JP2005522660A - Apparatus for purifying exhaust gas containing fluorine-containing compounds in a combustion furnace with a low nitrogen oxide emission level - Google Patents

Abstract

【Task】
The object of the present invention is to eliminate the disadvantages of state-of-the-art devices used for exhaust gas purification by thermochemical conversion.
[Solution]
In an apparatus for the purification of exhaust gases, in particular exhaust gases composed of fluorine-containing compounds, holes are provided for supplying combustion gas and oxygen separately to a single hole circle around a central exhaust gas supply (9). (7, 8) is made in the ring burner (5). The ring burner is arranged in the combustion chamber (1). The combustion chamber is close to the annular gap (20) between the cylindrical jacket (4) and the end face (16). Additional oxygen or additional air is introduced into the annular gap (20).

Description

  The present invention relates to an apparatus for purifying exhaust gas containing pollutants in a combustion chamber by thermochemical conversion.

  Vapor deposition units and facilities for removing materials using plasma processes used in specialized factories, particularly semiconductor factories, produce exhaust gases containing pollutants. An important group of these exhaust gases includes fluorine containing hydrocarbons and other fluorine compounds. In addition to these contaminants, the exhaust gas mainly contains nitrogen as a carrier gas. The pollutants and their reaction products are toxic and harmful to the environment. Therefore, the exhaust gases must be purified with appropriate equipment to remove them. In such an exhaust gas purification device, pollutants contained in the exhaust gas are converted thermochemically in the combustion chamber. In the combustion chamber, pollutants are easily affected by flames produced by burning fuel gas in pure oxygen or air (Patent Document 1). Thereafter, harmful by-products (eg, HF) of this conversion process are removed from the exhaust gas by being treated in the combustion chamber by an absorption or cleaning process.

  Typically, equipment for exhaust gas purification uses a multi-stage process. Sub-processes such as thermochemical decomposition, oxidation, cooling, absorption, hydrolysis, and removal of liquid and solid reaction products by washing are performed. For this purpose, exhaust gas is first introduced into the combustion chamber and then passes through at least one process device which works, for example, according to the principle of cleaning (Patent Document 2, Patent Document 3).

  An apparatus for exhaust gas purification must satisfy a number of requirements. The purification process must be very efficient. That is, the amount of main pollutants contained in the purified exhaust gas must be as small as possible. In addition, efficient removal of secondary contaminants must be realized in the cleaning unit. Furthermore, the exhaust gas purification process must be economical. In particular, the consumption of fuel gas must be small compared to the volume of exhaust gas flow to be cleaned. Finally, it must be ensured that no toxic carbon monoxide, especially nitrogen oxides, are produced during the purification process.

  The design of the combustion chamber, especially the burner design, has a decisive influence on efficiency, economy and non-production of secondary pollutant gases.

  The combustion chamber is generally configured as a cylindrical body, and a burner, typically a ring burner, is inserted into one of its end faces. A mixed gas of exhaust gas and fuel gas is supplied to the ring burner, usually through a central inlet, and most simply through an annular gap. Once the fuel gas is ignited by the igniter, a flame forms over the annular gap. Exhaust gas is introduced into this flame.

In a fuel gas flame, several reactions occur under the effect of oxygen (O ₂ ) supplied at the same time. Most importantly, the pollutant gas is thermally activated and the pollutant gases (eg, CF ₄ , C ₂ F ₆ , CHF ₃ ) are hydrolysable and absorbable harmful compounds (eg, HF). Burning a fuel gas, such as propane (C ₃ H ₈ ), methane (CH ₄ ), hydrogen (H ₂ ), or a mixture of said gases, for chemical conversion to a harmless compound (eg, CO ₂ ) That is. Due to the reaction kinetics, the desired conversion of the pollutant gas cannot be expected to be completed. This is not the case when the fuel gas and oxygen are supplied in a stoichiometric ratio (eg, a ratio of CH ₄ and O ₂ of 1: 2 or a ratio of C ₃ H ₈ and O ₂ of 1: 5). . The so-called λ value of the gas mixture is 1 (the air ratio λ is the ratio of the amount of oxygen supplied to the combustion process to the amount required for complete combustion). A high content of inert gas (N ₂ ) in the exhaust gas will negatively affect the reaction kinetics and reduce pollutant gas conversion.

