abstracts s04

Maria Cristina Pellegrini - e-mail: epg@cesp.com.br
CESP/IEE-USP Cia. Energética de São PauloRua da Consolação, 1875, 11o
01301-100 - São Paulo, SP, Brasil

Dorel Soares Ramos - e-mail: dorelram@pea.usp.br
Escola Politécnica da USP
Rua José Rubens, 212 Previdência
05515-000 - São Paulo, SP, Brasil

Silas Vieira - e-mail: vieirsla@usp.br
CGEEP/EPUSP Cia. de Geração de Energia Elétrica Paranapanema
Av. das Nações Unidas, 12901, 31o
04578-000 - São Paulo, SP, Brasil

This work aims at to analyze the repowering of medium sized sugar and alcohol plants located in the Southeast area of São Paulo State. Through a study case considering a standard unit that processes ten thousand tons of sugarcane per day, simulations were made using a mathematical model denominated Modelo de Despacho Hidrotérmico, which supports the decision process for the expansion of electric energy offers. As a result of these simulations, it was possible to get the standard dispatch profile for such cogeneration plants, expressed by a medium capacity factor of 89%, demonstrating, therefore, the significant participation that these units can have in the energy context. Furthermore, a brief discussion about the energy price and capital return time is introduced, emphasizing the attractiveness of this kind of enterprise.

Alexandre M. da Silva - amarcial@uol.com.br
José A. P. Balestieri - perrella@feg.unesp.br
Paulo Magalhães Filho - pfilho@feg.unesp.br
Unesp - Universidade Estadual Paulista, Departamento de Energia
Cx. P. 205 - 12516-410 - Guaratinguetá, SP, Brasil

Este trabalho apresenta o uso de recursos computacionais na simulação de um sistema de cogeração com ciclo combinado para análise de seu desempenho em base
energética. A demanda térmica é utilizada como entrada principal de dados, associada às características de desempenho de cada componente do sistema. É avaliada a influência de diversos parâmetros do sistema tais como: eficiência térmica do ciclo e eficiência global de cogeração. A linguagem computacional utilizada é o Visual Basic for Applications associada a uma planilha eletrônica e um banco de dados contendo informações de turbinas a gás disponíveis no mercado internacional. Duas configurações do sistema de cogeração com ciclo combinado são predefinidas: uma delas é composta de turbina a gás, caldeira de recuperação e turbina a vapor de contrapressão com uma extração que alimenta dois processos térmicos de diferentes níveis de pressão; a outra configuração apresenta como alternativa uma turbina a vapor de condensação com duas extrações, atendendo os mesmos níveis de pressão requeridos. O software possibilita a geração de tabelas e gráficos para análise comparativa das alternativas definidas.

Palavras-chave: Cogeração, Energia, Ciclo combinado, Simulação computacional

José Luz Silveira - joseluz@feg.unesp.br
Elisângela Martins Leal - elisange@feg.unesp.br
UNESP - Universidade Estadual Paulista, Departamento de Energia
Faculdade de Engenharia - Campus de Guaratinguetá
Cx. Postal 205, 12500-000, Guaratinguetá, SP, Brasil

In this paper, a methodology for the study of a molten carbonate fuel cell cogeneration system associated to an absorption refrigeration system, for the electricity and cold water production, and applied to two establishments, is presented. This system permits the recovery of waste heat, available between 600ºC e 700ºC. Initially, some technical information about the most diffusing types of the fuel cell demonstration in the world are presented. In the next step, an energetic, exergetic and economic analysis are carry out, seeking the use of fuel cells, in donditions of prices and interest of Brazil. In conclusion, the fuel cell cogeneration system may have an excellent opportunity to strehgthen the decentralized energy production in the Brazilian energy scene.

Keywords: Fuel Cell, Cogeneration, Energetic-exergetic and Economic Analysis, Cases Study

Ednildo A Torres - ednildo@ufba.br
Universidade Federal da Bahia/Escola Politécnica/DEQ/LEN
Rua Aristides Novis, 2 - Federação - Salvador, BA , Brasil - 40210-630
Waldyr L. R. Gallo - gallo@unicamp.br
Universidade Estadual de Campinas, Departamento de Energia
UNICAMP -FEM - DE 13083-970 - Campinas, SP, Brasil

This work presents an exergy analysis for a petrochemical cogeneration system (the greater operating in Brazil). The system is described, the method employed to simulate the system is presented, and the exergy efficiencies are defined. The analysis presents the exergy efficiencies and irreversibility for each sub-system. The results obtained from real data were used to compare operation strategies which are not clear from energy balances.

