WO1999046024A1

WO1999046024A1 - Granular-bed filter unit for filter bank composed of same

Info

Publication number: WO1999046024A1
Application number: PCT/IL1999/000132
Authority: WO
Inventors: Ytzhak Barzuza
Original assignee: Filtration Ltd.
Priority date: 1998-03-12
Filing date: 1999-03-08
Publication date: 1999-09-16
Also published as: IL123660A0; AU3271499A

Abstract

The invention provides a granular-bed, modular filter unit, including at least one chamber defined and delimited by a housing (2) surrounding said chamber and two end walls (4, 4'), and divided by an imaginary, axial, substantially horizontal plane into a lower part and an upper part; at least one strainer tube (14) passing at least indirectly through the lower part of said chamber from one of said end walls to the other one of said end walls; at least one strainer tube passing at least indirectly through the upper part of said chamber from one of said end walls to the other one of said end walls, and filtering granules substantially embedding at least one lower-part strainer tube; wherein all of said strainer tubes are accessible from the outside of said end walls, and wherein said filter unit is connectable to other, similar units serially and/or in parallel, to form filter banks. The invention also provides a method for back-flushing a granular-bed filter.

Description

GRANULAR-BED FILTER UNIT FOR FILTER BANK COMPOSED OF SAME

Field of the Invention

The present invention relates to a back-flushable, granular-bed, modular filter unit. It further relates to a back-flushable, granular filter bank composed of such units. The invention further provides a method for back- flushing granular-bed filter units. Background of the Invention

Granular filters are frequently used in liquid treatment, particularly in water treatment and purification, because of their high filtering efficiency and because of the relative low cost and availability of the filter medium: sand, crushed minerals, anthracite, and the like.

The size of a filter is obviously a function of the rated throughput as demanded by the consumer. While, therefore, filters of a given type come in a range of sizes and throughputs, for reasons of economy, the incremental steps in throughputs of such a range are relatively large. Thus, to make sure that demand will never exceed capacity, users are mostly compelled to acquire the "next larger size," which, for the above reason, is usually much larger. As a result, filters are rarely, if ever, used at their full capacity, which is uneconomical. Also, to produce a whole range of filters of a given type implies a heavy capital outlay in tooling and other production facilities, which is. of course, reflected in their cost.

In use, the liquid passes through the granular bed by force of gravity (slow. open filters) or pressure (rapid, closed filters), while the dirt is trapped inside the bed and on its surface. Depending on the contaminant load, filter beds must be cleaned periodically. In large, open filters this is often done by removing the upper, most heavily-contaminated parts of the granular bed and washing it elsewhere at the operator's convenience. In rapid, closed filters, however, cleaning is mainly effected by back- flushing, i.e.. by forcing liquid through the bed in a direction opposite to the filtering direction. Back-flushing by itself is. however, not quite effective, unless the granular bed is properly stirred up and thoroughly agitated during the back-flushing operation. That is the reason why, in spite of the basic simplicity of these filters, prior art back-flushing, granular filters are often quite complex pieces of machinery, comprising rotating drums, paddles, shakers, and the like. Summary of the Invention

It is thus one of the objects of the present invention to provide a granular-bed, modular filter unit which is small, compact and the bed of which, during back- flushing, is easily agitated, and with which, building-block fashion, it is possible to build up a filter bank of any practical size and throughput.

It is another object of the present invention to provide a modular filter unit from which it is possible to build filter banks of any practical size and throughput, in which unit the back-flushing flow can be made to sequentially enter the unit at more than one point and, inside the unit, to proceed in more than one direction towards more than one outlet, thereby greatly enhancing fluidization.

It is a still further object of the present invention to provide filter banks of optional size and throughput, in which banks the above-described filter units are interconnected in series and/or in parallel, and wherein there is provided a programmable manifold arrangement whereby, in the back-flushing mode, the back-flushing flow inside the units can be sequentially made to proceed in different directions.

It is yet another object of the present invention to provide a method for back-flushing a granular-bed, modular filter unit.

According to the invention, there is provided a granular-bed, modular filter unit, comprising at least one chamber defined and delimited by a housing wall surface surrounding said chamber and two end walls, and divided by an imaginary, axial, substantially horizontal plane into a lower part and an upper part; at least one strainer tube passing at least indirectly through the lower part of said chamber from one of said end walls to the other one of said end walls; at least one strainer tube passing at least indirectly through the upper part of said chamber from one of said end walls to WO 99/46024 .-, PCT/IL99/00132

the other one of said end walls, and filtering granules substantially embedding said at least one lower part strainer tube, wherein all of said strainer tubes are accessible from the outside of said end walls, and wherein said filter unit is connectable to other, similar units serially and/or in parallel, to form filter banks.