  After all, the efficiency of the purification process is undesirable. That is, the amount of contaminants remaining in the purified exhaust gas is too high.

  If the ratio of oxygen in the fuel gas changes and the amount of fuel gas becomes higher than that in the stoichiometric ratio (λ value <1), the degree of pollutant conversion improves and the formation of nitrogen oxides decreases. However, at the same time, harmful carbon monoxide and unburned fuel gas are released from the gas purification device. On the other hand, especially in the case of exhaust gas containing fluorine, an increase in the amount of oxygen contained in the fuel gas / oxygen mixed gas compared to the stoichiometric ratio (λ value of the supplied mixed gas> 1) The substance conversion is severely degraded, leaving an unacceptably high pollutant content in the purified exhaust gas. In addition, harmful nitrogen oxides are created with high temperature flames rich in oxygen.

Purifying exhaust gas containing pollutants, especially exhaust gas containing fluorine-containing compounds, by means of thermochemical conversion with a flame of fuel gas has been developed by using a burner with a central exhaust gas inlet . In this burner, a fuel gas / oxygen mixed gas is supplied through two concentric annular gaps or through perforations arranged in two concentric hole circles (Patent Document 4). When two fuel gas / oxygen mixtures of different composition are supplied spatially separately, two flame zones with different thermochemical effects are realized. A flame part having a reducing effect is obtained on the inner annular gap or inner perforation when the fuel gas exceeds (λ <1) compared to the stoichiometric ratio of oxygen, while the flame part having an oxidizing effect Is obtained on the outer annular gap or outer perforation by excess oxygen (λ> 1) (Patent Document 4). Due to the higher concentration of reducing reactants such as H atoms and CH _X groups, the increased pollutant molecules are decomposed in the O ₂ depleted flame zone. Here, the supplied fuel gas is not completely consumed. The complete combustion of the fuel gas and the conversion of CO produced by the reducing flame into CO ₂ occurs in the second oxygen-excess flame surrounding the first flame.

  However, in order to supply different gas mixtures spatially separately, a burner that creates a reducing inner flame part and an oxidizing outer flame part is used for gas purification. There is a limit. For example, the temperature required for the thermal reaction under reducing conditions is realized only at a distance from the burner and especially in a limited volume. On the other hand, oxygen must be supplied to the oxidizing flame to the extent that complete oxidation of the fuel gas and secondary pollutants (eg CO) is ensured. Eventually, the flame envelope contributes significantly to limiting the volume of the reducing flame. Therefore, a gas purifier having a burner as described above and separately supplied with a reducing and oxidizing fuel gas / oxygen mixture is only suitable for a relatively small exhaust gas volume. Suitable.

  Therefore, in order to efficiently purify a large amount of exhaust gas, a burner has been proposed in which two reducing flame parts are realized by using two concentric rings or perforations arranged on two concentric hole circles. ing. Both flame sections are operated with a fuel gas / oxygen gas mixture with a λ value of less than 1 in order to increase the volume where there is a favorable condition for the conversion of pollutants (US Pat. No. 6,057,049). In this solution, complete oxidation of the carbon monoxide produced by the unburned fuel gas and the reducing flame is achieved by an additional separate supply of oxygen or air. This additional oxygen or additional air is introduced through nozzles or slots placed around or near the burner. In this way, a fuel gas / oxygen gas mixture characterized by a λ value greater than 1 acts in the outer skin of the reducing flame. Eventually, the outer skin of the flame constitutes an additional oxidizing flame part (Patent Document 5).

  The solution described above still has drawbacks. That is due to the fact that the perimeter of the flame is exposed to the oxygen acting there, limiting the reducing flame which favors the conversion of pollutants. In addition, the additional oxygen inlet near the burner becomes part of the flame and becomes very hot, where harmful nitrogen oxides are created.

  Burners that use fuel gas / oxygen mixtures must also be accurately adapted to meet the specific operating conditions (type of pollutant gas, amount of exhaust gas, and amount of gas mixture produced) of the burner There is a problem in terms. If the ratio of fuel gas to oxygen is changed, the result is a change in the rate of release from the burner and the speed of the flame. However, the release rate of the fuel gas mixture higher than the flame velocity carries the risk that the flame will disappear. On the other hand, if the release rate of the gas mixture is smaller than the flame rate, backfire may occur. Both risks must be removed by properly adapting the burner. However, the gas purification device must be able to operate safely without having to adapt the burner to different types of pollutant gases and different amounts of exhaust gas. The need to adapt the burner is inconvenient.

