Otimização exergoeconômica de ciclos de absorção para geração de potência

AUTOR(ES)

José Augusto Borgert Júnior

DATA DE PUBLICAÇÃO

2003

RESUMO

In this work it was shown that an aqua-ammonia absorption cycle presents an economical advantage as a bottoming-cycle in a cogeneration plant. To accomplish that, two cycles were compared: a Rankine cycle and a Kalina cycle. The former is an especially designed cycle for use of aqua-ammonia mixtures as working fluid. A computational routine was implemented to evaluate the aqua-ammonia thermodynamic properties. In this routine, the chemical potential concept was used instead of fugacity. A remarkable characteristic of this routine is that it allows the determination of the mixture phase. In order to analyze these absorption cycles, an exergoeconomic approach was used, in which the exergetic analysis is complemented by an economical analysis. The theory of exergetic costs was used to quantify these economical costs. For a consistent comparison basis, an optimization was carried out by means of the Zoutendijk method of feasible directions. The value to be optimized was the cost of the power generated by the combined system formed of the cogeneration plant and the absorption cycle. The Rankine cycle analysis resulted in an increase of the combined system generated power by 3.18% and a decrease of the generated power cost by 3.06%. For the Kalina cycle the combined system generated power increased by 3.26% and the generated power cost decreased 3.14%. From these results a modified Kalina cycle was proposed with an additional heat exchanger in order to achieve a better internal heat recovery. After optimized, this new cycle increased the generated power by 3.43% while decreasing even more the power generated cost, now by 3.30%.

ASSUNTO(S)

exergia termodinâmica engenharia mecanica

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