Thermo-economic analysis and multi-objective optimization of waste heat recovery cycles of a gas engine

In this work, Organic Rankine cycle with open feed heater and Trilateral Flash cycle are used for waste heat recovery of exhaust gas and cooling water of a 34.3 kW stationary gas engine. The thermodynamic and thermo-economic performance of the bottoming cycles have been investigated, and then sensitivity analysis and multi-objective optimization have been done considering the objective functions of exergy efficiency and the special investment cost of the cycles. The optimal point is selected based on the LINMAP method on the Pareto Front. The results show that the exergy destruction rates in the heater and condenser of the Trilateral Flash cycle and the evaporator of the organic Rankin cycle are more than those of other components. Among the decision variables, the turbines isentropic efficiency and the condenser temperature of Trilateral Flash cycle have a significant effect on the objective functions. Employing waste heat recovery system on a gas engine results in an increase of 6.09% of the exergy efficiency of the overall system, including gas engine and bottoming cycles in the optimized state.