Chlorination and volatilization characteristics of minerals in coal ashes were studied for chemical modification of the ash composition and properties. The ash samples were prepared by burning three bituminous coals, a lignite and a brown coal in a muffle furnace at 1088 K (high-temperature ash; HTA) and in an O2 plasma asher (low-temperature ash; LTA). On heating the ashes at 10 K/min to 1273 K in atmospheric chlorine gas flow in a thermobalance reactor, chlorination of minerals was found to take place even without oxygen sink and was followed by vaporization of the metal chlorides formed. Elemental analysis of the original and chlorine-treated HTAs revealed that most of K, Na, Mg and Fe and a portion of Ca were extracted while others such as Si and Al were hardly volatilized. Some pure metal oxides and a carbonate abundant in the ashes were treated at the same conditions. The result showed that Fe2O3 and Fe3O4 were rapidly volatilized in a temperature range of 900 to 1200 K. MgO was slowly but completely volatilized at 1273 K. Chlorination of CaO and CaCO3 occurred at much lower temperatures but vaporization of CaCl2 proceeded very slowly even at 1273 K. Changes in the ash weight with increasing temperature widely varied for the type of the initial ash. The variation was explained on the basis of the initial contents of metal oxides and carbonates. The chlorination treatment resulted in a significant reduction of differences in the mineral compositions, melting point temperatures and acid-base indices of residual solids from HTAs derived from the bituminous coals.
|Number of pages||11|
|Journal||Nihon Enerugi Gakkaishi/Journal of the Japan Institute of Energy|
|Publication status||Published - 1997|
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