GB2024041A

GB2024041A - Process and apparatus for the purification of waste air

Info

Publication number: GB2024041A
Application number: GB7922035A
Authority: GB
Original assignee: DUERR OTTO ANLAGEN GmbH
Current assignee: DUERR OTTO ANLAGEN GmbH
Priority date: 1978-06-27
Filing date: 1979-06-25
Publication date: 1980-01-09
Also published as: IT1117236B; JPS555791A; GB2024041B; ES481950A1; FR2429611A1; IT7949497A0; DE2828130A1; BR7904050A

Abstract

A process for the purification of waste air comprises passing waste air containing entrained solids through a travelling filter bed (18) comprising a pourable filter medium falling under gravity and removing the filter medium charged with the solids removed from the waste air from the travelling filter bed. The filter medium can be regenerated (21) and recycled (22) to the travelling filter bed. Waste air which has been substantially purified of solids may be passed through one or more travelling adsorption beds (29) or fixed adsorption beds to remove gaseous and/or liquid substances from the waste air, and/or passed through a heat exchanger to recover heat from the waste air. The process is particularly applicable to purification of waste air from lacquer- spraying units (11)-(14). The purified air and/or recovered heat may be recycled to the spraying units. <IMAGE>

Description

SPECIFICATION Process and apparatus for the purification of waste air This invention relates to processes and apparatus for the purification of waste air, for example, from lacquer spraying units, the waste air surrendering solids it has taken up in the spraying unit, such as lacquer particles, to a filter medium capable of adsorbing the solids.

Filters hitherto used in practice are unsatisfactory because they either let a large proportion of the solids through, so that even the filtered waste air or gas is still contaminated with solids, or they become blocked in a relatively short time, so that their efficiency decreases at a corresponding rate and they must be replaced or cleaned after a very short time, often daily in the case of continuous operation. This cleaning means that the working cycle is interfered with, and in some cases interrupted. Arrangements using filters which can be connected and disconnected alternately is expensive and in many cases is unacceptable for economic reasons. Centrifugal separators are also unsuitable for purifying waste air enriched with lacquer residues becase the degree of purity is unsatisfactory and, in particular, all or some of the lacquer particles remain in the waste air.The use of scrubbers is likewise unsatisfactory from both an industrial and an economic point of view.

In the case of filters used hithereto, it was not possible to recover the heat energy contained in the filtered waste air in an economical usable manner since the solids still contained in the filtered air were deposited in the unit, for example a heat exchanger, for recovering the heat energy and contaminated this unit and rendered it useless.

This invention seeks to provide a process and apparatus for achieving, in a manner which raises no industrial and economic objections, as complete as possible a purification of the waste air enriched with, for example, lacquer particles or similar solids. The invention further seeks to provide as complete as possible separation of gaseous and/or liquid substances contained in the waste air which pollute the environment and utilisation thereof.

According to one aspect of the present invention there is provided a process for the purification of waste air comprising passing waste air containing entrained solids through a travelling filter bed composed of a pourable filter medium falling under gravity, and removing the filter medium charged with the solids removed from the waste air from the travelling filter bed.

Thus the waste air is always brought into contact with new uncharged filter medium which has a particular adsorption capacity for solids, in particular lacquer particles, so that a continuous unimpaired capacity of the filter medium to absorb the solids is ensured. In this procedure, the solids in the waste air are carried by the pourable filter medium falling under gravity, whilst the purified waste air continues its path independently thereof. The filter medium charged with the solids, which are as a rule tacky, from the waste air is recycled to the travelling filter bed after regenerating at least some of the filter medium in a reactor. The filter medium can be circulated continously or, in some cases, also intermit tenly or in cycles.

According to another characteristic of the invention, the waste air which is freed or largely freed from the solids but still contains the gaseous and/or liquid and/or partially gaseous substances, in particular solvents, is passed to surrender these substances through a travelling adsorption bed with an adsorption medium in particular active charcoal, passed through the waste air stream continuously or at intervals.

