GB2154153A - Liquid treatment apparatus - Google Patents

Abstract

Liquid treatment apparatus, for example for ultrafiltration or reverse osmosis, consists of at least one permeable walled tube 12 through which a liquid to be filtered or concentrated is passed, and in operation a fouling layer may be deposited on the tube wall, which is periodically removed by a rigid cleaning element 98 being pushed through the tube. As shown, liquid to be filtered flows from inlet 94 to outlet 23, with concentrated liquid discharged through the lower end of the tube 12 to outlet 56. Periodically this flow is suspended and liquid is delivered to inlet 94 to force element 98 up the tube, with a clearance of 0.05 to 1.0mm. <IMAGE>

Description

SPECIFICATION Liquid treatment apparatus This invention relates to liquid treatment apparatus comprising one or more ducts through which the liquid is passed, each duct having a wall permeable to at least a component of the liquid, and particularly but not exclusively to ultrafiltration apparatus.

A known ultrafiltration apparatus, described in British Patent No: 1468928 (Union Carbide Corp), comprises a plurality of parallel tubes arranged so that a liquid to be concentrated passed under pressure axially through the tubes. The tubes are porous and permeable, being composed of bonded carbon particles and an essentially continuous coating of metal oxide particles on the inside surface of the tubes. In operation of the apparatus some of the liquid and low molecular weight dissolved phases pass through the walls of the tubes, while most of the higher molecular weight dissolved phases, and any particulate matter, are carried through the tubes in the liquid concentrate.

Some of the higher molecular weight dissolved phases and the particulate matter may however form a deposited layer on the inside surfaces of the tubes, which may lead to a reduction in the flow rate of the liquid through the walls of the tubes and an increase in the pressure drop between the ends of the tubes.

This same problem has been found to occur in reverse osmosis apparatus, and M. Kikuchi et al.

(Hitachi) have proposed, in Nuclear Engineering and Design 44 (1977) pages 413-420, that the deposited layer should be periodically removed by passing a slightly-oversized sponge ball through the reverse osmosis tubes. They state that sponge balls have been found effective in removing the deposited layer, and have not been found to damage the surface of the membrane layer on the inner surface of the tubes. However, the sponge balls are porous and so tend to absorb some of the deposited material into their pores, and so for some applications, such as treatment of radioactive wastes, foam balls may not be acceptable. Furthermore, some deposited layers, such as those produced in the ultrafiltration of sludges with high solids content (e.g. 50- by weight), may be too dense to be satisfactorily removed by the deformable sponge balls.

The present invention therefore provides a liquid treatment apparatus including a duct along which liquid passes in operation of the apparatus, the duct having a wall permeable to at least a component of the liquid, an inlet port at one end of the duct for inflow of the liquid, and an outlet port at the other end of the duct for outflow of the portion of the liquid which does not pass through the wall of the duct; and impermeable cleaning element adapted to be passed along the duct in close proximity to the surface of the wall, the cleaning element being sufficiently rigid not to deform during passage along the duct; and at one end of the duct an end fitting to accommodate the cleaning element, the end fitting having a supply port arranged such that supply of a liquid to the supply port causes passage of the cleaning element along the duct.

Preferably, the cleaning element is adapted to pass in close proximity to the entire surface of the permeable wall of the duct, and desirably the cleaning element is of the same cross-sectional shape as the duct. The size of the cleaning element is desirably such as to provide a clearance on all sides between the cleaning element and the wall of the duct of width between about 0.05 and 1.0mum, preferably of width between about 0.15mm and 0.6mm.

Desirably the liquid treatment apparatus comprises a plurality of the ducts, arranged so the flows of liquid therethrough are in parallel, each duct having an end fitting, and the supply ports of all the end fittings are arranged to be in liquid communication with a common supply of liquid so that all the cleaning elements pass along the respective ducts simultaneously.

The invention will now be further described by way of example only and with reference to the accompanying drawing, in which: Figure 1 shows a medial sectional view through an ultrafiltration apparatus.

Referring to Figure 1, an ultrafiltration apparatus 10 comprises a permeable porous carbon ultrafiltration tube 12 with a bore 14, the surface 16 of the bore 14 being coated with an adherent porous coating of metal oxide particles, and the tube 12 extending vertically between a lower end fitting 20 and an identical upper end fitting 22. The tube 12 is surrounded by a cylindrical jacket 18 sealed to the end fittings 20 and 22 by gaskets 19, there being a port 23 through the wall of the jacket 18.

The tube 12 and the jacket 18 are clamped to the end fittings 20 and 22 by three rods 24 (only one of which is shown) extending parallel to the tube 12 and passing through holes (not shown) in the end fittings 20 and 22, both ends of each rod 24 bieng threaded and engaging respective washers 26 and wing nuts 28.