When fuel gas and oxygen are separately supplied to the burner, the operating conditions described above, namely the type of pollutant gas and the amount of exhaust gas, vary widely during operation without the need to change the burner design. The adaptation is done by appropriately controlling the amount of fuel gas and oxygen supplied. When the fuel gas and oxygen are separately supplied to the burner, the exhaust gas treatment in the flame part where the reducing and oxidizing action is performed is possible. A suitable burner comprises two concentric slots or perforations arranged on two concentric circles. Fuel gas and oxygen are introduced separately in a ratio corresponding to a λ value less than 1, and once the fuel gas and oxygen are mixed on the burner, a reducing flame is formed on the burner. When additional oxygen or air is supplied from around the burner to the flame skin, an oxidizing flame is obtained. Here, the remaining fuel gas is converted, and CO produced in the reducing flame portion is oxidized to CO ₂ .

The previously described burner design and mode of operation has the disadvantage that the reducing flame part remains limited, the efficiency of the pollutant gas conversion process and the nitrogen oxides in the hot oxidizing flame part. Manufacturing efficiency will be limited. Another disadvantage is that the local λ value of the directly surrounding gas mixture is very low, i.e., the soot is formed in a part close to unity.
US5183646 EP89110875 DE4320447 EP0735321A2 EP01120841

  The object of the present invention is to eliminate the disadvantages of state-of-the-art devices used for exhaust gas purification by thermochemical conversion. It must be ensured that a large amount of exhaust gas is clean, has high efficiency and is an economical pollutant in terms of fuel gas consumption. Soot should not accumulate on the burner. The purified exhaust gas must have a very low amount of unburned fuel gas, carbon monoxide, and in particular nitrogen oxides.

  According to the invention, this object is achieved by a device according to claims 1-13.

  The solution of the present invention is based on the following assumptions. In other words, exhaust gas containing pollutants, particularly fluorocarbon compounds, other fluorine-containing compounds, and exhaust gas containing nitrogen as a carrier gas are purified in a cylindrical combustion chamber by thermochemical conversion. The combustion chamber is equipped with a burner and is integrated with the subsequent cleaning unit. The burner has a central exhaust gas inlet. Fuel gas and oxygen are supplied separately to the burner and lead to a discharge nozzle for forming a flame. Hot treated exhaust gas exiting the combustion chamber is post-treated with a cleaning agent in a cleaning unit. During the aftertreatment, the hot exhaust gas is cooled and harmful secondary products are removed from the exhaust gas.

  According to the invention, the burner is a ring burner with perforations for separate supply of fuel gas and oxygen. The perforations are arranged on a single hole circle around the central exhaust gas inlet. This separate supply is achieved by introducing fuel gas and oxygen locally and alternately through adjacent perforations. For this purpose, two annular channels are arranged in the ring burner. This channel is alternately connected to the perforations on the hole circle. A connecting pipe exits the burner from each annular channel. Fuel gas is supplied to the burner through one of the connecting pipes, and oxygen is supplied through the other pipe.

  The alternating supply of fuel gas and oxygen through the perforations ensures that both gases are completely mixed as soon as they exit the burner. The flame forms in the immediate vicinity of the burner surface. In this way, only the hot flame is in contact with the emerging pollutant gas. The pollutant gas is prevented from mixing with part of the fuel gas. This clearly minimizes soot accumulation in the burner, particularly near the exhaust gas inlet.

The burner described above uses a fuel gas supplied separately from oxygen having an oxygen deficiency (defect) corresponding to a λ value of up to 0.6 in the fuel gas / oxygen gas mixture immediately above the burner. Especially suitable for burning. The ring burner ensures the formation of a stable and uniform flame with an effective energy output for a wide variety of fuel gases and oxygen flows, thus allowing adaptation to various pollutant gas and exhaust gas flows Become. This adaptation eliminates the need to replace the burner with another burner with a matched perforation. In addition to fluorocarbons and other fluorine compounds, the burners are suitable for removing reactive contaminants such as SiH ₄ , WF ₆ and TEOS.

