Thermodynamic, economic, and environmental analysis of new combined power and space cooling system for waste heat recovery in waste-to-energy plant

Abstract

Recently, the way that taking municipal solid waste (MSW) as fuel combustion for power generation is proposed to deal with increasing MSW, based on the method of waste-to-energy (WTE) technology. However, the energy efficiency of WTE plant is only 20% approximately, due to the energy loss of boiler and exhaust gas. A novel waste heat recovery (WHR) system has been developed to improve the thermodynamic and economic performance of WTE plant in this study. Rankine cycle (RC) is utilized to recover the waste heat (WH) of high-temperature boiler slag to generate power. Organic Rankine cycle (ORC) and absorption refrigeration cycle (ARC) are used for cascade recovery of WH from boiler exhaust gas to provide electricity and space cooling, respectively. Aiming to promote the overall performance of the WTE plant, comprehensive thermodynamic, economic, and environmental analysis are performed. Different environmental-friendly organic working fluids of the ORC are studied and compared based on the air pollutant emissions standards. Subsequently, several crucial parameters of proposed system are studied. Eventually, a comparison of the thermodynamic, economic, and environmental performance between original and new WTE plant is carried out. The results indicate that the use of butane can obtain the highest electric energy for ORC, compared with other working fluids. As well, the energy and exergy efficiency of WTE plant increase by 37.66% and 35.65%, respectively, with the choice of the WHR system. Furthermore, the dynamic payback period of new WTE plant is 4.63 year, with a decrease of 4.79 year, and the net present value (NPV) increases from 5.21 M$ to 18.12 M$. From the perspective of environmental analysis, the sustainability of the new WTE plant increases slightly, but the ecological efficiency has an increment of 11.28%.