|Title of Invention||
"MEMBRANE FILTER HOUSING AND METHOD OF USING THE SAME"
|Abstract||The invention relates to a membrane filter housing, comprising a housing (1) with a feed inlet (2), a permeate outlet (3) and at least two membrane filters (4, 4", 4", 4""), in the housing (1), wherein a fluid to be filtered is fed via the feed inlet (2) to the membrane filters (4, 4", 4", 4""), and a permeate stream is discharged via the permeate outlet (3) and wherein one of the permeate outlet(3) and the feed inlet (2) is located at least at one end (I) of the membrane filter housing (1) and the other one is located at a position (II) substantially in the middle of the membrane filter housing (I).|
|Full Text||Membrane filter housing and method of using the same
The present invention relates to a membrane filter housing of a dead-end filter, comprising a housing with a feed inlet, a permeate outlet and at least two membrane filters provided in the housing, wherein a fluid to be filtered is fed via the feed inlet to the membrane filters, and a permeate stream is discharged via the permeate outlet. The invention also relates to a method using such a membrane filter housing of a dead-end filter.
A membrane filter housing as mentioned above is generally known in practice. In such prior art membrane filter housings a plurality of membrane modules is placed in a housing such that in the direction of flow, they lie substantially in each others extended direction. A housing of this kind is shown in Figure 1. It can be clearly seen that the connections for the inlet of fluid to be filtered and for the outlet of permeate of said known filter housings are located at the ends of the housing.
However, these known housings have several drawbacks. The first is that the membrane flux through the various membrane modules in the housing is not the same. At reference numeral 2 the feed is let into the housing 1 and at reference numeral 3 the permeate is discharged. For filtration, the feed will therefore be conducted through the membrane modules 4, 4', 4", 4'" to the central permeate conduit 5. Consequently, the pressure at the feed side is the highest near I and the lowest near II. Correspondingly, the pressure is the lowest at the permeate side near I and the highest near II. The membrane flux is driven by the local pressure difference over the membrane (transmembrane pressure difference, TMD) and equals the feed pressure minus the permeate counterpressure. Due to pressure losses, this TMD will clearly be greater near I than near II. These pressure differences are caused by the counter-oriented pressure reductions occurring at the feed side and permeate side in the membrane filter modules. Due to the irregular membrane flux, the terminal modules will foul more heavily and will therefore be subjected to a greater mechanical load. The more centrally placed membranes will initially contribute less to the filtration. Moreover, such an irregular membrane flux will lead to the problem that during cleaning not all the membrane modules will be cleaned equally well. This has a negative effect on the entire productivity of the membrane filtering installation.
As a matter of fact, reference is made to Japanese patent applications JP 11128697A, JP 2000 300967A, JP 2001 219038A, JP 11207153A, WO 97/47375A, US-A 4,293,419, GB-A 1 566 675, JP 06 182163A, JP 2001137672A, JP 07 232037A, and an article by Karelin et al, "New solutions for construction of pressure-driven membrane equipment', Desalination, Elsevier Sc. Publ. Co., Amsterdam NL, vol. 108, no. 1/3, 1 February 1997, pp. 315-324, XP000782070 ISSN: 0011-9164, which relate to cross flow-filter systems. Cross-flow filter systems provide for an equalization of pressure in the filter housing, but do not provide for the same pressure difference over all membrane filters in the housing. Therefore, the flow rate is not the same through all membrane filters, as a consequence of which the fouling will be irregular. Since a backwashing will be performed with an irregular pressure difference over the membrane filters, the effect of the backwashing will be irregular as well.
So as to have the cross-flow filtration performed at a chosen flow rate, the pressure difference at some filters will be much higher than at other filters. This also applies to the back washing.
The object of the invention is to provide an improved membrane filter housing that does not exhibit the aforementioned drawbacks. A particular object of the invention is to provide an improved membrane filter housing having a regular membrane flux. The object of the invention is finally to provide a membrane filter housing that simplifies the construction and the continued operation of a filter installation using such membrane filter housings.
In order to realise the above mentioned objectives, the inventions provides a membrane filter housing of the kind mentioned in the preamble and which is characterised in that one of the permeate outlet and the feed inlet is located at least at one end of the membrane filter housing and the other one is located at a position substantially in the middle of the membrane filter housing. The housing according to the invention has a number of advantages. The most important advantage is an even pressure difference of the feed side relative to the permeate side, irrespective of the position in the housing. Another advantage is the spatial separation between the feed conduits and the permeate conduits.
