GB2088244A

GB2088244A - Discharging dust from air filter

Info

Publication number: GB2088244A
Application number: GB8038085A
Authority: GB
Original assignee: METALAIR Ltd
Current assignee: METALAIR Ltd
Priority date: 1980-11-27
Filing date: 1980-11-27
Publication date: 1982-06-09

Abstract

Dust which is blown or shaken from filter bags 1 falls on to porous floor 3, through which air is blown so that the dust slides past valve 4A into vessel 4. Periodically valve 4A is closed and air delivered to chamber 4B fluidises the contents of vessel 4 and conveys them up pipe 4C to large bunker 4D. In Fig. 3 (not shown) two parallel filters comprising outward- flow, open ended filter tubes act in sequence. The various valves are actuated by rams at regular intervals determined by respective cams gear to the air-compressor drive shaft. <IMAGE>

Description

SPECIFICATION A self-cleaning air filter arrangement This invention relates to a self-cleaning filter arrangement. As particularly disclosed herein, the invention aims to provide a compact and effective self-cleaning filter for the removal of dust particles from the residual air expelled from a pneumatic conveying system after the main burden of the conveyed powder has been removed from the air.

In general, self-cleaning filters at present in use, and used in the past, require a supply of electricity and the collected dust is removed by hand. It would be desirable to avoid the use of electricity and to have an automatic means of disposing of the collected dust. Such a filter would be very convenient for use in underground coal mines, although its use would not be limited to this application. In underground coal mines the preferred sources of energy for low-power applications are hydraulic fluid, compressed air or mechanical power drives taken as auxiliaries from main drives.

A filter as particularly disclosed herein is designed to be capable of use continuously for long periods and therefore, to avoid loss of efficiency and increase in the pressure drop across a porous cloth or like element used to separate the dust from the air stream, each porous element, hereinafter sometimes called a "bag", must be cleaned at frequent intervals whilst the main air stream is flowing through the filter.

According to the present invention, in one aspect, there is provided a self-cleaning filter arrangement for use with a plurality of filter bags, the arrangement having in a lower region thereof a container positioned and arranged for collecting dust or the like dislodged from the bags, the container having an outlet pipe and fluidising means associated with the container whereby dust therein can be fluidised and transported to a storage bunker via the outlet pipe, the arrangement also having a control system constructed and arranged to actuate the fluidising means to empty the container when same becomes substantially full of dust.

According to a second aspect of the invention there is provided a self-cleaning filter arrangement comprising a plurality of filter bags arranged to have air or gas to be filtered (herein called "gas" for brevity) fed to one side of the wall thereof, the gas flow being controllable to that it can be cut off from selected ones but not all of the bags and there being a feed means arranged to feed a blast of compressed air to the other side of the walls of those bags which are cut off in order to dislodge dust therefrom while the remainder remain in filtering operation.

According to a third aspect of the invention, there is provided a self-cleaning filter arrangement comprising a plurality of filter bags arranged for a gas to be filtered to be fed to one side thereof, there being firstly a control flap associated with each bag or group of bags for cutting off the gas flow thereto, and secondly a mechanical vibrator associated with each bag or group of bags for shaking the bag while the gas flow is cut off in order to dislodge dust particles from the bag.

In an embodiment of the second aspect of the invention, the bags are cleaned in turn by the compressed air used for cleaning being supplied through a series of valves which are actuated by a cam shaft driven by a hydraulic or compressed air motor in such a manner that the bags are cleaned in sequence, leaving at the same time some of the bags in use to enable continuous flow of the air stream which is to be filtered.

In an embodiment of the third aspect of the invention, the bags are divided into convenient groups with the outlets for the cleaned air from each group fitted with a movable flap to stop the air stream, the flaps being held either open or shut by pneumatic or hydraulic rams controlled by valves opened and shut in turn by a cam-shaft driven by a hydraulic or pneumatic motor. The cam-shaft also controls valves which control the liquid or gas supply to respective hydraulic or pneumatic motors when actuated in this way, these motors mechanically shake those bags in which the air stream has been stopped by means of linkages from cranks or eccentrics.

