GB1361418A - Process for the treatment of material by dry crushing grinding or milling - Google Patents

Abstract

1361418 Controlling mills KONINKLIJKE NEDERLANDSCHE HOOGOVENS EN STAALFABRIEKEN NV 11 Oct 1971 [12 Oct 1970] 47295/71 Heading B2A [Also in Division G3] The charge in a dry crushing, grinding or milling plant is maintained constant by an electrical control system. Material is passed into and out of the plant in continuous supply and discharge flows, one supply flow being controlled by a signal dependent on 1 the difference between measured values of supply and discharge flows and 2 the value of sound volume produced by the plant. Thus the supply flow is controlled so that supply and discharge flows are balanced but is modified when necessary to restore the degree of filling of the plant to a desired level. The raw material feed to the mill is measured by a weighbelt 36 and a first signal derived. This is delayed by a time t, corresponding to the time the material takes to pass from the weighbelt to the mill inlet. A second signal is derived from a system 10 which measures the mass per unit time of coarse material flowing at 9, from a cyclone 8, which is recycled back to the input of the mill and thus forms part of the total input. The first and second signals are added and the sum is delayed by a period t 2 corresponding to the time the material takes to pass through the mill 1. This combined delayed signal represents the mass of the delivered flow at the moment of discharge. This is compared with the actual discharge flow 5 by measuring the power used by a driving motor 14 of an elevator 4 and deriving therefrom a third signal which is compared with the combined delayed signal in a device C 1 whose output signal is used to control the motor 13 driving a belt feeder 3. A microphone 15 which responds to noise in the mill, is used to derive a signal which controls a device C 2 which in turn controls the adjustment of the device C 1 by determining its zero point and thus the charge in the mill. The mill system also monitors at 24 and 27 gas pressure upstream and downstream of the mill. The monitored gas pressure at 24 is used to control a cooling air valve 21, and the gas pressure at 27 similarly controls a motor 35 for a valve 34 in the outlet stack. The outlet gas temperature is monitored at 32 and used to control a fuel-supply-valve motor 19 for a drying gas heater 16. In operation of the plant material from a hopper 2 is fed to the mill 1 with hot gas from the heater 16, ground material being fed by the elevator 4 to a second elevator 6 and a cyclone 8. The fines at 11 constitute the product. The coarse faction is recycled at 9. The hot gas is separated at 28 from the coarse fractions which are returned at 26 to the elevator 4. The separated gas is further filtered in an electro-precipitator 29 and the dust is added to the product. The filtered gas is withdrawn by a fan 33 and discharged up the stack.