GB2056306A

GB2056306A - Gas filter

Info

Publication number: GB2056306A
Application number: GB8009471A
Authority: GB
Original assignee: WEST OF SCOTLAND METALLIC WORK
Current assignee: WEST OF SCOTLAND METALLIC WORK
Priority date: 1979-03-30
Filing date: 1980-03-20
Publication date: 1981-03-18

Abstract

A wet dust filter plant including a filter unit in which a filter drum revolves slowly in a casing containing water, has serious disadvantages arising from the need to transfer the slurry to a sedimentation tank and from the effect of the entering dust- laden gas on the drum. The difficulties are overcome by (a) mounting the filter unit 22 in the sedimentation tank 27 so that the sludge simply falls from the filter drum 28 directly through the open bottom 24 of the filter casing 23 on to the tank floor or on to conveying means in the tank, and (b) providing an air inlet duct 31 in the form of a downwardly and inwardly extending nozzle or venturi 34 whereof the outlet or throat is disposed below water level so that the issuing air stream is tangential to the drum and air impact against the drum is avoided. <IMAGE>

Description

SPECIFICATION Improvements in or relating to gas filters This invention relates to gas filters and is especially but not exclusively concerned with filters for use in cleaning the air discharged by dust separators of the cyclone type.

In our patent specification No. 1,271,455 there is described a gas filter comprising a casing having a bottom portion capable of containing water, a horizontal cylindrical filter drum rotatable in the casing with a bottom portion of the drum immersed in the water in the casing, inlet means in the casing to direct gas downwards and inwards into the water and under the drum whence gas flows upwards through the drum, an outlet at the top of the casing for the filtered gas, and an outlet at the bottom of the casing for a dust/water slurry. The casing has a sloped floor, and there is an outlet for the slurry at the bottom of the sloped floor. A rotary paddle drum mounted in the casing adjacent to the sloped floor is drivable to maintain the collected dust particles in suspension in the water and so assist the flow of dust particles to the bottom outlet.A discharge pump is connected through piping and valves to the bottom outlet and to a sedimentation basin to deliver slurry to the basin, and a feed pump is connected through piping and valves to the basin and to the filter casing to return the water to the filter-case. Valve-controlled sludge outlets are provided at the bottom of the sedimentation basin.

A serious disadvantage of the arrangement in specification No. 1,271,455 is that any blockage of the slurry discharge system, e.g. due to dust or ice, causes a rapid build-up of slurry in the bottom portion of the casing under the revolving filter drum, and this build-up of slurry causes damage to or blocking of the filter drum.

A further disadvantage of the arrangement in our patent specification No. 1,271,455 is that the dust-laden gas flowing from the gas inlet duct strikes the adjacent periphery of the revolving filter drum which is thus bombarded with large dust particles. These particles when in high concentration tend to block the filter material in the drum, and they also cause excessive wear of the drum.

Objects of the present invention include the obviation or mitigation of the aforesaid disadvantages.

According to one aspect of the present invention, a gas filter comprises an openbottomed casing having a gas outlet at the top thereof, a horizontal cylindrical filter drum rotatable in the casing, a container enclosing the bottom portion of the casing so that water in the container seals the bottom of the casing and covers a bottom portion of the drum, and gas inlet means in the casing to direct gas downwards and inwards into the water so that the gas flows under the drum and thence upwards through the drum to the top outlet and the dust falls through the open bottom of the casing to the bottom of the container.

The container thus serves as a sedimentation basin, and the open bottom of the casing of the filter provides for through passage of the slurry directly from the casing into the sedimentation basin. With the filter thus actually situated within the sedimentation basin, the need for a discharge system including a pump, piping and valves is removed, and consequently the danger arising from blockage of such a system is obviated.

Moreover, by providing for the free vertical fall of the slurry from the filter drum directly into the sedimentation basin, the rotary paddle drum of the earlier arrangement is no longer required; thus, the number of moving parts in the filter is reduced by half.

The sedimentation basin may be a tank, or may be a pond.

