Evolution of HCl from KCl, CaCl2 and NaCl in an SO2-O2-H2O Atmosphere under a Simulated Condition of Municipal Wastes Incineration.

Abstract

The HCl evolution behavior in the process of sulfation of KCl, CaCl2 and NaCl was studied by using a lab-scale gas flow-type tubular reactor, in simulated conditions of municipal waste incinerations, under mixed gas of SO2: 0.3–1.3 vol%, O2: 2.5–15 vol%, H2O: 5–20 vol%, in the temperature range of 623–1123 K. The sulfation rates of KCl, CaCl2 and NaCl changed distinguishably with the temperature above 923 K, for each inorganic chloride of KCl, CaCl2 and NaCl. Comparing the time-changes of the concentration of HCl released from KCl, CaCl2 and NaCl, the rate of HCl evolution from CaCl2 was the highest; the maximum concentration of HCl discharged from CaCl2 was more than 5 times higher than those from NaCl and KCl at 923 K. The reaction kinetic parameters like the rate constant and the reaction orders with respect to SO2, O2 and H2O partial pressure for the sulfation of NaCl, KCl and CaCl2 were determined. It was suggested that the mechanism of formation of HCl by sulfation of KCl, CaCl2 and NaCl was different above and below the temperature range of 850–900 K. A higher sulfation rate of KCl, CaCl2 and NaCl might be attributable to a partial melting and/or volatilization of these inorganic chlorides at the temperatures higher than the temperature range of 850–900 K. The effect of SO2 partial pressure on the sulfation rate was 2–4 times larger for NaCl than for KCl and CaCl2. For the sulfation of KCl, the reaction order with respect to the O2 partial pressure was almost a half of that of NaCl. On the other hand, the rate of sulfation of CaCl2 was almost independent on the O2 partial pressure. The dependence of H2O partial pressure on the sulfation rates of KCl, CaCl2 and NaCl was almost the same in lower temperatures of 623–923 K. However, the reaction order with respect to H2O at 923–1123 K became 2–4 times larger than that in the lower temperature regions.