In order to further improve the profitability of the process and to reduce energy losses to a minimum, according to another feature of the present invention, the purified waste air may be recycled to a lacquer spraying unit.

The waste air can also be subjected to a heat recovery process. In view of the prior intensive purification of the waste air by the travelling filter bed to remove solids, for example, lacquer particles and particles of dirt, contamination of heat exchanges or other heat recovery units by solids, such as occurred in filter processes used hitherto in lacquer-spraying units and, in spite of numerous efforts, could not be avoided in an economically acceptable manne'r, it is not to be feared. The heat can be recovered using a travelling filter bed before the waste air is fed to the travelling adsorption bed or even after waste air has already flowed through the travelling adsorption bed, which as a rule is more advantageous.

To increase the profitability, the adsorption medium which comes into contact with the waste air in the travelling adsorption bed is also advantageously recycled by being passed again to the travelling filter bed after being freed from solvents in a desorption or reactivation reactor. Particularly effective regeneration of the adsorption medium can be achieved by a double travelling bed, in particularly by a procedure such that the adsorption medium from a travelling bed through which the waste air has first flowed or from a corresponding travelling bed zone and the adsorption medium of a travelling bed through which the waste air has subsequently flowed or from a corresponding travelling bed zone are desorbed.

The filter medium can be regenerated by means of heat, in particular by combustion of the solids therein, or chemically or mechanically, for example by vacuum, or also by a combination of these methods.

The filter medium and the adsorption medium can be conveyed, for recycling, by any desired means, for example pneumatically, mechanically in some cases also hydraulically.

Furthermore, after being removed from the waste air, for example in a desorption or reactivation reactor, the solvent can be reused for the lacquer spraying unit or the like.

The heat exchange can be effected by a regenerative process, heat and moisture being released, or by a recuperative process, heat being released, for example to fresh air for the lacquer spraying unit, e.g. spray booth thereof.

To improve further utilisation of heat, the fresh air warmed by the heat from the waste air can be passed successively through the individual sections, arranged in series, of the spraying unit, so that the warmed fresh air is passed successively into the individual sections, for example first to a pre-lacquering by manual spraying, then to a mechanical lacquering and finally to an evaporation zone, and only then to the travelling filter bed. In comparison with a procedure in which these sections are arranged in parallel in the stream of fresh air, a saving in air fed in of 30% to 50% and thus a lower heat requirement are achieved.

According to another aspect of the present invention there is provided an apparatus for carrying out the process of the present invention comprising: one or more travelling filter beds the or at least some of which are arranged to be located downstream of process means for producing said waste air, the or each travelling filter bed having a pourable filter medium falling under gravity, to separate solids from the waste air.

The invention is illustrated, merely by way of example, in the accompanying drawings comprising Figs. 1 to 15 each of which shows schematically one embodiment of an apparatus according to the present invention for purifying waste air from a lacquer spraying unit.

Throughout the drawings like parts have been designated by the same numerals.

In the drawings, reference numeral 10 indicates a lacquer spraying unit which is divided, for example, into four chambers or zones 11 to 14, for example a rubbing down zone, a manual spraying zone, an automatic (mechanical) spraying zone and an evaporation zone, through which articles to be lacquered, for example vehicle bodies, are passed successively in the direction indicated by arrows, and fresh air is fed to the spraying unit via an air feed unit 15 and a line 16. The line 16 can be arranged so that it supplies only certain individual chambers of the zones 11 to 14 of the spraying unit, for example as shown in Figs. 1, 7 and 8, or all the zones as shown in Figs. 2 and 3.Any other arrangement of the line 16 is also possible, for example, an arrangement in which instead of the air being fed to the individual zones in parallel all or some of the air is fed successively, in series, through the zones which makes a saving in air fed in possible.

On flowing through the spraying unit 10, the air picks up lacquer particles and solvent and, waste air charged with these substances, passes via a collecting in 17 into a travelling bed filter 18 in which the waste air flows through a travelling bed 1 8a of a filter medium to which it surrenders the solid particles, in particular lacquer particles and particles of dirt, contained in the waste air.