A drag link conveyor, or a screw conveyor, or a rotary valve may be installed in the tank or pond to extend below the filter drum and so provide for continuous clearance of sludge from the vicinity of the filter drum. Alternatively, the clearance of the sludge may be effected with hand tools.

According to another aspect of the present invention we provide a gas filter including a casing for water and having a gas outlet at the top thereof and a slurry outlet at the bottom thereof, a horizontal cylindrical filter drum rotatable in the casing with the water in the casing covering a bottom portion of the drum, and gas inlet means in the casing to direct gas downwards and inwards into the water so that the gas flows under the drum and thence upwards through the drum and slurry falls downwardly through the bottom outlet, characterised in that the gas inlet means comprises a nozzle extending downwards and inwards into the casing and having a discharge opening located below water level in the casing.

By arranging the nozzle with its discharge opening below the surface of the water in the casing, the rotary filter drum is protected against direct bombardment by large dust particles which are in high concentration in the entering gas, so that the risk of blockage of the filter material of the filter drum by the particles is reduced, and moreover excessive wear of the filter drum due to said bombardment is avoided.

Preferably a water distributor is disposed at the inlet end of the nozzle to create a curtain of water across the inlet opening so that the dust-laden gas on entering the nozzle is first wetted and thereafter discharged downwards as a jet under water.

Preferably also the water distributor is disposed within the nozzle so that water wets the nozzle walls and flows from the nozzle to replenish the water in the container. The passage of the dustladen gas through the water curtain and then down the wetted walls of the nozzle ensures maximum absorption of water by the dust particles and results in a filter of greatly improved efficiency.

A filter plant as disclosed in our specification No. 1,271,455, when modified in accordance with the present invention, operates at increased efficiency, and with less servicing and therefore reduced running costs.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a diagram of a filter plant embodying the gas filter described in our earlier patent specification No. 1,271,455.

Fig. 2 is a diagrammatic sectional end view of a gas filter embodying the invention.

Fig. 3 is a view similar to Fig. 2 showing the gas filter in greater detail.

Fig. 4 is a sectional front view of the gas filter of Fig. 3.

Fig. 5 is a detail view of the gas inlet means of the gas filter of Fig. 3.

Fig. 6 is a sectional top plan view on the line VI-VI of Fig. 5.

Referring to the drawings.~ In the previously proposed plant (Fig. 1) a cyclone-type dust separator 1 has its air outlet connected through a pipe 2 and a pump 3 to the box-shaped air inlet duct 5 of a wet dust filter or arrester 4. The filter 4 includes a box-shaped casing 6 having a bottom portion 7 capable of containing water at a level 8, and a horizontal cylindrical filter drum 9 rotatable in the casing 6 with a bottom portion of the drum immersed in the water in the bottom portion 7 of the casing, as shown. The inlet duct 5 in the casing directs gas downwards and inwards into the water and against and under the revolving drum 9 whence the gas flows upwards through the revolving drum.There is an outlet 10 at the top of the casing 6 for the filtered gas, and an outlet 11 at the bottom of the casing 6 for the dust/water slurry.

The casing 6 has a sloped floor with the outlet 11 at the bottom thereof. A rotary paddle drum 13 mounted in the casing 6 adjacent to the sloped floor 12 is drivable to maintain the collected dust particles in suspension in the water and so assist the flow of dust particles to the bottom outlet 11.

The bottom outlet 11 of the filter is connected to a sedimentation basin 14 through piping 15 and a discharge pump 16 which delivers slurry to the basin 14. A clean-water compartment 17 in the basin 14 is connected to a water inlet pipe 18 in the casing 6 through piping 19 and a feed pump 20. Valve-controlled sludge outlets 21 are provided at the bottom of the sedimentation basin 14.

With the sedimentation basin 14 and the filter 4 separate from each other and interconnected by the piping and pumps shown, numerous disadvantages arise. Moreover, the inlet duct 5 of the filter is clearly so disposed as to cause bombardment of the portion 9A of the drum 9 with large dust particles, and this gives rise to more disadvantages.

