Patent GB-1183858-A (GB)
Title: Improvements relating to solids level detection on centrifuges.
IPC: B04B11/04
Filed: 1967-10-23
Abstract: 1,183,858. Centrifugal separator. PENNSALT CHEMICALS CORP. 23 Oct., 1967 [10 Nov., 1966], No. 48098/67. Heading B2P. Solids level detecting means in a centrifuge bowl 22 comprise an inwardly facing annular pocket 60 fed with control liquid and connected to a drain aperture which is obstructed by the solids upon build up of the latter, and sensing means such as 80, 82 for detecting a build up of control liquid in the pocket upon obstruction of the drain aperture. The bowl 22 is mounted by means of a bearing 20 in a housing 18 suspended by means 16 from standards 14 and is driven through belt and pulley 24 by a motor 26. The bowl is provided with radial vanes 34 and with a clear effluent discharge lip 32. Slurry to be centrifuged is fed through a stationary tube 38 provided with a solenoid operated valve 39, through a cup 40 rotating with the bowl and through conduits 42. A skimmer 50 is slidably mounted in bosses 54 on the housing 18 and may be driven alternately towards and away from the bowl wall 30 as by means 56 which may consist of pneumatic or electric motors. The pocket 60 is in the form of an annular channel which may be welded to the upper end of the vanes 34 and is provided in its base with circumferentially spaced openings in each of which is screwed a sensing nozzle 64 at the outer end of which is an orifice plate 66 whose orifice provides the drain aperture. Effluent discharging over the lip 32 of the bowl collects in the interior of the housing 18 and is removed via a conduit 44 into a tank 46. Control liquid is pumped from the tank via a line 70 which discharges into the channel 60 either continuously or intermittently under the control of a solenoid-operated, shut off valve 74. The means for sensing the level of the control liquid in the channel are electrically operated and may consist either of a pair of electric probes which may be shorted by the liquid to actuate the sludge-discharge cycle or, as shown, of a capacitance-actuated liquid detector 80 which has a depending probe 82 with its lower end disposed in the channel. The detector 80 is electrically connected to the feed valve 39, the drive means 56 of the skimmer 50 and to the valve 74. A trip 90 rigidly or adjustably mounted on the skimmer 50 is adapted to actuate a limit switch 92 in either direction of travel of the skimmer 50. The switch 92 is connected to a solenoid-operated valve which is adapted to divert the flow to either waste or effluent. In operation, the valves 39 and 74 are open so that slurry and control liquid are fed to the centrifuge bowl, the clear effluent discharging over the lip 32 and the control liquid escaping through the orifices at the outer end of each detecting nozzle 64. The sludge gradually builds up and eventually reaches the outer end of the detecting nozzle and covers the orifice in the plate 66. This blocks the escape of control liquid which gradually builds up in the channel 60 until detected by the detector 80 which then closes the valves 39, 74, and actuates the drive means 56 to drive the skimmer 50 rightwardly, as shown in Fig. 1, so that its mouth 52 engages the liquid in the bowl and discharges this liquid through the valve 94 which is open to effluent. Eventually the trip 90 on the skimmer 50 engages the switch 92 which causes the valve 94 to be connected to waste, this being effected just before the mouth 52 of the skimmer 50 reaches the sludge level in the bowl so that all the sludge is diverted to waste with none passing through the effluent liquid discharge. When the mouth of the skimmer reaches a point about " from the inner face of the bowl wall 30 the drive means 56 reverses the direction of travel of the skimmer. As the skimmer travels leftward, the trip 90 contacts the switch 92 which causes the valve 94 to divert the flow back to effluent discharge. When the skimmer reaches its leftward position, the drive means 56 again reverses itself ready for the next cycle. The valves 39 and 74 then open and the cycle is repeated. The centrifuge may be used for clarifying electrolyte, fruit juices or sodium alginate.