JPS6139087B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for obtaining high-purity carbon monoxide from exhaust gas from a converter or blast furnace, mainly a raw material gas containing carbon monoxide, carbon dioxide, and nitrogen, by a pressure fluctuation adsorption separation method (PSA method). Exhaust gas generated from refining vessels in steel plants contains a relatively large amount of CO gas. The composition of converter exhaust gas and blast furnace exhaust gas is within the range shown below.

[Table] Gas
If high-purity CO gas can be recovered at low cost from these exhaust gases, it could be used as a raw material for synthetic chemicals or as a gas to be injected into molten metal in refining vessels.
When considering this CO gas as a raw material for synthetic chemicals, it is essential to remove oxidizing gases that can damage the reaction vessel, as synthesis reactions are usually carried out under high temperature and high pressure conditions, and the CO ₂ concentration need to be reduced as much as possible. Furthermore, in order to increase reaction efficiency, it is desirable to remove as much as possible of N ₂ , which normally does not participate in the reaction. On the _other hand, gas injection _into a refining vessel is widely used for the purpose of improving the efficiency of refining molten metal. From this point of view, expensive Ar gas is usually used. If high-purity CO gas can be recovered at low cost from converter gas and blast furnace gas, which are generated in large quantities in steel plants, this can be converted into Ar
It is almost possible to replace it with At this time, it is desirable that the N ₂ concentration of the high-purity CO gas is low from the perspective of preventing an increase in the nitrogen concentration of molten iron, and the CO ₂ concentration also prevents oxidation damage to carbon-based refractories, which are commonly used as refractory linings for refining vessels. From this point of view, a low value is desirable. Conventionally, as a process for recovering high-purity CO gas using the above-mentioned exhaust gas as a raw material, a cryogenic separation method or a solution absorption method such as a copper liquid method or a Cosorb method has been considered. However, the former requires low temperature and high pressure, and the latter requires high temperature and high pressure, and both have the drawback that the equipment is complicated and expensive. Furthermore, in the cryogenic separation method, it is difficult to completely separate N ₂ and CO because the boiling points of N ₂ and CO are close to each other. In view of the above-mentioned current situation, the present inventors attempted to develop an adsorption method as a technique for recovering high-purity CO gas at low cost through a simpler process. The above-mentioned adsorption separation using the adsorption method (PSA method) is well-known, and is used for the purpose of recovering gas components that are difficult to adsorb to adsorbents (hereinafter referred to as difficult-to-adsorb components). 15045 etc. have been published as basic patents.In addition, gas components that are easily adsorbed to the adsorbent (hereinafter referred to as easily adsorbed components) are adsorbed onto the adsorbent, desorbed, and separated and recovered, thereby separating the easily adsorbed components with high purity. This method has been practiced for a long time. For example, there are specific examples using ethylene as an easily adsorbed component and applications to nitrogen separation. Conventional methods for recovering easily adsorbable components from adsorbents in gas mixtures usually include the following operations. By sequentially repeating the adsorption pressurization process, the reflux process, and the desorption process, a gas rich in easily adsorbable components can be extracted from the adsorbent. However, it has not been done to remove carbon dioxide and nitrogen from a mixed gas containing carbon monoxide, a gas component that is easily co-adsorbed, and recover and refine it as highly concentrated carbon monoxide, such as the exhaust gas in this case. The applicant previously proposed that N ₂ and CO ₂ or N ₂ , CO ₂ and
An application was filed for a method for removing N ₂ from a mixture consisting of CO by the PSA method (Japanese Patent Application No. 1983-
(See No. 159211). When carbon monoxide is concentrated from the mixed gas in the previous application No. 57-159211, nitrogen is removed and hydrogen and oxygen are completely removed, but when carbon monoxide and carbon dioxide coexist, they are adsorbed in the same way. The carbon monoxide concentration could not be sufficiently increased because the carbon monoxide was concentrated. As a result of various studies, it was found that by combining carbon dioxide removal technology using adsorption as a pretreatment process, it was possible to purify, separate, and concentrate high-concentration carbon monoxide easily and economically. The present invention provides a method for concentrating carbon monoxide in a raw material gas containing at least carbon dioxide, carbon monoxide, and nitrogen by a two-stage adsorption operation, in which: (a) the first stage adsorption operation is selected for carbon dioxide; The method consists of using two or more adsorption towers filled with an adsorbent substance having a specific property, and removing carbon dioxide from the raw material gas by pressure fluctuation adsorption separation in which adsorption and desorption are repeated in each adsorption tower. (b) The second stage adsorption operation uses an adsorbent material that is selective to carbon monoxide in the gas discharged from the first stage adsorption process (hereinafter referred to as the first stage product gas). Two or more packed adsorption towers are used, and the method is (i) pressurizing the adsorption tower with the first stage product gas, (ii) further flowing the first stage product gas through the adsorption tower to perform adsorption. an adsorption () step in which the adsorbent adsorbs the easily adsorbable component until the concentration of the easily adsorbable component at the tower outlet reaches the concentration of the easily adsorbable component at the adsorption tower inlet, or slightly before the point where both concentrations become equal; (iii) After the adsorption () process is completed, the adsorption tower is connected to the adsorption tower where vacuum desorption has been completed, and gas is introduced from the former adsorption tower to the latter adsorption tower to reduce the pressure in the former adsorption tower. , (iv) A purge step in which the second-stage product gas is introduced into the reduced pressure adsorption tower to purge the components that are difficult to adsorb. (v) After the purge step, the adsorption tower is evacuated to below atmospheric pressure and the adsorbent is and (vi) the adsorption column and adsorption () after the product gas recovery has been completed.
