GB2060433A - Gas filter - Google Patents

Abstract

A gas filter comprises a filter chamber (10) having an inlet (14) for contaminated gas and an outlet for clean gas, a plurality of filter bags (18) being radially disposed about a tubular member (16) whose interior communicates with the clean gas outlet and with the interiors of the bags, the tubular member and the bags being rotated within the chamber, and means for directing a pulse of cleaning gas into each filter bag in turn as it passes a cleaning station where an outlet (15) receives the dust removed from the filtering surfaces of the bags. A door (30) in the chamber wall enables individual bags to be inspected and withdrawn for cleaning or replacement. The bags can be rotated about a vertical or horizontal axis, by a motor or by the incoming unfiltered gas. <IMAGE>

Description

SPECIFICATION A gas filter This invention relates to gas filters of which there are many known types consisting in the main essentially of a chamber, one or more bags of a filter material disposed within the chamber, the or each bag defining a clean gas zone and a contaminated gas zone. The direction of flow of gases through the filter material is a matter of choice, although it is usual for the contaminated gas to be fed to the interior of the chamber outside of the or each filtering bag, the interior thereof being in direct communication with the clean gas zone.

Difficulties are often experienced in removal of the filter bags after a period of use. For example, in the case of a filter having a plurality of vertically suspended bags, it is often necessary to remove the bags from the top of the apparatus for subsequent cleaning and this operation requires the provision of sufficent headroom above the filter for the bags to be removed.

Increasing demand is placed upon manufacturers of filtering equipment of this general kind to ensure that filter bags are easily removable for cleaning or replacement, and from the so-called clean side of the filter.

An object of the present invention is to provide a gas filter of the kind incorporating a plurality of filter bags, wherein ready removal for cleaning or replacement is facilitated, especially in cases where limited headroom exists above the filter.

According to the present invention there is provided a gas filter comprising a filter chamber having an inlet for contaminated gas and an outlet for clean gas, a plurality of gas permeable filter bags disposed within the chamber between the inlet and the outlet, characterised in that the bags are radially disposed about a tubular member whose interior communicates with the clean gas outlet and with the interiors of the bags, the tubular member and the bags being driven in rotation within the chamber, the bags being removable individually through one or more openings in the chamber wall.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:~ Fig. 1 is a horizontal section taken on line I-I of Fig. 2 and illustrating a first embodiment; Fig. 2 is a vertical section taken on line Il-Il of Fig. 1; and Fig. 3 is a schematic vertical section of a second embodiment.

Referring now to Figs. 1 and 2, the filter comprises a chamber generally indicated at 10 defined by a cylindrical wall 11, and generally closed by top and bottom walls 12 and 13 respectively. In this example, the chamber has an inlet 14 for dusty gases and an outlet 1 5 for dust removed from the gas. An outlet for clean gas is formed by a tubular core 16 from which extends radially a plurality of filter bags 18 which, as will be described, are individually removable from the core 16.

The core 16 is rotatably mounted within the chamber 10 and is driven via a chain or belt 19 by a drive motor (not shown) thus to cause the body formed by the core 16 and the filter bags 18 to rotate about a generally central vertical axis. The speed of rotation provided by the motor is likely to be between ten minutes per revolution and one revolution per minute, as required.

Stationary within the core 16 is a pipe 21 connected via a solenoid-operated control valve 22 to a source of compressed air at 23. Each of the bags 18 communicates with the interior of the core 16, and a plurality of cleaning nozzles 24 serve to direct compressed air from the pipe 21 into an adjacent one of the bags 1 8. A fixed baffle 26 is disposed to each side of the nozzles 24 and pipe 21 thus to occlude the communication between the core and the two bags 18 immediately adjacent the bag to be cleaned.

As can be seen from Fig. 1, each of the filter bags 18 is slidably mounted in upper and lower supporting rails 27 and 28 and maintained therein by clamps 29. The cylindrical wall 11 of the apparatus includes an access door 30 which when opened provides for removal of an adjacent one of the filter bags 18. Thus, the bags are readily removable individually for cleaning and/or repair without the necessity for the operator to enter the filter chamber. Thus also, the bags can be inspected and removed individually as required.

In use, therefore, as the filter bags 18 are slowly rotated about their axis of rotation dusty gas is introduced via the inlet 14 and the dust is deposited onto the outer surfaces of the bags uniformly as they rotate. The passage of gas through the chamber is generated preferably by a fan 31 arranged to exhaust clean gas from within the core 16.

During rotation of the filter bags a sensor 32 detects the approach of a bag towards a position adjacent the nozzles 24, and transmits a signal to the solenoid-operated valve 22 to pass a pulse of compressed air into the pipe for transmission into the filter bag to shake the walls thereof and to effect a reverse flow of gas through the filtering medium of the bag thus releasing dust from the outer surface thereof and permitting the dust to pass downwardly into the outlet 15. An adjustable electronic timer controls the duration of the pulse.

