Role of the water-gas shift reaction in CO2 capture from gasification syngas using limestones

Abstract

The work in this paper aims at determining the effect of gasification syngas on the carbonation reaction and conversion for several naturally occurring calcium-based sorbents. Experiments were performed via the use of a thermogravimetric analyzer (TGA) and it was observed that the presence of CO and H2 caused an increase in initial rate of approximately 70.6%. The increase in reaction rate was attributed to the CaO surface sites catalyzing the water-gas shift reaction; as well, the shift reaction was assumed to be responsible for the increase in activation energy for limestone based on the formation of intermediate complexes. A pilot-scale dual fluidized bed reactor system was applied to further investigate the effect of the shift reaction on CO2 capture and sorbent conversion for two limestones (Polish and Cadomin limestone). During carbonation with steam present in the feed gas, it was observed that the high CO2 capture period was significantly extended as compared to carbonation with only CO2 present. This resulted in an increase in CaO conversion from approximately 16.1 to 29.7% for the initial carbonation cycle and reinforced the conclusions drawn via TGA experimentation. Based on the outlet gas analysis, it was confirmed that the CaO particles were in fact catalyzing the water-gas shift reaction, increasing the overall sorbent conversion to approximately 46.9% for the first cycle. In terms of sorbent regeneration, the oxy-fuel combustion conditions employed (high CO2 and O2 atmosphere), resulted in enhanced sorbent sintering, thus producing the negative effect on carbonation conversion.