In Fig. 1, the waste air, which is still enriched with solvent from the zones 11, 12, is first fed via a line 19, to the remaining zones 13, 14 if it is not, for example, recycycled to the air feed unit 15 via a line 19a, and, after flowing through the zones 13, 14 is removed via a line 20 for any other suitable treatment or further utilisation. In some cases, some of the waste air, for example from the zone 12, can also be removed to, for example, the outside via a line 20a thus by-passing the travelling bed filter 18.

The filter medium leaving the travelling bed 1 8 a is recycled via a reactor 21 with a gas outlet 21 a in which the filter medium is purified again by removing the solids (lacquer particles and particles of dirt), in particular by heating them or by combustion thereof, and via a line 22 to the inlet side of the travelling bed 18 so that the filter medium circulates continuously through the travelling bed filter 18. In some cases, some of the filter medium can also be recycled directly to the travelling bed 1 8 a by by-passing the reactor 21, as indicated by line 22a A change-over device can be provided to pass the filter medium via the reactor 21 or via the line 22a as desired.

Any substance, preferably a pourable substance, which is suitable for absorbing solids, that is to say, in particular, lacquer particles which as a rule are of a tacky nature, can in all cases be used as the filter medium for the travelling bed 1 8a. Thus the pourable substance may be, for example, corundum or an aluminium/silicon compound, steel balls or the like. It is possible, for example, for the filter medium to be further conveyed or recycled mechanically, in certain circumstances with the aid of gravity, or by a combination of methods, by a conveyor belt, by a pneumatic conveyor means or the like.

The apparatus shown in Fig. 2 differs from that shown in Fig. 1 in that the waste air flows through the zones 11 to 14 in parallel and the waste air purified in the travelling bed filter 18 is recycled to the air feed unit 15 via a line 30.

In the apparatus shown in Fig. 3, the waste air which has been purified by removing the solids therefrom is passed via a line 23 to a heat recovery unit 24, for example a heat exchanger, and is then either passed to the outisde via an outlet 35 or passed for further treatment or use. In the heat recovery unit 24, the heat the waste air contains and is taken up in the spray unit or in the travelling bed filter 18 or in heating devices connected beforehand or in between, is supplied either directly to air fed in via a line 26 and passed on to the air feed unit 15, or is transferred to another intermediate medium which, in turn, transfers as much as the heat as possible to the air fed into the air feed unit 15.An optimum balance of heat can be achieved by this heat recovery in connection with the purification of the waste air by the travelling bed filter and longlasting effectiveness of the heat exchanger thereby produced.

It is, of course, also possible for the heat recovered in the heat recovery unit 24 to be made available for other purposes. The heat exchange process can also be carried out in any desired manner, for example as a regenerative process with simultaneous transfer of moisture.

In contrast to the previous embodiments, in the apparatus shown in Fig. 4 the waste air which has been purified in the travelling bed filter 18 be removing solid particles is passed via a line 28 to a travelling bed absorber 29, a travelling bed 29a of which is part of a circulation formed by a adsorption medium such as active charcoal. In this procedure, the gaseous, in some cases also partly liquid, substances, in particular lacquer solvent, contained in the waste air are surrendered to the travelling bed 29a, the waste air flowing through the travelling bed 29a and then being removed to the outside via the line 30 or passed for further use but preferably it is recycled, as shown in Fig. 4, as part of the air fed into the air feed unit 15 or the spraying unit 10.

In a similar manner to the filter medium, the adsorption medium which forms the travelling bed 29a is passed, after adsorbing the gaseous substances of the waste air to a desorption reactor 31 with a feed 31 a of steam and moist flue gas, the waste air being heated, for example to about 250C. In the desorption reactor the gaseous substances are expelled from the adsorption medium and removed to the outside or passed to a further purification or recovery unit 32, for example for the recovery of the lacquer solvent. The regenerated adsorption medium leaving the reactor 31 is cooled, according to Fig. 4, in a cooler 33 and then recycled via a line 34 to the inlet side of the travelling bed 29a. The adsorption medium can again be conveyed mechanically, pneumatically or hydraulically in any desired manner.

