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Title:
APPARATUS FOR REMOVING ORGANIC VAPOURS FROM GASEOUS STREAMS
Document Type and Number:
WIPO Patent Application WO/2018/046900
Kind Code:
A1
Abstract:
An apparatus (2) for removing volatile organic compounds (VOCs) from gaseous streams is described. VOC contaminated air is passed across movable filter (4), As the VOC/air mixture (6) passes across both sides of filter means (4), VOCs are trapped in the cloth of filter means (4) and filtered exhaust air (32) is produced. A VOC laden part, of filter (4) is then moved, into heating chamber (8) and heated by infra-red radiation (34) produced by the catalytic heating means (10). Heating the moveable filter (4) causes VOCs to be released from the filter cloth to create an exhaust VOC/air mixture (12). Outlets (42) are provided in recirculation duct (36) and are positioned such that the exhaust VOC/air mixture is passed directly across the catalysts (10a, 10b) and (10c).

Inventors:
MCGEE, Donald Richard (7 Leith Road, Darlington Durham DL3 8BE, DL3 8BE, GB)
Application Number:
GB2017/052568
Publication Date:
March 15, 2018
Filing Date:
September 04, 2017
Export Citation:
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Assignee:
MCGEE, Donald Richard (7 Leith Road, Darlington Durham DL3 8BE, DL3 8BE, GB)
International Classes:
B01D53/06; B01D53/86; B01J20/28; F23G7/07; F26B23/02
Foreign References:
GB2285044A1995-06-28
EP1930065A22008-06-11
JP2013255893A2013-12-26
Attorney, Agent or Firm:
URQUHART-DYKES & LORD LLP (NEWC) (Urquhart-Dykes & Lord LLP, Cale Cross House 156 Pilgrim Street,Newcastle upon Tyne, Tyne & Wear NE1 6SU, NE1 6SU, GB)
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Claims:
CLAIMS

1. An apparatus for removing volatile organic compounds (VOCs)' from gaseous streams, the apparatus comprising: at least one moveable filter arranged to capture VOCs from a VOC/air mixture passed across said at least one moveable filter; at least one heating chamber in which a catalytic heating means is arranged, said at least one moveable filter moveable into said at least one heating chamber to enable heating of a portion of said at least one moveable filter to release VOCs to produce an exhaust VOC/air mixture; suction means arranged to direct said exhaust VOC/air mixture across said catalytic heating means to cause heating thereof.

2. An apparatus according to claim 1, wherein said suction means comprises: a recirculation duct having a first inlet disposed inside said at least one moveable filter and at least one outlet; at least one fan arranged to draw said exhaust VOC/air mixture into said first inlet; and wherein at least one said outlet is arranged to channel said exhaust VOC/air mixture across said catalytic heating means.

3. An apparatus according to claim 2, further comprising a second inlet to the recirculation duct through which filtered exhaust air can be introduced into the recirculation duct.

4. An apparatus according to any one of the preceding claims, wherein said moveable filter means comprises a laminated activated carbon cloth (ACC) belt disposed on rotation means, and wherein said laminated activated carbon cloth (ACC) belt is arranged in the flow of said VOC/air mixture such that said VOC/air mixture passes through two sides of said laminated activated carbon cloth (ACC) belt to produce an exhaust air flow.

5. An apparatus according to claim 1, wherein the

apparatus comprises: a first moveable filter arranged to capture VOCs from a VOC/air mixture passed across said first moveable filter to produce filtered exhaust air; a first heating chamber in which a first catalytic heating means is arranged, said first moveable filter moveable into said first heating chamber to enable heating of a portion of said first moveable filter to release VOCs to produce a first exhaust VOC/air mixture; a second moveable filter arranged in the path of said

filtered exhaust air to capture VOCs therefrom; a second heating chamber in which a second catalytic heating means is arranged, said second moveable filter moveable into said second heating chamber to enable heating of a portion of said second moveable filter to release VOCs to produce a second exhaust VOC/air mixture; wherein said first exhaust VOC/air mixture is passed across said second catalytic heating means to cause heating thereof and said second exhaust VOC/air mixture is passed across said first catalytic heating means to cause heating thereof.

