Exergo-environmental assessment and multi-objective optimization of waste heat recovery systems based on Organic Rankine cycle configurations

Abstract

Abstract Considering the high degree of environmental degradation that has been reached, the investigation of new methods to optimize processes, besides making them sustainable, is a topic highly studied within the scientific community. Therefore, in this study, an exergetic and an environmental impact assessment had been conducted of a waste heat recovery system from a natural gas engine exhaust gas based on a simple and a regenerative organic Rankine cycle using toluene, acetone, and cyclohexane as the working fluid. Current operational data measured in the engine exhaust gas line are used for analysis purposes, allowing them to develop some parametric case studies and a multi-objective pareto optimization to obtain the best exergy and environmental performance of the ORC configurations. The results show that the highest amount of irreversibilities are presented in the heat exchangers, which implies a high opportunity for improvement in the thermal process. At a base condition, (Toluene-RORC) presented the best global efficiency (26%) and a lower potential impact on the climate change category (0.00181 kg CO2 eq/kWh) due to the construction, the operation, the maintenance, and the decommissioning phase. In contrast, the lowest value of the environmental impact achieved under the RORC multi-objective optimization was 0.001776 kg CO2 eq/kWh, with operational values for RORC of exergetic efficiency (71.98%), thermal efficiency (34.01%), and net power (176.18 kW).