GB2068770A - Dust extraction apparatus - Google Patents

Abstract

Dust extraction apparatus including a fine mesh filter arrangement (26) and means for producing a curtain of atomised water upstream thereof. So that the fine mesh filter arrangement (26) does not require frequent maintenance, the water which is introduced into the apparatus is introduced into a flow passage upstream of said filter arrangement through spray jets (10, 11, 12) to form a curtain of atomised water in which some dust is extracted. Water droplets which impinge against the filter arrangement (26) gradually run down the latter and tend to clean the filter and prevent blockage. <IMAGE>

Description

SPECIFICATION Dust extraction apparatus The invention relates to dust extraction apparatus and has for its object to provide an improvement therein. In particular, it relates to dust extraction apparatus for use in ventilation systems such as the ventilation systems of coal mines.

Several different types of dust extraction apparatus are known, usually based upon one or more of the following techniques:- washing systems, fine mesh or material filters, electrostatic separators, cyclone collectors. When using these dust extraction methods, either individually or collectively in an industrial environment, other conditions often have to be satisfied as well as that of efficient dust removal. For example in a coal mine regulations governing electrical appliances due to explosion hazards have to be met alongside constraints imposed by the lack of physical space in certain areas, the requirement for low noise generation and, of vital importance, the imposition of a minimal pressure drop in the ventilation system so as not to seriously reduce the volume of air flowing through it.

There are at present three principle types of dust extraction apparatus used in coal mines. These will be described in turn. The first are generally known as irrigated filters. In this type of extraction apparatus an irrigated screen is used together with a ventilation fan. As well as providing the means for moving the dust laden air the fan is used as a water impeller and atomiser. This is achieved by directing a high velocity water jet axially towards the fan blades.

When it strikes the blades, the water breaks into fine drops which are projected in the direction of air flow.

The dust extraction washing process occurs when a water droplet and a dust particle coalesce, and run down into a collection tank. Due to the method employed to atomisethe water, a large quantity of water is necessary to achieve effective wetting of the dust.

This high water flow, which may be 5 to 30 gals per minute, causes additional difficulties. Most of the water is carried over downstream of the irrigated screen. This carried over water is removed by a 'droplet eliminator section', which adds to the size and cost of the total system but much more importantly, introduces a significant pressure drop in the ventilation system concerned. A further problem arising from the high water flow rate is its discharge.

It cannot be simply vented as drainage points are not usually available and it has to be recirculated in the filtration system. This means the provision of a water circulating pump, tank, ball valve level control means and the like, again adding to the cost and size of the installation. After some time it is found that the screen is being irrigated by dirty water.

It must be borne in mind that electrical devices such as fan motors or water pumps when used in a mine have to conform to very stringent flame and spark proof regulations and as a consequence tend to be extremely expensive.

Thus in summary the irregated filter type of dust extraction apparatus although highly efficient (around 93% by mass for respirable coal dust can be removed) is large and cumbersome, typically 3.5 m long and weighs around 1400 Kg when dry, noisy due to the integrated fan, expensive, requires regu lar service and maintenance due to its moving parts, and introduces a significant pressure drop into the ventilation system.

A second type of dust extraction apparatus used in coal mines is the fabric type dust filter. These are introduced into the ventilation system such that the dust laden air has to pass through their fine mesh, thus causing the dust to be trapped whilst the cleaned air passes through. The difficulty which arises with these filters is due to the progressive build up of extracted dust in the filter material with a corresponding impedance to the flow of airthrough it. Thus the more efficient they are at removing dust, the quicker they block and the faster the pressure drop against them rises. On their own they there fore require regular maintenance to clean or change the fabric, which is costly in terms of material and man hours, and of course means regular interruption of the ventilation system itself.

A third type of dust extraction apparatus used in coal mines is the precipitative wet dust collectors. In these, dust laden air is drawn along ducting into a tapered scrubber section shaped to create a self induced curtain of water. This action washes the dust particles from the air and the collected dust settles into the bottom of the tank. The system therefore has the advantage of no moving parts (other than a ball valve water level control on the water tank), does not continuously use large amounts of water and requires no electrical supply.It is claimed to be only slightly less efficient than the irrigated filter type of dust extraction apparatus referred to above (figures of 88% efficiency are quoted) but the tapered scrubber section, baffles and eliminators present an impedance to airflowthroughthe unit resulting in a significant pressure drop through the ventilation system concerned. Finally the system suffers from being very large and bulky which prevents it being usable in many areas. Its size and weight is such that it is designed to be dismantled into two or three separate sections so as to facilitate handling and transport to suitable underground working sites.