6. An apparatus according to claim 5, further comprising an outlet to atmosphere on an exhaust side of said second moveable filter» 7. An apparatus according to any one of claims 5 or 6, further comprising at least one inlet for atmospheric air1 arranged to feed into the stream of said first or second exhaust V0C7air mixture. 8. An apparatus according to any one claims 5 to 7, wherein said first and/or second moveable filter comprises a substantially cylindrical filter being arranged to rotate about its longitudinal axis. 9. An apparatus according to claim 8, wherein said first and/or second heating chamber defines a sector of the

circular cross section of said substantially cylindrical filter. 10. An apparatus according to any one of claims 5 to 7, wherein said first and/or second moveable filter comprises a pair of substantially planar filters arranged to be

alternately moved in and out of the respective said first or second heating chamber.

11. An apparatus according to claim 10, wherein said first and second moveable filter each comprise a pair of

substantially planar filters arranged to be alternately moved in and out of the respective said first and second heating chambers, wherein a first pair of said substantially planar filters is arranged to remain stationary whilst a second pair of said substantially planar filters is alternated in and out of the respective heating chamber.

12. An apparatus according to claim 10 or 11, further comprising labyrinth seals disposed between the respective heating chamber and each said pair of planar filters.

13. An apparatus according to claim 10 or 11, further comprising a pressurised air seal disposed between the respective heating chamber and each said pair of planar filters.

AMENDED CLAIMS

received by the International Bureau on 15 February 2018 (15.02.2018)

1. An apparatus for removing volatile organic compounds (VOCs) from gaseous streams, the apparatus comprising: at least one moveable filter arranged to capture VOCs from a VOC/air mixture passed across said at least one moveable filter; at least one heating chamber in which a catalytic heating means is arranged, said at least one moveable filter moveable into said at least one heating chamber to enable heating of a portion of said at least one moveable filter to release VOCs to produce an exhaust VOC/air mixture; suction means arranged to create a negative pressure to draw said exhaust VOC/air mixture from said at least one moveable filter and direct said exhaust VOC/air mixture through a recirculation duct; wherein said recirculation duct is arranged to channel said exhaust VOC/air mixture across said catalytic heating means to cause heating thereof. 2. An apparatus according to claim 1, wherein said suction means further comprises: a first inlet of said recirculation duct disposed inside said at least one moveable filter; at least one fan arranged to draw said exhaust VOC/air mixture into said first inlet; and at least one said outlet of said recirculation duct arranged to channel said exhaust VOC/air mixture across said catalytic heating means. 3. An apparatus according to claim 2, further comprising a second inlet to the recirculation duct through which filtered exhaust air can be introduced into the recirculation duct.

4. An apparatus according to any one of the preceding claims, wherein said moveable filter means comprises a laminated activated carbon cloth (ACC) belt disposed on rotation means, and wherein said laminated activated carbon cloth (ACC) belt is arranged in the flow of said VOC/air mixture such that said VOC/air mixture passes through two sides of said laminated activated carbon cloth (ACC) belt to produce an exhaust air flow.

5. An apparatus according to claim 1, wherein the

apparatus comprises: a first moveable filter arranged to capture VOCs from a

VOC/air mixture passed across said first moveable filter to produce filtered exhaust air; a first heating chamber in which a first catalytic heating means is arranged, said first moveable filter moveable into said first heating chamber to enable heating of a portion of said first moveable filter to release VOCs to produce a first exhaust VOC/air mixture; a second moveable filter arranged in the path of said

filtered exhaust air to capture VOCs therefrom; a second heating chamber in which a second catalytic heating means is arranged, said second moveable filter moveable into said second heating chamber to enable heating of a portion of said second moveable filter to release VOCs to produce a second exhaust VOC/air mixture; wherein said first exhaust VOC/air mixture is passed across said second catalytic heating means to cause heating thereof and said second exhaust VOC/air mixture is passed across said first catalytic heating means to cause heating thereof.

6. An apparatus according to claim 5, further comprising an outlet to atmosphere on an exhaust side of said second moveable filter.

7. An apparatus according to any one of claims 5 or 6, further comprising at least one inlet for atmospheric air arranged to feed into the stream of said first or second exhaust VOC/air mixture.

8. An apparatus according to any one claims 5 to 7, wherein said first and/or second moveable filter comprises a substantially cylindrical filter being arranged to rotate about its longitudinal axis.

9. An apparatus according to claim 8, wherein said first and/or second heating chamber defines a sector of the

circular cross section of said substantially cylindrical filter.

10. An apparatus according to any one of claims 5 to 7, wherein said first and/or second moveable filter comprises a pair of substantially planar filters arranged to be alternately moved In and out of the respective said first or second heating chamber.

