WO1990000437A1 - Process and device for purifying waste gases - Google Patents

Abstract

In a process for purifying waste gases laden with noxious and/or odourous substances, in particular flue gases, car exhaust fumes or outgoing air, the waste gases are fed into an aqueous bath containing a foaming agent. Most of the waste gases are incorporated in the foam bubbles as they pass through the surface of the bath and are transported from the surface of the bath together with the foam bubbles. During transport of the foam bubbles, noxious and odorous substances in the waste gases are absorbed onto the inside of the bubble skin. The foam bubbles are then liquefied, releasing the purified waste gases, and the noxious and odorous substances are trapped, together with the liquid from the foam bubbles, possibly concentrated and disposed of. To stabilize the foam, lignin derivatives such as lignin sulfonate are added to the foaming agents, which consist, for example, of anionic tensides.

Description

Method and device for cleaning exhaust gases

The invention relates to a method and a device for cleaning exhaust gases loaded with pollutants and / or odorous substances, in particular flue gases, engine exhaust gases, exhaust air or the like.

The wet cleaning of pollutant-containing waste gases is usually carried out in columns with trays, packing elements or packagings in the counterflow of waste gas and washing liquid and with gradual or continuous contact of these phases, in scrubbers with nozzle or dispersion systems for the gas or liquid phase, carried out in washers with rotating internals for dividing the washing liquid into the exhaust gas stream, in bubble columns and vessel absorbers with dispersion of the exhaust gas phase in the washing liquid and in bio-washers with special internals. The actual sorptive binding of harmful gases by the receiving scrubbing liquid often has to be preceded by mechanical dust removal from the exhaust gas flow. In the above-mentioned processes, it is considered advantageous that large exhaust gas flows can be treated. Depending on the procedure, however, disadvantages such as high energy input for conveying and dispersing the exhaust gas and scrubbing liquid phase, risk of contamination and fouling in the case of absorber construction, especially in the case of combined fine dust separation and harmful gas absorption, and in some cases high investment costs and considerable operating costs with large scrubbing liquid throughputs to be accepted.

The invention is therefore based on the object of developing a method and an apparatus for exhaust gas purification which, with a low use of conveying energy and a wringing liquid requirement ensures effective dedusting and sorptive binding of harmful gases even with changing exhaust gas compositions.

The solution to this problem is based on the idea that the exhaust gases are exposed to a large phase interface of the washing liquid with the longest possible residence time. According to the invention this is achieved in that the exhaust gases are introduced into an aqueous bath mixed with a foaming agent, that the majority of the exhaust gases introduced into the bath are enclosed in foam bubbles as they pass through the bath surface and with the foam bubbles from the Bath surface is transported away that pollutants and odorous substances are bound sorptively on the inner surface of the bladder membrane in the course of the bubble transport and that the foam bubbles are subsequently liquefied with release of the cleaned exhaust gases and entrainment of the bound harmful substances and odorous substances and collected in this form , cleaned and / or disposed of. The Schaumblaseπ are advantageously liquefied by bursting to form small droplets loaded with the harmful and odorous substances. In order to be able to reuse the foaming agent, the liquefied foam bubbles are at least partially returned to the bath liquid, if appropriate after the removal of solids.

The foam bubbles transported away from the bath surface and filled with the exhaust gas advantageously form a coherent foam column. The stripping effect (degree of dedusting and sorptive yield) depends on the residence time of the foam bubbles in the foam column, on the diameter distribution of the foam bubbles and on the absorption capacity of the scrubbing liquid, which can be adjusted to the type of exhaust gas, with their Additives. It has proven to be particularly advantageous if the residence time of the foam bubbles in the foam column from the formation to the liquefaction is on average about 1 to 20 seconds, preferably 3 to 10 seconds. Since the substances returned to the bath with the liquefied gas bubbles, such as C0 _? or S0 "if the bath is regularly acidified, the pH of the aqueous bath is expediently regulated by adding an alkali, such as sodium or potassium hydroxide. Likewise, level control in the aqueous bath by adding water and tracking foaming agents is required if water and foaming agent are evaporated or carried over in the course of the process.