  According to the invention, this burner is used in a combustion chamber that is closed, except for an annular gap between the cylindrical jacket of the combustion chamber and the end face of the combustion chamber located towards the burner. In this way, air, and thus oxygen, does not flow in the vicinity of the burner, for example via slots in the walls of the combustion chamber. The combustion chamber is at least sufficiently airtight and the air entering from the outside is less than about 3% of the oxygen supplied to the burner.

If the fuel gas and oxygen are separately supplied to the burner and the burner is operated in excess of the fuel gas corresponding to a mixed gas having a λ value of, for example, 0.8, a reducing flame part does not form on the burner. However, the entire flame has a reducing effect during the thermochemical conversion of pollutants. Since no air flows from the outside of the burner, i.e. the flame is not exposed to oxygen, a reducing condition is also obtained in the flame skin. Eventually, there exists a condition that reduces over almost the entire volume of the combustion chamber. Compared to the volume of a flame having a flame part that acts to reduce and oxidize, a high concentration of H atoms and CH ₃ groups, that is, contaminants (eg, C ₂ F ₆ , CF ₄ , CHF ₃ ) are reduced to be like HF Larger volumes with the reactants necessary to make other gaseous reaction products are realized. The energy required for thermal activation of the reactants is generated by burning a portion of the fuel gas, i.e., by an oxidation process that proceeds in parallel. Due to the conditions mentioned above, the device according to the invention can be operated at a lower temperature (T <˜1200 °) than a device with a reducing and oxidizing flame part. The higher concentration of the reducing reactant compensates for or overcompensates the positive effect that would have had on the reactant at higher temperatures. In this way, contaminants are converted very efficiently and at relatively low temperatures. The conditions for forming nitrogen oxides from the neutral gas portion of the exhaust gas are greatly limited because the thermochemical conversion of pollutants occurs at relatively low temperatures and oxygen depletion occurs in the reaction chamber. Eventually, the amount of nitrogen oxides contained in the treated exhaust gas stream leaving the combustion chamber is significantly reduced.

The mode of operation described earlier, the hot exhaust gas flow exiting from the cylindrical jacket of the combustion chamber comprises a reaction product of the combustion process and the thermochemical conversion, i.e. mainly CO _2, HF, and CO and H _{2 O} As well as unburned fuel gas components (CH ₄ and CO) due to the lack of oxygen in the combustion chamber. Hot exhaust gas is not completely oxidized at the end of the combustion chamber.

For complete combustion, the exhaust gas stream is subjected to other oxidation processes. For this purpose, in the first embodiment of the invention, two or more pipes are arranged in the annular gap between the cylindrical jacket of the combustion chamber and the end face of the combustion chamber located towards the burner. The These pipes are arranged around the gap and are directed towards the axis of the combustion chamber and serve to supply additional oxygen or air. In another embodiment, additional oxygen or air is supplied to the annular gap evenly along its circumference via an annular channel disposed at the end face of the cylindrical jacket of the combustion chamber. In addition, a body, preferably a plate made of a refractory material, is placed in front of the metal end face of the combustion chamber (eg by means of a retaining web) in an insulating manner. A hot exhaust gas stream strikes this plate. In order to reach the subsequent cleaning unit via the annular gap, it is bent at 90 ° and is distributed radially. This refraction and radial dispersion cause turbulence of the hot exhaust gas flow. The previously described plate prevents the hot exhaust gas stream from contacting the end face of the combustion chamber. The end face also defines the boundary of the cleaning unit and is therefore relatively cold because it is cooled by the cleaning liquid (temperature range 20-90 ° C.). In contrast, plates arranged in an adiabatic manner heat up to the temperature of the almost hot exhaust gas stream on the side facing the combustion chamber, ie T> 800 ° C. While hot exhaust gas flows out of the gap, oxygen (or air) enters through the pipes located in the gap, increasing turbulence in the exhaust gas flow in the area in contact with the latter. The amount of oxygen (or air) introduced is such that a λ value greater than 1 (preferably λ = 1.2) is achieved with a mixture of supplied oxygen (or supplied air) and hot exhaust gas. It is. This means the following: That is, oxygen (or air) is supplied to such an extent that oxygen deficiency in the combustion chamber is at least neutralized. As described above, the oxidization condition is realized at the main temperature (800 ° <T <1200 °) by the λ value of the mixed gas of hot exhaust gas and supplied oxygen (or supplied air). Preferably the reaction taking place here has secondary combustion properties. The CO and remaining unburned fuel gas produced in the combustion chamber in the main combustion process is converted to CO ₂ and H ₂ O. The temperature in the region between the end of the cylindrical jacket and the hot plate is lower than that required for the conversion of fluorine containing contaminants, but is high enough for the combustion of CO and the remaining fuel gas.

