WO1993007950A1

WO1993007950A1 - Granulated filter for the filtration of fine graded suspensions

Info

Publication number: WO1993007950A1
Application number: PCT/SE1992/000738
Authority: WO
Inventors: Karl Dunkers
Original assignee: Ingenjörsbyrå Karl Dunkers
Priority date: 1991-10-25
Filing date: 1992-10-24
Publication date: 1993-04-29
Also published as: AU2897592A

Abstract

The invention relates to a filter element for the filtration of a suspension containing pollutants in which the suspension is arranged for a substantially horizontal flow direction through the filter bed. The filter element comprises at least one inlet chamber (2) for the suspension, one outlet chamber (3) for collecting a filtered solution and at least a filter bed (1), which is substantially vertically arranged between permeable walls and located between the inlet chamber (2) and outlet chamber (3) for filtering the pollutants from the suspension entering the filter bed (1) in the flow direction from the inlet chamber (2) and directing the filtered solution into the outlet chamber (3), the filter bed (1) including a granular filter media with particle sizes less than about 0.6mm. The filter also comprises means (6, 7, 8) for washing the granular filter media, said means communicating with said filter bed (1) to separate the pollutants from the granular filter media and return the granular filter media to the filter bed (1) and means for washing at least one of the filter walls and wherein the vertically arranged filter bed (1) is substantially flat and the filter element is so formed as to provide possibility of arranging several such elements in modules and that the depth of said bed is less than 12 cm in the flow direction.

Description

GRANULATED FILTER FOR THE FILTRATION OF FINE GRADED SUSPENSIONS

BACKGROUND OF THE INVENTION

This invention relates to a granulated filter for the filtration of a suspension containing pollutants in which the suspension is arranged for a substantially horizontal flow direction through the filter bed which comprises at least one inlet chamber for the suspension, one outlet chamber for collecting a filtered solution, at least a filter bed, which is substantially vertically arranged between permeable walls and located between the inlet and outlet chambers for filtering the pollutants from the suspension entering the filter bed in the flow direction from the inlet chamber and directing the filtered solution into the outlet chamber, the filter bed including a granular filter media with particle sizes less than about 0.6 mm, means for washing the granular filter media, said means communicating with the filter bed to separate the pollutants from the granular filter media and to return the granular filter media to the filter bed and means for washing at least one of the filter walls. Such a filter is known from EP-B 1-2 1 538.

The invention is aimed at a granulated filter having the capability for removal of very fine particles from suspensions. The filter combines the advantages of efficiency in reusing the filter media through a backwash operation and a favorable economy due to an extreme low filter bed depth.

Recent environmental requirements are leading the developments of new filtration technology towards the task of fine particle removal within the municipal sewage treatment field and the industrial wastewater treatment field as well.

The existing technique for filtration of fine particles is mainly based on membrane filters and/or cartridges. While the cartridges may have small particle sizes and low filter bed depths, the filter media can not be backwashed in regular sequences, they have low flow capacities and they can not be arranged for large-scale installations within reasonable investment cost limits.

Other filters in the market are those with granular filter beds. The filter media are usually sand in different mesh sizes, anthracite, dolomite, activated carbon, etc. These filter beds can mostly be arranged for backwashing either in sequences or continuously. The filter beds can be loaded with much higher flow rates than what is possible for the membrane and cartridge filters. Consequently, the granular filters are more economical due to the operation costs and investment costs as well. However, a substantial disadvantage is the fact that existing granular washable beds cannot be arranged for filtration of fine-particles. The physics of the granular beds, the filter arrangement itself and the washing procedure do not make the filtration of fine particles possible. SUMMARY OF THE INVENTION

Filter techniques in accordance with this Invention will make it possible to achieve excellent fine-particle filtration efforts in washable beds without having the above mentioned disadvantages regarding membrane/- cartridge filters and conventional granular filter beds as well.

