Patent GB-1408997-A (GB)
Title: Decanter centrifuge
IPC: B04B1/20
Filed: 1973-08-22
Abstract: 1408997 Screw centrifuges PENNWALT CORP 22 Aug 1973 [6 Sept 1972] 39730/73 Heading B2P A decanter centrifuge comprises an elongate bowl 16, Fig 1, mounted for rotation about its longitudinal axis, and having, at one end, an inwardly tapering end section 30 in which is located a heavy phase discharge port 24 and, at its opposite end, means, e.g. ports 20, for discharging separated light phase material; a screw conveyor 32 coaxially mounted within the bowl for rotation relative thereto to convey separated heavy phase material axially along the interior wall of the bowl towards the port 24; means e.g. stationary feed tube 42, for feeding material to be separated into the bowl along the axis thereof; and a baffle 62 carried by the conveyor 32 and positioned between the point of entry 54 of the feed material into the bowl and the heavy phase discharge port 24, thereby to divide the interior of the bowl into a discharge zone 70 communicating with the heavy phase discharge port 24 and a separating zone 68 communicating with the feed entry point 54, the baffle extending radially a distance such that the outer edge thereof, in use, projects into the separated layer of heavy phase material and forms, with the adjacent internal wall of the bowl, a restricted passageway 74 through which the separated heavy phase material passes on its way towards the discharge port 24, and means being provided, operable independently of the conveyor, to apply a pressure head to the separated heavy phase material located on the side of the baffle remote from the port 24, thereby to assist the passage thereof through the restricted passageway. As shown in Fig 1, the baffle 62 is of frusto-conical shape and has its smaller end 64 attached to the hub 46 of the screw conveyor. Helical flights 50, 52 are provided on the hub 46 and the baffle 62 to remove the separated heavy phase material towards the port 24. A number of such ports are provided. The inner surface of the baffle may be provided with vanes 76 to accelerate incoming feed to the angular velocity of the separated phases in the zone 68 thereby minimising turbulence and improving separation. Accelerator vanes 60 are also provided in the feed chamber 44. The light phase discharge ports 20 are radially adjustable by providing an end wall 22 leaving the ports in the desired location. The radial distance of the ports 20 from the axis of the bowl is set so that the inner surface a of the separated light phase material is maintained radially inward of the heavy phase discharge ports 24. The layer of light phase material under centrifugal force subjects the underlying layer of heavy phase material to increased pressure in the zone 68 this increased pressure being transmitted via the restricted passageway 74 to the heavy phase material in the zone 70 thus helping to advance it to the discharge port 24. In a modification, Fig 2 (not shown), instead of the baffle being frusto-conical it is in the form of a flat annular plate carried by the screw conveyor hub.  In a further modification, Fig 5, the baffle is annular as shown at 66. In addition, an annular baffle 86 is carried by the hub 46 to seal the separating chamber 68 from the atmosphere via the ports 20. An annular auxiliary baffle 88 is carried by the bowl and extends radially inwardly beyond the separating line e of the phases to prevent the flow of heavy phase material towards the ports 20. Pressurisation of the heavy phase material is in this case effected by pressurised gas supplied through a conduit 90 extending through the feed tube 42 into the feed chamber 44 from which the gas passes via the passages 54 into the separating chamber 68 and acts on the inner surface of the light phase layer.