Patent GB-1444137-A (GB)
Title: Preparation of a fine fraction from viscous slurries
IPC: B01D21/02
Filed: 1973-09-07
Abstract: 1444137 Separating particulate material WAAGNER-BIRO AG and CHEMIE UND METALL GmbH RHEAX 7 Sept 1973 [7 Sept 1972] 42294/73 Headings B2H and B2P In a process for preparing from a viscous slurry a fine fraction of particulate material centrifugal separation in two stages 10, 20 to obtain a final fine fraction F removed as overflow of the second stage 20, at least the major portion of the underflow fraction U 1  from the first stage 10 is subjected to a hydraulic classifying step, the concentration of solids in the final fine fraction is adjusted as required by fresh water W introduced in the hydraulic classifying step and the overflow fraction 0 of the hydraulic classifying step is recycled to the inlet of the first centrifugal separation stage 10 while the underflow fraction C of the hydraulic classifying step as well as the remainder U1', if any, of the underflow fraction from the first centrifugal separation stage 10 constitute a fraction G of mainly coarse matter of the twostage centrifugal separation process. The centrifugal separation stages 10, 20 each contain at least one hydrocyclone. With each of the stages are associated a pump 12, 22. and a sump 11, 21. The overflow discharge lines 13, 23 may be connected via lines 14, 24 equipped with valves 15, 25 to the sumps 11, 21 respectively which are provided with floats 16, 26 for controlling the valves and hence adjusting the liquid level in the sumps 11, 12. The underflow discharge lines 17, 27 are connected to a washer classifier 30 of the kind described in British Patent No. 1133246 and to the sump 11 respectively. The line 17 may include a distributor 18 having a branch line 19 for discharge of a minor portion U 1  of the underflow fraction from the centrifugal separation stage 10. The line 27 may also include a distributor 28 having a branch line 29 connected to the washer classifier 30 for transferring a portion U2' of the underflow fraction U 2  from the centrifugal separation stage 20. The viscous liquid suspension R of pantioulate material to be classified is fed through a line 1 to the sump 11. Any required fine fraction entrained in the underflow U 1  from stage 10 is separated in classifier 30 and returned via line 33 as overflow fraction 0 to sump 11. Similarly any fine fraction present in the underflow U 2  from stage 20 is returned to sump 11 via line 27. If the concentration of fine fraction in the classifier 30 is too high, a minor portion U 1  of the underflow fraction U 1  is discharged through line 19; if it is too low, a portion U 2 ' of the underflow fraction U 2  is fed via line 29 to the classifier. In a modification, Fig. 2 (not shown), a ball mill (2) is provided upstream of the sump 11 to effect size reduction of the particulate material and is connected at its inlet end to lines 1 and 32, and, optionally, to line 19. The whole of 'the suspension discharging from the crusher is fed to the sump 11. In a further modification, Fig. 3 (not shown), the outlet of the mill (2) is connected to a vibratory rake classifier (40) to which are also connected lines 27 and 33. The underflow from classifier (40) is returned to the mill (2) while the overflow is fed to sump 11. The rake-classifier has an elliptically pulsating rake.