In figure 7 comparison is made between the conventional flat filter bed and the vertically arranged filter bed according to the invention. In a vertical flow filter system the majority of pollutants are trapped by the top layer while in a horizontal flow filter system according to the invention the filter material is separated into several filters each having the filtering capacity of the top layer in the shown vertical flow filter system. By using microsand of the type employed according to the invention also much smaller particles may be trapped. To remove the particles from the said, the filter media washed and then replaced on top of the uppermost part of the filter media. This also removes the danger of stratification in the filter media.

The object of the Invention is to provide a granulated filterbed, which can be adapted to different sizes of filter plants and which is space- reducing. Furthermore, a high degree of cleaning of the filter should be provided, said filter having provisions for the cleaning of the filter media, e.i. the granules, and for the cleaning of at least the permeable wall of the filter facing the inlet chamber, e.i. the outside of the bed encasement.

This object is attained according to the invention by the fact that the vertically arranged filter bed is substantially flat and the filter element is so formed as to provide possibility of arranging several such elements in modules and that the depth of said bed is less than 12 cm in the flow direction.

Other preferred embodiments of the invention are made the subject of the characterising parts of the subclaϊms.

This invention refers to a granular filter bed with particle sizes less than about 0.6 mm (600 microns) and where the filter bed depth - in the flow direction - is less than about 12 cm and the filter bed is encased between two mainly vertical and permeable walls. The suspension to be filtered is forced to flow mainly horizontally through the filter bed.

By reducing the particle size, the bed depth can be reduced accordingly while still maintaining the good filtering efficiency. As the particle size of the filter bed is reduced a better filtering effect will be accomplished as to the smallest parts of he suspension being filtered.

When decreasing the particle size in filter beds, the hydraulic loss of head will increase exponentially. Therefore, if fine bed particles, less than about 0.6 mm (600 microns) were used in conventional filter beds, then the hydraulic flow capacity would be extremely low. Consequently, in fine-particle filter beds it is necessary to decrease the bed depth down to values which are small enough to avoid unreasonable high hydraulic loss of head due to filter resistance.

Filter bed tests with this technique have shown that the depth in fine-particle beds can be decreased down to less than about 12 cm, even to ranges in order of 4-10 cm, while still maintaining an excellent filtration capacity as to filtered suspension particles. On the other hand, it is necessary to increase the filter area substantially in comparison with conventional filter beds.

The filtration capacity in this invention is further improved by the horizontal flow through the filter bed. High amounts of standardized vertical filter modules arranged in lines close to each other gives a favorable filter plant total capacity at relatively low specific costs.

A horizontal flow through filter bed is known before, for example from the Patent SE 378 361. Nota bene, this patent deals with sand filters having conventional particle sizes and conventional filter bed depths as well. Therefore, this filter is limited to applications only where conventional suspension particle sizes are to be removed, but it is not applicable within the defined technical fields of micro-filtration, ultrafiltration or membrane filtration. BRIEF DESCRIPTION OF THE DRAWINGS

This invention is characterized by the attached claims and it is further illustrated in the attached figures, wherein:

Fig. 1 is a side view of the granulated filter according to the invention;

Fig. 2 is a vertical cross-sectional view of the filter of Figure 1 taken along the line A A of Fig. 1; and Fig. 3 is a detailed view of the water supply system to the air lift pipe, i.e the mammoth pump.

Fig. Ψ is a view of the backwashing arrangement for backwash of the permeable fabric on the inlet side.

Fig. 5 is a top view of the filter.

Fig. 6 is a vertical section of a filter according to the invention in a direction perpendicular to the planes of the f ilterelements.

Fig. 7 is a schematic drawing showing the difference between a horizontal filter bed in accordance with the state of the art and the filter elements according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 shows an elevation through a group of filters beds 1 arranged mainly in vertical position and parallel to each other. This arrangement represents a preferred application of the invention.

On one side of each filter bed 1 is the inlet chamber 2, where the inlet suspension having pollutants therein will be fed. On the other side is the outlet chamber 3, where the filtered solution (the filtrate) is collected. According to Fig. 1, each outlet chamber 3 is serving two substanially flat filter beds 1 on both sides. These filter beds may also be slightly curved. Each bed 1 is fed with inlet suspension from the adjacent inlet chamber 2. This arrangement improves the filtration efficiency due to the decreased flow velocity on the inlet side. All inlet and outlet chambers are closed by top covers which enable each chamber to be under a certain desirable overpressure during operation and/or washing sequences.

