Monteiro Figueiredo - UNB
Frederico Mauad – USP
Helder Queiroz Pinto Jr. - UFRJ
Jaime Espinoza - USM - Chile
José Carlos César Amorim - IME
Marcelo Marques - IPH UFRGS
Marcos Aurélio V. de Freitas - COPPE UFRJ
Maria Inês Nogueira Alvarenga - IRN UNIFEI
Orlando Aníbal Audisio - UNCOMA - Argentina
Osvaldo Livio Soliano Pereira - UNIFACS
Zulcy de Souza - LHPCH UNIFEI
Projeto Gráfico
Diagramação e Arte
Tradução
Equipe Técnica
Artigos Técnicos
Technical Articles
Agenda
Schedule
13
37
Opinion
Camila Rocha Galhardo
Adriana Barbosa MTb-MG 05984
Adriana Barbosa
Camila Rocha Galhardo
Fabiana Gama Viana e
Fábio Couto
Orange Design
Adriano Silva Bastos
Adriana Candal
Cidy Sampaio da Silva
04
Balance: why not?
Opinião
Expediente
Editorial
Editor
Coord. Redação
Jornalista Resp.
Redação
03
38
Interligação e conexão de PCHs
SHP Connection and Interconnection
Curtas
News
40
PCH Notícias & SHP News
é uma publicação trimestral do CERPCH
The PCH Notícias & SHP News
is a three-month period publication made by CERPCH
Tiragem/Edition: 5.500 exemplares/issues
contato comercial: [email protected]
Av. BPS, 1303 - Bairro Pinheirinho
Itajubá - MG - Brasil - cep: 37500-903
e-mail: [email protected]
[email protected]
Fax/Tel: (+55 35) 3629 1443
ISSN 1676-0220
00041
9 771676 022092
02
ICOLD E CBDB realizam o 23º Congresso Internacional de Grandes Barragens
ICOLD and CBDB hold 23th International Meeting of Large Dams
Delegação do Brasil participa de evento internacional de PCH
Brazilian delegation participates in international event on SHPs
Limpador de Grades gera eficiência em PCH
First SAUR trash rake cleaning increases SHP efficiency
Prezados Leitores.
Dear readers,
A revista PCH Notícias & SHP News aborda, nesta edição, o deslocamento ambiental causado pelas construções de barragens de
hidrelétricas. A construção de grandes hidrelétricas e, consequentemente, suas barragens ocasionam uma série de impactos sociais
e ambientais negativos. No Brasil, por conta de sua opção energética por grandes empreendimentos hidrelétricos, essa questão torna-se ainda mais presente.
This edition of the magazine PCH Notícias & SHP News talks
about population displacement caused by the construction of the
dams of hydropower plants. The construction of large hydropower
plants and, consequently, their dams cause a series of negative social and environmental impacts. In Brazil, because of the option for
large hydropower enterprises, this issue becomes is even more significant.
Nessa matéria procuramos abordar toda a problemática envolvendo o deslocamento de comunidades causadas pelas barragens.
In that article we try to focus on the whole problem involving
comunity displacement caused by the dams.
Outro tema abordado nesta edição é o que diz respeito aos Procedimentos de Distribuição (Prodist), que foram aprovados pela
Agência Nacional de Energia Elétrica (Aneel) em dezembro de
2008, por meio da resolução 345/2008.
This magazine also approaches another topic that regards the
Distribution Procedures (Prodist), which were approved by Aneel
(Resolution 345/2008) in December, 2008.
Nosso leitor pode acompanhar, nesta edição, a cobertura do
23º Congresso da Internacional de Grandes Barragens promovido
pela Comissão Internacional de Grandes Barragens (ICOLDCIBG), e organizado pelo Comitê Brasileiro de Grandes Barragens
(CBDB), entre os dias 24 e 29 de maio, em Brasília.
Aproveito a oportunidade para salientar que temas como o papel das PCHs e demais fontes renováveis no desenvolvimento da
matriz energética brasileira, Mercado e Meio Ambiente serão apresentados e debatidos em nossa 5ª Conferência que será realizada
nos dias 5 e 6 de agosto, em São Paulo. Reitero aqui o convite a todos nossos leitores para que participem conosco desse encontro.
Mais informações podem ser obtidas no site: www.conferenciadepch.com.br.
Por fim, gostaria de informar que para melhor disseminar a pesquisa acadêmica nacional e internacional a partir da edição nº 41
estaremos ampliando nossa sessão técnica para artigos das áreas
de Recursos Hídricos, Meio Ambiente e Energias renováveis e não
renováveis.
Our reader can follow the covering of the 23rd International
Meeting of Large Dams promoted by the International Commission
of Large Dams (ICOLD-CIBG), and organized by the Brazilian Committee of Large Dams (CBDB) in Brasilia between May 24th and
29th.
I also want to use this opportunity to highlight that topics such
as the role of SHPs and of other renewables in the development of
the Brazilian energy matrix, market and environment will also be
presented and debated during our 5th Conference that will be held
in São Paulo on August 5th and 6th. Again, I would like to invite all
the readers to participate in the event. For more information:
www.conferenciadepch.com.br.
Finally, I would like to inform that we will increase the technical
segment of our magazine from issue 41 and on in order to disseminate more national and international researches covering the areas of Water resources, Environment, Renewable and NonRenewable Energy.
03
LEGISLAÇÃO
Por Fabiana Gama Viana
Quando se fala na construção de uma grande hidrelétrica, logo se pensa nos impactos sociais e ambientais inerentes a esse tipo de
empreendimento e no embate entre as entidades representativas das populações atingidas e os empreendedores. Não se pode considerar a geração de energia elétrica como algo negativo dentro de uma nação, pois ela certamente representa desenvolvimento e melhores
condições de vida para as populações atendidas. E obviamente quem defende as populações atingidas por esse tipo de empreendimento
não é contra a energia elétrica e, muito menos, o desenvolvimento.
Via de regra, a construção de grandes hidrelétricas e, consequentemente, suas barragens ocasionam uma série de impactos sociais
e ambientais negativos. No Brasil, por conta de sua opção energética por grandes empreendimentos hidrelétricos, essa problemática torna-se ainda mais presente.
Mesmo com todos os estudos ambientais prévios feitos, as ações de mitigação desses impactos podem não ser totalmente eficazes,
não compensando todos os efeitos negativos. O grande impacto causado por esses empreendimentos é o alagamento de grandes áreas,
ocasionando sérios e irreversíveis problemas ambientais e o deslocamento compulsório das populações que viviam na área do alagamento. Em relação a este último, as populações são atingidas direta e indiretamente com perdas e danos individuais e coletivos, materiais e imateriais, os quais mesmo depois de anos após a conclusão das obras ainda são sentidos.
Impactos Sociais
O impacto mais evidente é a perda de terras, casas e espaços
comuns, como igrejas, escolas e comércios. Entretanto, há vários
outros danos menos evidentes, como a destruição de laços e redes sociais. No caso de grupos indígenas e minorias étnicas, esse
tipo de impacto pode ser ainda maior devido à forte ligação espiritual e cultural com o território.
Vale ressaltar também uma maior incidência de casos de
stress, depressão e suicídios nessas comunidades, além das doenças sexualmente transmissíveis e parasitárias (esquistossomose
e malária, por exemplo), já que as barragens propiciam ambiente
favorável à proliferação de mosquitos, caramujos e outros animais transmissores dessas doenças.
Merece destaque ainda o tempo de viabilização (projeto e construção) de uma grande hidrelétrica. Nesse sentido, a partir do momento em que a construção de uma barragem é anunciada, a população a ser atingida começa a sofrer com a interrupção de investimentos públicos e privados. Dessa forma, os bancos deixam
de emprestar dinheiro, escolas e hospitais não são construídos,
serviços são interrompidos e mesmo as famílias deixam de investir na melhoria de suas terras e casas. Associado a isso, há a incerteza da população que desconhece quando e se de fato a barragem será construída, quantas casas e propriedades serão inundadas, quem será atingido e qual o valor da compensação.
Deslocamento Populacional Compulsório
Não se sabe ao certo quantas pessoas foram deslocadas até hoje por conta das barragens. A Comissão Mundial de Barragens, a
partir de dados de 2003, estima que esse número seja de 40 a 80
milhões. O Movimento dos Atingidos por Barragens (MAB), hoje o
principal movimento popular nacional de resistência à construção
de barragens, estima em 1 milhão de pessoas deslocadas em 130
anos de construção de barragens no Brasil e mais de 34 mil km2
de hectares de terras encobertos pelos reservatórios. Segundo Decio Michellis Jr., vice-presidente de engenharia e meio ambiente
da Rede Energia, esta estimativa é razoável, considerando que o
MAB contempla inclusive a modificação e/ou perda de laços familiares e o rearranjo ou a desagregação de famílias decorrentes da dinâmica de deslocamento populacional das famílias realocadas.
De acordo com a pesquisadora Raquel de Matos Viana, autora
do trabalho Grandes Barragens, Impactos e Reparações: um estudo de caso sobre a barragem de Itá (2003), a imprecisão na definição do número de atingidos está diretamente relacionada a um
problema maior: a definição do conceito de atingido. Segundo Via-
04
na, a maior parte das contagens feitas por governos e empresas
determina como atingidos pelos empreendimentos apenas as famílias deslocadas devido ao enchimento do reservatório e que possuem o título de propriedade. Dessa forma, acabam ficando de fora desses levantamentos as populações à montante e à jusante da
barragem, os posseiros e aqueles que não possuem o título de propriedade, além das populações deslocadas por conta de outras partes do empreendimento, como linhas de transmissão, por exemplo. Também não entram na contagem, aponta a pesquisadora, as
famílias que perdem suas terras ou parte delas, mas que permanecem com suas casas, as pessoas que vivem nas ilhas formadas
pelo reservatório e aquelas que fazem uso das terras comuns para
cultivo de frutos, vegetais, madeira e criação de gado e que têm o
acesso obstruído por conta da destruição e alagamento de estradas e acesso a escolas, hospitais, comércio e outros.
Ricardo Pigatto, presidente da Associação Brasileira dos Pequenos e Médios Produtores de Energia Elétrica (APMPE), explica
que, na fase de inventário, faz-se a primeira análise desse quesito, com o levantamento fundiário. Dessa forma, em função dos resultados obtidos e das consequências que a formação dos reservatórios pode trazer às comunidades e patrimônio histórico, definem-se as partições e potências das usinas. “Por questões 'oportunísticas' e, às vezes, levados por movimentos sociais assistencialistas, a população ao saber que haverá um aproveitamento hidrelétrico em um determinado local busca criar formas de alcançar benefícios não previstos originalmente”, lamenta Pigatto.
O vice-presidente de engenharia e meio ambiente da Rede
Energia, Decio Michellis, completa dizendo, nas últimas décadas,
o processo de licenciamento ambiental é meticuloso e detalhado
na definição de critérios para enquadramento como impactado pelos empreendimentos. Segundo Michellis, os últimos empreendimentos têm instalado comissões tripartites – impactados, empreendedores e poder público, com o acompanhamento do Ministério
Público – para tratar dos casos omissos, não previstos nos critérios de tratamento das populações impactadas pelos empreendimentos.
Michellis ainda destaca que as políticas operacionais dos agentes financiadores aplicáveis aos reassentamentos involuntários
também contribuíram para reduzir as distorções regionais. “Os
Princípios do Equador [criados pelo International Finance Corporation (IFC), instituição vinculada ao Banco Mundial] têm aglomerado um número crescente de bancos internacionais de primeira linha que passaram a incluir critérios de avaliação socioambiental
nas atividades de project finance e concessão de crédito”, explica.
E as pequenas centrais hidrelétricas?
LEGISLATION
Balance: why not?
Translation Adriana Candal
When the talk is about building a large hydropower plant, the first thought that come to our minds regard the social and environmental impacts that are inherent in this type of enterprise and in the arguments between the entities that represent the families and the entrepreneurs. Energy generation cannot be considered as something negative in the nation, given that it certainly represents development and better life conditions for the population. Obviously, the entities that defend the population in regards to this type of enterprise
are not against electric power, let alone, development.
Generally, the construction of large hydropower plants and, consequently, their dams cause a series of negative social and environmental impacts. As Brazil has chosen for this type of energy generation, carried out by large hydropower enterprises, this problem becomes even more present.
Even with all of the previous environmental studies that are carried out, the mitigation actions may not be completely efficacious and
they may not compensate all the negative effects. The greatest impact caused by this type of enterprise is the flooding of large areas,
causing serious and irreversible environmental problems and the mandatory displacement of the families who used to live in those areas. In relation to the latter, the population is hit directly and indirectly with individual and collective and material and non-material
losses, which are felt even many years after the works have been concluded.
Social Impacts
The most evident impact regards the loss of lands, houses and
public spaces such as churches, schools and shops. However, there are other more subtle damages such as the destruction of social
bonds and networks. In case of native Indian and ethical minority
groups, this type of impact may be even worse due to the strong
spiritual and cultural bond with their territory.
It is also important to highlight the existence of a higher number of cases of stress, depression and suicides within these communities, as well as more cases of sexually transmitted diseases
and parasitic diseases such as schistosomiasis and malaria, for
example, given that the dams provide a favorable environment for
the proliferation of mosquitoes, snails and other animals that
transmit these diseases.
The feasibility time (project and construction) of a large hydropower plant also deserves attention. In this case, as soon as the
construction of a dam is announced, the population of the area
starts to suffer with the interruption of public and private investments. This way, banks stop lending money, schools and hospitals
are not built, services are interrupted and even the families stop investing in the improvement of the properties. In addition, there is
the uncertainty; the population does not know when or whether
the dam will really be constructed, whose and how many properties will be flooded and the compensation value.
Mandatory Population Displacement
It is not certain how many people have been displaced so far
because of the construction of dams. Based on data from 2003,
the World Commission on Dams estimate this number to range between 40 and 80 million people. The people that were affected by
dams created a movement and it is the most important popular
movement of the country against the construction of dams, estimate that 1 million people have been displaced over 130 years in
Brazil and more than 34 thousand square kilometers of land have
been flooded by the reservoirs. According to Mr. Decio Michellis Jr.,
vice-president of engineering and environment of Rede Energia,
this figure is reasonable, considering that the MAB takes into account the modification and/or losses of family ties and the rearrangement or disaggregation of families caused by the population
displacement dynamics of the resettled families.
According to researcher Raquel de Matos Viana, author of “Large Dams, Impacts and Repairs: a case study about the Itá (2003),
the lack of accuracy in order to define the number of people that
were affected is directly related to a bigger problem: the definition
of the concept of “affected”. According to Viana most of the calculations carried out by governments and companies determine as
“affected” by the enterprise only the families that were displaced
because of the reservoir and that have the ownership document.
This way, the populations downstream and upstream of the dam,
those who live on the land but do not own it and those who do not
have an ownership certificate, in addition to the population that
was displaced because of other parts of the enterprise such as power lines, for example, are not taken into account. Also, the researcher did not take into account the families that lost their lands or
part of them, but kept their houses, people that live in the islands
created by the reservoir and those, who use common land for growing fruit, vegetables, wood and for livestock, whose access is
blocked because of the destruction and flooding of roads and
paths that lead to schools, hospitals, shops, etc.
Mr. Ricardo Pigatto, president of the APMPE (Brazilian association of small and medium electric power producers) explains that
the first part of the inventory stage is the asset analysis. This way,
based on the results and on the consequences that the formation
of reservoirs may bring to the communities and historical heritage, the partitions and power of the plant are defined. “Due to 'opportunistic' issues, which are sometimes led by social movements, the population, knowing that there will be a hydropower at
a certain place, looks for ways to reach benefits that were not originally forecast”, regrets Mr. Pigatto.
The vice-president of engineering and environment of Rede
Energia, Mr. Decio Michellis, states that within the past decades
the environmental licensing process has been meticulous and detailed regarding the definition of the criteria for the classification
of the impacts the enterprises will cause. According to Mr. Michellis
the last enterprises have installed tripartites commissions– the impacted population, the entrepreneurs and the public power;
everything followed by the Public Ministry to deal with the cases
that are not forecast in the criteria regarding the way to treat the
population that will suffer the impacts caused by the enterprises.
Mr. Michellis highlights that the operational policies of the funding agents that are applied to the involuntary resettlements also
contributed to the reduction of regional distortions. “Equator principals [created by the International Finance Corporation (IFC), an
institution associated to the World Bank] have gathered an increasing number of international banks that started to include socioenvironmental assessment criteria in their project finance activities and credit concessions”, he explains.
05
LEGISLAÇÃO
Por definição da Resolução nº 394/1998 da Agência Nacional
de Energia Elétrica (ANEEL), as pequenas centrais hidrelétricas
são empreendimentos de pequeno porte cuja capacidade instalada seja superior a 1 MW e inferior a 30 MW, com área do reservató2
2
rio inferior a 3 km , podendo chegar a 13 km em casos específicos, de acordo com Resolução nº 652/2003. Uma PCH típica opera
normalmente a fio d'água, ou seja, o reservatório não permite a regularização do fluxo de água. As pequenas centrais estão localizadas em rios de pequeno e médio portes com grandes desníveis em
todo o seu percurso, gerando potência hidráulica suficiente para
movimentar as turbinas.
Os pequenos empreendimentos hidroenergéticos estão entre
as opções defendidas por grande parte dos ambientalistas, sendo
colocados no mesmo patamar que outras formas de geração de
energia elétrica, como eólica, biomassa e solar. As vantagens das
PCHs são inúmeras frente às grandes hidrelétricas.
Vantagens das PCHs
Como as PCHs são centrais do tipo fio d'água, ou seja, sem armazenamento de água, não há necessidade de formação de grandes reservatórios. Dessa forma, o impacto ocasionado por uma
PCH é diminuto em comparação às UHEs (usinas hidrelétricas), pois não há grande interferência no regime do rio e uma menor quantidade de área é desmatada e menos terras desapropriadas.
Da mesma forma, há menores perdas na transmissão de energia elétrica por conta da energia gerada pelas PCHs, o que não exige a construção de extensas linhas de transmissão, muitas vezes
se conectando direto com a distribuição. Aliado a isso, segundo a
publicação da Revista Página 22 – Pequenas, porém invocadas
(29/04/09) – de Carolina Derivi, grande parte do potencial para a
construção de grandes hidrelétricas está nos rios da Região Amazônica, havendo a necessidade de instalação de longas linhas de
transmissão. Já no caso das PCHs, os rios mais apropriados para a
implantação destas estão nas regiões Sudeste e Centro-Oeste,
próximas aos grandes centros consumidores de energia.
Soma-se a todas essas vantagens uma série de incentivos aos
empreendedores de PCHs. Resoluções elaboradas pela Agência
Nacional de Energia Elétrica (ANEEL) permitem que a energia gerada pelas pequenas centrais hidrelétricas entre no sistema elétrico
nacional com o empreendedor tendo descontos nas taxas pelo uso
da rede de transmissão e distribuição. Além disso, as PCHs estão
dispensadas do pagamento de royalties aos municípios pela exploração dos recursos hídricos, podendo fornecer energia para o
Sistema Interligado, consumidores livres e sistemas isolados.
Quando construídas no sistema isolado da Região Norte em
substituição às geradoras térmicas a óleo Diesel, podem também
receber incentivo do fundo formado com recursos da Conta Consumo de Combustíveis Fósseis (CCC) para seu financiamento.
Isso para não falar de programas governamentais de incentivo como o PCHCOM, de 10 anos atrás e que não trouxe muitos resultados, e o Programa de Incentivo às Fontes Alternativas de Energia(Proinfa).
Sistema em Cascata
Contudo, o que era para ser incentivo à construção de mais
PCHs e, com isso, atenuar os impactos sociais e ambientais causados pelas grandes hidrelétricas acaba servindo como ponto de partida para os principais críticos dos pequenos empreendimentos hidroenergéticos.
Como apresentado no trabalho de Matos Viana, de acordo com
06
o relatório da Comissão Mundial de Barragens (2000), grande parte dos principais rios e bacias hidrográficas mundiais comportam
grande número de barragens, o que acaba ocasionando a fragmentação do ecossistema fluvial. Nesses casos, os impactos são
intensificados, resultando em um aumento cumulativo das perdas
de recursos naturais e da integridade do ecossistema.
E é exatamente essa a principal crítica em relação aos impactos sociais e ambientais advindos da construção de PCHs, ou seja,
quando há o sistema em cascata. Neste, várias pequenas usinas
são instaladas em um único rio, e os obstáculos (barragens) instalados nele podem impossibilitar a migração de peixes, necessária
à reprodução das espécies. Mesmo com os mecanismos de transposição de peixes, ainda são necessárias pesquisas a fim de solucionar essa problemática.
De acordo com Ricardo Pigatto, presidente da Associação Brasileira dos Pequenos e Médios Produtores de Energia Elétrica
(APMPE), o 'sistema' em cascata vale para qualquer 'categoria' de
usina hidrelétrica, grandes ou pequenas. “Muitas vezes um misto
disso tudo”. O que existe, completa Pigatto, é um dispositivo legal
que determina o aproveitamento ótimo do rio pelo qual a ANEEL
deve zelar, isto é, o máximo de geração elétrica combinado com os
menores impactos ambientais.
PCHs X UHEs
A publicação Energia Positiva para o Brasil de 2004 da organização não-governamental Greenpeace aponta que os impactos
combinados da construção de várias pequenas usinas em um mesmo rio podem ser comparados aos provocados por grandes hidrelétricas, mesmo as PCHs sendo uma alternativa às UHEs na geração de energia.
