JPH0422848B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an argon recovery method, and in particular to an argon-oxygen blowing method.
Decarburization (abbreviated as AOD) relates to a method of separating and purifying and recovering only argon contained in exhaust gas from a furnace, etc. The argon/oxygen blowing method in an AOD furnace can decarburize expensive chromium without oxidizing it and produce products of good quality, so it has attracted attention as a new molten steel method for high chromium steel. has been adopted. Argon in this AOD furnace exhaust gas is 60-80%
Since it is contained in high concentrations and is expensive, there is a method in which it is separated and recovered from the exhaust gas and reused. As such an argon recovery method, for example,
52-28750 oxidizes carbon monoxide in exhaust gas,
A method was proposed to recover argon by solidifying and separating the generated carbon dioxide using a cryogenic method, and in 1989-8999, a method was proposed to recover argon by converting carbon monoxide in AOD reactor exhaust gas into a copper-ammonia complex. A method is disclosed for recovering argon by removing carbon dioxide using an alkali. The former method requires deep cooling treatment to about -100°C, and therefore has problems in terms of device structure. On the other hand, the latter requires absorption and dissipation operations, which poses a problem in terms of utility. The present invention takes into account the above-mentioned circumstances in the conventional methods, and aims to provide a method for recovering argon that can be carried out efficiently, economically, and industrially. It removes the hydrogen contained in the exhaust gas composition,
The idea is to condense and recover argon by consuming coexisting oxygen and converting it into moisture that is easily adsorbed, and then separating it from the gas composition along with carbon monoxide, etc. using an adsorption/desorption method that utilizes a pressure difference. Consisting of That is, a feature of the present invention is a method for recovering argon from an exhaust gas composition discharged from an argon/oxygen blowing furnace and containing argon as a main component and containing carbon monoxide, hydrogen, oxygen, etc. a catalytic combustion process in which hydrogen contained in the hydrogen is selectively combusted by contacting the hydrogen with a catalyst;
It also includes an adsorption step of concentrating and collecting argon by adsorbing the components excluding argon from the gas composition that has undergone this step onto an adsorbent under pressure. Specifically, the hydrogen combustion treatment described above is carried out while maintaining the space velocity of the gas composition of 15000 h ^-1 or less and the combustion temperature (catalyst temperature) of 100 to 250°C. The flow of argon recovery from the AOD furnace exhaust gas composition in the present invention is shown in FIG. The AOD furnace 14 has a pipe 2 connected to its bottom.
Argon and oxygen are blown from ports 1 and 22, respectively. The gas composition discharged from the furnace 14 is led to the dust remover 2 through a pipe 23, where dust is removed, and further cooled in a cooler 3, and then exhausted by a blower 4. It is stored in the gas tank 5. Next, the exhaust gas sent out from the tank 5 is sent to an argon recovery device 10 consisting of a contact combustor 6, an adsorption tower 9, etc., where components other than argon are substantially removed, and purified argon is sent to a pipe 35. , 21 and then AOD furnace 14 again.
supplied to FIG. 2 shows an example of the configuration of the argon recovery device. In FIG. 2, by tube 27,
