EP0735322A2 - Process and device for purification of noxious exhaust gases by chemical conversion in a flame and hot surfaces - Google Patents

Abstract

Process for removing impurities, esp. fluorine cpds., from non-combustible waste gases in a combustion chamber has a burner gas flame which heats and/or chemically reacts the impurities and a unit for treating the hot gas stream from the burner gas flame. The process is novel in that a body or material which lets the hot gas stream through and which has a large internal surface is arranged in the hot gas flow inside the combustion chamber and heat-insulated from the combustion chamber casing and in this way is heated to above 500 degrees C, pref. 700-1400 degrees C. The gas passes through this body or material and contacts the inside surfaces of the same. The body or material is made of a material or material mixt. which forms volatile cpds. and/or causes additional activation and/or is catalytically active with one of the primary impurity and/or the secondary substance of the combustion. The hot gas stream leaving the body or material passes into a single or multi-stage unit at the exit of t he combustion chamber for further treatment and then after cleaning is passed into the exhaust air. Also claimed is the appts. for carrying out the above process having a burner gas flame (7) novel in that a large grain granulate, a sintered body or a number of sintered bodies, for example, in the form of a ring or, or in the case when silicon dioxide is used, also fused tubes are included.

Description

The invention relates to a method and a device for cleaning exhaust gases with different, preferably fluorine-containing pollutants, in particular from plants for the separation and removal by plasma processes and by chemical vapor phase separation. Such processes play a role in the manufacture of semiconductor circuits. The exhaust gases contain pollutants of different chemical compositions. Important groups of these pollutants are hydrides, e.g. Silanes. Fluorocarbons and other fluorine compounds are frequently produced. The pollutants or their reaction products have a toxic effect or, due to their harmful effects in the atmosphere, require ozone depletion and the greenhouse effect.

A whole series of methods are known for exhaust gas purification.

The cleaning is very often carried out by sorption of the harmful gases from the exhaust gas, for example by passing it through oxidizing, aqueous solutions (DE 3342 816 A1). The resulting water-soluble compounds can be processed in a second process step, e.g. be precipitated by basic solutions. Volatile pollutants or secondary products are processed in a third process stage, e.g. by means of activated carbon filters, removed from the exhaust gas.

Another group of cleaning processes uses solid-state reactions with indirectly electrically or inductively heated materials. Non-organic halides and hydrides as well as organometallic compounds can be decomposed on heated metal catalysts (European Pat. 0384803 A1). In order to use different chemical reactions for the removal of the pollutants and / or to remove pollutants in process sequences, the reactive materials are arranged in layers in an indirectly heated column (WO89 / 11905, WO91 / 08041). In this way, halogens and hydrides, for example, were chemically converted and converted into solid compounds. However, the effectiveness of such a procedure may be drastically reduced by sealing the surfaces with the solid connections as the process progresses. The cleaning process requires periodic renewal of the reactive materials.

In a combination of an indirectly heated thermal solid state reactor with a subsequent device for hydrolysis or neutralization in hydroxide solution, volatile fluorine compounds, for example, are removed from the exhaust gas. C ₂ F ₆ , SiF, ₄ COF ₂ and other substances are first converted into volatile silicon fluorides on hot silicon oxide surfaces and then precipitated as solid fluorine compounds, for example as CaF ₂ , in the aqueous solutions. Poisoning of the reactive surfaces in the solid-state reactor (eg by coal or carbides) can be reduced by adding oxygen to the exhaust gas (DD 221 088 A1). The limited reaction areas of the reactive materials and the limited throughput of pollutant-containing exhaust gases are problematic.

A large number of exhaust gas purification processes are based on the thermal decomposition or oxidation of the pollutants in a combustion chamber. If the pollutants themselves are not flammable or if they are only components of exhaust gases with a high proportion of inert gas, they are used for chemical conversion into a fuel gas flame, e.g. from a natural gas / oxygen or hydrogen-oxygen mixture, introduced (US 5 183 646). Harmful secondary substances of the conversion are subsequently, e.g. by sorption or washing processes, removed from the exhaust gas (US-A 288 9002).

Exhaust gas cleaning is usually a multi-stage process in which one or more of the following sub-processes, such as thermal decomposition or oxidation, cooling, sorption, hydrolysis and neutralization, take place (034 689 3 B1). by a device with a combustion chamber and at least one further device, e.g. one that works according to the washing principle.

