GB407316A - Improvements in or relating to the pulverising of coal - Google Patents

Abstract

407,316. Roller mills. CAREY, W. F., BRAWN, E. F., Norton Hall, The Green, Norton-on-Tees, and IMPERIAL CHEMICAL INDUSTRIES, Ltd., Millbank, London. Aug. 13, 1932, No. 22763. [Class 59.] A process for pulverizing coal to particles less than one twenty-fifth of an inch in size consists in crushing the coal in a .multi-stage roll crusher in which the individual stage reduction ratios, with the possible excepttion of the ratio for the last set of rolls, lie between 2.0 and 3.6, or in which the average stage reduction lies between these limits. As shown, coal of about “" size is passed over a magnetic pulley 9, which rejects tramp iron &c. down a shoot 10, and enters rollers A direct or after passing through a screen. It then passes through rolls B onto a screen 8 having a mesh about two or three times as wide as the gap between the preceding rolls which removes flakes to a shoot 12. After passing through rolls C, D the ground material is discharged through the bottom of the mill, preferably by a screw conveyer 7. The reduction ratio through A and B may be 3.16, C 2.0, and D 5.0. The R.P.M. assuming 10-inch rolls for A is 72.5 and the speed of the other rolls is in proportion to the reduction ratio. The critical stage reduction ratio lies between 3.1 and 3.6 according to the kind of coal used as above these limits wear of the pulverizing surfaces increases very rapidly whilst below these limits the amount of wear is nearly independent of the stage reduction. A lower limit of 2 is preferable as below this figure a large number of rolls &c. is required. The coal, distributed to the first set of rolls, leaves about 65 per cent free space in the gap so that the particles are presented singly and separately to the rolls. Each pair of rolls runs in the opposite direction at the same peripheral speed and the rolls are made, or surfaced with, nickel-chrome steel. The distance between the rolls may be adjusted by screws 14.