Key words: Energy, Exergetic Analysis, petrochemical, cogeneration, Irreversible processes.

Leonardo S. R. Vieira - lsrv@cepel.br
Centro de Pesquisas de Energia Elétrica, Área de Conhecimento de Materiais e Mecânica
Cx. P. 68007 - 21944-970 - Rio de Janeiro, RJ, Brasil

João L. M. Donatelli - donatelli@lttc.com.ufrj.br
Universidade Federal do Espírito Santo, Departamento de Engenharia Mecânica
29060-970 - Vitória, ES, Brasil

Manuel E. C. Cruz - manuel@serv.com.ufrj.br
Universidade Federal do Rio de Janeiro, Departamento de Engenharia Mecânica
Cx. P. 68503 - 21945-970 - Rio de Janeiro, RJ, Brasil

In this paper we perform exergetic and exergoeconomic analyses, a mathematical optimization and an exergoeconomic optimization of a gas turbine-heat recovery boiler cogeneration system with fixed electricity and steam production rates. The exergy balance is calculated with the IPSEpro thermal system simulation program. In the exergetic analysis, exergy destruction rates, exergetic efficiencies and structural bond coefficients for each component are evaluated as functions of the decision variables of the optimization problem. In the exergoeconomic analysis the cost for each exergetic flow is determined through cost balance equations and additional auxiliary equations from cost partition criteria. Mathematical optimization is performed by the metric variable method (software EES - Engineering Equation Solver) and by the successive quadratic programming (IMSL library - Fortran PowerStation .). The exergoeconomic optimization is performed on the basis of the exergoeconomic variables. System optimization is also performed by evaluating the derivative of the objective function through finite differences. This paper concludes with a comparison between the four optimization techniques employed.

WALTER N. BASTOS - e-mail wnovellob@openlink.com.br
ALCIR F. ORLANDO - e-mail afo@mec-puc-rio.br
Pontifícia Universidade Católica do Rio de Janeiro - PUC-Rio
Departamento de Engenharia Mecânica
R. Marquês de S. Vicente 225, Gávea, 22453-900, Rio de Janeiro, Brasil

A thermal and economic study, carried on by using the first and second law of thermodynamics concepts demonstrated the economic feasibility of the cogeneration system, and proposed modifications to be done in the studied criogenic plant, a typical T-240 NA MPL3 plant. The thermodynamic analysis showed that the second law efficiency of the processes could be improved, together with a 12% electric energy consumption reduction. Four cogeneration schemes were analyzed with both the first and second laws of thermodynamics and, then, the economic analysis was performed. Rankine, Brayton, Otto and Combined gas-steam basic cycles were used in this analysis.The combined gas-steam cycle was shown to be more economically feasible than others. Thermal and electric loads were well balanced, resulting in a higher second law efficiency. Although the initial investment for the modification was higher, the savings resulted to be higher, turning into a higher rate of return of the investment.

João L. M. Donatelli - donatelli@lttc.com.ufrj.br
Universidade Federal do Espírito Santo, Departamento de Engenharia Mecânica
29060-970 - Vitória, ES, Brasil

Leonardo S. R. Vieira - lsrv@cepel.br
Centro de Pesquisas de Energia Elétrica, Área de Conhecimento de Materiais e Mecânica
Cx. P. 68007 - 21944-970 - Rio de Janeiro, RJ, Brasil

Manuel E. C. Cruz - manuel@serv.com.ufrj.br
Universidade Federal do Rio de Janeiro, Departamento de Engenharia Mecânica
Cx. P. 68503 - 21945-970 - Rio de Janeiro, RJ, Brasil

