GB1269556A - Filter apparatus - Google Patents

Abstract

1,269,556. Liquid filter. B. D. BOHNA & CO. Inc. 8 April, 1969 [15 April, 1968], No. 17970/69. Heading B1D The useful surface area of a sand bed filter is extended by an array of flat distributing elements in the form of cloth bags 22 filled with coarse material 24 and extending vertically from the fine filtering medium 14 into the body of unfiltered liquid 30 above, so that filter cake 38 forms on the top of medium 14 and along the surfaces of the bags. The liquid is delivered to the body 30 by side nozzles (32) and is cleaned in passing a short distance into medium 14, and then percolates down into a coarse supporting layer (16) (Fig. 2, not shown). Alternatively, bags (54), similar to bags 22 but completely buried in sand 14 and extending down into layer (16), arranged between pairs of bags 22 receive the filtrate and conduct it easily to layer 16 (Fig. 6, not shown). The bags are suspended from horizontal cables (25) by ties 27. The bed is cleaned by backwashing from below or by jets of water from pipes (46, 50) extending between the bags and moving along the bed (Figs. 4, 5, not shown) to agitate the sand, the water and solids overflowing into discharge channels (48). Medium 14 may be sand, anthracite, lead or glass powder, the cloth 22 may be polypropylene, polyethylene, metal, natural fibre, P.T.F.E. or polyester and is woven of monofilament strands. Filtration may be under gravity, pressure or vacuum. The enclosing tank may be concrete or metal. The apparatus is used to filter water or to remove solids from a solution of phosphate rock in nitric acid. Fig. 7 illustrates flat hollow filter elements comprising fine sand enclosed between double walls of cloth, supported internally by coarse material and immersed in unfiltered liquid. The lower flaps of the cloth bags are clamped to a support plate by bars 74, and backwash liquid is delivered through valve 82 into the filtrate manifold 78. The claims cover only the Fig. 7 construction.