Plasma abatement method and device therefor

Abstract

A plasma abatement method: involves supplying an exhaust gas (E), which serves as a treatment target, to a plasma jet (P) ejected from a plasma torch (14) into a reaction chamber (18a) to thereby thermally decompose harmful components in the exhaust gas (E); and is configured as follows. The plasma abatement method is characterized in that a cooling gas (CG) is supplied to the plasma jet (P) ejected from the plasma torch (14) into the reaction chamber (18a) to thereby cool the plasma jet (P), and then the exhaust gas (E) is supplied to the plasma jet (P).

Description

Plasma abatement method and apparatus therefor

[0001] This invention relates to a plasma abatement method and apparatus for exhaust gas that enables the reduction of nitrogen oxides (reduction of NOx).

[0002] In the electronics industry, which manufactures semiconductors and liquid crystals, harmful gases such as toxic and flammable gases are frequently used in various film deposition processes, including silicon oxide CVD. Various types of abatement devices have been developed to safely handle these gases. One such abatement device is a plasma-type abatement device that uses thermal plasma, such as arc discharge, as a heat source. Because this plasma-type abatement device can obtain high temperatures, it can reliably process difficult-to-decompose substances such as PFCs (perfluorocompounds) in exhaust gases with high abatement efficiency.

[0003] As an example of technology related to such plasma-type abatement devices, Patent Document 1 (Japanese Patent Publication No. 2005-205330) discloses a technology that stabilizes the plasma and improves abatement efficiency by introducing exhaust gas as a swirling flow into a high-temperature plasma within a reaction chamber.

[0004] Japanese Patent Publication No. 2005-205330

[0005] However, the above-mentioned conventional technology had the following problems. Specifically, as mentioned above, the amount of NOx (nitrogen oxides) generated increases under the high heat conditions during plasma decomposition, resulting in the emission of a large amount of NOx as a byproduct.

[0006] Therefore, the main objective of the present invention is to provide a plasma abatement method and apparatus that can reduce the amount of NOx generated while maintaining the exhaust gas abatement performance.

[0007] To achieve the above objective, the inventors conducted extensive research and, as a result, discovered the following mechanism for NOx generation in a plasma abatement device using plasma generated by arc discharge, thus completing the present invention. Specifically, active dissociated nitrogen (N) is generated in a nitrogen plasma of over 3000K by arc discharge within the plasma torch. Subsequently, when an ultra-high temperature plasma jet is ejected from the nozzle of the plasma torch into the reaction chamber, a large amount of dissociated nitrogen is supplied to the reaction chamber along with the plasma jet, and OH radicals are generated from the water vapor in the reaction chamber near the nozzle due to the heat of the ultra-high temperature plasma jet of nearly 3000K. When the reaction rates of various NOx generation reactions in the reaction chamber were examined, it became clear that the amount of NOx generated by the reaction between dissociated nitrogen and OH radicals was orders of magnitude greater, as shown in Figure 1. In other words, in order to suppress NOx generation in the reaction chamber, it is important to lower the temperature in the reaction chamber to reduce the amount of OH radicals and dissociated nitrogen generated, and to reduce the reaction rate by reducing the opportunity for contact between the dissociated nitrogen and OH radicals.

[0008] Therefore, the present invention provides a plasma detoxification method in which harmful components in the exhaust gas E are thermally decomposed by supplying exhaust gas E to be treated to a plasma jet P ejected from a plasma torch 14 into a reaction chamber 18a, as shown in Figures 2 to 3, for example. Specifically, the method is characterized by supplying a cooling gas CG to the plasma jet P ejected from the plasma torch 14 into the reaction chamber 18a to cool the plasma jet P, and then supplying the exhaust gas E to the plasma jet P.