The membrane filter housing according to the invention is applied with "dead end" filtration. If, as may in practice be taken as starting point, all the membrane modules have an equal pressure drop, then all the modules will have a same transmembrane pressure and consequently a same membrane flux. This provides a very even load throughout the entire installation. Also in this case, all the membrane modules will exhibit substantially the same degree of fouling. This means that the membrane modules can be cleaned more reliably. An extra advantage of the invention is that because the pressure difference of the feed side compared with that of the permeate side is the same, the pressure losses no longer contribute to an uneven distribution of the membrane flux over the individual modules. Consequently it is not necessary to minimise the pressure losses of individual modules.
In accordance to a first further preferred embodiment, the housing according to the invention is characterised in that the feed inlet is located at a position in the middle of the membrane filter housing and the permeate outlets are located at the two ends of the membrane filter housing. This is a simple manner of realising the aforementioned embodiments.
Another embodiment entails the provision of feed inlets at both ends of the membrane filter housing, and of a permeate outlet at a position substantially in the middle of the membrane filter housing. According to a further embodiment, it is also an option to provide a concentrate outlet at a position substantially in the middle of the membrane filter housing.
The invention also provides a filter system in which at least one membrane filter housing according to the invention is applied. Preferably a filter system is used of the kind in which several membrane filter housings according to the inventions are used. The respective feed inlets may then be coupled to a common feed conduit such that the flow approaches the respective membrane filter housings successively.
Further preferred embodiments are mentioned in the dependent claims.
Herein below the invention will be further explained with reference to the appended drawings. The figures represent preferred embodiments of the invention without limiting the invention thereto.
Figure 1 shows a membrane filter housing according to the prior art.
Figures 2 to 2D show a membrane filter housing according to a first embodiment.
Figures 3 and 3A show a membrane filter housing according to a second embodiment of the invention.
Figure 4 shows a membrane filter housing according to the invention during cleaning.
Figure 1 shows a membrane filter housing 1 according to the prior art. Provided are feed connections 2 and permeate outlet connections 3. The fluid to be filtered streams through the membrane modules 4, 4', 4", 4"' and is discharged via the permeate conduit 5.
In accordance with the invention, a first embodiment provides a membrane filter housing as shown in Figure 2. The housing 1 comprises a plurality of modules 4, 4', 4" and 4'", and a central permeate conduit 5. The feed is supplied via the feed connection 2 and permeate is discharged via permeate outlet 3. Although the permeate conduit 5 is embodied continuous, it may optionally be omitted at position II. When fluid to be filtered is supplied at the inlet 2, it will penetrate through the membrane modules 4' and 4, and 4" and 4'", respectively, reach the permeate conduit 5 and will subsequently exit the housing via 3. Filtration is effected as a result of the transmembrane pressure difference between the feed side and the permeate side. The pressure difference is the driving force. Because of pressure losses in the membrane modules, the pressure will be higher at the feed side near II than near I. Accordingly, the pressure will be higher in the permeate conduit near II than near I. This results in the pressure difference being substantially constant over the entire membrane filter housing. This provides a very constant membrane flux over the entire membrane filter housing.
Figure 2A shows a filter system wherein two of the membrane filter housings shown in Figure 2 are linked together. Feed is supplied via the central feed conduit 6. The arrow A indicates the direction of flow of the feed through the central feed conduit 6. Initially feed will reach the membrane filter housing 1 and subsequently the membrane filter housing 1'. As the feed rate near position 7 will be greater than near position 8, the diameter of the feed conduit 6 is preferably designed to be larger at position 7. If the membrane filter housings 1 and 1' are identical, the flow rate near position 7 will generally be twice as large as near position 8. Therefore, near position 7 the diameter of the feed conduit 6 will preferably be so much larger than near position 8, that the velocity of the flow of the feed is constant.
