GB2128098A

GB2128098A - Multilayer filter bed regeneration

Info

Publication number: GB2128098A
Application number: GB08304995A
Authority: GB
Inventors: Rolf Burkle; Bernard Devit; Peter Sick
Original assignee: SICK KG OTTO
Current assignee: SICK KG OTTO
Priority date: 1982-10-01
Filing date: 1983-02-23
Publication date: 1984-04-26
Also published as: JPS5966313A; DE3326419A1; GB8304995D0; HU189240B; HUT35968A

Abstract

In order to regenerate a multilayer filter bed (11) which has been used for separating flocculated matter from liquid, the following steps are carried out. Firstly,the vessel (10) containing the filter (11) is filled with rinsing water supplied via a supply line (22) and nozzles (19a). Secondly, compressed air is supplied to the filter (11) via supply lines (23, 24, 25) and respective nozzles (19a, 20a, 21a) to break up the filter cake deposited on the filter (11) and to form a turbulent slurry above the filter (11). Thirdly, the supply of compressed air is discontinued, and filter particles in the slurry are allowed to settle. Fourthly, compressed air is forced into the vessel (10) via a supply line (18) so as to force the slurry out of the vessel (10) via a dip pipe (14). Finally, the filter (11) is rinsed with fresh rinsing water. <IMAGE>

Description

SPECIFICATION Method and apparatus for separating harmful or undesired matter from a liquid This invention relates to a method and apparatus for separating harmful or undesired matter dissolved in a liquid, more particularly for separating harmful or undesired matter (such as cellulose, carbohydrates, metal ions, organic acids and/or drink residues) from the wash liquor from a bottle-washing machine, wherein in a continuous process the harmful or undesired matter is selectively flocculated by a flocculating agent such as a polyelectrolyte of high molecular weight which is added to the liquid in a vessel, and accumulates on this agent, after which the agent with the harmful or undesired matter adhering thereto is separated by filtration and absorption by means of a mu Itilayer fitler which is housed in the vessel and through which the liquid flows from top to bottom.

A method and apparatus of the above type have already proved themselves in practice, more particularly with regard to the separation of harmful or undesired matter, such as carbohydrates and cellulose, which is otherwise difficult to separate. However, certain problems relating to the cleaning of the multilayer filter have arisen. Thus, an increasingly thick and impenetrable filter cake forms on the surface of the multi layer filter, with the result that after a period of operation, which depends on the amount of harmful or undesired matter in the liquid, it is necessary to clean the filter and, more particularly, to remove the filter cake. Simply passing rinsing water through the filter does not produce the desired effect.Until now, therefore, the practice has been to pass rinsing water and compressed air simultaneously in counterflow through the multilayer filter in order thereby to break up and wash away the filter cake. One disadvantage of this rinsing method, however, is that when air and water pressures which actually break up the filter cake are used, a considerable portion of the filter material that has a relatively low specific gravity is also washed out of the vessel and furthermore, there is not inconsiderable intermingling of the filter layers. In order to prevent filter material from being thus washed away, the multilayer filter is often enclosed in a sack-like net covering.In this way, although by an appropriate choice of the net the amount of filter material being washed away is substantially reduced, it has become apparent in practice that the purging air and, more particularly, the rinsing water find a way past the filter between the filter casing and the inner wall of the vessel, thereby by-passing the filter. The cleaning effect is thereby reduced considerably, or at the very least the cleaning time is prolonged considerably.

According to the present invention, there is provided a method of separating harmful or undesired matter from a liquid, which comprises selectively flocculating the harmful or undesired matter by adding a flocculating agent to the liquid and then absorbing and filtering the flocculated harmful or undesired matter by passing the liquid downwardly through a mutlilayer filter in a vessel, the multilayer filter being regenerated after a period of use by the following steps: (a) at least partially filling the vessel with rinsing liquid; (b) supplying compressed air to the multilayer filter and allowing it to rise through at least part of the multilayer filter to break up the filter cake deposited on the multilayer filter and to form a turbulent slurry above the multilayer filter; (c) discontinuing the supply of compressed air to the multilayer filter and allowing the filter particles in the slurry to settle; (d) forcing compressed air into the vessel above the slurry thereby forcing the slurry out of the vessel; and (e) if desired rinsing the multilayer filter with the fresh rinsing liquid.