Devices for purifying exhaust gas have also been proposed, in which the exhaust gas is passed successively through a combustion chamber for combusting the pollutants and a washing chamber, which are structurally combined to form a unit (EP 89 110 875). A multi-stage cleaning process was also implemented in a single reaction chamber in which the burned exhaust gas is passed through a finely divided liquid (sorbent or coolant) or is brought into contact with such a liquid film on the wall surfaces of the combustion chamber (DE 43 200 44).

However, the implementation of the pollutants in a fuel gas flame has a different efficiency in the cleaning effect for different pollutants. For example, the efficiency of the cleaning effect is not sufficient for fluorinated hydrocarbons and other fluorine compounds, to meet required standards. With justifiable consumption of fuel gas, the cleaned exhaust gases still contain critically high proportions of pollutants. An improvement in the efficiency of cleaning in the direction of a low pollutant content in the cleaned exhaust gas can be achieved to a certain extent by increasing the amount of fuel gas relative to the amount of the supplied exhaust gas, but leads to a critical deterioration in the economy of exhaust gas cleaning because of the increase in fuel gas consumption.

Since several reactions generally take place in the fuel gas flame with exhaust gas supply, the most important results of which are the combustion of the fuel gas (e.g. natural gas or hydrogen) under the influence of the oxygen supplied for the purpose of thermal activation of the harmful gases and the chemical conversion of the harmful gases into hydrolyzable and absorbable or are harmless solid and volatile compounds, it is not to be expected due to the reaction kinetics that the desired conversion of the harmful gases takes place completely in the flame of the combustion chamber. As a result of the proportion of inert gas in the harmful gas, the reaction kinetics are adversely affected and the proportionate conversion of the harmful gases in the flame is further reduced.

The cleaning of fluorine-containing exhaust gases in a combustion chamber with a fuel gas flame requires a specific procedure and equipment design if it is to be carried out both with high efficiency of the pollutant conversion and with economical economy. The results are not equally satisfactory for all pollutants when using a facility. The efficiency of the implementation is e.g. unfavorable for tetrafluoromethane in a fuel gas flame.

In addition, the currently constantly growing, high demands on the cleaning processes are often not met, since in the practice of cleaning exhaust gases from CVD and plasma processes, exhaust gases with different pollutants are produced at the same time. Adaptation of one and the same exhaust gas cleaning device with a fuel gas flame to such different harmful gases simply by adjusting the process parameters does not lead to satisfactory technical solutions.

The invention has for its object to increase the efficiency of cleaning in the removal of pollutants, in particular fluorine compounds, from non-combustible exhaust gases in a combustion chamber with a fuel gas flame. When cleaning in the combustion chamber, the degree of decomposition of compounds which can be thermally decomposed is to be improved and the degree of chemical conversion of other pollutants is to be increased for pollutants which react with components of the fuel gas flame. In particular, it is to be ensured that a high cleaning effect is achieved if the exhaust gas has different, toxic components contains. The economy of the cleaning process can be improved by reducing the fuel gas consumption and by longer uninterrupted operating times.

According to the invention the object is achieved by a method according to claims 1 to 8 and a device according to claims 9 to 14 .

The method assumes that a fuel gas mixture, preferably a hydrogen / oxygen mixture or a methane / oxygen mixture, is burned in a combustion chamber with the aid of a burner and that the pollutant-containing exhaust gas is fed into the flame. The exhaust gases are not combustible themselves, even if they contain combustible components, e.g. B. hydrides, since they usually consist of over 90% of non-flammable inert gases, such as N ₂ or Ar. If the pollutants in the flame are only to be activated for thermal decomposition, the components of the fuel gas mixture are supplied stoichiometrically. If a conversion of pollutants by chemical reactions in the flame is to take place, the hydrogen-containing component or the hydrogen is supplied in excess if this is done by reduction or air or oxygen is supplied in excess if oxidation is to be achieved. The efficiency of the pollutant conversion in the flame is set by precise dosing and / or by separate or additional supply of components. An increase in the efficiency of the pollutant conversion in the flame is achieved with special burner designs or devices for swirling the gas streams and for separately feeding the components of the fuel gas mixture.

