Membrane filtration assembly

Details Membrane filtration assembly Membrane filtration assembly

1996-09-03

1999-05-25

Fortuna, Ana

Liquid purification or separation

Casing divided by membrane into sections having inlet

Each section having inlet

2103232, 21032178, 21032179, 2103219, B01D 6300

Patent

active

059067390

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a membrane filtration assembly where the fluid to be filtered is recirculated on the retentate side of a membrane filter, and where the filtered fluid, i.e. the permeate, is recirculated on the permeate side of the membrane filter in such a manner that the two streams are passed cocurrently along the membrane filter, which membrane filter comprises several membrane units in form of tubular supporting structures, each supporting structure comprising one or more filter membranes, and where said membrane units are mounted in parallel in a common housing in such a manner that one stream flows inside the membrane units while the other stream flows in a space surrounding the membrane units.


BACKGROUND ART

U.S. Pat. No. 4,105,547 discloses a membrane filtration involving a recirculation of the fluid to be filtered on the retentate side of the filter membrane and a recirculation of the filtered fluid, i.e. the permeate, on the permeate side of the filter membrane. The two streams flow in the same direction, i.e. cocurrently, along the respective sides of the filter membrane so as thereby to ensure a uniform drop of pressure across the entire membrane. The object of such an assembly is to optimize the filtration capacity of the membrane. In practice the suitable equilibrium is obtained by adjusting the pressure on the permeate side. In order to obtain a sufficiently high pressure of the recirculated permeate a high pumping capacity is, however, necessary, especially in case of a high amount of permeate. Such a high requirement to the pumping capacity resulted, however, in operation costs which were considered unacceptable.
EP-PS No. 333,753 describes an improved membrane filtration assembly of the above type, where several membrane units in form of tubular membrane filters with surrounding tubular supporting structures are arranged in parallel in a common collecting space. In order to ensure a suitable, uniform drop of pressure along the permeate side, the collecting space of the membrane is filled with filler bodies. As a result a considerable, mechanical impediment to the flow of the circulating permeate is obtained. In order to retain the filler bodies in the collecting space and in order to distribute the stream of the circulating permeate, means are provided in the known assembly, at least at the inlet side, said means being provided in form of a disk with holes abutting an outer housing defining the collecting space. The disk with holes retains the filler bodies in the collecting space and distributes the stream of circulating permeate thereacross.
The use of filler bodies ensures an adjusted flow resistance to the permeate stream. The system involves, however, also some problems. The replacement of merely a single membrane unit necessitates a removal of all the filler bodies from the entire permeate collecting space. Thus the replacement of a unit is very difficult and time-consuming. In addition, the filler bodies render it difficult to clean the permeate space by way of circulation of cleaning fluid.
It turned out surprisingly that a membrane filtration assembly of the type mentioned in the introduction can be constructed in such a manner that the cleaning is facilitated and the replacement of membrane units is very easy because the use of filler bodies has been completely avoided.
The object of the present invention is to provide an alternative membrane filtration assembly where the above drawbacks of the assembly described in the EP-PS No. 333.753 are avoided while the desired uniform drop of pressure across the entire membrane surface is maintained in a very economical manner.


BRIEF DESCRIPTION OF THE INVENTION

The above object is obtained by means of a membrane filtration assembly, which according to the invention is characterised in that each membrane unit is provided with a separate space in form of a narrow passageway, which on the inner side is defined by the membrane unit and on the outer side by a channel tube of an inner cross section which

REFERENCES:
patent: 4105547 (1978-08-01), Sandblom
patent: 4522717 (1985-06-01), Brust
patent: 4526688 (1985-07-01), Schmidt, Jr. et al.
patent: 4704205 (1987-11-01), Ishii
patent: 4929259 (1990-05-01), Caskey et al.
patent: 5525144 (1996-06-01), Golland
patent: 5585009 (1996-12-01), Fusikata

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