The invention further provides a back-flushable, granular-bed filter bank, composed of a plurality of filter units as described herein, said bank comprising at least two computer-controllable valves associated with manifold means which, in the filtering mode of said filter bank, supply said at least one upper-part strainer tube with raw water and draw clean water from said at least one lower-part strainer tube and, in the back- flushing mode of said filter bank, supply said at least one lower-part strainer tube with flushing water and draw water containing the dislodged particulate from said at least one upper-part strainer tube.

The invention still further provides a back-flushable, granular-bed filter bank, composed of a plurality of filter units as described herein, comprising at least two computer-controllable valves associated with manifold means which, in the filtering mode of said filter bank, supply said upper-part strainer tubes with raw water and draw clean water from said lower-part strainer tubes and, in the back-flushing mode of said filter bank, selectively supply either one or more of said lower-part strainer tubes with flushing water and selectively draw water containing the dislodged particulate from either one or more of said upper-part strainer tubes, wherein a controllable and predeterminable flushing sequence of at least some possible combinations of lower and upper strainer tubes promotes fluidization of said granular-bed and enhances filter cleaning and efficiency.

The invention yet further provides a method for back-flushing a granular-bed filter, comprising the steps of providing a filter housing having a lower part and an upper part; at least two strainer tubes traversing said filter housing in the lower part thereof; at least two strainer tubes traversing said filter housing in the upper part thereof; said lower-part strainer tubes and said upper-part strainer tubes being accessible from the outside of said filter housing; a granular filter bed substantially enbedding said lower-part strainer tubes; and valves for controlling inflow into said lower-part strainer tubes and outflow from said upper-part strainer tubes; introducing back-flushing water either into one or more of said lower-part strainer tubes; drawing off said back- flushing water, including the dislodged fine particulate, from either one or more of said upper-part strainer tubes, and cyclingly switching the direction of the back- flushing water flow inside said filter housing, using at least some of the possible permutations of said lower-part strainer tube inlets and said upper-part strainer tube outlets. Brief Description of the Drawings

The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.

With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings: Fig. 1 is a perspective view of a first embodiment of the filter unit according to the invention; Fig. 2 is a similar view of the filter of Fig. 1, with the cylindrical housing portion removed to show the strainer tubes; Fig. 3 is a view of one of the end walls of the filter of Fig. 1; Fig. 4 represents a view, in cross-section along plane IV-IY, of the filter of Fig. 1 ; Fig. 5 is a perspective view of a portion of the strainer tubes of Fig. 2; Fig. 6 is a perspective view of a double-chamber embodiment of a filter unit according to the invention; Fig. 7 shows one of the end walls of the embodiment of Fig. 6; Fig. 8 is a view, in cross-section along plane VIII- VIII, of the filter of Fig. 7; Figs. 9 to 11 illustrate details of Fig. 8 to an enlarged scale; Fig. 12 is a schematic, perspective view of a filter bank composed of 32 filter units, as well as of the manifold units feeding the bank raw water and drawing off clean water; Fig. 13 is a view similar to Fig. 12, showing the other side of the filter bank; Fig. 14 is a table indicating the filtering and back-flushing sequences controlled by the solenoid valves; Fig. 15 is a graphic representation of the back-flushing sequence given in Fig. 14; Figs. 16 and 17 represent another embodiment of the single-chamber filter unit shown in Figs. 1 and 2; and Figs. 18 and 19 represent another embodiment of the double-chamber filter unit shown in Figs. 6 and 8. Detailed Description of Preferred Embodiments

Referring now to the drawings, there is shown in Figs. 1 to 4 a first embodiment of the invention, a single-chamber filter unit having a chamber defined by a tubular housing 2 and two end walls 4, 4'. The entire unit is held together by means of tie rods 6.

Fig. 2, in which housing 2 has been removed, shows the interior of the filter unit. As shown, a short neck 8 is provided on the inside face of each Of end walls 4, 4', over which fits housing 2 (see also Fig. 4). Sealing is effected by O-rings 10 (Fig. 4) seated in circumferential grooves 12.