11. An apparatus according to claim 10, wherein said first and second moveable filter each comprise a pair of

substantially planar filters arranged to be alternately moved in and out of the respective said first and second heating chambers, wherein a first pair of said substantially planar filters is arranged to remain stationary whilst a second pair of said substantially planar filters is alternated in and out of the respective heating chamber.

12. An apparatus according to claim 10 or 11, further comprising labyrinth seals disposed between the respective heating chamber and each said pair of planar filters.

13. An apparatus according to claim 10 or 11, further comprising a pressurised air seal disposed between the respective heating chamber and each said pair of planar filters.

Description:
Apparatus for Removing Organic Vapours from Gaseous Streams

The present invention relates to an apparatus for removing organic vapours from gaseous streams. For example, the present invention relates to an apparatus for removing solvent vapours from the drying and curing of paints,

lacquers, inks and other organic coatings.

Solvent vapours produced by the curing and drying of paints and inks are potentially flammable and toxic to persons who inhale or come into contact with such vapours. It is known to use catalytic infra-red heaters to provide the heat required to dry and cure paint. Catalytic infra-red heaters are advantageous because they do not require electric power to operate following an initial preheat period.

For example, passing an organic gas such as butane over a preheated platinum based catalyst in the presence of oxygen causes an exothermic reaction to produce carbon dioxide and water vapour, heating the catalyst to cause emission of infra-red radiation. The solvent vapours produced by paint, ink and solvent based coatings can be used in this process to> heat the catalyst. Such solvent vapours may be known as volatile organic compounds (VOCs) .

Catalytic infrared heaters are advantageous because they offer a flameless combustion of gasses without any harmful products of combustion. Also, the long or medium wave

infrared energy emitted from the catalytic heaters is more readily absorbed by organic coatings and solvents than any other heat source. A known apparatus using this process is described in

GB 2285044B. It is desirable to improve the efficiency and VOC extraction capabilities of such known apparatuses whilst reducing cost.

Preferred embodiments of the present invention seek to overcome the disadvantages of the prior art.

According to the present invention, there is provided an apparatus for removing volatile organic compounds (VOCs) from gaseous streams, the apparatus comprising: at least one moveable filter arranged to capture VOCs from a VOC/air mixture passed across said at least one moveable filter; at least one heating chamber in which a catalytic heating means is arranged, said at least one moveable filter moveable into said at least one heating chamber to enable heating of a portion of said at least one moveable filter to release VOCs to produce an exhaust VOC/air mixture; suction means arranged to direct said exhaust VOC/air mixture across said catalytic heating means to cause heating thereof.

This provides the advantage of an apparatus that efficiently self-fuels a catalytic heating means to remove volatile organic compounds from air. By providing suction means to draw the exhaust VOC/air mixture across the catalysts of the catalytic heating means, this improves the efficiency of heating of the catalysts to both remove more VOCs and

increase the heating effect on the filter means to release the VOCs. By providing at least one movable filter, this enables one portion of the filter to be used to filter air whilst another portion is heated to release VOCs to be passed across the catalytic heating means and converted into a harmless mixture of water vapour and carbon dioxide. The filter can then be moved to repeat the heating process with a different portion of filter, whilst the cleaned portion of filter is used to filter air.

In a preferred embodiment, said suction means comprises: a recirculation duct having a first inlet disposed inside said at least one moveable filter and at least one outlet; at least one fan arranged to draw said exhaust VOC/air mixture into said first inlet; and wherein at least one said outlet is arranged to channel said exhaust VOC/air mixture across said catalytic heating means.

This provides the advantage of a system for efficiently passing VOCs across the catalytic heating means. In a preferred embodiment, the apparatus further comprises a second inlet to the recirculation duct through which filtered exhaust air can be introduced into the recirculation duct.

This provides the advantage of a system for improving the heating effect of the catalytic heating means.

Said moveable filter means may comprise a laminated activated carbon cloth (ACC) belt disposed on rotation means, and wherein said laminated activated carbon cloth (ACC) belt is arranged in the flow of said VOC/air mixture such that said VOC/air mixture passes through two sides of said laminated activated carbon cloth (ACC) belt to produce an exhaust air flow.

