GB992138A - Improvements in or relating to filters - Google Patents

Abstract

992,138. Rotary filters. UCB (UNION CHIMIQUE - CHEMISCHE BEDRIJVEN) S.A., and PRODUITS CHIMIQUES PECHINEY-SAINT-GOBAIN S.A. July 20, 1962 [July 24, 1961], No. 28026/62. Heading B1D. A flat filter rotatable about a vertical axis comprises an annular screen and an endless peripheral flexible rim upstanding therefrom, the screen being provided, after removal of filter cake, with a subsequent clearing and cleaning zone, defined by a sector between two radial barriers and the edge of the sector, the portion of the endless rim opposite the sector being held away from the screen periphery, and the clearing and cleaning zone being provided with a filter-washing device located above the screen, and means for admitting compressed air below the screen. The endless rim may be made of e.g. natural or synthetic rubber. The invention provides a method of clearing and cleaning a filter cloth of a horizontal rotating table filter wherein a portion of the filter cloth or other filter medium is brought within a clearing and cleaning zone on the table as defined above and subjected therein to the action of compressed air and a washing liquid. The table is divided into sectors, each forming a box with bottom, side walls and a perforated top. In the course of one revolution, each sector is successively filled with liquid to be filtered e.g. under vacuum, and then passes to washing zones where the cake is washed, then beneath scraper blades or worms for removal of solids, and then to a clearing zone wherein the washing liquid and compressed air remove remaining particles of solids before recommencement of the cycle. In one embodiment, Fig. 1, flexible rim 3 engages in fluid-tight manner with edge 2 of rotating table I provided with apertures 5, covered by cloth 4. The flexible rim 3 projects upwardly to a height at least equal to the depth of liquid to be filtered. Between points 6 and 6<SP>1</SP>, the rim 3 is held away from edge 2 by rollers 7, 7<SP>1</SP>, 8 and 8<SP>1</SP>, so that zone B, for clearing and cleaning the cloth, is defined by external edge 2, internal rim 13, and radial barriers 9 and 9<SP>1</SP>. Each barrier is composed of one or more flexible scraper blades 10, Fig. 3, mounted on adjustable support 11 connected to the fixed superstructure of the filter. Zone B is provided with washing liquid device 12 fed through connection 14, and is also subjected to the action of compressed air passing through the cloth from bottom to top, end fed by a distributer underneath the table. Zone B may be located after the filter cake removal device and before the liquid feed device. Thus since the table 1 has no outer rim in the cleaning zone, efficient cleaning of the cloth is facilitated, since washing liquor containing suspended particles can overflow the edge of the table. The area of the clearing and cleaning zone may vary according to the nature of the material to be filtered. The filter is used for processing the slurry obtained when decomposing phosphate rock with sulphuric acid.