GB1144132A - Method and apparatus for sifting comminuted materials such as cements - Google Patents

Abstract

1,144,132. Classifying granular materials; centrifugal separators; ball mills; grinding cement. ESCHER WYSS A.G. 4 April, 1966 [6 April, 1965], No. 14900/66. Headings B2A, B2H and B2P. A pneumatic classifier comprises an inner housing 3, in which granular material, e.g. cement, fed from a hopper 6 on to a revolving plate 9 is scattered into a space 14 and classified into coarse and fine particles by an upward gas current induced' by fan blades 13, and an outer housing 1 defining with the inner housing 3 a separation chamber 15 in which there is arranged a ring of cyclone dust separators 20, 21 occupying an inner part of or, as shown, the whole of the radial extent of the chamber 15, the gas current carrying the fine particles leaving the housing 3 via a channel 16 and, after passage through the cyclones, being recirculated as substantially clean gas through the inner housing via air discharge pipes 25, 28 which open alternately at different levels in the hopper part 4 of the housing. The plate 9 carries a hub 10 on which are mounted the fan blades 13 and also beater blades 12. The coarse particles are separated out in the housing 3 due to their own weight and to the action of the beater blades 12 and, in falling down the hopper 4, impinge in cascade manner onto baffle plates 30, 31, 32 whereby very fine particles entrained by them are detached and carried in the separate current of recirculating gas, the coarse particles being discharged through a pipe 18. The cyclones have inlet guide members 24 and whirl blades 23, and open at their lower ends into the lower part of the chamber 15 for the discharge of the separated fine particles which are removed via the lower hopper part 2 of the casing 1 and through an outlet opening 19. A number of cyclones may be arranged concentrically in the space between the inner and the outer housings. The gas discharge pipes may open into annular or sector-shaped ducts which are connected by pipes to the space within the hopper 4. In a modification, Fig. 2 (not shown), cyclones (33, 34) having tangential inlets (42) communicating with the chamber (15) are secured to the hopper (4) by an annular disc (35) and are surrounded at their lower ends by a dust hopper (36) which is spaced from the hopper (2). Additional gas, for heating or cooling, is fed into the lower part of the hopper (4) by means of a pipe (46) and is superimposed on the main gas stream. In operation, coarse particles are separated in the inner housing and are discharged via a pipe (18) and a rotary valve (45), the upward current of additional gas providing further separation of the fine particles entrained with the coarse particles. The fine and very fine particles become separated from one another due to the centrifugal force imparted to the gas stream as it moves helically downwards. The fine particles are discharged through the opening (19) at the lower end of the hopper (2) while the very fine particles enter with the main gas stream into the cyclones (33, 34) where they are separated and are discharged in the hopper (36) to be removed through a pipe (38). The clean gas is recirculated into the interior of the inner housing by upwardly extending pipes (43, 34). A quantity of gas equal to the quantity of additional gas enters an annular duct (47) surrounding the lower end of the hopper (36) and is removed' through a pipe (49). In an arrangement for grinding and sifting cement, Fig. 3 (not shown), a classifier of the Fig. 2 (not shown) type is used in combination with a mill (50) to which raw material is fed via a pipe (52) and from which ground material is discharged at (53) onto a bucket conveyor (54) to 'be fed via a trough (60) to the supply pipe (7) of the classifier. The coarse material discharge pipe (18) of the classifier is connected to the raw material feed pipe (52). The very fine material discharge pipe (38) is connected to a final material pipe (59). The fine material discharge pipe (55) from the outlet (14) is connected to a distribution valve (56) which regulates the amount of fine material which is returned to the mill via a pipe (57) connected to the feed pipe (52) and which is discharged via a pipe (58) into the pipe (59) to adjust the final material to the desired degree of fineness.