JPH024651B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field This invention is a method for safely separating and recovering argon contained in exhaust gas exhausted from vacuum degassing equipment (reflux type vacuum degassing equipment), and for effectively utilizing the argon contained in the exhaust gas. Regarding processing method. Prior art and its problems Vacuum degassing equipment is used for purposes other than degassing, such as improving the quality of molten steel, improving the accuracy of ingredients, improving alloy yield, and making the temperature of molten steel uniform. As is well known, the principle of degassing is the vacuum degassing method, in which the surface area of the molten steel in contact with the vacuum is increased by circulating the molten steel, thereby enhancing the degassing effect. The means to circulate the molten steel is to blow inert gas into one of the immersion pipes (two pipes) and utilize the principle of an air lift pump. Examples of the inert gas used in this case include argon and nitrogen, but argon is currently used in most cases to prevent nitrogen from entering the molten steel. In addition, at the same time as the degassing process, the vacuum degassing equipment uses a temporary period during the process to blow in oxygen to decarburize and decarburize.
The vacuum chamber has an oxygen blowing pipe for raising the temperature and the like. Since this oxygen blowing pipe is installed near the molten steel bath surface in the vacuum chamber, it is normally cooled with inert gas. Argon is also used as the cooling inert gas in this case for the same reason as above. As described above, current vacuum degassing equipment uses large amounts of very expensive argon. Despite this, the reality is that the argon used in vacuum degassing equipment is dissipated into the atmosphere along with the exhaust gas and is not effectively utilized, making the cost of processing molten steel in vacuum degassing equipment high. On the other hand, among other steelmaking equipment that uses a large amount of argon, there is, for example, a tundish in continuous casting equipment. In a tundish, the surface of the molten steel is stirred and the area in contact with the atmosphere increases, so it is necessary to isolate it from the atmosphere with an inert gas to prevent oxidation, etc. In this case as well, argon is used as an inert gas in order to prevent nitridation of the molten steel, similar to the vacuum degassing equipment described above. Moreover, the argon used here is usually of high purity, which is one of the reasons for the high cost of producing slabs. As a technology for recovering argon from the exhaust gas generated during the manufacturing process, there is a method for recovering argon contained in the blown gas discharged from an AOD converter (Japanese Patent Application Laid-Open No. 1984-98404), and a method for recovering argon from a bottom-blown converter. A method of recovering argon from the exhaust gas generated when melting chromium steel is known (Japanese Patent Laid-Open No. 55-50419), but it is effective to recover argon contained in the exhaust gas exhausted from vacuum degassing equipment. I can't find any information on how to use it. Therefore, the inventors first proposed a method for recovering argon contained in the exhaust gas exhausted from vacuum degassing equipment at low cost and in high yield (Japanese Patent Application No. 129525/1986, −138626). The method is
In order to reduce the undesirable nitrogen component in the exhaust gas for argon separation and recovery, dissolved air removed water is used as the cooling water for the condenser of the vacuum evacuation equipment, and carbon dioxide is used as the sealing gas for the vacuum degassing equipment. That is. According to this method, since the nitrogen component ratio in the exhaust gas can be lowered, it is possible to recover argon in the exhaust gas with a high yield. However, during operation, the amount of air leaking from various flanges of the vacuum degassing tank may increase, and the oxygen concentration in the exhaust gas may rise, causing the exhaust gas to enter the explosive range. This is because carbon monoxide is generated from the carbon and oxygen in the molten steel, and _H2, etc. in the molten steel are also generated, resulting in explosive gas. Recovering argon under such conditions is extremely dangerous, and conventionally the following measures have been taken to avoid such danger. If gas within the explosive range is released, dilute with inert gas such as _N2 . When gas within the explosion range is exhausted, the argon recovery equipment will be stopped and the exhaust gas will be dissipated. However, in the case of (2), the argon yield is extremely reduced due to the increase in the amount of gas to be processed in the next step, argon separation and recovery equipment, and the decrease in the argon concentration in the raw material gas, and the equipment cost is also high. In other cases, the argon recovery equipment is stopped, causing problems such as argon dissipation during that time and a drop in argon purity when restarted. In both cases, it was necessary to measure the oxygen concentration to determine whether the exhaust gas was within the explosive range. Purpose of the Invention The present invention was made to solve the problem of the danger of exhaust gas explosion in the conventional argon recovery method.
The purpose of this project is to propose a method that can safely recover argon from exhaust gas by burning O ₂ without the risk of explosion. Structure of the Invention A method for treating exhaust gas in a vacuum degassing facility according to the present invention is a method for separating and recovering argon in exhaust gas using dissolved air removal water in cooling water for a condenser of the exhaust gas treatment facility. The feature is that CO in the exhaust gas is reacted with O ₂ using a catalyst and combusted, and then argon is recovered, and in addition to the dissolved air removed water, carbon dioxide is used as a sealing gas for vacuum degassing equipment. The method using carbon is characterized in that the CO in the exhaust gas is reacted with O ₂ and combusted using a catalyst in the same vacuum degassing equipment as described above, and then argon is recovered. The method of this invention will be explained in detail below. In the vacuum degassing method, as shown in the principle diagram in Figure 3, two immersion pipes 2 for suction and discharge are installed at the bottom of a vacuum chamber 1, and the suction pipe 2-1 is filled with argon. This is a method of blowing inert gas such as molten steel into the ladle 3 using the principle of an air lift pump and degassing it continuously. easily enters the exhaust gas, and a large amount of nitrogen from the air is contained in the exhaust gas. Therefore, when recovering argon from exhaust gas, if nitrogen in the exhaust gas is reduced in advance, argon can be recovered with a high yield. Therefore, in this invention, as a method for recovering argon in the exhaust gas of a vacuum degassing equipment with a high yield, a method of lowering the nitrogen component ratio in the exhaust gas is adopted. That is, lowering the nitrogen component ratio in the exhaust gas leads to an improvement in the argon recovery rate. As a method for lowering the nitrogen component ratio in the exhaust gas of vacuum degassing equipment, this invention includes a method of removing dissolved air in cooling water for a condenser using a vacuum degassing device;
