Waste heat recovery of two solar-driven supercritical CO2 Brayton cycles: Exergoeconomic analysis, comparative study, and monthly performance

Abstract

The waste heat from a supercritical Brayton cycle has a great potential to be recovered. However, there is a lack of research regarding the utilization of these cycles in multi-generation systems. In addition, different multi-generation systems based on supercritical Brayton cycles have not been compared in the literature. In the present study, two multi-generation configurations based on two supercritical Brayton cycles, namely regenerative (configuration 1) and recompression (configuration 2), are proposed and compared from thermodynamic and exergoeconomic standpoints. In both configurations, an organic Rankine cycle, a domestic hot water heat exchanger, and an LiCl-H2O absorption refrigeration system are employed to convert the waste heat of the two supercritical Brayton cycles into useful energy. Meanwhile, a thermoelectric generator is used instead of a condenser for efficient waste energy recovery of the organic Rankine cycle. The generated electricity by the organic Rankine cycle and thermoelectric generator is used to generate hydrogen in a proton exchange membrane electrolyzer. In addition, a direct integration method is employed to integrate the two supercritical Brayton cycles with a solar power tower as the heat source. The final results regarding the net output power, exergy efficiency, and economic performances of the two configurations reveal the superiority of configuration 2 over configuration 1. Net output power and exergy efficiency of configuration 2 are 6.55 MW and 4.06% points higher than configuration 1. Moreover, total cost rate and unit cost of products for configuration 2 are 0.4 $s-1 and 10.03 $GJ-1 lower than configuration 1. On the other hand, cooling, heating, and hydrogen rates of configuration 1 are respectively 2.93 MW, 4.23 MW, and 2.84 kgh-1 higher than configuration 2. Moreover, the monthly analysis of the two systems for Dhahran city (26.3°N/50.2°E) as a case study indicates that the best thermodynamic performance of the systems is achievable in February, June, and July.