Patent GB-841573-A (GB)
Title: Continuously operating cylindrical immersion pressure filter
IPC: B01D35/00
Filed: 1956-09-10
Abstract: 841,573. Rotary filters. JUNG, H. Sept. 10, 1956 [Sept. 12, 1955], No. 27635/56. Class 46 [Also in Group XXVI] A rotary inward-flow drum filter operating under pressure is characterised chiefly in that, between the various stations, resilient elements pressing on the cake are provided, that at the end of the filtering stage a milling tool is arranged parallel to the drum for regulating cake thickness, and that in at least the filtering station measuring devices are provided which are intended to govern the working of the apparatus. A cylinder Z, Fig. 1, rotates continuously or periodically in a casing 30 maintained at a pressure of e.g. 6 atmospheres above atmospheric. The cylinder is imperforate and divided circumferentially by partitions 38, Fig. 3, to provide eighteen spaces in each of which one or more filter blocks K are arranged axially, the blocks communicating by radial collecting pipes 25 at one end of the drum, Figs. 1 and 2, with an end structure S, P, D, Fig. 2. Filtration. Liquid to be filtered passes through a valve 19 into an arcuate region F opposite filter cells numbered 1 to 7 and flows into the interior of the blocks K, collecting in axially-disposed ducts 24 located therein, and flowing therefrom into the pipes 25. Filtration is assisted by an ultrasonic wave-generator U located in a chamber U<SP>1</SP> maintained at the same pressure as the casing interior. Where the solids present are coarse particles the generator U may be dispensed with, the chamber U<SP>1</SP> in that case forming part of the filtration region and containing one or more agitators. Two meters M having shoes 50 for sensing the thickness of the residue 23 serve through relay apparatus to regulate the drum speed. Just above an overflow pipe 20 through which liquid to be filtered flows back to the source, a rotating milling tool 29 levels off the residue 23 to the desired thickness. Elutriation of residue. The washing region W lies opposite cells numbered 8 to 11. Washing liquid is pumped from a container into a constant-level cylinder N having an overflow 35 (or a float member, not shown) and subjected through a pipe 32 to the pressure prevailing in the casing 30; the liquid flows thence along a pipe 34 and through a turbulence-reducing screen 45 to cover the cake completely, being confined between resilient axially-extending pressing-members 31, (see Fig. 2), and a chamber U<SP>11</SP> incorporating a sound wave generator U. Used washing liquid is returned to its container. De-humidicfiation of residue. The de-humidifying region E lies opposite cells numbered 12 to 14. Warm or cold compressed air or other gas is used, flowing inwards; in addition, steam may be used, or a gas which reacts with the residue 23. At the same time mechanical pressure is applied by further resilient pressing- members 31, the effect of the second one in this region being increased by ultrasonic waves from a generator U. The pressure exerted by the members 31 may be regulated pneumatically in the manner shown in Fig. 8; compressed air from the common supply pipe 28 is fed to a cylinder 64 having a pressure gauge 65 and containing a piston secured to a rack 66 meshing with a toothed segment secured to the member 31. Discharge of residue. Compressed air (with, optionally, steam) flowing outwards from cell 15 and a resilient stripper 48 discharge the cake into the trough of a worm conveyer 36, the cake eventually passing out of the filter casing by a discharge device operating on the rotary piston principle. Cleaning of filter blocks. At the cell numbered 17, (region R), compressed air is forced out periodically, while between the outward pulsations cleaning liquid passes inwards; cleaning is assisted by a plurality of ultrasonic wave-generators U arranged longitudinally of the casing 30, by a rotating brush 37 and by a rotating agitator (not shown). The cleaning liquid may be a separate liquid, and may have added to it scouring particles of quartz, corundum, silicon carbide or the like ; or it may be the liquid being filtered, and in this case it gains access to the region R past a resilient partition G which is drawn back from the drum surface for this purpose. Filter elements. Each filter block K, Fig. 3, is composed of porous ceramic or synthetic material or of porous or lamellar metal. In the case of ceramic material the ducts 24 can be produced by inserting fusible or sublimatable cores in the matrix and firing under pressure. The pores are closed on five sides of the block by spraying with an acid and alkali-resistant viscous solution but this sealing material 49 on the smaller sides does not extend as far as the unsealed side. The finished block is cemented to the cylinder Z. The porosity may be relatively coarse, and in this case the outer surface is sprayed with a layer 51 of finer porosity, or the complete drum is covered with wire gauze retained by a spiral wire winding. Driving and controlling. The part S of the end structure comprises a shaft 27 integral with the cylinder Z together with a worm wheel 39 driven e.g. by two out-of-phase pressure cylinders and pistons through a ratchet wheel. The part P is moved with the part S through an angular distance corresponding to one cell width and is then returned rapidly to its starting point, the cycle taking place repeatedly. It is connected by lengths of flexible tubing 42 with the part D, which is fixed, and incorporates an indicating member for each duct 26, e.g. a photo-electric cell or a density meter, and a device 44 for counting the number of resolutions of the drum. Warning signal means (not shown) are also provided. Other features. Where a filter aid is necessary the chamber R is adopted for the application of a slurry under pressure. Where filtering is effected through a thin layer of accumulated residue and cleaning is thereby rendered unnecessary the chamber R is used for normal filtration, the block G being further withdrawn and the brush 37 being used as agitator. The filtering pressure in the first cell 1 may be reduced below that prevailing in the casing 30 by applying a counterpressure to the ducts 24, successively lower counterpressures being also applied to cells 2, 3 and 4 in sequence, Figs. 5 and 6 (not shown). To effect sterilising filtration the whole casing is first filled with e.g. kieselguhr pulp and after its deposition the normal cycle is resumed. Where the liquid to be filtered contains only traces of solid particles the filter cylinder is maintained stationary for from 6 to 12 hours and filtration is conducted through the whole drum surface. There follows a single rapid working stage in which the various chambers are used for their normal functions. Where chemical cleaning of the filter surface is necessary all the filtering and treatment members are rendered inoperative, and acid or caustic soda is introduced into the chamber R to clean all the blocks successively.