  Due to the strong turbulence created, the resulting complete mixing, the temperature level of the exhaust gas flow in this region, and the adapted high λ value, it is completely efficient in a fairly limited space in the transition region to the cleaning unit After-burning is guaranteed.

  Once complete combustion is complete, the exhaust gas enters the cleaning unit. Here, the hot exhaust gas stream is cooled, HF is neutralized, and solid particles formed during the combustion process are washed away. The purified, cooled exhaust gas is then passed through the manufacturing plant exhaust channel.

The use of the device according to the invention is advantageous in that it ensures a reduction in the inherent amount of fuel gas required and thus improves the economics of the exhaust gas purification process. The reduction in the amount of fuel gas required is realized by the reduced overall flow due to the fact that air or O ₂ is prevented from reaching the vicinity of the burner. The special solution mentioned above ensures a very efficient pollutant conversion process. At the same time, the burner solution does not require adaptation (modification) of the burner design, with a wide range of different fuel gas / oxygen ratios, different pollutant gases in the exhaust gas, and different pollutant gas amounts. For, ensure a stable flame formation.

  A particularly significant advantage is that the amount of nitrogen oxides released with the purified exhaust gas is strongly reduced. This release is more than a state-of-the-art device that uses a ring burner, a fuel gas / oxygen mixture supply, and an additional supply of oxygen in the region of the ring burner if both devices are operated under similar conditions. About five times smaller.

Another advantage of the device according to the present invention is that the device can also be used to purify exhaust gases containing pollutants that require a relatively low energy input (eg, SiH ₄ ) without thermochemical conversion changing the design of the device. Is to be used.

  With regard to the ring burner design, it is convenient that the individual perforations are drilled with a uniform diameter on a single hole circle around the central exhaust gas inlet and distributed evenly around this circle. While alternately supplying fuel gas and oxygen to the perforations, the fact that the gas coming out of the holes is in direct contact with the gas coming out of two adjacent perforations ensures complete mixing of the fuel gas and oxygen.

  However, it is also useful that the perforations evenly distributed on the hole circle around the central exhaust gas inlet have two different diameters. For example, when the burner is operated with methane and oxygen, the conditions to reduce (corresponding to a λ value of 0.8 for gas (fuel gas and oxygen) that enters the combustion chamber and mixes directly on the surface of the burner) Is realized in the combustion chamber, the required methane gas flow is about 0.6 times that of oxygen. If the area of the perforations depends on the factors indicated above, it is possible to adapt the release rates of the two gases in the burner perforation to each other. In this way, for example, flame stability can be improved.

  In the previously described ring burner embodiment, alternating supply of fuel gas and oxygen to adjacent perforations on the burner surface places two annular channels inside the burner and these perforations on the burner surface This is achieved by alternately connecting to one of the annular channels. The burner has a fuel gas supply pipe in one of these annular channels and an oxygen supply pipe in the other annular channel.

  With respect to the body in front of the end face of the combustion chamber, this body is dome-shaped and has a soot depth of 15-60 mm, preferably 20 mm, with a diameter larger than the diameter of the combustion chamber but with an end face diameter. It is also effective to have a smaller diameter. The dome-shaped body is made of heat-resistant corrosion-resistant steel, and its concave surface faces the ring burner and is arranged in a heat-insulating manner. In this way, hot exhaust gas exiting the combustion chamber is prevented from stagnating in front of this body, which may adversely affect the mixing of additional oxygen that is introduced with the hot exhaust gas exiting the combustion chamber.

