Hydrogen production by hydrogen sulfide splitting using concentrated solar energy – Thermodynamics and economic evaluation

Thermodynamic and economic analyses were carried out to evaluate the use of concentrated solar energy for driving the endothermic dissociation reaction H2S → H2 + 0.5S2. Three different schemes were assessed: (1) a pure solar process; (2) a hybrid process, which uses both solar and natural gas combustion as the energy sources of high-temperature process heat; and (3) the Claus process. This study indicates that the pure solar process has the potential of lowering the disposal costs of H2S vis-à-vis the conventional Claus process while co-producing H2 without concomitant CO2 emissions. An economic assessment for a 40 MWth chemical plant using solar tower technology indicates savings of approximately 45% in comparison to the Claus process. Solar H2 production is estimated at a cost in the range of 0.061–0.086 $/kW h, based on its lower heating value and without credit attributed to H2S disposal. A sensitivity analysis revealed that the quench efficiency represents the parameter with the highest impact on the economics of the process. A hybrid natural gas/solar plant design able to operate 24 h-a-day is predicted to reduce the H2 production cost to 0.058 $/kW h at current fuel prices, however, at the expense of increased complexity related with the hybrid reactor design and operation plus the associated CO2 emissions of 0.42 kg/kW h.