The exhaust gas composition taken out from the exhaust gas tank 5 in FIG. 1 is led to the catalytic combustor 6. Here, hydrogen in the gas composition is selectively combusted by the action of the catalyst. In addition to the oxygen contained in the composition, oxygen supplied from the tube 30 as necessary is used for the reaction. The exhaust gas composition subjected to the catalytic combustion treatment is pressurized by a compressor 7, and the heat generated thereby is removed by a cooler 8. The gas composition is then forced into the adsorption tower 9a, 9b or 9c through the pipe 32 and the solenoid valve 51, 55 or 59, respectively. The concentrated argon with impurities adsorbed and removed by the pressurized adsorption treatment in these adsorption towers is stored in the product gas tank 11 via the pipe 33 from the solenoid valve 53, 57, or 61, and is extracted from the product gas tank 11 as needed via the pipe 35. Served. Platinum and alumina are used as catalysts to burn hydrogen.
There are palladium and alumina, but platinum is not preferable in systems where hydrogen and carbon monoxide coexist because it is strongly poisoned by carbon monoxide and causes a significant decrease in activity. On the other hand, palladium is suitable as a catalyst for a hydrogen/carbon monoxide coexistence system because its activity is less reduced by carbon monoxide than platinum. Based on these findings, a palladium-alumina catalyst is used in the catalytic combustor in the present invention. With this catalyst, hydrogen can be reduced to a minute residual concentration even in the presence of carbon monoxide. In practice, it is possible and advantageous to substantially remove hydrogen by supplementing the hydrogen content with oxygen in a slight chemical equivalent excess. Note that the catalyst carrier is not limited to argon, and other known carriers may also be used. Further, the adsorption tower is filled with an adsorbent that selectively adsorbs water, carbon monoxide, carbon dioxide, and water more easily than argon; for example, zeolite 5A can be used. The adsorption selectivity of the zeolite 5A for exhaust gas components is in the following order: hydrogen < argon = oxygen < nitrogen < carbon monoxide < hydrocarbons < carbon dioxide < water, and components other than hydrogen and oxygen can be adsorbed and removed. Note that zeolite 5A was used in the following examples. The adsorption pressure depends on the performance of the adsorbent, but may be about several gauge pressures. Next, the adsorption operation, that is, the cycle using the pressure difference adsorption/desorption method, consists of six steps as shown in Table 1 in the example of a series of three adsorption towers shown in FIG.
Each column has five functions: equalization, pressurization, adsorption, desorption, and barge.
Step by step. Pressure equalization stage Some of the argon concentrated in other towers in the adsorption stage is introduced into the adsorption tower under normal pressure, where the adsorbent has been regenerated by purging, and the pressures in both towers are averaged. As a result, the gas composition entering the next pressurization and adsorption stage will be richer in argon than the original exhaust gas composition, improving the concentration and yield of recovered argon. . Pressurization Stage The combustion treated exhaust gas composition is forced into the pressure equalized column until the desired adsorption operating pressure is reached. Adsorption stage Carbon monoxide, carbon dioxide, nitrogen and moisture in the exhaust gas composition are adsorbed, thereby concentrating the argon remaining after adsorption and being withdrawn from the top of the column and recovered. Desorption stage The pressure inside the column is lowered to atmospheric pressure and the carbon monoxide, carbon dioxide, nitrogen and moisture adsorbed in the previous stage are released. It is effective to operate the column at a reduced pressure below atmospheric pressure. Purge stage A portion of the concentrated argon from other columns in the adsorption stage is introduced into the tower under atmospheric pressure from the top, washes and regenerates the adsorbent, and then is purged from the bottom of the tower.