The apparatus may comprise: a first moveable filter arranged to capture VOCs from a VOC/air mixture passed across said first moveable filter to produce filtered exhaust air; a first heating chamber in which a first catalytic heating means is arranged, said first moveable filter moveable into said first heating chamber to enable heating of a portion of said first moveable filter to release VOCs to produce a first exhaust VOC/air mixture; a second moveable filter arranged in the path of said

filtered exhaust air to capture VOCs therefrom; a second heating chamber in which a second catalytic heating means is arranged, said second moveable filter moveable into said second heating chamber to enable heating of a portion of said second moveable filter to release VOCs to produce a second exhaust VOC/air mixture; wherein said first exhaust VOC/air mixture is passed across said second catalytic heating means to cause heating thereof and said second exhaust VOC/air mixture is passed across said first catalytic heating means to cause heating thereof. This provides the advantage that by cross-feeding an

exhausted VOC/air mixture over plural sets of catalytic heaters, the efficiency of removal of VOCs from air is greatly increased. This leads to increased scrubbing of VOCs from air whilst minimal electrical or other power is required for the heating steps required to catalyse VOCs.

The apparatus may further comprise an outlet to atmosphere on an exhaust side of said second moveable filter.

'The apparatus may further comprise at least one inlet for atmospheric air arranged to feed into the stream of said first or second exhaust VOC/air mixture.

Said first and/or second moveable filter may comprise a substantially cylindrical filter being arranged to rotate about its longitudinal axis.

This provides the advantage that the filter can be

continuously moved to constantly remove VOCs from intake air and produce a concentrated stream of VOC laden air to be fed to the catalytic heating means.

Said first and/or second heating chamber may define a sector of the circular cross section of said substantially

cylindrical filter.

This provides the advantage of a straightforward method of enabling construction of a heating chamber to accommodate a moveable filter that can be constantly moved in a process that does not require stoppage to refresh the filters. Said first and/or second moveable filter may comprise a pair of substantially planar filters arranged to be alternately moved in and out of the respective said first or second heating chamber.

This provides the advantage that one filter can remain operational whilst the other is heated to provide VOCs to fuel the catalytic heating means. Said first and second moveable filter may each comprise a pair of substantially planar filters arranged to be

alternately moved in and out of the respective said first and second heating chambers, wherein a first pair of said substantially planar filters is arranged to remain stationary whilst a second pair of said substantially planar filters is alternated in and out of the respective heating chamber.

This provides the advantage that the respective pairs of planar filters can be alternately moved for example at quarter hour intervals to enable a continuous cycle that does not require stoppage to refresh filters.

The apparatus may further comprise labyrinth seals disposed between the respective heating chamber and each said pair of planar filters.

The apparatus may further comprise a pressurised air seal disposed between the respective heating chamber and each said pair of planar filters.

Preferred embodiments of the present invention will now be described, by way of example only and not in any limitative sense with reference the accompanying drawings in which: Figure 1 is a schematic view of a first embodiment of an apparatus for removing volatile organic compounds (VOCs) from gaseous streams;

Figure 2 is a schematic view of a second embodiment of an apparatus for removing volatile organic compounds (VOCs) from agaseous streams; and Figure 3 is a schematic view of a third embodiment of an anparatus for removing VOCs from gaseous streams.

Referring to Figure 1, an apparatus 2 for removing volatile organic compounds (VOCs) from gaseous streams comprises at least one movable filter 4 arranged to capture VOCs from a VOC/air mixture 6 passed across the movable filter 4. A heating chamber 8 contains catalytic heating means 10. The movable filter 4 is movable into the heating chamber 8 to enable heating of a portion of the movable filter 4 by the catalytic heating means to releases VOCs to produce an exhaust VOC/air mixture 12. Suction means 14 is arranged to direct said exhaust VOC/air mixture 12 across the catalytic heating means 10 to cause heating thereof. Moveable filter 4 comprises an activated carbon cloth (ACC) belt which can be formed from for example, Zorflex

(Registered Trade Hark) ACC. The ACC materials can be varied in both depth and chemical makeup depending on the particular application in use. They can also be made in different grades of weave or in knotted form to allow for different mechanical properties which may be required and to regulate back pressures created in the gaseous streams. The ACC filter absorbs volatile organic compounds produced for example by the heating and curing of paint and hold the VOCs in the filter mesh until heated by catalytic heating means 10. The catalytic heating means preferably comprises platinum based catalysts.

The catalytic heating means 10 initially requires electricity to start and enter a pre-heat cycle. A donor fuel supply is also usually required to maintain the combustion process. Donor fuels such as natural gas, propane or butane are used. Once the heaters are started, the supply of electricity can be removed as the heating process is self-sustaining provided there is enough donor fuel being fed into the system.

