GB932099A - Coal drying - Google Patents

Abstract

932,099. Rotary drying drums; drying coal. W. L. PRITTS. Nov. 7, 1961 [May 5, 1961], No. 39760/61. Class 34 (2). In a process of drying combustible material, e.g. batches of coal, the material is dried in a rotary drying drum by the passage of hot gas therethrough, the dried coal and gas discharging from an outlet portion of the drum, and at least a portion of dried, pulverulent material being utilized as a main fuel to a combustion chamber to which it is fed together with at least a stoichiometric quantity of oxygen to provide the hot gas for the drying process. Batches of combustible material, e.g. coal, are dried in a rotary drying drum 40, which is rotated by an external ring gear 45 and which has rows of lifting vanes (not shown), by the passage therethrough of heated air produced in a stationary combustion chamber 24 by burning dried coal dust with a pilot flame which dust has been separated from the dried product. The dust is burned in a sufficient, but preferably excess, quantity of air to assure full combustion of the coal dust and the resultant hot gas is tempered in a non-rotatable chamber 35 through which the batch is introduced by a shoot 37 for entry into the rotary drum 40, the chamber 35 being intermediate the chamber 24 and drum 40 and the tempering, atmospheric air entering through ports 35c in the chamber 35. The dried coal passes from the drum to a discharge chamber 55, the larger particles being discharged on an endless belt conveyer 60 and the fires being carried upwardly by the hot gas through a duct 70 to a cyclone separator 75, the dust passing through a downwardlyconverging portion 75a and duct 78 to the conveyer 60 and the hot gas being exhausted to atmosphere through a discharge duct 80 by a suction blower 81. The portion of dried dust to be used as fuel is withdrawn from the duct 78 by suction applied to a branch duct 79, into a secondary separator 85, the suction being applied to the top of the separator by a suction duct 73 connected to the duct 70 and through which the separated gas is exhausted while the dust is discharged into a horizontal delivery duct 92 connected to a main supply duct 31. The duct 92 has a screw conveyer driven by a motor 95 which is variably driven via a potentiometer unit 110 in proportion to the temperature indication given by a thermocouple 71 in the duct 70 so that the rate of feed of the dust is controlled in accordance with the temperature of the gases leaving the drum. The dust is conveyed into the combustion chamber 24 by air from a blower 100. The pilot flame is supplied by an auxiliary fuel e.g. oil vapour, and air through pipes 13, 12 respectively to a chamber 10 mounted centrally of the inlet end of the combustion chamber 20 to provide a flame at all times during the drying operation, which flame may be turned off by a valve 14 in the supply line controlled from a main control electrical unit B and relit by a spark plug igniter 20.