Exergoeconomic optimization of a new four-step magnesium-chlorine cycle

In this study, an exergy based economic assessment of the four step MgCl cycle is performed and compared with other hybrid thermochemical cycles. The exergy values of streams are utilized to analyse the cost rate of all streams and component based cost rates of exergy destructions. A multi-objective optimization of the cycle is conducted to maximize the performance and hence minimize the cost of the cycle by using Genetic Algorithm (GA). The results of exergoeconomic analyses for the base design of the MgCl cycle give energy and exergy efficiency values of 44.3% and 53%, respectively, an annual plant cost of $458.5 million, and a hydrogen production cost rate of 3.67 $/kg for a 172.8 tons of daily H2 production. The multi-objective optimization results indicate an increase in exergy efficiency (56.3%), and decrease in total annual plant cost ($409.3 million). The results of both thermodynamic and thermoeconomic analyses indicate that the final design of the MgCl cycle shows lower hydrogen cost results than that of the Hybrid-sulfur Cycle (HyS) and shows a similar trend with the hybrid CopperChlorine (CuCl) cycle.