GB703695A - Improvements in or relating to methods of and apparatus for filtration - Google Patents

Abstract

<PICT:0703695/III/1> In a continuous filtering process, for example for separating wax from a suspension thereof in a mineral lubricating oil, a filter medium under suction is passed in succession through a filtration zone in which a filter cake is formed on the filter medium, then through a washing zone consisting of a confined body of solvent liquid for the filtrate succeeded by a spray washing zone fed with the solvent liquid and then through a drying zone in which an inert gaseous medium, such as flue gas, is drawn through the cake; the liquid solvent may be, at least in part, supplied from the solvent of the spray zone running over the cake. As shown, a rotary filter drum apparatus for carrying out the process comprises a hollow rotating cylinder 2 in a casing 1, the cylindrical filter surface such as fabric 6 of the filter being divided interiorly of the drum into separate segmental sections 5, each of which is connected by conduits 9, 10 and headers 7, 8 through ports in an end plate 12 of one of the trunnion supports for the cylinder to an annular valve 11. This valve is divided by means of valve blocks 14, 15, 16, 17 into a series of valve chambers A, B, C, D, E, and during rotation of the drum each segment 5 is connected in sequence to these chambers. The annular space between the lower portion of the casing 1 and the drum 2 is divided into compartments X, Y by a radial dividing member 29 which is preferably located at 30 degrees to the vertical and extends longitudinally of the casing 1 and radially at the end portions thereof and extends towards the filter drum portions so as just to allow the passage of the filter cake formed on the drum in the compartment X. The liquid suspension of solids, for example a cooled mixture of wax in a mineral lubricating oil and a solvent for the oil consisting of a mixture of ketone and aromatics, is supplied to the compartment X through a pipe 28 and the solvent mixture alone is supplied to the compartment Y through a pipe 25 and to the sprays 23 in such a way as to maintain the liquids in the compartments X, Y at a common level L. On rotation of the drum in an anti-clockwise direction filtrate is withdrawn in the filtering zone from the chamber A through pipe 18 and solvent with the oil or mother liquor it has extracted as it is drawn through the cake in the washing zone is withdrawn from chamber B through the pipe 19 preferably at a higher suction value than that in pipe 18 and during the passage through the drying zone inert gas drying medium together with any of the washing liquid or solvent it has picked up is withdrawn from chamber C through pipe 21. In chamber D a slight gas pressure is provided by pipe 22 to loosen slightly the filter cake prior to contact of the filter with the scraper 26 which dislodges the cake to fall into the trough 24 from which it is discharged by a rotary scroll 27. The chamber E is a dead space.