The dust which is collected on the filter bags and is then dislodged from the bags as described above needs to be removed from the body of the filter periodically, otherwise the whole filter would become blocked. According to an especially preferred feature of the present invention the dust dislodged from the bags as described falls onto fluidizing beds which cause the powder to move under the influence of gravity down very shallow angles. Such an arrangement affords a saving in height compared to the height of ordinary collection hoppers. The powder (or dust) which moves down such a shallow slope is arranged to fall into a collection container, and is thence transported by fluidising air to a storage bunker, as mentioned above.

The fluidising beds are supplied with air to cause the fluidising action either from a main compressed air supply or by a fan or blower driven by a hydraulic motor particular to the filter arrangement.

The invention will be better understood from the following non-limiting description of examples thereof given with reference to the accompanying drawings in which:~ Figure 1 is a front view and Figure 2 is a side view of one self-cleaning filter arrangement according to the invention; and Figure 3 is a diagrammatic representation showing the air stream paths and dust disposal arrangements according to another example of the invention.

Referring to Figures 1 and 2, a filter casing 6 contains filter elements 1 which are arranged so that some of them may be shaken to remove dust therefrom while others remain in filtering operation. The base of the casing 6 is formed by a sloping bed 3 which is formed by a porous material laid over an air plenum chamber 3A. In operation, despite the shallow slope of the bed 3, dust or other filtered-off material is caused to slide downwardly towards the lowermost corner when fluidising air under pressure is fed to the plenum chamber 3A. At the lowermost corner is located a collector chamber 4 separated from the interior of the casing 6 by a slide valve 4A.Surrounding the chamber 4 is a high pressure blow pot 4B arranged to be able to feed high pressure transporting air to the interior of the chamber 4 so causing any particulate material such as dust to be conveyed rapidly along a pipe 4C to a large storage bunker 4D.

The slide valve 4A and the valves which control flow of air or gas to be filtered into selected ones of the filter elements are all controlled by control gear 5 driven by an air or hydraulic motor 5A. A baffle 2 is located within the casing. The filter elements 1 take the form of bags 20 suspended from a slotted plate 22, the mouths of the bags being fixed around the margins of the slots. The bags hang down into a space 24 which is bounded by walls 26 and the aforementioned sloping bed 3.

The fluidising bed 3 is so shaped and has a slope such that in operation the accumulated dust falling onto it is conveyed by gravity to the inlet of a vessel fitted with a valve at its inlet and a pipe at its outlet, thus when the vessel inlet valve is open the accumulated dust can flow into the vessel and fill it. When the vessel is full or partially full the inlet valve is closed by a hydraulically or pneumatically powered actuator controlled by valves actuated by the cam-shaft. When the inlet valve is closed air under pressure is fed into the vessel through a valve controlled by the camshaft. This pressurized air conveys the accumulated dust from the vessel into a suitable receiver, in the present invention this receiver will be the hopper or bunker into which the main mass of conveyed powder is received.After discharge of the accumulated dust from the vessel the pressurized air supply is disconnected from the vessel and the vessel inlet valve is opened by hydraulic or pneumatic means controlled by valves actuated by the cam-shaft.

In operation, air to be filtered carrying dust or other powder particles is fed along an entry pipe 28, Figures 1 and 2, in the direction of the arrow 29 and into the casing 6. It then passes through the walls of the filter bags, from outside the bags to inside the bags, and the filtered air exits through openings in a top wall 6A of the casing. Baffles or louvres 6B are provided to direct the issuing air as may be required. In Figure 2 the arrows 29 indicate the airflow.

in the event of sufficient height being available to dispense with the fluidising beds and use ordinary slope angles to make a hopper slope to cause the accumulated dust to fall by gravity alone it is possible to collect the accumulated dust at a point in the lower part of the filter casing and use either a pressurized conveyor system as described or a mechanical elevator, conveniently a screw elevator to transfer the accumulated dust to the receiving hopper. This means of removal can also be used with a fluidising bed, the elevator being driven either hydraulically or pneumatically and caused to start and stop at suitable intervals by a camshaft driven valve.

There has been particularly disclosed herein a means of continuously removing dust particles from a stream of air, of sequentially cleaning the accumulated dust from the filter elements (bags), collecting the dust and removing the collected dust from the filter into a storage vessel or bunker.

Figure 3 is a diagrammatic representation of a filter system according to the invention.