Further shown in Fig. 2 are strainer tubes 14, illustrated to an enlarged scale in Fig. 5, which serve to retain gross impurities. By means of rings 16 and O-rings 17 (shown to better advantage in Fig. 9), strainer tubes 14 are tightly seated in bores 18 in end walls 4. The filter unit has four strainer tubes 14, which, for purposes of explanation of the filter operation to be given presently, are designated UL (upper left), UR (upper right), LL (lower left) and LR (lower right).

The provision of two upper, spaced-apart strainer tubes UL, UR and two lower, spaced-apart strainer tubes LL, LR, is a major feature of the present invention, as will become apparent presently.

In the filtering mode, the filter unit (or the filter bank composed of filter units) operates in the conventional manner, whereby raw water is introduced into the filter via UL, UR, passes through the filter bed, during which passage the solid pollutants are retained in the bed, and exits as purified water through LL and LR.

In the back-flushing mode, however, in which the back-flushing water is introduced from below, a programmable valving mechanism (see Figs. 12, 13) permits a sequence of periodically changing combinations of back-flushing flow targeting, such as LR→UR, LL→UL, LR→UL and LL→UR. These sequences, which the program automatically changes every so many seconds, greatly contribute to the fluidization of the filter bed and, consequently, to thorough washing of the filter bed granules and the prying off and flushing away of even the most clinging solids.

Also indicated in Fig. 4 is the level h of the granule bed relative to the internal diameter d of housing 2, with h/d » 3/4. Granules to be used with the filter unit according to the invention are advantageously of a size as small as 25 microns.

Fig. 5 shows a section of one of strainer rubes 14, which in fact consist of two components: a carrier tube 20 having relatively large perforations in the form of round holes or elongated slits, and a wire-mesh sleeve 22, of a mesh size small enough to prevent the penetration into the chamber of gross raw water impurities and the escape of filtering granules from the chamber during the filtering mode of the unit, yet of a mesh size large enough to permit the passage of dislodged fine particulate during the back-flushing mode.

As will be explained further below in conjunction with Figs. 12 and 13, filter units such as those discussed above can be combined and interconnected to form filter banks of optional size and throughput. However, as the length of the chamber of the unit of Fig. 1 is not much greater than the housing diameter, the assembly of larger filter banks, while in principle possible, would entail the interconnection of many such units, with concomitant sealing and stability problems. For larger filter banks, it is therefore advantageous to use filter units of greater length. This, however, poses another problem: the horizontality of the granule bed surface which, with increased chamber length, is liable to be compromised, mainly due to fluidization phenomena during back-flushing, thereby producing differences of depth in the granule bed within the chamber which may impair filter efficiency.

The above problem is addressed by the double-chamber filter unit shown in Figs. 6 to 11. Fig, 6 illustrates a double-chamber filter unit of a length about twice the length of the filter unit of Figs. 1 to 4, in which this problem is solved by providing a central partition 24 in which are mounted the inner ends of each of the eight strainer tubes 14, that is, four for each chamber (see Figs. 9 to 11). Here, too, end walls 4, 4' . are clamped together by rods 6.

It is these double-chamber units that make up the filter bank schematically represented in Figs. 12 and 13. In order to set up such a bank, in which four stacked layers of eight filter units are arranged, each unit is connected in series with another unit, forming a pair. Four of these pairs form a layer and are connected in parallel with raw-water and clean-water manifolds, and four of these layers are then stacked upon each other. Details of this arrangement will be discussed further below.

For the series connection of the filter units mentioned above, there are provided sleeves 26 carrying O-rings 17, tightly seated in bores 18 in end wall 4'. Having been connected by four such sleeves, each pair of units is secured by means of bolts (not shown) led through holes 28 (Fig. 6) provided in the respective end walls 4' of each double-chamber filter unit.

Bore 18 in the other end wall 4 is provided with an internal thread 30, either for a plug 32 or for a short length of pipe (not shown), whereby the strainer tubes 14 of each pair are connected to the manifold system, to be discussed below in conjunction with Figs. 12 and 13. Figs. 12 and 13 show a filter bank consisting of 32 double-chamber filter units according to the invention, as seen from the front and the rear, respectively.

