PRETREATMENT OF COAL FOR LIQUEFACTION

PURPOSE:To obtain coal for liquefaction, which has a low ash content, by removing free minerals by dehydrating and drying up-graded coal froth obtd. by feeding a liquefied product from a coal liquefaction process as a collector to a pulverized coal/water slurry and carrying out flotation. CONSTITUTION:A pulverized coal 11 having such a particle size distribution that at least 80% of the coal powder is composed of particles having a particle size of 3mm. or below, and water are introduced into a wet-process grinder 15, where coal is ground to form a coal power/water slurry which has a coal content of 3-15% and in which coal powder has such a particle size distribution that 70-80% of the powder is composed of particles having a particle size of 200 mesh or below. If necessary, the sluury is diluted with water. The slurry is then fed to a flotator 25. A recycling solvent 21, which is a liquefied product from a coal liquefaction process, is fed as a collector in a quantity of 300-2,500g per ton of coal. Further, a foaming agent and optionally, a pH adjustor are fed through a line 25 to adjust the pH of the slurry to 3-6 and coal is recovered by flotation as up-graded coal froth 29 having a coal content of 6-30%, and liberated ash is separated as flotation tail 27. The froth 29 is dehydrated in a dehydrator 30 and the dehydrated cake 31 having a high coal content and a water content of 20-40% is dried in a dryer 32 to a water content of 10% or below, thus obtaining coal for liquefaction, which has a low ash content.