Liquid purification or separation – Filter – Material
Patent
1994-04-15
1995-10-03
Dawson, Robert A.
Liquid purification or separation
Filter
Material
21050026, 210504, 210506, 55523, B01D 2400
Patent
active
054549477
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a ceramic filter element for tangential flow filtration of liquids and gases where the filter element has an elongated support body of a porous ceramic material, at least two-coaxial channels running through the support body with at least one ceramic membrane on the surface of the channels.
Ceramic membrane filters have proven their worth especially in hydroeconomy and in the beverage industry for the filtration of beer, wine and fruit juices in which tangential flow (cross-flow) filtration enjoys preference in continuous processes. With this application, called "dynamic filtration," suspensions can be filtered without clogging the membrane. The liquid to be filtered is not forced directly through the membrane but made to flow past the surface of the membrane with an appropriately high velocity of flow ranging from 2 to 7 meters per second, while only a part of the liquid stream passes through the membrane as filtrate (permeate). The dogging of the membrane, i.e., the formation of a filter cake on the membrane, is prevented by the fact that, due to its high velocity of flow and the microturbulences occurring at the membrane surface, the suspension constantly flushes away the particles held on the membrane surface.
Ceramic filters for tangential flow filtration, such as those known, for example, from DE-A-35 19 620, have combined layers of different porosity and defined pore size. The thin top membrane layer performs the separating function, and the coarse ceramic layer beneath it serves as a supporting layer. Filter elements are said therein to be especially effective which in general have an elongated, cylindrical form of the supporting layer structure, referred to hereinafter as the "support body", with a plurality of bores extending through the support body and with a very thin ceramic membrane applied to its surface as the separating means.
Filter elements with a plurality of coaxial cylindrical channels through which only unfiltrate flows have proven their worth in the beverage industry. The filtrate penetrating through the membrane surface of the channels flows through the support body under pressure and exits at its circumferential surface. The disadvantage of these known multichannel filter elements lies in the low rate of flow of the filtrate through them. Particularly the inner channels contribute little to the performance of the filter, although they have a comparatively large portion of the membrane surface. Experiments have shown that the support body itself has a non-negligible resistance. A test of this kind is given as an example further below.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a cross section through a ceramic filter element of a preferred embodiment of the invention;
FIGS. 2, 3 and 4 each illustrate cross sections of alternate embodiments of the invention; and
FIG. 5 is a bar graph comparing the rates of flow through a commercial multi-channel filter element with 19 channels and 12 channels.
THE INVENTION
An object of the present invention is to provide an improved ceramic filter element for the tangential-flow filtration of liquids and gases which has a support body offering reduced resistance to permeation so as to obtain a higher rate of permeation the filtrate at the same difference in pressure between the unfiltrate and the exiting filtrate.
The above stated object is obtained in accordance with the invention in that channels are arranged coaxially about an imaginary central axis of the support body, while, as seen in cross section, the contour of the outwardly facing channel wall is adapted to the external contour of the support body, so that the support body here has a uniform thickness, a wall thickness corresponding to the mechanical stress, and the contour of the other walls of the channel is configured such that the webs remaining between the channels flare outwardly wedge-like, the width of these webs increasing to a maximum of 3 times the thinnest wall thickness.
The solution according to the invention i
REFERENCES:
patent: 4233351 (1980-11-01), Okumura et al.
patent: 4383974 (1983-05-01), Fratzer et al.
patent: 4694749 (1987-02-01), Miura
patent: 4894160 (1990-01-01), Abe et al.
patent: 4902319 (1990-02-01), Kato et al.
patent: 5104546 (1992-04-01), Filson et al.
"Microporous Alumina Membranes", Hsie et al., Journal of Membrane Science, 39 (1988) 221-241.
Kielwein Manfred
Michell Winfried
Olapinski Hans
Simmich Hans-Erich
Ziegelbauer Helmut
Cerasiv GmbH Innovatives Keramik-Engineering
Dawson Robert A.
Fortuna Ana M.
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