Nesse sentido, a coordenadora socioambiental da Associação
Brasileira dos Investidores em Autoprodução de Energia Elétrica
(ABIAPE), Adriana Coli Pedreira, afirma que não há uma resposta
positiva ou negativa para essa questão. “Depende das características tanto do rio, das PCHs que serão construídas em cascata
quanto da UHE na qual será feita a comparação dos impactos sociais e ambientais”, explica. O que vem sendo feito, aponta Pedreira, é um estudo integrado dos empreendimentos em cascata no
mesmo rio, hoje conhecido como Estudo Integrado de Bacia Hidrográfica ou uma Avaliação Ambiental Integrada, que identifica
os efeitos sinérgicos e cumulativos resultantes dos impactos ambientais ocasionados pelo conjunto de aproveitamentos hidrelétricos na bacia hidrográfica. Através desses estudos, são apresentados indicadores de sustentabilidade, áreas de fragilidade ambiental e de conflitos são delimitadas e há a identificação das potencialidades socioeconômicas relacionadas aos aproveitamentos e diretrizes ambientais para a concepção de novos projetos de geração
de energia elétrica.
Pigatto explica que, quando demonstrado e evidenciado que a
implantação de uma ou mais UHEs causarão maiores impactos socioambientais que o somatório de algumas PCHs, cabe ao desenvolvedor demonstrar e buscar a melhor partição de quedas com o
maior aproveitamento energético e menor impacto. “Só existirão
rios com PCHs em cascata se demonstrado que este é o melhor resultado da combinação energia-ambiente”, destaca.
Tirar vantagem da vantagem
Pigatto ainda ressalta que a ANEEL é bastante diligente no controle dos inventários e respectivas partições de quedas. Assim,
sendo constatado que no local deveriam ser implantadas UHEs em
vez de PCHs, a agência toma as providências para a devolução do
LEGISLATION
What about the Small Hydropower Plants?
According to a definition established by Resolution 394/1998
from ANEEL (National Agency for Electric Energy) the Small
Hydropower Plants (SHPs) are small enterprises whose installed
2
capacity lies between 1 MW and 30 MW, with a reservoir of 3 km at
2
most, which can reach 13 km in specific cases, according to Resolution 652/2003. A typical SHP normally operates at run-of-river
scheme, i.e., the reservoir does not allow the regulation of the water flow. SHPs are located on small and medium sized rivers with
significant difference of levels along their course, generating
enough hydraulic power to move the turbines.
As well as wind, solar and biomass energy, small hydropower
enterprises are among the electric power generating options defended by a considerable part of the environmentalists. SHPs have
countless advantages when compared to large Hydropower
plants.
great number of dams, which causes the fragmentation of the fluvial ecosystem. In these cases, the impacts are intensified, resulting in the increase in the losses of natural resources and in the integrity of the ecosystem.
And this is exactly the principal criticism in relation to the social and environmental impacts that come with the construction of
SHPs, i.e., when there is a cascade system. In this case, several
SHPs are installed in the same river and the obstacles (the dams)
may make the migration of fish impossible. Even with the fish diversion mechanisms, a lot of research is still necessary to solve
this problem.
According to Mr. Pigatto, the cascade system may cause problems for any type of hydropower plants, small or big ones or both
of them together. Mr. Pigatto goes on saying that there is a legal device that determines the optimum use of a river, and Aneel must
see to it – the maximum generation combined with the lowest environmental impacts.
Advantages of SHPs
As SHPs are run-of river schemes plants, i.e., they do not have
water storage, so there is no need for large reservoirs. This way,
the impacts caused by SHPs are considerable smaller than the
ones caused by Large Hydropower Plants (LHP), given that there
is not a significant interference in the river's natural regime, a
smaller area is deforested and less land is expropriated.
In the same way, the losses in the transmission of energy generated by SHPs are also lower because there is no need to build
long power lines, and the SHPs are, many times, connected directly to the distribution. Also, according to the magazine Página
22 – “Small, but with an attitude” (29/04/09) by Carolina Derivi,
most part of the potential for the construction of large power
plants is on the rivers of the Amazon region, so the installation of
long power lines is necessary. On the other hand, the SHPs can be
implemented on rivers that are located in the southeast and center-west regions, closer to the large energy consuming centers.
In addition to all of these advantages, there is a number of incentives that are given to those who want to invest in SHPs. Resolutions elaborated by ANEEL Allow the energy that is generated by
SHPs to enter in the national electric system granting discounts to
the entrepreneurs for the use of the transmission and distribution
grids. Besides, SHPs are exempt from paying royalties to the cities
for the use of the water resources, being able to supply energy to
the National Interconnected System (SIN), free consumers and
isolated systems.
Instead of diesel thermal power plants, when SHPs are build in
the north region, they can also receive incentives from the fund
created with resources of the Fossil Fuels Consumption Account
(CCC) for their funding. This not to mention government programs such as PCH-COM, created ten years ago but without good
results, and the program to encourage alternatives sources of energy (PROINFA).
Cascade Hydropower Plants
However, what was supposed to be an encouragement to build
more SHPs and, consequently mitigate the social and environmental impacts caused by the large hydropower plants, ended up
serving as a starting point for the most important critics against
SHPs.
As it was shown in the study carried out by Matos Viana, according to a report from the World Commission on Dams (2000)
most part of the main rivers and hydrographic basins accept a
SHPs X LHPs
The publication Energia Positiva for Brazil 2004 carried out by
the NGO Greenpeace shows that the impacts of the construction of
several SHPs on the same river can be compared with the impacts
caused by large hydropower plants, even if the SHPs are an alternative to the LHPs for the generation of energy.
In this sense, the socio-environmental coordinator of the Brazilian Association of Investors in Electric Energy Self-production
(ABIAPE), Ms. Adriana Coli Pedreira, says that there are no positive or negative answers to this question. “It depends on the characteristics of the rivers, on the SHPs that will be constructed in a
cascade way and on the LHP that will be used for comparing the
socio-environmental impacts”, she explains. She said that what is
being carried out is an integrated study of the cascade enterprises
on the same river, which is known today as Integrated Study of a
Hydrographic Basin or an Integrated Environmental Assessment,
which identifies the sinergetic and cumulative effects resulting
from the environmental impacts caused by the set of hydropower
plants in the basin. These studies present sustainability indicators, outline areas of conflict and environmental fragility and identify the socio-economic potentialities related to the SHPs and the
environmental guidelines for the conception of new electric energy generating projects.
Mr. Pigatto explains that when it is evident and proved that the
implementation of one or more LHPs will cause more socioenvironmental impacts than the sum of some SHPs, the developer
is in charge of searching the best partition of the heads, i.e., with a
better energy use and lower impacts. “There will only be rivers
with cascade SHPs if it is demonstrated that this is the best result
of the relation energy/environment”, he says.
Taking advantage from the advantage
Mr. Pigatto also highlights that ANEEL is very detailed when it
comes to the control of the inventories and respective head partition. This way, if it is evident that LHPs should be installed instead
of SHPs, the agency will be in charge of returning the inventory
studies so that the necessary adjustments can be carried out.
Ms. Pedreira, on the other hand, says that ANEEL must assess
whether the entrepreneur only wants the incentives granted to
SHPs and ends up proposing projects of cascade plants instead of
proposing a LHP, where the potential would be much better used.
Mr. Michellis says that the possibility of dividing some LHPs into
07
LEGISLAÇÃO
estudo de inventário para os ajustes necessários.
Já Pedreira afirma que a ANEEL deve avaliar se o empreendedor visa apenas aos incentivos concedidos às PCHs e acaba propondo projetos de usinas em cascata em detrimento de uma UHE
onde seria melhor aproveitado o potencial. Michellis completa dizendo que a possibilidade de fracionar algumas UHEs em várias
PCHs é pouco provável e viável. “As características intrínsecas do
rio a ser inventariado e sua vocação natural para UHEs e PCHs acabam sendo determinantes na escolha da divisão de quedas a ser
analisada e aprovada pela ANEEL”.
O desenvolvimento e o progresso de um país não precisam ser
excludentes. É preciso sim um melhor planejamento de ações para que a melhoria das condições de vida em uma região não ocasione a piora e deterioração de outra.
É fato que a energia elétrica é algo fundamental dentro de um
país, e qualquer ação do homem sobre o meio vai causar algum tipo de impacto, seja ele ambiental ou social, considerando-se todas as formas de geração de energia elétrica. Nesse caso, o planejamento torna-se essencial, pois diferenças culturais e de valores
e tradições, da mesma forma que as relações sociais e a interação
com os recursos naturais, tornam os impactos sociais e ambientais singulares em cada projeto, região e comunidade. Assim, incluir
os projetos hidrelétricos em um rol específico de regras sistematizadas e metodologias pré-definidas vai de encontro às diversidades sociais, culturais e ambientais.
Reduzir o desperdício ocasionado por equipamentos obsoletos
e manutenção inadequada das linhas de transmissão, repotenciar,
modernizar e reativar antigas usinas hidrelétricas são opções viáveis para a geração de energia elétrica sem causar grandes danos
ou perdas à comunidade e ao meio ambiente; da mesma forma, os
pequenos empreendimentos hidroenergéticos não devem ser descartados.
LEGISLATION
several SHPs is unlikely and unfeasible. “In the end, the natural
characteristics of the river will determine the choice of head partition that will be analyzed and approved by ANEEL”.
Why not balance?
The development and progress of a country do not need to be
excluding. Of course, it is necessary a better planning of actions so
that the improvement of life conditions in one region does not
cause the worsening and the deterioration of the conditions in another.
It is a fact that electric energy is of utmost importance for a
country, and any actions made by man towards this goal will cause
some kind of impact, social or environmental, considering all of
the ways to generate electric energy. In this case, planning be-
comes essential, given that cultural, principles and tradition differences, as well as social relations and interaction with natural resources, will made the social and environmental impacts unique in
each project, community and region. This way, including
hydropower projects in a specific list of systematized rules and
pre-defined methodologies meets the needs of social, cultural and
environmental diversities.
Reducing energy waste caused by obsolete equipment and inappropriate maintenance of the power lines, repowering, refurbishing and commissioning old hydropower plants are feasible options for electric energy generation without causing serious damages or losses to the community and the environment; and the
Small hydropower plants must not be discarded.
LEGISLAÇÃO
Por Fábio Couto
A entrada em vigor de novas regras para o setor de distribuição
também refletirá no setor de Pequenas Centrais Hidrelétricas. Os
Procedimentos de Distribuição (Prodist), foram aprovados pela
Agência Nacional de Energia Elétrica em dezembro do ano passado
- Resolução 345/2008. Elas são normas que disciplinam o relacionamento entre consumidores e usinas de geração distribuída que
estejam conectados em sistemas em tensão abaixo de 230 kV e as
respectivas distribuidoras -total de 64–, entre outros aspectos.
mentação prévia, entre a qual a que estabelece o acesso à rede de
distribuição ou transmissão.
Essas regras começaram a ser elaboradas em 1999, por conta
do Projeto Reseb - Reestruturação do Setor Elétrico Brasileiro, e levou nove anos para receber uma regulação específica. Entre os
principais objetivos do Prodist estão o de propiciar o acesso aos sistemas de distribuição, assegurando tratamento não discriminatório entre agentes. Para o caso das Pequenas Centrais Hidrelétricas
- entre outros empreendimentos que podem ser conectados em linhas de distribuidoras, existem regras específicas.
Para Said, a saída poderia estar na concessão de um parecer
prévio, com base na consulta do empreendedor, para a participação nos leilões. A questão é importante, observa, pois a maioria
das PCHs conecta-se em redes de distribuição, por conta dos descontos que essa fonte pode obter nas Tarifas de Uso dos Sistemas
de Distribuição – por ser classificada como fonte incentivada.
Uma delas estabelece que as usinas deverão realizar Contrato
de Uso do Sistema de Distribuição (Cusd) como unidade consumidora ao Cusd que foi celebrado como gerador. Esse contrato será verificado pela Aneel e, se necessário, receberá propostas para ser
adequado às características do empreendimento.
Para o sócio da Excelência Energética, José Said de Brito, as novas regras vieram dar uma luz ao setor, definindo com clareza
ações e prazos a serem cumpridos pelos agentes. "Até então o tempo para a definição de acesso era longo", disse Said. Ele lembra que
o módulo que trata da relação entre centrais geradoras e distribuidoras estabelece que a consulta de usinas para a conexão à rede deve ser respondida em até 60 dias.
Além disso, a resposta deve deixar claro as condições do acesso e o papel de cada um na realização de investimentos, participação financeira e responsabilidades prévias. Como exemplo, o Prodist determina que conexão de unidades consumidoras com carga
instalada superior a 50 kW, incluindo eventuais aumentos de carga, deve ocorrer com participação financeira da unidade consumidora – como as PCHs, conforme regras específicas da Aneel.
Outro ponto presente nas novas regras é a fixação de quatro
etapas para obtenção de acesso – consulta, informação, solicitação
e parecer, sendo algumas delas opcionais ou obrigatórias dependendo da condição da central geradora – se concessão, autorização
ou registro. Entre a solicitação e o parecer de acesso, o prazo varia
de 30 dias, para conexão sem necessidade de realização de obras,
a 120 dias, para empreendimentos que demandarão obras para a
conexão. Essa exigência é obrigatória para PCHs que solicitam registro na Aneel. Com o parecer, os contratos devem ser celebrados
em até três meses.
Para PCHs que pleiteiam autorização, os prazos são mais longos, mas definidos. A partir da consulta de acesso, o prazo é de 60
dias para a resposta sobre a informação. De posse da informação
do acesso, o empreendedor tem 60 dias para solicitar a autorização. Quando ela é publicada no Diário Oficial, inicia-se novo prazo,
agora, de 60 dias, para o gerador fazer a solicitação de acesso. E a
partir dessa data, conta-se 30 dias para liberação do parecer, caso
não seja necessária realização de obras. O prazo passa para 120 dias em caso de obras. Com o parecer em mãos, o prazo de assinatura dos contratos é de 90 dias.
Said destaca que as regras abriram necessidade de ajuste em
pontos que são considerados como obscuros. Um deles tem referência aos leilões de energia nova. O consultor comenta que uma
das regras dos leilões exige a apresentação de uma série de docu-
10
No entanto, a obtenção de acesso à rede requer a autorização
do empreendimento, o que só acontece após a negociação de energia no leilão. Uma das regras para a participação de PCHs em leilões de energia nova, de acordo com a legislação setorial, determina que empresas só podem participar desses certames se não tiverem sido autorizados pela Agência Nacional de Energia Elétrica.
Tanto é que as PCHs não entraram com força no cadastro para
as Instalações Compartilhadas de Geração, as ICGs. A razão, comenta Said, é que naquela ocasião, os empreendedores de biomassa estavam dispostos à expandir participação na matriz energética. No entanto, eventual insucesso em leilões de energia nova
não inviabilizariam plantas de álcool do empreendedor, já que esses projetos seriam instalados de qualquer maneira. Já as PCHs dependeriam do sucesso nos leilões para definir se entrariam em
ICGs, que são instalações de rede básica. “No caso da rede de distribuição, as PCHs ficam dentro do conceito de geração distribuída”
LEGISLATION
Once the new regulations regarding the power distribution sector are in force, there will be consequences within the sector of
Small Hydropower Plants (SHPs). The Distribution Procedures
(Prodist) were approved by ANEEL (National Agency for Electric
Power) in December 2008 – Resolution 345/2008. These rules regulate the relation between consumers and distributed generation
plants that are connected to systems whose voltage is below 230
kV and the respective distributors – 64 altogether – among other
aspects.
ing plants and distributors establishes that the enquiries of plants
regarding the connection to the grid must be answered in 60 days
at the most.
These norms started to be elaborated in 1999 due to the Reseb
Project – Restructuring of the Brazilian Electric Sector and took
nine years to receive a specific regulation. Among the main objectives of the Prodist we can mention the possibility of access to the
distribution systems, assuring a non-discriminatory system among
the agents. As far as SHPs are concerned and other enterprises
that can be connected to power lines, there are specific rules.
Another aspect that was present in the new rules is the establishment of four stages for the access attainment – consult, information, request and assessment. Some of them are optional and
others are mandatory, depending on the condition of the generating plant, whether it is concession, authorization or registry. The access request and assessment must take place within a period of 30
days for the connection without any type of work, the period is 120
or the enterprises that will demand some sort of work for the connection. This requirement is mandatory for SHPs that request the
registry with Aneel. With the assessment, the contracts must be
signed within three months at most.
One of these rules establishes that the generating plants must
sign a Contract for the Use of the Distribution System (Cusd) as
they use the distribution system. This contract will be verified by
Aneel and, if it is necessary, it will receive proposals so that it will be
adjusted to the features of the enterprise.
According to Mr. José Said Brito, Excelência Energética, the new
rules came to shed light on the sector, defining the actions and
deadlines that must be fulfilled by the agents. "The time for the definition of the access used to be very long", said Mr. Brito. He goes on
saying that the part that deals with the relation between generat-
Besides, the answer must be clear about the access conditions
and the role of each party regarding the investments, financial participation and previous responsibilities. For example, Prodist determines that consuming units with an installed power above 50 kV, including eventual power variations, must pay the financial participation of the consuming unit, which is the case of SHPs.
For SHPs that request authorization, the periods are longer, but
they are also defined. After the access consult, the answer must
come within a period of 60 days. After having the access information, the entrepreneurs have 60 days to request the authorization.
When this authorization is officially published, the generator has
60 days to request the access. And after this date, there are 30
days to liberate the assessment, in case no works are necessary. In
case some works must be carried out, this period is extended to
120 days. Once the assessment is ready, the contracts must be
signed in 90 days at most.
Mr. Brito highlights that the rules demand the adjustment f
some issues that are considered blurred.Um of them regards the actions of new energy. He says that one of the rules of the auctions demand the presentation of a series of previous documents, among
them one that establishes the access to the distribution or transmission grid.
However, the attainment of the access to the grid demands the
authorization of the enterprise, which only happens after the negotiation of the energy in the auction. One of the rules for the participation of SHPs in actions of new energy, according to the legislation
of the sector, determines that companies can only participate in
these auctions if they had not been authorized by the National
Agency for Electric Power.
According to Mr. Brito the solution could be on the concession of
a previous assessment, based on the consult of the entrepreneurs,
in order to participate in the auctions. The issue is important because most of the SHPs are connected to distribution grids because
of the discounts that this source of energy can receive in the Tariffs
for the Use of the Distribution Systems, as it is classified as clean energy (it receives an incentive).
That is the reason why the SHPs did not put a lot of strength in
the registration for Generating Shared Installations, the ICGs. It is
because at that time, the biomass entrepreneurs were willing to increase their participation in the energy matrix. However, the eventual lack of success in the auction of new energy did not make the alcohol plants unfeasible, for these projects would be installed any
way. On the other hand, the SHPs would depend on the success of
the auctions to define whether they would be part of the ICGs,
which are basic grid installations. “In the case of the distribution
grid, the SHPs fall in the concept of distributed generation”.
11
Technical Articles Seccion
ÍNDICE
IMPORTANCE OF DRAFT TUBE IN REHABILITATION PROJECTS
14
Fabrice Loiseau, Vincent De Henau, Michel Sabourin
NUMERICAL STUDY OF FLUID FLOW IN A FRANCIS TURBINE
18
Marcelo Kruger, Regis Ataídes, Martin Kessler, Paulo de Tarso R. A. Cordeiro
ESTUDO DE EMISSÕES DE GASES DO EFEITO ESTUFA DE RESERVATÓRIOS BRASILEIROS
21
Rafael Balbino Cardoso, Luiz Augusto Horta Nogueira
26
SENSITIVITY OF DRAFT TUBE FLOW PREDICTIONS TO BOUNDARY CONDITIONS
F.A. Payette, V. De Henau, G. Dumas, M. Sabourin
30
UNSTEADY FLOW WITH CAVITATION IN VISCOELASTIC PIPES
Alexandre K. Soares, Dídia I. C. Covas, Helena M. Ramos, Luisa Fernanda R. Reis
Áreas de:
Recursos Hídricos
Meio Ambiente
Energias Renováveis e não Renováveis
Classificação Qualis/Capes
B5
ENGENHARIAS III
B5
INTERDISCIPLINAR
B5
ENGENHARIAS I
13
ARTIGOS TÉCNICOS
IMPORTANCE OF DRAFT TUBE IN REHABILITATION PROJECTS
1
Fabrice Loiseau
2
Vincent De Henau
3
Michel Sabourin
ABSTRACT
Some recent rehabilitation projects of low head turbines performed by Alstom present a drop off in efficiency due to the draft tube design, this hydraulic accident is located near the best efficiency operating condition. For the St-Lawrence project, even if the drop off was
still over the envelop of efficiency guarantees, the customers were concerned about the stability and the interaction with the governor. A
solution based on a draft tube modification was developed on model but was not required on the prototype. This modification fills the notch
in the efficiency curve increasing locally the efficiency. However, it has been observed the drop off does not produce any unstable operation of the unit.
For low head rehabilitation projects, the draft tube has an important impact on performance and it is not only the new runner that contributes to the efficiency. The runner blade profile can reduce or push outside the operation range this effect but sometimes modification of
the draft tube is a necessity and can be justified economically and permits to reach a level of performance such as the turbine can perform
as a new one.
Different phenomena due to the draft tube behaviour are presented, from model to prototype, describing different types of hydraulic
problems as well as investigations. Comparisons of field test and model test scaled up to the prototype conditions are also presented.
Key words: Low head turbines, Draft tube behaviour and Field test
INTRODUCTION
Rehabilitation projects present the largest challenge for the engineer. The existing water passages are usually issued from design
criteria not as optimal as one would expect today. The main difficulties reside in the knowledge of the behaviour of the existing turbine
and in the relation between the geometry of the water passages
and the actual performances. We can imagine that replacing the
runner makes the turbine as new. However, the other components
of the turbine can influence greatly the performance. Often, the existing water passages are not so far from the optimal frame. The resulting performances of the rehabilitation are very close to ones of
a new turbine, but sometimes, it is not the case.
