GB1604108A

GB1604108A - Backwash fast filter installation

Info

Publication number: GB1604108A
Application number: GB22888/78A
Authority: GB
Original assignee: Sulzer AG; Gebrueder Sulzer AG
Current assignee: Sulzer AG
Priority date: 1978-04-26
Filing date: 1978-05-26
Publication date: 1981-12-02
Also published as: FR2424051A1; CH628821A5; DE2818729B2; DE2818729C3; DE2818729A1

Abstract

The backwashable rapid filter unit has a plurality of filter zones (8). During backwashing, the level or pressure difference (A-B) between an overflow edge (9) for the clean water and sludge orifices (10) in each filter zone (8) force the clean water serving as flushing water from a communicating system of buffer chambers (6) containing clean water through each filter zone (8) to be flushed. The flushing water flows simultaneously against the filtering direction always through only one filter zone (8) to be backwashed, while the remaining zones (8) operate in the filtering mode. The difference in levels (A and B) is matched to the necessary amount of flushing water in this case; it is selected so that a sufficient, but not too large, quantity of water is always available as flushing water. The number of the filter zones (8) of the unit exceeds the ratio of backwash to filtering rate by at least one unit, so that during a backwash procedure, at least as much clean water is generated as is required for backwashing. As a result of the concept of the unit illustrated, the expenditure required for backwashing is considerably reduced. <IMAGE>

Description

(54) BACKWASH FAST FILTER INSTALLATION (71) We, SULZER BROTHERS LI MITED, a Company organised under the laws of Switzerland, of Winterthur, Switzerland, do hereby declare this invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a backwash fast filter installation for the treatment of liquids, comprising a number of parallel filter beds having a bulk fill of a granular filter composition, which are separated by filter floors from at least one treated liquid chamber for collection and removal of the filter, a head-producing weir separating the intercommunicating treated liquid chamber or chambers from a liquid delivery chamber, each filter bed having associated therewith a sludge removal aperture through which soiled backwashing liquid is removed.

Installations of the kind described, which are of use mainly in water and/or sewage engineering, are embodied as open or closed units made of concrete or steel or glass fibre reinforced plastics and can be either of the single-bed or multi-bed filter kind. Also, after installations of this kind have been operating for some time it becomes necessary to remove dirt retained and collected on the granular filter composition by backwashing. Various methods are known for this purpose wherein water, air and/or air-water mixtures are used for backwashing, with a flow through the filter composition against the direction of filtration, and carrying the collected dirt along with them, the dirt leaving the installation together with the backwashing liquid through sludge removal apertures.

If there are stringent requirements concerning the purity of the filter composition after backwashing, the usual practice is to use a combined air-water washing in which at least one washing or cleansing with air is given, followed by a mixed air-water wash and concluding with a final water wash; in some cases - i.e., in the case of multi-bed filters - the procedure is followed by a separating phase which redistributes in accordance with the original layering of the filter bed, the different grain fractions of the combined filter composition which have been mixed with one another during washing, such a separating phase uses a high water flow speed and large quantities of water. This requires in many instances a second additional washing water pump for the separating phase.

The backwashing processes described call for a considerable outlay for machinery and apparatus, more particularly in the case of installations having a number of parallel filter beds, since it is necessary for each filter bed to have associated with it a raw water input, a discharge line for treated water, a discharge line for contaminated washing water and supply lines for washing water and cleaning air together with the associated stop valves and control elements.

Electrical equipment is also required for switching, controlling and supervising these elements of the installation (cf. e.g. F. Lipp, H. Kubli "Seewasserwerk fiirdie Trinkwasserversorgung der Stadt Biel", Technische Rundschau Sulzer No. 1/1976, pages 19 27).

In another known backwashing procedure disclosed by Swiss Patent Specification No.