A method using carbon dioxide as a sealing gas in vacuum degassing equipment was adopted. Since the cooling water for the condenser of the exhaust gas in the vacuum degassing equipment brings in dissolved air, it is inevitable that nitrogen from the air will be mixed into the exhaust gas. Therefore, by removing dissolved air in the condenser cooling water, the amount of nitrogen in the exhaust gas can be reduced. The exhaust gas condensed in the cooling water from which dissolved air has been removed by the vacuum deaerator is stored in a holder, and then argon is separated and recovered by the argon separator. On the other hand, nitrogen is conventionally used for sealing various parts of vacuum degassing equipment. Therefore, in addition to the nitrogen in the invading air, this sealing gas also intruded into the exhaust gas. Therefore, in this invention, carbon dioxide is used as the sealing gas. Note that the carbon dioxide used as the sealing gas may be carbon dioxide that is separated and recovered by oxidizing and dehumidifying the remaining gas after recovering argon using the argon separator. As a result, the exhaust gas exhausted from the vacuum degassing equipment contains only the nitrogen in the invading air, and together with the effect of removing dissolved air in the cooling water for the condenser, the nitrogen component ratio in the exhaust gas can be significantly reduced. However, during operation, if the amount of air leaking increases due to deterioration of the gaskets on various flanges of the vacuum degassing tank, the oxygen concentration in the exhaust gas increases, creating the risk of an exhaust gas explosion. In order to avoid this danger of exhaust gas explosion, the present invention employs a method in which a catalytic combustion device is provided within the vacuum degassing equipment, and CO in the exhaust gas is reacted with O ₂ and combusted there. In this case, it is desirable to provide the catalytic combustion device on the primary side of the vacuum deaerator (booster). In other words, the pressure on the primary side of the booster is close to vacuum, and the explosion range is narrow or the conditions are such that no explosion occurs, so there is no risk of explosion even if the fuel is combusted with a catalyst. Note that the catalyst is not particularly limited, but platinum, palladium, or the like may be used. FIG. 1 is a flow sheet showing an example of the configuration of an apparatus for carrying out the method of this invention. In the vacuum degassing process, after inserting both the suction pipe 2-1 and the discharge pipe 2-2 into the molten steel 4 in the ladle 3,
When the vacuum chamber 1 is evacuated, argon gas 5 is blown into the suction pipe 2-1. As the amount of gas blown into the ladle 3 increases, the speed at which the molten steel circulates within the vacuum chamber 1 gradually increases, and degassing progresses. Thereafter, the alloy is added to the molten steel from the alloy addition device 6. Further, at the same time as the degassing treatment, oxygen is blown from the oxygen blowing pipe 7 to decarburize, raise the temperature, etc. Exhaust gas forcibly sucked through the exhaust port 8 of the vacuum chamber 1 passes through a catalytic combustion device 27 provided inside the exhaust port 8 on the primary side of the booster 9 . At this time, CO and O ₂ in the exhaust gas react and the CO is combusted. In this case, the pressure on the primary side is close to vacuum, and as shown in Figure 2, the explosion range is extremely narrow, or the conditions are such that no explosion occurs, so even if the fuel is combusted with a catalyst, no explosion will occur. The exhaust gas after combustion is introduced into the condenser 10 via the booster 9 and washed with cooling water from which dissolved air has been removed in advance. The cooling water for the condenser is sent from the cooling tower 11 by a pump 12 to a vacuum deaerator consisting of a condenser 13, an ejector 14 and a pump 15, where dissolved air is removed. Exhaust gas exiting the condenser 10 is compressed by a compressor 16 and stored in a gas holder 17. This exhaust gas is transferred from the gas holder 17 to the compressor 18.
, where it is further compressed and sent to the argon separator 19 . Argon separation devices using adsorbents, for example, are known. Argon 25 separated and recovered by this argon separator 19
is stored in a compressor 20 and an argon holder 21. It is then used, for example, as a tundish sealing gas in continuous casting equipment. On the other hand, the exhaust gas after argon recovery is sent from the argon separator 19 to the carbon dioxide separator 22, where the exhaust gas is oxidized and dehumidified to produce carbon dioxide 26.
can be separated and recovered, recirculated to the vacuum degassing equipment via the compressor 23 and the carbon dioxide holder 24, and used as a gas for sealing the top of the vacuum chamber 1, the exhaust port, and the alloy addition device 6. Example When molten steel having the components shown in Table 1 is degassed using actual vacuum degassing equipment under the operating conditions shown in Table 2, and argon is recovered from the exhaust gas exhausted at that time, the exhaust gas components under normal conditions The third
Shown in the table. Here, Table 4 shows the exhaust gas components when air leakage increases due to aging of the gaskets on the flanges of various parts of the vacuum degassing equipment. The exhaust gas in this case is clearly within the explosive range. Therefore, when the exhaust gas exhausted from the vacuum chamber was combusted using a catalytic combustion device installed at the vacuum chamber exhaust port shown in Figure 1, the exhaust gas components shown in Table 5 could be obtained, avoiding the risk of explosion. We were able to. In addition, the components of the recovered argon are argon 85
%, nitrogen is 15%, and the amount of argon recovered is 0.3Nm ³ /T compared to the amount of argon used in the vacuum degassing equipment.
0.285Nm ³ /T was recovered, giving an argon recovery rate of 95%. For comparison, Table 6 shows the components of the vacuum degassing equipment exhaust gas when using an _N2 seal and not removing dissolved air.