Referring to Figs. 2 to 6, a wet dust filter or arrester 22 includes a box-shaped casing 23 which has an open bottom 24 and is mounted with its bottom portion 25 (Fig. 2) centrally within the upper zone 26 of a sedimentation tank 27 so that with water filling the sedimentation tank to the level L, the water seals the bottom of the casing 23. A horizontal rotary cylindrical filter drum 28 is mounted in the casing 23 so that the drum revolves with its bottom portion immersed in the water in the casing. In operation of this filter the dust particles fall vertically from the drum 28 through the open bottom 24 of the casing 23 to the floor 30 of the tank 27, as indicated by the arrow 29. With this arrangement the troublesome piping, valves and pumps are no longer required.

The ample free space between the drum 28 and the floor 30 provides for unimpeded downward flow of sludge which can accumulate without fouling the drum. Obviously the rotary paddle drum of the arrangement of Fig. 1 is not required.

Again referring to Fig. 2, dust-laden air is fed into the casing 23 through an inlet duct 31 in which there is a baffle plate 32 which forms with the bottom plate 33 of the duct a nozzle or venturi passage having an outlet throat 34 which is disposed below the level L of the water in the casing so that the gas flow is directed downwards and inwards tangentially of the drum. There is thus no longer any direct bombardment of the drum with dry, dust-laden gas.

Replenishment water is supplied to the tank 27 through a perforated feed pipe 35 disposed at the inlet end of the nozzle and adjacent to the plate 32 so as to direct a curtain 36 of water across the nozzle entry. The water from the feed pipe 35 in its passage through the nozzle into the casing 23 wets the walls 32 and 33 of the nozzle. As the dust particles in the entering gas are thoroughly wetted in their passage through the water curtain and down the wet walls of the nozzle, the efficiency of the filter is greatly enhanced.

As shown in Figs. 3 and 4, the casing 23 with its open bottom 24 sealed by the water in the sedimentation tank 24 is supported in the tank by four corner legs 37 connected at their upper ends to the sides of the casing 23 and having their lower ends engaging the floor 30 of the tank 27.

As shown in Figs. 5 and 6, the water-feed pipe 35 within the duct 31 includes a pair of end sleeves 37 and 38 mounted in a watertight manner in the side walls 39 and 40 of the duct 31, and has therein a row of perforations 41 through which the feed water passes as jets to create the water curtain 36 within the upper end of the duct.

The baffle plate 32 is pivotally mounted at its upper end on the end sleeves 37 and 38 for hingeing movement about the pipe axis to vary the size of the outlet throat 34 in accordance with operating conditions. The hingeing movement of the plate 32 is effected by an adjustment screw 42 (Fig. 5), and the plate is locked in adjusted position by a pin 43.

Claims

1. A gas filter comprising an open-bottomed casing having a gas outlet at the top thereof, a horizontal cylindrical filter drum rotatable in the casing, a container enclosing the bottom portion of the casing so that water in the container seals the bottom of the casing and covers a bottom portion of the drum, and gas inlet means in casing to direct gas downwards and inwards into the water so that the gas flows under the drum and thence upwards through the drum to the top outlet and the dust falls through the open bottom of the casing to settle on the bottom of the container.

2. A gas filter according to claim 1, wherein the open-bottomed casing is box-shaped and has at the corners thereof elongate legs engaging the floor of the container so that the casing is supported centrally within the container with its bottom clear of the container floor.

3. A gas filter according to claim 1 or 2, wherein the gas inlet means comprises a nozzle extending downwards and inwards into the casing and having a discharge opening located below water level in the casing.

4. A gas filter according to claim 3, wherein a water distributor is disposed at the inlet end of the nozzle to create a curtain of water across the inlet opening so that the dust-laden gas on entering the nozzle is first wetted and thereafter discharged downwards as a jet under water.

5. A gas filter according to claim 4, wherein the water distributor is disposed within the nozzle so that water wets the nozzle walls and flows from the nozzle to replenish the water in the container.