Surfactants, in particular a mixture of anionic and nonionic surfactants, are particularly suitable as foaming agents, which ensure sufficiently stable bubble formation when the exhaust gases are introduced into the bath. To regulate the bubble size and to stabilize the bubbles during their residence time in the foam column, a water-soluble lignin derivative, in particular lignin sulfonic acid (ligπinhydrogeπsulfite) or lignin sulfonates, such as a calcium, magnesium, NH.- or Na salt of lignin sulfonic acid, is expediently used , added to the foaming agent or directly to the aqueous bath. Particularly advantageous in this regard are an aqueous concentrate of anionic and nonionic surfactants, on the one hand, and the water-soluble calcium salt of lignosulfonic acid in a weight ratio of 80:20 to 30:70, preferably 50:50, in the form of a mixture or as a separate mixture Proven additives in the aqueous bath. For example, 1 to 4 liters, preferably 2 liters of surfactant concentrate and 1 to 4 liters, preferably 2 liters of liquid lignosulfonate, can be used as foaming agents in a 1000 liter aqueous bath. Without the lignin sulfonate Additive would have to be added at least 10 liters of surfactant concentrate to ensure a foam formation with sufficient quantity and foam stability.

According to a further preferred embodiment of the invention, the liquefied foam bubbles are largely collected before hitting the foam column and bypassing the foam column into the water bath or into a separate collecting container. This prevents the droplets from the bursting foam bubbles from destroying part of the foam in the foam column and thereby forming an undesired channel through which exhaust gases could escape unhindered.

In order to keep coarse dirt and dust particles away from the aqueous bath and to avoid an unnecessary increase in temperature of the aqueous bath, the hot exhaust gases are passed according to a preferred embodiment of the invention through a spray section to which water is applied before they enter the aqueous bath be initiated. The spray liquid can be conducted in a circuit which is preferably fed from the aqueous bath, where it can be cleaned and temperature-controlled at a suitable point.

In order to achieve an even better cleaning effect, the exhaust gases can also be passed through two or more aqueous baths with foam-forming agents arranged in steps one behind the other with foam formation, the washing liquids in the various stages adapting to the existing exhaust gases different pH values can be adjusted.

Furthermore, it has turned out to be especially Proven partially if the foam column is deflected relative to the surface normal of the water bath, preferably into a drip and / or condensation space offset to the side of the water bath. The liquefied foam bubbles collected in the draining and / or condensation space can be passed into a settling basin, the liquid being drawn off or decanted from the surface of the settling basin and returned to the aqueous bath.

In the case of engine exhaust gases, the exhaust gases are introduced into the aqueous bath under their own pressure, the aqueous bath at the same time being able to be used as an effective silencer.

In the case of exhaust gases in the form of combustion smoke gases or exhaust air and when an upstream cleaning stage is used, a pressure increase with the aid of a blower will be necessary before being introduced into the aqueous bath.

In order to carry out the exhaust gas purification method according to the invention, a device is proposed which has an aqueous bath mixed with a foaming agent, into which an exhaust pipe charged with the exhaust gases on the inlet side and with outlet openings opening into the aqueous bath, which further immerses one above the surface of the Aqueous bath arranged space for receiving a foam column composed of a plurality of foam bubbles formed during the passage of the exhaust gases introduced into the aqueous bath and which also has a receptacle for receiving the pollutants laden with liquefaction, in particular bursting of the foam bubbles Contains droplets. The collecting container can also be formed by the container containing the aqueous bath become. The proportion of foaming agent, the pH value and the temperature in the aqueous bath are adjusted in accordance with the type of exhaust gas in accordance with an optimal foaming, while the pollutants which are deposited are drawn off from the aqueous bath.

By using the foaming agent and foam stabilizer specified in detail above, a foam column with coherent foam bubbles with a diameter of 1 to 5 mm of high stability is produced. The high stability of the ^'foam bubbles requires the Verwen¬ dung of a mechanical foam destroyer, which ensures that, so gases at the end of quasistationäreπ foam column at the end of Traπsportstrecke of containing the foam column foam bubbles, any bubbles, releasing the purified Ab¬ made to rupture become. Such a foam destroyer preferably contains a plurality of perforated plates arranged one behind the other, which are equipped with sharp edges and tips for piercing the foam bubbles.

