On the synthesis of hydrogen producing alternative thermochemical cycles with electrochemical steps

Here we expand on our process systems engineering-based methodology for the initial evaluation of alternative thermochemical cycles for hydrogen production. A new identification algorithm is presented, which includes thermochemical cycles with electrochemical steps, referred to as hybrid cycles, in the reaction cluster search space. The resulting formulation is a mixed integer non-linear program, which we show can be solved as a set of mixed integer linear sub-problems using branch and bound. With a target base level, or theoretical maximum efficiency of 35%, as to be competitive with bottoming cycle based hydrogen production technologies, identified hybrid cycles are screened with an evaluation procedure based on heat pinch analysis. The strength of the expanded formulation is demonstrated with a case study for a hybrid copper–chlorine system. Results from our systematic evaluation suggest the proposed methodology is robust over a wide range of temperatures and candidate species. In this case study, we identify several hybrid cycles with estimated base efficiencies of up to 36%, exceeding our target efficiency.