GB1534274A - Size reduction - Google Patents

Abstract

1534274 Impact pulverizers; comminuting at low temperatures BOC INTERNATIONAL Ltd 21 Jan 1976 [21 Jan 1975] 2670/75 Heading B2A Particulate material is comminuted by a method which includes precooling of the particulate material feeding it to a rotary impact mill, in which it is comminuted, cold gas being passed around a circuit of which the interior of the mill forms a part, the cold gas being formed by evaporating cryogenic liquid in the circuit outside the mill. The system comprises a hopper 2 and feed screw 4 feeding a main hopper 6. The main hopper feeds a mill 22 via a screw conveyor 8. The mill includes a screen, (not shown). Ground product is discharged via a pocket wheel valve 56. In operation, when the material in hopper 6 reaches a level sensor 14 the screw feeder is stopped, and restarted when the level falls appropriately. Liquid nitrogen is sprayed into a passage 26 communicating with the mill 22 and the hopper 24; the liquid nitrogen being stored in a vessel 32 The liquid nitrogen is also sprayed into the conveyor 8. A temperature sensor 44 or 44A is arranged in the passage 26 or under the mill and a controller 42 is programmed to open a solenoid valve 40 and close a valve 38. Liquid being sprayed into the conveyor 8. If the temperature falls below the range both valves are closed and if it rises above the range both valves are open.