Abstract: A heavy medium low-specific gravity method for recovering coarse clean coal within a size range of about +28 m and fine clean coal and coal-bearing particles within a size range of -28 x Om from a raw coal feed wherein heavy medium is recovered as a substantially clean product which can be recycled in the heavy medium system. In the method a raw coal feed containing coal, shale and other impurities within a size range of about 3.81 cm.times.0 is mixed withi a heavy medium to produce a slurry of low specific gravity between about 1.27 and 1.70. The slurry is treated in at least one cyclone to separate an overflow product containing substantially all coal and coal-bearing particles from an underflow product containing all shale and sulfur-bearing rejects.The overflow product is treated on standard equipment to separate coarse coal from fine coal and heavy medium. The coarse coal is recovered as a usable product.

Abstract: A duel feed hydrocyclone is proposed for separating an aqueous slurry of particles into a bottom stream which contains the heavy/large particles and a top stream which contains the light/small particles. The aqueous slurry is delivered through a common feed conduit and is divided into two initially parallel horizontally spaced-apart streams. The first stream enters the cylindrical chamber of the hydrocyclone through a side wall opening near the top thereof; the second feed stream is delivered around the outer surface of the cylindrical chamber and is introduced into the cylindrical chamber through a second side wall opening, remote from the first side wall opening. The heavy/large particles of the slurry descend adjacent to the inner wall of the hydrocyclone in helical paths which are distinct from one another. Some particle segregation occurs in the second passageway prior to introduction of the second partial feed stream into the hydrocyclone.

Abstract: An improved froth flotation installation for separating solid particles from an aqueous slurry by delivering a stream of the aqueous slurry directly into a vortex chamber along with a supply of bubble-forming gas. The kinetic energy of the slurry creates necessary froth bubbles, and provides mechanical agitation of the contents of a froth flotation separation zone upon discharge from the bottom of the vortex chamber. In multi-zone froth flotation installations, the direction of flow of the aqueous slurry of unrecovered solid particles is deliberately changed at least twice between a first froth flotation zone and a last froth flotation zone to improve solids-froth contact and to minimize the possibility of particles adopting a short circuit path through the installation. Multiple froth flotation zones are serviced by a single slurry pump in a preferred embodiment.

Abstract: An improved froth flotation installation for separating solid particles from an aqueous slurry by delivering a stream of the aqueous slurry directly into a vortex chamber along with a supply of bubble-forming gas. The kinetic energy of the slurry creates necessary froth bubbles, and provides mechanical agitation of the contents of a froth flotation separation zone upon discharge from the bottom of the vortex chamber. In multi-zone froth flotation installations, the direction of flow of the aqueous slurry of unrecovered solid particles is deliberately changed at least twice between a first froth flotation zone and a last froth flotation zone to improve solids-froth contact and to minimize the possibility of particles adopting a short circuit path through the installation. Multiple froth flotation zones are serviced by a single slurry pump in a preferred embodiment.

Abstract: A vortex chamber aerator is provided with a split feed conduit whereby the liquid feed is introduced into the vortex chamber through two opposed passageways to provide more even distribution of the liquid currents within the vortex chamber. This results in reduced wear in the vortex chamber and more importantly presents a uniform discharge pattern of the liquid and entrained gas bubbles.

Abstract: An intrinsically safe system controls all miner hydraulic and electrical functions from a hand held miner remote control pendant. Pendant control devices provide on/off control signals to interfaces with miner drive and pump controllers, as well as a group of .+-.6 VDC differential proportional and on/off control signals to respective electronic valve drivers. Valve driver outputs are fed to respective force motors on pilot stage valves which control each hydraulic function. Each valve driver output is modified by offset and dither signals to overcome power stage valve dead band and frictional characteristics. Pilot stage valves have an internal feedback sleeve coacting with a pilot valve spool in a hydraulic servo circuit. Pilot stage valves operate in a pilot oil system which may be isolated from power oil systems.