It will be appreciated that the two bags immediately adjacent the bag being cleaned are sealed off from the main gas stream by the baffle 26 thus preventing the removed dust from being immediately transferred to the adjacent bags.

Thus, as the bags rotate they are cleaned in turn by the pulses of compressed air, and this occurs once for each revolution of each bag so that the bags are in filtering service during their passage around almost 3600 of their rotational axis. Preferably, scrapers or brushes 25 are attached to the bottom rails 28 of several of the filter bags thus to ensure that any dust falling from the surfaces of the bags is swept around the bottom of the chamber towards the outlet 1 5.

Referring now to Fig. 3, it will be seen that the chamber may be disposed with the filter bags arranged to rotate about a horizontal axis 33, and a dusty gas inlet 34 may be arranged tangentially with respect to the rotation of the bags. With the bags rotatable about a horizontal axis, the dust outlet is arranged on the circumference of the chamber so that when the dust is removed from the outer surfaces of the bags by the compressed air nozzles, it is allowed to fall into a hopper 35, formed at the bottom of the housing. Again, an access door (not shown in Fig. 3) is provided in a suitable position for inspecting and removing the bags.

The tangential flow of dusty air into the chamber can be used to effect rotation of the bag assembly thus obviating the need for a drive motor. A speed control device may be needed to prevent fluctuations in the rotational speed. In this example, it is possible to avoid the presence of any electrical device in the apparatus, which may be particularly important in an environment where there is a risk of explosion.

A number of advantages are provided by a filter made in accordance with the invention. For example, deterioration of the filtering surfaces as a result of dust impingement thereon in the region close to the inlet is experienced uniformly throughout as the bags rotate thus avoiding the disadvantage often found with conventional filters in premature failure of a single one of the filter bags. Furthermore, as the bags rotate relative to the cleaning nozzles, only one bag at a time is cleaned and one row of nozzles serves the entire filter. Thus, a very small part of the total filter area is taken out of filtering service during cleaning.

Preferably, so-called air movers are used in the compressed air cleaning nozzles which provide a more economical use of the compressed air than do conventional venturi/nozzle arrangements. This is further enhanced by the use of short, flat bags when compared with conventional filters employing longer cylindrical bags, wherein a considerable volume of compressed air is needed to clean the full length of the bags.

As only a small part of the total filter area is cleaned at one time it is unnecessary to provide the conventional conical collection hopper beneath the filter which usually is required to serve all the filter bags. With the present arrangement, dust removed from a single filter bag is deposited directly into the dust outlet which may be of dimensions approximately equal to those of the cross-section of each filter bag, thus reducing the overall height of the filter installation.

The low height of the bags when compared with the conventional cylindrical bags results in the dust removed from the bags having less distance to fall to the outlet, and thus reduced entrainment of the dust in the air within the bag.

As a result of the construction, little or no headroom above the filter is required on site, therefore, two or more filters may be mounted in superimposed relationship thus saving floorspace and increasing the capacity of the filter.

Claims (10)

1. A gas filter comprising a filter chamber having an inlet for contaminated gas and an outlet for clean gas, a plurality of gas permeable filter bags disposed within the chamber between the inlet and the outlet, characterised in that the bags are radially disposed about a tubular member whose interior communicates with the clean gas outlet and with the interiors of the bags, the tubular member and the bags being driven in rotation within the chamber, the bags being removable individually through one or more openings in the chamber wall.

2. A gas filter according to claim 1, in which fixed nozzle means are provided within said tubular member and adapted to direct a pulse of cleaning gas into the filter bags in turn as they rotate past the nozzle means, thus to remove dust from the exterior surfaces of the bags for collection.

3. A gas filter according to claim 2, wherein said chamber includes an outlet for removed dust said outlet being disposed directly below a cleaning station occupied by a filter bag when said pulse is applied.

4. A gas filter according to claim 2 or claim 3 including means for arresting the normal flow of gas through each filter bag when a pulse of cleaning air is applied thereto.

5. A gas filter according to claim 3, including means for detecting the presence of a filter bag as it approaches the cleaning station, said means causing actuation of a valve supplying compressed air to said fixed nozzle means.

6. A gas filter according to any preceding claim, wherein said tubular member and said bags are rotated together about a vertical axis.

7. A gas filter according to any one of claims 1 to 5, wherein said tubular member and said bags are rotated together about a horizontal axis.

8. A gas filter according to any preceding claim, wherein said contaminated gas inlet is arranged to direct the gas substantially tangentially towards said rotating filter bags thus to effect said rotation.

9. A gas filter according to any preceding claim, wherein a suction fan is connected to said tubular member thus to draw gas through said filter bags.

10. A gas filter substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.