The object of the present invention is to provide dust extraction apparatus which will at least alleviate some if not all of the difficulties referred to above.

According to the invention, there is provided dust extraction apparatus including a fine mesh filter arrangement disposed within a filter section of the apparatus and means for introducing a water spray or water sprays into a flow passage upstream of said filter arrangement to form a curtain of atomised water through which dust laden air must pass before passing through said filter arrangement. The curtain of atomised air will preferably be produced by a plurality of water spray jets equally spaced around The drawings originally filed were informal and the print here reproduced is taken from a later filed formal copy.

the flow passage and arranged to direct respective sprays of water radially inwards of the flow passage.

The fine mesh filter arrangement may be constituted by first and second filter panels spaced apart within the filter section of the apparatus, and in this case the first filter panel may be constituted by a fine steel mesh and the second filter panel may be constituted by a fine fabric screen. The filter section of the apparatus will preferably be of box-like shape with a removable side panel covering an aperture through which the fine mesh filter arrangement can be removed for the cleaning or replacement of the filter panel or filter panels of which it is composed. The filter arrangement may be of rectangular shape and be slidably mounted in the filter section of the apparatus.A sump will preferably be formed beneath the filter section of the apparatus, the sump being for the reception of droplets of water which are arrested by their impingement against the filter arrangement and which run down the filter arrangement for collection in the sump. In this case the sump will preferably be provided with a tap through which water which has collected in the sump can be drained. A dribble bar spray may conveniently be connected to the tap so that, if the apparatus is located above a moving belt conveyor device, the water collecting in the sump can be distributed across the width of the moving belt by said dribble bar.

In order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example only, with reference to the accompanying drawings, of which:~ Fig. 1 is a side view of dust extraction apparatus embodying the invention, Fig. 2 is a side view of the apparatus with a cover panel removed, Fig. 3 is an end view, and Fig. 4 is a perspective exploded view of the apparatus.

Referring now to the drawings, the dust extraction apparatus there illustrated includes two tubular steel sections 1 and 2 welded to suitably apertured respective end walls 3 and 4 of a box-like section 5.

(In use of the apparatus the tubular steel sections will form part of a flow passage of a ventilation system in which the apparatus is installed. Forthis reason, as shown in Fig. 4, the free ends of the tubular steel sections are flanged for connection to what will be adjacent lengths of ducting in the ventilation system). The box-like section 5 constitutes a filter section within which a fine mesh filter arrangement generally indicated 26 is disposed, said filter arrangement being constituted by first and second filter panels 14 and 19 spaced apart within said filter section. The first filter panel is constituted by a fine steel mesh and the second filter panel is constituted by a fine fabric screen.

The apparatus also includes means for introducing water sprays into what, in use of the apparatus, will be the upstream end of the flow passage through the apparatus, that is to say into a part of the flow pas sage upstream of the filter arrangement, to form a relatively narrow curtain of atomised water through which, in use of the apparatus, dust laden air must pass before passing through the filter arrangement.

These means, in the illustrated embodiment, are constituted by three water spray jets 10, 11 and 12 which are equally spaced around the flow passage, said jets extending through respective holes in the tubular steel section 1 and being connected to a water supply pipe 22 extending around the outer periphery of the section 1. The arrangement is such that, in use of the apparatus, the jets direct respective sprays of water radially inwards of the flow passage so that the whole cross sectional area of the flow passage is covered by the relatively narrow curtain of atomised water. In passing through the curtain of atomised water, the dust laden air will be partially cleaned because much of the dust and grit entrained in the air flow will be "knocked down" by droplets of water with which they collide and coalesce.Other droplets of water which have not collided with particles of dust and grit will become entrained in the flow of air through the apparatus and will impinge upon the fine mesh filter arrangementto run down the filter panels 14 and 19. Asump 16 is formed beneath the filter section of the apparatus for the reception of droplets of water running down the filter panels 14 and 19. The sump is shown to be provided with a tap 18 through which water which has collected in the sump can be drained.