Instead of the desorption reactor 31, in some cases a reactivating reactor, for example at a temperature of about 750 C, can also be used.

In the apparatus shown in Fig. 5, in contrast to that shown in Fig. 4, a fixed bed adsorber 35 is provided. The solvents separated out in the adsorber can again be passed to the solvent recovery unit 32. In order to regenerate the adsorption medium, after interrupting the feed of waste air, the adsorber can be connected to a desorption system, for example with steam fed in by a line 32a.

The apparatus shown in Fig. 6 differs from that of Fig. 4 primarily in that a heat recovery unit 24, for example substantially corresponding to Fig. 3, is connected in the waste air line 23 leaving the adsorber 29.

The embodiment shown in Fig. 7 is a combination of apparatus of Fig. 1 and Fig. 4 and differs from that of Fig. 3 in that the fresh air fed in is first passed, as in Fig. 1, to only some of the zones of the spraying unit 10, then, according to Fig. 1, to a travelling bed filter 18 and only then to the remaining zones of the spraying unit 10. The waste air finally removed from the spraying unit 10 is in this case passed viaa line 1 7 a to a second travelling bed filter 18, which corresponds to the travelling bed filter 18 of Fig. 4. Fig. 7 shows the further lines 19 a, 19b, 17 b which can optionally be provided.

The embodiment according to the present invention as shown in Fig. 8 is a combination of the embodiments of Figs. 7 and 6 inasmuch as the waste air, which has been purified by removing solid particles and gaseous constituents, from the line 23 is used for recovering the heat in a heat recovery unit 24 by a direct or indirect release of heat to the air fed in.

The embodiment shown in Fig. 9 corresponds in principle to that shown in Fig. 6, but differs from that embodiment in that a double bed adsorber 129 with travelling beds 1 29 a, 129 b is used instead of a single travelling bed adsorber 29. The desorption medium, in particular active charcoal, is passed to the two travelling beds separately, from the top, and leaves the travelling bed separately, at the bottom.The adsorption medium charged in the travelling bed with the adsorbable gaseous and/or liquid substances of the waste air, in particular lacquer solvents, is passed to a desorption reactor 31 on leaving the travelling bed 1 29 a and to a reactivation reactor 131 on leaving the travelling 1 29 b, desorption taking place in the desorption reactor 31 whilst passing in steam and/or moist flue gas at line 32a at about 250 C, whilst combustion of the harmful substances adsorbed by the adsorption medium takes place in the reactivation reactor at considerably higher temperatures, for example about 750 C. The desorbed substances from the desorption reactor, in particular lacquer sol vents, can again be passed to a recovery unit 32, whilst the substances burned in the reactivation reactor are removed to the outside via a line 131 a or are passed to a further unit for utilisation of the heat they contained.

Preferably the waste air entering the double bed adsorber 129 from the line 128 is first passed to the travelling bed 1 29 b connected to the reactivation reactor 131 and only then to the travelling bed 129a connected to the desorption reactor 31, as is also shown in the embodiment of Fig. 9. The harmful substances first deposited are then subjected to the more intensive action of the reactivation reactor, whilst the subsequent travelling bed 129a is particularly suitable for adsorbing the solvent to be recovered. The adsorption medium regenerated in the reactivation of the reactor 131 and the desorption reactor 31 can then be recycled together to the double bed adsorber 129, after flowing through a cooler 33. However, if desired, they can also be recycled separately.

Instead of separate travelling beds 129 a, 129b, these can also be combined as a common travelling bed, for example, in a manner such that the layer of the travelling bed through which the waste air flows is connected to the reactivation reactor 131 and the layer through which the waste air then flows is connected to the desorption reactor 31.