When using two or more aqueous baths which are connected step by step and mixed with foam formers, foam destroyers of the type mentioned are likewise arranged between the individual steps in order to prevent foam bubbles from being carried over from one step to the other, which causes the Introducing the exhaust gases into the aqueous baths of the higher levels could hinder.

According to a further advantageous embodiment of the device according to the invention, the exhaust pipes immersed in the aqueous bath (washing liquid) have a plurality of baffles arranged on one side on their lateral surface, preferably with the baffles pointing downwards. Chen provided outlet openings. The outlet openings, which are preferably triangular in outline, can be formed by punching and bending the guide surfaces out of the jacket surface of the exhaust pipe.

The measures according to the invention have the advantage that, compared to the conventional wet cleaning processes, a much smaller pollutant-laden washing liquid stream is obtained. This advantage particularly affects the disposal of the pollutant-containing washing liquid, which can be supported by conventional processing methods, such as mechanical solid separation, thermal, chemical and biological decomposition and regeneration. The surfactants and lignin sulfonates to be used according to the invention are amenable to biological process engineering regeneration.

In the following, the invention is explained in more detail with the aid of some exemplary embodiments shown in the drawing. Show it

Fig. La is a circuit diagram of a foam scrubber with spray cleaning precursor;

Fig. Lb shows a section through the foam bubble destroyer according to Fig la in an enlarged view.

Fig. A Priπzipdarstellung a two-stage foam gas scrubber with pre-cleaning stage;

3 shows a basic circuit diagram of a foam gas scrubber with a foam column deflected into a drip container. The foam gas scrubber shown in the drawing has a reactor vessel 10 which has in its lower region a trough 12 for receiving a washing liquid 14 which is designed as an aqueous bath, and at least one approximately horizontally oriented exhaust gas on the inlet side and with im Exhaust pipe 16, which is arranged at a distance from one another and points downward and opens into the washing liquid, and has a space 20 for receiving a foam bed 22 above the liquid level 18. The space 20 has an extraction opening 24 at the top, which either via a discharge tube equipped with foam destroyers for the cleaned exhaust gases (FIGS. 1 and 2) or via a deflection pipe 30 into a separate drip and / or condensation container 32 (Fig. 3) opens. In the latter case, the foam destroyers 26 are located in the drip and / or condensation container or in a discharge pipe 28 'connected to them. In the exemplary embodiment shown in FIG. 1b, the foam destroyers 26 consist of a plurality of perforated plates arranged one behind the other, which are designed with sharp edges or tips 33 for breaking the incoming foam bubbles and whose holes 34 allow the exhaust gases released from the burst foam bubbles to pass through . The liquid droplets formed when the foam bubble bursts are collected in a collecting ring 36 (FIGS. 1a and

2) or in the drip and / or condensation container 32 (FIG.

3) collected and, if necessary, returned to the washing liquid 14 in a sedimentation basin 38 (FIG. 3) after intermediate cleaning.

In the exemplary embodiment shown in FIG. 1 a, the hot exhaust gases arriving via line 40 are first passed through a pre-cleaning and pre-cooling stage 42 before they are fed to the foam gas scrubber via a blower 44. The pre-cleaning and pre-cooling stage essentially consists of several pipe sections 46 arranged in parallel, which are equipped with water-spraying devices 48. In the exemplary embodiment shown, the spray water is branched off from the washing liquid 14 and fed to the spray nozzle 48 of the spray devices 48 by a circulation pump 50 via lines 52. The spray water takes up the majority of the coarse solid particles in the exhaust gases in contact with the exhaust gases. In addition, the temperature of the hot exhaust gases is reduced by heat transfer. The correspondingly contaminated and heated spray water then passes via the overflow 54 of the pipe section 46 to a settling basin 56, in which a heat exchanger 58 is also arranged for cooling the washing liquid. From there, the washing liquid is conveyed back via line 60 into the tub 12 of the reactor vessel 10.

