Testing of hydrotalcite based sorbents for CO_2 and H_2S capture for use in sorption enhanced water gas shift

摘要

The sorption enhanced water-gas shift technology is attractive for pre-combustion decarbonisation of power production based on IGCC, but only when the SEWGS technology can be applied for sour syngas. To this extend, it was recently demonstrated that 2000 ppm of H_2S did not influence the CO_2 sorption behaviour of a potassium promoted hydrotalcite material at a relatively low pressure of 5 bar. This paper highlights ongoing sorbent testing at pressure swing operation between 30 bar adsorption and 2 bar regeneration, crucial for the successful development of the technology. The sorbent has good catalytic activity for the water-gas shift reaction during SEWGS conditions. At 30 bar pressure and 400°C feed temperature, a CO, CO_2 and H_2S free H_2 product is obtained when feeding a syngas containing 200 ppm H_2S. This implies that mixing in a separate WGS catalyst is not needed, which significantly simplifies the technology. Moreover, multi-cyclic testing at 30 bar and 400°C for 110 cycles shows good sorbent stability in the presence of 200 ppm H_2S. Deliberately induced slips of CO_2 and H_2S stabilize within a limited number of cycles. By simply reducing the adsorption period, the mass-transfer zones for both CO_2 and H_2S are readily pushed back into the column, again producing a product free of CO_2 and H_2S. These observations suggest that reversibility of sorption processes on the material that have been tested is fully appropriate for the further development of the long-term operation of sour-SEWGS technology.