Process for producing an aqueous high concentration coal slurry

Claim 1

A process for producing an aqueous high concentration coal slurry, comprising the steps of: (1) pulverizing a coal material at a high concentration of 60 to 80% by weight in an aqueous medium containing a dispersing additive, to provide a slurry moiety (E) consisting of a high concentration aqueous coal slurry containing coal particles having a size of 100 μm or less; and (2) separately providing a cake moiety (F) consisting of dehydrated coal cakes containing coal particles having a size of 500 μm or less, by pulverizing a coal material in a low concentration of from 30% to 50% by weight in water free from the dispersing additive, and dehydrating the resultant low concentration aqueous coal slurry; and (3) mixing and kneading the cake moiety (F) with one or both of an aqueous medium and portion of the final high concentration coal aqueous slurry to provide a slurry moiety (G) consisting of an aqueous slurry of coal particles in a concentration of 60% to 80% by weight; and then (4) mixing the slurry moiety (E) with the slurry moiety (G) in a mixing ratio such that the ratio in weight of the coal particles in the slurry moiety (E) to those in the cake moiety (F) is in the range of from 8:2 to 5:5, wherein the resultant aqueous high concentration coal slurry contains coal particles having a size of 5 μm or less in an amount of 15% by weight or more based on the total weight of the coal particles, and the resultant high concentration aqueous coal slurry comprises coal particles having a particle size of 500 μm or less and dispersed in an aqueous medium in the presence of a dispersing additive, at a particle size distribution in which a coefficient of variation in size of the coal particles is from 0.3 to 0.75 determined in accordance with the equation (I): C=σ/M (I) wherein C represents the coefficient of variation in the size of the coal particles, M represents an average general logarithmic size of the coal particles calculated in accordance with the equation (II): M=Σ(log.sub.10 Si)×Vi (II) in which M is as defined above, Si represents an average size in μm of the coal particles in fraction No. i which is one of a plurality of fractions provided by dividing the entire amount of the coal particles in accordance with the order of the particle size, each fraction consisting of coal particles having a size in a predetermined range, and Vi represents a ratio of the amount in weight or volume of the portion of the coal particles in fraction No. i to the entire amount of the coal particles, and σ represents a standard deviation of the size of the coal particles calculated in accordance with the equation (III): σ=(Σ((log.sub.10 si-M).sup.2 ×Vi)).sup.0.5(III) in which Si, M and Vi are as defined above.