The filter media consists of either sand or any of the above mentioned granular filter media. According to this Invention, the particle size should however not exceed about 0.6 mm (600 microns). Preferably it shall be within the range of 0.05 to 0.50 mm. This range has been noticed in tests as the optimum, which means highest possible fine-particle filtration efficiency at lowest loss of head and lowest washwater consumption.

Referring to Fig. 1, the filter bed depth is defined as the horizontal distance the suspension has to flow through the bed 1. In order to achieve the highest possible filtration flow capacity and filtration removal capacity as well, the bed depth has to be selected in a certain relation to the particle size of the filter media. Consequently, at filtration of normal fine-particle suspensions, the bed depth shall preferably be in the range of about 6 to 10 cm when using bed particles within the range of about 0.1 to 0.5 mm.

The mainly parallel intermediate walls which surround the filter bed are equipped with flow-through openings 5 covered with permeable fabric supported by a perforated steel plate and/or netting wire. The permeable fabric shall be tight enough for avoiding any escape of the granular filter bed media.

Figure 2 shows a cross section through the filter bed 1 with the flow-through openings 5 including the fabrics and the supporting plates and nets. Figure 2 further illustrates one possible way for washing the bed media. An air lift pipe 6 communicates with the filter bed 1 and transports the filter bed media from the bottom to the top. The washwater is pumped through nozzles 7 into a base of the lift pipe 6. The transporting action is caused by feed of compressed air through pipes 8 into the base of the air lift pipe 6. During this pumping and transportation action, the filter media is thoroughly washed. After being washed in the air lift pipe 6, the bed media is equally distributed over the bed surface by means of openings 9. Any air bubbles will discharge upwards through the open end 6A of the pipe 6 located in an extension of the pipe above the opening 9. The washed pollutants (the reject) will rise with the washwater stream toward the surface, be withdrawn through overflow weir channels 10 and then discharged from the system. The washing system can be arranged for either continuous or intermittent operation. That is, the washing apparatus can operate when the suspension is flowing in the flow direction for filtering or when the flow of suspension is interrupted.

Figure 3 shows one arrangement of the mammoth pump according to the invention where the water is injected through nozzles 7 separetely and in a direction which is at angles with both the direction of the injected air 8 and the air lift pipe 6. It should not be restricted to the angle shown in figure 3. Other angles can we used as well.

Other additional washing devices can be arranged in the filter. For instance, the permeable fabric on the inlet chamber side can be separately rinsed by means of fixed rinsewater nozzles fed by a separate pipe/valve system. The outlet chamber side of the filter may, of course, also be rinsed in a similar manner.

Backwashing of the filter bed and fabrics can take place simultaneously or separately with the above mentioned fabric rinsing with nozzles.

Figure shows a system for backwashing of the filter, which in this embodiment shows two filter elements combined in a mirror arrangement having the outlet chamber 3 In common. This backwashing system needs corresponding pipes and valves. The backwashing is accomplished with a flow of backwashwater from the outlet chamber 3 through the bed and into the inlet chamber 2 for further discharge. The inlet chamber 2 is provided with a pipe 12 and corresponding valve 12a for the inlet of the suspension to be filtered. There is also a disharge pipe 15 and corresponding valve 15a for the disharge of the backwashing liquid, which normally consist of water. In the outlet chamber 3 there is provided an outlet pipe 13 with corresponding valve 13a for the outlet of the filtrate and a inlet pipe 1* for backwash water and corresponding valve 14a. The backwashwater has to be fed at a sufficient overpressure. For the nozzle rinsing of fabrics and/or the fabric backwashing, the filter operation has to be shut off. However, during the washing through the air lift pipe, the regular filter operation can go on.

During the use of the filter for filtering purpose the inlet valve 12a for the suspension is open and also the outlet valve 13a for the filtrate. During the backwashing of the filter these valves 12a and 13a are closed and the valve 14a is opened to let the backwash water enter the outlet chamber 3 and the valve 15a is opened to let the backwash water leave the inlet chamber 2.