In contrast to the prior art, therefore, rinsing liquid and purging air do not flow through the multilayer filter simultaneously; rather, in the first instance the vessel is at least partially filled with rinsing liquid, the rinsing liquid supply is disconnected, the compressed air inlet is opened, and, after breaking up the filter cake and producing a layer of slurry above the filter, the compressed air is shut off again, the filter particles contained in the layer of slurry then being allowed to settle. Only then is the layer of slurry forced out of the vessel by means of compressed air.

This chronological sequence on the one hand produces excellent filter cleaning and on the other hand prevents filter material from being washed out of the vessel.

The invention also provides an apparatus for use in carrying out a method according to the invention, the apparatus comprising a vessel having a multilayer filter therein, a first supply line for the supply of the liquid containing harmful or undesired matter to the upper region of the vessel, a second supply line for the supply of the flocculating agent to the upper region of the vessel, a first discharge line for the discharge of the liquid from which the harmful or undesired matter has been separated from the lower region of the vessel, a third supply line for the supply of either rinsing liquid or compressed air to the multilayerfilter and connectable either to a supply of rinsing liquid or to a supply of compressed air, a second discharge line extending into the vessel and terminating in the vicinity of the upper surface of the multilayer filter for the discharge of the flocculated harmful or undesired matter from the vessel and for the discharge of the liquid containing harmful or undesired matter form the vessel, and a fourth supply line for the supply of compressed air to the upper region of the vessel.

The apparatus of the invention preferably has one or more of the features set forth in claims 6 to 20 hereinbelow.

Exemplary embodiments of the apparatus according to the invention will now be described with reference to the drawings, in which: Figure 1 is a vertical section through a vessel and multilayer filter, according to a first embodiment of the invention; Figure 2 is a vertical section through a vessel and multilayerfilter, according to a second embodiment of the invention; and Figure 3 is a vertical section through a multilayer filter cartridge.

In Figure 1,there is shown a vessel 10 housing a multilayer filter 11, the vessel 10 having a supply line 12 for the liquid to be purified, such as a wash liquor, and a discharge line 13 for the purified wash liquor.

In addition to the two lines 12 and 13, which are intended for use during the normal operation of purification of the wash liquor, the vessel has a series of further supply lines and discharge lines for backwashing. Thus, a discharge line in the form of a dip pipe 14 projects through the cover of the vessel 10 and extends into the vessel 10 so that it is directly above the surface of the multilayer filter 11. The mouth of the dip pipe 14 is provided with a screen 14a. Outside of the vessel 10, the dip pipe 14 branches into a discharge line 15 with a valve 15a and another discharge line 16 with a valve 16a.

Furthermore, a compressed air supply line 17 discharges into the dip pipe 14, in the region between the vessel cover and the point at which the pipe 14 branches. A further compressed air supply line 18 discharges directly into the vessel through the vessel cover.

There are disposed in the vessel 10, within the mutilayer filter 11, three horizontal nozzle pipes 19, 20 and 21 having nozzles 19a, 20a and 21a, respectively. The lower nozzle pipe 19 is connected both to a rinsing water supply line 22 and to a compressed air supply line 23, whereas the middle nozzle pipe 20 and the upper nozzle pipe 21 are connected only to compressed air supply lines, namely lines 24 and 25 respectively.

During normal operation, i.e. for separating harmful or undesired matter from wash liquor, the apparatus functions in the usual and known manner.