[0009] In this invention, before supplying the exhaust gas E to the plasma jet P, by supplying the cooling gas CG to the plasma jet P, the water vapor concentration existing in the high-temperature part on the upstream end side of the plasma jet P can be decreased to suppress the generation of OH radicals. In addition, while decreasing the temperature of the plasma jet P, the dissociation nitrogen concentration in the reaction chamber 18a can also be diluted. For this reason, the contact between the dissociation nitrogen and the OH radicals in the reaction chamber 18a can be reduced to decrease the reaction rate, and the generation of NOx can be significantly reduced. Incidentally, although the temperature of the plasma jet P is decreased by the supply of the cooling gas CG, it is natural that the temperature of the plasma jet P after the temperature decrease is set to be not lower than the thermal decomposition temperature of the component to be detoxified in the exhaust gas E.

[0010] In the present invention, the cooling gas CG is preferably formed of at least one selected from the group consisting of N ２ , Ar, He, NH ３ , H ２ , CH ４ , CO ２ , O ２ and air. In this case, when using inert gases such as N ２ , Ar, He as the cooling gas CG, in addition to being able to efficiently decrease the temperature of the plasma jet P and dilute the dissociation nitrogen concentration in the reaction chamber 18a, since the plasma torch 14 is in an inert gas atmosphere, corrosion of the plasma torch 14 by corrosive gases such as halogen can be prevented and the long life of the plasma torch 14 can be achieved. Further, when using reducing gases such as NH ３ , H ２ , CH ４ as the cooling gas CG, in addition to the effect of reducing the generation amount of NOx, NOx generated in the reaction chamber 18a can also be decomposed and removed. Furthermore, when using gases having oxidizing power in a nitrogen atmosphere such as CO ２ , O ２ , air as the cooling gas CG, for example, decomposition of PFC or the like which is a component to be treated in the exhaust gas E can be performed more efficiently.

[0011] Furthermore, in the present invention, it is preferable that the cooling gas CG is supplied so as to swirl around the outer circumference of the upstream end of the plasma jet P. In this case, the plasma jet P can be effectively cooled without causing any physical effects that would cause the plasma jet P to misfire. In addition, even if solid products such as powder are generated by the decomposition of the exhaust gas E, it is possible to prevent these solid products from adhering to the torch, thereby preventing a decrease in the efficiency of the abatement performance due to torch blockage.

[0012] Furthermore, the second invention in the present invention is an apparatus for carrying out the above-described methods, and for example, as shown in Figures 2 to 3, the plasma abatement apparatus is configured as follows: The apparatus comprises a decomposition furnace 12 including a plasma torch 14 that ejects a plasma jet P from an ejection hole 14a, a cooling gas supply cylinder 16 whose internal space surrounds the ejection hole 14a and which supplies a cooling gas CG that does not contain OH radicals toward the plasma jet P, and a reaction cylinder 18 in which a reaction chamber 18a is formed, which is connected to the plasma torch 14 via the cooling gas supply cylinder 16 and supplies exhaust gas E to be treated toward the plasma jet P ejected into the reaction chamber 18a.

[0013] In the apparatus of the present invention, similar to the method of the present invention described above, the cooling gas CG is N ２ ,Ar,He,NH ３ , H ２ CH ４ , CO ２ , O ２ Preferably, it is formed of at least one selected from the group consisting of and air.

[0014] Furthermore, in the present invention, it is preferable that the cooling gas CG is supplied to the cooling gas supply cylinder 16 in a swirling manner around the outer circumference of the upstream end of the plasma jet P, and more preferably, the internal space of the cooling gas supply cylinder 16 is formed in a substantially frustoconical shape. In this case, forming the internal space of the cooling gas supply cylinder 16 in a substantially frustoconical shape improves the mixing of the plasma jet P and the cooling gas CG, and allows the height of the cooling gas supply cylinder 16 to be reduced.

[0015] Furthermore, in the present invention, it is preferable that the minimum inner diameter D of the cooling gas supply cylinder 16 is within the range of 10 mm to 50 mm. In this case, the plasma jet P and the cooling gas CG are mixed well, and the cooling effect and the dilution effect of dissociated nitrogen can be efficiently exerted. If the minimum inner diameter D is less than 10 mm, the distance between the plasma jet P and the cooling gas supply cylinder 16 becomes too close, and there is a risk that the cooling gas supply cylinder 16 will be damaged by heat. Conversely, if it exceeds 50 mm, it becomes difficult for the plasma jet P and the cooling gas CG to mix, and the cooling effect and the dilution effect of dissociated nitrogen may decrease.

