Enhancement of Indirect Sulphation of Limestone by Steam Addition

摘要

The effect of water (H_2O_((g))) on in situ SO_2 capture using limestone injection under (FBC) conditions was studied using a thermobalance and tube furnace. The indirect sulphation reaction was found to be greatly enhanced in the presence of H_2O_((g)). Stoichiometric conversion of samples occurred when sulphated with a synthetic flue gas containing 15% H_2O_((g)) in under 10 h, which is equivalent to a 45% increase in conversion as compared to sulphation without H_2O_((g)). Using gas pycnometry and nitrogen adsorption methods, it was shown that limestone samples sulphated in the presence of H_2O_((g)) undergo increased particle densification without any significant changes to pore area or volume. The microstructural changes and observed increase in conversion were attributed to enhanced solid-state diffusion in CaO/CaSO_4 in the presence of H_2O_((g)). Given steam has been shown to have such a strong influence on sulphation, whereas it had been previously regarded as inert may prompt a revisiting of the classically accepted sulphation models and phenomena. These findings also suggest that steam injection may be used to enhance sulfur capture performance in fluidized beds firing low-moisture fuels such as petroleum coke.