The influence of H2O and SO2 on CO2 uptake in fluidized bed calcium looping

The effect of steam and sulfur dioxide on CO2 capture during calcium looping was studied in a novel lab-scale twin fluidized bed device. Tests were carried out under typical calcium looping operating conditions with or without the presence of H2O and/or SO2 during the carbonation stage. Carbonation was carried out at 650°C in presence of 15% CO2, 10% steam (when present) and by investigating two SO2 levels, representative of either raw (1500ppm) or pre-desulfurised (75ppm) typical flue gas derived from coal combustion. The sorbent used was a reactive German limestone. Its performance was evaluated in terms of CO2 capture capacity and sulfur uptake. Results demonstrated the beneficial effect of H2O and the detrimental effect of SO2 on the CO2 capture capacity. When both species were simultaneously present in the gas, steam was still able to enhance the CO2 capture capacity even outweighing the negative effect of SO2 at low SO2 concentrations. A clear relationship between the degree of Ca carbonation and sulfation was observed. Microstructural porosimetric characterizations aided in explaining the observed trends.