The hot gas stream at the end of the effective area of the flame then consists of the combusted fuel gas mixture (mostly CO ₂ and H ₂ O), heated inert gases (mostly N ₂ and Ar) and either the products of thermal decomposition in an O ₂ atmosphere (e.g. SiO ₂ and water vapor) or from products of chemical conversion (e.g. hydrogen fluoride, silicon fluoride, carbon dioxide and water vapor when burning silane and tetrafluoromethane in a detonating gas flame). Solid reaction products are deposited on components of the combustion chamber, eg SiO ₂ ).

The hot gases at the exit of the combustion chamber are fed to a device for further treatment. One or more sub-processes such as cooling, hydrolizing, neutralizing and washing out are usually carried out. Such sub-processes are carried out, for example, in spray washers or columns. The gas stream treated in this way, ie largely freed from toxic pollutants, is now fed to the exhaust air duct with the aid of an extraction system.

Even after executing the procedure described, according to the currently best available technology, there are still portions of primary pollutants in the exhaust gas and, to a small extent, secondary pollutants that arise in the flame in the exhaust air because of the incompleteness of the reactions described. The proportion of pollutants in the exhaust air is still particularly high if the exhaust gas contains pollutants that are difficult or difficult to decompose or convert chemically in the flame.

According to the invention , a body that is permeable to the hot gas flow or material with a large inner surface in the hot gas flow is arranged inside the combustion chamber, thermally insulated from the casing thereof, and in this way to temperatures above 500 ° C., preferably in the range from 700 ° C. to 1400 ° C, heated. As is known, the thermal energy content of the flame is initially used to heat the exhaust gas and in this way in the volume of the flame to bring about the effects which are typical for treatment in a fuel gas flame. These are the thermal decomposition of pollutants and the chemical conversion in thermally stimulated reactions between components of the fuel gas mixture and the pollutants. The energy content of the hot gas stream is now also used to bring said body or material to high temperatures. If heat radiation protection plates, possibly additional heat-insulating materials, are introduced in or around the combustion chamber in the area between the flame and the end of the combustion chamber, the energy content of the hot gas stream is efficiently used to heat the body.

The said gas is passed through this body (or through this material) and brought into intimate contact with the surfaces thereof. Said body consists of a material or material mixture which forms volatile compounds with one of the primary pollutants and / or secondary substances of the combustion at the specified temperature and / or causes an additional activation and / or is catalytically active.

Due to the intimate contact between the inner surfaces and the gas flow, the body (or the materials) with the given thermal insulation will almost assume the temperature that is given in the flame when the hot gases enter the body. There is a slight difference in the radial and in the direction of expansion of the gas flow due to unavoidable but low heat losses. Overall, however, by regulating the temperature by controlling the supply of the components of the fuel gas mixture, the body can be set to a temperature required for the thermal cleaning process. This temperature is also about that of the respective gas flowing through the body.

Similar conditions are created in the inner volume of the permeable body (or material) as in the flame i.e. The reactions of thermal decomposition and chemical conversion also take place within the body. In this way, these reactions are continued beyond the area of the flame, ie they take place in a larger volume or over a longer distance than without said body (or material). Corresponding to this enlargement or lengthening, the degree to which the pollutants decompose or are converted chemically improves.

It is crucial for the qualitative improvement, however, that through the selection of the material for said body (or material), this additionally acts as a surface-active, thermal reactor within the combustion chamber. The choice of material is adapted to the type of pollutants to be disposed of. It may be expedient that the same pollutants as in the flame and secondary pollutants generated in the flame are converted into volatile products by additional solid-state reactions.

According to the invention, silicon dioxide is used as the material. Is e.g. Disposing of hexafluoromethane as a harmful gas, this is known to be largely converted into carbon dioxide and hydrogen fluoride in the flame containing hydrogen and oxygen. However, the degree of implementation is not entirely sufficient for the current strict environmental requirements. According to the invention, the further conversion of the pollutants, in the example that of hexafluoromethane, takes place by volume reaction in the gas-permeable body (or material) heated by the flame, which further significantly reduces the pollutant content. Extremely low levels of pollutants are achieved, however, since surface reactions with silicon dioxide are also effective in the hot body. In this way, residual hexafluoromethane is converted into volatile silicon fluoride.

