Effect of the presence of NaCl vapour on indirect sulphation of limestone

The effects of the presence of NaCl vapour on limestone SO2 capture behaviour were examined. When NaCl was present in the sulphation atmosphere, the effects of the presence of H2O, reaction temperatures, particle sizes and NaCl concentrations on limestone SO2 capturing were studied in a tailor-made three-section control horizontal furnace. The presence of NaCl in the sulphation atmosphere clearly improves the limestone SO2 capturing capacities. H2O has a strong impact on the effect of NaCl vapour on limestone sulphation. In the absence of H2O, the enhanced effect of NaCl vapour on limestone sulphation is reinforced further. The presence of NaCl vapour changes the effects of reaction temperatures on limestone SO2 capturing capacities. The optimum sulphation temperature for limestone in the presence of 1058 ppm NaCl is 1000 °C rather than the optimum temperature of 850 °C in the absence of NaCl. A higher limestone SO2 capturing capacity is achieved with a smaller particle size in the presence of NaCl. The presence of NaCl vapour reduces differences in limestone SO2 capturing capacities with different particle sizes. At 850 and 1000 °C, the SO2 capturing capacity of limestone increases and later decreases with the Na/S mole ratio increasing. While, the SO2 capturing capacity of limestone increases monotonically with the Na/S mole ratio increasing at 1200 °C. The Na+ of NaCl vapour doped into the product layer during sulphation, which enhances the SO2 capturing capacity of limestone. The reaction between NaCl vapour and SO2 reduces SO2 concentrations, negatively affecting limestone sulphation, while the generated HCl promotes limestone SO2 capturing through changes in the surface morphology of the product layer. The effect of NaCl vapour on limestone sulphation is thus dependent on the extent of reactions between NaCl vapour and SO2.