GB2080694A - A granular material filter - Google Patents

Abstract

The filter includes a bed of granular material resting on an impervious flat supporting surface, and a single manifold (8) provided with branches (9) also rests on the surface and serves for draining the filtrate and for supplying reverse flow air and water to the bed. Separate pipes are provided for the delivery of air to manifold (8) and for the discharge of treated water and for the delivery of washing water. Nozzles (10 and 11) are provided at the upper regions of the manifold (8) and its branches (9) and are mounted in such a way that slits (16) provided at their lower ends are all et the same level inside the manifold and its branches. <IMAGE>

Description

SPECIFICATION A granular material filter The present invention relates to granular material filter and particularly concerns such a filter of the type which comprises one or more layers of granular filtering material arranged in a chamber, an inlet for water to be treated above the bed of filtering material,as well as a recovery means for treated water and a washing device arranged at the base of the filtering mass.

Known granular material filters take the form either of an open chamber made, for example, of concrete or of a metallic or plastics closed chamber.

The correct functioning of these filters depends, among other factors, on the perfect distribution through the filtering mass ofthe water to be filtered and the washing fluids, water or air and water injected successively or simultaneously. The bed of filtering materials rests either on a floor surmounting a space for recovering the filtered water and for introducing washing fluids, or on the bottom of the filter constituted by a layer of granular materials of large granulometry or a layer of concrete.

It has been known for a long time that the most efficient method of washing a granular material bed filter is by washing it with air and with water injected into the filtering mass from bottom to top.

If the filtering material rests on a floor, this washing operation is generally performed using nozzles fixed in perforations made in this floor. These nozzles comprise a hollow rod which has one or more vertical slits at its bottom and is immersed in the space situated beneath the floor and in which the washing air and water are injected, and a perforated head emerging above the floor in the filtering mass.

It is well known that this arrangement is unsuitable for filtering a fluid which is very likely to cake and/or is corrosive. In fact, the perforated plate constituting this floor is subjected at the end of the filtration cycle to a high differential pressure corresponding to the loss of charge due to the flow of the fluid through the filtering mass, and, in the case of a filter operating under pressure of which the bushes might accidentally be obstructed, at the operating pressure of the said filter which may amount to several bars. In this case, this floor should be reinforced by vertical iron bars, producing a very heavy and very inconvenient structure.

Moreover, if the fluid to be filtered is of a corrosive nature, all the parts of the filter in contact with it must be provided with a coating which is inert to corrosion and which must be applied in a particularly careful manner. It is well known that the operations involved in applying this coating and in the preliminary preparation of the surfaces inside the space limited by the bottom of the filter and the underside of the floor are very awkward and inconvenient. Owing to the difficulty of these operations, measures have to be taken to permit periodic inspection of the state of the coating of this space.

To overcome the disadvantages of this arrangement, it is generally proposed either to produce an impervious floor resting on a certain number of supports transmitting to the bottom of the apparatus the stresses generated by the operating pressure due to the flow through the granular material, or to fill the bottom of the filter with an inert concrete which, in this case too, transmits to it the stresses due to the charge pressure. In both cases, there will be arranged on the flat surface made up in this way a first collector provided with perforated branches allowing collection of the filtered fluid and distribution of the washing water and, above it, a second collector also provided with perforated branches and intended to distribute the washing air.If the fluid to be filtered is corrosive, these distribution units can be produced from plastics or metal protected by an anti-corrosion coating and, in this case, the coating can be made outside the filter without difficulty.

However, this last solution has four main disadvantages: i) it is inconvenient as it necessitates the use of two distribution systems; ii) it does not permit the distribution of a water and air admission at the moment of washing since the two fluids are injected separately. The washing operation is not therefore as effective as that obtained with a floor with nozzles; iii) the distribution of air and water is generally allowed only through the branches, so the material arranged above the collectors is poorly washed.If the collectors themselves are perforated, it is difficult to distribute the fluids well owing to the difference in level between the collector and its branches; iv) it necessitates the arrangement between the two distribution systems of a layer of granular material of sufficient granulometry not to expand under the influence of the flow of washing water but not so large as to prevent penetration of the filtering layer in its pores.

It is an object of the invention to provide a granular material filter which overcomes the disadvantages of the two arrangements described above.

The filter according to the invention comprises a granular material filter comprising means placed beneath a bed of granular material for recovering the filtered water and for simultaneously intrdoucing washing air and water in order to permit countercurrent washing of the bed of granular material, said means comprising a single collector provided with branches and resting on an impervious supporting surface, a pipe for the intake of washing air, and a pipe for the discharge of treated water and the intake of washing water, the collector and its branches bearing at their upper regions nozzles of a known type arranged in such a way that slits provided at their lower ends are all at the same level inside the collector and its branches.

This arrangement permits good distribution of the water to be treated during filtration by allowing preferential passages and dead zones in the filtering mass to be avoided. It also permits the distribution of a water and air emulsion which is well distributed during the washing operation with a flow of air and of water which is strictly identical for each nozzle, whether it is fixed on the collector or on its branches.

The pipe for the intake of washing air can open out at the top of the collector or can be lateral. The pipe for the intake of washing water can open out at the bottom of the collector or at the top thereof.

The impervious supporting surface can be constituted by a floor or by a concrete filling arranged on the bottom of the filter.