[0016] Furthermore, in the present invention, it is preferable that the length L of the cooling gas supply cylinder 16 is within the range of 10 mm to 100 mm. In this case, the plasma jet P and the cooling gas CG are mixed well, and the cooling effect and the dilution effect of dissociated nitrogen can be efficiently exerted. If the length L is less than 10 mm, the distance between the cooling gas inlet and the outlet of the cooling gas supply cylinder 16 becomes too short, and the plasma jet P and the cooling gas CG are not mixed well, making it difficult to exert the dilution effect of dissociated nitrogen, etc. Conversely, if it exceeds 100 mm, the plasma jet P is cooled too much, and the detoxification performance decreases.

[0017] Furthermore, in the present invention, it is preferable to include at least one of an inlet scrubber 20 for pre-washing the exhaust gas E to be treated before being introduced into the decomposition furnace 12, or an outlet scrubber 22 for cooling and washing the exhaust gas E that has been thermally decomposed in the decomposition furnace 12. The present invention also preferably includes the specific configurations described in the embodiments described later.

[0018] According to the present invention, a plasma-type abatement method and apparatus can be provided that can reduce the amount of NOx generated while maintaining the exhaust gas abatement performance.

[0019] This graph shows the reaction rates of various chemical reactions involved in NOx generation inside and outside the plasma torch. This is an explanatory diagram showing an overview of the entire plasma abatement apparatus according to one embodiment of the present invention. Figure 3A is a partial cross-sectional view showing the main part of the plasma abatement apparatus according to one embodiment of the present invention, and Figure 3B is a cross-sectional view taken along the line A-A' in Figure 3A.

[0020] Hereinafter, one embodiment of the present invention will be described with reference to Figures 2 to 3. Figure 2 is a diagram showing an overview of the entire plasma abatement apparatus 10 of one embodiment that implements the plasma abatement method of the present invention, and Figure 3 is a diagram showing its main parts. As these figures show, the plasma abatement apparatus 10 of this embodiment is preferably an apparatus that performs abatement treatment on exhaust gas E (gas to be treated) containing harmful components (e.g., flammable gas, etc.) discharged from a gas source such as a film deposition apparatus, and is generally composed of a decomposition furnace 12, an inlet scrubber 20 and an outlet scrubber 22.

[0021] The decomposition furnace 12 is installed in one or more units to thermally decompose harmful components in the exhaust gas E using the heat of a plasma jet, and is equipped with a plasma torch 14, a cooling gas supply cylinder 16, and a reaction cylinder 18.

[0022] The plasma torch 14 is used to generate plasma. It generates an arc plasma by applying a discharge voltage between electrodes (anode and cathode), and also generates N around this arc plasma. ２A working gas such as nitrogen or argon is supplied to generate a high-temperature gas flow with significantly increased energy density, i.e., a plasma jet P. This plasma jet P, ejected from an ejection hole 14a drilled approximately in the center of the lower end surface of the plasma torch 14, is used to decompose refractory CF. ４ The extremely high temperature is sufficient to thermally decompose CF in PFC-containing exhaust gas, which is difficult to completely decompose with conventional heater-type abatement devices, etc. ４ These can also be rapidly and irreversibly decomposed. In this embodiment, N is used as the working gas. ２ Use this.

[0023] A known plasma torch 14 can be used. Specifically, (not shown in the figure) this plasma torch 14 has a torch body, and an anode is provided at the tip (lower end) of the torch body, and the space surrounded by the anode constitutes the plasma generation section. A rod-shaped cathode is provided in the plasma generation section surrounded by the anode. An insulator is provided between the anode and the cathode to prevent electrical short circuits, and an ejection hole 14a is drilled in the center of the anode. A power supply that provides DC power is connected to this anode and cathode.