Fig. 12 shows a raw water feeder pipe 34, to which are connected four solenoid valves A, B, C and D, each valve controlling all UR strainer tubes 14 of a respective one of the four layers of the filter bank. Valves A, B, C and D are three-way valves, with one port of each valve leading to feeder pipe 34, one to manifold pipes 36, and one to a drain pipe 35. Each of valves K, L, and N controls all LR strainer tubes 14 of a respective one of the four layers of the filter bank. Valves K, L, M and N are two-way valves, with one port of each valve leading to a clean-water collecting pipe 38 and one to manifold pipes 40. It should be noted that pipe 38 is always under pressure and that manifold tubes 36 and 40 are closed at their free ends. Also shown are connectors 42, which connect manifold pipes 36 and 40 to UR strainer tubes 14 and LR strainer tubes 14, respectively. It is further seen that all UL and LL strainer tubes are plugged up by means of plugs 32 (Fig. 9).

Fig. 13 shows the rear side of the filter bank of Fig. 12. Seen are raw- water feeder pipe 34, drain pipe 35 and clean- water collector pipe 38. Valves E, F, G and H, connected to raw-water feeder pipe 34, are the exact analogues of valves A, B, C and D, while valves O, P, Q and R, connected to clean- water collector pipe 38, are the analogues of valves K, L, M and N. On the rear side of the filter bank, all UL and LL strainer tubes are plugged up by means of plugs 32.

The table of Fig. 14 lists the status of all sixteen valves A-R during a back- flushing sequence of the top layer of a filter bank according to the invention.

Letters in the first column relate to the valves as marked in Figs. 12 and 13, while the numerals refer to the status of each valve and its effect on the respective filter unit. Roman numerals I-V signify the flow regime in the filter chambers with respect to strainer tubes UL, UR, LL, RR, as indicated also in Fig. 15. The letters pbf (prior to back-flushing) indicate the status of all valves during regular filtration activity, before the filters have become loaded to such a degree that back-flushing is required. WO 99/46024 <-, PCT/IL99/00132

Valves A, B, C, D, E, F, G, H can assume three possible states:

1) valve connects associated filter unit to raw water pipe 34;

2) valve connects associated filter unit to drain pipe 35;

3) valve is closed.

Valves K, L, M, N, O, P, Q, R can assume two possible states:

1) open

2) closed.

Back-flushing operations are initiated either at predetermined time intervals or as soon as the pressure loss, indicated by a sensor, exceeds a predetermined limit.

As can be seen from the table in Fig. 14, during back- flushing, one- fourth of the filter units in the bank are in the back-flushing mode; the rest are in the filtering mode.

Fig. 15 is a graphic representation of the back-flushing sequence shown in the table of Fig. 14, with pbf signifying filtration prior to the initiation of back- flushing. The Roman numerals indicate the flow inside the chambers as produced by the respective states of the valves. The change of flow directions, which, as already explained, enhances fluidization of the filter bed and thus of the cleaning effect, is clearly perceivable.

It should be noted that stages I-V as shown are examples only, with different or additional stages being possible.

After stages I-V have been repeated until the first layer filter units are clean, the second layer valves B, F, L and P are activated in the same sequence as were valves A, E, K and O, and so forth.

As stated above, the valves are controlled by a computer program, which also determines the operational sequence, the duration of each stage and the number of cycles.

While the modular filter units shown in Figs. 1 to 8 give excellent service in all filtration tasks, some of these tasks involve lower levels of pollution and larger solids to be intercepted, and thus permit the use of larger-size granulates. Units for such tasks therefore need not make use of the direction-changing, back-flushing flow according to the above-described method, and consequently will often give a satisfactory performance with one upper-part and one lower-part strainer tube only.

Such a modular filter unit is shown in Figs. 16 and 17. This unit is fully analogous to the unit shown in Figs. 1 and 2, except that it has only one lower-part strainer tube 14 and one upper-part strainer tube 14.

Figs. 18 and 19 represent what could be called a "double-chamber" unit similar to the unit of Figs. 6, 8, except that the "double" feature is not achieved by partition 24, but by tightly joining end walls 4, 4' of two single-chamber units, using longer tie rods 6 and ensuring fluid-tightness by providing a rubber gasket 44 having appropriately located holes for the passage of water, as well as for tie rods 6.

While the term "water" was used herein throughout the description, it will be appreciated that the filter units and the filter banks according to the invention are also suitable for the filtration of other liquids.

