Patent GB-1214505-A (GB)
Title: Slurry particle size distribution determination
IPC: G01N15/02
Filed: 1967-12-11
Abstract: 1,214,505. 505. Automatic control systems for grinders. WESTINGHOUSE ELECTRIC CORP. Dec.11, 1967 [Dec.14, 1966], No. 56191/67. Heading G3R. The particle size distribution in a grinding device supplying an output slurry to a cyclone  classifier is calculated by a computer which is supplied with signals respectively representative of the velocity F1 of the slurry to the classifier, the density D1 of this slurry, the velocity F2 of the overflow slurry from the classifier and the density D2 of this slurry, the computer calculating the cumulative percentage of solids # in the overflow slurry from the formula for two successive values of the velocity F1 and corresponding values of F2, D2 and D1, the computer also storing previously-measured values of limiting particle size d corresponding to the values of F1 so that it can determine the relationship between cumulative percentage of solids and limiting particle size, from which relationship it calculates the particle size modulus K of the output slurry, this modulus being representative of the particle size distribution. In Fig. 1 the output from a grinder 10 is passed to a tank 30 and thence to a measurement cyclone classifier 16 whose input and overflow are monitored to provide the signals F1, F2, D1, D2 for the computer 46. The classifier 16 is initially calibrated manually to determine the limiting particle size d in the overflow 18 corresponding to a flow F1 at the input 48. The flow F1 is maintained constant at a set value by varying a valve 36 controlled by members 12, 38, 46. The density D1 is maintained constant for the set value by the control circuit 14, 42, 40, the member 34 being a constant flow pump supplied with a mixture of slurry from tank 30 and water from source 39. The computer makes on-line periodic calculations of the particle size modulus K by adjusting valve 36 to obtain a first set of values F1, F2, D1, D2 and calculating the value #, repeating this procedure for a second set of valves F D and obtaining the characteristic of # against d, Fig. 3 (not shown) from whence K is obtained. The calculated value of K and hence the corresponding particle size distribution may be maintained constant by varying the size of the classifier underflow valve 20 under the control of a regulating signal from the computer. The arrangement of Figure 1 may be used to control the underflow valves of a number of production cyclone classifiers supplied by the grinder, Fig. 2 (not shown). In another embodiment, Fig. 4 (not shown) the overflows of the production classifiers are sequentially sampled and fed to an arrangement similar to Figure 1, the computer adjusting the underflow valve of each classifier. In Figure 5 the arrangement of Figure 1 is used to determine the particle size distribution in the output 85 from the classifier 60 and to maintain a desired particle size distribution in the container 89 input to the grinder, by varying the speed of a motor 87 controlling the feed of new material to the container 89. The invention can be applied to a dry grinding process by extracting a sample, mixing it with water, measuring and calculating as in Figure 1 and returning the sample to the mill. The various equations used in the computer calculations are discussed.