6. A gas filter according to any one of claims 3 to 5, wherein the nozzle includes top and bottom downwardly and inwardly extending convergent plates whereof the top plate is pivotally mounted at its upper end for hingeing adjustment from and towards the bottom plate to vary the size of the outlet opening of the nozzle.

7. A gas filter including a casing for water and having a gas outlet at the top thereof and a slurry outlet at the bottom thereof, a horizontal cylindrical filter drum rotatable in the casing with the water in the casing covering a bottom portion of the drum, and gas inlet means in the casing to direct gas downwards and inwards into the water so that the gas flows under the drum and thence upwards through the drum and slurry falls downwardly through the bottom outlet, characterized in that the gas inlet means comprises a nozzle extending downwards and inwards into the casing and having a discharge opening located below water level in the casing.

8. A gas filter according to claim 7, wherein a water distributor is disposed at the inlet end of the nozzle to create a curtain of water across the inlet opening so that the dust-laden gas on entering the nozzle is first wetted and thereafter discharged downwards as a jet under water.

9. A gas filter according to claim 8, wherein the water distributor is disposed within the nozzle so that water wets the nozzle walls and flows from the nozzle to replenish the water in the container.

10. A gas filter according to claim 1 and substantially as hereinbefore described with reference to Figs. 2 to 6 of the accompanying drawings.

10. A gas filter according to any one of claims 7 to 9, wherein the nozzle includes top and bottom downwardly and inwardly extending convergent plates whereof the top plate is pivotally mounted at its upper end for hingeing adjustment from and towards the bottom plate to vary the size of the outlet opening of the nozzle.

11. A gas filter according to claim 10, wherein the water distributor consists of a perforated pipe extending from side to side of the nozzle and the top plate is pivotally mounted on the pipe for hingeing adjustment from and towards the bottom plate to vary the size of the outlet opening of the nozzle.

12. A gas filter substantially as hereinbefore described with reference to the accompanying drawings.

New claims filed on 22nd October 1980.

Superseded claims 1-12.

1. A gas filter comprising an open-bottomed casing having a gas outlet at the top thereof, a horizontal cylindrical filter drum rotatable in the casing, a container enclosing the bottom portion of the casing so that water in the container seals the bottom of the casing and covers a bottom portion of the drum, and gas supply means connected to the casing to create a stream of gas in the water so that the gas rises upwards through said bottom portion of the drum to the top outlet and slurry falls downwardly through the open bottom of the casing to the bottom of the container.

3. A gas filter according to claim 1 or 2, wherein the gas supply means comprises a nozzle device whereof the discharge opening is disposed so as to lie wholly below the water level in the casing.

4. A gas filter according to claim 3, wherein the nozzle device comprises box-section ducting sloped downwards and inwards towards the casing and having downwardly convergent top and bottom walls forming with the side walls a venturi passage terminating at its lower end in an outlet throat.

5. A gas filter according to claim 4, wherein the ducting consists of a box-section duct and a baffle plate in the duct sloping downwards towards the bottom wall of the duct to form with the bottom and side walls of the duct the venturi passage, said baffle plate being pivotally mounted at its upper end for hingeing adjustment from and towards the bottom wall to vary the size of the outlet throat.

6. A gas filter according to claim 4 or 5, wherein a water distributor is disposed at the inlet end of the ducting to create a curtain of water across the entry to the ducting so that the dry dust-laden gas entering the ducting is first wetted then discharged as a jet under water.

7. A gas filter according to claim 6, wherein the water distributor is disposed within the ducting so that water wets the walls of the ducting and flows from the outlet throat to replenish the water in the casing.

8. A gas filter according to claim 7, wherein the water distributor consists of a perforated pipe extending from side to side of the ducting.

9. A gas filter according to claim 5, wherein a water-distributing perforated pipe is disposed within the duct at the upper end thereof to create a curtain of water across the entry to the duct so that the water wets the dry entering gas and flows down through the duct to wet the walls thereof and replenish the water in the casing, and the baffle plate is pivotally mounted at its upper end on the perforated pipe.