The process consists of an adsorption () process in which the gas from the latter adsorption tower is introduced into the former adsorption tower by connecting the adsorption tower after the process has been completed, and the flow between the adsorption towers is changed periodically.
The present invention relates to a method characterized by repeating the above operations. The details of the invention will be explained below. The present invention is a method for concentrating, separating and purifying carbon monoxide from a raw material gas consisting of carbon monoxide, carbon dioxide, nitrogen, hydrogen and oxygen as main components by a pressure fluctuation adsorption separation method. 2 containing an adsorbent consisting of a
Use more than one adsorption column. The step of removing carbon dioxide from the raw material gas in the first stage may be carried out by the usual PSA method, that is, repeating adsorption, depressurization, purging with product gas, and pressurization with product gas, or may be carried out by other methods. Also good. A preferred method of removing carbon dioxide is as follows. Using two or more adsorption columns filled with an adsorption material selective for carbon dioxide, the method comprises (i) a pressurizing step of pressurizing the adsorption columns with the first stage product gas, preferably in a countercurrent direction; , preferably 1-
Pressurizing to 3Kg/cm ² G, (ii) adsorption step in which the raw material gas is passed through an adsorption tower and mainly adsorbs carbon dioxide onto the adsorbent, (iii) adsorption is preferably carried out in a countercurrent direction, followed by depressurization to near atmospheric pressure. (iv) an evacuation step, preferably in a countercurrent direction, and then evacuating the adsorption tower by a vacuum pump or the like (preferably evacuation is carried out to 60 to 300 Torr); and (v) preferably in a countercurrent direction. This method consists of a purge step in which the waste gas from the N ₂ PSA device is then used to purge while performing vacuum evacuation, and the above operation is repeated by periodically changing the flow between the adsorption towers. Step (i) in the second stage of the present invention is an adsorption tower pressurization step in which the first stage product gas is introduced into the adsorption tower.In the present invention, the gas to be recovered is an easily adsorbed component, so a high adsorption pressure is required. Not necessary, 1-3Kg/cm ²
An adsorption pressure of approximately G is sufficient, and an adsorption pressure lower than that may be sufficient. Step (ii) is an adsorption () step. The point at which the concentration of easily adsorbed components (carbon monoxide gas) at the outlet of the adsorption tower becomes equal to the concentration of easily adsorbed components at the inlet of the adsorption tower means that It means a breakthrough point.
