WO2001003808A1

WO2001003808A1 - A filter bag and an air filter device

Info

Publication number: WO2001003808A1
Application number: PCT/DK2000/000374
Authority: WO
Inventors: Arne Grønbæk JENSEN; Keld Christensen
Original assignee: Simatek A/S
Priority date: 1999-07-09
Filing date: 2000-07-07
Publication date: 2001-01-18
Also published as: AU5805800A; DE20080312U1

Abstract

A filter bag (5) for vertically suspension in an air filter device (1). The filter bag (5) comprises suspension means positioned inside the filter bag (5) and comprises an elongate, tube-shaped, flexible outer skirt (18) manufactured from a substantially liquid impermeable sheet material and a bottom part at one end of said elongate, tube-shaped, flexible outer skirt (18). The bottom part comprises means that allows a liquid to leave the filter bag (5) under influence only of gravity and/or air pressure provided inside the filter bag (5). Furthermore, an air filter device having such a filter bag is provided.

Description

A filter bag and an air filter device

The invention relates to a filter bag for vertically suspension m an air filter device, said filter bag compris- ing suspension means positioned inside the filter bag, said filter bag comprising an elongate, tube-shaped, flexible outer skirt manufactured from a substantially liquid impermeable sheet material and a bottom part at one end of said elongate, tube-shaped, flexible outer skirt. The invention further relates to an air filter device comprising such filter bags.

Air filter devices are used m a number of industries for separating dust and powdered material from a stream of air. The air stream typically comes from a spray drying device or the like and may be milk powder, powder for the pharmaceutical industry, etc. Air filter devices are also used m other applications, such as smoke cleaning, and the air may be atmospheric air or other gasses.

An air filter device generally comprises a housing divided by a separating wall into a dusty air chamber and a clean air chamber. In the air filter device according to the invention the separating wall is positioned horizon- tally, having the dusty air chamber positioned below the separating wall and the clean air chamber above the separating wall. The separating wall is provided with a number of openings and filter elements, e.g. filter bags, are suspended m the openings and extend into the dusty air chamber. The dusty air chamber is provided with an air stream inlet and a powder outlet and the clean air chamber is provided with an air stream outlet.

In use, an air stream containing powdered material is fed into the dusty air chamber via the air stream inlet. Heavy powdered material immediately falls against the bottom of the chamber where they can be removed through the powder outlet. The air stream containing powdered ma- terial is forced through the filter elements that are suspended from the separating wall and due to the filter material used m the filter elements the powder m the air stream is deposited on the outside of the filter elements. The cleaned air m the clean air chamber leaves the air filter device through the clean air outlet.

The powder material deposited on the outside of the filter elements has to be removed regularly m order to keep the air filter device running. Removal of deposited mate- rial is achieved by regularly providing rinsing air pulses m the opposite direction into each filter element. Thereby the powder material deposited on the outside of each filter element is ^Xblown off" and the filter element recovers its filtering efficiency.

It is also known to wet clean the filter elements by ap^¬ plying a rinsing liquid to the outside of the filter ele^¬ ments which may be accomplished without removing the fil^¬ ter elements from the filter device, the so-called clean- mg in place or CIP. If a thorough CIP is required it is possible also to apply a rinsing liquid to the interior of each filter element. A CIP method of this type is disclosed in e.g. US-A-5, 795, 359.

In general, applying a rinsing liquid to the interior of a filter element is only feasible if the filter material is liquid permeable such that the rinsing liquid can leave the filter elements through the filter material. If the filter material is not - or hardly not - liquid permeable, it would be chosen not to provide a rinsing liq- uid to the interior of the filter elements.

However, EP-Al-0, 572, 356 discloses filter device provided with CIP means for applying rinsing liquid to the interior of filter elements provided with a filtering mate- rial that may be liquid impermeable. In this filter device each filter element is provided with a manually operated valve positioned m the bottom part of the filter element. After the rinsing liquid has been applied to the interior of the filter element, the valve is opened and the rinsing liquid is allowed to leave the filter element through the open valve. This arrangement, however, requires control and operation means for opening the valve at the correct time during the cleaning process.

It is an object of the present invention to provide a filter bag as mentioned m the opening paragraph which is suitable for interior cleaning with a rinsing liquid without having the drawbacks described above.