568 776, vertical partitions sub-divide a filter bed into a chamber of chambers above the filter floor, so that a number of filters which are fed in common and which have a common treated-water chamber arise. Each of the intermediate chambers produced by the subdivision are washed individually while filtration continues in the other such intermediate chambers. For backwashing, one of the intermediate chambers is covered with a kind of hood or dome or the like which rests on the chamber-bounding walls and provides a relatively sealing-tight closure of such chamber. The intake side of sludge water pumps is connected to the dome. In operation such pumps suck pure water in countercurrent from the common treated-water chamber through the filter floor and through the filter composition of the intermediate chamber which it is required to backwash, so that such chamber is washed with water.

Further outlay on apparatus is required for the construction necessary to carry out this process, such construction entailing a very sealing-tight closure of the dome, lifting and moving equipment to move the dome from one chamber to another and - if dome movement is to be fully automated as part of an automated filtering and washing operating - switching and control means.

The weight of the dome and the requirement for a relatively sealing-tight closure means that the intermediate chambers thus contrived in a filter bed are bound to be relatively small.

It is an object of the invention to reduce the outlay necessary for backwashing in filter installations of the kind mentioned.

Accordingly the present invention provides a backwash filter installation for the treatment of liquids comprising a plurality of filter beds each having a bulk fill of a granular filter composition supported by a filter floor and separated thereby from a treated-water chamber for collecton and removal of the filtrate, a head-producing weir separating the treated-water chambers from a treated-water delivery chamber, and each filter bed being associated with a sludge removal aperture through which soiled b ackwashin liquid is removed, in which the level of the weir is above the level of the sludge removal aperture by an amount such that the liquid head is sufficient to ensure, during backwash of the filter bed, the flow back of a quantity of filtrate as backwashing liquid from the commdnicating treated-water chamber.

In another aspect the invention provides an installation comprising a plurality of such filter beds with their treated water chambers in communication with one another and with the weir, and in which the number of filter beds is greater by at least one than the ratio of the backwash flow rate to the filter flow rate of the installation.

In an installation which is devised along these lines and in which, as in the procedure described, one filter bed at a time is washed while the other filter beds remain in operation, the head resulting from the difference between the level of the weir for treated water and the level of the sludge removal apertures forces treated water, as washing water, from the treated-water chamber of the filter bed to be cleaned - in countercurrent to the flow during filtering operations through the filter composition. Thus there is no need to provide additional coverings, sealings and suction pumps. The installation according to the invention can therefore be constructed using standard size filter beds and they are also suitable for a combined air-water cleaning phase, something which would require further additional expenditure in the previous kind of installation described.

The difference between the level of the weir and the level of the sludge removal apertures must be such as to ensure the flow of an adequate quantity of washing water through the filter composition of whichever filter bed it is required to clean. The difference must be at least sufficient for the backwash resistance of the filter composition to be overcome; however, the difference must not be so great that the backwash water flows so violently back through the filter composition as to cause excessive eddying of the bed material and removal thereof from the filter bed through the sludge removal apertures.

The speed of backwashing and therefore the quantity of backwashing water depend upon the nature and extent of the dirt present in the filter material, upon filter construction - whether it is a single-bed or multi-bed filter - and upon the kind of backwashing used - i.e., whether backwashing is performed in a single phase or in two phases or in three phases.

The quantities of treated water required for backwashing can be, referred to the square metre of filter surface, approximate from 10 to 30 m3/m2.h for single-bed Nters.

Backwash speeds must be much higher for multi-layer filters in which, as previously mentioned, it is required to separate the various grain fractions of the bed material as well as to have backwashing. Accordingly, the sludge removal aperture of such a filter is higher above the level of the stationary filter composition than is the case of a single-layer filter; moreover, the difference between the level of the weir and the level of the sludge removal aperture must therefore be increased. Consequently, the quantities of backwash water required for multi lasyer2filters may be e.g., from 60 to 80 m3/m2.h.