[0024] The cooling gas supply cylinder 16 is a cylindrical member made of a metal material with excellent heat resistance and corrosion resistance, such as stainless steel or Hastelloy (Haines Ltd. registered trademark), and its upper end is airtightly connected to the lower end of the plasma torch 14 such that its internal space surrounds the ejection hole 14a. The downstream end of the cooling gas supply pipe 24, which supplies cooling gas CG to cool the plasma jet P ejected from the ejection hole 14a, is connected to the side surface of the cooling gas supply cylinder 16. Furthermore, the lower part of the cooling gas supply cylinder 16 is connected to the upper part of the reaction cylinder 18.

[0025] In this embodiment, as shown in Figure 3B, the downstream end of the cooling gas supply pipe 24 is connected to the cooling gas supply cylinder 16 in a manner substantially parallel to the tangential direction of the side surface, thereby supplying the cooling gas CG within the cooling gas supply cylinder 16 in a swirling flow that circulates around the plasma jet P. The method of connecting the cooling gas supply cylinder 16 and the cooling gas supply pipe 24 is not limited to this, and any method of connection that allows the cooling gas CG to form a swirling flow within the cooling gas supply cylinder 16 is acceptable. On the other hand, if it is not necessary for the cooling gas CG to form a swirling flow, the method of connecting the cooling gas supply cylinder 16 and the cooling gas supply pipe 24 is not particularly limited and any method is acceptable.

[0026] Furthermore, a cooling gas supply source 26, such as a tank or cylinder where the cooling gas CG is stored, is connected to the upstream end of the cooling gas supply piping 24. In addition, a flow control means consisting of a flow meter and a flow control valve, although not shown, is installed in the middle of the cooling gas supply piping 24. The cooling gas CG supplied from the cooling gas supply source 26 can be any gas that can cool the plasma jet P, but as mentioned above, N ２ ,Ar,He,NH ３ , H ２ CH ４ , CO ２ , O ２ Preferably, it is at least one selected from the group consisting of and air.

[0027] Furthermore, in the embodiment shown in Figure 3, the internal space of the cooling gas supply tube 16 is made to be approximately frustoconical in shape, so that the plasma jet P and the cooling gas CG mix well and the height of the cooling gas supply tube 16 is kept down. However, in cases where it is not necessary to keep the height of the cooling gas supply tube 16 down in this way, the internal space of the cooling gas supply tube 16 may be made to be, for example, a straight cylindrical shape.

[0028] Further, the minimum inner diameter D of the cooling gas supply cylinder 16 is preferably within the range of 10 mm to 50 mm as described above, and the length L of the cooling gas supply cylinder 16 is preferably within the range of 10 mm to 100 mm as described above.

[0029] The reaction cylinder 18 is a cylindrical member made of a metal material excellent in heat resistance and corrosion resistance such as stainless steel or Hastelloy (registered trademark of Haynes), and the exhaust gas E to be processed is supplied toward the plasma jet P ejected into the reaction chamber 18a formed therein, and is for thermally decomposing harmful components in the exhaust gas E.

[0030] The upper part of this reaction cylinder 18 is connected in communication with the plasma torch 14 (more specifically, the ejection hole 14a of the plasma torch 14) via the cooling gas supply cylinder 16, and the lower part thereof is connected in communication with the internal space of a water tank 28 described later.

[0031] Further, at the upper part of this reaction cylinder 18, the downstream end of an exhaust gas introduction pipe 30 for feeding the exhaust gas E washed with water by an inlet scrubber 20 described later to the reaction chamber 18a is connected in communication. In the embodiment shown in FIG. 3, the downstream end of the exhaust gas introduction pipe 30 is connected so as to face the radial direction of the reaction cylinder 18, but it may be connected so that the exhaust gas E forms a swirling flow in the reaction chamber 18a, like the cooling gas supply pipe 24 described above.

