Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Patent
1997-08-08
2000-12-12
Fortuna, Ana
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
21033301, 210798, B01D 6100
Patent
active
061593737
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to concentration of solids in a suspension using a hollow fibre membrane and, in particular forms, to methods and apparatus for periodically cleaning by backwashing the hollow fibre membranes.
BACKGROUND ART
Prior art methods of concentrating solids in a liquid suspension are described in Australian patent specifications 576,424 and 582,968. The text and drawings of these specifications are incorporated herein by cross-reference. In that prior art, concentration is effected by a filter element that comprises a bundle of hollow, porous, polymeric fibres in a closed cartridge or shell. Polyurethane potting compound is used to hold the respective ends of the fibres in place within the cartridge without blocking the fibre lumens and to close off each end of the cartridge.
The transmembrane pressure differential necessary to effect concentration of the solids in the prior art is achieved by pressurising the feedstock which necessitates the use of pumps, other ancillary equipment and, of course, a closed filter cartridge.
Backwashing of such prior art concentrators involves increasing the pressure on both sides of the hollow fibres within the closed shell to a relatively high value before suddenly releasing that pressure on the shell side of the fibre walls to effect a sudden pressure differential across the walls which causes a backwash action.
DISCLOSURE OF INVENTION
It is an object of this invention to provide an improved method of using a reverse-flow mode to dislodge solids retained by filter elements to ensure rapid removal of those retained solids and in which the separation and dislodgement modes may be repeated for prolonged periods of time.
The present invention, in at least some embodiments, provides a method of backwashing a hollow fibre filter which retains some of the features of the prior art, but optimizes a number of these features to provide improved performance.
Accordingly, in one broad form of the invention, there is provided a method of backwashing a plurality of hollow fibres having microporous walls which have been subjected to a filtration operation wherein feed containing contaminant matter is applied to the exterior surface of said hollow fibres and filtrate withdrawn from the ends of the lumens of the fibres, the fibres being contained within a shell or housing, said method comprising: exterior surface of said fibres, said lumens, same time as, or just after opening the shell to atmosphere, to cause explosive decompression through the walls of the fibres whereby said fluid under pressure passes through said walls; for a sufficient time following said decompression to cause substantial portions of contaminant matter lodged within and/or on said fibre walls to be dislodged; of liquid over the external surface of said fibre walls; and feed to said exterior surface of said fibres.
For preference, during the backwash phase, the time lapse between the start of an increase in negative transmembrane pressure (TMP) and such TMP reaching a maximum value corresponding to the explosive decompression, is in the range of about 0.05 seconds to about 5 seconds.
Preferably, the fibres are rewetted prior to recommencing the filtration operation.
Preferably, feed liquid is pumped into the shell side of the filter while fluid pressure is still being applied to said lumens. This results in liquid/fluid turbulence or fronting around the membrane pores causing further improved dislodgement of retained solids. The fluid pressure during this phase preferably should exceed the shell side pressure by about 10 kPa to about 800 kPa.
Preferably, the steps of the method are carried out as a continuous process utilizing repetitive cycles of solids retention and backwash.
As an alternative preferred form, step (b) is effected by allowing said remaining filtrate to drain out of said lumens of its own volition.
According to a further broad aspect, the present invention provides a concentrator for recovering fine solids from a liquid feed suspension and having an oper
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International Publication No. WO 93/02779; Publication Date: Feb. 18, 1993.
Communication Pursuant to Article 96(2) and Rule 51(2) EPC.
Beck Thomas William
Drummond Humphrey John Jardine
Johnson Warren Thomas
Kopp Clint Virgil
Lee Matthew Brian
Fortuna Ana
USF Filtration & Separations Group Inc.
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