An essential, further effect of the use of the surface reactor which is additionally effective in the combustion chamber for the fuel gas flame is that not only the primary pollutant (in the example hexafluoromethane) is converted chemically, but that in the flame and in the interior of the permeable body (or material ) resulting from thermal decomposition and chemical conversion, often also toxic secondary products, are also converted chemically by surface reactions. For example, the reaction of hexafluoromethane in the flame and in the volume of the body in addition to volatile hydrofluoric acid and carbon dioxide produces various fluorhexamethane degradation products, such as CHF ₃ , which also form volatile silicon compounds with silicon dioxide, which also forms harmless inert gases.

The surface reactions of the primary and, in this sense, secondary pollutants take place in the presence of hydrogen and oxygen in the hot gas stream. The chemical conversion of these pollutants can be influenced further favorably if excess oxygen or air is fed into the burner to generate the fuel gas flame. In this way, the reactions take place on the surfaces of the permeable body (or material) in the presence of an excess of oxygen. This improves the conversion of pollutants on the surfaces by forming further volatile intermediates, such as SiOF ₂ . The presence of oxygen in the reaction of primary or secondary pollutants with the introduced material also has the advantage that the deposition of solid substances, for example silicon carbide or coal, is avoided. In this way, a "poisoning" of the surfaces for the intended conversion into gaseous substances is avoided. The additional feeding of oxygen or air can also take place in the area of the entry of the hot gases into the permeable body (or material). In this way, the surface reactions can be optimally adjusted with regard to the required amount of oxygen, regardless of the volume reactions in the flame.

A further, decisive effect of the procedure according to the invention is that pollutants which are only slightly or not thermally decomposed or chemically converted in the fuel gas flame are still chemically converted by the surface reaction in the combustion chamber. A high degree of implementation can also be achieved for such pollutants as SF ₆ , CHF ₃ and CF ₄ . Since two different mechanisms are effective in the combustion chamber with the volume reaction, predominantly in the fuel gas flame, and the surface reaction in the permeable body (or material), the process is well suited for cleaning exhaust gases that contain different pollutants. If the exhaust gas contains NF ₃ and CF ₄ , for example, NF _{3 is} mainly converted in the fuel gas flame, while the predominant portion of CF _{4 is converted} on the surfaces of the hot, permeable body (or material).

The selection of the material for said body (or material) is thus determined on the one hand by chemical requirements with regard to the pollutants to be disposed of, on the other hand by aspects of ensuring permeability for the hot gas flow and the formation of large internal surfaces with low flow resistance for the hot gas.

In addition to said silicon dioxide, it is according to the invention to use silicon dioxide as a mixture with silicon and / or with other silicon-containing compounds as the material. Pollutants, such as For example, chlorobenzene easily react with the silicon in such a mixture at temperatures above 600 ° C. The permeable bodies can be designed as sintered bodies or as sintered ceramic bodies which contain Al ₂ O ₃ or / and other sinterable materials in addition to silicon oxide or the other substances mentioned.

If only the additional activation for the purpose of further thermal decomposition and / or chemical conversion in the heated, permeable body (or material) is sufficient for the exhaust gas cleaning after the treatment in the flame, this can also be made of materials not involved in the reaction, such as Al ₂ O ₃ or a ceramic.

In order to make said hot body catalytically effective, it may be expedient to partially coat the surfaces of said permeable body with metals or metal oxides (e.g. with Cu, CuO etc.) or to incorporate them into the sintered body.

Another procedure according to the invention is that the material for the permeable body (or material) is replenished in accordance with the consumption by the chemical reactions in the hot area of the flame of the burner. In this way it is ensured that the cleaning process in the combustion chamber can be carried out continuously over long periods.

An additional, inventive feature is that the infrared radiation of the heated material is registered in the combustion chamber with the aid of a sensor, and that the measurement signal from this sensor is used to control the process. For example, the temperature of the chemically reacting surfaces of the body (or material) can be regulated by controlling the flows of the fuel gas mixture. In this way, optimal reaction conditions in volume and on the surfaces of the material introduced can be set. In addition, the sensor signal can be used to control the refill devices in the form of a point control.

The hot gas stream emerging from the permeable body (or material) is fed to a device for further, one-stage or multi-stage treatment at the outlet of the combustion chamber and is then discharged into the exhaust air in a purified manner.

It had already been pointed out that known sub-processes can be used for this part of the overall process for exhaust gas purification. The gas released into the exhaust air as a result of the exhaust gas purification contains extremely low levels of pollutants.