Air to be filtered is fed along line 30 and according to whether valve 32 or valve 34 is open, is fed to the interior of filter tubes or bags 36 or 38. As shown, valve 32 is closed and 34 is open.

Bags 38 continue to filter and filtered air leaves at 40. Bags 36 are mechanically vibrated (or subjected to a sudden reverse air flow) with the result that dust and like filtered material is dislodged therefrom and falls onto sloping fluidising beds 42 having respective plenums 44 fed from a supply 46 of fluidising air under pressure. The dust dlides down and into a collector chamber 48, there being a slide valve 50 at the entry thereof. The collector chamber 50 has a fluidising air plenum 52 at its base, also fed with air from the supply 46, and when the chamber 48 is full, a valve 56 is opened and the contents of the chamber 48 are conveyed by air under pressure via a line 58 to a collection bunker 60.

When it is desired to free the filter elements 38 of filter material, valve 32 is opened, valve 34 is closed, valve 56 is closed, valve 57 is opened, and a similar procedure adopted, which, for the sake of brevity, will not be described in detail. The valves 59 may be cam-controlled or operated by timers, or manually, as desired, to control the fluidising air fed to the plenums 44.

The valves 32, 34, 50 and 56 are preferably all controlled by a cam from the shaft of an engine of a compressor (e.g. 46) supplying air under pressure, and hence they are opened and shut in a time-cycled manner. The length of the period for which bags 36 (or 38 as the case may be) effect filtering is determined by prior tests to establish the time taken to fill the collector chamber with dust under the most severe conditions of operation. Hence, the arrangement provides automatic cleaning in a time cycled manner of filter bags or groups of filter bags, leading to reduced costs and more efficient operation, and healthier working conditions.

Claims

1. A self cleaning filter arrangement for use with a plurality of filter bags, the arrangement having in a lower region thereof a container positioned and arranged for collecting dust or the like dislodged from the bags, the container having an outlet pipe and fluidising means associated with the container whereby dust therein can be fluidised and transported to a storage bunker via the outlet pipe, the arrangement also having a control system constructed and arranged to actuate the fluidising means to empty the container when same becomes substantially full of dust.

2. A self cleaning filter arrangement comprising a plurality of filter bags arranged to have air or gas to be filtered (herein called "gas" for brevity) fed to one side of the wall thereof, the gas flow being controllable so that it can be cut off from selected ones but not all of the bags and there being a feed means arranged to feed a blast of compressed air to the other side of the walls of those bags which are cut off in order to dislodge dust therefrom while the remainder remain in filtering operation.

3. A self cleaning filter arrangement comprising a plurality of filter bags arranged for a gas to be filtered to be fed to one side thereof, there being firstly a control flap associated with each bag or group of bags for cutting off the gas flow thereto, and secondly a mechanical vibrator associated with each bag or group of bags for shaking the bag while the gas flow is cut off in order to dislodge dust particles from the bag.

4. An arrangement according to claim 1 or 2 in which the bags are cleaned in turn by the compressed air used for cleaning being supplied through a series of valves which are actuated by a cam shaft driven by a hydraulic or compressed air motor in such a manner that the bags are cleaned in sequence, leaving at the same time some of the bags in use to enable continuous flow of the air stream which is to be filtered.

5. An arrangement according to claim 1 or 3 in which the bags are divided into convenient groups with the outlets for the cleaned air from each group fitted with a movable flap to stop the air stream, the flaps being held either open or shut by pneumatic or hydraulic rams controlled by valves Opened and shut in turn by a cam-shaft driven by a hydraulic or pneumatic motor.

6. An arrangement according to claim 5 in whch the cam-shaft also controls valves which control the liquid or gas supply to respective hydraulic or pneumatic motors in such a manner that, when actuated in this way, these motors mechanically shake those bags in which the air stream has been stopped by means of linkages from cranks or eccentrics.

7. An arrangement according to any preceding claim in which the dust dislodged from the bags as described falls onto fluidising beds which cause the powder to move under the influence of gravity down very shallow angles.

8. An arrangement according to any of claims 1-7 in which the fluidising beds are supplied with air to cause the fluidising action either from a main compressed air supply or by a fan or blower driven by a hydraulic motor particular to the filter arrangement.

9. An arrangement for cleaning filter bags substantially as herein particularly described with reference to and as illustrated in the accompanying drawings.