Particularly, for low head turbines, the draft tube behaviour has
a direct effect on the shape of the hill chart. Flow behaviour is extremely complex and can be unstable in the draft tube.
In this paper, we first present different case studies observed
during developments performed on model test, describing phenomena and observations. This will be followed by the description
of a recent prototype feed back and comparison with model tests.
MODEL TEST DEVELOPMENT AND INVESTIGATION
Alstom is a world leader in design and fabrication of propeller
turbines. In North America, its experience is mainly on major refurbishment projects. Alstom has been selected to provide more than
50 propellers at LG1, KIPLING, BEAUHARNOIS, CHATS FALLS GS,
ST-LAWRENCE and KELSEY, as well as LITTLE LONG and HARMON
more recently. All these contracts have taken advantage of the latest improvements in propeller design and fabrication process (see
papers ref. 1, 2 and 3). It includes also the experience acquired
with regards to the analysis and investigation performed on various casings.
For low head machines, the draft tube is the main geometrical
component that defines the turbine global performance level. Flow
behaviour is extremely complex and can be unstable in the draft
tube. In some cases, the flow pattern changes suddenly due to a
non-perceptible perturbation. We can observe two distinct behav-
iours for the same hydraulic point of operation or more commonly a
range of operation, observing a drop off in performance accompanying the different flow patterns like flow separation at the pier
nose area and a change in the ratio of discharge rate at the outlets
of the draft tube. We observe that the efficiency drop off occurs
when the velocity field at the runner outlet shows a very low rotational component. The flow condition is unstable in the sense that a
very small perturbation can make the machine to drop from one
condition to the other condition. But this is not reversible at the
same point, there is hysteresis.
During the bid phase for the rehabilitation of a low head machine, the risk of being faced with the draft tube flow phenomenon
described above has to be evaluated. One approach is analysing
the draft tube performance with the help of Computational Fluid Dynamics (CFD). Although CFD simulations do provide some assistance and guidance, to date the prediction of the drop off in efficiency in draft tubes with CFD simulations has proven to be unreliable. The predicted flow patterns in draft tubes are strongly related
to boundary conditions as well as the choice of turbulence models
(see paper ref. 4). Even with today's state of the art of CFD tools,
the most reliable approach to investigate a draft tube behaviour in
the context of a rehabilitation project remains the model test conducted during the contract phase.
The example used below is a typical example, describing the
project management at the model development phase and concerning a recent development for which all guaranties (power, efficiency, cavitation, etc) were met with the first runner design.
From the beginning of the development, the model test showed
a drop in efficiency of about 0.8% in the area of best efficiency at
the rated head. The client was concerned with the drop-off, mainly
with regards to operation stability and capacity to operate the turbine with its governor, and of course, a loss of productivity compared to the potential performance of the new runner design.
When such problem is detected, one test consists to validate
the turbine runner simply by changing the existing draft tube with a
modern design. These experimental investigations on model are
typically easy to implement. Even if it does not correspond to real-
1,2,3 - ALSTOM Hydro, 1350 Chemin Saint-Roch, Sorel-Tracy, Québec, Canada +1-450-746-6500 ext 5127
1 - [email protected]
14
TECHNICAL ARTICLES
ity for the prototype, it allows to validate the turbine layout and to
confirm that the objectives in terms of power, performance and cavitation can be reached and to define ways of future investigation.
Nevertheless, this does not indicate that the turbine runner is developed to fit perfectly with the existing draft tube, the existing
draft tube may be sensitive to the inflow and its velocity profile, it
only confirms the designer in his initial choices and provides ways
of investigation to solve the problem.
draft tube, progressively disappeared. It is true that the prototype
Reynolds value could not be tested (see Figure4 ) and it is tempting
to think that the Reynolds number is the answer to the problem. Nevertheless, other factors can affect these results. For example, the
very small deformation of the model blade profile due to the load increase during model test can modify slightly the inflow conditions
at the entrance of the elbow.
The figure below (see Figure 1) describes such comparison,
showing a curve without accident obtained with a modern draft
tube design and allowing a full analysis of the upgraded runner with
regards to different topics.
Figure3. Draft tube behaviour depending on how the load variation is described.
Figure1. Performance and validation of the runner design using a modern
draft tube design - Model efficiency versus model power -
Complementary to the performance measurements, pressure
fluctuations have been measured on the existing frame using dynamic strain gauges located downstream to the runner: in the draft
tube cone and in the elbow. Results show that the pressure fluctuations level is not significant and is really low in the main operating
range (see Figure 2).
Figure4. Variation of the Reynolds number versus Prototype value.
To solve or to reduce the influence of such accidents on performance, one solution consists to modify the hydraulic blade profile.
It is possible to decrease/avoid the hydraulic phenomena that is responsible of the separated flow in the draft tube (see Figure 5), but
blade modifications are usually limited.
Figure2. Pressure fluctuation measurement from the existing draft tube Model efficiency and global RMS fluctuation versus model flow -
With regards to such hydraulic behaviour, turbulence phenomena are unfortunately difficult to capture and to approach with
current turbulence models and computer capacity. Nevertheless,
numerical tools coupled with experimental analysis performed on
model test-rig (probes downstream to the turbine runner, and visual observations performed inside the draft tube, etc.) provide significant assistance and help consolidating or guiding future developments.
Another aspect concerns information acquired with the results
of some scale effects performed on test rig. Such tests allow understanding the draft tube hydraulic behaviour by varying the model test head value (and consequently the Reynolds number).
In the example described below (see Figure3 ), similar tests
showed the draft tube behaviour changed with an increase in the
model test head; the flow separation phenomena, located in the
Figure5. typical modification of a model runner allowing to reduce the
impact of a separated flow on performance curve
Sometimes, draft tube modifications are the only solution.
When such modifications appear to be necessary, the hydraulic designer has to consider the manufacturing and implementation on
the prototype, in other words: delay and cost.
The section law of the draft tube can appear to be not optimal,
not enough flow acceleration at the elbow outlet for example. We
know that this acceleration is needed to increase the quality of the
flow upstream of the draft tube extension. Without this acceleration, we usually observe a flow recirculation downstream of the
draft tube elbow, which results in a non-homogenous repartition of
the velocity at the draft tube outlet, increasing the total kinetic
15
ARTIGOS TÉCNICOS
energy and consequently the head losses.
Typical draft tube modifications are tested below (see Figure 6)
taking into account previous observations during model test development as well as numerical investigations even if turbulence phenomena are very complex in a draft tube.
Figure6. Draft tube modifications and performance increasing.
These model developments performed on test rig provide different solutions to reduce the impact of a “bad” draft tube. Depending on the situation, some observations performed during this
model development can reduce the necessity to implement such solution on prototype (scale effect). It is a real challenge to reduce
the cost as well as the delay.
PROTOTYPE FEED BACK
We will describe below recent experiences on prototype for
which constraints concerning draft tube behaviour were detected
at the model step. For them, an important part of the time was
spent to manage these constraints.
Figure7. Output variation measured by data acquisition system
at 2 openings on both side of the drop off.
·KELSEY CASE
One of our main challenge happened with the upgraded runner
developed for the Kelsey power Dam owned by Manitoba Hydro.
The new upgraded runner is a propeller turbine of 5.816 m in diameter operating under a nominal head of 15.5 m and capable of producing 45 Mw each at 102.9 rpm.
During the model test development, an efficiency drop was observed and occurred at an output that exceeds the original output
guarantee. However, the customer was interested by the additional
power and a solution based on a draft tube modification was developed on model. According to previous model test results showing
sensitivities to Reynolds number, it was decided not to implement
the draft tube modification on the first prototype and wait for the
prototype field test to validate the necessity of draft tube modification on prototype (see paper ref. 5).
Figure8. Field test results, comparison with model test results transposed
to prototype conditions - Prototype efficiency versus power -
Hydraulic performance testing of the unit was performed using
current meters located in the intake and supplemented by index
tests. Hydraulic conditions during the field test were exactly the
conditions initially defined for the model test, design net head and
tailrace level.
During the load variation, we observed an efficiency drop-off as
well as a local flow reduction at a wicket gate opening corresponding of about 92% of the servo-motor stoke; for higher opening, performance level appears to be constant, the measurement acquired
during the run is stable as well as its repeatability. In fact, this operating range was fully transparent for the control room, the operating conditions were smooth and only the field test allowed demonstrating the presence of this phenomenon. To complete this example, two data acquisitions are provided below, one just before the
16
Figure9. Field test results, comparison with model test results transposed
to prototype conditions -Wicket gate opening versus power-
TECHNICAL ARTICLES
accident (point A) and the second one (point B) in the drop-off area
(see Figures 7, 8 and 9).
Field performance was compared to the expected one using
model test data (IEC 995 step-up) obtained with exactly the same
geometrical configuration.
For different reasons, we were obliged to adjust the prototype
measured flow; this adjustment was based by comparison on low
load performance obtained from the model step. For practical reasons on site, it was difficult to describe exactly the shape of the
curve where the drop-off occurs; nevertheless this comparison
showed a good coincidence with model test and most of all, the efficiency level in the area where the flow separation occurs is similar.
do not explain what is happening. On model test, we cannot forget
that we reproduce the geometrical environment of the prototype
turbine, from the inlet of the intake to the outlet of the draft tube.
This last point is particularly important for low head machines,
where the downstream part of the power plant can influence the
draft tube behaviour.
These results confirm the ones observed during the model test
development as well as the solution developed to solve the problem. Consequently, it has been logically decided to implement the
modification on the next units.
·CHATS FALLS CASE
A different problem was observed during the upgrade of the
Chats Falls Generating Station. The upgraded runner is a propeller
turbine of 4.978 m in diameter operating under a nominal head of
15.2 m and capable of producing 25 Mw each at 120 rpm.
For this project, a homologous model test was also performed.
During the development phase, some difficulties concerning the
draft tube behaviour had been met, showing separated flows and
instability associated to a Reynolds Number influence (see references). A fine-tuning of the runner design allowing to obtain an adapted velocity profile at the runner outlet solved the problem.
The first prototype runner was tested using Intake Current Meters System selected by Ontario Power Generation (OPG) as the
most accurate method. The field test was performed by OPG. The
new runner showed that expected performances were achieved.
The generator outputs at best gate and full load were exceeded. At
best gate, the measured power is approximately 25.4 Mw and at
full gate opening, the maximum output reached is about 27 Mw without power saturation.
Independently of these contractual considerations, the difference between model and prototype was clear; the operating range
was strongly increased compared to the expected one. The relative
gain in efficiency is about 2.5% (peak to peak), and most of all the
performance curve doesn't indicate separated flow at full load as it
was observed with the existing runner.
Different scale-up methods were studied and were compared
with model to prototype observed step-up. The shows the Chats
Falls model performances transposed to the prototype using the
IEC60193 step-up formula (including power step-up) and the prototype field performance test result. However, when comparing the
ICM test for the new runner with model test results (with IEC stepup on efficiency and power), we obtain a less significant correlation. As illustrated in , the upgraded runner reacts with greater impact than expected with IEC step-up. A margin of error is drawn
over the prototype test to demonstrate that the error alone could
not be responsible of that difference since repeating of measurements shows better behaviour than the expected total uncertainty
of 1.82%. Moreover, the power reached with the new runner is
even better than the optimistic IEC power step-up and no saturation seems to occur.
Figure10. Performance comparison between the existing and upgraded runners.
·ST. LAWRENCE CASE
Our last example concerns the upgraded runner of the St.
LAWRENCE power Dam concerning the Allis Chalmers units and owned by New York Power Authority. The new upgraded runner is a
propeller turbine of 6.096 m in diameter operating under a nominal
head of 24.7 m and capable of producing 75 Mw each at 84.9 rpm.
Up to now and with regard to actual operation of the first upgraded AC unit, no problems have been reported by the site, they operate the unit in the 60 to 64 MW range, where some draft tube sensitivity effects would be expected based on the model tests. NYPA
had concluded that the governors would probably not have any problems since when the efficiency falls off suddenly, the governor
would simply open the gates a bit farther to compensate and deliver the requested power. Prototype field test is planned next fall
with particular intention to the area of best efficiency.
CONCLUSION
The on-going market of refurbishment is mainly guided by a
unit capacity improvement and an enhancement of the efficiency level. The risks at each step of the project, from the bidding to the
prototype exploitation, have to be managed, the goal being to minimize the customer's risk as well as for the supplier.
The experience acquired on low head turbines and draft tubes
is important. The test rig for model test development appears to be
a tool guiding towards an optimized solution and validated at the
model scale. In this sense, it is always a challenge for the engineer
to optimize the frame and to improve the turbine. We should keep
in mind that the feedback from field test and prototype operating
conditions is a key point to improve our knowledge and to deliver a
better product to our customers.
BIBLIOGRAPHICAL REFERENCES
[1] LOISEAU F., VINH P. AND SABOURIN M., September 2001.
Rehabilitations of propeller turbines, Hydro Power & Dams, Riva del
Garda, Italy.
Actually, it appears that the draft tube react differently than
that was expected during model test development. One explanation can be the sensitivity of the inflow with regards to Reynolds
number that can not be fully reproduces on a test rig.
[2] ST-HILAIRE A., SABOURIN M., KIREJCZYK J., LOISEAU F.,
August 2002. Fixed-blade Turbines: a Natural Solution for Rehabilitation of Large Low Head Power Plants, HydroVision 2002, Portland, Oregon, U.S.A.
With this example, typical recommendations and scale effects
[3] ST-HILAIRE A., LUDEWIG P., LOISEAU F., TADEL J.,
17
ARTIGOS TÉCNICOS
NUMERICAL STUDY OF FLUID FLOW IN A FRANCIS TURBINE
1
Marcelo Kruger
1
Regis Ataídes
1
Martin Kessler
2
Paulo de Tarso R. A. Cordeiro
ABSTRACT
Francis turbines are the most common water turbine in use today. It is an inward flow reaction turbine that combines radial and axial
concepts. They operate in a head of ten to several hundred meters and are primarily used for electrical power production.
Cavitation is a typical problem found in this kind of turbine and most of times it is the responsible for turbine unbalancing due to blade
erosion. Thus, understanding and knowing the regions and causes of the problem are very important to predict and prevent
great damages.
In order to evaluate this issue, a computational model of fluid flow in a Francis Turbine of CEMIG has been developed. The methodology
employed consisted in solving numerically the flow equations inside the turbine using the computational package ANSYS CFX®, which
uses finite volume methodology. A first model was built as steady-state, turbulent and single phase flow and the cavitation regions were
identified through the vapor pressure value. Then, to verify the methodology a new model considering cavitation and multi phase flow, has
been developed. Both cases were compared between them and with visual data from CEMIG. With the methodology of single phase validated, based on visual information from CEMIG, some geometry modifications on blade aiming to reduce the regions of cavitation
have been implemented.
Key words: Francis turbine, cavitation, computational model, numerical methods.
INTRODUCTION
Used for a wide head range from 10 to
700 meters, the Francis Turbine, shown in
Figure 1, has been the most widely used turbine in the world. They are designed for
each site and can operate with efficiency
over 90%. On the other hand, the project
and design need to be done carefully to
avoid problems frequently found in this
kind of turbine. One of them is cavitation
phenomena, which consists in a process
where a void or bubble in a liquid rapidly collapses, producing a shock wave. The highly
localized collapses can erode metals, such
as steel, over time. After a surface is initially affected by cavitation, it tends to
erode at an accelerating time. The process
of erosion can cause a turbine unbalancing,
which is very prejudicial and dangerous for
the turbine operation.
tion, the possible cavitation regions have
been identified by the water saturation pressure value. The numerical results were compared to visual data from CEMIG and the
agreement between them was very good,
even with the simplifications in the computational model.
In a second step, a new computational
model, considering phase changing with
cavitation, has been developed to compare
with the first one and extract the real values of pressure on blade surfaces, since the
first one did not consider the phase changing due to cavitation phenomena.
Finally, some modifications on blades
have been implemented in order to reduce
the cavitation regions.
In this context, the computational
model has shown to be a very important
tool for understanding and knowing the behavior of flow inside the turbine. It permits
to identify low pressure regions,
recirculation areas, and implement geometric modifications aiming to reduce the
cavitation regions.
In order to evaluate this, a computational model of flow in a Francis Turbine of
CEMIG has been developed.
In a first step, a computational model
considering the flow to be steady-state, turbulent and single-phased has been developed. Due to the single phase simplifica-
Figure 1 – Francis Turbine rotor –
courtesy of CEMIG.
METHODOLOGY
Mathematical formulation
The numerical model for fluid dynamics simulations must describe the most
relevant aspects of the real physical problem. For the modeling of the flow inside the
turbine domain, Navier-Stokes equations
have been used.
Navier-Stokes equations are used in order to get the solution of the fluid flow, but
the complexity
of this coupled
and
strongly non-linear system of equations
does not allow an analytical solution, even
for simple cases. Based on that, the numerical solution
of Navier- Stokes is
largely used in industrial applications and
it can provide results with very good
agreement when compared to experimental data. A Reynolds average is used in order to simulate the average behavior of the
turbulent flow. The result set of equations
of this process is known as Reynolds Average
Navier-Stokes
(RANS) equations
which were employed in this work. Taking
the time average of the Navier-Stokes equations and after some algebraic manipulation, a new term, known as Reynolds tensor, appears. This new term carries the turbulent characteristics of the flow. One of
the most usual ways to modeling this tensor is through the Boussinesq's Approach
which gives to the Reynolds tensor a similar
formulation from Stokes tensor, but based
on the turbulent viscosity. This turbulent
viscosity is modeled using the k (turbulent
(1)ESSS – Engineering Simulation and Scientific Software – Rodovia SC 401, km 01, n°600, Parquetec Alfa.88030-000–Florianópolis–SC (48)3953-0053
(2)CEMIG – Companhia Energética de Minas Gerais - Av. Barbacena, 1200 - Bairro Santo Agostinho. 30190-131 - Belo Horizonte - MG (31) 3506-4521
[email protected]; [email protected]; [email protected]; [email protected]
18
TECHNICAL ARTICLES
kinetic energy) and ε (turbulent eddy dissipation).
The mass conservation equation, considering a steady state
and incompressible flow is given by:
∇.V = 0
where V is the time averaged velocity vector.
The momentum equation (Newton’s second Law), for an incompressible and steady state flow, is given by:
∇.(ρV ⊗V) = ∇(μeff (∇V + (∇) ))-∇p + SQM
T
where ρ is the density,p is the pressure and SQM={SQMx,SQMy,SQMz}
is the momentum source term.The effective viscosity μeff is given
by:
μeef = μ0 + μt
μ 0 is the molecular viscosity and μ t is evaluated from the turbulent quantities for the k −ε
2
mt =Cmr k
e
model:
The transport equations for the k −ε model are [2]:
Figure 3 – Geometric modifications.
On the three cases simulated the following assumptions have
been considered:
Steady-state flow;
Turbulent flow - k − ε model;
where Φ is defined as:
Incompressible;
Stationary domain for spiral and draft tube;
Rotating domain for the rotor.
Computational Mesh
The geometric domain has been divided in three regions: spiral, rotor and draft tube.To apply the equations on the model, the
geometry has been discretized in a hybrid computational mesh,
containing about 1.3 million of elements, between tetrahedrons,
prisms and hexahedrons. In order to reduce the number of elements on the global mesh, a simplification of periodicity on the rotor has been considered, and only one section containing one blade
has been discretized, as shown in Figure 4. The full superficial
mesh of the model can be visualized in Figure 2.
Boundary Conditions
A rotational velocity of 300 rev/min and periodic condition has
been employed to the rotor domain. Periodicity assumption allows
working only with one section (one blade) of the rotor. This simplification is often used in rotational domains in order to reduce the
number of elements in the computational mesh. The Figure 4
shows the simplification.
Figure 4 – Rotor simplification.
In all cases, the surfaces of the spiral, rotor and draft tube have
been modeled as wall with no-slip condition ( V = 0 ).
A boundary condition of total pressure considering a wide head
of 31 m has been applied as inlet condition. For the draft tube outlet
mass flow of 15000 kg/s has been specified.
Figure 2 – Computational mesh.
Numerical Model
As mentioned before, two geometric configurations have been
developed. For the first configuration, two different numerical methodologies have been evaluated. One of them was simulated considering a single phase model, while the other one a multiphase flow
with cavitation model was evaluated. The second geometric configuration includes some differences on blade shape and the single
phase model has been performed. The geometry configurations
can be seen in the Figure 3.
On the single phase simulations water has been used as work
fluid and for the multiphase simulation, water and water vapor
have been used. The properties of each fluid are in the Table 1.
Table1: Fluid properties
Property
3
Density (kg/m )
Viscosity (kg/m.s)
Saturation Pressure (kPa)
Water
Water Vapor
997
0.02308
0.0008899
9.8626e-06
3.1
19
ARTIGOS TÉCNICOS
A homogeneous model has been used to solve the multiphase
flow in the multiphase simulation. In this model all fluids share a
common flow field. Most simulations can use the homogeneous
multiphase model since the vapor velocity field is often assumed to
be the same as that of the liquid.
RESULTS
To evaluate cavitation regions and get a better understanding
of the fluid flow inside the turbine, the predicted saturation pressure profile has been analyzed.
As previously mentioned, in this work, phase change has not
been considered for the first and third simulations. Then, to identify regions where cavitation phenomena could potentially occur,
the regions of pressure below saturation value for the given temperature has been analyzed.
First of all, the results compared the first case with second to
evaluate the accuracy of simplification from multiphase to single
phase approach. A cut plane on the draft tube with pressure contours are shown in Figure 5. The profiles are very similar on both
configurations, with low pressures in the center of the outlet rotor.