The nozzles borne by the branches are preferably identical to those borne by the collector. The heads of the nozzles are thus also at the same level.

In an advantageous embodiment of the invention each nozzle is mounted in an orifice in the upper end of the collector or of one of the branches thereof by means of an expandible ring fitted in a collar, a collar and ring mounted on the collector being smaller in height than a collar and ring mounted on a branch thereof.

An embodiment of a filter according to the invention will now be described as a non-limiting example with reference to the attached drawings.

Figure 1 shows a sectional view of the filter, and Figure 2 is a cross-sectional view of the collector to the right of its connection to a pair of branches.

As shown in Figure 1, the filter comprises a closed metal chamber 1 containing a bed of granular materials 2 resting on an impervious floor 3 the flatness of which is ensured by concentric supporting ferrules 4 which transmit the pressure stress on to the curved bottom la of the filter.

This chamber is provided with a pipe 5 for the intake of the water to be treated and the discharge of washing water, with a pipe 6 for the discharge of treated water and the intake of washing water, and with a pipe 7 for the intake of washing air.

A collector 8 which is diametrical in this case rests on the floor 3. It comprises a plurality of branches 9.

The collector and the branches are provided with nozzles 10 and 11 respectively of which the heads all emerge at the same level in the bed of granular materials 2. The pipes 6 and 7 open into the collector 8, at its bottom and its top respectively, whereas the pipe 5 opens into the top of the chamber 1.

The nozzles 10 and 11 are identical. Each one comprises a head 12, which is provided with a number of slits 13 and communicates with a tube 14.

The tube 14 has a hole 15 at its upper end and a slit 16 at its lower end.

Each of the nozzles is surrounded by a plastics collar 17 or 17' which is mounted directly on the collector or on one of its branches with its lower face perfectly matching the shape thereof whereas its upper face is flat. This collar has an axially extending hole which coincides with the orifice provided in the upper wall of the collector or of the branch forte passage of the tube 14 of the nozzle. An expandible ring 18 or 18' is arranged in the hole of each collar and surrounds the tube 14 of the nozzle with clearance. The ring 18, 18' comprises a flange 18a or 18'a which is interposed between the collar and the head 12 of the nozzle. The lower portion of the ring is expanded and permits the mechanical locking of the assembly and maintains the imperviousness.

The collar 17 and the ring 18 are smaller in height than the collar 17' and the ring 18' respectively so that, in spite of the difference in level of the order of from 40 to 50 mm existing between the upper wall of the collector 8 and that of a branch 9, the heads 12 of the nozzles are at the same level. Since the nozzles are identical, their slits 16 are also at the same level.

During filtration, the liquid to be fiiterest is intro duced via the pipe 5, is filtered via the bed 2, enters the branches 9 and the collector 8 via the nozzles 10 and 11 and is removed via the pipe 6.

the moment of washing, washing air and wash ing water are introduced into the collector via the pipe 7 and via the pipe 6 respectively. An air cushiion 19 is formed inside the collector 8 and the branches 9 above the washing water 20, the level of separation being substantially half way up the slits 16. The air and water form an emulsion which traverses the tubes 14 of the nozzles and to which there is added air which enters into the tubes 14 via the holes 15 and then enters into the bed 2 via the slits 13. Since the slits 16 are at the same level, the air to water ratio of the emulsion is the same for each nozzle.

The collector 8 and its branches 9 as well as the nozzles 10 and 11 are made of metal or plastics material.

In one arrangement of the invention, the collector and its branches have a rectangular cross-section. In this case, the collar situated on the collector is omitted if desired.

Instead of the floor 3, an impervious supporting surface for the collector may be constituted by a concrete filling arrangement at the bottom of the filter.

Afilter according to the invention is particularly suitable for the filtration of sea water on off shore platforms. In fact, it combines the advantages of reduced bulkiness and weight with the efficiency of simultaneous air and water washing.

Claims (7)

1. Agranular material filter comprising means placed beneath a bed of granular material for recovering the filtered water and forslmuftaneously intro ducing washing air and waterin order to permit counter-current washing of the bad of granular material, said means comprising a single collector pro vided wiffi branches and resting on an impervious supporting surface, a pipe for the Intake of washing air, and a pipe for the discharge of treated water and the intake of washing water, the convector and its branches bearing at their upper regions nozzles of a known type arranged in such away that slits provided at their lower ends are all at the same level inside the collector andes branches.

2. A fi Iter as claimed in claim 1, wherein the imprevious supporting surface is constituted by a floor.

3; A filter as claimed in claim I t wherein the impervious supporting surface is constituted b# a concrete filling arranged atthe bottormofthefiilter.

4. A filter as claimed in any one of lhe preceding claims, wherein the nozzles borne bvlihe branches are identical to tbenozzles bome byte collector.

5. A filter as daimed in any one Qf the pre~dingo claims, wherein each nozzle is mounted in an orifices.

in the upper end ofthe collector or of one of the branches thereof by means of an expandible ring fitted in a collar, a collar and ring mounted on the collector being smaller in heightthan a collar and ring mounted on a branch thereof.

6. A filter as claimed in claim 5, wherein the expandible rings and collars are of plastics material.

7. Use of the filter as claimed in any one of the preceding claims for the filtration of sea water or corrosive liquids.