Change in composition and porous structure of coal on thermal conditioning

Abstract

Attention focuses here on methods of coal processing that require minimal quantities of water and yield products that may be effectively used as commercial and secondary raw materials. In the heat treatment of coals associated with semicoking, the accompanying physicochemical transformation of the coal significantly affects its potential for further processing. In semicoking, the filtration system within the coal pieces changes. The initial coal sample contains phytopores of equivalent diameter d_e up to 0.22 μm. More than 54% of these are pores smaller than 10 μm, mainly (65%) of slot and disk form. A small proportion (10%) of supercapillary cavities (d_e > 0.1 μm) is also observed. After heat treatment, the content of small pores is sharply reduced to 10% (450°C semicoke) and 6.6% (550°C semicoke)–that is, almost sixfold–while the content of supercapillary cavities is increased approximately fourfold (in 550°C semicoke).