Figure 7 – a) CEMIG turbine; b) CFD single phase model.
Once numerical model presented good agreement with the visual data, some geometric modifications in the rotor blade shape,
as shown in Figure 3, have been performed in order to reduce the
regions of cavitation.
In Figure 8 streamlines of velocity on the draft tubes are shown
for both cases.
On the first model it is possible to identify a central vortex
where the greatest velocities are concentrated. On the third model
on other hand, the geometric modifications caused reduction on
the velocities values on the center and augmentation of them near
the wall draft tube.
b
a
Figure 5 – Cut plane of pressure distribution
a) single phase flow; b) multiphase flow (cavitation model)
On the Figure 6(a) the isosurfaces of pressure below saturation
value, for the first simulation are shown. The isosurfaces of water
vapor considering volume fraction of 0.5 in the multiphase case is illustraded on Figure 6(b).
a
Third Case
Figure 8 – Streamlines on the draft tube.
This can be evidenced in Figure 9, where the isosurfaces of pressure below the saturation value were plotted with zoom in a rotor
blade for both cases. The increasing of pressure, improved by the
new flow pattern, decreased significantly the regions of cavitation.
b
Figure 6 – a) isosurface of pressure below saturation value;
b) isosurface of water vapor considering volume fraction of 0.5.
It is possible to verify that the results with the single phase model are very close to the multiphase simulation. It shows that the
single phase model can be used for this simulation. The usage of
this simplified approach allows having a decrease of computational
time, compared to multiphase model.
In order to check and validate the computational methodology,
the results between single phase simulation and visual data from
CEMIG have been compared. The agreement between them was
very good, even with the simplifications. Those results can be seen
on Figure 7, which a circle on the blade presents the regions where
cavitation occurs.
20
First Case
Figure 9 – Isosurface of pressure below the saturation value.
FINAL CONSIDERATIONS
The development of the numerical model allowed to better understand the flow behavior inside the turbine. The reliability of the
results has given CEMIG engineers increasing of confidence in the
computational model for implementing new configurations. Flow
pattern, pressure, velocity distribution and possible regions of cavitations are difficult to be seen in laboratory facilities and the simulation has shown to be a very useful tool on this situation. Once numerical model is validated it could give useful insights to CEMIG engineers to make important decisions concerning the improvement
of turbine efficiency.
TECHNICAL ARTICLES
Estudo de Emissões de Gases do Efeito Estufa de Reservatórios Brasileiros
1
Rafael Balbino Cardoso
2
Luiz Augusto Horta Nogueira
RESUMO
Responsável por apenas 3% das emissões globais de Gases do Efeito Estufa – GEE, o Brasil é um dos países com maior potencial para
reduzir competitivamente as emissões desses gases. O reduzido nível de emissões no setor energético brasileiro se justifica pelo fato da
energia primária utilizada ser de origem renovável, como energia hidráulica, que respondeu por 85,6% da geração observada em 2007.
Embora renovável, essa energia não é nula em emissões, pois a decomposição da matéria orgânica nos reservatórios produz gás carbônico e metano, estimando-se que as usinas hidrelétricas brasileiras emitem aproximadamente 0,10 tCe/MWh. Considerando ainda que as
termoelétricas no Brasil emitem cerca de 0,52 tCe/MWh, com base na participação das diversas fontes primárias pode-se concluir que a
geração de energia elétrica no Brasil emite em média 0,12 tCe/MWh. Procurando explorar as relações entre tais emissões de GEE e a geração hidrelétrica, no presente trabalho foram utilizados os dados do Inventário Brasileiro de Emissões Antrópicas de GEE e informações de
reservatórios representativos de usinas hidrelétricas brasileiras. Foi possível concluir preliminarmente pela inexistência de uma relação direta entre as emissões de GEE e a área alagada dos reservatórios, bem como a potência instalada. Do mesmo modo, na base de dados estudada, não se detectou uma relação entre a participação do metano no total das emissões e o tempo de residência da água nos reservatórios, embora existam indícios de uma relação entre as emissões totais e o tempo de residência.
Palavras chave: Emissões de Gases de Efeito Estufa, Reservatórios, CH4 e Co2.
ABSTRACT
Responsible for only 3% of the global emissions of Greenhouse Gases - GHG, Brazil is a country with a great potential to reduce competitively the emissions of such gases. The lower level of emissions in the Brazilian energy sector is justified by the intense use of renewable
sources of energy, as hydraulic energy, which corresponds to 85.6% of the electric energy produced in 2007. Although renewable, the
hydro power stations present some GHG emissions, associated to the decomposition of the organic substance in the reservoirs which produces gas carbonic and methane. It is evaluated that Brazilian hydroelectric plants emit approximately 0.10 tCe/MWh. Considering that
Brazilian thermoelectric plants emit about 0.52 tCe/MWh and taking into account the contribution of each primary energy source, it is estimated that power plants in Brazil emit annually on average 0.12 tCe/MWh. To explore the relations between GHG emissions and hydroelectric plant parameters, this work uses data from the Brazilian GHG Emissions Inventory and information of reservoirs of representative
actual Brazilian hydroelectric plants. It was possible to conclude preliminarily for the inexistence of clear association among GHG emissions and flooded area of reservoirs, as well as the installed capacity neither the methane share in the total GHG emissions and the residence time of the water in the reservoirs. Even so it seems that a correlation between the total emissions and such residence time exists.
Key Words: Greenhouse Gases Emission, Reservoirs, CH4 e CO2.
1. INTRODUÇÃO
A matriz de fontes primárias na geração de energia elétrica em
escala mundial é predominantemente fóssil, sendo ainda pouco intenso o uso de fontes renováveis de energia. Depois das fontes fósseis, a hidrelétrica ocupa o segundo lugar, seguida das centrais nucleares e, com participação marginal têm-se as centrais geotérmicas, solares e eólicas, como mostra a Figura 1.
12%
Norte e Europa, são responsáveis por 91% das emissões de GEE do
mundo. Nesses continentes a base da matriz energética é composta por carvão mineral e derivados do petróleo.
3%
2%
2% 1%
38%
27%
1%
22%
65%
27%
Ásia
Termoelétrica
Hidroelétrica
Nuclear
Outros
Europa
América do Norte
América do Sul
Africa
América Central
Oceania
Figura 2: Emissões de GEE por continente (World Resources Institute, 1996)
Figura 1: Tecnologias adotadas na geração global de eletricidade (ANEEL,2006)
Segundo IPCC (2005) as ações antrópicas, principalmente associadas à intensificação do uso de combustíveis fósseis no mundo,
são as principais responsáveis pela elevação da concentração dos
Gases do Efeito Estufa – GEE, o que vem provocando mudanças climáticas no planeta. Como mostra a Figura 2, a Ásia, América do
Apesar da maior parte das emissões globais serem provenientes da Ásia, o continente apresenta uma das menores valores de
emissões per capita do mundo, enquanto a América do Norte possui os maiores índices, com cada pessoa emitindo cerca de 4
tCO2/ano, como mostra a Figura 3.
1 - e-mail: [email protected]
2 - e-mail: [email protected]
Universidade Federal de Itajubá – UNIFEI - Av. BPS 1303, 55-35-36291000, Itajubá-Mg - Centro de Excelência em Eficiência Energética - EXCEN
21
ARTIGOS TÉCNICOS
são de GEE para os diferentes combustíveis (IPCC, 2005), ponderados de acordo a sua participação na geração termelétrica no Brasil, a emissão média na usinas termelétricas brasileiras seria de
0,52 tCe/MWh, dez vezes mais que a emissão estimada para as hidrelétricas, por unidade de energia elétrica gerada.
4,0
3,5
3,0
ton/ano
2,5
2,0
1,5
1,0
0,5
0,0
Ásia
Europa
América do América do
Norte
Sul
África
América
Central
Oceania
Figura 3: Emissões per capita de GEE por continente (Beil, 1999)
No Brasil, responsável por apenas 3% das emissões globais de
GEE, a situação é bastante diferente quando comparada aos países
europeus, Estados Unidos e China. Com efeito, a maior parte da geração de energia elétrica nas centrais brasileiras provém das fontes
primárias de origem hídrica, onde as usinas hidrelétricas – UHE´s
que respondem por 78% da capacidade instalada em dezembro de
2007 (incluindo a importação) e 85,6% da geração observada nesse ano (EPE, 2008). Esse amplo uso da hidroeletricidade, associada ao intenso uso de biocombustíveis, são os principais fatores que
explicam os baixos índices de emissões do setor energético no Brasil, pelo menos até o presente. No Brasil, a geração das usinas termoelétricas – UTE´s corresponde a uma participação de cerca de
10% na oferta de energia elétrica e são usualmente despachadas
no horário de ponta ou nos períodos de baixa hidraulicidade, quando a demanda por energia elétrica é maior que a oferta das UHE´s.
Por esse motivo que, em geral, o fator de capacidade das UTE´s no
Brasil é baixo e, como conseqüência, são menores seus índices de
emissões de GEE (Sugai e Santos Jr., 2006).
Nesse contexto, o presente trabalho procura explorar novas relações e avançar na compreensão da geração de GEE nas hidrelétricas brasileiras, inicialmente apresentando estimativas das emissões de GEE para um grupo representativo com nove UHE´s do sistema elétrico brasileiro, seguindo-se da análise comparativa da média desses valores com as emissões totais do setor elétrico e o estudo das correlações dessas emissões com parâmetros como a área
alagada, potência e tempo de residência da água.
2. EMISSÕES DE GASES DO EFEITO ESTUFA – GEE DOS
RESERVATÓRIOS DE UHE´S BRASILEIRAS
No Quadro 1 são apresentados os resultados médios de duas
campanhas de medições de emissões de GEE em reservatórios de
algumas UHE´s brasileiras, estimados com base na metodologia
de cálculos de emissões anuais do IPCC (1996) e disponibilizados
no Inventário Brasileiro de Emissões Antrópicas de Gases do Efeito
Estufa (Rosa et.al., 2006).
0,2%
1,3%
1,9%
Há uma razoável dispersão nos valores de emissões de GEE em
UHE´s. Embora as hidrelétricas sejam em geral consideradas uma
alternativa para mitigar as emissões de GEE no setor energético,
estudos recentes realizados em UHE´s da Amazônia constataram
que todas elas estavam emitindo mais GEE que termelétricas de
mesma potência (FAPESP, 2007) e levantamentos no reservatório
da UHE de Balbina mostraram que as emissões desse reservatório
podem ser dez vezes maiores que as emissões de uma UTE a carvão mineral com a mesma capacidade de geração de energia (Kemenes et. al, 2007). Com efeito, de acordo com Fearnside (1997) é
de extrema relevância que se calculem as emissões dos reservatórios brasileiros de modo a avaliar o grau de contribuição das emissões de gás carbônico e metano para o aquecimento global e comparar com as emissões de termoelétricas de capacidade equivalente. Além disso, segundo Reis (2002), para efeitos de comparação
de emissões de GEE na geração de energia elétrica na matriz energética brasileira, é interessante que se estabeleçam critérios para a
determinação de linhas de base que representam cenários de referência quanto às emissões desses gases.
6,8%
3,8%
4,2%
10,6%
Quadro1–Emissões médias de GEE dos reservatórios brasileiros
(Rosa et al.,2006)
kg Ch4/
km²/dia
kg Co2/
km²/dia
Miranda
154,2
4.388
38.332
Três Marias
196,3
1.117
540.335
20,9
3.985
137.341
8,8
2.695
23.497
Reservatório
71,2%
Hidrelétrica
Nuclear
Gás
Carvão Mineral
Petróleo
Eólica
Biomassa
Importação
Figura 4: Fontes primárias para geração elétrica no Brasil (EPE, 2008)
Barra Bonita
Segredo
Xingo
De um modo geral, as UHE´s apresentam vantagens interessantes sobre as UTE´s, como menores custos na implantação, maior simplicidade na operação e uma menor emissão de GEE (devido
à decomposição anaeróbia da matéria orgânica nos reservatórios
das usinas hidrelétricas). Segundo o Inventário Brasileiro de Emissões Antrópicas de GEE (Eletrobrás, 2007), as emissões médias
de GEE para as centrais elétricas da Eletrobrás são da ordem de
0,05 tCe/MWh, onde 90% da geração é feita por hidroelétricas, estimativa baseada no Greenhouse Gás Protocol Initiative – CHG Protocol (Eletrobrás, 2007). Por sua vez, com base nos fatores de emis-
22
tCe/ano
40,1
6.138
41.668
Samuel
104,0
7.448
535.407
Tucuruí
109,4
8.475
2.602.945
Itaipu
20,08
171
93.269
No Quadro 2 são apresentados os valores estimados de emissões e outros dados sobre essas UHE´s (Rosa et al., 2006) incorporando também os estudos referentes à hidrelétrica de Balbina (Kemenes et.al., 2007). É notável como a área inundada, avaliada em
(MW/km²), varia entre as centrais estudadas, afetando diretamente as emissões.
TECHNICAL ARTICLES
Quadro 2 – Emissões médias de GEE e densidade de potência
dos reservatórios brasileiros
Reservatório
Emissões
anuais
(tCe/ano)
38.332
Miranda
Potência
instalada
(MW)
Área do
reservatório
(km²)
390,0
Densidade de
Potência
(MW/km²)
50,6
7,7
Três Marias
540.335
396
1.040
0,4
Barra Bonita
137.341
140,8
312
0,5
Segredo
23.497
1.260
82
15,4
Xingo
41.668
3.000
60
50,0
Samuel
535.407
216
559
0,4
Tucuruí
2.602.945
4.240
2.430
1,7
93269
12600
1.549
8,1
6.700.000
250
2.600
0,1
Itaipu
Balbina
onde: W – Energia gerada pela UTE (MWh/ano)
C – Coeficiente de emissão (tCe/MWh)
h - Eficiência da UTE (varia entre 30% e 45%)
Segundo Sugai e Santos Jr. (2006), utilizando os coeficientes
de emissões para combustíveis fósseis fornecidos pelo Natural Resources Canadá (2000) e adotando uma eficiência média das
UTE´s brasileiras de 35%, a linha de base das emissões das UTE´s
brasileiras é cerca de 0,52 tCe/MWh.
As centrais ligadas ao sistema interligado nacional geraram
437.060 GWh em 2007, sendo 93% com UHE´s e 5% com UTE´s
(ONS, 2008). Adotando as emissões médias de GEE para as UHE´s
e UTE´s calculadas anteriormente, é possível estimar em 0,12
tCe/MWh as emissões associadas à geração de energia elétrica no
Brasil nesse ano. Na Figura 6 são apresentadas as emissões para
as diferentes tecnologias e o valor médio obtido.
Adotando um Fator de Capacidade igual a 0,6, representativo
para as UHE´s brasileiras (ONS, 2008), foi possível estabelecer
uma relação entre as emissões de GEE e a energia gerada, como
mostra a Figura 5. A linha destacada na Figura 5 corresponde à média ponderada pela potência das UHE´s estudadas, conforme a
Equação (1).
EUHE =
å E .P
åP
i
i
i
onde:
EUHE - Emissões médias de GEE para as UHE´s estudadas
(tCe/MWh)
Ei – Emissões médias da UHE “i” (tCe/MWh)
Pi – Potência instalada da UHE “i” (MW)
Figura 6: Emissões de GEE das Usinas Hidrelétricas brasileiras
3,5
Como mostrado na Figura 6, em média, as UHE´s brasileiras
emitem cerca de cinco vezes menos GEE que as UTE´s do país. Como uma clara exceção, os elevados índices emissões da UHE de Balbina diferem dos níveis observados nas UHE´s estudadas, em função da grande área do reservatório dessa central, tema que será
abordado a seguir.
3
tCe/MWh
2,5
2
1,5
1
4. AVALIAÇÃO DA CORRELAÇÃO ENTRE AS EMISSÕES DE
GEE E PARÂMETROS DAS UHE´S
Emissões médias das UHE´s estudadas (0,10 tCe/MWh)
0,5
0
Miranda
Três
Marias
Barra
Bonita
Segredo
Xingó
Samuel
Tucuruí
Balbina
Reservatório
Figura 5: Emissões de GEE por unidade de energia elétrica
gerada das UHE´s brasileiras
As centrais apresentadas na Figura 5 abrangem cerca de 30%
da capacidade instalada nas UHE´s brasileiras, cobrindo as diferentes tecnologias e regiões e assim a média de suas emissões,
0,10 tCe/MWh, podendo ser considerada uma amostra representativa para as UHE´s no Brasil.
3EMISSÕES DE GEE DO SISTEMA ELÉTRICO BRASILEIRO
As emissões anuais de GEE associadas à geração de energia elétrica no Brasil devem incluir as centrais hidrelétricas, como estimado no tópico anterior, e as emissões das centrais termelétricas, cujas emissões anuais de carbono podem ser calculadas pela seguinte equação (modificada de Rosa e Santos, 2000):
EUTE =
W.C
η
Procurando identificar eventuais relações causais no processo
de emissões de GEE em reservatórios, a seguir essas emissões são
comparadas com parâmetros como área alagada, potência instalada e tempo de residência da água dos reservatórios (relação entre
o volume do reservatório e a vazão média afluente).
Em termos de emissões de GEE por unidade de área alagada do
reservatório, como mostrado na Figura 7, as UHE´s de Balbina, Tucuruí e Samuel apresentam maiores índices, enquanto a UHE de
Itaipu apresenta os menores índices.
A emissões da UHE de Balbina não são notáveis apenas em termos absolutos, devido a sua grande área alagada, mas também
em termos específicos, como visto. Acredita-se que essas elevadas
emissões se justifiquem especialmente pelo fato da área alagada
do reservatório não ter sido desmatada previamente ao seu enchimento, como também ocorreu em grande parte do reservatório da
UHE de Tucuruí. Além disso, as medições de emissões de GEE foram feitas a partir de amostras coletadas na profundidade média
do reservatório (30 metros), local de maior concentração de CH4,
que poderia incrementar os valores estimados para as emissões
(Kemenes et al., 2007).
23
ARTIGOS TÉCNICOS
3000
zada é limitada e como mostrado na Figura 10, não se constatou
uma relação forte entre as emissões de metano (Rosa et al., 2006)
e o tempo de residência da água dos reservatórios.
2500
Quadro 3 – Tempo de residência da água dos reservatórios estudados
tCe/km²
2000
Reservatório
1500
1000
500
0
Itaipu
Segredo
Barra
Bonita
Três
Marias
Xingó
Miranda
Samuel
Tucuruí
Balbina
Figura 7: Emissões anuais de GEE por unidade de área alagada dos
reservatórios das UHE´s brasileiras
10.900
50,2
1.279
São Francisco
2.700
21,0
2.160
Iguaçu
1.413
3,0
589
Tucuruí
Tocantins
Três Marias
Segredo
Xingó
São Francisco
Itaipu
Samuel
Tempo de
Capacidade
residência
(km³)
(horas)
Vazão
média
(m³/s)
Rio
2.700
0,7
72
Paraná
120.000
29,0
67
Jamari
396
3,2
2.244
14%
10
Balbina
1
100
1000
10000
100000
Itaipu
Participação do CH4 nas emissões
Não foi observada uma relação forte das emissões de GEE e a
potência instalada e área alagada, como pode ser observado pelas
Figuras 8 e 9. Uma possível justificativa é o fato de que cada UHE
brasileira tem suas particularidades de construção e operação, como por exemplo, desmatando ou não a área alagada, o que interfere diretamente nas emissões de GEE.
12%
Três Marias
10%
8%
6%
4%
Tucuruí
Samuel
2%
Xingó
Samuel
Segredo
tCe/MWh
0%
Barra Bonita
0,1
Miranda
10
100
Quadro 4 – Emissões de GEE e tempo de residência
da água dos reservatórios estudados
0,01
Segredo
Tucuruí
Itaipu
0,001
Reservatório
MW
Figura 8: Relação das emissões de GEE com a potência instalada
das UHE´s brasileiras
10
Balbina
1
100
1000
10000
tCe/MWh
Samuel
Barra Bonita
0,1
10000
Figura 10: Relação entre as emissões de CH4 com o tempo de
residência da água dos reservatórios
Três Marias
10
1000
Tempo de Residência - TR (horas)
Xingó
Três Marias
Rio
Emissões
(tCe/ano)
Tempo de
residência
(horas)
Itaipu
Paraná
93.269
Xingó
São Francisco
41.668
72
Segredo
Iguaçu
23.497
589
Tucuruí
Tocantins
2.602.945
1.279
Três Marias
São Francisco
540.335
2.160
Samuel
Jamari
535.407
2.244
67
Tucuruí
10.000.000
Miranda
Tucuruí
0,01
Segredo
1.000.000
Itaipu
0,001
km²
Figura 9: Relação das emissões de GEE com a área alagada
das UHE´s brasileiras
Do ponto de vista do efeito estufa, o metano apresenta um impacto bem superior ao dióxido de carbono, sendo tipicamente gerado em condições anaeróbias que por sua vez dependem do tempo
de residência da água no reservatório, para o material orgânico em
suspensão. O Quadro 3 apresenta as informações de vazões médias e capacidade dos reservatórios para as UHE´s estudadas (Santos, 2006), que permitiram o cálculo do tempo de residência médio
da água nestes reservatórios. Infelizmente, a base de dados utili-
24
t Ce /a no
Xingó
Três Marias
Samuel
Itaipu
100.000
Xingó
Segredo
10.000
10
100
1000
10000
Tempo de Residência (horas)
Figura 11: Relação entre emissões de GHG e o tempo de residência
da água dos reservatórios
TECHNICAL ARTICLES
Finalmente, ao se comparar as emissões anuais de GEE dos reservatórios estudados com os tempos de residência da água, observou-se, preliminarmente, uma razoável correlação entre essas
duas variáveis (R²=0,76) como indicado no Quadro 4 e Figura 11.
A relação apresentada é preliminar, pois, um estudo com maior número de reservatórios e mais detalhado sobre a variação do tempo
de residência da água em função do período do ano, influenciado
pelo regime de vazão dos rios dos reservatórios, poderiam permitir
a melhor verificação dessa relação. Outro efeito a estudar seria a
temperatura média do reservatório, que também depende de levantamentos mais detalhados.
3.
Eletrobrás, Inventário de Emissões de Gases do Efeito
Estufa - Ano base 2005, SCMA/GT3, 2007.
4.
EPE, Empresa de Pesquisas Energéticas, Plano Decenal de
Expansão de Energia 2008/2017, Oferta de Energia Elétrica, 2008.
5.
FAPESP, Fundação de Amparo a Pesquisa do Estado de
São Paulo, www.fapesp.com.br, acessado em 08/10/2007.
6.
Fearnside, P.M., “Greenhouse-gas emissions from Amazonian hydroelectric reservoirs: the example of Brazil's Tucuruí
Dam as compared to fossil fuel alternatives”, National Institute for
Research in the Amazon (INPA), Manaus, Brazil, 1997.
7.
IPCC, International Panel on Climate Change, 2005,
www.geovivencia.com.br/ativ.asp?atividades=9,2005, acessado
em 15/08/2006.
5. CONCLUSÕES
A partir de estimativas das emissões de GEE dos reservatórios
das UHE´s e das emissões das UTE´s foram estimadas as emissões
associadas à geração de energia elétrica no Brasil. Em síntese, conclui-se que os reservatórios das UHE´s brasileiras emitem anualmente 0,10 tCe/MWh e as UTE´s 0,52 tCe/MWh, levando à uma
emissão média anual de 0,12 tCe/MWh, ponderando a contribuição
de cada fonte primária.
8.
Kemenes, A., B. R. Forsberg, and J. M. Melack, “Methane
release below a tropical hydroelectric dam”, Geophys. Res. Lett.,
34, L12809, doi:10.1029/2007GL029479, 2007.
9.
Natural Resources Canadá, Retscreen International Renewable Energy Project Analysis Software, version, 2000 – Release 2,
Minister of Natural Resources 1997-2000, 2000.
10. ONS, Operador Nacional de Sistemas, 2007, www.ons.org.br, acessado em 26/04/2008.
O estudo não identificou relação entre capacidade de geração
ou área alagada dos reservatórios das UHE´s com as emissões de
GEE, no entanto, verificou-se que existe alguma relação entre as
emissões de GEE e os tempos de residência da água dos reservatórios brasileiros. Estudos com mais detalhes sobre a operação dessas plantas, bem como com maior número de reservatórios e dados sobre a variação do tempo de residência da água em função do
período do ano, influenciado pelo regime de vazão dos rios dos reservatórios, poderiam permitir uma melhor verificação dessa relação.
11. Reis, T.V.M., “Emissões de Gases do Efeito Estufa no Sistema Interligado Nacional Metodologia para a definição de Linha de
Base e Avaliação do Potencial de Redução das Emissões do
PROINFA”, dissertação de mestrado apresentada a Universidade
Salvador – UNIFACS, Salvador, 2002.
12. Rosa, L.P., et al, “Primeiro Inventário Brasileiro de Emissões Antrópicas de Gases do Efeito Estufa”, Ministério da Ciência e
Tecnologia, 2006.
13. Rosa, L.P., Santos, M.A., “Certainty and Uncertainty in the
Science of Greenhouse Gas Emissions from Hydroelectric Reservoirs”, WCD, Environmental Issues, 2000.
Vale ainda observar que os valores de emissões estimados nesse estudo representam médias anuais para as tecnologias estudadas, não podendo ser considerados para efeito de redução de emissões quando da introdução de tecnologias mitigadoras das emissões, que impõe uma análise detida da fonte de energia deslocada
a cada caso
14. Santos, E.O., “Contabilização das emissões líquidas de
GEE de hidrelétricas: Uma análise comparativa entre ambientes naturais e reservatórios hidrelétricos”, Tese de doutorado apresentada à COPPE/UFRJ, 178 p., Rio de Janeiro, 2006.
1.
ANEEL, Agência Nacional de Energia Elétrica, 2006,
www.aneel.gov.br, acessado em 25/09/2006.
15. Sugai, H.M. e Santos Jr., M.F., “As Pequenas Centrais Hidrelétricas e os Créditos de Carbono”, PCh Notícias, edição 29, ano
8, p. 10-15, 2006.
2.
Beil, S., “Evolution and design of an emissions trading
market of greenhouse gases”, 2° Annual Emissions Trading Forum,
1999.
16. World Resources Institute, 1996, “Forest and land use
change carbon sequestration projects”, www.wri.org, acessado em
15/05/2007.
6. REFERÊNCIAS
Procurando PCHs para
investir ou suprir
sua demanada?
entre em contato conosco
[email protected]
25
ARTIGOS TÉCNICOS
SENSITIVITY OF DRAFT TUBE FLOW
PREDICTIONS TO BOUNDARY CONDITIONS
1
F.A. Payette
2
V. De Henau
3
G. Dumas
4
M. Sabourin
ABSTRACT
This numerical study aims to assess the influence of boundary conditions and mesh refinement on the flow topology in draft tubes, using the commercial code ANSYS CFX and two equations turbulence models, especially Menter's SST. The final objective of this investigation is to improve the RANS predictions of draft tubes and more specifically the flow characteristics associated with a significant turbine efficiency drop occasionally observed near the best efficiency point in rehabilitation projects. The first step of the study is to reproduce a
well-documented test case, the swirling flow inside a conical diffuser available on the ERCOFTAC's database.
Among the most important parameters, it is found that the inlet radial velocity must be specified with great care for this test case since
it is directly related to wall separation or core flow recirculations. Further, we observe that the outlet treatment used to simulate a discharge to ambient air mainly impacts the outlet pressure distribution. Actual draft tube geometry from the Chute-à-la- Savane project is
then used to confirm and extend the results validity. One of the most important results obtained in this geometry comes from the inlet turbulence. It is found that this parameter alone is sufficient to modify the flow topology and radically change the draft tube's efficiency. The
apparent sensitivity of the physics associated with the efficiency loss near the design point of some rehabilitated turbines thus requires for
a very careful and advised, complete specification of the boundary conditions.
Key words: Draft tube, RANS modelling, boundary conditions sensitivity.
INTRODUCTION
In assessing turbine global efficiency, the importance of the
draft tube simulation is widely recognized among the scientific and
industrial communities, especially when dealing with low-head
power plants. In the past years, many research projects focussed
on draft tubes simulations and proposed some guidelines on the calculations parameters to use. Among them, the FLINDT [1] and Turbine-99 [2] projects as well as related doctoral thesis such as
Mauri's [3] or Cervantes' [4] are a good source of information on
this subject. The main objective of Turbine-99 was to assess the potential of CFD to accurately predict draft tubes flows while FLINDT
focused specifically on the particular efficiency drop phenomenon
described below. There is also an ongoing measurement campaign
taking place at Laval University's Laboratory for Hydraulic Machines aiming to characterize the flow within the turbine and to
help fine-tuning computer simulations. These references, however, do not provide sufficient details on the specific impact of some
key simulation parameters and modelling approaches involved.
The present paper addresses these issues and summarizes the
work done as part of a Master Degree [5].
Since draft tube calculation confronts the CFD analyst to an inlet plane located inside the region of interest and to an outlet
boundary also very close to it, a good understanding of their individual effect is essential. Such knowledge helps understand the
sources of the errors induced when the entire geometry cannot be
modelled or, in other cases, it may also allow minimising the use of
unnecessary buffer zones or computing domain extensions while
being conscious of the resulting effect on the investigated result.
In some rehabilitation projects, the behaviour of the existing
draft tube is difficult to anticipate in relation with the newly designed runner. The interaction between those components has
sometimes been observed to cause a sudden drop in the efficiency
curve near the best efficiency point [1,6]. This phenomenon unfortunately seems to be highly sensitive and approximate numerical simulations have most often failed to predict it properly. In the
present paper, the impact of various calculation parameters reconsidered keeping mind the volatility of this particular phenomenon.
1 ALSTOM Hydro - [email protected]
26
METHODOLOGY
The first test case chosen to evaluate those parameters is the
ERCOFTAC's [7] swirling flow in a conical diffuser. It is particularly
well suited for this task due to the availability of the detailed experimental data of Clausen et al. [8] and to its similarities with actual
draft tube flows. The paper then addresses the Chute-à-la-Savane
draft tube case since this particular geometry is known to cause the
efficiency drop mentioned previously. The results help to confirm
the conclusions of the first test case and to extend the study to new
parameters as well.
The numerical investigation was conducted using ANSYS CFX
11.0 which solves three- dimensional Reynolds-averaged NavierStokes (RANS) equations. Turbulence is modelled using the implemented SST model of Menter [9] and results are in some cases compared with a standard k-є turbulence model with wall functions.
PART 1 : CONICAL DIFFUSER TEST CASE
The ERCOFTAC's test case features a swirling flow of air entering a 10o half-angle diffuser that discharges to ambient atmosphere. The area ratio of the geometry is 2.84 and the level of rotation imposed to the inlet flow was carefully adjusted during the experiment to avoid wall separation as well as the appearance of
recirculation bubble in the core flow. The inlet swirl number,
Sw =
ò R0 r 2 U q U Z dr
ò 0R rU Z2 dr
often used to quantify the level of rotation in the flow in relation
to the axial component of velocity is in this case considered representative of many draft tube flows. The geometry is schematically
reproduced in Figure 1 along with the two sets of coordinate axes
used. The velocity components Ur, Uθ and Uz are associated with the
standard cylindrical coordinates (r, θ, z) whereas Us is the wall parallel velocity component in the xs direction.
The numerical results presented in the following sections were
all obtained on a one-cell thick pseudo-2D mesh with 115 × 165 elements in the radial and axial directions, respectively. The slice is 2o
wide and the wall resolution assures 0.52 < y+ < 1.38 everywhere
3 Université Laval - [email protected]
TECHNICAL ARTICLES
along the diffuser wall whenever the SST turbulence model is used.
This mesh has proved to be fine enough to lead to mesh independent results for velocity profiles as well as turbulence profiles.
ments in the radial and axial directions, respectively. The slice
is 2o wide and the wall resolution assures 0.52 < y+ < 1.38 everywhere along the diffuser wall whenever the SST turbulence model
is used. This mesh has proved to be fine enough to lead to mesh independent results for velocity profiles as well as turbulence profiles.
radial gradient of Ur is much greater for the approximated curve
than for the computed one, which leads to an increased velocity
peak on the corresponding Us profile as shown in Figure 2b. Also
note that the grey zone in Figure 2a defines a region where the flow
should be accelerating according to the computed profile but is instead decelerating, causing the axial velocity peak to be closer to
the diffuser wall. Since the mass flow must be the same in all three
cases, a higher near-wall velocity leads to a lower level of kinetic energy around the axis. Accordingly, a recirculation bubble is shown
by the solid curve.
Opposite from this behaviour, imposing no radial velocity in the
inlet plane implies that no kinetic energy is transferred toward the
boundary layer, and its weakness eventually leads to the separation of the flow from the wall, as visible at location S7 presented.
The fluid is thus forced to flow in the middle of the diffuser yielding
higher speeds in this area and very poor comparison with experimental data. From these evidences, we conclude that the inlet radial velocity component is of high importance in correctly reproducing this swirling flow.
Fig 1: Sketch of the diffuser with experimental measurement stations and
reference systems used. Dimensions are in mm.
INLET RADIAL VELOCITY AND TURBULENCE
The first simulations of the conical diffuser were made using a
zero radial velocity on the inlet boundary condition which was
thought to be a reasonable choice since the inlet plane is located in
a cylindrical duct, 25 mm upstream from the diverging section.
However, the unsatisfying results obtained quickly showed the importance of the radial component of velocity in the development of
the whole flow field. A rotating cylinder was then added upstream
of the domain to simulate the swirl generator used in the experimental study. This addition revealed the disregarded presence of a
small, but essential, radial velocity component at the inlet plane.
Adding this numerically computed velocity component dramatically improves the agreement with the experimental data even
though Ur peaks at less that 3% of the average inlet axial velocity.
Next, the common approximation
U r = Uz tan θ
where θ is a function of the diffuser half-angle defined by θ = θ
wall (r/R) is compared with the other two cases. Figure 2 illustrates
the velocity profiles near the exit of the diffuser for the three radial
velocity profiles specified at the inlet. Clearly, the effect of Ur must
not be neglected.
The results presented in Figure 2 can be examined using the
continuity equation expressed in cylindrical coordinates. Under the
hypothesis of axisymmetry, the equation simplifies to ∂ /θ∂ term
drops and the equation simplifies to
¶U Z 1¶rUr
+
=0
¶Z
r¶r
Interestingly, additional verifications proved that the inlet radial velocity affects the flow predicted by the k-ε turbulence model
in a different manner, most probably due to the use of wall functions. Using equation (2) in a k-ε model yields the same conclusion
than with the SST, but imposing Ur = 0 leads to a k-ε solution that is
much better than for the SST case. This is thought to explain the acceptable agreement between the k-ε solution with no inlet radial velocity and the experimental data reported in the past by some authors (e.g. Mauri [3] and Page et al. [10]). However, other authors
using the SST turbulence model have faced difficulties in matching
the experimental results with this test case [11,12]. It thus appears that the inlet radial velocity is needed to re-energize the
boundary layer in a SST simulation, and that it is the wall function
approximation in k-ε model with no inlet radial velocity that compensates with its intrinsic, increased boundary layer robustness.
However, relying on log-layer wall functions to compensate for the
lack of precision of the inlet boundary should not be viewed as reliable in our opinion.
Since in most cases no information is available on the inlet turbulence parameters, qualified guesses also have to be made to estimate them as accurately as possible. To assess the role played by
these assumptions, five different approaches, divided in two categories are compared and summarized in Table 1. The first category
uses the available measured profile of turbulent kinetic energy k
while it estimates the turbulence dissipation rate ε using two different equations. The first of them is proposed by Armfield et al [13] in
his numerical study of this test case, and the second is taken from a
one-equation model reported in Cousteix & Aupoix [14]. The other
approach considered is to make approximations on both k and ε using constant turbulence intensity and a length scale being a fraction of the inlet diameter, Di.
Results presented in Figure3 confirm that the imposed turbulent parameters do have an influence on the solution's accuracy.
For the present test case, best results are obtained using the meaTable 1: Turbulence parameters imposed at the inlet boundary.
Fig 2: Radial velocities imposed at the diffuser inlet and resulting
velocity profiles at station S7.
We deduce from this expression that the presence of a nonzero radial velocity thus imposes the spatial rate of change of the
one is decelerating. It can be noted on Figure 2a that the near-wall
27
ARTIGOS TÉCNICOS
sured k profile and Armfield's equation for ε or, alternatively, using
the combination I=0.05 with Le=10%Di. However, a fundamental
difference exists between these two modelling approaches. The effective viscosity is the sum of the fluid viscosity and the eddy viscosity, the latter being related to both k and ε in the following way:
ut µ
K
e
2
Fig 4: Outlet extensions geometry.
Fig 3: Effect of the inlet turbulence on axial velocity profiles
and eddy viscosity.
The effective viscosity is therefore modified by the turbulent
quantities imposed at the diffuser inlet. As can be seen in Figure
3b, it is considerably larger in the case using Le = 10%Di, despite
the similarity in the predicted Us profiles. As expected, a higher viscosity tends to damp the fluctuations in the flow as visible in region
A of Figure 3a. The opposite behaviour is also seen in region B
where the fluidity of the flow in the case Le = 0.1%Di allows the
boundary layer to briefly separate at station S4, as showed by the
local negative velocity, but to reattach before station S7.
Despite the good results noted here, using the approximation
Le = 10%Di appears to be a risky operation due to the resulting
damping that tends to makes the flow artificially robust, and because of the difficulty to determine the correct turbulence length
scale to privilege in other applications. Moreover, the problematic
approximation does not seem to lie in the eddy length scale itself
but rather in the constant turbulence intensity imposed. Looking
back at Armfield's equations presented in Table 1, it can be noted
that this model also needs a fraction of the inlet diameter to characterize the turbulence. It thus seems that the error may mostly be
attributed to the use of a uniform intensity I, which gives a turbulence kinetic energy, profile very different from the measurements.
In this case, imposing Le = 10%Di only hides the induced error and
should not in any case be associated with a reliable modelling procedure.
TREATMENT OF THE OUTLET CONDITION
The impact of the outlet geometry is determined by comparing
five extensions downstream of the diffuser. The size and geometry
of the discharge tanks added (with solid and/or permeable walls)
are shown on Figure 4, the simplest being no extension at all.
As a first step, boundaries 1 & 2 are specified to be standard noslip walls as to represent a physical tank. The effect of varying the
geometry is in most cases negligible for the axial and tangential velocity profiles, but the pressure distribution in the outlet plane is indeed changed. On the left hand side of Figure 5, it is seen that the
Pwall - Patm
wall pressure normalized as,
Cp =
1 / 2r U i
begins to be affected by the extension geometry at 70% of the
diffuser wall length, L. In the outlet plane, the pressure distribution
along r varies considerably between all simulations as shown by
the right hand side of the figure.
The geometry of the extension thus affects the pressure results
near the diffuser's exit. However, the shape of the extension do-
28
Fig 5: Pressure evolution along the diffuser wall and
profile in the outlet plane.
main is not the only parameter be considered to model the test
case properly. The boundary conditions imposed on the extension
also have to be as accurate as possible and this is why two additional simulations using the medium tank are presented on Figure
5. In both cases, the standard no-slip walls are removed on boundary 1 and 2. In the first case, a zero total pressure is imposed on the
extension's back and top (boundary 1 & 2) to make the best representation possible of a large volume of fluid at rest. In the other
case, only the back of the tank (boundary 1) uses this condition
while boundary 2 is a free slip-wall. Both pressure curves are
superposed but differ from the one using standard no-slip walls.
This leads to the conclusion that the treatment of the extension's
boundaries is significant, but in this particular case, the results remain unaffected as long as fluid entrainment by the free jet is free
to occur. It is to be noted that the flow topology within the extension box is considerably altered between the two cases, but this
has no effect on the results inside the diffuser itself since the velocities are small (see flow fields presented in [5]).
The radial variation of the pressure in the outlet plane is not to
be neglected since it is directly related to the machine's efficiency.
One way to quantify the quality of a diffuser is to look at the amount
of kinetic energy converted into pressure via the recovery coeffiP2 - P1
cient, defined as
X=
2
1 æç Q ö÷
rç
2 è Aref ÷ø
The static pressures P1 and P2 can be determined from an integration of the values in the entire plane or from an average of the
wall pressure values. These two options were evaluated for the diffuser with extensions using no slip walls and results are presented
in Table 2. The variables χwall(1) and χwall(2) use the parietal pressure at positions defined in Figure 4. The first of these two coefficients includes the last portion of the geometry, thus being more affected by the extension than the same measure taken farther inside the diffuser. Although the velocity profiles inside the diffuser
are not significantly affected by the extension's shape, it is important to keep in mind that it is likely to influence the pressure recovery coefficient, especially when calculated from wall pressure and
close to the outlet.
TECHNICAL ARTICLES
Table2:Diffuser's recovery coefficients for various extension boxes(no slip walls).
PART 2 : CHUTE-A-LA-SAVANE DRAFT TUBE STUDY
The Chute-à-la-Savane draft tube has been selected for a comparative study aiming to confirm and refine the investigation on the
sensitivity of numerical results to calculation parameters. This particular draft tube was chosen despite the absence of experimental
results since it is known to clearly present the efficiency loss described in Loiseau et al. [6].
MESH SIZE
The first step conducted was to evaluate mesh independency to
confirm the validity of the results and to give an idea of the refinement needed to properly evaluate draft tube performances. Three
meshes containing 1.15, 2.02 and 3.60 millions of structures hexahedral elements were used. Quite surprisingly, all three meshes led
to similar results in terms of performances as well as flow topology.
Obviously, the most refined case gave a little more details in the
flow field but the main flow characteristics were present in the
three cases, confirming that an acceptable mesh independency
had been reached. The relative error made on the IEC losses, eval2
æ
1 æ Q ö ö÷
uated as
P
- ç P + rç
÷
tot , in
IEC _ losses =
ç
è
2 çè Aout ÷ø ÷
ø
rgH n
out
is of the order of 2.5%, the absolute values ranging from
1.93% to 1.89% and 1.88% as the mesh is refined. We thus infer
that refining the mesh to a very high number of elements is not the
parameter that has the most influence on the flow topology. In
cases where only a good approximation is sought and computing
time is a critical factor, it seems reasonable to use a moderate-size
mesh. For the following investigations, the intermediate 2.02M elements mesh is used.
AXISYMMETRY OF THE INLET BOUNDARY CONDITION
When experimental data is available at the inlet boundary, it is
often measured on a single axis. Although this is well suited for
axisymmetric geometries such as that of the ERCOFTAC's conical
diffuser, it is found that making a 1D approximation only has a moderate impact on the computed CEI losses. The error induced by
such an approximation in the case of the Chute-à-la-Savane draft
tube is just a little more that 0.1%.
INLET TURBULENCE LEVEL
The conical diffuser test case showed that two different methods of specifying the inlet turbulence led to similar results. It was
then said that using a turbulence intensity of 5% and an eddy
length scale equal to 10% of the runner diameter is risky since it
tends to artificially smooth the flow characteristics. Results obtained in the Chute-à-la-Savane geometry are very convincing on
this point. Figure 6 shows contours of the axial velocity in the draft
tube channels. In the first case, the turbulence was taken from a
simulation including the distributor and runner. In the second case,
imposing the combination I & Le leads to a much more uniform distribution of the flow where the recirculation bubble blocking the
right channel disappears. As a consequence, the calculated losses
considerably decrease from 1.89% to 1.42%.