In the device according to the invention for carrying out the method , a permeable body or material is arranged in the interior of the combustion chamber at a distance from the ring burner, which does not hinder the formation of the fuel gas flame. In the area of this body (or material), one or more, preferably cylindrical radiation protection plates are arranged between it and the burner wall. In addition, heat-insulating, temperature-resistant insulation materials are arranged between the burner wall and the casing of the combustion chamber.

In the simplest case, a coarse granulate, a sintered body or a multiplicity of sintered bodies, for example in the form of rings, or sintered pipes, which in the case of using silicon dioxide are also melted, are shaped or used from the materials for the said body. These shapes on the one hand ensure a large surface in the body (or material) for contact or for reaction with the hot gas. On the other hand, a high permeability for the flowing hot gas is achieved. When using pipes, their inner and outer jacket surfaces act as reaction surfaces.

The sintered body can be inserted directly into the combustion chamber with appropriate holders. The granules or packing are used in a net-like, basket-shaped storage vessel. If sintered or melted tubes are used as permeable bodies, they are combined by brackets to form a bundle in the combustion chamber in such a way that their longitudinal direction coincides with the direction of flow of the hot gases through the combustion chamber.

The permeable body (or the permeable material) is exchanged when it is consumed by reactions with a corresponding flow rate of pollutants. Depending on the consumption of material due to the reactions with the harmful gases, it can also be useful in the interest of long, uninterrupted operating times of the cleaning system if the materials, e.g. Granules or packing e.g. with a vibratory conveyor, be refilled.

If a bundle of tubes is used as a permeable, reactive body, the burn-off thereof can be compensated for as a result of the reactions by longitudinal movement of the holders against the direction of flow of the hot gases. In this case, a sufficient length of the tube bundle serves as a supply for an uninterrupted operating time to be achieved. Through the feed the holder, despite the erosion, a constant distance of the tubes from the flame, and thus a constant temperature on the reaction surfaces.
With the aid of the sensor for temperature control described, controlled end-feeding of the reactive materials can also be achieved by intervening in the vibrating conveyor device or in the feed of the holder for the tubes, by means of an end point control.

Another useful device are openings or inlet pipes on the combustion chamber in the region of the entry of the hot gases into the permeable body. It can cause said additional feeding of oxygen or air. On the one hand, this optimizes the conditions in the flame with regard to the implementation of one of the pollutants, e.g. by setting an excess of hydrogen in the fuel gas mixture, on the other hand, optimizing the conditions in the body (or material) for the implementation of another pollutant by an excess of oxygen on the hot reaction surfaces.

Another useful device for the device for carrying out the method is a baffle in the immediate vicinity of the permeable body (or material). When the hot gases hit the surfaces of this bafl, the solid, secondary products are separated, which are produced by the volume reaction in the flame. This prevents them from depositing on the surfaces of the hot body in question and poisoning their surfaces for reaction with other pollutant components.

The invention is explained in more detail below on the basis of a method example and on the basis of the preferred embodiment of the device shown in FIG. 1. 1 shows a schematic longitudinal section.

The device according to the invention essentially consists of a cylindrical combustion chamber (1) made of corrosion-resistant material. It is 18 cm in diameter and 80 cm high. This combustion chamber is thermally insulated in an outer casing (2). In the area of an end face (3) of the combustion chamber (1) there is an annular burner (4) to which the fuel gas mixture of hydrogen and oxygen is fed via a feed (5). The ring burner (4) has a diameter of 25 mm. The fuel gas flame (7) forms above the ring channel (6). The exhaust gas with pollutants of different compositions is fed to the burner (4) via the central feed (8). It enters the fuel gas flame (7) centrally through the bore (9).

At a distance of 40 cm from the burner is a basket-like container (10) made of corrosion-resistant wire mesh with a mesh size of 2 mm and one Permeability of approx. 55% arranged. Between the cylinder surface of this container and the cylinder wall of the combustion chamber there are two cylindrical radiation protection plates (11) at a radial distance of 3 mm from one another and from the inner surface of the combustion chamber. Plate-shaped radiation protection plates (11) are arranged on the end face of the container. In the area of the basket-like container, about 4 cm thick thermal insulation (12) made of rock wool is inserted between the combustion chamber wall and the casing (2). The basket-like container is filled with packing elements (13) made of quartz rings (diameter 4 mm, wall thickness 1 mm, length 4 mm).

