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Abstract(s)
Uma vez chegado o momento de elaborar uma tese para a conclusĆ£o do segundo ciclo de estudos em Engenharia QuĆmica, a escolha dentro das opƧƵes disponĆveis, foi por um lado o contexto laboral, onde me insiro, como trabalhador estudante e por outro lado um tema relacionado com Ć”gua. Surge entĆ£o, como oportunidade de trabalho a avaliaĆ§Ć£o do desempenho de uma Torre de Arrefecimento.
Os objectivos foram definidos, apĆ³s formaĆ§Ć£o da equipa de suporte e concepĆ§Ć£o, no local onde se desenvolveu o trabalho.
A motivaĆ§Ć£o base deste trabalho foi responder Ć s seguintes perguntas: TerĆ” a Torre de Arrefecimento capacidade para remover toda a carga tĆ©rmica, Ć mĆ”xima capacidade, na Ć©poca de VerĆ£o? Em caso negativo, que medidas poderĆ£o ser tomadas?
Inicialmente inventariaram-se os aspectos relevantes e formularam-se as hipĆ³teses no sentido de responder Ć s questƵes levantadas. Considerou-se a necessidade de avaliar a torre de arrefecimento e toda a rede de permuta de calor do sistema, face ao aumento de carga do caudal tĆ©rmico devido Ć expansĆ£o da fĆ”brica.
A variĆ”vel mais importante da torre de arrefecimento (TA), temperatura de termĆ³metro hĆŗmido, foi redefinida com recurso aos melhores dados disponĆveis, aplicando-se a anĆ”lise clĆ”ssica recomendada (Cheremisinoff et al., 1989). O valor atribuĆdo para a temperatura de termĆ³metro hĆŗmido foi de 22 ĀŗC.
A exploraĆ§Ć£o e estratĆ©gia para alcanƧar os objectivos passaram por mediƧƵes tĆ£o rigorosas quanto possĆvel, pela anĆ”lise da literatura especializada, bem como da utilizaĆ§Ć£o do simulador Aspen Plus e da folha de cĆ”lculo Excel. Os modelos teĆ³ricos foram verificados com as ferramentas computacionais, confrontados com a realidade e suportados pela experiĆŖncia de recursos humanos tanto internos como externos.
A metodologia seguida passou pelo doseamento teĆ³rico/prĆ”tico, orientado para os resultados. Dada a diversidade das fontes de informaĆ§Ć£o e variedade de ferramentas optou-se por apresentar as unidades em Sistema Internacional (SI) e Inch Pound Second (IPS).
Fez-se toda a verificaĆ§Ć£o dos cĆ”lculos de projecto, construĆram-se as curvas de desempenho, determinou-se a capacidade e eficiĆŖncia da TA, avaliaram-se os requisitos hidrĆ”ulicos, bem como imposiƧƵes operatĆ³rias como a necessidade da Ć”gua de arrefecimento deixar a torre a 26ĀŗC.
A resposta Ć s perguntas inicialmente formuladas indica que a TA actual nĆ£o tem capacidade para remover toda a carga tĆ©rmica (35 MW) quando a fĆ”brica opera Ć mĆ”xima capacidade e quando a temperatura de bolbo hĆŗmido sobe para valores iguais ou superiores a 22ĀŗC. Assim, nĆ£o e possĆvel manter a temperatura da agua de fornecimento a 26 oC sem reduzir a produĆ§Ć£o. As propostas sem custos de investimento passam por reduzir a razĆ£o L/G e neste caso diminuir o caudal de L porque o aumento de caudal G requer investimento. Numa anĆ”lise \retrofit. Procura-se rearranjar a rede de permutadores de calor de forma a diminuir o caudal de Ć”gua de arrefecimento procurando substituir arranjos em paralelo por serie. Como reforƧo fazer a purga na corrente de retorno e manter uma manutenĆ§Ć£o geral preventiva de acordo com as melhores tĆ©cnicas disponĆveis (BAT fs) (Hensey, John C., 2006).
As propostas mais eficazes e versĆ”teis mas que requerem investimento sĆ£o as seguintes: substituir o enchimento por um de maior desempenho, aplicar extractores com maior capacidade e melhorar Ć”rea de retenĆ§Ć£o de gotĆculas.
Este estudo foi levado a cabo com os recursos existentes, cujas limitaƧƵes experimentadas, aconselham a testes mais rigorosos, com equipamento especĆfico e dedicado. Existem no mercado empresas certificadas e especializadas que executam testes, de modo a diminuir a variabilidade, aumentando a exactidĆ£o de acordo com as normas internacionais ASME PTC-23 e ATC-105 (Hensey, John C., 2006).
Neste tipo de equipamento de desempenho tĆ©rmico em que a ciĆŖncia e a tecnologia estĆ£o jĆ” bem estabelecidas, nĆ£o encontra, no entanto, resultados totalmente conclusivos, por isto e importante seguir as referĆŖncias existentes. Por ser tambĆ©m um mercado muito competitivo e de grande valor acrescentado, a informaĆ§Ć£o especializada, as inovaƧƵes e o desenvolvimento tĆ©cnico estĆ£o protegidos no sentido de manter a vantagem competitiva de quem as detĆ©m.
Since I had a task to submit a thesis to get the second cycle of Chemical Engineer Degree, the option between available opportunities was: first to do it in my workplace and second to find a theme related with water. To fulfill these two conditions the Cooling Tower water system was chosen. The general aim of the work was the reevaluation of the existing project in a retrofit situation. The objectives defined after conceptualization were: Preparation of the index flow sheet, material and energy balance of the total system, hydraulic assessment of total network, assessment of pumping system in place and Cooling Tower capacity and efficiency evaluation. At the beginning, all the previous work done was analysis of described objectives where hypotheses were formulated to face the question: will the cooling tower remove the increased heat load after revamping the plant, in summer time? In case of negative answer which proposals are suggested? The more important variable that defines the project like this one is the wet bulb temperature that was redefined with the best available data and proper method applied for these cases. The value of 22 ĀŗC is the actual setting number for wet bulb temperature. The exploration and strategy to achieve the objectives were by measurement as stringed as possible, by analysis of specialized literature and use of simulator Aspen Plus and Excel spreadsheets. The theoretical model was verified by the computational tools and the internal human resources experiences as well as external were not forgotten. The methodology used was a mixture of theoretical/trial and error approaches for oriented results. Because of the diversified sources of information and variety of tools used, it was decided to work with the two main unit systems: International System (SI) and Inch Pound Second system (IPS). Project recalculation and verification was made, both built up performance curves and capacity and efficiency analysis. Operation parameters and hydraulic services were reassessed and 26 ĀŗC water supply temperature confirmed. The answer to the previous question is: The actual Cooling Tower doesnāt remove the total heat (35 MW) load in Summer time. In periods when wet bulb temperature equals or surpasses 22 ĀŗC the TA needs to reduce heat load with consequent production reduction in order to maintain the cold water temperature at 26 ĀŗC, otherwise we will expect greater values according to simulators and practice tests. The second answer is: As demonstrated, it is possible to increase the TA performance with less L/G and as a complementary action change a cold blowdown by a hot one without investment. As a general recommendation preventive maintenance with best practices is the key ( Hensey, John C.,2006). The most effective proposals but that requires investment are: Replace filling with one with best performance, apply extractors with greater capacity and improve the drift eliminator. The tower performance was determined with existing resources whose limitations require more precise tests with specified equipment technology available in the market, which will permit good accuracy according with international ATC 105 and CTR 23 standards.
Since I had a task to submit a thesis to get the second cycle of Chemical Engineer Degree, the option between available opportunities was: first to do it in my workplace and second to find a theme related with water. To fulfill these two conditions the Cooling Tower water system was chosen. The general aim of the work was the reevaluation of the existing project in a retrofit situation. The objectives defined after conceptualization were: Preparation of the index flow sheet, material and energy balance of the total system, hydraulic assessment of total network, assessment of pumping system in place and Cooling Tower capacity and efficiency evaluation. At the beginning, all the previous work done was analysis of described objectives where hypotheses were formulated to face the question: will the cooling tower remove the increased heat load after revamping the plant, in summer time? In case of negative answer which proposals are suggested? The more important variable that defines the project like this one is the wet bulb temperature that was redefined with the best available data and proper method applied for these cases. The value of 22 ĀŗC is the actual setting number for wet bulb temperature. The exploration and strategy to achieve the objectives were by measurement as stringed as possible, by analysis of specialized literature and use of simulator Aspen Plus and Excel spreadsheets. The theoretical model was verified by the computational tools and the internal human resources experiences as well as external were not forgotten. The methodology used was a mixture of theoretical/trial and error approaches for oriented results. Because of the diversified sources of information and variety of tools used, it was decided to work with the two main unit systems: International System (SI) and Inch Pound Second system (IPS). Project recalculation and verification was made, both built up performance curves and capacity and efficiency analysis. Operation parameters and hydraulic services were reassessed and 26 ĀŗC water supply temperature confirmed. The answer to the previous question is: The actual Cooling Tower doesnāt remove the total heat (35 MW) load in Summer time. In periods when wet bulb temperature equals or surpasses 22 ĀŗC the TA needs to reduce heat load with consequent production reduction in order to maintain the cold water temperature at 26 ĀŗC, otherwise we will expect greater values according to simulators and practice tests. The second answer is: As demonstrated, it is possible to increase the TA performance with less L/G and as a complementary action change a cold blowdown by a hot one without investment. As a general recommendation preventive maintenance with best practices is the key ( Hensey, John C.,2006). The most effective proposals but that requires investment are: Replace filling with one with best performance, apply extractors with greater capacity and improve the drift eliminator. The tower performance was determined with existing resources whose limitations require more precise tests with specified equipment technology available in the market, which will permit good accuracy according with international ATC 105 and CTR 23 standards.
Description
Mestrado em Engenharia QuĆmica - Ramo OptimizaĆ§Ć£o EnergĆ©tica na IndĆŗstria QuĆmica
Keywords
Impulsor ForƧa impulsionadora IntegraĆ§Ć£o OptimizaĆ§Ć£o ReutilizaĆ§Ć£o Torre de arrefecimento Impeller Driving force Integration Optimization Reutilization Cooling Tower
Citation
Publisher
Instituto PolitƩcnico do Porto. Instituto Superior de Engenharia do Porto