  If pipes are arranged to supply oxygen (or air) additionally to the gap at the end of the combustion chamber, the axis of these pipes is 60 ° to 85 ° with respect to the axis of the combustion chamber, It is convenient to be inclined by an angle of preferably 80 °. This ensures that the cleaning agent from the cleaning unit does not enter the combustion chamber and flows outward along the inclined pipe.

  In addition, the pipe conveniently extends about 15-50 mm, preferably 25 mm, beyond the end of the end face of the combustion chamber and into the gap between the cylindrical jacket and the end face of the combustion chamber. Is not exceeded. This dimension ensures that the cleaning agent does not enter the pipe for the additional supply of oxygen (or air) and that the end of the pipe does not get too hot and consequently does not corrode.

If the annular channel is arranged for additional supply of oxygen (or air) to the annular gap, the annular channel is conveniently realized using a cylindrical pipe arranged concentrically with the combustion chamber. And an oxygen (or air) supply pipe is disposed at the opposite end of the annular channel. In this way, an even distribution along the periphery of the channel is achieved. In addition, it is convenient for the annular channel to have a width of 1.5-2 mm.
The present invention will now be described with reference to the drawings of FIGS. 1-4 using an exemplary embodiment of the apparatus.

  The device basically consists of a cylindrical fuel chamber (1) which is arranged in a housing (2) made of corrosion-resistant steel and made of a corrosion-resistant material. The fuel chamber has a diameter of 100 mm and a height of 400 mm. In the region of the base plate (3) and the cylindrical jacket (4), the combustion chamber is closed. So outside air can not flow. A ring burner (5) having an outer diameter of 50 mm is arranged in the center of the base plate (3). The ring burner (5) comprises a central bore (6) with a diameter of 12 mm and a connection (9) for supplying exhaust gas to the combustion chamber (1). On the surface of the ring burner (5), in order to supply fuel gas and oxygen separately to the ring burner (5), a 1 mm diameter perforation (7) and a 1.2 mm diameter perforation (8) They are alternately arranged on the 30 mm hole circle (28) at equal distances from each other. The ring burner is supplied with fuel gas via the connection (10) and oxygen via the connection (11). Inside the ring burner (5), the supplied fuel gas is distributed along the annular channel (29) and the supplied oxygen is distributed along the annular channel (30). The perforations (7) connect to the annular channel (29) and the perforations (8) connect to the annular channel (30).

To operate the combustion chamber, 20 slm (standard liters per minute) CH ₄ and 32 slm oxygen are fed to the ring burner. The mixed gas of oxygen and CH ₄ generated just above the burner corresponds to a λ value of 0.8. That is, it is a hypostoichiometric mixture of oxygen and fuel gas. During operation of the ignition device (12), an annular flame (13) forms on the ring burner (5) near its surface. This flame turns into a flame (14) with a uniform cross-section away from the surface of the ring burner (5). The supply of oxygen and fuel gas is controlled using the sensor signal of the monitor (15) facing the flame (14). 160 slm exhaust gas is introduced into the flame via the connection (9) and the central perforation (6). This exhaust gas basically consists of 158 slm nitrogen and about ₂ slm C ₂ F ₆ . Due to the lambda value of the separately supplied oxygen and CH ₄ separately supplied gas, the flame (14), once fully developed, has a reducing effect over its entire cross section. Since the flame is not exposed to air, ie oxygen acting on the flame from the outside in the region of the ring burner (5), this reducing effect on the pollutant gases is effective in the flame skin and virtually the entire volume of the combustion chamber (1). This is also realized over (17). Basically CH ₄ , O ₂ and C ₂ F ₆ are converted to HF, CO ₂ , CO and H ₂ O in the flame (13, 14) and the remaining volume of the combustion chamber. Nitrogen oxide production is largely avoided. A mixed gas of high temperature treated exhaust gas (consisting of N ₂ , HF, CO ₂ and CO) and unburned CH _{4 in} the temperature range of 800-1200 ° C. is hot, as indicated by arrow (18). Out of the cylindrical part of the combustion chamber (1) towards the body (19).