A reason for specifying a minimum number of filter beds in an installation is to ensure that even during the backwashing of one bed at least no more treated water is used as washing water than is being produced and supplied by the beds actually doing filtering work. In conventional installations the ratio referred to of backwash speed to filtering speed is e.g., approximate ly from 2 to 8.

Since neither backwash pumps nor backwash lines nor backwash valves are necessary, the outlay for backwashing is reduced considerably as compared with installations in which, as is conventional, each filter bed is backwashed independently of the others and has its own individual facilities for this purpose. Also, the reduced number of steps required for backwashing reduces the outlay needed for automating the filtration and washing process.

Advantageously, communication between the filter beds on the treated-water side can be provided either by a treatedwater chamber common to all the beds or by the treated-water chambers of the discrete filter beds being interconnected by a collector which extends to the weir.

To facilitate the servicing of a filter bed in an installation having individual treatedwater chambers for the various filter beds, communication between the treated-water chambers and the collector can be interrupted by means of closure elements.

In order to promote a fuller understanding of the above and other aspects of the present invention, some embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a view in diagrammatic form of an installation having three filter beds interconnected by a common treated-water chamber, while Figure 2 is a similar view of a second similar installation but having separate treated-water chambers.

Basically, all that both Figures show - in purely diagrammatic form - are just those parts of the installation which are necessary or backwashing; constructional details of the filter beds, stop valves and water pipework and ducting part omitted. Also, the control system for the filtering and backwashing process is omitted from the drawings.

Branch pipes 7 having raw water stop valves 2 extend from a raw water line 1 to raw water inlets 26 of individual filter beds 8; as illustrated the beds 8 are separate from one another, but they can be disposed in immediately adjacent relationship to one another and separated from one another just by a partition. Each filter bed 8 contains a loose fill of a granular filter composition 4, above which is a flood or header chamber 3.

The composition 4 is borne by a perforated or porous filter floor 5 below which is a treated-water chamber 6 common to all the beds 8.

Chamber 6 communicates by way of a head-producing weir 9 with a chamber 11 from which treated water can be removed through a line 12 for further use. The level A of the weir 9 is higher than level B of a sludge removal aperture 10 which is present in each individual bed 8 and to each of which a sludge removal line 16 with associated stop valve 19 is connected. The lines 16 extend to a common collecting line 20 through which the soiled backwash water leaves the installation.

Extending into the chamber 6 below the beds 8 are airlines 17 one of which is provided for each bed 8 and each of which has a stop valve 15. The lines 17 lead off from a common distribution line 14 supplied with compressed air by a compressor 13 which takes in air through a filter 18. A stop valve 24 and a check valve 25 are provided in the line 14 after the compressor 13, the drive for which is not shown.

The embodiment shown in Figure 2 differs only in details from the embodiment shown in Figure 1. In Figure 2, the communication between the various beds 8 is provided by a treated-water header or collector 22 to which the discrete treated-water chambers 6 of the various beds 8 are connected by way of connection passages 21. Disposed in the passages 21 are slidmg closure members 23, such as stop logs, which enable the filter beds to be isolated individually from the rest of the system, e.g.

for servicing.

A short description will now be given of how back-washing proceeds in the above installations. During filtration the raw water enters the top chamber 3 of a bed 8 by way of the raw water line 1, the raw water valve 2 and the raw water inlet 26. The raw water then flows through the filter composition 4 and filter floor 5, the filtered water collecting in the treated water chamber 6. The treated water leaves the same by way of the weir 9, which controls the water levels in the chambers 3, to enter chamber 11 whence it can be removed through a line 12 for further use or to a sewer. During filtration the stop valves 15 for the scavenging air and valves 19 for sludge water remain closed. When it is required to wash a bed 8, the raw water feed thereto it interrupted by closure of the valve 2, whereafter the water building up above the filter composition 4 drops as far as the level A of the weir 9. The stop valve 19 which is of large flow capacity is opened rapidly and causes the level of the liquid in the bed 8 to be washed to drop rapldly to level B; because of the head arising from the difference between the levels A and B, water rising from the treated water chambers 6 (or collector 22) starts to flow back through the filter composition 4 of the filter bed 8 which it is required to wash and to wash the same.