Since in general it is construction-technically awkward to provide the central feed conduit 6 with a diameter different to that of the membrane filter housing 1 if the latter is directly connected thereto, as shown in Figure 2A, the connection of the membrane filter housing to the common feed conduit 6 is preferably embodied as shown in Figure 2B. In this way it is simple to adjust the diameter as desired. For example, it is possible to embody the feed conduit near position 9, as shown in Figure 2B, conical (not shown) for a gradual transition from the larger diameter (not shown) near 7' to the smaller diameter (not shown) near 8'.
Of course, the invention is not limited to the filter system combining only two membrane filter housings 1, 1' into one filter system. It is also possible to combine more membrane filter housings to obtain a filter system with many membrane filter housings. Figure 2C shows an embodiment wherein four membrane filter housings are combined into one filter system. However, in such a case it will be particularly preferred to adapt the diameter of the common feed conduit 6 to the amount of feed to be conducted therethrough, as is shown in Figure 2B.
Figure 3 shows another embodiment of the membrane filter housing according to the invention, wherein feed inlet connections 2 are provided at the ends of a membrane filter housing 1, and a permeate outlet 3 in the middle of the filter housing 1. The principle of operation of a membrane filter housing according to Figure 3 is substantially the same as that of Figure 2. But the direction of flow through the membrane modules is reversed.
Figure 4 shows an embodiment in which the filtering apparatus according to Figure 2 is being rinsed. To this end rinse water is supplied near the permeate outlet 3, flows via the permeate conduit 5 through the membrane modules 4 and exits the apparatus via the feed inlet 2. The system as shown in Figure 3 can be cleaned similarly by back-flushing permeate.
To a person skilled in the art it is , moreover, obvious that the direction of filtration can be reversed. In the Figures 1-3 filtration takes place from the inside to the outside. This means that the feed is at the inside of the membrane while the permeate is at the outside. When the filtering apparatus is reversed, feed will be at the outside and the permeate at the inside (see Figure 4).
Rinsing of the installation will then take place in reversed direction.
The invention is not limited to the embodiments shown in the figures. After reading the foregoing description, further modifications will become clear to a person skilled in the art, and these fall under the protective scope of the present invention. For maintenance purposes it is, for example, possible to drain the housing by opening the connections 14 shown in the figures (see for example Figure 2C). The entire apparatus can be emptied very easily, for example, by also opening the remaining connections, or by using locally applied pressure, which may be realised, for example, with the aid of liquid or gas such as compressed air.
1. A dead end membrane filter system comprising: a housing (1) with a feed inlet (2), a permeate
outlet (3) and at least two membrane filter modules (4, 4', 4", 4"') provided in the housing (1),
wherein a fluid to be filtered is fed via the feed inlet (2) to the membrane filter modules (4,4', 4",
4"'), and a permeate stream is discharged via the permeate outlet (3), characterized in that:
(a) the feed inlet (2) is located at a positioning in the middle of the membrane filter housing (1) and the permeate outlet (3) consists of outlets located at the two ends of the membrane filter housing (1), or
(b) the feed inlet (2) consists of inlets provided at both ends of the membrane filter housing (1) and the permeate outlet (3) is located at a position substantially in the middle of the membrane filter housing (1).
2. A filter system as claimed in claim 1, wherein said system comprises at least one dead end membrane filter.
3. A filter system as claimed in claim 2, wherein each of the said dead end membrane filters being coupled with the respective feed inlet to a common feed conduit, such that the flow approaches the respective membrane filters successively.
4. A filter system as claimed in claim 3, wherein the diameter of the said common conduit decreases
in the direction of flow.
5. A filter system as claimed in claim 4, wherein the diameter decreases such that the velocity of the
flow of the liquid to be filtered is substantially constant in the entire common feed conduit.
6. A method of filtering a liquid by means of dead-end filtration wherein the same uses a dead-end membrane filter system as claimed in claim 1, or a filter system as claimed in any one of the preceding claims 2 to 5.
|Indian Patent Application Number||1661/DELNP/2004|
|PG Journal Number||45/2011|
|Date of Filing||14-Jun-2004|
|Name of Patentee||NORIT MEMBRAAN TECHNOLOGIE B.V.|
|Applicant Address||MARSSTEDEN 50, 7547 TC ENSCHEDE, THE NETHERLANDS.|
|PCT International Classification Number||B01D 65/00|
|PCT International Application Number||PCT/NL02/00830|
|PCT International Filing date||2002-12-13|