Assessment of a waste energy recovery (WER) unit for power and refrigeration generation: Advanced thermodynamic examination

Present work focuses on the advanced exergy analysis of a combined system to recover energy from a regenerative supercritical CO2 Brayton cycle. Through thermodynamic analysis of the system, a simulation code in Engineering Equation Solver (EES) has been developed. However, the conventional exergy analysis is a useful tool to determine the location with a higher irreversibility rate; it is not able to predict the part of exergy destruction rate, which can be neglected in different components. Advanced exergy analysis can provide valuable information about different aspects of exergy destruction rate in each component with taking into account the technological limitation with thermodynamic principles. Conventional exergy analysis of regenerative supercritical CO2 Brayton cycle reveals that the turbine with 48.35 kW has the main exergy destruction rate, and the second-largest exergy destruction rate belongs to an intermediate heat exchanger with 45.21 kW. Additionally, conventional exergy analysis reveals that 38% of the total exergy destruction rate takes place at the turbine, intermediate heat exchanger, pre-cooler and compressor. Advanced exergy analysis represents that about 61.6% of total exergy destruction rate is avoidable exergy destruction rate, which can be reduced. A close look at results indicates that 77% of endogenous exergy destruction is unavailable. As an example, in the solution heat exchanger (SHX), 23% and 77% of exergy destruction are endogenous and exogenous, respectively. It means the SHX performance improving can be achieved by improvement other system components. It can be found that a large amount of exogenous exergy destruction rate can be removed because the avoidable exogenous part of exergy destruction for the SHX is about 73.4%.