FIELD OF THE INVENTION

This invention relates to air filtration apparatus, in particular but not exclusively, to an improved low maintenance mineral dust remover adapted to operate with reduced noise and reduced energy consumption but having high dust removal efficiency.

BACKGROUND OF THE INVENTION

Equipment designed for use in maintaining air quality in high dust environments have been developed to overcome problems associated with, for example, the inhalation of mineral dust in mining operations which causes medical conditions such as asbestosis, silicosis, industrial asthma and mesothelioma. These debilitating diseases are an occupational hazard for workers in the mining industry and the cost to the community is high in insurance premiums and payouts.

Prior art air filtration devices include wet scrubbers which remove mineral dust particulate matter by passing dust laden air through a curtain of mist wherein the dust particles are trapped by water droplets. Such equipment requires high energy to operate as contaminated air is inducted at high velocity and pressure into the scrubbing vessel where it passes through a fine mist of water. The dust laden mist is then removed downstream by means of a mist eliminator contained in a suitable housing.

Because of the high velocities and air pressures involved, not all droplets are eliminated and there are usually additional vane eliminators downstream of the primary filter to provide a further catchment system to remove residual water

droplets. As there is high resistance to the flow, prior art scrubbers require large motor driven fans that correspondingly consume large amounts of electricity or diesel fuel. There is also the problem of high noise generation levels with the use of large fans and motors.

The scrubber disclosed in my PCT Application WO2004/025081 overcomes these problems to a large extent. The novel positioning of the primary filter to create a parallel or in line flow reduces the power required for operation and cuts down on the amount of water used and the noise generated. However this scrubber still uses water to create a mist to trap dust particles and water is usually a scarce resource in mining environments.

OBJECT OF THE INVENTION

It is therefor an object of the present invention to reduce the disadvantages and limitations of the prior art scrubbers, or at least to provide a useful alternative.

SUMMARY OF THE INVENTION

According to the present invention a dust extractor comprises a housing having an inlet and an outlet, a rotating filter, and a fan which draws dust laden air in through the inlet, through the rotating filter and out through the outlet.

Preferably the rotating filter comprises a filter medium formed in a generally cylindrical shape with end caps mounted on a central shaft supported in the housing axially in the direction of the air flow.

In preference, the end caps may be configured shape wise or have vanes or flights to augment airflow in contact with the filter.

The rotating filter can also be configured by having grooves or channels to increase the surface area of the filter.

5 Preferably the inlet end cap of the rotating filter is impermeable requiring the flow to pass through the filter medium of the generally cylindrical wall before exiting through holes in the outlet cap.

In another preferred version, the inlet is positioned such that airflow is channeled in a counter current direction with respect to the rotating filter. io Preferably the filter medium is a steel or nylon mesh the filaments of which are between 0.05 and 2.5 mm in diameter.

Preferably the rotating filter rotates at speeds up to 200rpm. Preferably, the filtration rate can be controlled by varying the speed of rotation of the filter, /j

Preferably the fan is located downstream of the rotating filter.

In an alternative version, the filter may be rotated in a countercurrent direction to the direction of the airflow to increase the filtration effect.

The dust extractor may be oriented horizontally or vertically or at any angle in 20 between.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention be more readily understood and put into practice reference is now made to the accompanying drawings wherein:

Figure 1 is a side elevation of a dust extractor according to Example 1 of the invention and

Figure 2 is an end elevation from the left of Figure 1.

Figure 3 is a side elevation of a dust extractor according to Example 2 of the invention and

Figure 4 is an end elevation from the left of Figure 3. Figure 5 is a plan view of a dust extractor according to Example 2, and Figure 6 is a side elevation from the left of Figure 5. Figure 7 is a pictorial view of a dust extractor according to Example 3. Figure 8 is a side elevation of a dust extractor according to Example 4, and Figure 9 is a plan view through section line AA of Figure 8. Figure 10 shows a dust extractor of Example 4 mounted on a tunneling machine. Figure 11 shows a dust extractor of Example 4 on a trolley.

DETAILED DESCRIPTION OF THE DRAWINGS

Example 1

The dust extractor shown in Figure 1 and Figure 2 has a cylindrical housing 1 with a reduced cylindrical inlet 2 and fan 3 at outlet 4. Housing 1 contains a rotating filter 5 with a cylindrical wall 6 formed preferably from steel mesh and having end caps 7 and 8, mounted on central shaft 9 which is supported along the axis of housing 1. Inlet end cap 7 is impermeable and forces the flow around it and through cylindrical wall 6 whence it exits through holes 10 in outlet 4 end cap 8.