It is a further ob ect of the invention to provide an air filter device having means for CIP cleaning without having the drawbacks described above. The first object is achieved by providing the air filter bag mentioned m the opening paragraph m such a way that the bottom part comprises means that allows a liquid to leave the filter bag under influence only of gravity and/or air pressure provided inside the filter bag.

Thereby it is ensured that a rinsing liquid applied to the interior of the filter bag is able to leave the fil- ter bag through the bottom part without use of any mechanical means that must be operated manually.

In a preferred first embodiment the bottom part consists of a flexible sheet material that is substantially more liquid permeable than the sheet material that constitutes the elongate, tube-shaped outer skirt. In this embodiment the filter bag is very simple and has an appearance that is very similar to ordinary filter bags, though it is made of to different materials having different perme- abilities.

A filter bag of this type may preferably have an elongate, tube-shaped outer skirt that is manufactured from a material having a layer of polytetrafluorethylene (PTFE) and a bottom part that is manufactured from felt. These materials are ordinary filter materials, used m a new combination.

In a second embodiment of a filter bag according to the invention, the bottom part is provided with a one-way valve that prevents dusty air to enter the filter bag but allows a rinsing liquid to leave the interior of the filter bag. The one-way may be of any suitable type, but preferably it is a lip valve which may be supplemented by a float valve .

According to the invention the air filter device for filtering a dusty or powdered air stream comprises a dusty air chamber and a clean air chamber separated by a substantially horizontal separating wall, said separating wall being provided with a number of openings m which filter bags are suspended, means being provided m the clean air chamber for applying a liquid to the interior of the filter bags for CIP cleaning, each filter bag comprising an elongate, tube-shaped, flexible outer skirt manufactured from a substantially liquid impermeable sheet material and a bottom part at an lower end of said elongate, tube-shaped, flexible outer skirt. The second object is achieved by providing the bottom part of the filter bags with means that allows a liquid to leave the filter bag under influence only of gravity and/or air pressure provided inside the filter bag.

Hereby is obtained that the interior of the substantially liquid impermeable filter bags can be CIP cleaned without use of any manually operated means as m the prior art.

Each of the filter bags may preferably have a structure as described above with relation to the bottom part, i.e. being provided with a less liquid impermeable bottom sheet material or a one-way valve.

In a further embodiment, the bottom part of each filter bag comprises a hollow pipe that is connected to the lower end of the elongate, tube-snaped, flexible outer skirt, said hollow pipe leading to the exterior of the dusty chamber. This embodiment ensures that the lower end of the filter bag is never open to the interior of the dusty chamber so that a high filtration efficiency is maintained at all times.

Preferably, the means for applying a liquid to the interior of the filter bags comprises a movable arm provided with spray nozzles that successively are movable to posi- tions above different filter bags.

The use of a movable arm provided with spray nozzles has some general advantages over the prior art m which the spray nozzles are immovable mounted above or inside each filter bag. When using a movable arm, it is possible to use fewer spray nozzles than what is used m the prior art air filter devices, which m turn calls for a use of fewer pipes m a less complicated structure positioned inside the filter device. This minimizes the manufactur- mg costs and it also calls for a pipe structure that is much easier to clean by using other spray nozzles than the complicated immovable pipe structure of the prior art devices .

In a first embodiment the filter bags are arranged m concentric circles m the separating wall while the movable arm is rotatable around an axis m the centre of the concentric circles, and m a second embodiment the filter bags are arranged m rows while the movable arm spans across more rows and is movable along the rows.

It should be mentioned that the above-described use of a movable arm provided with spray nozzles is applicable not only m connection with an air filter device according to the invention, but may be used m other air filter devices as well m which interior CIP cleaning of filter elements is required.

Therefore, an air filter device for filtering a dusty or powdered air stream and comprising a dusty air chamber and a clean air chamber separated by a substantially horizontal separating wall being provided with a number of openings in which filter elements are suspended, may be provided with a movable arm provided with spray nozzles that successively are movable to positions above different filter elements.

Again, the filter elements may be arranged m concentric circles m the separating wall while the movable arm is rotatable around an axis m the centre of the concentric circles, or the filter elements may be arranged n rows while the movable arm spans across more rows and is mov^¬ able along the rows. The filter elements may be filter bags or other types of air filter elements.

