GB453126A - A new or improved method and apparatus for washing or grading coal or similar or other granular material - Google Patents

Abstract

453,126. Washing granular materials. PARTRIDGE, H. E., 79, Craiglockhart Road, and OLIVER, W., 70, Notherby Road, both in Edinburgh. March 2, 1935, Nos. 6602, 6603, and 6604. [Class 82 (ii)] Coal or other granular material of mixed sizes and specific gravities is first graded according to size and the grades are then introduced separately into a ribbon or stream flow of washing liquid, controllable as regards depth, velocity, or both these factors, which is produced in a tank containing the washing liquid, means being provided to collect or discharge separately materials falling through the flow at different distances from the point at which the material is introduced. The separate grades are preferably treated in separate wash boxes, each box having means such as an air lift for producing the ribbon or stream flow. The washing tank 5 is divided by vertical partitions 6 into compartments 7, 8, 9, 10 in each of which the water is caused to circulate so as to produce a stream or ribbon flow along the bottom. The circulation is effected by air lifts 23, three air lifts being provided in each compartment, each comprising a perforated pipe connected to a compressed air supply, the pipes being arranged at different distances from the bottom of the tank and from the end wall, so that by shutting off the air supply to one or more of the pipes the depth of the ribbon flow in the compartment can be reduced. Baffles 24 are provided adjacent the two inner air lifts to form boundaries for the currents. The bottom of each compartment is provided with a number of discharge shoots or hoppers 26 the area of the opening to the shoots being adjustable by means of pivoted vanes 25 actuated by screw adjustment means 28. The shoots 26 lead to discharge means, e.g. screw conveyers 29 leading to openings 30, or the material collected in the shoots may be raised above the water level by air lifts The material to be treated is fed by a hopper 20 into one end of a rotary screen 12 which passes through openings in the partitions 6 and is perforated so that grades of increasing size fall into the compartments 7, 8 and 9 and the oversize from the discharge end of the screen falls into the compartment 10. The screen is provided with a conveying spiral baffle 19 and during its passage along the screen the material is washed by a countercurrent of water from a pipe 22. The rotary screen may be replaced by a reciprocating screen. Each group of sized particles from the screen is separated according to specific gravity in one of the wash boxes 7-10, the screen being situated so that the material falls into the ribbon flow across the bottom of the compartments. Water containing very light material, clay, &c. overflows from the tank at 11 and is conducted to separating tanks constructed for example as described in Specification 407,001, the clarified liquid being returned by a pump to the pipe 22. The material separated in the clarification may be carried by a portion of the washing water over a submerged belt conveyer at such a rate of flow that any valuable light particles, e.g. fine coal, settle out on the belt, and are recovered and de-watered, the clay &c. which remains in suspension being separated from the water in a final separation tank and the water returned to the pipe 22. The treatment of coal, ashes, breeze, bauxite, and clays is referred to and in certain cases the water may be loaded with other materials to increase its specific gravity. According to the first and third Provisional Specifications, the method of grading by means of a ribbon or stream flow may be used to separate materials either according to specific gravity or according to size.