The combined effect of SO2 and H2O on CO2 capture performance by calcium looping

The combined effects of SO2 and H2O in the carbonation stage of calcium looping were investigated by means of a customized constant temperature thermogravimetric analyzer. Pore structures were measured by N2 adsorption and SEM to elucidate their effects. By itself, SO2 reduces the carbonation conversion significantly, while H2O increases it. H2O can enhance both the carbonation and sulfation of CaO. Thus, when carbonation and sulfation reactions occur simultaneously, the presence of H2O can promote the sulfation reaction, which can inhibit the carbonation reaction (called here the indirect inhibiting effect of H2O). Under conditions with 0.05 %-0.1 % SO2, H2O levels of 10 %-20 % can mitigate the negative effect of SO2 on the carbonation reaction. This means that the direct improvement of carbonation by 10 %-20 % H2O is stronger than the indirect inhibiting effect. Compared with conditions without SO2 and H2O, the carbonation conversions under conditions with 0.05 % SO2 and 10 %- 20 % H2O were always lower. Therefore, the improvement produced by 10 %-20 % H2O on carbonation is less than the inhibiting effect of 0.05 % SO2. Pore structure measurement shows that under conditions with SO2 present, H2O still increased the pore volumes with width >20 nm and accelerated the diffusion of CO2 in the sorbents, which helps explain how it mitigates the negative effect of SO2 on the carbonation reaction.