In this paper we apply exergoeconomic principles to perform a comparative analysis of the use of internal combustion engines or gas turbines as prime movers of cogeneration plants. A preliminary comparison of these movers can be obtained by analysing them individually, considering the complete utilization of the generated products rated on a common exergetic basis. However, when these movers are integrated in a cogeneration plant, it is necessary to perform a global system analysis, which will consider the coupling between generation capacity and demand, under the design conditions. The design of a cogeneration plant should, ideally, consider all the aspects that affect its performance. In this paper we take into account several aspects which are not normally collectively considered in similar analyses encountered in the literature. Specifically, the comparative procedure considers the electrical tariff on an hourly basis, the electrical and thermal load profiles, the influence of the environmental conditions on the performance of the prime movers, sizing and operation mode options to meet plant loads, part-load efficiency, different criteria for cost partitioning, and, finally, the effect of size on plant cost. Once the operating conditions of the cogeneration plant are defined, the procedure attributes costs to all the fluxes, allowing for the identification of the ranges of capacity where each mover is economically advantageous. We apply the procedure to the energetic supply analysis of a typical process of Brazilian shopping centers.

MARIO A.B. ERNST - basulto1 @ uol.com.br - basulto@feg.unesp.br
JOSÉ A.P. BALESTIERI - perrella@feg.unesp.br
Universidade Estadual Paulista - UNESP - Departamento de Engenharia Mecânica
Av. Dr Ariberto Pereira da Cunha, 333 - Guaratinguetá - SP - CEP 12500-000

This article presents some aspects relative to the effects of changing loads on steam.generators and turbines. When the equipment solicitation varies due to industrial process demand changes, the equipment work in off-design point, altering its efficiency and the specific fuel rate. This work do not look for a detailed and exhaustive determination of the performance variation with the load but shows that in the selection of equipments this variation can have effects over the consume and the costs. In the present article it is assumed that the load variations are known, and the effects on the equipment efficiency were took from the correlated literature. An example of a Rankine cycle and other of a Brayton cycle are discussed, altering the operational conditions estimating the operating cost for each case.

Jeppe Grue - jeg@iet.auc.dk
Aalborg Universitet, Institute of Energy Technology,
Pontoppidanstaede 101, 9220 Aalborg OE, Denmark

Inger Bach - ib@iet.auc.dk
Aalborg Universitet, Institute of Energy Technology,
Pontoppidanstaede 101, 9220 Aalborg OE, Denmark

The power generation system in Denmark is extensively based on small combined heat and power plants (CHP plants), producing both electricity and district heating. This project deals with smaller plants spread throughout the country. Often a heat accumulator is used to enable electricity production, even when the heat demand is low. This system forms a very complex problem, both for sizing, designing and operation of CHP plants. The objective of the work is the development of a tool for optimisation of the operation of CHP plants, and to even considering the design of the plant. The problem is formulated as a MILP-problem. An actual case is being tested, involving CHP producing units to cover the demand. The results from this project show that it is of major importance to consider the operation of the plant in detail already in the design phase. It is of major importance to consider the optimisation of the plant operation, even at the design stage, as it may cause the contribution margin to rise significantly, if the plant is designed on the basis of a de-tailed knowledge of the expected operation.

Domingo Wilson Garagatti Arriola - wgarriol@usp.br
Escola Politécnica da USP - Depto. de Engenharia Mecânica
Av. Prof. Mello Morais, 2231 - Cidade Universitária Armando de Salles Oliveira, 05508-900 - São Paulo - SP

Silvio de Oliveira Júnior - olivsilj@ipt.br
Escola Politécnica da USP - Depto. de Engenharia Mecânica e
Instituto de Pesquisas Tecnológicas do Estado de São Paulo (IPT)
Av. Prof. Almeida Prado, 532 - Cidade Universitária Armando de Salles Oliveira, 05508-901 - São Paulo - SP

This paper presents the description and the exergy and thermoeconomic evaluation of a new cogeneration system, called tetra-combined cogeneration system, that generates electricity and chilled water (for air conditioning purposes) and eventually steam. This system is composed of a gas turbine, a heat recovery steam generator, a condensation/extraction steam turbine and a hybrid absorption/steam ejection chiller. The exergy and thermoeconomic performance (exergy based costs of electricity, steam and chilled water production) of this system is compared with the performances of conventional cogeneration systems, pointing out the advantages and disadvantages of this new system.

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