[0032] The decomposition furnace 12 configured as described above is erected on the water tank 28. This water tank 28 is mainly for storing the circulating water W supplied to the reaction cylinder 18 as cooling water, and the internal space above the liquid surface of the circulating water W is utilized as a transfer path for the exhaust gas E. Further, on this water tank 28, in addition to the above-described decomposition furnace 12, an inlet scrubber 20 is also erected, and the internal space of the water tank 28 is also in communication with the inside of the inlet scrubber 20. For this reason, a partition wall 28a for partitioning the internal space is provided in the water tank 28 so that the reaction chamber 18a of the decomposition furnace 12 and the inside of the inlet scrubber 20 do not communicate with each other. The internal space of the water tank 28 partitioned by this partition wall 28a is connected in communication with the upstream end of an exhaust gas discharge pipe 32, and the upstream end of a circulating water discharge pipe 34 is connected in communication below the liquid surface of the water tank 28.

[0033] The inlet scrubber 20 is a wet scrubber that pre-washes (by water washing) the exhaust gas E introduced into the cracking furnace 12, and one or more units are provided as required. The exhaust gas E is supplied to this inlet scrubber 20 via an exhaust gas supply pipe 36 from an exhaust gas discharge source such as a CVD process. In the embodiment shown in FIG. 2, as described above, the inlet scrubber 20 is erected on the water tank 28, and its interior and the interior space of the water tank 28 communicate with each other, and the washing water used in the inlet scrubber 20 is sent to the water tank 28. Further, the downstream end of the exhaust gas supply pipe 36 is communicatively connected to the lower side surface of the inlet scrubber 20, and the upstream end of the exhaust gas introduction pipe 30 is communicatively connected to the top of the inlet scrubber 20. Inside the inlet scrubber 20, although not shown, washing water is jetted downward from a spray nozzle attached to the upper part. For this reason, the washing water and the exhaust gas E come into contact in a countercurrent manner, and the washing water obtained by water-washing the exhaust gas E flows into the water tank 28 and is reused as the circulating water W.

[0034] The outlet scrubber 22 is a wet scrubber that liquid-washes (by water washing) and cools the exhaust gas E pyrolyzed in the cracking furnace 12, and one or more units are provided as required. The downstream ends of an exhaust gas lead-out pipe 32 and a circulating water lead-out pipe 34 are communicatively connected to the lower part of this outlet scrubber 22, respectively.

[0035] Here, in the embodiment shown in FIG. 3, an exhaust pump 38 is provided in the middle of the exhaust gas lead-out pipe 32, and a check valve 40 is attached to the downstream side (delivery side) of the exhaust pump 38. Also, a drain pump 42 is provided in the middle of the circulating water lead-out pipe 34, and a check valve 44 is attached to the downstream side (delivery side) of the drain pump 42. Then, as required, the above exhaust pump 38 and drain pump 42 are operated so that the pressures inside the inlet scrubber 20 and inside the cracking furnace 12 are controlled to be in a reduced pressure state within a range of, for example, 133 Pa or more and 93.1 kPa or less.

[0036] The upstream end of the treated gas outlet pipe 46 is connected to the top of the outlet scrubber 22. Inside the outlet scrubber 22, cleaning water is sprayed downward from a spray nozzle mounted on the top (not shown). As a result, the cleaning water and the exhaust gas E come into contact in a counterflow direction, and the cleaning water that has washed the exhaust gas E is stored in the lower part of the outlet scrubber 22. In addition to the cleaning water, circulating water W is also supplied to the lower part of the outlet scrubber 22 via the circulating water outlet pipe 34. This cleaning water and circulating water W are used for cooling and cleaning the inner surface and outlet of the reaction cylinder 18 and as cleaning water in the inlet scrubber 20 via a pumpless circulation line (piping) (not shown), and then returned to the water tank 28. If the amount of cleaning water or circulating water W stored in the lower part of the outlet scrubber 22 exceeds a predetermined amount, the excess is drained into a drainage duct (not shown).

[0037] Each part of the plasma abatement device 10 configured as described above is connected to a control device, power supply, etc. (not shown).

