Thermodynamic Analysis of Hydrogen Production by a Thermochemical Cycle Based on Magnesium-Chlorine

Abstract

Most thermochemical cycles require complex thermal processes at very high temperatures, which restrict the production and the use of hydrogen on a large scale. Recently, thermochemical cycles producing hydrogen at relatively low temperatures have been developed in order to be competitive with other kinds of energies, especially those of fossil origin. The low temperatures required by those cycles allow them to work with heats recovered by thermal, nuclear and solar power plants. In this work, a new thermochemical cycle is proposed. This cycle uses the chemical elements Magnesium-Chlorine (Mg-Cl) to dissociate the water molecule. The configuration consists of three chemical reactions or three physical steps and uses mainly thermal energy to achieve its objectives. The highest temperature of the process is that of the production of hydrochloric acid, HCl, estimated between 350-450℃. A thermodynamic analysis was performed according to the first and second laws by using Engineering Equation Solver (EES) software and the efficiency of the proposed cycle was found to be 12.7%. In order to improve the efficiency of this cycle and make it more competitive, an electro-thermochemical version should be studied.