The preferably basic washing liquid is mixed with a foaming agent consisting of surfactants and ligπiπ derivatives in such an amount and composition that the exhaust gases entering the washing liquid 14 via the exhaust pipe 16 below the liquid level 18 pass through the surface of the bath predominantly be enclosed in foam bubbles. The foam bubbles, which have a diameter of approximately 1 to 5 mm, form a coherent foam column 64 which, in the stationary operating state, largely fills the space 20 of the reactor container 10 and, if appropriate, a subsequent drip container as a foam bed 22. In order to avoid premature bursting of the foam bubbles 62 within the foam column 64, the foam must be stabilized in this way by means of a stabilizer (preferably a lignin sulfonate) be that it is retained for at least 30 minutes, preferably for 1 to 2 hours, without external intervention. The foam bubbles stabilized in this way have an optimal residence time of 1 to 20 s, preferably 3 to 10 s, within the foam column, depending on the geometrical design of the system and the amount of exhaust gas, and must burst at the end of the foam column at the foam destroyer 26, releasing the cleaned exhaust gases to be brought. The liquid droplets loaded with pollutants and odorous substances from the burst bubbles are collected in the collecting ring 36 or the drip and / or condensation container 32 and, if appropriate, returned to the washing liquid 14 with the interposition of a settling basin 38. A pH controller 66 as well as level regulators and metering devices for foaming agents (not shown) ensure that the optimal operating conditions of the washing liquid are maintained despite the absorption of pollutants and the evaporation and carryover of constituents of the washing liquid.

2 is equipped with two washing stages. For this purpose, two troughs 12, 12 * are provided for receiving a washing liquid 14, 14 'mixed with foaming agent, a space 20, 20' for receiving a foam bed 22, 22 'over the liquid level 18, 18'. is arranged. The space 20 with the foam bed 22 is connected to the tub 12 'below the liquid level 18' of the second scrubber stage via a deflection section 68 equipped with foam destroyers (not shown). The incoming exhaust gases (arrow 70) pass through a feed pipe 72 equipped with spray nozzles 48 to the outlet openings 17 of the exhaust pipe 16 located below the liquid level 18 of the washing liquid 14. The spray nozzles 48 are thereby connected via a circulation pump 50 with the Wash liquid 14 is applied from the tub 12. The spray water is returned to the tub 12 with the solids particles removed during the spraying operation, the solids 74 settling on the bottom of the tub 12.

The foam bubbles 62 formed when the exhaust gases pass through the liquid level 18 initially rise in the foam bed 22 and are burst before they pass into the tub 12 'via the deflection section 68 on the foam destroyer (not shown). The polluted droplets of the foam bubbles fall back into the washing liquid 14, while the pre-cleaned exhaust gases pass into the tub 12 'with the washing liquid 14'. When passing through the liquid surface 18 ', further foam bubbles 62' are formed, which assemble in space 20 'to form a further foam column 64' and finally reach the discharge opening 24 via the deflection path 75, which is delimited at the bottom by a collecting channel 36. There, the foam bubbles 62 'are burst at several foam destroyers 26 arranged one behind the other, releasing the cleaned exhaust gases. The cleaned exhaust gases then reach the outside via the exhaust pipe 28, while the liquefied foam bubbles laden with pollutants return to the tub 12 'via the catch 36. Heat exchangers 57, 57 'are provided in the tubs 12, 12' for temperature control. Furthermore, pH probes 78 and alkali supply lines 80 intervene in the various washing stages for pH control. Furthermore, level regulators 82 are provided in both tubs for the water supply via the lines 84.

The two-stage foam gas scrubber is used primarily for those exhaust gases that would lead to the destruction of the foam bubble before the optimal dwell time was reached. This is the case, for example, with strongly hydrocarbon-containing or fatty exhaust gases.

In the exemplary embodiment shown in FIG. 3, the foam column 64 generated in the reactor vessel 10 is deflected into a drip and / or the condensation vessel 32. With this measure, the length of the foam column can be increased in spite of its low construction and thus the length of time of the exhaust gases in the foam bubbles 62 can be increased. Another advantage of this arrangement can be seen in the separation of the settling basin 38 from the tub 12, which is a simple pre-cleaning of the liquid collected from the drained foam bubbles before it is returned to the washing liquid and thus a longer service life every batch possible.

Exemplary embodiment 1

In a reactor corresponding to FIG. La without Vorreinigungsstu¬ fe with a Waπneπvolumen of 1 m ³ and about be¬-sensitive foam bed volume of 3 ³ were charged 1000 1 Lei¬ tung water, which were adjusted by adding NaOH to pH 10.

Furthermore, 2 l soft cleaner with the trade name π ESTE LENSEX 15 VP 1817 from Wiego-Werk Kreuznach Chemische Fabrik GmbH in Bad Kreuznach, which contained anionic and nonionic surfactants as the main constituents in concentrated aqueous solution, were added to the water bath as foaming agent. In addition, 2 liters of a water-soluble ligπin sulfonate were added to the water bath as a combined foam stabilizer and foaming agent. Eiteten over-the so before _^ foam scrubber initiated a powered with 400 kW cogeneration plant in the washing liquid through the exhaust pipe fumes. The exhaust gas temperature at the entrance to the scrubber was 340 ° C. in the stationary operating state, while the temperature in the scrubbing liquid was set at 38 to 40 ° C. An exhaust air temperature of 35 ° C. was measured at the outlet of the scrubber.

After a total operating time of the scrubber with the above-mentioned scrubbing liquid filling of about 45 hours, the following harmful gas concentrations at the entrance and exit of the scrubber were measured with the aid of gas test devices in which the test gas was sucked through suitable test tubes ("Dräger tubes"):

Entrance to scrubber Exit to scrubber

Concentration Concentration ppm mg / m ^: ppm mg / m 3

N0 ₂ : -250 -480 ~ 2 <3.8 2 <3.8

C0: -1400 -1650 <2.5 <2.9

<2.5 <2.9

S0 ₂ : <10 <27 Embodiment 2

A foam gas washer according to FIG. 1 a was used for flue gas cleaning in a tower smoke installation for smoking meat and sausage products. The tower smoke system is Doppelkammerπ, which are installed over several floors. The smoke generated in the basement from spruce sawdust and brushwood brushes through the individual chambers, causing the goods to be smoked. The natural chimney draft allows the excess smoke to reach the atmosphere through the roof.

For the experiment, the foam gas washer was connected to the flue gas chamber with the aid of a flexible aluminum tube and its exhaust air was introduced into the scrubbing liquid via a fan. La had a height of 2 m, a diameter of 1.5 m at a water level of 0.5 and a foam height of 1.5 m. The washing liquid was adjusted to pH 10 and a foam former and foam stabilizer according to Example 1 were added.

During the measurement, ham was smoked with a product consumption of approx. 10,000 kg with a consumption of incense (spruce sawdust and spruce twigs) of 19 kg / h. The mass concentration of organically bound carbon at the inlet and outlet of the foam scrubber was determined by adsorption on silica gel using a coulometric method.

The mass concentrations of organically bound carbon determined in five series of measurements were as follows: Measurement input scrubber output scrubber