Referring now in particular to Fig. 4, it will be seen that the box-like filter section n of the apparatus is provided with a removable side panel 6 covering an aperture 23 through which the fine mesh filter arrangement can be removed forthe cleaning or replacement of the filter panels. A resilient gasket 7 makes an air tight seal when the panel has been secured in position. The side wall of the filter section is provided with quick release securing elements 24 for the removable panel so that the filter arrangement can be removed and subsequently replaced with a minimum of time and trouble.

It has been found that dust extraction apparatus as just described has alleviated virtually all of the disadvantages of the various types of dust extraction apparatus referred to previously. This is because:- a) the apparatus is of relatively light weight and of relatively small size so that it can be installed with relative ease in many situations where previously known dust extraction apparatus could not be employed, b) the apparatus uses relatively small volumes of water so that the disposal of water running from the apparatus is not a problem. Coupled with this is the fact that since the water does not need to be recirculated, the water which is used for irregating the filter panels is clean water, c) the fact that droplets of water are constantly collected on the filter panels and gradually run down the latter tends to clean the filter panels and prevent their blockage. Consequently, the apparatus does not require frequent maintenance and the pressure drop across the apparatus is minimal.

Various modifications may be made. For example, it will be understood that the filter arrangement need not necessarily be constituted by first and second filter panels spaced apart within the filter section of the apparatus; the filter arrangement could be constituted by a single filter panel or on the other hand by three or more filter panels. Furthermore, the curtain of atomised air need not necessarily be produced by a plurality of water spray jets equally spaced around the flow passage. For example, it may be found that an adequate water curtain can be produced by a single water spray jet located at one side of the flow passage or located substantially at the centre of the flow passage and arranged to project a water spray radially outwards or substantially in the form of a hollow cone.

As previously mentioned, dust extraction apparatus embodying the invention is so small and light that it can be installed with relative ease in all sorts of situations where previously known apparatus could not be used. For example, it can be mounted on a road making machine in a coal mine, e.g. on a "BOSCO", "ROBBINS" or "THYSSEN" road header. It will be understood that where the air is particularly dust laden, apparatus embodying the invention may be used in series with another similar item of apparatus or for example, with an item of apparatus comprising only the means for forming a curtain of atomised water through which the dust laden air must pass before entering the second and more effective item of apparatus.

It has been found that, typically, an item of apparatus embodying the invention may use only in the region of 2 gallons of water per minute. This is a quantity of water which can very easily be disposed of, for example by being distributed across the width of the moving belt of a conveyor by means of a socalled dribble bar (not shown) connected to the tap 18. The water which is allowed to dribble onto coal carried by the conveyor can serve the additional function of damping down the dust arising at transfer points and is of course carried away by the coal.

Claims (10)

1. Dust extraction apparatus including a fine mesh filter arrangement disposed within a filter section of the apparatus and means for introducing a water spray or water sprays into a flow passage upstream of said filter arrangement to form a curtain of atomised water through which dust laden air must pass before passing through said filter arrangement.

2. Dust extraction apparatus according to claim 1, in which the curtain of atomised air is produced by a plurality of water spray jets equally spaced around the flow passage and arranged to direct respective sprays of water radially inwards of the flow passage.

3. Dust extraction apparatus according to either one of the preceding claims, in which the fine mesh filter arrangement is constituted by first and second filter panels spaced apart within the filter section of the apparatus.

4. Dust extraction apparatus according to claim 3, in which the first filter panel is constituted by a fine steel mesh and the second filter panel is constituted by a fine fabric screen.

5. Dust extraction apparatus according to either one of claims 3 and 4, in which the filter section of the apparatus is of box-like shape with a removable side panel covering an aperture through which the fine mesh filter arrangement can be removed for the cleaning or replacement of the filter panel or filter panels of which it is composed.

6. Dust extraction apparatus according to any one of the preceding claims, in which the filter arrangement is of rectangular shape and is slidably mounted in the filter section of the apparatus.

7. Dust extraction apparatus according to any one of the preceding claims, in which a sump is formed beneath the filter section of the apparatus, the sump being for the reception of droplets of water which are arrested by their impingement against the filter arrangement and which run down the filter arrangement for collection in the sump.

8. Dust extraction apparatus according to claim 7, in which the sump is provided with a tap through whichwaterwhich has collected in the sump can be drained.

9. Dust extraction apparatus according to claim 8, in which a dribble bar spray is connected to the tap so that, if the apparatus is located above a moving belt conveyor device, the water collecting in the sump can be distributed across the width of the moving belt by said dribble bar.

10. Dust extraction apparatus constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.