The operation of apparatus 2 is as follows. VOC contaminated air, produced for example in a paint spray booth, is drawn by intake fan 22 into an intake duct 16 and is diverted by bypass plate 18 across first and second dust filters 18 and 20 to remove any particulates. The VOC/air mixture 6 then passes across the movable filter 4 which in the embodiment shown comprises an activated carbon cloth (ACC) belt disposed on rotating drums 22 and 24. A belt tensioner 26 maintains tension in the belt. The first rotating drum 22 is driven by variable drive motor 28 to periodically move the filter means 4 to cycle between different parts of the belt being either in heating chamber 8 or filtering chamber 30. Air seals 48 around the filter belt 4 isolate the heating chamber from the filtration chamber 30.

As the VOC/air mixture 6 passes across both sides of filter means 4, VOCs are trapped in the cloth of filter means 4 and filtered exhaust air 32 is produced. A VOC laden part of filter 4 is then moved into heating chamber 8 and heated by infra-red radiation 34 produced by the catalytic heating means 10 which in the embodiment shown comprises three catalysts 10a, 10b and 10c. The operation of such catalysts will be familiar to persons skilled in the art. Heating the moveable filter 4 causes VOCs to be released from the filter cloth to create an exhaust VOC/air mixture 12. This is drawn into a suction means comprising recirculation duct 36 and recirculation fan 38. Inlet 40 of recirculation duct 36 is located inside the movable filter 4 such that recirculation fan 38 creates a negative pressure the inside of the moveable filter 4 in heating chamber 8. Several outlets 42 are provided in recirculation duct 36 and are positioned such that the exhaust VOC/air mixture is passed directly across the catalysts 10a, 10b and 10c of the

catalytic heating means 10 to cause an exothermic reaction which converts VOCs and oxygen into infra-red energy, water vapour and carbon dioxide.

Ά second inlet 44 is provided to the recirculation duct 36 to enable filtered exhaust air 32 to be introduced and passed across catalytic heating means 10 to increase the amount of oxygen available for the exothermic reaction. Filtered air 32 is also exhausted to the atmosphere at extraction duct 46. Referring to Figure 2, a second embodiment of an apparatus 102 for removing volatile organic compounds (VOCs) from gaseous streams is shown. The apparatus 102 comprises a first moveable filter 104 arranged to capture VOCs from a VOC/air mixture 106 passed across the first moveable filter 104 to produce filtered exhaust air 108. A first heating chamber 110 comprises catalytic heating means 112. The first moveable filter 104 is moveable into the heating chamber 110 to enable a portion of filter 104 to be heated by the catalytic heating means 112 to release VOCs from the moveable filter 104 to produce a first exhaust VOC/air mixture 114.

A second moveable filter 116 is arranged in the path of filtered exhaust air 108 to capture remaining VOCs therefrom. Second heating chamber 118 comprises a second catalytic heating means 120, the second moveable filter 116 being moveable into the second heating chamber 118 to enable heating of the second moveable filter means 116 to release VOCs to produce a second exhaust VOC/air mixture 122. The first exhaust VOC/air mixture 114 is passed across the second catalytic heating means 120 to cause heating thereof and said second exhaust VOC/air mixture 122 is passed across the first catalytic heating means 112 to cause heating of catalysts 128.

The catalytic heating means 112 and 120 initially require electricity to start and enter a pre-heat cycle. A donor fuel supply 129 is also usually required to maintain the

combustion process. Donor fuels such as natural gas, propane or butane are used. Once the heaters are started, the supply of electricity can be removed as the heating process is self- sustaining provided there is enough donor fuel being fed into the system.

The first and second moveable filters 104 and 116 comprise cylindrical rotating cylinders formed from wire mesh filters 124 on which various grade and weaves of laminated activated carbon cloth (ACC) filters 126 are disposed. As a part of the cylindrical filter of the first moveable filter 104 rotates into the first heating chamber 110, VOCs absorbed in the filter mesh are released as a result of radiant heat produced by the first catalytic heating means 112 to form first exhaust VOC/air mixture 114 which using suction means comprising recirculation fan 134 is drawn across the second catalytic heating means 120 to produce radiant heat for the second heating chamber 118.

