WO1992000134A1

WO1992000134A1 - Filter apparatus for removing particles from gas flows

Info

Publication number: WO1992000134A1
Application number: PCT/DK1991/000181
Authority: WO
Inventors: Bent Larsen
Original assignee: Bent Larsen
Priority date: 1990-06-28
Filing date: 1991-06-28
Publication date: 1992-01-09
Also published as: DK157490D0; AU8053391A

Abstract

Filter apparatus for removing solid particles in a gas flow comprise suspended filter elements (11) with a filter blanket (16). A nozzle (19, 20) mounted in the centre axis (31) can be stepwise pivotable above each filter element (11) and blow compressed air through this for the cleaning of the filter blanket (16). To increase the air volume through the filter blanket (16) a mouthpiece (19) in front of the nozzle (20) carries additional air besides the air blowing through the nozzle (20). The filter elements (11) have an air-reflecting bottom (14) and a narrowed-down portion (15) at the top ensuring uniform bulging and cleaning of the filter blanket (16). This ensures an efficient cleaning of the bag filter with reduced consumption of compressed air compared to the known apparatus.

Description

FILTER APPARATUS FOR REMOVING PARTICLES FROM GAS FLOWS.

The invention relates to a filter apparatus for the removal of particles from gas flows, such as air, smoke and waste gases, which flow through the apparatus, said apparatus comprising an inlet channel for the flow of gas to a chamber with a bag-type or tubular filter which the gas passes before being led out in cleaned state through an outlet channel, said filter comprising a number of filter elements consisting of a tubular frame with an external filter blanket suspended by the end in a wall in the chamber, and with means for the cleaning of the filter by blowing with air in the opposite direction through the filter, and means for the collection of the particles deposited in the chamber and the filter.

Apparatus of this kind is used for the removal of particles from industrial plants, either in order to be able to collect valuable materials from the flows of gas, or to prevent materials from escaping to the surrounding environ¬ ment and constituting a health risk, causing damage by corrosion or giving rise to general pollution.

The materials which are hereby removed by such filter apparatus can be solid materials, dust particles or liquid particles in the form of drops.

The known apparatus of this kind is encumbered with draw¬ backs and disadvantages which limit the use and efficiency. First and foremost, the known apparatus cannot work at high temperatures, the reason being that the parts of the apparatus are relatively temperature sensitive, especially the filter blanket, which cannot function at high temperatures at which it breaks down.

Consequently, the flow of gas in such an apparatus must be cooled, either before or in the apparatus, which can give rise to vapour in the gas flow condensing in the apparatus, and that solid particles collect in the condensate. The filter can thus be blocked, and a continuous cleaning of gases with such a composition cannot be effected.

In such cases, forms of separation other than filtration have to be used. This makes the cleaning of such gases a great deal more complicated and problematic, which makes the cleaning considerably more expensive.

Moreover, the maintenance cleaning of the filter element necessary for operation is troublesome and conditional upon the halting of the flow of gas through the apparatus, in order for the filter to be blown clean by an air flow in the opposite direction to that of the gas flow. It is naturally a considerable disadvantage that operations must be stopped at regular intervals, but also that the capacity of the apparatus decreases towards the time for the clean- ing of the filter.

This irregular operation and effect not only demands extensive supervision, but is also very work-demanding.

From the description of US Patent no. 3,487,609, there is known a filter apparatus in which a number of filter ele¬ ments in the form of elongated filter bags with rectangular cross-section are mounted in a circular arc. At the centre axis of this circular arc there is mounted a pivotable nozzle. This nozzle can be turned around above the upper opening of the filter bag and blow air down into the inside of the bag. The cleaning of the filter elements can thus be effected during operation, in that after the cleaning of one element the nozzle is turned further to another element. However, the cleaning of the filter elements is not particularly effective, in that the resulting influence on the filter blanket is not of sufficient strength to blow the packed-together particles from the filter blanket. This is especially difficult when the particles are moist and thus form a sticky mass.

This incomplete cleaning is due to the shape of the filter and the influence to which the filter blanket is exposed from the supplied amount of cleaning air, which does not have the character of a pulsation, but which is merely a simple discharge of a given amount of air. In practice, the result will be slow and ineffecient operation of the filter apparatus.

It is the object of the invention to overcome these draw¬ backs and disadvantages, and this is achieved with an apparatus in which the filter elements are disposed in concentric circular arcs, and where the air for the clean- ing of the filter elements is supplied through nozzles which are mounted on a pipe which, externally on the wall, can be turned around the centre axis of the circular arcs for positioning over one or more of the filter elements.

By this division of the filter in elements which are placed in one or more circular arcs, the possibility is provided for a continuous cleaning of the individual filter elements by blowing against the flow of gas through the element during operation, which therefore does not need to be in- terrupted. Moreover, it provides the possibility of regular cleaning of the individual elements by turning the nozzles in over the element or elements which are to be cleaned. It can thus be ensured that the apparatus always has a high effect, and with only one or more elements out of operation during ordinary cleaning. Since in practice the cleaning takes only about one second, this does not involve any significant reduction in the capacity of the apparatus.