  The hot body (19) is made of corrosion-resistant steel and has a diameter of 260 mm and a thickness of 2 mm. It is in the form of a dome with a depth of 20 mm and is thermally insulated in front of a cooled end face (16) having a diameter of 300 mm, with its concave face towards the ring burner (5). In the device according to the exemplary embodiment, the cooled end face (16) is also domed with a ridge depth of 40 mm. The convex surface of the cooled end face (16) faces the cleaning unit (25). In one embodiment (FIG. 1), three pipes (21) arranged at an angle of 120 ° to each other in front of the body (19) and having an outer diameter of 6 mm extend beyond the end of the end face (16), It extends 25 mm to a wide gap (20) of 60 mm between the cylindrical jacket (4) and the end face (16) of the combustion chamber (1). However, it does not reach the combustion chamber beyond the end of the cylindrical jacket (4). The pipe is inclined at an angle of 80 ° with respect to the axis of the combustion chamber (1). The pipes (21) are connected to each other via an annular pipe (22). The annular pipe is arranged outside the housing (2), where additional oxygen is supplied via the connection (23). 11 slm of oxygen is fed through the pipe (21) at a speed of about 60 m / s.

  In another embodiment (FIG. 2), a double pipe (33) is arranged concentrically with the cylindrical combustion chamber (1), so that an annular channel (32) is formed between the cylindrical combustion chamber and the double pipe. Is done. Additional oxygen is evenly supplied through this annular channel along its circumference to the annular gap (20). 20 slm oxygen (or 100 slm air) is supplied to the annular channel (32).

The hot exhaust gas stream and the introduced oxygen mix together due to turbulence in the region of the gap (20) in front of the body (19). Here, the hyper-stoichiometric ratio of oxygen to unburned fuel gas causes mixing of the additional oxygen supplied and unburned CH ₄ . The λ value of this gas mixture is higher than 1.2. Therefore, the hot exhaust gas and the additional oxygen turbulent gas mixture supplied have an oxidizing effect. In the second combustion process, the components of the unburned exhaust gas are completely burned. In particular, CO produced in the reducing volume of the combustion chamber (1) is converted into CO ₂ and H ₂ O.

  Next, the treated exhaust gas flows out from the gap (20) toward the cleaning unit (25) as shown by the arrow (24). A cleaning liquid (27) is supplied to the unit via the connection (26). The liquid cools the hot exhaust gas to below 50 ° C. Hydrogen fluoride (HF) contained in the cooled exhaust gas is hydrolyzed and neutralized with a cleaning solution (1% sodium hydroxide solution).

  The cleaned exhaust gas is discharged into the surrounding atmosphere as indicated by an arrow (31) either directly through the exhaust device or through the central exhaust gas unit of the semiconductor factory.

The amount of carbon monoxide in the exhaust gas that has been cleaned is 10 ppm. Nitrogen oxide emissions are significantly reduced. In the exemplary exhaust gas purification process, it is on the order of 0.1 mol / m ³ .

1 is a schematic longitudinal sectional view of an apparatus for purifying exhaust gas in which additional oxygen is supplied through a pipe. 1 is a schematic longitudinal sectional view of an apparatus for purifying exhaust gas in which additional oxygen is supplied via an annular channel. It is a schematic plan view of a ring burner. It is a schematic sectional drawing of a ring burner.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Combustion chamber 2 Housing 3 Base plate 4 Cylindrical jacket 5 Ring burner 6 Center drilling 7 Burner drilling 8 Burner drilling 9 Connection for exhaust gas 10 Connection for fuel gas 11 Connection for oxygen 12 Ignition Equipment 13 Annular flame 14 Uniform flame 15 Monitor 16 Cooled end face 17 Combustion chamber volume 18 Arrow 19 Body 20 Gap 21 Pipe for additional oxygen 22 Annular pipe 23 Connection for oxygen 24 Arrow 25 Cleaning unit 26 Connection for cleaning liquid 27 Cleaning liquid 28 Hole circle 29 Annular channel for fuel gas 30 Annular channel for oxygen 31 Arrow 32 Annular channel for additional oxygen 33 Cylindrical double pipe 34 Connection for oxygen

Claims (13)