A second stage is provided by passing exhaust air 108 through the cylindrical filter of the second moveable filter 116. VOCs contained in exhaust air 108 are held by the second moveable filter means 116 and released by heating in the second heating chamber 118 to form a second exhaust VOC/air mixture 122 which is drawn by suction means across the first catalytic heating means 112 to produce radiant heat. This two stage process therefore cross-feeds VOC/air mixtures to heat two sets of catalytic heaters 112 and 120.

The operation of apparatus 102 of Figure 2 will now be described. VOC laden air 106 produced for example by the heating and curing of paint enters first expansion chamber 130 under pressure from intake fan 132. The gas stream 106 is passed through the cylindrical filter of the first moveable filter 104 which removes VOCs from the air stream. Exhaust air 108 exits and is passed into second expansion chamber 132. As the first cylindrical filter rotates, the portion

containing VOCs held in the ACC mesh moves into first heating chamber 110. Radiant heat produced by first catalytic heaters 112 causes the VOCs to be released from the ACC mesh and a concentrated stream of air containing VOCs 114 is drawn out by recirculation fan 134 and passed across the second set of catalytic heaters 120. Inlet feeds 136 are provided to supply atmospheric air to aid combustion in the VOC/air mixture lines. Dampers may be provided in the inlet feeds. Exhaust air 108 is at the same time drawn across the

cylindrical filter of the second moveable filter 116 which removes remaining VOCs to be held in the ACC mesh of the rotating cylinder. The VOC laden portions of the mesh are then moved into the second heating zone 118 which heats the " filter by radiant heat produced by the second catalytic heating means 120 which is fuelled by the VOC/air mixture 14 produced in the first heating chamber 110. This produces the second VOC/air mixture 122 which is passed back across the first catalytic heating means 112.

Clean air is exhausted by outlet 138 under the pressure of fan 140. A series of dampers 142 are used to pressure balance the system and an inline chemical filter 144 passes surplus recirculation air back into the intake duct. Inline chemical filter 114 is used to clean any residual gases created by the oxidation process of the catalytic heaters. Referring to Figure 3, a third embodiment of the present invention will now be described. Many of the features of the air circuit of the third embodiment of Figure 3 are similar to those of the Figure 2 embodiment, the main difference being the construction and shape of the first and second stage filters.

Referring to Figure 3, an apparatus 150 for removing VOCs from a gas stream comprises first moveable filter 152

arranged to capture VOCs from a VOC/air mixture 154 passed across the first moveable filter 152 to produce filtered exhaust air 156. A first heating chamber 158 in which a first catalytic heating means 160 is arranged is provided into which said first moveable filter 152 is moveable to be heated to release VOCs to produce a first exhaust VOC/air mixture 162.

A second moveable filter 164 Is arranged In the path of filtered exhaust air 156 to capture VOCs therefrom. A second heating chamber 166 In which a second catalytic heating means 168 is arranged such that second moveable filter 164 is moveable into the second heating chamber 168 to be heated and released VOCs to produce a second VOC/air mixture 170. The first exhaust VOC/air mixture 162 is passed across the second catalytic heating means 168 to cause heating thereof and the second VOC/air mixture 170 is passed across the first

catalytic heating means 160 to cause heating thereof.

The first moveable filter comprises two substantially planar filters 152a and 152b formed from mesh and ACC similar to the filters of the second embodiment. The first and second filter elements 152a and 152b are arranged to be slidably moved in and out of the first heating chamber 158 by use of motor 172. Labyrinth seals 174 and an air seal 176 are provided to isolate the heating chambers 158 and 166 from the filtration expansion chamber 178.

The second moveable filter 164 comprises first and second moveable planar filters 164a and 164b moveable by means of a motor 180 in the same manner as the first set of planar filters. The third embodiment 150 therefore operates in substantially the same manner as the second embodiment of Figure 2, the difference being the shape of construction and method of movement of the filters. The first set of filters 152a and 152b are arranged to be moved at different times to second filters 164a and 164b. For example, the first set of filters might switch over between the first heating chamber 158 and expansion chamber 178 at a time interval of for example, 15 minutes when the second filter 164a and 164b are switched. The cross-feeding of the VOC/air mixture outputs from VOCs exhausted from the filters operates the catalytic heating means 160 and 168 in substantially the same manner as the second embodiment. It should also be understood that the first embodiment of Figure 1 has been shown single filtration stage for the purposes of clarity. It is envisaged that a second stage comprising a second moveable filter 4 and second heating chamber 8, and the cross feeding technology disclosed above in the second and third embodiments of Figures 2 and 3 could be added to the Figure 1 embodiment.

It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.