Figure 5 shows a top view with the filter beds 1, the inlet chambers 2 and the outlet chambers 3, all arranged in modules in one line close to each other. The air lift pipe 6 is here illustrated with a rectangular cross section. It can however be alternatively made with a circular cross- section. Figure 3 further illustrates the overflow weir channels 10 where the air lift washwater will be discharged. According to Figure 3, the filter modules are coupled by means of bolts and flanges 11. Each module consists of two beds 1, two inlet chambers 2 and one outlet chamber 3. The amount of individual modules and amounts of module rows form together the size and capacity of the filtration plant. The auxiliary equipment, consisting of pipes, valves, switches, timers, etc. can be installed close to each module.

Figure 6 illustrates how the narrow spaced and vertically arranged filter bed system gives an optimized total filter area on a certain available volume. This filter system does not have any limitations as to unit dimensions. It can therefore be installed even for very large-scale plants operating for microfiltration and ultrafiltration as well.

This fine granular filter system is suitable for several applications as the final or polishing stage for use in industrial wastewater, drinking water, sewage water, lake water and stormwater treatment plants. The pilot plant test results obtained are excellent, indicating a phosphorous and suspended solids removal of 80-90%, bacteria removal of 62% and algae mass and chlorophyll A removal of 75% for a bed depth of 4 cm and a particle size of about 0.0 to 0.5 mm.

Although this description has dealt with a preferred application of this filtration system (which is not intended to be limiting), there is a mulitude of applications recognized by those skilled in the art. Various changes and modifications may therefore be made without departing from the scope of the appended claims. As for instance, the filter beds can be arranged for a certain inclination still having a hydraulic crossflow pattern. Furthermore, the amount and the location of the inlet chamber -filter bed - outlet chamber within a module can be arranged as to different alternatives.

Claims

CLAIMS 1. A filter element for the filtration of a suspension containing pollutants in which the suspension is arranged for a substantially horizontal flow direction through the filter bed comprising: at least one inlet chamber (2) for the suspension; one outlet chamber (3) for collecting a filtered solution; at least a filter bed (1), which is substantially vertically arranged between permeable walls and located between the inlet chamber (2) and outlet chamber (3) for filtering the pollutants from the suspension entering the filter bed (1) in the flow direction from the inlet chamber (2) and directing the filtered solution into the outlet chamber (3), the filter bed (1) including a granular filter media with particle sizes less than about 0.6 mm; means (6,7,8) for washing the granular filter media, said means communicating with said filter bed (1) to separate the pollutants from the granular filter media and return the granular filter media to the filter bed (1); and means for washing at least one of the filter walls, characterized in that the vertically arranged filter bed (1) is substantially flat and the filter element is so formed as to provide possibility of arranging several such elements in modules and that the depth of said bed is less than 12 cm in the flow direction.2. The filter element of claim 1, characterized in that the element is so formed as to be arranged in modules have their substantially plane filter beds arranged parallell to each other3. The filter element of claim 1 or 2, characterized- in that the granular filter media includes granules with a particle range from 0,05 to 0,50 mm and a bed depth of 4 to 10 cm.4. The filter element of claim 1, 2 or 3, characterized in that the the means (6,7,8) for washing the granular filter media is a mammoth pump, which can be used while the suspension flows in the flow direction.5. The filter element of claim 4, characterized in that the mammoth pump may be used continously or intermittantly.6. The filter element of claims 4 or 5, characterized in that the mammoth pump comprises an air lift pipe (6) defining an opening at the bottom portion and an opening at the top portion said opening at the bottom portion communicating with the granular filter media; pumping means for introducing washing water into the bottom portion of the air lift pipe for washing and/or transporting purposes; transport means for directing said water and granular filter media from the bottom portion to the top portion of the air lift pipe; and separation means for separating the water and pollutants from the granular filter media and returning the granular filter media to the filter bed.7. The filter element of any of the preceeding claims, characterized in that said means for washing at least one of the walls comprises at least one inlet (14) for backwash water which opens into the outlet chamber (3) and a discharge pipe (15) for the used water from the inlet chamber (2), the means operated in such a way that the backwash water entering the outlet chamber (3), flows through said bed (1) and is discharged from the inlet chamber (2).8. The filter element of any of the claims 1 to 6, characterized in that said means for washing at least one of the walls comprises fixed wash water nozzles to clean the wall facing said nozzles. AMENDED CLAIMS[received by the International Bureau on 25 March 1993 (25.03.93); original claims 1-8 replaced by amended claims 1-8 (2 pages)]