Thus, the wash iiquorto be purified is supplied through the supply line 12, and there is added to it, by a dosing device (not shown) a polyelectrolyte to which the undesired matter adheres. The wash liquor is passed through the mutlilayer filter 11 and discharges through the discharge line 13. If, after a determined operating period, the multilayer filter 11 has to be cleaned, then, in the first instance, the lines 12 and 13 are closed, and the valve 15a is opened. By introducing compressed air through the line 18, residual wash liquor above the multilayer filter 11 is discharged upwards through the dip pipe 14 and the discharge line 15. After the vessel 10 has been completely drained, the valve 15a and the compressed air supply line 18 are closed. The rinsing water supply line 22 is now opened, and the vessel 10 is filled with rinsing water.As soon as the filling process is over, the rinsing water supply line 22 is closed and the compressed air supply lines 23,24 and 25, and the valve 16a, are opened. The compressed air flowing into the vessel breaks up the filter cake which is located on the surface of the mutlilayer filter 11, and a layer of turbulent aqueous slurry forms above the filter 11, which layer contains particles of the undesired matter of the disintegrated filter cake, particles of undesired matter from inside the filter 11 and also entrained filter particles. The compressed air supply lines 23, 24 and 25 can be opened and closed simultaneously.Preferably, however, the procedure is such that in the first instance, in order to break up the filter cake, only the compressed air supply line 25 is opened, and the compressed air supply lines 24 and 23 are opened one after the other only after the filter cake has been broken up. Closing can take place in reverse sequence.

After a selected rinsing period, the supply of compressed air is stopped, whereby the filter particles in the turbulent layer settle. Naturally, the filter particles must have a greater specific gravity than the slurry particles. Moreover, the structure of the mutilayer filter must be such that the top filter layer contains filter particles having the smallest specific gravity and that the bottom filter layer contains the filter particles having the highest specific gravity, in order thus to counter any intermixing of the filter layers which is otherwise possible. The appropriate selection of the particle sizes of the filter layers is also of importance.However, it has been shown in practice that when using conventional filter materials it is quite possible to select filter materials such that the filter particles located in the turbulent layer settle comparatively quickly, or at any rate faster than the slurry particles, and such that, in addition, the settle process is such that the filter layers and their boundaries are maintained.

As soon as the filter particles have settled, compressed air is introduced into the vessel 10 via the line 18, with the result that the mixture of slurry and rinsing water is discharged via the dip pipe 14 and the discharge line 16. After discharging has been completed, the compressed air line 18 is closed again and once again rinsing water is passed via the line 22 through the multilayer filter 11 for rinsing purposes.

Before the rinsing process is carried out, it is advantageous to send a short burst of compressed air via the line 17 into the dip pipe 14 in order to clear its screen 14a of deposits.

Naturally, the processes described can be repeated as often as required in order to produce perfect cleaning even when the filter and vessel are heavily contaminated. However, in the repeat processes it is generally sufficient to supply compressed air only via the bottom nozzle pipe 19.

Figure 2 shows a second embodiment of the invention, wherein the basic arrangement corresponds essentially to the emodiment of Figure 1. For the sake of clarity, identical and similar components have the same reference numerals. The main difference between the embodiments is that the reaction vessel 10 is sub-divided into three portions, namely an inverted domed shaped bottom portion 10a, a cylindrical central portion 10b and a domed shaped upper portion 10c. The portions have, at the adjoining edges, flanges which are clamped together by flange clamps 30 and 31. Screens 32 and 33 are inserted between the flanges. Furthermore, the multilayer filter 11 is subdivided into two filter beds 1 la and 11 b. The lower filter bed 1 la which serves more particularly for absorption, rests on the lower screen 32, and the upper filter bed 11 b, which serves more particularly for filtration, rests on the upper screen 33. There is an air space between the two filter beds 1 la and 11 b. In order to be able to rinse both filter beds 1 1a and 11 b separately, in addition to the rinsing water and compressed air supply lines 22 and 23, there are provided further rinsing water and compressed air supply lines 22a and 23a, and, in addition to the rinsing water discharge line 16, a further rinsing water discharge line 16a.The supply lines 22 and 23, which serve to rinse the filter bed 11 a discharge into the bottom 1 0a of the vessel, and the additional supply lines 22a and 23a, for rinsing the fitler bed 11 b, discharge into the air space between filter beds 1 1a and 11 b. The discharge line 16 for the bed block 11a communicates with the air space between the filter beds 11 a and 11 b, and the discharge line 16a for the filter block 11 b communicates with the interior of the vessel cover 1 Oc.