To this can be added that the apparatus is constantly held at the same efficiency, since as mentioned a continuous cleaning of the elements can take place. Furthermore, by the blowing in of cooled compressed air, the filter blanket will also be cooled, which not only extends its lifetime but also provides the possibility of operation at higher gas-flow temperatures, whereby the cooling of the gas can be reduced or possibly avoided completely.

As disclosed in claim 2, by introducing further air from the surroundings to the flow of cleaning air, the volume of air becomes greater, whereby the consumption of compressed air can be considerably reduced. This is a great economic advantage, not only regarding operation, but also in that the possibility is provided of reducing the dimensions of the source of compressed air.

As disclosed in claim 3, by providing the filter elements with a baseplate, the air flow will be reflected from the bottom and vertical oscillations will arise in the filter element, whereby the bag is more quickly cleaned due to the vibrations.

As disclosed in claim 4, by narrowing-down the filter pipe's inlet end for compressed air from the nozzles, in the form of a conical pipe piece, the filter blanket also here will be cleaned, since the pressure effect also effectively influences these inclined surfaces.

As disclosed in claim 5, by insulating the chamber around the filter elements and the nozzles, the dewpoint will be raised so much that no concentration can take place in the apparatus, and thus no sullying of the insides of the apparatus. As disclosed in claim 6, by controlling the position of the nozzles in relation to the filter elements and the supplied compressed air when the nozzles are in the cleaning position, compressed air can be saved and an effective and quick cleaning of the individual filter elements can be ensured.

Finally, it is expedient, as disclosed in claim 7, to control the cleaning of the filter elements dependently of the degree of blockage, in that an economical operation of the apparatus is hereby ensured.

The invention will now be described in more detail with reference to the drawing, where

fig. 1 shows a sectional view of an apparatus during operation seen in the direction I-I in fig. 2,

fig. 2 shows a sectional view of the apparatus seen in the direction II-II in fig. 1, and

fig. 3 shows an enlarged view of a pair of filter ele¬ ments during cleaning and filtration respectively.

In the drawing is shown an example of a preferred embodi¬ ment of an apparatus according to the invention.

The apparatus is built in a tower which comprises a side- wall consisting of a shroud 1 and an insulation layer 2, and a heating element, for example in the form of a heating spiral 3, in a part of the tower as shown in fig. 1.

The flow of gas is introduced into the side of the tower through a channel 4 to a chamber 10 in the tower, this chamber serving as a sedimentation chamber, in that the heavy particles 8 will fall to the bottom at the end of a funnel 5 and be collected in a container 7 placed under the funnel. The container 7 can be removed for emptying as required through a hatch 6 in the side of the tower.

The top of the chamber 10 is closed by a wall 18 to which the filter is mounted. This comprises a number of filter elements 11 which, for example, can be placed in two con¬ centric circular arcs as shown in fig. 2, and in such a manner that the elements 11 lie in pairs on a radius through the centre 31. In the example shown, there are mounted twenty-four elements, but this figure can be increased or reduced according to requirements.

As shown in fig. 3, each of the elements is built up of an inner grid of longitudinal stiffeners 12 which, at the top, are bent to form a conical narrowed-down portion 15. The stiffeners 12 are held together by a number of rings 13. At the bottom there is secured a shell-like baseplate 14.

The top of the grid is secured to the wall 18 around a hole formed in the plate. The filter blanket 16, which can be bag -shaped or tubular, can hereafter by drawn onto the grid and bent over at the top around the upper ring 13.

A bush 17 can now be pressed down from above through the the hole 18 in the plate to secure the filter blanket 16 around the grid.

The filter blanket can be of any suitable material, but at temperatures up to and above 800^βC it will consist of a ceramic material.

Above the wall 18 there is mounted a pivotable pipe 22 for the introduction of compressed air for use in the cleaning of the filter elements 11 when these are blocked. This is effected by means of a set of nozzles 20 mounted on the end of the pipe 22 and a pair of mouthpieces 19 which are suspended in a holder 21, see especially fig. 3. The mouthpieces 19 are configured as inlet cones and outlet cones with a narrowed-down portion between them.

When compressed air from the nozzles 20 is blown through the inlet portion 19, air from the surroundings will be carried down to the inside of the filter elements 11, as shown on the left in fig. 3. A relatively small amount of air, supplemented with the air carried down as mentioned above, will quickly fill the filter element and be reflected by the baseplate 14. There will thus arise some vertical oscillations in the air column, which will impart a vibrating movement to the filter blanket 16. This move¬ ment will loosen the dust particles 9 from the outside of the filter blanket, whereby they are given off to the chamber 10 where they are collected in the container 7.

In this manner, the filter elements 11 will quickly be blown clean, for example in one second, by pressure which can vary between one and twelve bar, depending on the conditions. The volume will naturally depend on the dimensions of the elements, but since it is supplemented with about a corresponding amount of air from the surround¬ ings, the consumption of compressed air for the cleaning is strongly reduced in comparison with known systems.