Each end fitting 20 and 22 comprises a tubular member 30 defining an axial bore 32 of the same diameter as the bore 14. At one end 34 of the member 30 is an external flange 36, and a wider bore 38 which accommodates an end portion 40 of the tube 12, a circumferential groove 41 around the bore 38 locating an O-ring seal 42. The tube 12 is thus sealed to the member 30 with the bore 32 aligned with the bore 14. At the other end 43 of the member 30 is a narrower axial bore 44, defined by a threaded insert 45.

The tubular member 30 locates centrally within a bowl-shaped inner member 46 with a circular base 48 and a rim 50, the member 30 passing through a central hole 52 in the base 48 so that the flange 36 abuts the base 48, and being sealed to the base 48 by an O-ring seal 54 located in a groove 5 within the hole 52. A threaded hole 56 through the rim 50 enables a threaded pipe connector (not shown) to be connected to the inner member 46. The rim 50 abuts one side 58 of an annular plate member 60 with a central hole 62 through which the tubular member 30 extends, and the other side 64 of the plate member 60 abuts a rim 66 of a bowl-shaped outer member 70 with a circular base 72.The plate member 60 is sealed to the inner member 46 the outer member 70 and the tubular member 30 by O- ring seals 74, 75 and 76, locating in circular grooves 78 and 79 on the sides 58 and 64, and in a circumferential groove 80 within the central hole 62, respectively. The inner member 46, the plate member 60 and the outer member 70 are clamped together by three threaded rods 82 (only one of which is shown for each end fitting 20, 22) extending through holes 83 equally spaced around the end fitting 20 or 22, and engaging with a washer 84 and a wing nut 85 at each end of each rod 82.

The plate member 60 and the inner member 46 thus define an annular chamber 88 around the tubular member 30. Four equally spaced stepped holes 90 (only three of which are shown) through the tubular member 30 provide communication between the bore 32 and the chamber 88. Similarly the plate member 60 and the outer member 70 define a generally cylindrical chamber 92 into which the tubular member 30 extends, the narrower bore 44 providing communication between the bore 32 and the chamber 92. A threaded hole 94 through the centre of the base 72 enables a threaded pipe connector (not shown) to be connected to the outer member 70.

Within the bore 32 of the tubular member 30 of the lower end fitting 20 is 3 rigid impermeable stainless steel cylinder 98 of diameter slightly less than the bore 32. In the apparatus 10 the bore 32 is of diameter 6.0 mm, and the cylinder 98 of diameter 5.7 mm and of length 15.7 mm.

To operate the apparatus 10, a supply of liquid to be treated, for example water contaminated by suspended particulate matter and dissolved material, is connected via a one-way valve 102 and a pump 100 to the hole 94 in the upper end fitting 22 (labelled as "IN A"), and an outlet for treated liquid is connected via a control valve 104 to the hole 56 in the lower end fitting 20 ("OUT A"). A supply of liquid, which might be the same as the liquid to be treated or might be clean water, is connected via a one way valve 106 and a pump 110 to the hole 94 in the lower end fitting 20 (labelled "IN B"), and an outlet is connected via a control valve 108 to the hole 56 in the upper end fitting 22 ("OUT B").

Then, with the control valve 108 closed and the pump 110 off, the pump 100 is used to pump the liquid to be treated downwardly through the tube 12. Filtered liquid passes through the wall of the tube 12 into the jacket 18, to emerge from the port 23, while the remainder of the liquid emerges through the hole 56 from the lower end fitting 20.

During operation of the apparatus 10 a layer of particulate and higher molecular weight dissolved material may be deposited on the surface 16.

When it is desired to remove this layer, the pump 100 is turned off, the control valve 104 closed, the control valve 108 opened and the pump 110 turned on. Liquid is thus forced to flow upwardly through the tube 12, the cylinder 98 being pushed up the tube 12 by the flow of the liquid and pushing with it the bulk of the deposited layer.

The dislodged material will thus emerge from the hole 56 of the upper end fitting 22, while the cylinder 98 remains within the apparatus 10.

This cleaning process is completed as soon as the cylinder 98 reaches the upper end fitting 22.

The pump 110 is then turned off again, the control valve 108 re-closed, the control valve 104 reopened and the pump 100 turned on again. The cylinder 98 will fall back down the tube 12, being urged down by the flow of the liquid, and return to the position as shown in the Figure, within the bore 32 in the lower end fitting 20. The cylinder 98 is of greater diameter than the narrower bore 44, so it cannot emerge from the end 43 of the tubular member 30.

The ultrafiltration apparatus 10 has been used experimentally to ultrafilter an aqueous 0.1% (by weight) titanium (IV) hydroxide suspension. Operation was carried out as described above until a deposit of titanium hydroxide had built up to about 8 mglcmz over the surface 16. At this stage the rate of flow of water through the walls of the tube 12 had decreased by 10% of its initial value. The cleaning process was then performed as described above, and over 80% of the deposit was removed.

The cycle of operation and cleaning was repeated several times, each time the deposited layer being reduced to the same thickness and the rate of flow of water through the walls of the tube 12 returning to the same value.

