Coal-water mixture using upgraded low-rank coal and process for producing said mixture

A process for producing a coal-water mixture usable as a fuel as is, using upgraded low-rank coal having an equilibrium moisture content of less than 11 percent of less at 100 percent relative humidity, said coal-water mixture having a particle size of the coal such that the proportion of the coal portion passing through a 200-mesh filter is 80 percent by weight or more, which process comprises:

• heat-treating a low-rank coal having a carbon content of 75 percent or less on dry ash-free basis and an inherent moisture content of 10 percent or more, or an equilibrium moisture water content of 15 percent or more at room temperature and 98 percent relative humidity, in the presence of water and carbon monoxide at the critical temperature of water, 647.3.degree. K., below in a pressure vessel, wherein the weight ratio of the water and low-rank coal used in the heat treatment of low-rank coal is 0.3 to 3.0 and the amount of carbon monoxide present in the reaction system is 1 to 5 MPa in terms of the partial pressure of carbon monoxide during the reaction, said heat treatment being conducted until the coal, after heat treatment, has an equilibrium moisture content of less than 11 percent at 100 percent relative humidity, and
• recovering the reaction mixture comprising coal and water, from the pressure container, using humic acid as a surfactant as is in the water which has been produced by the heat treatment whereby addition of another surfactant added thereto is eliminated or minimized, and adding the required amount of water to obtain a slurry.