The influence of HCl on SO 2 absorption in the spray dry scrubbing process

Abstract

To examine the influence of HCl on SO 2 removal in the spray dry scrubbing process, preliminary experiments on the effect of adding CaCl 2 to the lime slurry on SO 2 absorption efficiency were performed in a laboratory scale spray dryer. It was found that the SO 2 removal efficiency is augmented at CaCl 2 concentrations up to 1.2 g/l in the lime slurry. This is ascribed to the influence of the prolonged drying process. However, SO 2 absorption efficiency cannot be improved further at higher CaCl 2 concentrations. A simple estimation shows that this cannot be ascribed solely to the influence of the drying behavior of the droplets and more complex explanations have to be found. Subsequently, experiments on the simultaneous absorption of SO 2 and HCl were performed. It was found that the SO 2 removal efficiency is enhanced at low HCl concentrations in the flue gas. This is ascribed to the formation of CaCl 2 in the droplets, resulting in a prolonged drying process. After reaching a maximum, the SO 2 removal efficiency falls again at higher HCl concentrations. This can be explained with the competing absorption process in which HCl is thermodynamically favored.