Grindability of Coal Treated with Liquid Ammonia

Abstract

Two Japanese coals and a Chinese coal were treated with liquid ammonia. The behavior of the coal particles during the liquid ammonia treatment was visually observed. The microscopic observations of surfaces of the coals before and after ammonia treatment were also made. The grindability of the untreated and treated coal grains was investigated with a ball mill or a mortar grinder.
Results obtained are as follows; ( 1 ) Shin-Yubari coal was partially comminuted during the immersion of the coal in liquid ammonia and most of the coal particles were comminuted upon evaporation of liquid ammonia after the immersion treatment (Fig. 1). Taiheiyo coal was not comminuted during the immersion and even upon evaporation of the liquid ammonia. ( 2 ) The width of cracks in the coal particles formed by the ammonia treatment was larger in Taiheiyo coal than in Shin-Yubari coal (Fig. 2). ( 3 ) Microscopic observations of the treated Tatung coal showed the dependence of cracking behavior upon the maceral constituents (Fig. 3). ( 4 ) The compressive strength of the treated Shin-Yubari coal particles and of the treated Taiheiyo coal particles was reduced to one fourth and a half of that of the respective parent coal (Figs. 4, 5). ( 5 ) The size distribution of the coal particles was interpreted with the Rosin-Rammler equation. For Shin-Yubari coal, the liquid ammonia treatment gave the n value increased from 1.0 to 1.5, and the D_e value decreased from 560 to 100 μ after 30 min grinding (Fig. 8). ( 6 ) For Shin-Yubari coal, the energy required to grind up to 200 mesh size was reduced from 34 to 25 kWh/t by this treatment.