Calcium Looping Process for Enhanced Catalytic Hydrogen Production with Integrated Carbon Dioxide and Sulfur Capture

Enhancement in the production of high purity hydrogen (H-2) from fuel gas, obtained from coal gasification, is limited by thermodynamics of the water gas shift reaction. However, this constraint can be overcome by the concurrent water gas shift and CaO carbonation reaction to enhance H-2 production by incessantly driving the equilibrium-limited water gas shift reaction forward and in situ removing the carbon dioxide (CO2) product from the gas mixture. The in situ removal of CO2 is achieved by using a calcium oxide (CaO) sorbent which also reacts with and removes sulfur and halide contaminants present in the syngas stream. The water gas shift reaction is achieved by the high temperature shift (HTS) iron oxide catalyst while the CO2 capture is achieved using CaO sorbent. The spent sorbent from the system is regenerated by calcining it to produce a pure stream of CO2 and CaO which can be reused. The steam addition for the water gas shift reaction is reduced to a large extent in this process which aids in reducing the parasitic energy consumption. In addition, the extent of sulfur removal by the CaO sorbent is also enhanced by operating at lower steam partial pressures. Experiments conducted in a bench scale facility have revealed that high purity H-2 of 99.7% purity can be produced by this calcium looping process.