An exhaust gas containing nitrogen and pollutants, particularly an exhaust gas containing fluorocarbon compounds and other fluorine compounds, is purified by thermochemical conversion in a cylindrical combustion chamber integrated with a subsequent cleaning unit,
In an apparatus using a burner with a central exhaust gas supply and a separate supply of fuel gas and oxygen,
The ring burner is arranged on a single hole circle and is provided with perforations that ensure a local alternating simultaneous supply of fuel gas and oxygen,
The combustion chamber is closed except for an annular gap between the cylindrical jacket and the end face of the combustion chamber located towards the burner;
A body, preferably a plate made of heat and heat insulating material, is placed in front of the end face of the combustion chamber;
Several pipes for supplying additional oxygen or additional air are arranged in the gap, these pipes being distributed around the gap and extending to the gap in a direction towards the combustion chamber axis. Features device. An exhaust gas containing nitrogen and pollutants, particularly an exhaust gas containing fluorocarbon compounds and other fluorine compounds, is purified by thermochemical conversion in a cylindrical combustion chamber integrated with a subsequent cleaning unit,
In an apparatus using a burner with a central exhaust gas supply and a separate supply of fuel gas and oxygen,
The ring burner is arranged on a single hole circle and is provided with perforations that ensure a local alternating simultaneous supply of fuel gas and oxygen,
The combustion chamber is closed except for an annular gap between the cylindrical jacket and the end face of the combustion chamber located towards the burner;
A body, preferably a plate made of heat and heat insulating material, is placed in front of the end face of the combustion chamber;
A device characterized in that a double pipe is arranged concentrically with the cylindrical jacket of the combustion chamber and thus forms an annular channel for supplying additional oxygen or additional air.   3. A device according to claim 1 or 2, characterized in that the perforations on the surface of the ring burner are evenly distributed over the hole circle and all have the same diameter.   3. A device according to claim 1 or 2, characterized in that the perforations in the surface of the ring burner are evenly distributed over the hole circle and have two different diameters alternating. In the device according to any one of claims 1 to 4,
Two annular channels are provided in the ring burner,
The perforations of the ring burner alternately connect to one of these annular channels;
The ring burner comprises a connection for supplying fuel gas to one of these annular channels and a connection for supplying oxygen to the other annular channel. In the device according to any one of claims 1 to 5,
A body, preferably a plate, is arranged in front of the end face of the combustion chamber in the region of the gap in an insulating manner;
The apparatus according to claim 1, wherein the body or plate is made of a heat-resistant material and has a diameter larger than that of the combustion chamber but smaller than that of the end face (16). In the device according to any one of claims 1 to 5,
A dome-shaped body having a soot depth of 15 mm to 60 mm, preferably 20 mm, is arranged in front of the end face of the combustion chamber in the region of the gap in a heat-insulating manner, the concave surface of the ring burner (5) Looking towards
An apparatus characterized in that the body is made of heat-resistant and corrosion-resistant steel and has a diameter larger than that of the combustion chamber.   8. A device according to any one of claims 1 or 3 to 7, wherein the axis of the pipe for the additional supply of oxygen is at an angle of 60 ° to 85 °, preferably 80 ° with respect to the axis of the combustion chamber. A device characterized by being tilted at.   8. The apparatus according to claim 1, wherein a pipe for additional supply of oxygen extends 15-50 mm, preferably 25 mm, beyond the end of the end face of the combustion chamber. An apparatus characterized in that it reaches the gap between the cylindrical jacket of the chamber and the end face, but does not exceed the end of the cylindrical jacket.   8. Apparatus according to any one of claims 2 to 7, wherein the cylindrical jacket of the combustion chamber and the double pipe for the supply of additional oxygen or additional air concentrically disposed therein. A device characterized in that the annular channel in between has a radial width of 1.5-2 mm.   11. The apparatus according to any one of claims 2 to 7 or 10, wherein the annular channel leads to the gap between the cylindrical jacket and the end face of the combustion chamber, and the shaft of the combustion chamber. A device characterized by being parallel to the direction of.   11. The apparatus according to any one of claims 2 to 7 or 10, wherein the annular channel leads to the gap between the cylindrical jacket and the end face of the combustion chamber, and the shaft of the combustion chamber. , Characterized in that it is directed radially towards the axis at an angle of 90 ° to the axis.   11. The apparatus according to any one of claims 2 to 7 or 10, wherein the annular channel leads to the gap between the cylindrical jacket and the end face of the combustion chamber, and the shaft of the combustion chamber. The device is characterized in that it is oriented radially away from the axis at an angle of 90 ° to the axis.

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