The rinsing process is the same as that described with reference to Figure 1. Preferably, however, the two filter beds 11 a and 11 b are rinsed at different times. Advantageously, in the first instance, the upper filter bed 11b is rinsed in orderto remove its filter cake. However, the reverse procedure can also be carried out since, even when there is still filter cake on the filter bed 11 b it is possible to rinse the filter bed 11 a, in view of the presence of the discharge line 16 between filter beds 11 a and 11 b.

However, it is essential that at least when rinsing the upper filter bed 11 b, after compressed air has been passed through the compressed air supply line 23a, a stabilization period is allowed for the setting of filter particles, after which the aqueous slurry is forced out of the vessel 10 via the discharge line 16a by means of compressed air supplied via the supply line 18.

The subdivision of the vessel 10 into three portions 1 0a, 1 0b and 1 0c has the advantage that, if necessary, the vessel can be opened and both the screens 32 and 33 and the filter beds 11 a and 11 b can be cleaned manually. It is true that this advantage is offset by a considerably increased cost, since, in order to ensure that the vessel 10 is resistant to pressure, very exact flanged connections are required. In general, however, this construction cost is unnecessary since, when backwashing according to the method of the invention is carried out, manual intervention is not necessary.

In practice, therefore, the embodiment of Figure 2 is usually modified in that the subdividing the vessel is dispensed with. On the other hand, subdividing the filter into two or more filter beds is advantageous, more particularly as the aforementioned selection of the filter layers with regard to particle size and specific gravity is thereby facilitated. Furthermore, it is then unnecessary to have compressed air flow so vigorously through the lower filter bed or beds. In many cases, rinsing water alone suffices as a filter cake forms in the main only on the top filter bed.

Figure 3 shows a section through a multilayer filter cartridge, which can be inserted into the vessel 10 of the embodiments according to Figures 1 and 2. As shown in Figure 3, the multilayer filter 11 is disposed in a cylindrical container 40 which is closed at both ends by screen netting or mesh 41 and 42. The openings of the netting or mesh 41 and 42 are chosen so that they essentially secure the filter material during backwashing, although during normal purification ofthewash liquor they do not substantially affect the wash liquor flowing through the filter. In order to prevent, during backwashing, the rinsing water from flowing upwards between the container 40 and the inner wall of the vessel 10, thereby by-passing the filter 11, sealing rings 43 of soft elastic material, for example natural or synthetic rubber, are mounted on the container 40.

The use of a multilayer filter 11 in the form of a cartridge produces advantages in manufacture and in the insertion of the filter into the vessel. When separate filter beds, for example filter beds 11 a and 11 b according to Figure 2, are used, these can be housed in a common housing; in many cases, however, it is also advantageous to provide each filter bed with a separate housing 40,41 and 42. The individual cartridges are then stacked one above the other, with or without interspacing.

Finally, it is also possible to make the container 40 of a screen netting, thereby to enclose the filter 11 in a one-piece netting sack. However, in this case, also, it is of importance that sealing rings 43 be mounted on the lateral faces of the container. Naturally, it is also possible to mount the sealing rings 43 on the inside of the vessel wall and to provide such rings both on the container 40 and on the vessel 10, in order thereby to form a labyrinth seal.

Claims

1. A method of separating harmful or undesired matter from a liquid, which comprises selectively flocculating the harmful or undesired matter by adding a flocculating agent to the liquid and then absorbing and filtering the flocculated harmful or undesired matter by passing the liquid downwardly through a multilayer filter in a vessel, the multilayer filter being regenerated after a period of use by the following steps: (a) at least partially filling the vessel with rinsing liquid; (b) supplying compressed air to the multilayer filter and allowing itto rise through at least part of the mu Itilayer filter to break up the filter cake deposited on the multilayer filter and to form a turbulent slurry above the multilayer filter; (c) discontinuing the supply of compressed air to the multilayer filter and allowing the filter particles in the slurry to settle; (d) forcing compressed air into the vessel above the slurry thereby forcing the slurry out of the vessel; and (e) if desired rinsing the multilayer filter with fresh rinsing liquid.

