Advanced Exergo-Environmental Assessments of an Organic Rankine Cycle as Waste Heat Recovery System from a Natural Gas Engine

Abstract

This paper aims to present the real improvement opportunities of a simple organic Rankine cycle (ORC) as waste heat recovery system (WHRS) from the exhaust gases of a natural gas engine using toluene as the working fluid, based on the exergy and environmental point of view. From the energy and exergy balances, the advanced exergetic analysis was developed to determine the irreversibilities and opportunities for improvement. Since the traditional exergo-environmental analysis, it was found that the component with the greatest potential environmental impact associated with exergy (bF = 0.067 mPts/MJ) and per unit of exergy (ḂD = 8.729 mPts/h) was the condenser, while the exergy-environmental fraction was presented in the turbine (52.51%) and pump-2 (21.12%). The advanced exergo-environmental analysis showed that the environmental impact is more associated with the operational behavior of the components, with 75.33% of the environmental impacts being of endogenous nature, showing that the environmental impacts are generated to a reduced magnitude through the interactions between components. However, it was identified that much of the environmental impacts in ITC 1 could be reduced, with 81.3% of these impacts being avoidable. Finally, the sensitivity analysis results revealed that steel is the material of the components with the least environmental impact.

Keywords

• exergetic analysis
• life cycle assessment
• ORC
• traditional/advanced environmental analysis
• waste heat recovery system