The invention will be described m detail m the follow^¬ ing with reference to the drawings in which

Fig. 1 shows generally an air filter device having CIP cleaning means,

Fig. 2 shows a top part of a filter bag according to the invention,

Fig. 3 shows a bottom part of a first embodiment of a filter bag according to the invention, Fig. 4 shows a bottom part of a second embodiment of a filter bag according to the invention,

Fig. 5 shows a bottom part of a modified second embodi- ment of a filter bag according to the invention, and

Fig. 6 shows an air filter device according to a specific embodiment of the invention.

Fig. 1 shows generally an air filter device, m this embodiment a bag filter 1, said bag filter comprising a dusty air chamber 2 and a clean air chamber 3 separated by a horizontal separating wall 4. The separating wall 4 comprises a number of openings that suspend filter bags 5 that hang down from the separating wall 4. For clarity, only six filter bags 5 are shown m Fig. 1 whereas the number of filter bags may vary from one to several thousands depending on the actual use of the bag filter 1.

Above the filter bags 5 a number of ventuπes 6 are arranged, said venturies 6 being able to provide a downwardly directed air stream into the filter bags 5. In operation, this so-called rinsing air is provided regularly to each filter bag 5 m order blow off deposited material from the outer surface of the filter bags 5. At the left side of Fig. 1 three venturies 6 are positioned above three filter bags 5. Similarly, at the right side of Fig. 1 two venturies 6 are positioned above two not shown fil^¬ ter bags. In the shown embodiment, the filter bags 5 are arranged m concentric circles while the venturies 6 via an arm are connected to a rotatable air distribution means 7 positioned centrally m the clean air chamber 3. This arrangement means that the number of venturies 6 can be substantially less than the number of filter bags 5, since each venturi 6 is capable of providing rinsing air to all the filter bags 5 arranged m the same concentric circle.

In order to accommodate CIP cleaning at the outer surfaces of the filter bags, spray nozzles 8 are arranged at the underside of the separating wall 4 between the filter bags 5 and other spray nozzles 9 are arranged m the dusty chamber 2 below the filter bags 5. A cleaning liquid can be led to the spray nozzles 8, 9 through feeding tubes 10 and 11. During the CIP cleaning the outer surfaces of the filter bags 5 are sprayed with the cleaning liquid which dissolve and/or sweep away any deposited material. The liquid containing deposited material drips from the bottom of the filter bags 5 and runs to the outlet 12 of the dusty chamber 2.

The dusty chamber 2 further has a tangential inlet 13 for the air stream containing powdered material.

The bag filter 1 is further provided with spray nozzles 14 which m the shown embodiment are mounted on a ro- tatable arm like the venturies 6. At the right side of Fig. 1 the spray nozzles 14 are positioned above the open upper end of the filter bags 5 while the spray nozzles 14 at the left side of Fig. 1 are positioned above other not shown filter bags. A cleaning liquid can be led to the spray nozzles 14 via a feed line 15. CIP cleaning of the filter bags 5 may be provided each time the product is changed or regularly as a preventive measure preventing bacteria growth or at any other time if required. As mentioned above, CIP cleaning is accommo- dated by spraying the outer surface as well as the inner surface of the filter bags 5 with a cleaning liquid led to the spray nozzles 8, 9 and 14. Further spray nozzles 16 may be provided m the clean air chamber 3 for cleaning the clean air chamber 3 as such. An outlet 17 is pro- vided at the rim of the separating wall 4 for collecting used cleaning liquid.

The spray nozzles 14 are preferably arranged m such a way that they spray the cleaning liquid at the inner sur- face of the filter bags 5 as well as onto the upper surface of the separating wall 4 between the filter bags 5. This is shown m Fig. 2 which shows a cross-section through the separating wall 4 with a filter bag 5 and a spray nozzle 14 positioned above the filter bag 5.

The filter bag 5 comprises a filter cloth 18 that is sup^¬ ported by a wire skeleton comprising longitudinal wire elements 19 interconnected by circular ring elements 20. The upper end of the filter bag 5 is arranged in such a way that it can be supported closely m an opening m the separating wall 4.