Fig. 6 : Axial velocity contours in the draft tube channels with
turbulence calculated from a) upstream components and
b) the approximation I=5% and Le=10%Di.
It is clearly seen from this example that modifying the inlet turbulence level can, by itself, modify the whole flow field even if the
imposed velocity profiles are unchanged. In the present case, using 10% of the inlet diameter as the eddy length scale leads to an
obviously too viscous flow and the calculated losses are underestimated of 0.5% (absolute), which could lead to costly penalties in a
contractual context.
FINAL CONSIDERATIONS
Simulating diffusers using computational fluid dynamics has always been a difficult task due to the unstable nature of the flows under adverse pressure gradients. It has been showed by studying
two test cases — the ERCOFTAC's swirling flow in a conical diffuser
and the Chute-à-la-Savane draft tube — that the imposed boundary conditions have an important impact on the calculated flow topology. Among these parameters, the inlet radial velocity was
shown to have the greatest impact on the conical diffuser's flow
since it is directly related to the appearance of wall separation or
core flow recirculation. The second most important parameter is
probably the inlet turbulence and its role is best seen in the draft
tube geometry. Overestimating the incoming turbulent mixing artificially rises the viscosity and leads to a much more uniform flow
which tends to underestimate the draft tube losses. The third aspect to recall is the outlet treatment. The addition of an outlet discharge extension did not influence much the velocity profiles inside
the conical diffuser, but it did modify the outlet static pressure distribution and consequently altered the calculated recovery coefficient. It is not excluded that, in some cases, it might even have an
impact on velocity profiles within the diffuser, especially in the last
part of the geometry.
On the other hand, refining the mesh and imposing an
axisymmetric boundary condition did not appear to have a first order influence on the computed results. These two parameters
should however be taken into account as precisely as possible
when suspecting the presence of very sensitive phenomena such
as the efficiency drop near the best efficiency point.
ACKNOWLEDGEMENT
The first author would like to thank the Natural Sciences and Engineering Research Council of Canada for its financial support to
this research project.
[1] AVELLAN, F., 2000, Flow Investigation in a Francis Draft
Tube : The FLINDT Project, Proceedings of the Hydraulic Machinery
and Systems, 20th IAHR Symposium, Charlotte, USA.
[2] Turbine-99 website : www.turbine99.org
[3] MAURI, S., 2002, Numerical Simulation and Flow Analysis
of an Elbow Diffuser, Doctoral Thesis, École Polytechnique de
Lausanne, Switzerland.
29
ARTIGOS TÉCNICOS
UNSTEADY FLOW WITH CAVITATION IN VISCOELASTIC PIPES
1
Alexandre K. Soares
1
Dídia I. C. Covas
1
Helena M. Ramos
2
Luisa Fernanda R. Reis
ABSTRACT
The current paper focuses on the analysis of transient cavitating flow in pressurised polyethylene pipes, which are characterized by viscoelastic rheological behaviour. A hydraulic transient solver that describes fluid transients in plastic pipes has been developed. This solver
incorporates the description of dynamic effects related to the energy dissipation (unsteady friction), the rheological mechanical behaviour
of the viscoelastic pipe and the cavitating pipe flow. The Discrete Vapour Cavity Model (DVCM) and the Discrete Gas Cavity Model (DGCM)
have been used to describe transient cavitating flow. Such models assume that discrete air cavities are formed in fixed sections of the pipeline and consider a constant wave speed in pipe reaches between these cavities. The cavity dimension (and pressure) is allowed to grow
and collapse according to the mass conservation principle. An extensive experimental programme has been carried out in an experimental
set-up composed of high-density polyethylene (HDPE) pipes, assembled at Instituto Superior Técnico of Lisbon, Portugal. The experimental facility is composed of a single pipeline with a total length of
203 m and inner diameter of 44 mm. The creep function of HDPE pipes was determined by using an inverse model based on transient
pressure data collected during experimental runs without cavitating flow. Transient tests were carried out by the fast closure of the ball valves located at downstream end of the pipeline for the non-cavitating flow and at upstream for the cavitating flow. Once the rheological behaviour of HDPE pipes were known, computational simulations have been run in order to describe the hydraulic behaviour of the system
for the cavitating pipe flow. The calibrated transient solver is capable of accurately describing the attenuation, dispersion and shape of observed transient pressures. The effects related to the viscoelasticity of HDPE pipes and to the occurrence of vapour pressures during the
transient event are discussed.
Key words: cavitating flow; fluid transients; viscoelasticity; pipelines; experimental data.
INTRODUCTION
Typically, hydraulic transient analysis is carried out in the design of pressurised pipe systems in order to guarantee their security, reliability and good performance for various normal operating
conditions [2, 6, 18]. This analysis is equally important in the operation stage for the diagnosis of existing problems and the calculation of different operational scenarios. Prediction of maximum transient pressures is used for the verification if pipe materials, pressure classes and wall-thicknesses are sufficient to withstand predicted pressure loads to avoid pipe rupture or system damage. Verification of minimum allowable pressures is important to prevent air
release, cavitation and water column separation, and, consequently, avoid pipe collapse or pathogenic intrusion into the system. When severe transients cannot be avoided, either pipe layout
and system parameters are changed (e.g., operating conditions),
or surge protection devices are specified (e.g., pressurised vessels
or air-relief valves), so as to sustain extreme transient pressures
within acceptable limits. Usually, the decision is the most economical and reliable solution that yields an acceptable transient pressure response.
Classic water hammer theory is generally used, as it reasonably well describes extreme transient pressures. Most software
packages available are based on this theory. The classic approach
assumes that the pipe-wall has a linear-elastic rheological behaviour, friction losses are described by quasi-steady formulae, flow is
one-phase and the pipe is completely constrained axially [18].
These assumptions are not always valid, as there are natural phenomena that rapidly attenuate or increase transient pressures
such as fluid friction during fast-transients [19], leaks [7], the mechanical behaviour of plastic pipes [8, 9, 13], dissolved or entrapped air [10-12] and multi-pipe systems.
The aim of the current paper is to present the results of the com
bination of different dynamic effects (i.e., pipe-wall
viscoelasticity and cavitation) in hydraulic transient calculations
as well as to discuss the importance of these phenomena in the
analysis of each particular situation. For this purpose, physical data
were collected from an experimental polyethylene (PE) pipeline, assembled in the Hydraulic Laboratory of Civil Engineering Department of Instituto Superior Técnico (Lisbon, Portugal). A series of
transient tests were carried out collecting pressure at four different
locations. A hydraulic transient solver incorporating the description
of different phenomena (e.g., unsteady friction, pipe-wall
viscoelasticity, distributed cavitation) has been developed and
used to analyse these case studies. An inverse transient solver has
been used to calibrate several parameters. Collected data are compared with the results of numerical simulations. Conclusions are
drawn concerning the importance of considering these effects in design and during the system operation.
MATHEMATICAL MODELS
Viscoelastic model
Equations that describe the one-dimensional transient-state
flows in viscoelastic closed conduits are the momentum and continuity equations (Eq. 1 and 2, respectively). Since the flow velocity
and pressure (dependent variables) in transient flows are functions
of time and space (independent variables), these equations are a
set of two hyperbolic partial differential equations [2, 6, 9, 18]:
1dQ
¶H
+g
+ gh f = 0
Adt
¶x
dH a 2 ¶Q 2 a 2 de r
+
+
=0
dt gA¶x
gdt
where x = coordinate along the pipe axis; t = time; H =
piezometric head; Q = flow rate; a = celerity or elastic wave speed
1 Technical University of Lisbon - TULisbon - Portugal; [email protected]
2 São Carlos School of Engineering, USP, Brazil; [email protected]
30
TECHNICAL ARTICLES
(dependent on the fluid compressibility, and on the physical properties and external constraints of the pipe); g = gravity acceleration; A = pipe cross- sectional area; εr = retarded strain component (in viscoelastic pipes the total strain can be decomposed into
an instantaneous-elastic strain and a retarded strain); and hf =
head loss per unit length (hf = fQ|Q|/2DA2 in turbulent conditions,
in which f = Darcy-Weisbach friction factor and D = pipe inner diameter). These equations assume: pseudo-uniform velocity profile;
linear viscoelastic rheological behaviour of the pipe-wall; onephase, homogenous and compressible fluid, though with negligible
changes in density and temperature; uniform and completely constrained from axial or lateral movement pipe.
piezometric head; Q = flow rate; a = celerity or elastic wave
speed (dependent on the fluid compressibility, and on the physical
properties and external constraints of the pipe); g = gravity acceleration; A = pipe cross- sectional area; εr = retarded strain component (in viscoelastic pipes the total strain can be decomposed into
an instantaneous-elastic strain and a retarded strain); and hf =
head loss per unit length (hf = fQ|Q|/2DA2 in turbulent conditions,
in which f = Darcy-Weisbach friction factor and D = pipe inner diameter). These equations assume: pseudo-uniform velocity profile;
linear viscoelastic rheological behaviour of the pipe-wall; onephase, homogenous and compressible fluid, though with negligible
changes in density and temperature; uniform and completely constrained from axial or lateral movement pipe.
The set of differential equations (Eqs. 1 and 2) can be solved by
the Method of Characteristics. The stability of this method requires
the verification of a numerical restriction for the time and space
steps, given by the Courant-Friedrich-Lewy stability condition,
dx/dt = V±a. This condition allows the transformation of these
equations into a set of total differential equations valid along the
characteristic lines dx/dt = ±a:
The set of differential Equations 1 and 2 together with the
strain-stress equation (Eq. 4) can be solved by the Method of Characteristics. The total strain generated by a continuous application
of a stress σ(t) is:
in which J0 is the instantaneous creep compliance and J(t') the
creep function at t' time.
In these equations, the retarded strain time-derivative term
cannot be directly calculated and requires further numerical
discretization. In order to numerically describe the rheological mechanical behaviour of the pipe-walls (creep function), the generalized Kelvin-Voigt mechanical model of a viscoelastic solid is incorporated in the hydraulic transient equations [1]:
where J0 = creep compliance of the first spring defined by J0 =
1/E0; E0 = Young's modulus of elasticity of the pipe; Jk = creep
compliance of the spring of the Kelvin-Voigt k-element defined by
Jk = 1/Ek; Ek = modulus of elasticity of the spring of k-element; tk
= retardation time of the dashpot of k-element, tk = μk/Ek; μk =
viscosity of the dashpot of k-element; and NKV = number of KelvinVoigt elements. Parameters Jk and tk are determined by inverse
calculation from experimental data. According to this mathematical model, the terms ∂ εr/∂ t and εr are calculated as the sum of
these factors for each Kelvin-Voigt element k:
where the function F(i,t) is defined by:
where g = fluid volumetric weight; e = pipe-wall thickness; and
α=dimensionless parameter (function of pipe cross-section dimensions and constraints).
At any interior grid intersection point, the two compatibility
equations (Eq. 3) and Eqs. 6 and 7 are solved simultaneously for
the unknowns εr(i,t), Qi,t and Hi,t. In this research work, a general, simplified linear form for the linear-elastic conduit or the linear-viscoelastic pipe useful for complex, multi-pipe systems has
been used [16]. To complete the solution at any time instant, appropriate boundary conditions have been introduced specifying additional equations at the ends of each pipe [2, 6, 18].
Discrete vapour cavity model (DVCM)
The discrete vapour cavity model (DVCM) is widely used in standard water hammer software packages for column separation and
distributed cavitation analyses [3]. This model is based on the column separation hypothesis that the flow of liquid in the tube is instantaneously and completely separated by its vapour phase when
the cavity is formed. Cavities are allowed to form at any of the computational sections if the pressure is computed to be below the
vapour pressure. Pure liquid with a constant wave speed is assumed to occupy the reach in between two computational sections.
The absolute pressure in a cavity is set equal to the vapour pressure (p*=pv*). The upstream and downstream discharges QPu
and QP at a cavity are computed from the compatibility relations
(Eq.3), and, ignoring mass transfer during cavitation, its volume
follows then from:
which is numerically approximated in the Method of Characteristics with a staggered grid by:
in which ∀ tp and∀ pt−2Δt are the volumes at the current time and
at 2Δt earlier, and ψ is a P numerical weighting factor. The cavity collapses when its calculated volume becomes less than zero. The liquid phase is re-established and the standard water hammer procedure is valid again.
Although the vapour column separation model is easily implemented, it has some serious deficiencies as stated by Shu [14]: (i)
to avoid the prediction of negative cavity sizes (or the prediction of
negative absolute pressures), artificial restrictions are imposed,
which result in unrealistically large pressure spikes that discredit
the overall value of the numerical results;
(ii) the internal boundary condition permits vapour cavities to
be formed only at computing nodes, and the simulation results are
biased according to where the computing nodes are located; (iii) because the size of the cavity and its mass transfer are ignored, the
model is clearly limited in its ability to model cavitation correctly;
(iv) at each computing node, a flow rate discontinuity is assumed
and there will be two predicted values of flow rate, which is clearly
31
ARTIGOS TÉCNICOS
inconsistent with the observed behaviour at each point. In addition, the difference between the two predicted values increases
when there is a high degree of cavitation and also when the number
of computing nodes is small. On the other hand, when a large number of computing nodes is used, there are a corresponding number
of discontinuities leading to a mathematical model that is ill defined. Simpson and Bergant [15] recommended that the maximum
volume of discrete cavities at sections is less than 10% of the reach
volume.
Discrete gas cavity model (DGCM)
Transient flow of a homogeneous gas-liquid mixture can be described by the classical water hammer equations in which the liquid
wave speed a is replaced by the wave speed am [17]:
time, respectively; CT = a parameter which affects the wave speed
time variation. The wave speed variation was carried out at the
same time by a time step variation Δt, in order to avoid Courant
modification.
For the description of fluid and pipe material non-elastic behaviour, two reduction coefficients (KH and KQ) were included in the
MOC equations:
where I = the head loss term; ΔH and ΔQ = head and discharge
variation, respectively. Parameter KH gives a reduction in the head
variation when induced by a discharge variation by non-elastic fluid
(due to the presence of free gas) and pipe (plastics) deformation.
KQ is a reduction coefficient in the discharge value caused by a
head variation, due to a non- elastic response in the recuperation
phase of the deformation.
CASE STUDY
where αg = gas void fraction; and ρ = liquid mass density.
An alternative to modelling free gas distributed throughout the
liquid in a homogeneous mix can be achieved by lumping the mass
of free gas at computing sections leading to the discrete gas cavity
model (DGCM). Each isolated small volume of gas expands and contracts isothermally as the pressure varies, in accordance with the
perfect gas law [18]:
An isothermal volume versus head relationship is assumed at a
gas cavity:
in which the constant C3 can be computed from:
where p0*=a reference absolute pressure; a0 = void fraction
at p0 (ratio of volume of free gas to the mixture volume); z = elevation of the pipe; and Hv=gauge vapour pressure head of the liquid.
An extensive experimental programme has been carried out in
an experimental set-up composed of high-density polyethylene
(HDPE) pipes, assembled at Instituto Superior Técnico of Lisbon,
Portugal (Figure 1). The experimental facility is composed of a single transmission pipeline with a total length of 203 m and inner diameter of 44 mm. This pipeline is connected to an air vessel at the
upstream end and to a free discharge outlet into a constant water
level at the downstream end. A ball valve is installed immediately
downstream the air vessel and it is used to interrupt the flow in order to perform a fast closing manoeuvre. The air vessel was used to
keep the upstream pressure constant as an elevated reservoir.
Transient pressure data have been collected using pressure transducers located at four pipe sections with a frequency of 500 Hz (at
the air vessel; downstream the ball valve at upstream end of the
pipeline - Section 1; at the middle of the pipeline - Section 5; and at
downstream end of the pipeline – Section 6).
As in the DVCM, between each computing section, or concentrated gas volume, pure liquid with a constant wave speed is assumed without free gas. The DGCM is also able to simulate vaporous cavitation by utilizing a low initial gas void fraction (a0 ≤ 10-7)
at all computational sections [15, 17].
Borga et al.'s model
Borga et al. [4] presented numerical results, which were obtained based on the traditional vapour-liquid model, introducing
several modifications in order to better simulate observed dissipation and dispersion of transient pressures due to mechanical, frictional and inertial dynamic effects. The following changes have
been incorporated: (i) modification of Courant number; (ii) modification of friction loss coefficient (or head loss); (iii) modification of
wave speed by an exponential law in time but uniform along the
pipe axis; and (iv) modification of coefficients of the characteristic
equations which affect the transformation of kinetic energy into
elastic one and vice-versa.
The modification of the head loss coefficient is obtained by using a multiplicative coefficient, KR, and a coefficient of second order term in the integration of head loss, KT.
In the simulation of the variable celerity, it is considered an exponential variation along time, uniform along the entire pipe, according to the following equation:
where a0 and a0.af = the wave speed values at initial and final
32
Figure 1. Experimental set-up with high-density polyethylene pipes
MODEL CALIBRATION
In order to analyze the pressure transients in the system, two
different tests have been carried out: (i) fast closure of downstream end ball valve (without cavitating flow) for creep function
analysis; and (ii) fast closure of the upstream end ball valve for
cavitating flow analyses utilizing DVCM, DGCM and Borga et al.'s
[4] model.
Pipe-wall viscoelasticity analysis
In order to determine the mechanical behaviour of the HDPE
pipe system, transient tests were carried out by closing the downstream end ball valve (without cavitation). The viscoelastic transient solver developed in this study was used neglecting unsteady
friction and the HDPE creep function was numerically determined
by means of inverse calculations.
The creep compliance function J(t) is numerically described by
the generalized Kelvin- Voigt mechanical model. This model is represented by the instantaneous elastic creep J0 and the retarded coefficients, Jk and τk for each Kelvin-Voigt element. Usually this
TECHNICAL ARTICLES
creep compliance function is unknown and it has to be experimentally estimated, either by using an inverse procedure (calibration)
or by carrying out mechanical tensile tests of pipe specimens.
downstream the ball valve - Figure 3) and Section 5 (middle pipe
section – Figure 4).
An inverse model based on Levenberg-Marquardt search
method (LM) has been developed and was used to determine the
coefficients of the creep compliance function J(t). Elastic wave
-1
speed was estimated as 315 m/s (E0 = 1.43 GPa; J0 = 0.70 GPa ;
Δt = 0.002 s; and Δx = 0.63 m).
Several initial numerical simulations were run to find the best
number of Kelvin-Voigt elements. The optimal number of KelvinVoigt elements was obtained by using three elements (T1 = 0.018
s;J1 = 0.256 GPa-1;T2 = 0.50 s;J2 = 0.238 GPa-1; and T3 = 3.0 s; J3
-1
= 0.290 GPa ). A complete calibration analysis of the HDPE pipe rig
can be found in Carriço [5].
Numerical results obtained by using the linear viscoelastic transient solver are presented in Figure 2 (Q0 = 2.72 L/s; Re ≈ 80,000)
for the Section 6 of the pipe rig (downstream end of the pipeline
and immediately upstream the ball valve). Numerical results fitted
observed pressure data extremely well. Unsteady friction losses
are assumed to be described by the creep function calibrated.
Figure 2.Numerical results (without cavitation and taking into account
pipe-wall viscoelasticity) versus experimental data at
Section 6 (Q0 = 2.72 L/s; Re ≈ 80,000)
Figure 3.DVCM numerical results (neglecting and taking into account
pipe-wall viscoelasticity) versus experimental data
at Section 1 (Q0 = 4.0 L/s; Re ≈ 120,000)
Figure 4.DVCM numerical results (neglecting and taking into account
pipe-wall viscoelasticity) versus experimental data
at Section 5 (Q0 = 4.0 L/s; Re ≈ 120,000)
Numerical results during cavitating flow
Transient tests were carried out by closing the upstream end
ball valve to originate cavitating pipe flow in the system. Initially,
the creep function calibrated for non-cavitation tests was used in order to describe the system mechanical behaviour. Actually, when
pressure decreases and reaches the vapour pressure, a gas cavity
is formed and consequently decreases the wave speed. In this way,
a new set of viscoelastic parameters was determined and it has
been assumed that unsteady friction losses, pipe-wall
viscoelasticity and wave speed variation due to localised gas cavities were described by the creep function.
Elastic wave speed was estimated as 250 m/s (Δt = 0.08 s and
Δx = 20.0 m) and three Kelvin-Voigt elements were used (T1 = 0.10
-1
-1
s; J1 = 0.60 GPa ; T2 = 0.50 s; J2 = 0.35 GPa ; and T3 = 3.0 s; J3 =
-1
0.50 GPa ).
The discrete vapour cavity model (DVCM) and the discrete gas
cavity model (DGCM) developed in this study were used in order to
describe the cavitating flow in the system. In the later, a small void
fraction was adopted (α0 ≤ 10-7), since the flow did not exhibit distributed air bubbles at the beginning of the tests.
Numerical results obtained by using the DVCM and the linear
viscoelastic transient solver are presented for two locations of the
pipe rig: Section 1 (upstream end of the pipeline and immediately
Figure 5. DGCM numerical results (taking into account pipe-wall
viscoelasticity) versus experimental data
at Section 1 (Q0 = 4.0 L/s; Re ≈ 120,000)
The use of DVCM taking into account pipe-wall viscoelasticity
has shown that the attenuation and dispersion in the transient pressures were not described. In addition to the deficiencies pointed
out by Shu [14], this is due to the assumption of the absolute pressure in the gas cavities being set equal to the vapour pressure and
the energy dissipation during the expansion and contraction of the
gas cavities being neglected.
