Sulfation and carbonation competition in the treatment of flue gas from a coal-based power plant by calcium hydroxide

Abstract

In this work, a gas containing CO2 and SO2 at the usual concentrations on the coal combustion flue gas reacted with calcium hydroxide to evaluate and quantify the influence of SO2 on the CO2 capture and vice versa. This influence was quantified with a continuous gas analyzer and by thermogravimetry (TG). Results show that the CO2 retained increases in general as its concentration does and decreases as the SO2 concentration increases. A similar behavior was found for the SO2 retention at different CO2 concentrations being more relevant the influence of the presence of SO2 on the CO2 capture than the opposite one. Results suggest that for a high CO2 capture, SO2 should be eliminated previously. With respect to the reaction process it was found that the desulfurization product clearly identified was CaSO3·½H2O; in the reaction between Ca(OH)2 and CO2, CaCO3 is mainly obtained, the complex CaO·CO2 being another possible product synthesized in low amount. Gas analyzer shows that SO2 and CO2 react simultaneously and that a part of the CaCO3 reacts with the SO2 and releases CO2. Sulfation values calculated by TG and from the gas analyzer are very similar but the amount of CO2 captured is not possible to know clearly by TG due to the synthesis and decomposition of CaCO3 during the process. The study of the evolution of the sorbent porosity in the process reveals that the presence of both acid gases produces a lower blockage of the pores than when only one gas is present probably due to the generation of new pores in the reaction of CaCO3 and SO2.