[Table] Next, the operating procedure of the adsorption tower shown in FIG. 2 will be described in detail according to Table 1. In the first step, adsorption towers 9a, 9b, and 9c
enter the adsorption, pressure equalization, and desorption stages, respectively.
At that time, solenoid valves 53, 54, 58, and 60 are opened, and solenoid valves 51, 52, 55, 56, 57, and 5 are opened.
9, 61, 62, 63, and 64 are closed. Through this valve operation, carbon monoxide, carbon dioxide, nitrogen, and moisture are adsorbed by the adsorbent from the exhaust gas composition in the adsorption tower 9a, and the remaining argon passes through the electromagnetic valve 53 and the pipe 33 to the product gas tank 11. enter. On the other hand, the adsorption tower 9b is in the pressure equalization stage, and the adsorption tower 9b is in the pressure equalization stage.
The pressure is increased from atmospheric pressure by a portion of concentrated argon introduced from a through the solenoid valve 54, pipe 34, and solenoid valve 58. Further, in the adsorption tower 9c in the desorption stage, components of the exhaust gas adsorbed in the previous stage are discharged via the electromagnetic valve 60 and the gas discharge pipe 36, and the internal pressure of the tower is accordingly lowered. In the second step, the adsorption furnace 9a continues to be in the adsorption stage, and the adsorption towers 9b and 9c are pressurized and
Enter the purge stage. At that time, the solenoid valves 53, 54,
55, 60 and 62 were opened, and 51, 52,
56, 57, 58, 59, and 61 are closed. By this valve operation, the exhaust gas composition is supplied to the adsorption tower 9b, which has been pressure-equalized in the previous step, through the compressor 7, the cooler 8, the gas feed pipe 32, and the solenoid valve 55, and is pressurized. Furthermore, the adsorption tower 9c that has entered the purge stage is connected to the solenoid valve 54 and the pipe 3 from the adsorption tower 9a.
Concentrated argon is introduced through 4 and solenoid valve 62 to regenerate the adsorbent. The purge gas after the regeneration process is discharged to the outside of the system via the electromagnetic valve 60 and the pipe 36. In the third step, adsorption towers 9a, 9b, and 9c enter desorption, adsorption, and pressure equalization stages, respectively. In this case, the solenoid valves 52, 57, 58
and 62 were opened, and 51, 53, 54, 5
5, 56, 59, 60 and 61 are closed.
By this valve operation, the components of the exhaust gas composition adsorbed in the previous stage are discharged from the adsorption tower 9a via the electromagnetic valve 52 and the gas discharge pipe 36, and at the same time, the internal pressure of the tower gradually decreases to atmospheric pressure. The adsorption tower 9b is in the adsorption stage, and concentrated argon is passed from the tower through the solenoid valve 57 and the pipe 33 to the product gas tank 1.
1 will be collected. Further, the adsorption tower 9c enters the pressure equalization stage, and a portion of concentrated argon is introduced from the adsorption tower 9b via the electromagnetic valves 58 and 62. Similarly, in the fourth step, the adsorption tower 9
a, 9b, and 9c are purge, adsorption,
Operated as a pressurization stage. At that time, among the solenoid valves 52, 54, 57, 58 and 59 are opened, and 51, 53, 55, 56, 60 and 61 are closed. In the fifth step, adsorption towers 9a and 9b are operated as pressure equalization and desorption stages, respectively, and adsorption tower 9c is operated as an adsorption stage. At that time, the solenoid valves 54, 5
6, 61 and 62 are opened, 51, 52, 5
3, 55, 57, 58, 59 and 60 are closed. In addition, in the sixth step, adsorption towers 9a, 9
b, and 9c are operated as pressurization, purge, and adsorption stages, respectively. At this time, electromagnetic valves 51, 56, 58, 61 and 62 are opened, and electromagnetic valves 51, 53, 54, 55, 57, 59 and 60 are closed. In the previous description, the concentrated argon introduced into the adsorption tower in the pressure equalization stage and the barge stage was supplied from the adsorption tower in the adsorption stage, but it could also be supplied from the product gas tank through the solenoid valve 64. Furthermore, as shown in FIG. 5, a vacuum pump 12 can be connected to the pipe 36 to allow the adsorbed gas components to be desorbed under reduced pressure. According to this method, since the adsorbent is efficiently regenerated, the aforementioned purge step may be omitted, thus improving the argon recovery rate. In the present invention, the number of adsorption towers is not limited at all, and FIGS. 4 and 5 only show examples of embodiments. Now, the gas discharged from the AOD furnace is a composition containing argon as a main component, carbon monoxide, carbon dioxide, nitrogen, oxygen, hydrogen, water, and the like. For gas compositions in the composition ranges listed in Table 1, actual measurements were made by setting the catalyst layer temperature (combustion temperature) and gas space velocity in the ranges in Table 2 in a combustor filled with palladium-alumina catalysts. As a result, the relationship between the space velocity of the exhaust gas composition and the combustion end temperature T ^E _H of hydrogen and the combustion start temperature T ^g _cp of carbon monoxide was obtained as shown in FIG. Also, the spatial velocity
At 15,000 h ^-1 , the dependence of the unreacted remaining fraction of hydrogen and carbon monoxide, C/C ₀ , on combustion temperature was as shown in FIG. Here, C ₀ is the initial concentration of each gas contained in the exhaust gas composition, and C is the concentration of each gas after combustion treatment.