33
ARTIGOS TÉCNICOS
In this way, the DGCM has been used in order to describe the
system behaviour, considering a small initial void fraction (α0 ≤ 107). Numerical results obtained by using the DGCM and the linear
viscoelastic transient solver are presented for two locations of the
pipe rig: Section 1 (upstream end of the pipeline and immediately
downstream the ball valve – Figure 5) and Section 5 (middle pipe
section – Figure 6).
system behaviour.
The wave speed variation is shown in Figure 7, considering the
creep function determined. Starting from 250 m/s, the wave speed
becomes nearly constant after 8.0 s with a final value of 167 m/s.
Numerical results obtained by using Borga et al.'s model are depicted in Figure 8 for transient pressures collected at Section 1, and
in Figure 9 for pressure variation at Section 5, considering the following parameters: a0 = 300 m/s; af = 0.8; CT = 5; KR = 1.0; KT =
0.5; KH = 0.4; and KQ = 1.4.
A third attempt in order to describe the system behaviour has
been done by using Borga et al.'s [4] model. In this model, the authors have incorporated modifications in different characteristic parameters, such as wave celerity, head losses and coefficients of
the characteristic equations. The numerical results were obtained
by using the discrete vapour cavity model (DVCM).
Whilst numerically less complex than the viscoelastic model
this simplified model can provide better results than those obtained by using both DVCM and viscoelastic model. Actually, the
viscoelastic mechanical behaviour of the pipe-walls is described by
Eq. 15 and the energy dissipation during growth and collapsing of
gas cavities is reproduced by the multiplicative coefficients of head
loss and characteristic equations.
Figure 6. DGCM numerical results (taking into account pipe-wall
viscoelasticity) versus experimental data
at Section 5 (Q0 = 4.0 L/s; Re ≈ 120,000)
Figure 8. Borga et al.'s model numerical results versus
experimental data at Section 1(Q0 = 4.0 L/s; Re ≈ 120,000)
Figure 7. Wave celerity variation
The use of DGCM taking into account pipe-wall viscoelasticity
has shown that:
(i)
a better adjustment to the experimental data was obtained by DGCM than those one when utilizing the DVCM;
(ii) the assumption of the ideal gas law is more appropriate
than the simple adoption of vapour pressure when pressure
reaches vapour pressure (DVCM) – this influences the energy dissipation during the expansion and contraction of gas cavities. In
DGCM formulation, the exponent of the polytropic gas is assumed
to be equal to 1.0 in order to obtain explicit equations and considering that the free gas is assumed to behave isothermally, which is
valid for tiny bubbles. In this study, large bubbles were formed on
the upper part of the pipe cross-section and growth along the pipe
axis. Large bubbles and column separations tend to behave adiabatically. It is recommended further analyses of the exponent of
the polytropic gas and of the implicit formulation;
(iii) some features of the HDPE pipe rig during the transient
tests, such as pipe displacement and a free discharge outlet at the
downstream end of the pipeline, lead to more uncertainties on the
34
Figure 9. Borga et al.'s model numerical results versus
experimental data at Section 5 (Q0 = 4.0 L/s; Re ≈ 120,000)
CONCLUSIONS
The current paper presented experimental tests and numerical
analyses of water hammer with cavitation in a pressurised single
transmission pipeline composed of high-density polyethylene
pipes. Pressure data in turbulent conditions were collected during
transient events caused by valve closure. A hydraulic transient
solver that takes into account pipe-wall viscoelasticity mechanical
behaviour has been developed. Such measured data were used to
TECHNICAL ARTICLES
calibrate and verify three developed mathematical models to the
description of cavitating pipe flow: discrete vapour cavity model
(DVCM), discrete gas cavity model (DGCM) and a simplified model
proposed by Borga et al. [4].
Obtained numerical results showed that DVCM is imprecise for
the description of hydraulic system behaviour. Whilst such model is
on the safest side for design purposes as it predicts higher
overpressures, it is not accurate for calibration purposes due to the
neglecting of the energy dissipation during the expansion and contraction of the gas cavities. The assumption of the ideal gas law
(DGCM) is more appropriate than the simple adoption of vapour
pressure when pressure reaches vapour pressure (DVCM) and induces more attenuation and dispersion of transient pressures. For
cavitating flows, a new set of viscoelastic parameters was determined and it was assumed that unsteady friction losses, pipe-wall
viscoelasticity and wave speed variation due to the formation of
localised gas cavities were described by the creep function.
The simplified model proposed by Borga et al. [4] provided
better results than those obtained by using DVCM. This model can
be an alternative numerically less complex than the viscoelastic
model.
Considering the analysis carried out in this work, cavitation
flows in pressurised systems composed of plastic pipes have to be
better analyzed. The study of new numerical methods, such as
two-dimensional (2D) methods, can be the solution for the description of pressure transients during cavitation.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the financial
support
of: "Coordenação de Aperfeiçoamento de Pessoal de Nível Superior" [(CAPES, Brazil), who provided a post- doctoral scholarship to
the first author]; the Portuguese Foundation for Science and Technology [(FCT) for grants reference POCTI/ECM/58375/2004,
PTDC/ECM/65731/2006, PTDC/ECM/64821/2006, FP7 HYLOW212423, and for the post-doctoral scholarship provided to the first
author (SFRH/BPD/34018/2006)]; CEHIDRO Hydrosystems Research Centre from DECivil/IST; and"Gabinete de Relações Internacionais da Ciência e do Ensino Superior" (GRICES, Portugal).
[1] Aklonis, J. J. and MacKnight, W. J. (1983). Introduction to
Polymer Viscoelasticity, John Wiley & Sons, New York, USA.
ter supply systems." Water Science and Technology: Water Supply,
4(5-6), 365-374.
[8] Covas, D., Stoianov, I., Mano, J., Ramos, H., Graham, N.,
and Maksimovic, C. (2004). "The Dynamic Effect of Pipe-Wall
Viscoelasticity in Hydraulic Transients. Part I - Experimental Analysis and Creep Characterization." Journal of Hydraulic Research,
42(5), 516-530.
[9] Covas, D., Stoianov, I., Mano, J., Ramos, H., Graham, N.,
and Maksimovic, C. (2005). "The Dynamic Effect of Pipe-Wall
Viscoelasticity in Hydraulic Transients. Part II - Model Development, Calibration and Verification." Journal of Hydraulic Research,
43(1), 56-70.
[10] Covas, D., Stoianov, I., Ramos, H., Graham, N., and
Maksimovic, C. (2003). "The Dissipation of Pressure Surges in Water Pipeline Systems." Pumps, Electromechanical Devices and Systems Applied to Urban Management. Volume 2, The Netherlands,
Balkema Publishers, 711-719.
[11] Martin, C. S. (1976). "Entrapped Air in Pipelines." Proc.
2nd Int. Conf. on Pressure Surges, BHRA, F2.15-F2.27.
[12] Pearsall, I. S. (1965). "The Velocity of the Water Hammer
Waves." Proceedings of the Institution of Mechanical Engineers.
Symposium on Pressure Surges 1965-66, 12-20.
[13] Ramos, H., Borga, A., Covas, D., and Loureiro, D. (2004).
"Surge damping analysis in pipe systems: modelling and experiments." Journal of Hydraulic Research, 42(4), 413-425.
[14] Shu, J. J. (2003). "Modelling Vaporous Cavitation on Fluid
Transients." International Journal of Pressure Vessels and Piping,
80, 187-195.
[15] Simpson, A. R. and Bergant, A. (1994). "Numerical comparison of pipe-column- separation models." Journal of Hydraulic
Engineering, ASCE, 120(3), 361-377.
[16] Soares, A. K., Covas, D. I. C., and Reis, L. F. R. (2008).
"Analysis of PVC Pipe-Wall Viscoelasticity during Water Hammer."
Journal of Hydraulic Engineering, ASCE, 134(9).
[17] Wylie, E. B. (1984). "Simulation of vaporous and gaseous
cavitation." Journal of Fluids Engineering, ASME, 106(3), 307-311.
[18] Wylie, E. B. and Streeter, V. L. (1993). Fluid Transients in
Systems, Prentice Hall, Englewood Cliffs, N.J..
[19] Zielke, W. (1968). "Frequency-dependent friction in transient pipe flow." Journal of Basic Engineering, Trans. ASME, Series
D, 90(1), 109-115.
[2] Almeida, A. B. and Koelle, E. (1992). Fluid Transients in Pipe
Networks, Computational Mechanics Publications, Elsevier Applied
Science, Southampton, UK.
[3] Bergant, A., Simpson, A. R., and Tijesseling, A. (2006). "Water Hammer with Column Separation: A Historical Review." Journal
of Fluids and Structures, 22, 135-171.
[4] Borga, A., Ramos, H., Covas, D., Dudlik, A., and Neuhaus, T.
(2004). "Dynamic effects of transient flows with cavitation in pipe
systems." The Practical Application of Surge Analysis for Design
and Operation - 9th International Conference on Pressure Surges
(Chester, UK: 24-26 March 2004) - Volume II, BHR Group Ltd., Bedfordshire, UK, 605-617.
[5] Carriço, N. G. (2008). "Modelling and Experimental Analysis of Non-Conventional Dynamic Effects during Hydraulic Transients in Pressurised Systems." Master Thesis, Instituto Superior
Técnico, Technical Unviersity of Lisbon, Portugal.
[6] Chaudhry,M.H.(1987). Applied Hydraulic Transients,Litton
EducationalPublishingInc,VanNostrandReinhold Co,New York,USA.
[7] Covas, D., Ramos, H., Graham, N., and Maksimovic, C.
(2005). "Application of hydraulic transients for leak detection in wa-
Acesse todos os nossos artigos em:
www
http://
CERPCH.ORG.BR
35
INSTRUCTIONS FOR AUTHORS TO PREPARE TO
HAVE ARTICLES TO BE SUBMITTED
INSTRUÇÕES AOS AUTORES
Forma e preparação de manuscrito
Form and preparation of manuscripts
Primeira Etapa (exigida para submissão do artigo)
O texto deverá apresentar as seguintes características: espaço 1,5; papel A4 (210 x 297 mm), com margens superior, inferior, esquerda e direita de
2,5 cm; fonte Times New Roman 12; e conter no máximo 16 laudas, incluindo quadros e figuras.
Na primeira página deverá conter o título do trabalho, o resumo e as
Palavras-Chaves. Nos artigos em português, os títulos de quadros e figuras
deverão ser escritos também em inglês; e artigos em espanhol e em inglês,
os títulos de quadros e figuras deverão ser escritos também em português.
Os quadros e as figuras deverão ser numerados com algarismos arábicos consecutivos, indicados no texto e anexados no final do artigo. Os títulos das figuras deverão aparecer na sua parte inferior antecedidos da palavra Figura
mais o seu número de ordem. Os títulos dos quadros deverão aparecer na
parte superior e antecedidos da palavra Quadro seguida do seu número de ordem. Na figura, a fonte (Fonte:) vem sobre a legenda, à direta e sem pontofinal; no quadro, na parte inferior e com ponto-final.
O artigo em PORTUGUÊS deverá seguir a seguinte seqüência: TÍTULO
em português, RESUMO (seguido de Palavras chave), TÍTULO DO ARTIGO
em inglês, ABSTRACT (seguido de key words); 1. INTRODUÇÃO (incluindo revisão de literatura); 2. MATERIAL E MÉTODOS; 3. RESULTADOS E
DISCUSSÃO; 4. CONCLUSÃO (se a lista de conclusões for relativamente curta, a ponto de dispensar um capítulo específico, ela poderá finalizar o capítulo anterior); 5. AGRADECIMENTOS (se for o caso); e 6. REFERÊNCIAS, alinhadas à esquerda.
O artigo em INGLÊS deverá seguir a seguinte seqüência: TÍTULO em inglês; ABSTRACT (seguido de Key words); TÍTULO DO ARTIGO em português; RESUMO (seguido de Palavras-chave); 1. INTRODUCTION (incluindo
revisão de literatura); 2. MATERIALAND METHODS; 3. RESULTS AND
DISCUSSION; 4. CONCLUSIONS (se a lista de conclusões for relativamente
curta, a ponto de dispensar um capítulo específico, ela poderá finalizar o capítulo anterior); 5. ACKNOWLEDGEMENTS (se for o caso); e 6. REFERENCES.
O artigo em ESPANHOL deverá seguir a seguinte seqüência: TÍTULO em
espanhol; RESUMEN (seguido de Palabra llave), TÍTULO do artigo em português,
RESUMO
INTRODUCCTIÓN
em
português
(incluindo
(seguido
revisão
de
de
palavras-chave);
literatura);
2.
1.
MATERIALES
YMETODOS; 3. RESULTADOS YDISCUSIÓNES; 4. CONCLUSIONES (se a lista
de conclusões for relativamente curta, a ponto de dispensar um capítulo específico, ela poderá finalizar o capítulo anterior); 5. RECONOCIMIENTO (se
for o caso); e 6. REFERENCIAS BIBLIOGRÁFICAS.
Os subtítulos, quando se fizerem necessários, serão escritos com letras
iniciais maiúsculas, antecedidos de dois números arábicos colocados em posição de início de parágrafo.
No texto, a citação de referências bibliográficas deverá ser feita da seguinte forma: colocar o sobrenome do autor citado com apenas a primeira letra maiúscula, seguido do ano entre parênteses, quando o autor fizer parte
do texto. Quando o autor não fizer parte do texto, colocar, entre parênteses,
o sobrenome, em maiúsculas, seguido do ano separado por vírgula.
O resumo deverá ser do tipo informativo, expondo os pontos relevantes
do texto relacionados com os objetivos, a metodologia, os resultados e as
conclusões, devendo ser compostos de uma seqüência corrente de frases e
conter, no máximo, 250 palavras.
Para submeter um artigo para a Revista PCH Noticias & SHP News o(os)
autor (es) deverão entrar no site www.cerpch.unifei.edu.br/Submeterartigo.
Serão aceitos artigos em português, inglês e espanhol. No caso das línguas estrangeiras, será necessária a declaração de revisão lingüística de um
especialista.
Segunda Etapa (exigida para publicação)
O artigo depois de analisado pelos editores, poderá ser devolvido ao (s)
First Step (required for submition)
The manuscript should be submitted with following format: should be
typed in Times New Roman; 12 font size; 1.5 spaced lines; standard A4 paper (210 x 297 mm), side margins 2.5 cm wide; and not exceed 16 pages, including tables and figures.
In the first page should contain the title of paper, Abstract and Keywords.
For papers in Portuguese, the table and figure titles should also be written in
English; and papers in Spanish and English, the table and figure titles should
also be written in Portuguese. The tables and figures should be numbered
consecutively in Arabic numerals, which should be indicated in the text and
annexed at the end of the paper. Figure legends should be written immediately below each figure preceded by the word Figure and numbered consecutively. The table titles should be written above each table and preceded by
the word Table followed by their consecutive number. Figures should present
the data source (Source) above the legend, on the right side and no full stop;
and tables, below with full stop.
The manuscript in PORTUGUESE should be assembled in the following order: TÍTULO in Portuguese, RESUMO (followed by Palavras-chave), TITLE in
English; ABSTRACT in English (followed by keywords); 1.INTRODUÇÃO (including references); 2. MATERIAL E METODOS; 3. RESULTADOS E
DISCUSSAO; 4. CONCLUSAO (if the list of conclusions is relatively short, to
the point of not requiring a specific chapter, it can end the previous chapter);
5. AGRADECIMENTOS (if it is the case); and 6. REFERÊNCIAS, aligned to the
left.
The article in ENGLISH should be assembled in the following order:
TITLE in English; ABSTRACT in English (followed by keywords); TITLE in Portuguese; ABSTRACT in Portuguese (followed by keywords); 1.
INTRODUCTION (including references); 2. MATERIAL AND METHODS;
3.RESULTS AND DISCUSSION; 4. CONCLUSIONS (if the list of conclusions is
relatively short, to the point of not requiring a specific chapter, it can end the
previous chapter); 5. ACKNOWLEDGEMENTS (if it is the case); and 6.
REFERENCES.
The article in SPANISH should be assembled in the following order:
TÍTULO in Spanish; RESUMEN (following by Palabra-llave), TITLE of the article in Portuguese, ABSTRACT in Portuguese (followed by keywords); 1.
INTRODUCCTIÓN (including references); 2. MATERIALES Y MÉTODOS; 3.
RESULTADOS Y DISCUSIÓNES; 4. CONCLUSIONES (if the list of conclusions
is relatively short, to the point of not requiring a specific chapter, it can end
the previous chapter); 5.RECONOCIMIENTO (if it is the case); and 6.
REFERENCIAS BIBLIOGRÁFICAS.
The section headings, when necessary, should be written with the first
letter capitalized, preceded of two Arabic numerals placed at the beginning
of the paragraph.
Abstracts should be concise and informative, presenting the key points
of the text related with the objectives, methodology, results and conclusions; it should be written in a sequence of sentences and must not exceed
250 words.
References cited in the text should include the author\'s last name, only
with the first letter capitalized, and the year in parentheses, when the author
is part of the text. When the author is not part of the text, include the last name in capital letters followed by the year separated by comma, all in parentheses
For paper submission, the author(s) should access the online submission Web site www.cerpch.unife.edu.br/submeterartigo (submit paper).
The Magazine SHP News accepts papers in Portuguese, English and Spanish. Papers in foreign languages will be requested a declaration of a specialist in language revision.
Second Step (required for publication)
Comitê Editorial da Revista.
After the manuscript has been reviewed by the editors, it is either returned to the author(s) for adaptations to the Journal guidelines, or rejected because of the lack of scientific merit and suitability for the journal. If it is judged as acceptable by the editors, the paper will be directed to three reviewers to state their scientific opinion. Author(s) are requested to meet the reviewers\' suggestions and recommendations; if this is not totally possible,
they are requested to justify it to the Editorial Board
Obs.: Os artigos que não se enquadram nas normas acima descritas, na
sua totalidade ou em parte, serão devolvidos e perderão a prioridade da ordem seqüencial de apresentação.
Obs.: Papers that fail to meet totally or partially the guidelines above described will be returned and lose the priority of the sequential order of presentation.
autor (es) para adequações às normas da Revista ou simplesmente negado
por falta de mérito ou perfil. Quando aprovado pelos editores, o artigo será
encaminhado para três revisores, que emitirão seu parecer científico.
Caberá ao(s) autor (es) atender às sugestões e recomendações dos revisores; caso não possa (m) atender na sua totalidade, deverá (ão) justificar ao
36
AGENDA/SCHEDULE
6º Congresso Brasileiro sobre Eficiência Energética
Data: 23 de junho de 2009
Local: Novotel Center Norte - São Paulo - SP
Informações: http://www.metodoeventos.com.br/6eficienciaenerget
Andean and Central America Energy Congress
Data: 10 de julho de 2009
Local: Colômbia - Local: Bogotá - AC
Informações: http://www.acaec2008.com
33rd International Association of Hydraulic Engineering & Research
(IAHR) Biennial Congress
Data: August 10-14, 2009
Local: Vancouver - Canadá
Informações: [email protected]
Energy Summit 2009
Data: 11 a 13 de agosto de 2009
Local: Rio de Janeiro - RJ
Informações: www.energysummit.com.br
V Conferência de PCH Mercado & Meio Ambiente
Data: 5 e 6 de agosto de 2009.
Local: São Paulo – SP
Informações: www.conferenciadepch.com.br
XX SNPTEE - Seminário Nacional de Produção e Transmissão de
Energia Elétrica
Data: 22 a 25 de novembro de 2009
Local: Olinda - PE
Informações: http://www.xxsnptee.com.br
a
ri
B r as
il
e
0s
2
ano
a
ir
E n g en
h
a
e
i
*
n a
l
o
ASSOCIADOS
*
CONSULTORES
a
I n
t e r n
c
A RDR Consultores Associados foi fundada em dezembro de 1989 por um grupo de
técnicos de alto nível com larga experiência na concepção e implantação de
empreendimentos na área de energia elétrica, tendo por objetivo prestar serviços em
estudos, projetos, consultoria e gerenciamento, tanto para clientes do setor público quanto
privado.
No gerenciamento de programas, atua nas áreas de meio ambiente, educação e saúde,
com financiamento internacional.
No campo das hidrelétricas, a RDR atua desde a busca dos locais para os aproveitamentos até o Gerenciamento
da implantação das Obras. O quadro da capacitação da RDR é:
·
·
·
·
·
·
·
Estudo deAvaliação de Potencial
Estudo de Inventário Hidrelétrico
Projeto Básico
Projeto Básico, para contratação de serviço e aquisições de equipamentos ou para contratação de EPC
Projeto Executivo
Gerenciamento da Implantação das Obras
Engenharia do Proprietário
C O N S U L T O R E S
A S S O C I A D O S
RUA MARECHAL DEODORO, 51 - 15º ANDAR - GALERIA RITZ
C U R I T I B A
8 0 . 0 2 0 - 9 0 5
P A R A N Á
55 41 3233-1400
r d r @ r d r. s r v. b r
w w w. r d r. s r v. b r
OPINIÃO
Interligação e conexão de PCHs
Por Decio Michellis Jr.
No projeto e construção da transmissão para interligação e conexão de PCHs nem sempre o caminho mais curto é o
melhor caminho. Considere adequadamente a variável socioambiental no processo decisório.
As demandas ambientais são cada vez mais complexas e caras.
Cada vez mais é transferido ao empreendedor o tratamento de
questões que competem ao Poder Público, harmonizando regionalmente os conflitos entre políticas públicas e os interesses de proteção do meio ambiente. No projeto e construção da transmissão para interligação e conexão de PCHs merecem cada vez mais atenção
os aspectos físicos, bióticos, sociais e de mudanças climáticas,
abrangendo todas as etapas do empreendimento.