The embodiment of the present invention shown in Fig. 10 differs from that of Fig. 9 solely in that only a single travelling bed 29a of the adsorber 29 is used and the adsorption material which forms the travelling bed 29 a is divided, only after leaving the travelling bed, in order to be passed to the desorption reactor 31 on the one hand to the reactivation reactor 131 on the other hand.

The embodiment illustrated in Fig. 11 shows a unit in which a fixed bed adsorber 35 is connected downstream of the travelling bed adsorber 29. After adsorber the gaseous or still liquid substances from the waste air, the adsorption medium, for example active charcoal, is passed to the reactivation reactor 131 and, after being regenerated therein, is recycled to the travelling bed adsorber via a line 34.

The waste air which has been partially purified in the adsorber 29 is passed via a line 23ato one or morn in the embodiment shown both-adsorbers 35 connected in parallel and is then passed, in the purified state, to the heat recovery unit 24 via the line 23.

The substances in the waste air, in particular lacquer solvent, which are separated out in the fixed bed adsorbers under the action of the mixed gases produced in the combustion chamber 36 and of the steam fed in and which are still usable can be passed to further use via a recovery unit 37.

The travelling adsorber bed 29a has three zones 29a', 29a", 29a"' which are connected in series, both in the conveying direction of the adsorption medium and in the flow direction of the waste air, such that the waste air first flows through the zone 29 a"', through which the adsorption medium flows last, essentially in counter-current. However, other flow sequences can also be provided.

Fig. 12 illustrates an embodiment of the present invention which is similar to that according to Fig. 9. In contrast, however, the travelling beds of the filter 18 and of the adsorber 129 are combined to form a common filter/adsorber unit 11 8, the waste air leaving the spraying unit flowing successively through first the travelling fed 18a and then the travelling adsorber beds 129 b, 129 a re- spectively.

In a particular compact design, it is also possible for all or some of the travelling beds 18 a, 129 b, 129 a to be arranged immediately adjacent to one another and for the distance between the individual travelling bed to be zero in the limiting case, as shown in Fig. 13.

In this case it is also possible, for example, for only a single travelling adsorber bed to be provided.

An alternative embodiment is shown in Fig.

14 in which a preliminary adsorber or preliminary separator, and in some cases also a dehumidifier, is connected upstream of the travelling adsorber bed 29a. It can itself be designed as a travelling bed filter and operate with a travelling bed 1 8b, for example consisting of aluminium oxide (Al2O3). In some cases a travelling bed filter 18 according to the preceding embodiments can also be connected upstream from the travelling bed adsorber 18b.The waste air leaving line 28a is passed through the travelling bed or travelling bed filter and then, in counter-current to the movement of the travelling adsorber bed 29a, is passed through this bed or successively through the zones thereof, the travelling absorber bed 1 8 b or the travelling bed filter extending over only part of the travelling adsorber bed 29a.

The embodiment illustrated in Fig. 15 differs from that shown in Fig. 14 only in that part of the adsorption medium leaving the travelling adsorption bed 29a is passed to a desorption reactor 31 and the other part is passed to a reactivation reactor for regeneration, before it is passed via a line 34 to the travelling bed 29a of the travelling bed adsorber 29.

In the above embodiment it is of particular advance, but not absolutely necessary, that a travelling bed adsorber is also used in association with a travelling bed filter. The waste air purified by a travelling bed filter can optionally also be freed from the gaseous substances in other ways, for example by using a fixed bed adsorber However, a particularly complete purification of the waste air can be acjieved by simultaneously using a travelling bed filter and a travelling bed adsorber, and this is also particularly desirable in connection with a subsequent heat recovery unit.

Even though the embodiments of the present invention described above are advantageous, above all, for lacquer-spraying units, they can also be used for other applications, for example in connection with drying chambers, if similar demands are made by the process concerned It will be appreciated that in the above described embodiments of the present invention a heat recovery unit can be connected directly or indirectly downstream of the travelling bed filter and preferably downstream from a travelling bed adsorber which follows the travelling bed filter. Individual elements or units can accordingly be otherwise combined with one another in any desired manner.