[0038] Next, a method for plasma abating exhaust gas E using the plasma abating device 10 of this embodiment will be described. First, the various parts of the plasma abating device 10 are activated to reduce the pressure inside the inlet scrubber 20 and the decomposition furnace 12 to a reduced pressure state within the range of 133 Pa or more and 93.1 kPa or less. Subsequently, a discharge voltage is applied to each electrode of the plasma torch 14 to generate an arc plasma, and N is added as a working gas around this arc plasma. ２Gas is supplied, and a plasma jet P is ejected from the ejection port 14a. After the plasma jet P stabilizes, the supply of cooling gas CG to the cooling gas supply cylinder 16 is started, and the amount of cooling gas CG supplied is controlled based on the temperature of the plasma jet P in the reaction chamber 18a. When the temperature of the entire reaction chamber 18a reaches a predetermined temperature above the thermal decomposition temperature of the harmful components in the exhaust gas E, the acceptance of the exhaust gas E is started. The exhaust gas E is then washed with water in the inlet scrubber 20 under reduced pressure, thermally decomposed in the decomposition furnace 12, and after passing through the check valve 40, is washed with water in the outlet scrubber 22 under atmospheric pressure. The exhaust gas E washed in the outlet scrubber 22 is discharged into the atmosphere as treated gas via the treated gas outlet pipe 46.

[0039] According to the plasma abatement method and plasma abatement apparatus 10 of this embodiment, since the exhaust gas treatment in the inlet scrubber 20 and decomposition furnace 12 is performed under reduced pressure, the amount of nitrogen gas used for diluting the exhaust gas E can be reduced. Furthermore, the ultra-high temperature plasma jet P ejected from the plasma torch 14 cools down upon contact with the swirling flow of the cooling gas CG in the cooling gas supply cylinder 16, while the cooling gas CG absorbs the heat from the plasma jet P and rises to a predetermined temperature (for example, 1400°C or higher) necessary for the thermal decomposition reaction of the exhaust gas E. The high-temperature cooling gas CG, which flows down from the cooling gas supply cylinder 16 into the reaction chamber 18a while swirling, generates a pressure gradient due to the centrifugal force of the swirl, and is thoroughly mixed with the exhaust gas E while spreading radially outward, thus decomposing harmful components (for example, PFCs, etc.) in the exhaust gas E. By introducing the cooling gas CG directly below the plasma torch 14 in this manner, the resulting swirling flow dissipates the heat from the plasma jet P and prevents contact between active dissociated nitrogen and OH radicals, thereby significantly reducing the generation of NOx.

[0040] In the above-described embodiment, the exhaust gas treatment in the inlet scrubber 20 and the decomposition furnace 12 is shown to be performed under reduced pressure, but these treatments may also be performed under atmospheric pressure.

[0041] Furthermore, although the above-described embodiment shows a case where both an inlet scrubber 20 and an outlet scrubber 22 are provided, it is also possible to provide only one of the inlet scrubber 20 and the outlet scrubber 22 as needed, or to provide only the decomposition furnace 12 without both.

[0042] Furthermore, in the above embodiment, a port may be provided in the reaction cylinder 18 that can supply a liquid such as urea solution. By doing so, NH ３ Ya H ２ This makes it possible to remove NOx by-products without using flammable gases.

[0043] Furthermore, it goes without saying that various modifications can be made within the scope that a person skilled in the art could foresee.

[0044] 10: Plasma abatement device, 12: Decomposition furnace, 14: Plasma torch, 14a: Outlet, 16: Cooling gas supply cylinder, 18: Reaction cylinder, 18a: Reaction chamber, 20: Inlet scrubber, 22: Outlet scrubber, P: Plasma jet, E: Exhaust gas, CG: Cooling gas, D: Minimum inner diameter (of the cooling gas supply cylinder), L: Length (of the cooling gas supply cylinder).