An IR sensor (15) is directed with its receiver surface onto the hot filler body through a bore (14) in the wall of the combustion chamber and in the casing. Offset to this are three bores on the periphery of the combustion chamber for interconnected inlet pipes (16), through which air or oxygen is admitted into the area where the hot gases enter the quartz fillers.

A flat baffle (17) made of corrosion-resistant steel sheet with a length of 4 cm (in the direction of the flowing gases) is arranged in the area between the flame propagation space in the immediate vicinity of the basket-like container.

From the fuel gas flame (7), the hot gases first flow through the baffle in the direction of the arrow (18), then through the packing (13) and then through the opening (20) in the direction of the arrow (19) and then through the spray washing device (21).

The spray washer has the same diameter as the combustion chamber. It is 30 cm long. It is integrated into the casing together with the combustion chamber. Wash rings (23) are arranged between holding sieves (22) in the central region of the spray washing device. A one-percent aqueous potassium hydroxide solution is let in via the feed (24) and sprayed into the washing device by means of the spray device (25) (arrow direction 26). The hot gas stream and the aqueous solution flow through the washing rings in the direction of the arrow (27). The cleaned and cooled gas stream collects in the room (28) and is sucked off via a tubular connection (29) and fed to the exhaust air. The aqueous solution collects in the lower part of the room (28) and is fed to the reprocessing via the connection (30).

Example of the execution of the procedure:

In a plasma CVD coating system, 60 l / min of exhaust gas is produced when silicon dioxide is deposited on semiconductor wafers. The exhaust gas consists of 30 l / min nitrogen and 3 l / min silane as the predominant pollutant. In another system with a parallel technological process, the coating chamber of a plasma CVD coating system cleaned by a plasma etching process. This process is carried out with a mixture of tetrafluoromethane and oxygen as the process gas. The resulting exhaust gas consists of 30 l / min N ₂ , 1 l / min N ₂ O and 2 l / min tetrafluoromethane from a few tenths l / min of silicon tetrafluoride as the main pollutants, in addition to small amounts of fluorine and other substances that decompose tetafluoromethane , eg CHF ₃ , in the presence of SiO ₂ in the plasma.

Both exhaust gases arrive mixed in the exhaust gas purification device via the exhaust pipe.

The fuel gas flame (7) is maintained on the burner (4) of the combustion chamber (1) by letting 20 l / min of hydrogen and 10 l / min of oxygen into the feed (5). This means that a total of approx. 85 l / min is introduced into the ring burner (4) via the feed (8) and thus into the fuel gas flame.

In the selected example, the pollutant conversion largely takes place according to two different reaction principles, which are determined by the main pollutants mentioned, namely silane and tetrafluoromethane. The volume of the hydrogen / oxygen flame mainly converts the silane to silicon dioxide and water vapor. Silicon dioxide settles on the walls of the combustion chamber and on the flame-side surfaces of the baffle (18). From these surfaces, it can be easily removed using devices known per se, possibly also under operating conditions.

To a certain extent, the volume of tetrafluoromethane is also converted chemically, mainly to hydrogen fluoride and carbon dioxide. In addition, a number of intermediate products are created in the flame, such as CHF ₃ .

Mainly tetrafluoromethane, carbon dioxide, water vapor, volatile secondary pollutants such as SiF ₄ , F ₂ , CHF ₃ and HF enter the hot body (13) made of quartz rings. The body is heated to around 1300 ° C by the hot gases flowing through it. The pollutants come into intimate contact with the surfaces of the hot quartz fillers. The predominant surface reaction is that of tetrafluoromethane to volatile silicon tetrafluoride. Pollutants still contained in the hot gas stream. such as hydrogen fluoride and fluorine are partially converted to volatile silicon tetrafluoride on the hot surfaces. Traces of silanes that have not yet been converted in the volume of the flame are decomposed in the volume of the permeable, hot body or are chemically converted to silicon dioxide with the oxygen which is still present at the same time.

The hot gases with the secondary and tertiary reaction products enter through the gap (20) into the spray washing device (21), in which the aqueous absorbent is effective. The hot gases are cooled to around 50 ° C. The hydrogen fluoride and the silicon fluoride are absorbed by the basic active components of the solution, for example by KOH or K ₂ CO ₃ .

