Abstract: A method is provided for inhibiting an increase in viscosity of coal/water slurries when such slurries are caused to contact petroleum oil during fuel changeover in power generation systems, the method comprising maintaining in the coal/water slurry during transitional contact with petroleum oil an effective amount of an agglomeration-inhibiting agent selected from the group consisting of nonionic and anionic dispersing agents sufficient to inhibit the formation of coal/oil agglomerates and provide a flowable mixture during transitional contact having a Brookfield viscosity of below about 50,000 cP.

Abstract: Powdered coal is upgraded in utility and heat value by removal of ash and pyrite constituents by successively pressure caustic leaching the coal slurry at a temperature of at least about 175.degree. C., hydrochloric acid leaching the caustic leached coal to dissolve ash and pyrite residues not dissolved by the caustic, and pressure leaching the acid leached coal to remove alkali metals and chloride. Vanadium is also removed by the process.

Abstract: A method for cleaning fine coal is provided which includes: mixing the coal with a fluid of such a specific gravity that clean coal particles would float while refuse particles would sink therein, pretreating the coal-fluid slurry by adding a surfactant, subjecting the mixture to ultrasonic dispersion, and separating the entire mixture into higher and lower specific gravity fluid streams by means of centrifugal separation. The fluid of the chosen specific gravity and the surfactant may be recovered from the fluid streams and recycled if desired.

Abstract: An aqueous slurry containing coal and dextrin as a dispersant. The slurry, in addition to containing dextrin, may contain a conventional dispersant or, alternatively, a pH controlling reagent.