Extremum analysis based on exergy and economic principle for ejector-absorption cycles combined with regenerative organic-Rankine and gas-turbine cycles

Abstract

A combined cooling and power cycle is proposed for the establishment of a new system for the waste heat recovery process. The new system consists of a gas turbine coupling a heat recovery steam generator with the regenerative organic Rankine cycle and an ejector-absorption refrigeration cycle. The system analysis is carried out comprehensively through thermodynamic and economic viewpoints. The principal goal of the present study is to address the thermodynamic and economic viability of the proposed system and identify some possible improvements. In addition, the cost-effectiveness of the proposed cycle and the implemented methodologies has been examined. The key results show that the combustion chamber is the major source of irreversibility and it is responsible for 45.81% % of the total exergy destruction. Furthermore, the exergoeconomic factor of a combustion chamber is 0.0051 indicating that the cost of exergy destruction is more than that of the investment cost. In order to assess the effect of major design parameters, a parametric study is conducted. A thermodynamic study using R141b, R601a, and R123 is made and compared at various conditions. It is found that R141b is more suitable for improving the power output from the regenerative organic Rankine cycle. Finally, a multi-objective optimization is performed to determine the overall exergy efficiency and the total product cost as objective functions. At optimum conditions, the overall exergy efficiency and the total product cost are obtained as 0.4418 and 54.84 $/GJ, respectively. The operating temperature range in the generator of the ejector absorption system changes with respect to the conventional system values and the range of the optimum performance condition obtained is to be more practicable to avoid the crystallization state.