In my earlier design disclosed in WO 2004/025081 where the filter is a stationary fixture inside the housing, it is necessary to create a water mist for the dust particles

to be caught by the filter. However when the filter 5 of the present invention is rotated at speeds up to 200 rpm the dust particles are caught by the steel mesh without the aid of water.

The dimensions of the steel mesh are important for effective removal of the dust particles without the use of water. It has been found that the filament size and the mesh size which is optimum for the capture of the dry dust particles varies depending on the size and nature of the particles. Preferably, the filaments of the filter are between 0.05mm and 2.5mm in diameter depending on the filtering efficiency and application requirements.

Example 2

The dust extractor shown in Figure 3 and Figure 4 has a cylindrical housing 10 with a side cylindrical inlet 12 and fan 13 with outlets 14 and 14a. Housing 10 contains a rotating filter 15 with a cylindrical wall 16 formed preferably from steel mesh and having end caps 17 and 18 mounted on central shaft 19 which is supported along the axis of housing 10. The rotating filter in this example is shown with vanes or flights 15a, 15b, 15c, 15d to augment the airflow around and through the filter 15. Inlet end caps 17 and 18 in close proximity to housing end walls 10a, 10b forces the flow through cylindrical wall 16 of the filter whence it exits through the holes 17a, 18a of the end caps 17, 18 respectively.

Example 2A

Figure 5 and Figure 6 show plan and side elevation views respectively of another version of the dust extractor of Example 2.

The dust extractor of Figures 5 and 6 has a cylindrical housing 20 with an offset side inlet 22 and fan 23 with outlets 24, 24a. Housing 20 contains a rotating filter 25 with a cylindrical wall 26 formed preferably from steel mesh and having end caps 27 and

28 mounted on central shaft 29 which is supported along the axis of housing 20.

The rotating filter 25 is shown with vanes or flights 25a, 25b, 25c, 25d to augment the airflow around and through filter 25. Inlet end caps 27 and 28 in close proximity to housing and walls 20a, 20b forces the flow through cylindrical wall 26 of the filter whence it exits through the holes 27a, 28a of the end caps 27, 28, respectively.

The offset position of side inlet 22 together with flow baffle 22a causes a further acceleration of the airflow around the filter 25 pushed by vanes or flights 25a, 25b, 25c, 25d thereby increasing the filtration rate.

Example 3

Figure 7 shows another example of a dust extractor of a similar design to that of

Example 1

In this example, the dust extractor 30 has a cylindrical housing 31 with a cylindrical inlet 32 incorporating a fan 33. This differs from the arrangement of Example 1 where the fan is positioned at the outlet and not the inlet. Air 34 is drawn by the fan 33 through the inlet 32 and channeled against inlet and cap 35 so that it flows around and through rotating filter 36 before exiting the extractor through the outlet

37. Dust particles 38 thrown by centrifugal force against the inside wall 31a of the housing 31 are caught by dust box 39 which is preferably emptied by vacuum or other means.

The rotating filter 36 in this example is supported by an internal frame 36a preferably of lightweight steel or aluminum.

Example 4

Figure 8 and Figure 9 show an elevation and sectional plan view, respectively of a dust extractor according to Example 4.

The dust extractor of Example 4 is of an elongated configuration having a pair of fans 41 , 42 at either end of the housing 43. In this version of the invention, air is drawn by fan 41 at the inlet 44 and is directed by inlet end cap 45 of a conical shape to flow around rotating filter 46. Dust 47 thrown by centrifugal force against the inside wall 40a of housing 40 is collected by dust box collector 40b.

Air 48 flowing through the rotating filter 46 is drawn by exhaust fan 42 located at the outlet 49. The exhaust fan 42 and outlet 49 are shown of larger diameter than inlet fan 41 and inlet 44 to create a suction effect.

Figure 10 shows a dust extractor 50 of the design of Example 4 located on a tunneling machine 51. Dust created by the tunneling activity is drawn into the inlet 52 and cleaner air exits downstream of the tunneling machine via the outlet 53.

Figure 11 shows a portable version of the dust extractor of Example 4. The dust extractor 60 is mounted on a trolley 61 having castor wheels 62, 63, 64, and can be wheeled into position in a workshop or other work environment to clean the air.

The advantages of the present invention include improved efficiencies in dust removal without the use of water. The new dust extractor removes from 98.0% to 100% of respirable dust as compared to the prior art scrubbers which remove only about 95.0% of respirable dust. In terms of total dust removal, the present invention removes from 98.0% to 100% of the total dust content as compared to about 98.0% removed by prior art dust scrubbers. Furthermore, the present invention provides a power consumption saving in the order of 30% to 50% and noise levels are reduced by about 15%.

VARIATIONS It will of course be realised that while the foregoing has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is herein set forth.

Throughout the description and claims this specification the word "comprise" and variations of that word such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps.