METHOD AND DEVICE FOR TREATING AND NEUTRALISING ENVIRONMENTALLY HARMFUL AND/OR TOXIC EXHAUST GASES

Abstract

A method for treating and neutralizing environmentally harmful and/or toxic exhaust gases from industrial process plants through thermal conversion or splitting of the exhaust gases in a combustion chamber includes mixing the exhaust gases in the combustion chamber with remotely generated heated air from a separate air heater to a temperature above the ignition temperature of the exhaust gases, and, after ignition of the exhaust gases, the air fed from the air heater continues to be fed at a temperature below the ignition temperature of the exhaust gases so as to continue the thermal splitting.

Description

The invention relates to a method and an apparatus for treating and neutralizing environmentally harmful and/or toxic exhaust gases from industrial process plants. For the cleaning of exhaust gases, which originate for example from semiconductor manufacturing processes such as CVD, LP-CVD, plasma CVD, plasma etching or similar processes, various methods have been disclosed. In most cases, use is made of methods in which the exhaust gases are burned and/or thermally decomposed. This produces reaction products that are gaseous or solid or soluble but harmless. The latter are conducted through a scrubber, in which the solid and/or soluble reaction products are removed from the exhaust gases by scrubbing with the aid of a sorbent. Water is usually suitable as sorbent.

One example of such an exhaust-gas cleaning apparatus has been disclosed in WO 96/23173. This apparatus contains a combustion space with a burner to which fuel gas, such as hydrogen and oxygen or air, and the process exhaust gas to be decomposed are fed. Located above the combustion space is a scrubbing space with a spraying apparatus for spraying the sorbent. In this case, the combustion space is located within an outer pipe and is delimited by an inner pipe, wherein the outer pipe also encloses the scrubbing space located above the combustion space.

The reaction products produced in the combustion space are conducted between the inner and the outer pipe into the scrubbing space and from there via a suction-removal means into the ambient air.

Such an exhaust-gas cleaning apparatus can be used to dispose of the wide variety of gases, such as SiH4, PH3, B2H6, TEOS (tetraethoxysilane) from CVD processes, C2F6, CF4, CH3F, Cl2, BCl3 from dry etching processes and other processes, with a very high degree of effectiveness. It is a prerequisite that the parameters of the exhaust-gas cleaning system are matched in each case to the type and amount of the gases or vapors to be cleaned, such that it is ensured that the combustion or the thermal decomposition is effected by the combustion of fuel gas and oxygen with an excess of oxygen.

A further example of an exhaust-gas cleaning apparatus emerges from EP 1 796 820B1 , in which a reactor chamber is provided and consists of an outer wall and an inner wall, the inner wall tapering downward in the form of a funnel. Located on the reactor chamber is an apparatus for treating exhaust gases which upwardly closes said reactor chamber and is provided with feeds for feeding the fuel gases, oxygen and hydrogen, and the exhaust gases into the reactor chamber. The tapering reactor chamber is furthermore provided, at the upper edge, with an overflow for a sorbent, such that a water film that flows uniformly downward can form on the inner side of the reactor chamber. The outer wall and the downwardly tapering inner wall are connected to one another by an annular plate and the intermediate space is filled with the sorbent.

The lower end of the reactor chamber is provided with an exhaust-gas outlet and ends in a water tank for receiving the water which flows down in the reactor chamber and by means of which at the same time solid reaction products are flushed out.

The exhaust-gas outlet is connected to a scrubbing column which is arranged next to the reactor chamber and filled with a filling material, such that an aftertreatment of the already thermally treated reaction exhaust gases can be effected, by removing the water-soluble constituents from the reaction exhaust gas by means of spray nozzles, the spraying directions of which are directed counter to the rising gas stream.

A similar exhaust-gas cleaning apparatus is described in US 20200018630A1 .

Furthermore, EP 1 129 763 B1 describes a method for the abatement of pyrophoric gases in a gas stream, which comprises introducing preheated damp air with a relative humidity of up to 90% and a maximum temperature of 300° C.-500° C. into the gas stream into a container, in which the pyrophoric gases are abated.

Heating means in the form of fins for heating the damp air are located in the container, wherein water is sprayed into the container in order to reduce the accumulation of solids.

The invention is based on the object of providing an effective method and an apparatus for treating and neutralizing environmentally harmful and/or toxic exhaust gases, by means of which at the same time a reduction in the consumption of fuel gases and a reduction in the emission of CO/CO2/NOx is achieved.

This is achieved by means of a method for treating and neutralizing environmentally harmful and/or toxic exhaust gases from process plants through thermal conversion or splitting of the exhaust gases in a combustion chamber, in that the exhaust gases in the combustion chamber are mixed with remotely generated heated air from a separate air heater to a temperature above the ignition temperature of the exhaust gases, and in that, after ignition of the exhaust gases, the air fed from the air heater continues to be fed at a temperature below the ignition temperature of the exhaust gases so as to continue the thermal splitting.

In a development of the invention, the air heated remotely outside the combustion chamber is at least temporarily heated to a temperature above the ignition temperature of the exhaust gases, that is to say to approx. 700° C. to 900° C., in the air heater.

Furthermore, after ignition of the exhaust gases in the combustion chamber, the remotely heated air may continue to be fed at a reduced temperature of approx. 200° C., at least as long as the flame burning in the combustion chamber does not go out. In this way, the exhaust gases can be thermally treated with the lowest possible energy consumption.

In order to achieve a complete conversion of the exhaust gases to harmless constituents, ambient air should be fed to the air heater in such an amount that stoichiometrically an excess of oxygen is established in the combustion chamber upon mixing with the exhaust gas.

In order to ensure that exhaust gases and air are mixed sufficiently, the exhaust gas and the remotely heated air should be fed to the combustion chamber in substantially parallel flow, but at different flow rates.

Better mixing of the exhaust gases with the heated air is achieved when the remotely heated air is swirled with the fed exhaust gas when entering the combustion chamber.

A further refinement of the invention is characterized in that, in order to convert hardly flammable or non-flammable exhaust gases in the combustion chamber, an additional injection of fuel gas is effected by way of one or more fuel gas nozzles during the feed of such exhaust gases, wherein the additionally injected fuel gas is mixed with the simultaneously injected air from the air heater within the meaning of external-mixing combustion.

Preferably, the additional fuel gas injected is hydrogen, with other fuel gases such as acetylene, ammonia, propane, propylene or methane etc. also being suitable.

The object on which the invention is based is also achieved in the case of an apparatus for carrying out the method for treating and neutralizing environmentally harmful and/or toxic exhaust gases from process plants in the semiconductor industry through thermal conversion or splitting of the exhaust gases in a combustion chamber, said apparatus being provided with a feed apparatus for air and exhaust gases and ending in the combustion chamber, in that a central air nozzle for feeding heated air into the combustion chamber is provided which, on the one hand, is connected to an air heater outside the combustion chamber by way of the feed apparatus and, on the other hand, is equipped on the inlet side to the combustion chamber with a swirl-inducing device consisting of a round insert which is provided with baffle plates and air passages and is arranged centrally in the outlet of the central air nozzle, in order to swirl the air fed from the air heater and air entering the combustion chamber in a mixing region to form a cone of flame.

Preferably, the round insert is a pressed sheet-metal part which is provided with parallel baffle plates arranged at a distance relative to one another and air passages therebetween or an array of passage openings in at least one plane.

Furthermore, the baffle plates have a V-shaped or U-shaped or semicircular cross section, wherein the opening direction is directed in each case counter to the flow direction of the heated air flowing past.

In a further development of the invention, a plurality of exhaust gas nozzles are provided on the inlet side to the combustion chamber and surround the central air nozzle for the remotely heated air on a circular ring, and wherein the exhaust gas is introduced obliquely with respect to the center of the combustion chamber or obliquely with respect to the axis of symmetry.

As an alternative, instead of the individual exhaust gas nozzles, an annular gap which concentrically surrounds the central air nozzle and is possibly interrupted once or multiple times may be provided.

Preferably, the exhaust gas nozzles arranged on a circular ring around the central air nozzle or the annular gap or gaps are oriented obliquely with respect to the center of the combustion chamber at an angle of 40° to 60°, but preferably about 45°.

For the reliable conversion of incombustible exhaust gases or incombustible exhaust-gas constituents, additional fuel gas nozzles are provided, which are arranged around the exhaust gas nozzles in the cover of the combustion chamber around or between the exhaust gas nozzles or the annular gaps and inject the additional fuel gas, hydrogen, at an oblique angle into the combustion chamber.

The oblique angle is 70°to 88°, but preferably about 84.5°, with respect to the horizontal.

The method according to the invention and the associated apparatus make it possible for all exhaust gases from industry and in particular from the semiconductor industry to be converted with reduced energy costs and less fuel gas and in an environmentally friendly manner with lower CO/CO2/NOx emissions.

In particular, the invention achieves considerable savings on hydrogen, since for example in the semiconductor industry in many processes combustible gases are used during 90-95% of the total process time, such that it suffices in this time to feed heated air to the exhaust gases for the purposes of combustion, whereas hydrogen is required only in the remaining very short process time during cleaning and etching processes, that is to say 5-10% of the total process time.

Furthermore, significantly fewer nitrogen oxides are produced, because for most of the time the flame temperature lies far below 1000° C.

The invention will be explained in more detail below in relation to an exemplary embodiment. Shown in the accompanying drawing figures are:

FIG. 1: an overview of an apparatus for treating and neutralizing environmentally harmful and/or toxic exhaust gases, consisting of a downwardly tapering combustion chamber which is open at the bottom, is equipped at the top with a cover having a feed apparatus for feeding heated air and the exhaust gases and is at least partially provided by a cylindrical container for sorption liquid having an overflow for forming a liquid film on the inner surface of the combustion chamber, wherein the lower end of the combustion chamber is connected, by way of a transfer line, to a scrubber column for wet cleaning the thermally pretreated exhaust gases;

FIG. 2: the apparatus according to FIG. 1 with a partial sectional illustration of the feed apparatus for remotely heated air and exhaust gases, and of the combustion chamber;

FIG. 3: the apparatus according to FIG. 2 with additional fuel gas injection;

FIG. 4: details of the air heater, provided with heating rods or heating coils, in the feed apparatus for heated air and the exhaust gases;

FIG. 5: the air heater with baffle plates and air passages therebetween in the air outlet to the combustion chamber, and the exhaust gas and fuel gas feed;

• • FIG. 6: a detail illustration of the air outlet to the combustion chamber with a round insert provided with baffle plates, and

FIG. 7: the air outlet to the combustion chamber as seen from below.

FIG. 1 shows an overview of an apparatus for treating and neutralizing environmentally harmful and/or toxic exhaust gases from process plants in the semiconductor industry or comparable industries, and process plants in which such toxic exhaust gases are produced.

Such exhaust gases, which originate for example from process modules for the manufacture of semiconductors for example for microelectronics or photovoltaics, such as CVD, LP CVD, plasma CVD, plasma etching or similar processes, are generally extremely poisonous or at least environmentally harmful and are generally neutralized by thermal processes, such as by oxidation or some other conversion in a flame at high temperatures, to such an extent that there is no longer any danger to health or the environment. However, the high temperatures in the conversion of the exhaust gases have the disadvantage that environmentally harmful NOx, CO and CO2 arise in considerable quantities from a combustion temperature of approximately 1000° C. The formation of NOx increases exponentially as the temperature increases.

Such a known apparatus consists of a vertically oriented combustion chamber 1 which is open at the bottom, tapers conically downward and is closed at the top with a cover 2 (FIGS. 1 and 2). The cover 2 is equipped with a feed apparatus 3 for feeding air and the exhaust gases into the combustion chamber 1. Furthermore, the combustion chamber 1 is at least partially surrounded by a container 4 for receiving a sorption liquid 5, such as water, said container being provided at the top with an overflow 6 (FIGS. 4 and 5), directed into the combustion chamber 1, for forming a liquid film 8 that runs down on the conically tapering inner surface 7 of the combustion chamber 1. As is known, this liquid film 8 has the function of preventing accumulations of solid reaction products on the inner surface 7 of the combustion chamber 1. The container 4 surrounding the combustion chamber 1 is simultaneously used for the cooling thereof.

The lower end of the combustion chamber 1 ends in a liquid tank 9 for receiving the liquid running down from the combustion chamber 1 and is connected, by way of a transfer line 10, to a scrubber column 11, located next to the combustion chamber 1, for wet cleaning/aftertreating the exhaust gases thermally pretreated in the combustion chamber 1 (FIG. 1). With the generally multi-stage scrubber column 11, the constituents that are solid and/or can be removed by scrubbing or are soluble, which are still present in the exhaust gas or are formed in the thermal conversion, are removed in counterflow from the exhaust gas by the exhaust gas in the scrubber column 11 being conducted upward past a plurality of spray nozzles (not illustrated) that are located one above the other (FIG. 1). The cleaned exhaust gas is finally released at the top from the scrubber column 11 into the environment by way of pipelines and a filter apparatus or an exhaust-gas system 12.

Both the water running down from the combustion chamber 1 and the water from the scrubber column 11 is collected in the liquid tank 9 by way of the transfer line 10 up to a predefined liquid level 13. Furthermore, the liquid tank 9 is connected to the container 4 by way of a return line 14 and a filter (not illustrated) with a pump 15, such that, together with the overflow 6 into the combustion chamber 1, a circuit for the sorption liquid 5 is formed (FIGS. 4 and 5).

It is essential to the invention that the feed device 3 in the cover 2 ends with a central air nozzle 16 for feeding remotely heated air 17 into the combustion chamber 1 (FIGS. 2 and 3), by virtue of fresh and compressed ambient air 18 being fed to the feed device 3 simultaneously by way of a side-channel compressor 17′ (not illustrated). Furthermore, a plurality of exhaust gas nozzles 19 surrounding the central air nozzle 16 are provided, which are directed into the combustion chamber 1 and are used to feed exhaust gases to be thermally treated also from different process modules into the combustion chamber 1 (FIG. 2).

The exhaust gas nozzles 19 surround the central air nozzle 16 in one or more concentric rings, with for example four or more exhaust gas nozzles 19 being provided in FIG. 1. Instead of the individual exhaust gas nozzles 19, an annular gap 20 which concentrically surrounds the central air nozzle 16 and is possibly interrupted once or multiple times may also be provided (FIG. 6).

In order for the heated air fed via the central air nozzle 16 from an air heater 21 in the feed apparatus 3 into the combustion chamber 1 to be sufficiently and rapidly mixed with the exhaust gases fed via the exhaust gas nozzles 19, it is expedient either for the air heated outside the combustion chamber 1 and the exhaust gases to be fed at different flow rates to the combustion chamber 1 or for at least the heated air to be fed via a swirl-inducing device 22 (FIGS. 6 and 7), the latter consisting of a round insert 24 which is provided with baffle plates 23 and is arranged centrally in the outlet of the central air nozzle 16 (FIGS. 6 and 7). The insert 23 is, for example, a pressed sheet-metal part which is provided with parallel baffle plates 23 arranged at a distance from one another and air passages 23′ therebetween in at least one plane. In principle, it is also possible for an array of pressed passage openings (not illustrated) to be provided in the insert instead of the baffle plates 23.

The baffle plates 23 may have a V-shaped, U-shaped or semicircular cross section which is angled/directed counter to the flow direction of the heated air (FIGS. 4 to 6), that is to say the opening of the cross section is directed counter to the flow direction of the fed remotely heated air 17. In this way, the heated air 17 directed onto the baffle plates 23 is subjected to particularly strong swirling and enters, in the form of an air vortex, the mixing region 25 in the combustion chamber 1.

The swirl-inducing device 22 performs two functions, namely firstly acting as a flow resistor in the central air nozzle 16, such that, as seen in the flow direction of the air, an overpressure is produced upstream of the insert 24 and thus in the air heater 21, such that the heated air 17 exits the central air nozzle 16 into the combustion chamber 1 in an accelerated manner, and secondly subjecting the air passing through the central insert 24 to strong swirling already before it exits the air nozzle 16 or while it exits the nozzle 16 (FIG. 6).

The heated and swirled air fed in this way into the combustion chamber 1 is, in the combustion chamber 1 with the exhaust gas to be treated, which is tangentially fed via the exhaust gas nozzles 19 to the injected heated air, intensively mixed therewith in the mixing region 25, such that the exhaust gas is ignited by the heated air and can be chemically converted, a cone of flame 26 being formed (FIG. 3).

The mixing of the heated air with the fed exhaust gases may also be improved when the exhaust gas nozzles 19, 20 arranged on a circular ring around the central air nozzle 16 are oriented obliquely with respect to the center of the combustion chamber 1 at an angle of approximately 40° to 60°, preferably of approximately 45°. As an alternative, the exhaust gas nozzles 19, 20 may also be oriented in the same direction obliquely with respect to the axis of symmetry of the combustion chamber 1, such that the exhaust gas additionally obtains a swirl by way of the plurality of exhaust gas nozzles 19, 20. This achieves even more rapid mixing of the centrally fed heated air with the exhaust gas. The heated air and the exhaust gases may also be fed at different flow rates, such that, according to Bernoulli's principle, transverse forces are produced at the interfaces between the gases, which also promote the mixing thereof.

The heated air is generated in a separate air heater 21 in the feed device 3 remotely outside or above the combustion chamber 1. The air heater 21 is connected, on the outlet side, to the central air nozzle 16 and, on the inlet side, to an air compressor (not illustrated), for example a side-channel compressor, which sucks in cold ambient air 18 (FIG. 4).

In order to heat the air that is sucked into the air heater 21, a heating apparatus 27 is provided, for example heating rods which are arranged in the air heater 21, in one plane or in a plurality of planes, in each case next to one another and transverse to the flow direction of the fed ambient air 18 (FIG. 3), with customary electric or halogen heating rods being able to be used for this (FIG. 3). The heating rods 27 may alternatively be arranged in the air heater 21 longitudinally with respect to the fed ambient air 18, or heating coils may be used.

It is important that it is possible for the air that is sucked into the air heater 21 to be heated at least temporarily to 700 to 900° C. by means of the heating apparatus 27 and to be injected at this temperature into the combustion chamber 1 in a swirled manner.

In order for the exhaust gases introduced via the exhaust gas nozzles 19, 20 into the combustion chamber 1, also referred to as raw gas, to be thermally degraded and converted into products that can be removed by scrubbing, the air heated to approx. 900° C. is simultaneously fed via the central air nozzle 16 to the combustion chamber 1 and mixed with the exhaust gases. The exact required temperature of the fed air as fuel gas is dependent on the respective current ignition temperature of the exhaust gases or exhaust gas mixture introduced into the combustion chamber 1, that is to say the heated fed air has to have at least the current ignition temperature. The thermal conversion may also be improved when the exhaust gases are also preheated before being introduced into the combustion chamber 1.

If these are combustible exhaust gases, which often originate from coating processes, they ignite and a flame is formed, whereupon the temperature of the air heated in the air heater 21 can be reduced to down to 200° C., as a result of which a considerable amount of energy can be saved.

If the flame goes out, the feed of exhaust gas has to be stopped immediately and the fed air has to be reheated to 900° C. or the ignition temperature, such that the thermal treatment can be continued after the interruption of the exhaust gas feed.

For a complete and reliable thermal conversion of the exhaust gases in the combustion chamber 1, the oxygen fed with the ambient air has to be fed in stoichiometric excess.

The particular advantage of arranging the air heater 21 outside the combustion chamber 1 can be seen in the fact that only ambient air flows around the electric heating apparatus 27 in the air heater 21, and therefore it is ensured that no disruptive accumulations can form on the heating rods or heating coils of the electric heating apparatus 27.

Many processes in the semiconductor industry consist of a coating step and a cleaning step. During the cleaning step, use is often made of combustible gases which can be treated as described above.

However, in cleaning steps, use is made of gases which often are not combustible and/or which require a particularly high temperature for conversion. In order to achieve this high temperature in the combustion chamber 1, an additional injection 28 of fuel gas, preferably hydrogen, or another suitable fuel gas, is provided by means of one or more fuel gas nozzles during the feed of such exhaust gases, said fuel gas nozzles being arranged around the exhaust gas nozzles 19, 20 in the cover 2 of the combustion chamber 1 (FIGS. 2, 4 and 5) and injecting the fuel gas at an angle of 70° to 88°, preferably at an angle of 84.5°, with respect to the horizontal, that is to say at a very steep angle, into the combustion chamber 1. The fuel gas is in this case mixed with the simultaneously centrally injected and swirled air from the air heater 21 within the meaning of external-mixing combustion, such that repercussions on the feed apparatus 3 can be ruled out.

The temperature, required for the conversion, in the combustion chamber 1 can, for example, be achieved through the use of hydrogen as fuel gas and the air injected in parallel into the combustion chamber 1 from the air heater 21. It goes without saying that, instead of hydrogen, other fuel gases such as acetylene, ammonia, propane, propylene or methane may also be used.

In order to be able to monitor the existence of the flame, which is required in each case for the thermal conversion of the exhaust gases, in the combustion chamber 1, a flame monitoring system is provided.

LIST OF REFERENCE NUMERALS

• • 1 Combustion chamber
  • 2 Cover
  • 3 Feed apparatus
  • 4 Container
  • 5 Sorption liquid
  • 6 Overflow
  • 7 Inner surface
  • 8 Liquid film
  • 9 Liquid tank
  • 10 Transfer line
  • 11 Scrubber column
  • 12 Filter apparatus/Exhaust-gas system
  • 13 Liquid level
  • 14 Return line
  • 15 Pump
  • 16 Central air nozzle
  • 17 Heated air
  • 17′ Side-channel compressor/compressor
  • 18 Ambient air
  • 19 Exhaust gas nozzles
  • 20 Annular gap
  • 21 Air heater
  • 22 Swirl-inducing device
  • 23 Baffle plate
  • 23′ Air passage
  • 24 Round insert
  • 25 Mixing region
  • 26 Cone of flame
  • 27 Heating apparatus
  • 28 Fuel gas nozzles

Claims

1. A method for treating and neutralizing environmentally harmful and/or toxic exhaust gases from industrial process plants through thermal conversion or splitting of the exhaust gases in a combustion chamber, comprising mixing the exhaust gases in the combustion chamber with remotely generated heated air from a separate air heater to a temperature above the ignition temperature of the exhaust gases, and after ignition of the exhaust gases, the air fed from the air heater continues to be fed at a temperature below the ignition temperature of the exhaust gases so as to continue the thermal splitting.

2. The method as claimed in claim 1, wherein the air heated remotely outside the combustion chamber is at least temporarily heated to a temperature above the ignition temperature of the exhaust gases, to approx. 700° C. to 900° C., in the air heater.

3. The method as claimed in claim 1, wherein after ignition of the exhaust gases in the combustion chamber the remotely heated air continues to be fed at a temperature of approx. 200° C.