Claims

1. A plasma abatement method comprising supplying exhaust gas (E) to be treated to a plasma jet (P) ejected from a plasma torch (14) into a reaction chamber (18a) to thermally decompose harmful components in the exhaust gas (E), characterized in that a cooling gas (CG) is supplied to the plasma jet (P) ejected from the plasma torch (14) into the reaction chamber (18a) to cool the plasma jet (P), and then the exhaust gas (E) is supplied to the plasma jet (P).

2. In the plasma abatement method of claim 1, the cooling gas (CG) is N ２ ,Ar,He,NH ３ , H ２ CH ４ , CO ２ , O ２ A plasma abatement method characterized by being formed of at least one selected from the group consisting of and air.

3. A plasma abatement method according to claim 1 or 2, characterized in that the cooling gas (CG) is supplied so as to swirl around the outer circumference of the upstream end of the plasma jet (P).

4. A plasma decomposition apparatus comprising a plasma torch (14) that ejects a plasma jet (P) from an ejection port (14a), a cooling gas supply cylinder (16) whose internal space surrounds the ejection port (14a) and supplies cooling gas (CG) toward the plasma jet (P), and a reaction cylinder (18) having a reaction chamber (18a) formed inside, which is connected to the plasma torch (14) via the cooling gas supply cylinder (16) and supplies exhaust gas (E) to be treated toward the plasma jet (P) ejected into the reaction chamber (18a), and a decomposition furnace (12).

5. In the plasma pest control device according to claim 4, the cooling gas (CG) is N ２ , Ar, He, NH ３ , H ２ , CH ４ , CO ２ , O ２ and is formed of at least one selected from the group consisting of air, a plasma pest control device characterized by that.

6. A plasma abatement apparatus according to claim 4 or 5, characterized in that the cooling gas supply cylinder (16) is supplied such that the cooling gas (CG) swirls around the outer circumference of the upstream end of the plasma jet (P).

7. A plasma abatement apparatus according to claim 6, characterized in that the internal space of the cooling gas supply cylinder (16) has a substantially frustoconical shape.

8. A plasma abatement apparatus according to claim 4 or 5, characterized in that the minimum inner diameter (D) of the cooling gas supply cylinder (16) is in the range of 10 mm to 50 mm.

9. A plasma abatement apparatus according to claim 4 or 5, characterized in that the length (L) of the cooling gas supply cylinder (16) is in the range of 10 mm to 100 mm.

10. A plasma abatement apparatus according to claim 4 or 5, characterized in that it comprises at least one of an inlet scrubber (20) for pre-washing the exhaust gas (E) to be treated before introducing it into the decomposition furnace (12), or an outlet scrubber (22) for cooling and washing the exhaust gas (E) that has been thermally decomposed in the decomposition furnace (12).

11. A plasma abatement apparatus according to claim 6, characterized in that it comprises at least one of an inlet scrubber (20) for pre-washing the exhaust gas (E) to be treated before introducing it into the decomposition furnace (12), or an outlet scrubber (22) for cooling and washing the exhaust gas (E) that has been thermally decomposed in the decomposition furnace (12).

12. A plasma abatement apparatus according to claim 7, characterized in that it comprises at least one of an inlet scrubber (20) for pre-washing the exhaust gas (E) to be treated before introducing it into the decomposition furnace (12), or an outlet scrubber (22) for cooling and washing the exhaust gas (E) that has been thermally decomposed in the decomposition furnace (12).

13. A plasma abatement apparatus according to claim 8, characterized in that it comprises at least one of an inlet scrubber (20) for pre-washing the exhaust gas (E) to be treated before introducing it into the decomposition furnace (12), or an outlet scrubber (22) for cooling and washing the exhaust gas (E) that has been thermally decomposed in the decomposition furnace (12).

14. A plasma abatement apparatus according to claim 9, characterized in that it comprises at least one of an inlet scrubber (20) for pre-washing the exhaust gas (E) to be treated before introducing it into the decomposition furnace (12), or an outlet scrubber (22) for cooling and washing the exhaust gas (E) that has been thermally decomposed in the decomposition furnace (12).

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