2. A method according to claim 1, wherein the liquid is wash liquorfrom a bottle-washing machine.

3. A method according to claim 1 or 2, wherein the compressed air for breaking up the filter cake is supplied only to the upper layer or layers of the multilayer filter.

4. A method according to claim 1, substantially as hereinbefore described with reference to Figure 1, Figure 2, Figures 1 and 3, or Figures 2 and 3, of the drawings.

5. An apparatus for use in carrying out a method according to claim 1, the apparatus comprising a vessel having a multilayer filter therein, a first supply line for the supply of the liquid containing harmful or undesired matter to the upper region of the vessel, a second supply line for the supply of the flocculating agent to the upper region of the vessel, a first discharge line for the discharge of the liquid from which the harmful or undesired matter has been separated from the lower region of the vessel, a third supply line for the supply of either rinsing liquid or compressed air to the multilayer filter and connectable either to a supply of rinsing liquid orto a supply of compressed air, a second discharge line extending into the vessel and terminating in the vicinity of the upper surface of the multilayer filter for the discharge of the flocculated harmful or undesired matter from the vessel and for the discharge of the liquid containing harmful or undesired matter from the vessel, and a fourth supply line for the supply of compressed air to the upper region of the vessel.

6. An apparatus as claimed in claim 5, wherein the third supply line is connected to a nozzle pipe in the lower region of the vessel.

7. An apparatus as claimed in claim 6, wherein one or more additional nozzle pipes are arranged above said nozzle pipe, and wherein the apparatus further comprises a fifth supply line connected to the or each additional nozzle pipe for the supply of compressed air thereto.

8. An apparatus as claimed in any of claims 5 to 7, wherein the mouth of the second discharge line is provided with a filter, and wherein the apparatus further comprises a sixth supply line for the supply of compressed air to the second discharge line.

9. An apparatus as claimed in any of claims 5 to 8, wherein, outside of the vessel, the second discharge line branches into two lines, namely a line for the discharge of the flocculated harmful or undesired matter and a line for the discharge of the liquid containing harmful or undesired matter.

10. An apparatus as claimed in any of claims 5 to 9, wherein all of the supply and discharge lines are provided with separately-controllable valves.

11. An apparatus as claimed in claim 10, wherein the valves are solenoid valves.

12. An apparatus as claimed in any of claims 5 to 11, wherein the multilayer filter is subdivided into at least two filter beds each having associated therewith a supply line for the supply of either rinsing liquid or compressed air to the respective bed and a discharge line for the discharge of rinsing liquid and compressed air from the respective bed.

13. An apparatus as claimed in any of claims 5 to 12, wherein the vessel is subdivided into portions adjacent ones of which are connected in a pressuretight manner by flanged connections.

14. An apparatus as claimed in claim 13, wherein one or more screens extend across the vessel, the periphery of the or each screen being held within the flanges of one or said flanged connections.

15. An apparatus as claimed in any of claims 5 to 14, wherein the multilayer filter is housed in a substantially cylindrical housing having one or more peripheral sealing rings.

16. An apparatus as claimed in claim 15, wherein one or more additional sealing ring or rings are disposed on the inner wall of the vessel.

17. An apparatus as claimed in claim 15 or 16, wherein the housing comprises a tubular member having a mesh at each end.

18. An apparatus as claimed in claim 15 or 16, wherein the housing comprises a single sack-like member made of mesh.

19. An apparatus as claimed in any of claims 15 to 18, wherein the multilayer filter comprises a plurality of filter beds stacked one upon another, each bed having a separate housing.

20. An apparatus as claimed in any of claims 5 to 19, wherein the upper layer of the multilayerfilter comprises a material having a particle size and specific gravity such that its rate of deposition in the slurry is higher than that of the harmful or undesired matter but lower than that of the filter material of the lower layer or layers of the multilayer filter.

21. An apparatus substantially as hereinbefore described with reference to, and as shown in, Figure 1, Figure 2, Figures 1 and 3, or Figures 2 and 3, of the drawings.