The spray nozzle 14 preferably sprays the cleaning liquid m the shape of a cone and even more preferably m the shape of a pyramid whereby more spray nozzles can be brought to cover the entire surface of the separating wall 4 without overlapping. According to the invention, the filter cloth 18 consists of a substantially liquid impermeable sheet material having very small openings providing good filtrating abil- lty. The filter cloth 18 may be of the so-called membrane type which allows air to enter the interior of the filter bag 5 while even very fine dust particles and powdered material is deposited on the outer surface of the filter bag 5. A filter cloth 18 of this type could be a fabric provided with a layer of polytetrafluorethylene (PTFE) .

Using a substantially liquid impermeable sheet material as the filter cloth means, however, that a cleaning liquid that is sprayed into the interior of a filter bag 5 can not leave the filter bag 5 unless some special arrangements has been provided for. Therefore, according to the invention, the bottom part of the filter bags 5 comprises means that allows a liquid to pass out of the filter bag 5 under influence only of gravity and/or air pressure provided inside the filter bags 5.

Fig. 3 shows a first embodiment of the bottom part of a filter bag 5 according to the invention. The filter bag 5 comprises a filter cloth 18 made of a substantially liq- uid impermeable material as described above, said filter cloth 18 forming the elongate tube part of the filter bag 5. A bottom cloth 21, which is sewn or otherwise connected to the tube part, comprises a sheet material that is substantially more liquid permeable than the filter cloth 18. Thereby liquid, which has entered the interior of the filter bag 5, is able to leave the filter bag 5 simply by passing through the bottom cloth 21. The bottom cloth 21 may be made of felt or another material typically used in filter bags 5.

Because the bottom cloth 21 is liquid permeable whereas the filter cloth 18 is not, the bottom cloth 21 will allow larger dust particles to enter the filter bag 5 than the filter cloth 18. However, since the bottom cloth 21 constitutes only about l-5⁼- of the total filtering area of the filter bag 5, the efficiency of the filter bag 5 is hardly notable.

However, if it is strictly required that a liquid impermeable filter cloth is to be used also at the bottom part another arrangement has to be accomplished.

Fig. 4 shows a second embodiment of a filter bag 5 according to the invention. In this embodiment the bottom part comprises a substantially liquid impermeable sheet material 22 which may be made of the same material as the filter cloth 18. The central part of the bottom part is configured to form a lip valve 23 which under filtration prevents any dust particles to enter the filter bag 5 but under CIP cleaning allows cleaning liquid inside the filter bag 5 to leave the filter bag 5.

The lip valve 23 is so configured that it effectively closes the bottom part whenever the pressure m the clean air chamber 3 is lower than the pressure in the dusty air chamber 2 as is the case during filtration. Thus, the filter bag 5 has a filtration efficiency that corresponds to that of a filter bag made completely of a substan- tially liquid impermeable material without any valve m the bottom part.

However, during the CIP cleaning process where a cleaning liquid is fed to the interior of the filter bag 5, the lip valve 23 opens and allows cleaning liquid to leave the filter bag 5 by influence of gravity alone and/or by applying a positive pressure inside the filter bag 5.

Fig. 5 shows a principally modification of the embodiment shown m Fig. 4. In this modified embodiment the lip valve 23 is supplemented by a float valve having a ball shaped float 24 and a seat 25 for the float 24. The lip valve 23 ensures that no dusty air enters the filter bag through the bottom part during filtration whereas the float valve ensures that the filter bag bottom does not open when rinsing air pulses are provided to the interior of the filter bag m order to blow off" material deposited on the outside of the filter bag. It is thereby en- sured that the rinsing air leaves the filter bag through the elongate, tube-shaped flexible outer skirt and not through the bottom part. However, the valve combination allows a cleaning liquid supplied to the interior of the filter bag to leave the filter bag through the bottom part.

The bottom part of the filter element may comprise another valve arrangement than a lip valve or a lip valve combined with a float valve. A person skilled in the art of valves would easily think of oher valve constructions that would be applicable. Fig. 6 shows yet another embodiment m which the filtration efficiency is maintained at a high level even though liquid provided to the interior of the filter bags 5 is able to leave the filter bag during CIP cleaning. The air filter device corresponds essentially to the bag filter disclosed m Fig. 1 and like reference numerals are used for like parts. Likewise, the bag filter shown m Fig. 6 essentially also operates m the same manner as the bag filter of Fig. 1 and the operation will not be repeated here.

In Fig. 6 the lower end of each filter bag 5 is connected to a connecting piece 26 that together with other connecting pieces 26 are connected to one or more dram- age pipes 27 which m turn are led to the exterior of the dusty chamber 2.