Claims

1. A process for the purification of waste air comprising passing waste air containing entrained solids through a travelling filter bed composed of a pourable filter medium falling under gravity, and removing the filter medium charged with the solids removed from the waste air from the travelling filter bed.

2. A process as claimed in claim 1 in which the filter medium is used to filter not only solids but also liquid and/or gaseous substances from the waste air.

3. A process as claimed in claim 1 or 2 including regenerating the filter medium charged with solids and recycling it to the travelling filter bed.

4. A process as claimed in any preceding claim including recycling the filter medium leaving the travelling filter bed, part of the filter medium during recycling by-passing a reactor and another part passing through the reactor.

5. A process as claimed in any preceding claims in which in order to surrender gaseous or liquid substances from the waste air which has been substantially purified of solids is passed through a travelling adsorption bed or adsoprtion medium.

6. A process as claimed in any of claims 1 to 4 in which in order to surrender gaseous substances from the waste air all or some of the waste air has been substantially purified of solids is passed to one or more fixed bed adsorbers.

7. A process as claimed in any preceding claim in which at least some of the waste air which has been purified of solids is recycled or otherwise re-used.

8. A process as claimed in any preceding claim in which the waste air which has been substantially purified of solids by the travelling filter bed is subjected to a heat recovery process.

9. A process as claimed in claim 8 in which the recovery of heat from the waste air is carried out only after gaseous and/or liquid substances in the waste air have been substantially surrendered through a travelling adsorption bed.

10. A process as claimed in claim 8 or 9 in which the purified waste air is recycled and the heat recovered from the purified waste air is used to heat air fed to a subsequent process.

11. A process as claimed in any of claims 5 to 10 in which the adsorption medium is regenerated and re-cycled.

12. A process as claimed in claim 11 in which liquid substances recovered by said regeneration from the adsorption medium are re-used.

13. A process as claimed in any preceding claim in which the waste air is the product of air successively fed to a plurality of zones of a process.

14. A process as claimed in claim 12 in which the air is first passed through at least one of said zones, then through the travelling filter bed which filters solids therefrom and then through at least one further of said zones.

15. A process as claimed in any preceding claim in which the waste air charged with solids is passed succesively through a plurality of travelling filter beds.

16. A process as claimed in claim 14 or claim 15 when dependent thereon in which the waste air is passed through a first travelling filter bed between the zones through which it first flows and the zones through which it subsequently flows, and is then passed through a second travelling filter bed before adsorption of gaseous and/or liquid substances.

17. A process as claimed in any of claims 5 to 16 in which after leaving the travelling adsorption bed, the adsorption medium is regenerated by desorption and/or reactivation.

18. A process as claimed in any of claims 5 to 17 in which the purified waste air is subject to a plurality of adsorption processes or stages.

19. A process as claimed in any of claims 5 to 18 in which the purified waste air is passed successively through a plurality of travelling adsorption beds or zones and the adsorption medium of each travelling adsorption bed or zone is regenerated separately.

20. A process as claimed in claim 19 in which the adsorption medium of the travelling adsorption bed or zone through which the waste air first flows is regenerated by reactivation and the adsorption medium of the travelling adsorption beds or zones through the waste air subsequently flows is regenerated by desorption.

21. A process as claimed in any of claims 5 to 20 in which the waste air, immediately after passing through the travelling adsorption bed or zone and/or an adsorption filter, is passed through a further travelling adsorption bed or zone.

22. A process as claimed in any of claims 5 to 21 in which at least some of the waste air is passed through the travelling adsorption bed in counter-current to the movement thereof.

23. Apparatus for carrying out the process as claimed in any preceding claim comprising one or more travelling filter beds the or at least some of which are arranged to be located downstream of process means for producing said waste air, the or each travelling filter bed having a pourable filter medium falling under gravity, to separate solids from the waste air.

24. An apparatus as claimed in claim 23 in which at least one travelling adsorption bed and/or at least one fixed adsorption bed is arranged to be connected downstream of the travelling filter beds.