In the next phrase, after rapid closure of the valve 19 the blower or compressor 13 delivers cleaning or scavenging air through the distribution line 14 and the valve 15 which is opened for that purpose, and through the composition 4 in addition to the water already flowing therethrough. This combined air-water wash continues until the level of liquid above the bed in the filter is restored to the level A.

After closure of valve 15 in line 17, valve 19 in the sludge removal line 16 is reopened until the water level above the composition 4 returns to level B. The new flow of washing water carries the dirt detached from the granular filter composition upwards and out of the same; the dirt and the washing water are removed from the installation through the lines 16, 20 and go to be treated or otherwise used. The valve 19 is then closed to terminate the washing process, whereafter opening of the raw water valve 2 restarts the filtering process.

In the case of multi-bed filters, the second washing water phase is always the phase in which different filter media are separated from one another. The pressure difference between the head levels A and B is therefore increased in such cases to ensure that despite the pressure drop through the filter floor 5 and composition 4, the washing water moves fast enough to separate the different grain size fractions of the bed material.

WHAT WE CLAIM IS: 1. A backwash filter installation for the treatment of liquids comprising a plurality of filter beds each having a bulk fill of a granular filter composition supported by a filter floor and separated thereby from a treated-water chamber for collection and removal of the filtrate, a head-producing weir separating the treated-water chambers from a treated-water delivery chamber, and each filter bed being associated with a sludge removal aperture through which soiled backwashing liquid is removed, in which the level of the weir is above the level of the sludge removal aperture by an amount such that the liquid head is sufficient to ensure, during backwash of the filter bed, the flow back of a quantity of filtrate as backwashing liquid from the communicating treated-water chamber.

2. A filter installation as claimed in Claim 1, in which the number of filter beds is greater by at least one than the ratio of the intended backwash flow rate to the intended filter flow rate of the installation when in operation.

3. A filter installation as claimed in Claim 2, in which the treated-water chambers of the various filter beds are interconnected by a treated-water collector means.

4. A filter installation as claimed in Claim 3, in which communication between each treated-water chamber and the collector means may be interrupted by means of respective closure elements.

3. A backwash filter installation sub- stantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the distribution line 14 and the valve 15 which is opened for that purpose, and through the composition 4 in addition to the water already flowing therethrough. This combined air-water wash continues until the level of liquid above the bed in the filter is restored to the level A. After closure of valve 15 in line 17, valve 19 in the sludge removal line 16 is reopened until the water level above the composition 4 returns to level B. The new flow of washing water carries the dirt detached from the granular filter composition upwards and out of the same; the dirt and the washing water are removed from the installation through the lines 16, 20 and go to be treated or otherwise used. The valve 19 is then closed to terminate the washing process, whereafter opening of the raw water valve 2 restarts the filtering process. In the case of multi-bed filters, the second washing water phase is always the phase in which different filter media are separated from one another. The pressure difference between the head levels A and B is therefore increased in such cases to ensure that despite the pressure drop through the filter floor 5 and composition 4, the washing water moves fast enough to separate the different grain size fractions of the bed material. WHAT WE CLAIM IS:

1. A backwash filter installation for the treatment of liquids comprising a plurality of filter beds each having a bulk fill of a granular filter composition supported by a filter floor and separated thereby from a treated-water chamber for collection and removal of the filtrate, a head-producing weir separating the treated-water chambers from a treated-water delivery chamber, and each filter bed being associated with a sludge removal aperture through which soiled backwashing liquid is removed, in which the level of the weir is above the level of the sludge removal aperture by an amount such that the liquid head is sufficient to ensure, during backwash of the filter bed, the flow back of a quantity of filtrate as backwashing liquid from the communicating treated-water chamber.