Taking into account the fact that a high proportion of the tetratrafluoromethane is already chemically converted in the volume of the flame and that the proportion of silicon fluoride primarily contained in the noxious gas is relatively low, about 60 g masses of the quartz rings are converted per hour, i.e. consumed. A corresponding amount is replenished.

In the preceding description, the behavior is only described for process-typical, mainly occurring substances.

The process has a high cleaning effect for chemically very differently behaving pollutants. In particular, the pollutant content of fluorine-containing, very toxic compounds in the exhaust air of the exhaust gas cleaning device is reduced to a few ppm.

Claims (15)

1. A method for removing pollutants, in particular fluorine compounds, from non-combustible exhaust gases in a combustion chamber with a fuel gas flame, which is used for heating and / or the chemical conversion of the pollutants, and with a device for treating the hot gas stream from the fuel gas flame, thereby characterized in that within the combustion chamber, thermally insulated from the envelope of the combustion chamber, a body or material which is permeable to the hot gas flow and has a large inner surface is arranged in the hot gas flow and in this way to temperatures above 500 ° C, preferably in the range of 700 ° C to 1400 ° C, is heated, that the said gas is passed through this body or material and brought into intimate contact with the surfaces thereof, that said body or material consists of a material or material mixture which at the specified temperature with one of the primary pollutants and / or sec andary substances of combustion form volatile compounds and / or cause additional activation and / or become catalytically active, and that the hot gas stream emerging from the permeable body or permeable material is fed to a single-stage or multi-stage device for further treatment at the outlet of the combustion chamber and then released into the exhaust air after cleaning. 2. The method according to claim 1, characterized in that silicon dioxide is used as the material for the permeable body (or permeable material). 3. The method according to claim 1, characterized in that a mixture of silicon dioxide with silicon or of silicon dioxide with silicon-containing alloys is used as the material for the permeable body (or permeable material). 3. The method according to claim 1, characterized in that a mixture of silicon dioxide, of silicon dioxide with silicon or of silicon dioxide with silicon-containing alloys and with aluminum oxide is used as the material for the permeable body (or permeable material). 4. The method according to claim 1, characterized in that a mixture of silicon dioxide, of silicon dioxide with silicon or of silicon dioxide with silicon-containing alloys and with sinterable ceramic materials is used as the material for the permeable body (or permeable material). 5. The method according to claim 1 to 4, characterized in that oxygen or air is fed in excess in the burner for generating the fuel gas flame. 6. The method according to claim 1 to 4, characterized in that additionally preheated oxygen or preheated air is fed into the flame in the region of the entry of the hot gases into the permeable body (or permeable material). 7. The method according to claim 1 to 6, characterized in that the material for the permeable body (or permeable material) is replenished in the hot area of the flame. 8. The method according to claim 1 to 7, characterized in that the infrared radiation of the heated material in the combustion chamber registered with the aid of a sensor, and that the measurement signal of this sensor is used to control the process. 9. device for performing the method according to claim 1 to 8 with a combustion chamber and with a burner for generating a fuel gas flame, characterized in that a coarse granulate, a sintered body or a plurality of sintered body, for example in the form of rings or, in If silicon dioxide is also used, molten pipes can be used. 10th Device for carrying out the method according to claim 1 to 8 with a combustion chamber and with a burner for generating a fuel gas flame, characterized in that an oscillating conveyor device is provided in the basket-like storage vessel for refilling granules or packing elements. 11. A device for performing the method according to claim 1 to 8 with a combustion chamber and with a burner for generating a fuel gas flame, characterized in that the holder of the bundle of sintered or melted tubes can be moved in the longitudinal direction. 12. A device for performing the method according to claim 1 to 8 with a combustion chamber and with a burner for generating a fuel gas flame, characterized in that an opening or a in the wall of the combustion chamber in the region between the flame and permeable body (or material) Window for an IR sensor is provided. 13. A device for performing the method according to claim 1 to 8 with a combustion chamber and with a burner for generating a fuel gas flame, characterized in that in the wall of the combustion chamber in the region of the entry of the hot gas flow into the permeable body (or material) openings or inlet pipes are arranged. 14. A device for performing the method according to claim 1 to 8 with a combustion chamber and with a burner for generating a fuel gas flame, characterized in that within the combustion chamber in the area between the burner and the permeable body (or material), in the immediate vicinity the same device is provided, which acted as a baffle for the hot gas flow.

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