Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Patent
1986-10-27
1990-06-05
Spear, Frank
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
210798, B01D 1300
Patent
active
049311867
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the concentration of fine solids in a liquid feed suspension.
The problem of concentration of fine solids in a suspension is complementary to the problem of recovering clear liquid from that suspension.
BACKGROUND ART
The producers of clear liquids usually regard all visible traces of solids as wastes. The methods used often involve the addition of flocculants and filter aids which contaminate the solids. The solids content tends to be low, encouraging the use of methods which remove clear liquid from a continuously fed feed suspension tank in which the solids content increases until some deleterious effect arises, necessitating the dumping of the contents of the feed suspension tank into some other device. Invariably the accumulating solids have been steadily slowing production and productivity could benefit from some device which continuously rejected concentrated solids.
In contrast thereto, the producers of finely divided solids are usually food, mining or manufacturing industries for which the solids are desired and the liquid is best recycled. Also, the solids have specifications for size and purity, often need further processing and mostly need to be obtained at high solids content as concentrates. Filter aids will, of course, contaminate the product.
A detailed recent discussion of such needs in cross flow microfiltration is given by R. Bertera, H. Steven and M. Metcalfe, The Chemical Engineer, pp. 10-14, June, 1984.
As shown in FIG. 8 of the above publication even the latest 1984 commercial Enka Membrana A.G. filter module rapidly fouled and the clarified liquid flux continued to decline when backwashed with transmembrane clarified liquid in the constant concentration cross flow (diafiltration) mode on a fine inorganic filler.
Economically, the ability to cope with strongly fouling solids without filter aids is most pressing. This fouling problem has long been recognised and the art records some attempts to substitute gas for clarified liquid during backwashing to avoid the recycle of clarified liquid to the feed suspension. Thus Japanese unexamined Patent Kokai Publication No. 53(1978)-108882 states: reverse cleaning, the serious defect of the prior art method, that is, returning the filtrate substantially to the crude liquid is eliminated, with obvious industrial merits."
Transmembrane gas backwashing is impossible in very finely pored filters such as reverse osmosis membranes and ultrafilters because the pressures needed to overcome surface tension are far beyond the strengths of normal hollow fibre membranes used for these purposes; wetting liquids may pass but not gases. Any gas bubbles passing through such a membrane indicate the presence of pin hole defects in the membrane. Hence this invention has no application to reverse osmosis or to true ultrafilters.
This invention is concerned with microfilters which contain larger pores than those of ultrafilters and which range from 0.01 to 10 microns. Usually, the larger of the pores are so distributed that clarified liquids are free of all visible turbidity. Turbidity involves more than particle size, obeying and arising from well known optical laws.
Early microfilters fouled quickly since they treated particles which were not suspended by Brownian motion nor diffusion but which penetrated into the pores of a similar size range as the particles in the manner of sieve blinding.
One prior art approach to solving this problem was to operate hydrophilic microfilters in a cross flow mode with clarified liquid transmembrane backwash. High cross-flow velocities required feed suspension to be to the smaller internal filtering surface of the lumen as opposed to the larger external surface of the fibre. Thus, backwash pressures had to be limited to avoid fibre crushing. The smaller filtering surface reduced output and thus this approach was frequently not a useful solution to the fouling problem.
Another prior art approach is disclosed in Japanese Patent Kokai Publication No. 53(1978)-108882 where a holl
REFERENCES:
patent: 3838776 (1974-10-01), Brun
patent: 3912624 (1975-10-01), Jennings
patent: 3992301 (1976-11-01), Shippey et al.
patent: 4125462 (1978-11-01), Latty
patent: 4214020 (1980-07-01), Ward et al.
patent: 4220535 (1980-09-01), Leonard
patent: 4414113 (1983-11-01), Laterra
patent: 4545940 (1985-10-01), Mutoh
patent: 4767539 (1988-08-01), Ford
"Membrane Filtration" by Brock, 1983, published by Science Tech., Inc.
Anderson Eric W.
Ford Douglas L.
Kopp Clinton V.
Memtec Limited
Spear Frank
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