In this embodiment the bottom of each filter bag 5 is open into the connecting piece 26. This means that the bottom of each filter bag 5 itself is not provided with any special means preventing dust to enter the filter bag 5. In stead, the bottom of each filter bag 5 is provided with connecting means for connecting the filter bag 5 tightly to the connecting piece 26.

During interior CIP cleaning of the filter bags 5, a cleaning liquid is led to the spray nozzles 14 positioned successively above the filter bags 5 as described above. The cleaning liquid dissolves and/or sweeps away any ma- teπal deposited on the inner surface of each filter bag 5 and since the outer skirt 18 of the filter bag 5 is substantially liquid impermeable the cleaning liquid re- mains on the inner surface and runs to the connecting piece 26 and further to the drainage pipe 27 from where it can be collected for possibly reuse.

Claims

C l a i m s

1. A filter bag (5) for vertically suspension m an air filter device (1), said filter bag (5) comprising suspension means positioned inside the filter bag (5), said filter bag (5) comprising an elongate, tube-shaped, flexible outer skirt (18) manufactured from a substantially liquid impermeable sheet material and a bottom part at one end of said elongate, tube-shaped, flexible outer skirt (18), characterised in that the bottom part comprises means that allows a liquid to leave the filter bag (5) under influence only of gravity and/or air pressure provided inside the filter bag (5) .

2. A filter bag according to claim 1, characterised in that the bottom part consists of a flexible sheet material (21) that is substantially more liquid permeable than the sheet material that constitutes the elongate, tube-shaped outer skirt (18).

3. A filter bag according to claim 2, characterised in that the elongate, tube-shaped outer skirt (18) is manufactured from a material having a layer of polytetrafluo- rethylene and that the bottom part is manufactured from felt.

4. A filter bag according to claim 1, characterised in that the bottom part is provided with a one-way valve.

5. A filter bag according to claim 4, characterised in that the one-way valve is a lip valve (23) .

6. A filter bag according to claim 5, characterised in that the lip valve is supplemented by a float valve.

7. An air filter device for filtering a dusty or powdered air stream, said air filter device comprising a dusty air chamber (2) and a clean air chamber (3) separated by a substantially horizontal separating wall (4), said separating wall (4) being provided with a number of openings m which filter bags (5) are suspended, means being pro- vided m the clean air chamber (3) for applying a liquid to the interior of the filter bags (5) for CIP cleaning, each filter bag (5) comprising an elongate, tube-shaped, flexible outer skirt (18) manufactured from a substantially liquid impermeable sheet material and a bottom part at an lower end of said elongate, tube-shaped, flexible outer skirt (18), characterised in that the bottom part comprises means that allows a liquid to leave the filter bag (5) under influence only of gravity and/or air pressure provided inside the filter bag (5) .

8. An air filter device according to claim 7, characterised in that the bottom part consists of a flexible sheet material (21) that is substantially more liquid permeable than the sheet material that constitutes the elongate, tube-shaped outer skirt (18).

9. An air filter device according to claim 8, characterised in that the elongate, tube-shaped outer skirt (18) is manufactured from a material having a layer of polytetrafluorethylene and that the bottom part is manufactured from felt.

10. An air filter device according to claim 7, characterised in that the bottom part is provided with a one-way valve .

11. An air filter device according to claim 10, characterised in that the one-way valve is a lip valve (23) .

12. An air filter device according to claim 10, characterised in that the lip valve is supplemented by a float valve.

13. An air filter device according to claim 7, characterised in that the bottom part of each filter bag (5) comprises a hollow pipe (24) that is connected to the lower end of the elongate, tube-shaped, flexible outer skirt (18), said hollow pipe (24) leading to the exterior of the dusty chamber (2) .

14. An air filter device according to any one of claims 7-13, characterised in that the means for applying a liq^¬ uid to the interior of the filter bags (5) comprises a movable arm provided with spray nozzles (14) that succes^¬ sively are movable to positions above different filter bags (5) .

15. An air filter device according to claim 14, characterised in that the filter bags (5) are arranged m concentric circles m the separating wall (4) and that the movable arm is rotatable around an axis at the centre of the concentric circles.

16. An air filter device according to claim 14, characterised in that the filter bags (5) are arranged m rows and that the movable arm spans across a number of rows and is movable along the rows.