Energetic and Exergetic Performance Comparisons of Various Flow Sheet Options of Magnesium-Chlorine Cycle

During the past decade thermochemical and/or hybrid cycles using essentially heat (without/with some electricity) are preferred over conventional electrolysis where the electricity is the main energy input. Therefore, such cycles help significantly reduce the electrical work consumption by adapting some consecutive chemical reactions which utilize thermal energy at medium to low temperatures that can match with renewable and existing nuclear energy sources. The ideal magnesium-chlorine cycle consists of three steps, namely hydrolysis of MgCl2, chlorination of MgO, and electrolysis of HCl. In this particular study, we develop two newly proposed configurations to compare with the ideal version of this cycle. The first configuration uses an intermediate step through the hydrolysis reaction while a fourth step is introduced in the second configuration where HCl production is accomplished in dry form. Thermodynamic comparisons are carried out using energy and exergy analysis, and the four-step configuration practically shows the highest performance and can compete with the conventional splitting of water by electrolysis. In summary, the present options provide potential solutions for sustainable hydrogen production.