4. The method as claimed in claims 1, wherein ambient air is fed to the air heater in such an amount that stoichiometrically an excess of oxygen is established in the combustion chamber upon mixing with the exhaust gas.

5. The method as claimed in claim 1, wherein the exhaust gas and the remotely heated air are fed to the combustion chamber in substantially parallel flow or at different flow rates.

6. The method as claimed in claim 1, wherein the remotely heated air is swirled when entering the combustion chamber

7. The method as claimed in claim 1, wherein in order to convert hardly flammable or non-flammable exhaust gases in the combustion chamber, an additional injection of fuel gas is effected by way of one or more fuel gas nozzles during the feed of such exhaust gases, and wherein the additionally injected fuel gas is mixed with the simultaneously injected air from the air heater within the meaning of external-mixing combustion.

8. The method as claimed in claim 7, wherein the additional fuel gas injected is hydrogen, acetylene, ammonia, propane, propylene or methane.

9. An apparatus for carrying out the method for treating and neutralizing environmentally harmful and/or toxic exhaust gases from industrial process plants through thermal conversion or splitting of the exhaust gases in a combustion chamber, said apparatus being provided with a feed apparatus for air and exhaust gases and ending in the combustion chamber, comprising: a central air nozzle connected to an air heater outside the combustion chamber by way of the feed apparatus and, wherein the central air nozzle is equipped on the inlet side to the combustion chamber with a swirl-inducing device including a round insert which is provided with baffle plates and air passages therebetween and is arranged centrally in the outlet of the central air nozzle in order to swirl the air fed from the air heater and air entering the combustion chamber in a mixing region to form a cone of flame.

10. The apparatus as claimed in claim 9, wherein the insert is a pressed sheet-metal part which is provided with the parallel baffle plates arranged at a distance relative to one another and the air passages therebetween or an array of passage openings in at least one plane.

11. The apparatus as claimed in claim 10, wherein the baffle plates have a V-shaped or U-shaped or semicircular cross section, wherein the opening direction is directed counter to the flow direction of the heated air.

12. The apparatus as claimed in claim 9, wherein a plurality of exhaust gas nozzles are provided on the inlet side to the combustion chamber and surround the central air nozzle for the remotely heated air on a circular ring, and wherein the exhaust gas is introduced obliquely with respect to the center of the combustion chamber or obliquely with respect to the axis of symmetry.

13. The apparatus as claimed in claim 12, wherein an annular gap which concentrically surrounds the central air nozzle and is possibly interrupted once or multiple times is provided.

14. The apparatus as claimed in claim 9, wherein the exhaust gas nozzles arranged on a circular ring around the central air nozzle or the annular gap or gaps are oriented obliquely with respect to the center of the combustion chamber at an angle of 40° to 60°, preferably about 45°.

15. The apparatus as claimed in claim 9, wherein fuel gas nozzles for additional fuel gas are provided, which are arranged in the cover of the combustion chamber around the exhaust gas nozzles or the annular gaps and inject the additional fuel gas, namely hydrogen or another suitable fuel gas, at an acute angle into the combustion chamber

16. The apparatus as claimed in claim 15, wherein the acute angle is from 70°-88°, preferably about 84.5°.

17. The method as claimed in claim 3 wherein ambient air is fed to the air heater in such an amount that stoichiometrically an excess of oxygen is established in the combustion chamber upon mixing with the exhaust gas.

18. The method as claimed in claim 17, wherein the exhaust gas and the remotely heated air are fed to the combustion chamber in substantially parallel flow or at different flow rates.

19. The method as claimed in claim 18, wherein the remotely heated air is swirled when entering the combustion chamber.

20. The method as claimed in claim 19, wherein in order to convert hardly flammable or non-flammable exhaust gases in the combustion chamber, an additional injection of fuel gas is effected by way of one or more fuel gas nozzles during the feed of such exhaust gases, and wherein the additionally injected fuel gas is mixed with the simultaneously injected air from the air heater within the meaning of external-mixing combustion.