[Table] The following is known from these drawings. In order to completely burn hydrogen at a space velocity of 15,000 h ^-1 or higher, it is necessary to raise the temperature of the catalyst layer to 250°C or higher. In that case, the combustion of carbon monoxide also occurs before the combustion of hydrogen is completed, so the amount of heat generated by combustion is large, causing a rise in the catalyst layer temperature, and
After the treatment, a large amount of thermal energy must be removed from the gas composition before entering the next adsorption step. On the other hand, when the gas space velocity is below 15000 h ^-1 and the catalyst layer temperature is below 100°C, hydrogen cannot be burned sufficiently. Therefore, in order to selectively burn hydrogen,
Space velocity 15000h ^-1 or less, combustion (catalyst layer) temperature 100
Preferably, conditions of ~250°C are maintained. The exhaust gas composition from the AOD furnace was treated according to the conditions as described above and the operating method according to Table 1. The gas composition and equipment conditions at that time are
As shown in the table.

[Table] As a result of actual measurements, the concentration of hydrogen contained in the gas composition adopted from the outlet of the catalytic combustor was 0.01% or less.
The concentration of oxygen was less than 0.1%. Further, by adsorbing the gas composition, argon was recovered at a concentration of 95 to 99.5% and a yield of 50 to 65%. The composition of the recovered argon gas is that nitrogen is
3.5% or less, oxygen 0.1% or less, carbon monoxide 0.1%
Below, the hydrogen content was 0.01% or less. Furthermore, during the desorption stage, the inside of the adsorption tower is
Operating at reduced pressure to mmHg and omitting the purge step resulted in recovery of 95-99.5% argon in 50-75% yield. As mentioned above, by applying the two-stage treatment of the catalytic combustion treatment and the pressure difference adsorption treatment of the present invention to the exhaust gas composition from the argon-oxygen blowing furnace, a high yield of highly concentrated argon containing no hydrogen can be obtained. It can be recovered at a certain rate. Furthermore, since carbon monoxide is also concentrated, it opens the door to its recovery and use as fuel and chemical raw materials.

[Brief explanation of drawings]

Fig. 1 is a flowchart when the present invention is applied to an argon-oxygen blowing furnace, Fig. 2 is a system diagram for explaining the catalytic combustion process and pressure difference adsorption/desorption process, and Fig. 3 is a flowchart for explaining the catalytic combustion process and the pressure difference adsorption/desorption process. The relationship between the space velocity and the hydrogen combustion point and the monoxide combustion start point is shown, and FIG. 4 shows the dependence of hydrogen and carbon monoxide combustion on the catalyst layer temperature at a space velocity of 15000 h ^-1 . Moreover, FIG. 5 is an example of a system diagram of a pressure difference adsorption/desorption process when desorption is performed under reduced pressure. 14... Argon-oxygen blowing furnace, 2... Dust remover, 3... Cooler, 4... Blower, 5... Tank, 6... Catalytic combustion device, 7... Compressor, 8...
Cooler, 9... Adsorption tower, 11... Product gas tank, 12... Vacuum pump, 51-64... Solenoid valve, 65, 66... Throttle valve.

Claims (1)

[Claims] 1. A method for recovering argon from an exhaust gas composition mainly composed of argon and containing carbon monoxide, hydrogen, oxygen, etc., discharged from an argon-oxygen blowing furnace, wherein the temperature is 100°C. A catalytic combustion process in which hydrogen is selectively combusted by bringing an exhaust gas composition with a space velocity of 15,000 h ^-1 or less into contact with a catalyst layer maintained at 250°C from A method for recovering argon, comprising an adsorption step of concentrating and collecting argon by adsorbing it to an adsorbent under pressure. 2. The method for recovering argon according to claim 1, characterized in that palladium is used as a catalyst. 3. A plurality of adsorption towers filled with synthetic zeolite-based adsorbents are used, and the adsorption step includes a step of pressurizing (pressurizing) the exhaust gas composition into the adsorption tower, in which the components of the gas composition except argon are removed. A step of concentrating and extracting argon by adsorption under pressure (adsorption), a step of desorbing the adsorbed component by reducing the pressure inside the adsorption tower to atmospheric pressure (desorption), and a step of desorbing the adsorbent after desorption. A washing and regenerating (purging) step using a part of the concentrated argon, and equalizing the pressure in both columns by communicating the column in which the adsorbent has been regenerated and the column in which adsorption has been completed. A method for recovering argon according to claim 1, characterized in that the method comprises a (pressure equalization) step. 4. Claim 3, characterized in that in the desorption stage, the adsorption column is depressurized to below atmospheric pressure to desorb the adsorbed components and regenerate the adsorbent, and the purge stage is omitted. Argon recovery method described in section.