The supply of this cleaning air is effected via an over- lying unit which is mounted on top of a headplate 24, so that the nozzles 19, 20 and the pipe 22 are disposed in a limited space 23 for the gas flow from the filter elements 11 to the outlet channel 35. From here, the cleaned flue- gas is led through an exhaust system 36 with regulation damper and discharged through an outlet 37, see fig. 1. The exhaust can be adjusted according to temperature and the pressure variations in the apparatus in order to produce a so-called balanced ventilation, which contributes towards the stable cleaning in the apparatus.

The compressed air is fed through a pipe 26 to a tank 27, from which via a solenoid valve 28 it is conducted to an air lock 33, which enables through-flow for the compressed air during the turning of the pipe 22 around the centreline 31, see fig. 2.

To control the turning of the nozzles 19, 20 and the supply of cleaning air to the nozzles, there is mounted a control disk 30 which turns together with the pipe 22. This can be effected by means of a drive 33 with motor.

A scanning arm 29 scans the disk 30 and hereby provides pulses for the regulation of the turning movement of the pipe 22, so that cleaning air is not supplied until the nozzles 19, 20 are disposed above the filter elements 11, after which a signal is sent to the solenoid valve 28 for the opening of the supply of cleaning air through the nozzles.

The supply of cleaning air is then closed, and the pipe with the nozzles is turned away to a new position, depend¬ ing on which of the filter elements is required to be cleaned. A not-shown differential pressure meter will be able to register the degree of blockage of the filter bags 16, so that cleaning takes place precisely when there is need for it, hereby ensuring that the cleaning capacity of the apparatus is always constant and at an optimum.

Experiments have shown that an apparatus can effect clean- ing with dust particles of a size right down to lμ, and with a cleanliness of a maximum of 5 g dust per m³ gas. A further advantage of this apparatus is that the filter blanket 16 is cleaned so effectively that no dust particles are left on the filter blanket 16 after a blowing out, and consequently that no injurious bacteriological growth can take place, and also that no infestants will be able to thrive on these filter elements.

As will appear from the drawing, the pressure applied is of the same temperature as the surroundings, in that the upper compartment is ventilated through channels 25. The filter blanket is hereby effectively cooled when blown clean, which contributes towards the longer durability of the filter blanket. The apparatus can herewith clean gas flows with higher temperatures than with apparatus which does not use cooled air for the blowing clean of the filter.

Claims

C L A I M S

1. Filter apparatus for the removal of particles from gas flows, such as air, smoke and waste gases, which flow through the apparatus, said apparatus comprising an inlet channel for the flow of gas to a chamber with a bag-type or tubular filter which the gas passes before being led out in cleaned state through an outlet channel, said filter com¬ prising a number of filter elements consisting of a tubular frame with an external filter blanket suspended by the end in a wall in the chamber, and with means for the cleaning of the filter by blowing with air in the opposite direction through the filter, and means for the collection of the particles deposited in the chamber and filter, c h a - r a c t e r i z e d in that the filter elements (11) are placed in concentric circular arcs, and that the air for the cleaning of the filter elements is introduced through nozzles (19, 20) which are mounted on a pipe (22) which, externally on the wall (18), can turn around the centre axis (31) of the circular arcs for positioning above one or more of the filter elements (11).

2. Filter apparatus according to claim 1, c h a r a c ¬ t e r i z e d in that the nozzles comprise a tubular mouthpiece (19) mounted in such a manner in relation to the actual air nozzle (20) that the surrounding air can be carried through the mouthpiece (19) and blown into the fil¬ ter element (11).

3. Filter apparatus according to claim 1, c h a r a c ¬ t e r i z e d in that the end of the filter element (11) is closed by a baseplate (14).

4. Filter apparatus according to claims 1 and 3, c h a r a c t e r i z e d in that the filter element (11), at its outlet end (15) towards the wall (18), is narrowed- down in relation to the remaining part of the element.

5. Filter apparatus according to claims 1-4, c h a r a c ¬ t e r i z e d in that the chamber (10) with the filter elements (11) and the chamber (23) with the nozzles (19, 20) are surrounded by an insulating wall (1, 2), and that the chamber (10) with the filter elements (11) is provided with means (3) for the heating of the chamber (10).

6. Filter apparatus according to claim 1, c h a r a c ¬ t e r i z e d in that the air for the cleaning of the filter elements (11) is supplied to the pipe (22) by a valve (28) which, via a control arrangement (29, 30), supplies compressed air to the pipe (22) and herewith to the nozzles (19, 20) when said nozzles are positioned over the filter elements (11).

7. Filter apparatus according to claim 6, c h a r a c ¬ t e r i z e d in that the control is connected to a diffential pressure meter for the regulation of the clean¬ ing of the individual filter elements (11), dependently of the pressure loss through the apparatus.