No. mg / m ³ mg / m ³

1 192.4 28.4 2 189.0 30.8 3 194.6 29.5 187.4 31.0 5 190.7 29.8

Claims

Claims 1. Process for cleaning exhaust gases loaded with harmful and / or odorous substances, in particular flue gases, engine exhaust gases or exhaust air, characterized in that the exhaust gases are introduced into an aqueous bath mixed with a foaming agent, that at least a part of the exhaust gases introduced into the bath is enclosed in foam bubbles as it passes through the bath surface and is transported away from the bath surface with the foam bubbles so that in the course of the bubble training, harmful substances and odorous substances are sorptively bound to the inside of the bubble skin and that the foam bubbles are then liquefied with the release of the cleaned exhaust gases and entrainment of the harmful and / or odorous substances and are collected in this form. 2. The method according to claim 1, characterized in that the foam bubbles are liquefied by bursting to form small droplets loaded with the harmful and / or odorous substances. 3. The method according to claim 1 or 2, characterized gekennzeich¬ net that the liquefied Schaumblaseπ are at least partially returned in the bath liquid. 4. The method according to any one of claims 1 to 3, characterized ge indicates that the transported away from the bath surface, filled with the exhaust gas foam bubbles form a coherent foam column. 5. The method according to claim 4, characterized in that the residence time of the Schaumblaseπ in the foam column from formation to liquefaction is on average about 1 to 20 s, preferably 3 to 10 s. 6. The method according to any one of claims 1 to 5, characterized ge indicates that foaming agent is added to the aqueous bath via a drip control. 7. The method according to any one of claims 1 to 6, characterized ge indicates that the pH of the aqueous bath is regulated. 8. The method according to any one of claims 1 to 7, characterized ge indicates that the aqueous bath is heated by hot exhaust gases introduced into the bath. 9. The method according to claim 8, characterized in that the bath temperature is controlled by a heat exchanger. 10. The method according to any one of claims 1 to 9, characterized ge indicates that the exhaust gases, preferably formed as exhaust gases, are introduced into the aqueous bath under autogenous pressure. 11. The method according to any one of claims 1 to 9, characterized ge indicates that the preferably designed as Verbreππuπgs- flue gases or exhaust gases are introduced under pressure increase in the aqueous bath. 12. The method according to any one of claims 1 to 11, characterized in that the contaminants which are deposited in a collecting container or in an aqueous bath deducted continuously or discontinuously. 13. The method according to any one of claims 1 to 12, characterized in that the foaming agent contains an ioπogenic surfactant. 14. The method according to any one of claims 1 to 13, characterized in that the foaming agent contains a mixture of aπionic and nonionic surfactants. 15. The method according to any one of claims 1 to 14, characterized in that a foam stabilizer is additionally added to the aqueous bath in addition to the foaming agent. 16. The method according to any one of claims 1 to 15, characterized in that the aqueous bath as a foaming agent and / or foam stabilizer is a water-soluble lignin derivative, in particular ligninsulfonic acid or ligninsulfate, such as e.g. Ca, Mg, NH.- or Na salt of liginsulfanic acid is added. 17. The method according to any one of claims 13 to 16, characterized in that the surfactants and / or lignin derivative are added to the aqueous bath in liquid or concentrated dissolved form. 18. The method according to any one of claims 13 to 17, characterized in that an aqueous Tensidkoπzeπtrat and a lignin sulfonate in a weight ratio of 80:20 to 30:70, preferably 50:50 as a mixture or separately are added to the water bath. 19. The method according to any one of claims 13 to 18, characterized in that at 1000 1 water a lye, preferably sodium hydroxide solution, until pH 10 to 12 and 1 to 4 1 surfactant concentrate are reached. and 1 to 4 1 Lig πiπsulfonats are added. 20. The method according to claim 19, characterized in that about 2 1 aqueous concentrate of aπioπischen and πichionic surfactants and about 2 1 liquid calcium salt of lignin sulfonic acid are added to the water bath. 21. The method according to any one of claims 13 to 20, characterized in that in the course of the Reiπigungsvorgaπgs according to a predetermined Schaumsäuleπhöhe ten-side concentrate and / or lingin derivative are preferably added to the aqueous bath as a mixture. 22. The method according to any one of claims 1 to 21, characterized in that the liquefied foam bubbles are largely collected and passed bypassing the foam column in the water bath or in a collecting container. 23. The method according to any one of claims 1 to 22, characterized in that the hot exhaust gas in cross-current or countercurrent is passed through a spray section acted upon with water before it is introduced into the aqueous bath. 24. The method according to claim 23, characterized in that the spray liquid is guided in a circuit preferably fed from the aqueous bath and is cleaned and temperature-controlled there. 