The length of the cylinder 98 is not critical to the cleaning process, but it is preferable that the cylinder 98 have blunt corners to avoid scraping the surface 16 of the tube 12. Furthermore a cleaning element of a different shape, such as spherical, may be used in place of the cylinder 98. It will be appreciated that the invention may be used to clean ultrafiltration apparatus with non-circular tubes, the cylinder 98 being replaced with a solid cleaning element of substantially the same crosssectional shape as the bore of the respective tube, and of such a size as to provide a clearance on all sides between the cleaning element and the tube of width between 0.05 and 1.0mum. In each case the preferred width of the clearance is about 0.15mm and 0.6mm on each side of the cleaning element, depending on the permeability of the deposited layer. For example, an ultrafiltration apparatus (not shown) similar to the apparatus 10 but using a spherical cleaning element in place of the cylinder 98 has been used experimentally to ultrafilter an aqueous 20% (by weight) ferric hydroxide sludge.

In this case the deposited layer is more permeable than that produced in the ultrafiltration of titanium (IV) hydroxide, and the preferred diameter of the cleaning element is 5.0mm, providing a clearance of 0.5mm on every side. Regular use of the clean ing element enabled a membrane flux greater than 1m3/m2 day to be maintained for several days, while without the use of the cleaning element, the tube 12 became blocked after a few hours' operation.

It will be understood that although the apparatus 10 has been described as having the tube 12 aligned vertically, the apparatus 10 may be operated in a different orientation, for example with the tube 12 aligned horizontally. It will also be understood that although the apparatus 10 is shown with only one ultrafiltration tube 12, an ultrafiltration apparatus (not shown) might comprise a plurality of tubes 12, aligned parallel to each other, each extending between respective tubular members 30, and each tube 12 having a respective cylinder 98, or other cleaning element, located in the tubular member 30 at one end of the tube 12.At each end of the apparatus, a plurality of the tubular member 30 may be located within an end fitting member (not shown) defining a first chamber communicating through the stepped holes 90 with the bores 32, and a second chamber communicating through the narrower bores 44 with the bores 32, so that the cleaning process is performed simultaneously in the corresponding tubes 12.

Although the cylinder 98 has been described as being of stainless steel it will be appreciated that it may be of any material which neither dissolves in nor reacts with the liquid undergoing treatment, and which is sufficiently rigid not to deform significantly during the cleaning process. For example in some situations a hollow cylinder 98 of carbon fibre reinforced plastics with at least one end closed may be used. If desired, the cleaning element may have a density substantially equal to that of the liquid so as to have neutral buoyancy.

In the apparatus 10 the supply of liquid to be treated, connected to the pump 100 (and to IN A) is shown as separate from the supply of liquid connected to the pump 110 (and in to IN B), but it will be appreciated that if the liquids are the same, there may be a common supply and a common pump, with a three-port valve (not shown) connecting the pump either to IN A or to IN B. Furthermore in the apparatus 10, when the pump 110 is on, the liquid emerges through the hole 56 from the annular chamber 88 of the upper end fitting 22 (OUT B), but in a modified version (not shown) no annular chamber 88 or hole 56 is provided in the upper end fitting 22 and a three-port valve (not shown) is used in place of the one-way valve 102, so that the liquid is used in place of the one-way valve 102, so that the liquid instead passes through the hole 94 of the upper end fitting 22 (out of IN A), to emerge from the third port of the valve.

Claims (6)

1. A liquid treatment apparatus including a duct along which liquid passes in operation of the apparatus, the duct havng a wall permeable to at least a component of the liquid, and an outlet port at the other end of the duct for outflow of the portion of the liquid which does not pass through the wall of the duct; and impermeable cleaning element adapted to be passed along the duct in close proximity to the surface of the wall, the cleaning element being sufficiently rigid not to deform during passage along the duct; and at one end of the duct an end fitting having a supply port arranged such that supply of a liquid to the supply port causes passage of the cleaning element along the duct.

2. A liquid treatment apparatus as claimed in Claim 1 wherein the cleaning element is of the same cross-sectional shape as the duct, and is of such a size as to provide a clearance on all sides between the cleaning element and the wall of the duct of width between about 0.05 and 1.0mm.

3. A liquid treatment apparatus as claimed in Claim 2 wherein the cleaning element is of such a size as to provide a clearance of width between about 0.15mm and 0.6mm.

4. A liquid treatment apparatus as claimed in any one of the preceding Claims also including an end fitting at the other end of the duct defining an outlet port for the contents of the duct during passage of the cleaning element along the duct.

5. A liquid treatment apparatus as claimed in any one of the preceding Claims and including a plurality of said ducts arranged so that the liquid flows therethrough are in parallel, and each duct having a said end fitting to accommodate a said cleaning element, wherein the supply ports of all the end fittings are arranged to be in liquid communication with a common supply of liquid so that the supply of liquid occurs to all the supply ports simultaneously.

6. A liquid treatment apparatus substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.