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[Table] Effects of the invention As explained above, according to the method of this invention, the nitrogen component ratio in the exhaust gas of vacuum degassing equipment can be significantly reduced, and argon with low nitrogen content can be recovered with high yield. In addition, even if air enters the exhaust gas due to deterioration of the seals in various parts of the vacuum degassing equipment and the exhaust gas falls within the explosion limit, the oxygen concentration in the exhaust gas can be reduced by combustion using a catalyst in a vacuum. Since the argon can be lowered, explosions can be avoided and argon can be recovered safely. Further, the recovered argon can be used, for example, as a tundish sealing gas in continuous casting equipment, so that the cost of producing slabs can be reduced. Further, carbon dioxide in the exhaust gas of the vacuum degassing equipment can be recycled and used as a sealing gas in the vacuum degassing equipment, which is economical.

[Brief explanation of drawings]

Figure 1 is a flow sheet showing an example of the equipment configuration for carrying out the method of this invention, Figure 2 is a diagram showing the lower explosive limit of CO under reduced pressure in this invention, and Figure 3 is a diagram showing the principle of the vacuum degassing method. FIG. 1... Vacuum tank, 2... Immersion tube, 3... Ladle, 4... Molten steel, 5, 25... Argon, 9... Booster, 1
0, 13... Condenser, 11... Cooling tower, 19... Argon separation device, 22... Carbon dioxide separation device, 27...
Catalytic combustion equipment.

Claims (1)

[Scope of Claims] 1. A method for separating and recovering argon in the exhaust gas using dissolved air removed water as cooling water for a condenser in a vacuum degassing equipment exhaust gas processing equipment, wherein a catalyst is used in the vacuum degassing equipment. in the exhaust gas
A method for treating exhaust gas from a vacuum degassing facility, characterized by recovering argon after reacting CO with O ₂ and burning it. 2 Vacuum degassing equipment A method for separating and recovering argon in the exhaust gas by using dissolved air removed water as the cooling water for the condenser in the exhaust gas processing equipment and using carbon dioxide as the sealing gas in the vacuum degassing equipment. A method for treating exhaust gas from a vacuum degassing facility, which comprises reacting CO in the exhaust gas with O ₂ and combusting it using a catalyst in the degassing facility, and then recovering argon.