Na etapa de estudos básicos e viabilidade o ideal é: i) selecionar traçado para a transmissão que evite ao máximo a interferência em áreas de florestas, áreas alagadas, travessias de corpos
d´água, áreas com restrições legais ou especialmente protegidas e
respectivas zonas de amortecimento (unidades de conservação,
áreas prioritárias para criação de unidades de conservação da biodiversidade, terras indígenas e remanescentes de quilombos) mesmo de forma indireta possam se transformar em barreiras intransponíveis na implantação do empreendimento. Indígenas em geral
alegam que tem direito à isenção de pagamento da energia elétrica
quando suas terras são cortadas por linhas de transmissão, mesmo
de PCHs. Acordos verbais são tão relevantes quanto os legais, bem
como a próxima geração pode não se sentir compensada com os
acordos anteriormente firmados, consistindo num desafio permanente de articulação e gestão socioambiental; ii) verificar a possibilidade de construção da mesma sem a necessidade de criação de
estradas de acesso/serviço, utilizando a servidão/proximidade das
estradas existentes; iii) manter registros documentais que foram
consideradas receitas com créditos de carbono desde as etapas iniciais dos estudos da PCH; iv) iniciar a articulação com os proprietários e as lideranças locais onde será realizado o empreendimento,
acompanhada de ações afirmativas de responsabilidade socioambiental antes mesmo de iniciar o processo de licenciamento.
Na etapa de projeto executivo o ideal é: i) utilizar no projeto as
melhores soluções técnicas e práticas de gestão socioambiental disponíveis e economicamente viáveis, incluindo a possibilidade de
uso de cruzetas ecológicas e postes de concreto; ii) o projeto deve
visar a mínima interferência com o meio ambiente, especialmente
em áreas de vegetação densa, evitando desmatamento desnecessário e futura susceptibilidade a processos erosivos; iii) o risco associado à segurança ambiental é inversamente proporcional à qualidade dos estudos realizados.
Na etapa de construção o ideal é: i) assegurar o planejamento
de conformidade ambiental da contratada; ii) evitar ao máximo o
corte de vegetação natural existente no local, não tocar nas áreas
de preservação permanente, exceto o mínimo necessário ao deslocamento de pessoas e equipamentos; iii) procure contratar ao máximo a mão de obra local; iv) utilizar, sempre que possível, fornecedores locais de materiais e serviços; v) dar atenção especial à
adequada desmobilização de canteiros e alojamentos, bem como a
recuperação das áreas degradadas na limpeza da faixa.
Na etapa de operação o ideal é: i) fornecer informações
adequadas às comunidades afetadas e fornecedoras de mão de
obra, incluindo orientação quanto ao risco de acidentes com a rede
elétrica e práticas sustentáveis de uso do solo e dos recursos
naturais; ii) acompanhar a evolução do uso do solo embaixo da LT –
Linha de Transmissão, avaliando a velocidade de degradação
ambiental e seus impactos na perda de cobertura vegetal,
aumento de erosão, etc.; iii) articular e apoiar ações de
38
preservação ambiental e correto manejo do solo, com ações
concretas que podem incluir o fornecimento de mudas para
reflorestamento.
É mais barato ser inteligente. Um meio ambiente ecologicamente equilibrado é bom também para redução dos custos de operação e manutenção: menor freqüência de interrupções, riscos menores de queimadas e incêndios florestais, menores custos de manutenção e redução de penalizações pelo não fornecimento da energia contratada. No projeto e construção da transmissão para interligação e conexão de PCHs nem sempre o caminho mais curto é o
melhor caminho. Considere adequadamente a variável socioambiental no processo decisório.
OPINION
SHP Connection and Interconnection
In the project and construction of the transmission for SHP connection and interconnection, the shortest way is not
always the best. Consider the socio-environmental variable in the decision-making process.
Environmental demands are increasingly more complex and expensive. The Public Power is continually transferring issues that
they must deal with to the entrepreneur, regionally harmonizing
the conflicts between public policies and the interests in protecting
the environment. In the project and construction of the transmission for SHP interconnection and connection, the physical, biotic, social and climatic change aspects deserve significant attention along
all of the stages of the enterprise.
During the stage of basic and feasibility studies it is ideal to ideal é: i) select the route of the transmission, avoiding the interference in forest areas, flooded areas, transposition of streams or lakes,
area that have legal restrictions or are especially protected and zo-
ne that present any sort of interest (conservation units, areas whose priority is the creation of biodiversity conservation units, land
that belongs to native populations and land that belong to the families of old runaway slaves) that even in an indirect way may become obstacles that are impossible to overcome for the implementation of the enterprise. Native Indians populations, in general, claim
that they are exempt from paying electric power when there are power lines in their lands, even from SHPs. Verbal agreements are as
relevant as the legal ones, as well as the next generation may not
feel well-compensated by the agreements that were previously settled, which is a permanent challenge in relation to articulation and
socio-environmental management; ii) check the possibilities of building the SHP without the need to create access/service roads,
using already existing ones; iii) keep documental records that were
considered income with carbon credits since the stages of the SHP
initial studies; iv) initiate discussions with owners and local leaders
of the place where the enterprise will be implemented, followed by
socio-environmental positive actions, before the beginning of the licensing process.
During the stage of executive project it is ideal: i) to use the
best technical, practical and economically feasible available solutions regarding socio-environmental management in the project, including the possibility of using ecological crossarms and concrete
posts; ii) the project must aim at the minimum environmental interference, particularly in areas of dense vegetation, avoiding unnecessary deforestation and the future susceptibility to erosion processes; iii) the risk associated to the environmental safety is inversely proportional to the quality of the studies that were carried out.
During the stage of construction it is ideal to: i) assure that the
environmental planning will be followed; ii) avoid cutting down the
natural vegetation of the place, do not touch areas of permanent
preservation, unless it is absolutely necessary for the displacement
of people and the transport of equipment; iii) hire local work power; iv) whenever it is possible, use local suppliers of material and
services; v) pay special attention to the appropriate removal of working sites and barracks, as well as the recuperation of the degraded
areas.
During the operation it is ideal to: i) give appropriate information to the affected communities and to the labor suppliers, including information regarding the risk of accidents with the electric grid
and sustainable practices of using the soil and natural resources; ii)
follow the use of the soil under the power lines, assessing the
speeding of environmental degradation and its impacts on the vegetation cover, erosion; iii) articulate and support environmental preservation actions and the correct management of the soil with concrete actions that may include the supply of seedlings for reforestation.
It is cheaper to be intelligent. An ecologically balanced environment is also good for the reduction of O&M costs: smaller number
of interruptions, lower risks of burnings and forest fires, lower maintenance costs and reduction in the penalties caused by not supplying the energy that was agreed. In the project and construction
of transmission for connections and interconnection of SHPs, the
shortest route is not always the best one. It is important to consider the socio-environmental variable in the decision making process.
39
CURTAS
ICOLD E CBDB realizam
o 23º Congresso Internacional de Grandes Barragens
Por Adriana Barbosa
Cerca de 1400 participantes de mais de 80 países participaram
do 23º Congresso da Internacional de Grandes Barragens promovido
pela Comissão Internacional de Grandes Barragens (ICOLD-CIBG), e
organizado pelo Comitê Brasileiro de Grandes Barragens (CBDB), entre os dias 24 e 29 de maio, em Brasília.
Com a presença do atual presidente da ICOLD, Luis Berga e do
presidente eleito, Jia Jinseng, o evento foi citado pelos componentes
da mesa de abertura como a referência mundial na troca de experiências, informação e aprimoramento técnico entre especialistas de
diversos países. “É uma satisfação receber o evento mais importante
do mundo na área de construção de barragens”, disse o presidente
do CBDB, Edilberto Maurer. Segundo ele foi uma grande desafio organizar o evento diante das crises que se instalaram no mundo durante
a organização. “O Congresso será uma oportunidade única para que
os técnicos e especialistas em construção de barragens possam trocar experiências”, disse.
O presidente da ICOLD, Luis Berga, disse que a escolha do Brasil
para sediar o Congresso levou em consideração o grande potencial hidrelétrico do país. “O Brasil tem mais de 1000 barragens existentes,
com cerca de 650 delas destinadas à produção de energia elétrica.
Mais de 70% de toda capacidade de produzir energia é originada das
hidrelétricas, sendo o segundo país no mundo em geração hidráulica”, afirmou. Berga lembrou ainda que, apesar de toda capacidade
de produção, apenas 30% estão desenvolvidos e explorados. Outro
motivo, segundo o presidente, é que o Brasil tem, atualmente, 80 hidrelétricas sendo construídas.
O presidente da ICOLD lamentou que cerca de 1,6 bilhão de pessoas no mundo ainda não tenham eletricidade em suas casas. “A solução é desenvolver sustentavelmente a construção de barragens e aumentar a capacidade de armazenamento de água. Isso deve ser prioridade”, defendeu Berga.
A abertura do evento contou ainda com a participação do
secretário-geral da ICOLD, Michel de Vivo, do diretor de Engenharia
e Planejamento da Eletronorte, Adhemar Palocci, e do
vicepresidente do World Water Council (WWC), Benedito Braga, diretor
da Agência Nacional de Águas (ANA).
O novo presidente da ICOLD, Jia Jinseng, eleito durante a 77ª
Reunião Anual da entidade, realizada durante o encontro, lembrou
que a ICOLD não tem apenas o papel técnico, mas também o de
trabalhar de forma economicamente sustentável. “A situação atual é
desafiadora e por isso é preciso promover, principalmente, o
desenvolvimento social”, disse. Jia Jinseng destacou ainda a
necessidade de desenvolver a construção de barragens na África
que, segundo ele, deve ser prioridade. “A ICOLD tem muito a
contribuir com o mundo”, concluiu.
ICOLD and CBDB hold
23th International Meeting of Large Dams
About 1400 people from over 80 countries participate in the 23rd
International Meeting of Large Dams promoted by the International
Commission of Large Dams (ICOLD-CIBG), and organized by the Brazilian Committee of Large Dams (CBDB) in Brasilia between May
24th and 29th.
the second country in hydropower generation in the world”, he said.
Mr. Berga also highlighted that in spite of all this production capacity
only 30% have been developed and used. Another reason, according
to the president, is that Brazil has 80 hydropower plants that are being built.
With the presence of the ICOLD's president, Mr. Luis Berga, and
the elected president, Mr. Jia Jinseng, the members of the opening ceremony stated that the meeting is a world reference regarding the exchange of experiences, information and technical improvement
among the experts of the area for several countries. “It is a great satisfaction to receive the most important event in the world on the
area of dam construction”, said the president of the CBDB, Mr. Edilberto Maurer. According to him it was a challenge to organize the
event face the crises that broke out in the world during the organization. “The Meeting will be an opportunity for the technicians and experts on dam construction to exchange experiences”.
The president of ICOLD regretted the fact that 1.6 billion people
in the world still do not have electric power in their homes. “The solution is to develop a sustainable way to build dams and increase the
water storing capacity. This must be a priority”, Mr. Berga said.
The president of ICOLD, Mr. Luis Berga, said that the choice of
Brazil to held the Meeting took the great hydropower potential of the
country into account. “Brazil has over 1000 dams – 650 of them are
destined to the production of electric power. More than 70% of the capacity of producing energy comes from hydropower plants. Brazil is
40
ICOLD's general secretary, Mr. Michel de Vivo, Eletronorte's director of engineering and planning, Mr. Adhemar Palocci, the vicepresident of the World Water Council (WWC), Mr. Benedito Braga, director of the National Agency of Water (ANA) participated in the opening ceremony of the event.
The new president of ICOLD, Mr. Jia Jinseng, elected during the
its 77th Annual Meeting said that ICOLD does no have just a technical role, but it also works in a economically sustainable way. “Today's
situation is challenging and it is necessary to promote social development”, he said. Mr. Jia highlighted the need to build dams in Africa,
which according to him, must be a priority. “ICOLD has a lot to contribute”, he concluded.
CURTAS
Limpador de Grades gera eficiência em PCH
Informe Publicitário / Advertising Information
A primeira Máquina de Limpeza de Grades - MLG 17140, produzida pela SAUR foi adquirida pela Coprel Cooperativa de Geração de
Energia e Desenvolvimento, de Ibirubá, Rio Grande do Sul. O equipamento foi instalado na Pequena Central Hidroelétrica (PCH) Cotovelo do Jacuí, no Município de Victor Graeff/RS.
O limpador de grades tem a função de remover detritos que ficam acumulados nas grades de entrada da água em direção às turbinas como galhos, folhas, madeiras de diversos tamanhos e espécies, bem como resíduos de lixo urbano, principalmente embalagens de bebidas e agrotóxicos, obstruindo o acesso da água e fazendo diminuir a potência gerada.
A MLG 17140 possui uma profundidade de limpeza de 10m e
uma calha, o que possibilita a retirada dos detritos do rio. Esses são
lançados num contêiner por uma esteira rolante. Posteriormente
são levados a um aterro reflorestado, separados e encaminhados
para o destino correto.
O projeto foi desenvolvido em parceria com a Coprel, resultando em um moderno e eficiente equipamento. De acordo com Nélio
Koch, Orientador de Geração da Coprel o equipamento é muito importante para aumentar a geração de energia. "Nós já percebemos
um ganho em torno de 3% a 4%, além de contribuir para a preservação do meio ambiente e, de uma forma direta, proporciona mais
segurança para a execução da atividade. Foi um trabalho em conjunto, que resultou em um equipamento simples, eficiente e que
não exigiu reestruturação física do local", avalia Nélio.
Além de fornecer máquinas de limpeza de grades para pequenas centrais hidrelétricas, a SAUR é representante da empresa austríaca Künz, que possui limpadores de grades, para aplicação em
usinas de médio e grande porte.
First SAUR trash rake cleaning increases SHP efficiency
The first trash rake cleaning equipment – MLG 17140, produced
by SAUR was purchased by Coprel – Power Generation and Development Cooperative, from Ibirubá. The equipment was installed on
the Small Hydroelectric Plant (SHP) Cotovelo do Jacuí, located in
Victor Graeff/RS.
The rake cleaner removes debris accumulated on the water intakes protection, in front of the turbines. Typical debris are
branches, leaves and all sorts of wood, as well as urban trash,
mostly bottles and embty pesticide containers, blocking water access, reducing generated power.
MLG 17140 will clean up to 33 feet depth. Is equipped with a
chute to hold the debris. These are carried to a container by means
of a rolling track. They are then taken to a landfill to be sorted and
42
taken to the proper destination.
The project was developed in partnership with Coprel, resulting
on an efficient and modern equipment. According to Nélio Koch,
Coprel Generation Leader, the equipment is very important to increase power generation. “We have measured 3 to 4% gains. Besides contributing to the environment preservation, results on increased safety at the power plant. This was a joint work, which resulted in a simple and efficient equipment, and did not require any
physical change to the dam structure”, tells Nélio.
Besides building trash rake cleaning equipment for SHP's,
SAUR is the representative for the Austrian company Künz, which
builds the same equipment for medium and large size plants.
National Center of Reference for Small Hydropower Plants
CURTAS
Delegação do Brasil participa de evento internacional de PCH
Por Camila Galhardo
Nos dias 28 e 29 de abril de 2009 foi realizado o Small Hydro 2009, em Vancouver no Canadá, onde se reunirão representantes da
Associação Européia de Pequenas Centrais Hidrelétricas, Centro Latino americano de PCH, autoridades canadenses, mexicanas e norte
americanas, além de uma delegação brasileira.
O objetivo do evento foi discutir o rápido crescimento das PCHs, dado suas vantagens ambientais e possibilidade de atendimento de
comunidades onde o sistema de transmissão é de difícil acesso. E com a crescente preocupação com o aquecimento global destacou-se o
balanço de emissões de CO2 numa PCH.
Desafios
Nas apresentações de Brasil e Canadá foram destacados os
entraves tecnológicos para exploração do potencial remanesceste
e ambas as delegações apontaram na mesma direção, o
desenvolvimento de tecnologia para aproveitamentos de baixa e
baixíssima queda e a busca por soluções de menor impacto sobre a
ictiofauna.
Encontra-se em fase de implantação um termo de cooperação
entre os dois países para o desenvolvimento de pesquisa para
turbinas de baixa queda e mecanismos de transposição de peixes,
além de outros temas de interesse comum. A iniciativa é fruto da
parceria entre o Ministério de Ciência e Tecnologia do Brasil e o
consulado do Canadá.
Apresentações
A equipe do CERPCH apresentou dois artigos técnicos durante o
evento, um estudo dos impactos sócios econômicos causados
pelas PCH do PROINFA e uma análise de viabilidade para
investimentos em PCH utilizando os benefícios do Crédito de
Carbono. Os trabalhos foram desenvolvidos pelo Prof. Geraldo
Lúcio Tiago Filho, Secretário Executivo, e a MSc. Camila Galhardo,
Gerente de Comunicação.
Brazilian delegation participates in international event on SHPs
On April 28th and 29th, 2009, the Small Hydro 2009 was held in Vancouver, Canada, where representatives of the European Small
Hydropower Association, the Latin American Center Of Small Hydropower Plants, Canadian Mexican and North-American authorities and a
Brazilian delegation participated in the event.
The objective of the meeting was to talk about the rapid growth of the SHPs due to their environmental advantages and the possibility
to assist communities where there is a difficult access for the power lines. Also, because of the increasing concern about global warming,
the CO2 emission balance of a SHP was highlighted.
Challenges
The presentations of Brazil and Canada highlighted the technological obstacles regarding the use of the remaining potential and
both delegations point to the same direction: the development of a
technology aiming at low and very low heads and the search for solutions that have a smaller impact on the Ichthyofauna.
Both countries are working on an agreement towards the development of research for low head turbines and fish diversion
mechanisms, among other topics of mutual interest. The initiative
44
started from the partnership between the Ministry of Science and
Technology and the Canadian.
Presentations
CERPCH team presented two technical papers during the
event: a study on the socio-economic impacts caused by the
PROINFA SHPs and a feasibility analysis for investments in SHPs using Carbon Credits benefits. The papers were developed by Professor Geraldo Lúcio Tiago Filho, CERPCH's executive secretary, and
Ms. Camila Galhardo, MSc, Communication manager.
05 e 06 de Agosto de 2009
Centro de Convenções do Novotel Center Norte
Av. Zaki Narchi, nº 500 - São Paulo - SP
EXPOPCH 2009
Exposição de Equipamentos, Tecnologias e Serviços para Projeto,
Implantação e Operação de PCHs.
05 e 06 de agosto de 2009
Centro de Convenções do Novotel Center Norte – SP
Maior evento do mercado de PCH
Confira a programação no site:
www.conferenciadepch.com.br
EXPOPCH - Exposição de Equipamentos, Tecnologias e Serviços para Projeto, Implantação e Operação
de Pequenas Centrais Hidrelétricas, que consolida o Salão de Negócios existente nas edições
anteriores;
RODADA DE NEGÓCIOS EM PCH - Espaço durante o evento para realização de reuniões previamente
agendadas entre os inscritos;
PRÊMIO PCH – Apresentação e entrega dos melhores trabalhos técnicos.
Contato: CERPCH: (35) 3629-1443
(35) 3629-1439
E-mail: [email protected]
Organização
Realização
Patrocínio Ouro
Apoio
46
Patrocínio Prata
Patrocínio Bronze
CURSO DE ESPECIALIZAÇÃO EM
PEQUENAS CENTRAIS HIDRELÉTRICAS
Este curso é voltado para a capacitação profissional na área de gestão e
projetos de pequenas centrais hidrelétricas (PCH). Direcionado para
engenheiros, administradores, advogados, economistas e todos os
profissionais correlacionados com a área de PCH, o curso destaca-se como
um diferencial exigido pelo mercado profissional.
GARANTA JÁ A SUA PARTICIPAÇÃO
AULAS EM SETEMBRO DE 2009
ANTECIPE-SE E GARANTA SUA VAGA.
FAÇA HOJE MESMO SUA INSCRIÇÃO PELO SITE.
PÚBLICO ALVO:
ENGENHEIROS
ECONOMISTAS
ADMINISTRADORES
GERENTES
ADVOGADOS
INVESTIDORES
EMPRESÁRIOS
PROFISSIONAIS DO SETOR
Dividido em 10 módulos presenciais, este curso visa o ensino de procedimentos para a viabilidade técnica e econômica, dimensionamento e especificação de componentes
hidromecânicos e elétricos, elaboração de projeto básico,
aspectos regulatórios e ambientais.
O curso pode ser integralizado em um período máximo de
24 meses. Com a conclusão de 9 módulos teóricos e a defesa do trabalho de conclusão de curso, o aluno será avaliado
por uma banca para receber o título de especialista. É permitido cursar os módulos individuais, dando direito a certificação técnica.
Local: Itajubá-MG
Aulas concentradas em uma semana por mês
10 módulos presenciais
Traslado Gratuito: Rio/Itajubá e São Paulo/Itajubá
Integralização: mínimo de 10 e máximo de 24 meses
INVESTIMENTO:
R$ 1.800,00
R$ 16.000,00
por módulo
à vista
Apoio
Realização
Para mais informações, acesse: www.cerpch.org.br/cepch
47

pro Powerstep

Transcrição

Documentos relacionados

É tempo de analisar e fazer uma completa reflexão sobre a vida

Questions 1-4 refer to Reading A Reader`s Digest, Sept. 2006

Sentinela - Zelia Fonseca

Tantas vezes me foi dito, na minha busca por

Interzone 245(Interzone #245)

For Our World Para Nosso Mundo.

Mother Road(Route 66 #1) by Dorothy Garlock

Por favor, não matem a cotovia Realizador

TRIBUNA LAYOUT 160.pmd

TRIBUNA 152.pmd