1. A substantially flat filter element for the filtration of a suspension containing pollutants in which the suspension is arranged for a substantially horizontal flow direction therethrough, comprising: at least one inlet chamber (2) for the suspension; one outlet chamber (3) for collecting a filtered solution; at least one filter bed (1) which is substantially vertically arranged between permeable walls and located between the inlet chamber (2) and outlet chamber (3) for filtering the pollutants from the suspension entering the filter bed (1) in the flow direction from the inlet chamber

(2) and directing the filtered solution into the outlet chamber (3), said filter bed (1) including a granular filter media with particle sizes less than about 0.6 mm; first means (6,7,8) for washing the granular filter media communicating with said filter bed

(1) to separate the pollutants from the granular filter media; and second means for washing at least one of the filter walls; said filter being so formed as to provide possibility of arranging several such elements in modules and the depth of said bed is less than 12 cm in the flow direction, c h a r a c t e r i z e d in that said first means (6,7,8) for washing the granular filter media comprises a mammoth pump having an air lift pipe (6) defining a first opening at the bottom portion thereof communicating with the granular filter media, second openings

(9) at the top portion thereof, and a third opemng (6A) at the top end thereof for discharge of air bubbles, and separation means (9, 10) for separating the wash water with pollutants from the granular filter media and returning the granular filter media to the filter bed, whereby after being washed in the air lift pipe (6), the filter media is equally distributed over the filter bed surface by means of said second openings (9).

2. The filter element of claim 1, c h a r a c t e r i z e d in that said second means for washing at least one of the walls comprises at least one inlet (14) for backwash water which opens into the outlet chamber (3) and a discharge pipe (15) for the used water from the inlet chamber (2), the means operated in such a way that the backwash water entering the outlet chamber (3), flows through said bed (1) and is discharged from the inlet chamber (2).

3. The filter element of claim 1 or 2, characterized in that said second means for washing at least one of the walls further comprises fixed wash water nozzles to clean the wall facing said nozzles.

4. The filter element of claim 3, characterized in the said second means for washing may be provided on the inlet and/or the outlet chamber side.

5. The filter element of any of the claims 1 to4, char cterize din that the element is so formed as to be arranged in modules having their substantially plane filter beds arranged parallel to each other.

6. The filter element of any of the claims lto5, characterizedin that the granular filter media includes granules with a particle range from 0,05 to 0,50 mm and a bed depth of 4 to 10 cm.

7. The filter element of any of the preceeding claims, characterized in that the mammoth pump is used intermittently.

8. The filter element of any of the preceeding claims, characterized in that the mammoth pump comprises an air lift pipe (6) defining an opening at the bottom portion and an opening at the top portion, said opening at the bottom portion communicat¬ ing with the granular filter media; pumping means for introducing washing water into the bottom portion of the air lift pipe for washing and/or transporting purposes; and transport means for directing said water and granular filter media from the bottom portion to the top portion of the air lift pipe. STATEMENT UNDER ARTICLE 19

The claims of the International Application PCT/SE92/00738 filed on the 24th of October, 1992, in the name of Ingenjόrsbyra Karl Dunker et. al. has been revised taking into account the relevant priot art as revealed in the International Search Report.

In amending the claims the cited DE, A, 2136877 (Bohna Engineering & Resarch Inc.) has been decided upon as being the closest relevant prior art. The subject-matter of claim 1 has been properly delimited from the disclosure of DE, A, 2136877.

The subject matter of the new claims have full support in the original description, claims and figures as filed.