Clean coal slurry is a possible alternative to liquid fuel. The mine problems in use of coal in engines (ash content and particles size) are solved via a novel slurry processing technique consisting in superfine grinding of the coal, selective separation of the coal particles and other inorganic ingredients, and finally combustion of the fine fraction coal in slurry droplets. An experimental rig for column flotation and selective flocculation has been built. A vibroinertial grinding facility reduces the coal particles to 40 microns or less. After addition of appropriate amounts of a suitable oil and water an emulsion flotation step produces coal-water slurry with ash content under 4%, which in turn coal under 20 microns in size with ash content 0.4% by film-flotation.