End walls 4, 4', which are shown hereinabove to be square and planar, can also have other configurations.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

CLAIMS:

1. A granular-bed, modular filter unit, comprising: at least one chamber defined and delimited by a housing wall surface surrounding said chamber and two end walls, and divided by an imaginary, axial, substantially horizontal plane into a lower part and an upper part; at least one strainer tube passing at least indirectly through the lower part of said chamber from one of said end walls to the other one of said end walls; at least one strainer tube passing at least indirectly through the upper part of said chamber from one of said end walls to the other one of said end walls, and filtering granules substantially embedding at least one lower-part strainer tube; wherein all of said strainer tubes are accessible from the outside of said end walls, and wherein said filter unit is connectable to other, similar units serially and/or in parallel, to form filter banks.

2. The filter unit as claimed in claim 1, wherein there are provided at least two spaced-apart, lower-part strainer tubes and at least two spaced-apart, upper-part strainer tubes.

3. The filter unit as claimed in claim 1, wherein connection between said similar units is effected by joining their end walls to one another, whereby the strainer tubes of the second of said joined units become extensions of the corresponding strainer tubes of the first of said joined units.

4. The filter unit as claimed in claim 1 , wherein said strainer tubes are perforated and covered with wire mesh of a mesh size small enough to prevent the penetration into said chamber of gross raw-water impurities and the escape from said chamber of filtering granules in the filtering mode of said unit, yet of a mesh size large enough to permit the passage of dislodged fine particulate in the back-flushing mode of said unit

5. The filter unit as claimed in claim lor claim 2, further comprising at least one central partition wall substantially parallel to said end walls, which partition wall divides said unit into two chambers, the strainer tubes of the first one of said two chambers extending from the end wall of the first of said chambers to said central partition wall, and the strainer tubes of the second one of said two chambers extending from the end wall of the second of said chambers to said central partition wall.

6. The filter unit as claimed in claim 1 or claim 2, comprising more than one partition wall, said more than one partition wall dividing said unit into more than two chambers.

7. A back-flushable, granular-bed filter bank, composed of a plurality of filter units as claimed in claim 1, said bank comprising: at least two computer-controllable valves associated with manifold means which, in the filtering mode of said filter bank, supply said at least one upper-part strainer tube with raw water and draw clean water from said at least one lower-part strainer tube and, in the back-flushing mode of said filter bank, supply said at least one lower-part strainer tube with flushing water and draw water containing the dislodged particulate from said at least one upper-part strainer tube.

8. A back-flushable, granular-bed filter bank, composed of a plurality of filter units as claimed in claim 2, said bank comprising: at least two computer-controllable valves associated with manifold means which, in the filtering mode of said filter bank, supply said upper-part strainer tubes with raw water and draw clean water from said lower-part strainer tubes and, in the back-flushing mode of said filter bank, selectively supply either one or more of said lower-part strainer tubes with flushing water and selectively draw water containing the dislodged particulate from either one or more of said upper-part strainer tubes, wherein a controllable and predeterminable flushing sequence of at least some possible combinations of lower and upper strainer tubes promotes fluidization of said granular bed and enhances filter cleaning and efficiency.

9. The filter bank as claimed in claim 8. wherein said filter bank comprises at least one layer consisting of a plurality of filter units connected in parallel with said manifold means.

10. The filter bank as claimed in claim 9, wherein said plurality of filter units is arranged in groups of at least two series-connected units.

11. The filter bank as claimed in claim 9, wherein each of said layers is provided with four valves and four manifold means.

12. The filter bank as claimed in claim 11, wherein two of said valves are three-way valves, and two are two-way valves.

13. The filter bank as claimed in claim 12, wherein said three-way valves are connected in parallel to a raw-water feeder pipe and said two-way valves are connected in parallel to a clean-water collector pipe.

14. The filter bank as claimed in claim 7 or claim 8, wherein said manifold means are pipes communicating with said valves and provided with connectors, whereby said pipes communicate with said strainer tubes.

15. A method for back- flushing a granular-bed filter, comprising the steps of: providing a filter housing having a lower part and an upper part; at least two strainer tubes traversing said filter housing in the lower part thereof; at least two strainer tubes traversing said filter housing in the upper part thereof; said lower-part strainer tubes and said upper-part strainer tubes being accessible from the outside of said filter housing; a granular filter bed substantially enbedding said lower-part strainer tubes; and valves for controlling inflow into said lower-part strainer tubes and outflow from said upper-part strainer tubes; introducing back-flushing water either into one or more of said lower-part strainer tubes; drawing off said back- flushing water, including the dislodged fine particulate. from either one or more of said upper-part strainer tubes, and cyclingly switching the direction of the back-flushing water flow inside said filter housing, using at least some of the possible permutations of said lower-part strainer tube inlets and said upper-part strainer tube outlets.