25. An apparatus as claimed 23 or 24 in which a reactor for separating solids from the filter medium or liquid and/or gaseous substances from adsorption medium of the adsorber beds is connected downstream of the travelling filter beds and/or the travelling adsorption beds.

26. An apparatus as claimed in claim 24 or 25 including a waste air recycle line between the travelling adsorption beds and the process means.

27. An apparatus as claimed in any of claims 23 to 26 including a heat exchanger unit downstream of the travelling filter beds for recovery of the heat contained in the waste air.

28. An apparatus as claimed in claim 24 or any of claims 25 to 27 when dependent thereon in which both a reactivation reactor and a desorption reactor are connected downstream of the travelling adsorption beds to regenerate the adsorption medium.

29. An apparatus as claimed in claim 24 or any of claims 25 to 28 when dependent thereon in which there are a plurality of adsorption beds, a reactivation reactor being connected downstream of at least one of the adsorption beds and a desorption reactor is connected downstream of the other or at least one of the other adsorption beds to regenerate the adsorption medium.

30. An apparatus as claimed in claim 24 or any of claims 25 to 29 when dependent thereon in which the travelling adsorption beds is in the form of a double bed adsorber with a plurality of travelling beds or zones directly adjacent one another, through which the waste air, in operation, flows successively, and a reactor is connected downstream of each of the travelling beds or zones in order to generate the adsorption medium, in the direction in which it is moving.

31. An apparatus as claimed in claim 30 in which a reactivation reactor is connected downstream of the first travelling bed or zone, in the direction of flow of the waste air and a desorption reactor is connected downstream of the subsequent travelling bed or zone in the direction of flow of the waste air.

32. An apparatus as claimed in claim 24 or any of claims 25 to 31 in which the travelling filter bed and travelling absorption bed are combined to form one element.

33. An apparatus as claimed in claim 32 in which the travelling bed of the travelling filter bed and the travelling bed of the travelling absorption bed are adjacent to one another forming zones or layers across which the waste air flows successively.

34. An apparatus as claimed in any of claims 30 to 33 in which the first travelling bed of a travelling filter bed or of a double travelling adsorption bed to which the waste air flows extends over only part of the length of the other travelling bed of a travelling adsorption bed or of the double travelling adsorption bed through which waste air flows immediately thereafter, and after entering this travelling bed the waste air is passed through the travelling bed last mentioned in counter current to the travelling filter or adsorption medium.

35. A device as claimed in claim 24 or any of claims 25 to 34 when dependent thereon arranged so that the waste air is passed through the travelling adsorption beds successively through travelling bed zones connected in series in the conveying direction of the adsorption medium of the travelling adsorption beds.

36. An apparatus as claimed in claim 35 arranged so that the waste air is first passed through a following travelling bed zone in the conveying direction of the adsorption medium and then through one or more of the preceding travelling bed zones of the travelling adsorption bed.

37. An apparatus as claimed in any of claims 23 to 36 in which a reactivation reactor and a desorption reactor downstream of a travelling adsorption'bed are connected to the travelling adsorption bed by a recycle line in order to recycle the regenerated adsorption medium.

38. An apparatus as claimed in claim 37 in which the reactivation reactor is connected to an outlet for burned solids or liquid substances and/or the desorption reactor is connected to unit for recovering the solids or liquid substances.

39. An apparatus as claimed in any of claims 23 to 38 in which one or more fixed adsorption beds are connected downstream of the travelling absorption bed.

40. An apparatus as claimed in claim 39 in which a heat recovery unit is connected downstream of the fixed adsorption beds.

41. An apparatus as claimed in claim 39 or 40 in which the fixed adsorption beds is connected to a mixed gas producer or flue gas producer and to a unit for recovering the solids and/or liquid substances.

42 A process for the purification of waste air substantially as herein described with reference to the accompanying drawings.

43. An apparatus for the purification of waste air substantially as herein described with reference to and as shown in the accompanying drawings.