25. Verfahriπ nach.eiπem of claims 1 to 24, characterized in that the exhaust gases are passed through at least two successively arranged, with Schaumbild¬ ners offset aqueous baths with foaming hiπ- passed. 26. The method according to claim 25, characterized in that the aqueous baths in the various stages are regulated to different pH values. 27. The method according to any one of claims 1 to 26, characterized in that the foam column is redirected relative to the surface normal of the water bath into a drip and / or condensate space which is preferably laterally offset relative to the water bath. 28. The method according to claim 27, characterized in that the liquefied foam bubbles collected in the draining and / or cooling chamber are passed into a settling basin. 29. The method according to claim 28, characterized in that the liquid is drawn off or decanted from the surface of the sedimentation tank and is returned to the aqueous bath. 30. The method according to any one of claims 1 to 29, characterized in that the liquid level in the aqueous bath is regulated by a level controller. 31. The method according to any one of claims 1 to 30, characterized in that the aqueous bath is used as a silencer in the case of exhaust gases. 32. Device for cleaning exhaust gases loaded with harmful and / or odorous substances, in particular flue gases, engine exhaust gases or exhaust air, for carrying out the method according to one of claims 1 to 31, characterized by a aqueous bath (14, 14 '), at least one exhaust pipe (16) charged with the exhaust gases on the inlet side and with outlet openings (17) opening into the aqueous bath (14, 14'), and one above the surface (18, 18 ') of the aqueous bath (20, 20') for accommodating a foam column (62, 62 ') formed from a large number of foam bubbles (62, 62') formed during the passage of the exhaust gases introduced into the aqueous bath (14, 14 '). 64,64 '), and a container for collecting the pollutant-laden droplets formed during the liquefaction, in particular bursting of the foam bubbles (62,62'). 33. Apparatus according to claim 32, characterized in that the collecting container is formed by the container (12, 12 ') containing the aqueous bath (14, 14'). 34. Apparatus according to claim 32 or 33, characterized by a drip control for the addition of foam formers in the aqueous bath (14, 14 '). 35. Device according to one of claims 32 to 34, characterized in that the pH of the aqueous bath (14, 14 ') can be regulated by adding an alkali, preferably sodium hydroxide solution. 36. Device according to one of claims 32 to 35, characterized in that the washing liquid within the aqueous bath (14, 14 ') can be circulated. 37. Device according to one of claims 32 to 36, characterized by a heat exchanger immersed in the aqueous bath (14, 14 ') for temperature control and heat recovery. 38. Device according to one of claims 32 to 37, characterized in that an emergency cooler is additionally arranged in the aqueous bath (14, 14 '). 39. Device according to one of claims 32 to 38, characterized in that the aqueous bath has a temperature of 40 to 80 ° C. 40. Device according to one of claims 32 to 39, characterized in that the contaminants which settle out can be removed from the aqueous bath and / or from a settling tank. 41. Device according to one of claims 32 to 40, characterized in that a foam destroyer (26) is arranged on the end of the foam column (64) opposite the surface (18, 18 ') of the aqueous bath (14, 14'). 42. Apparatus according to claim 41, characterized in that the foam destroyer (26) has at least one perforated plate for the passage of the cleaned exhaust gases. 43. Apparatus according to claim 41 or 42, characterized gekenn¬ characterized in that the foam destroyer (26) with sharp edges or tips (33) for piercing the foam sheet sen (62,62 ') is provided. 44. Device according to one of claims 32 to 43, characterized by a hot exhaust gas on the input side and preferably on the output side via a blower (44) with the exhaust pipe (16) opening into the aqueous bath (14, 14 '). connected pre-cleaning and cooling stage (42). 45. Apparatus according to claim 44, characterized in that the pre-cleaning and cooling stage (42) has a spray device (48) acted upon with water. 46. Apparatus according to claim 45, characterized in that the water of the spray device is cooled in a closed circuit by a settling tank (56) cooled with a heat exchanger (48). 47. Apparatus according to claim 45 or 46, characterized gekenn¬ characterized in that the spraying device (48) is fed with water from the aqueous bath (14, 14 '). 48. Device according to one of claims 32 to 47, characterized by at least two successive water baths (14, 14 ') connected one behind the other and mixed with foam formers, which are connected to one another via a foam destruction section (68). 49. Device according to one of claims 32 to 48, characterized in that the exhaust pipe has a plurality of outlet openings (17) arranged on one side on its outer surface at a distance from one another, preferably provided with downwardly directed guide surfaces. points. 50. Apparatus according to claim 49, characterized in that the outlet openings (17), which are preferably triangular in outline, are formed by punching out and bending open the guide surfaces from the outer surface of the exhaust pipe (16).