Waste Heat recovery from Flue Gas Containing SO2 Through CO2 Based Combined Power and Refrigeration cycle

Abstract

CO2  at supercritical state is a preferable working fluid for low grade waste heat recovery due to a low critical temperature of CO2. In the present study a CO2 based combined power and refrigeration cycle is proposed in which CO2 coming out from the evaporator of the refrigeration system is pressurized to heat recovery unit pressure. The cycle is driven by the low grade waste heat of industrial flue gas containing small amount of SO2.The basic objective of this study is to explore operating parameters for the best possible performance of the proposed combined power and refrigeration cycle driven by low grade waste heat. It is observed that refrigeration effect increases as a larger mass fraction of CO2 enters the evaporator. However, this leads to a reduction in net cycle power output. Overall cycle performance (represented by 1st law efficiency) improves as larger mass fraction of CO2 enters the evaporator. Exponential growth of the physical size (i.e. NTU) of the regenerator limits the maximum practical value of CO2 mass flow into the evaporator.