Characteristics of Vaporization of Coal Ash Minerals Chlorinated by Gaseous Hydrogen Chloride

When heated in contact with PVC under argon gas flow, minerals in coal ash were chlorinated by HCl evolved from pyrolyzing PVC at 550-600 K and formed chlorides were vaporized above 900 K. The volatilization characteristics were thus systematically measured by heating coal ash at a rate of 10 K/min up to 1273 K in a thermogravimetric reactor under a continuous flow of HCl. The results indicated that Fe in ash was extracted nearly completely at 1000-1273 K. Complete chlorination of Ca compounds occurred above 600 K, but vaporization of CaCl₂ hardly proceeded. Vaporization of chlorides of Si, Al, and Mg was also found but was much less extensive. The volatilization characteristics were explained by considering interactions among minerals, i.e., enhanced chlorination of Fe₂O₃ and CaSO₄ by Al₂O₃. Fe₂O₃ volatilization resulted in a similarity of the mineral composition for the residual solids derived from bituminous coal ashes.