If the component to be recovered is a difficult-to-adsorb component (for example, oxygen gas in the case of separating oxygen gas from air), the adsorption process must be carried out at a level above the breakthrough point in order to obtain a high-purity difficult-to-adsorb component. It is desirable to terminate. However, in the present invention, since the component to be recovered is an easily adsorbed component, adsorption is carried out until the breakthrough point or just before the breakthrough point is reached. In step (iii), the adsorption tower that has undergone the adsorption () step and the adsorption tower that has undergone vacuum desorption are connected, preferably in a parallel flow direction, to introduce gas from the former adsorption tower into the latter adsorption tower, and to Decrease the pressure in the column to or near atmospheric pressure. In this step, gas in the space between the adsorbents housed in the adsorption tower is released and used for adsorption () pressurization of the adsorption tower after vacuum desorption. This operation is maintained until the pressure in the former adsorption tower reaches approximately atmospheric pressure. In step (iv), the second-stage product gas is introduced into the reduced pressure adsorption tower to purge the difficult-to-adsorb components (nitrogen gas, etc.) remaining in the adsorption tower. In this case, the introduction pressure of the product gas is preferably lower than the adsorption pressure and higher than atmospheric pressure, and in this case, there is no need to use a pump or the like, and purging is performed by connecting the product gas tank and the adsorption tower. Step (v) is to evacuate the adsorption tower after the purge step to below atmospheric pressure using a vacuum pump, ejector, blower, etc., preferably to 300 Torr or less, most preferably to a range of 300 to 30 Torr, and remove the adsorbent. Components (carbon monoxide gas, etc.) that have been adsorbed on the gas are desorbed and recovered as product gas. Step (vi) is an adsorption () process in which the adsorption tower that has completed the product gas recovery and the adsorption tower that has completed the adsorption () process is connected, and the former adsorption tower is pressurized and adsorbed by the gas from the latter adsorption tower. It is a process. In this case, since the introduction of gas is stopped when the latter adsorption tower reaches approximately atmospheric pressure, the pressure in the former adsorption tower does not reach atmospheric pressure. The present invention will be explained in detail below based on a typical example of the present invention, which is a method for removing nitrogen gas from converter exhaust gas and separating and recovering carbon monoxide. The examples are not limited. FIG. 1 is a flow sheet for continuously removing carbon dioxide and nitrogen from converter exhaust gas by adsorption method and separating and concentrating carbon monoxide gas. Adsorption towers A and B house adsorbents that selectively adsorb carbon dioxide. Adsorption towers A and B are evacuated using a vacuum pump to a pressure of preferably 300 Torr or less.
The pressure was increased to 30 Torr, and now the raw material gas was introduced into the adsorption tower A under pressure, and valve 1 was opened to increase the pressure from the vacuum state. At this time, all valves except valve 1 are closed. Adsorption tower B still maintains a vacuum state at this step. Adsorption tower A has an adsorption pressure of 0.01 after increasing the pressure.
Maintaining an adsorption pressure of Kg/cm ² G to 3.0 Kg/cm ² G, preferably 0.2 Kg/cm ² G to 1.0 Kg/cm ² G, valve 2 is opened to release carbon dioxide, carbon monoxide and other containing gases. A portion is adsorbed by the adsorbent, and the remainder is discharged from the other end of the adsorption tower. After completion of the adsorption process for a certain period of time or a certain amount, the raw material supply valve 1 and the outlet valve 2 are closed, and the valve 3 is opened to reduce the internal pressure of the adsorption tower A to near atmospheric pressure. When the adsorption tower A reaches atmospheric pressure, the valve 3 is closed, and the valve 4 is opened from the bottom of the adsorption tower to evacuate the adsorption tower under reduced pressure using a vacuum pump to desorb the carbon dioxide component adsorbed on the adsorbent.
The exhaust pressure at this time is preferably 300 Torr or less.
Perform up to 30Torr. When the decompression exhaustion is completed, valve 5 is opened (at this time, the amount of purge gas is adjusted with manual valve 14), and the waste gas from the de _- N2 PSA device is used to remove the adsorbent from the adsorbent. The carbon dioxide contained in the adsorbent is expelled from the adsorbent by entrainment desorption with barge gas. The pressure of evacuation is determined by the amount of this evacuation and barge gas.
It will be as high as 270Torr. When the exhaust barge is completed, valves 4 and 5 are closed, and valve 6 is opened to pressurize the adsorption tower with product gas to the adsorption pressure. By sequentially repeating the above operations in each adsorption tower, CO ₂ is continuously adsorbed and removed by the adsorbent. The first stage of withdrawal
The gas from which carbon _dioxide has been removed by the CO ₂ PSA device is then used in the second stage to remove hydrogen, oxygen, and nitrogen, and to concentrate and separate the carbon monoxide to a high concentration. The method is to use adsorption tower CDEF for easily adsorbed components (here carbon monoxide and carbon dioxide).
Contains an adsorbent that selectively adsorbs. The adsorption tower CDEF is depressurized and evacuated using the vacuum pump 41.
The reaction is carried out at 300 Torr or less, preferably up to 30 Torr, and the raw material gas (from which carbon dioxide has been removed in the first stage PSA device) is now introduced under pressure into the adsorption tower C. This is done by opening the valve 16 to further increase the pressure of the regenerated vacuum. The pressure increase rate at this time is valve 1
5. Valve 17, 18 after boosting pressure
At the same time as the valve 16 is opened, the valve 16 is closed and the mixed gas passes through the adsorption tower. At this time, carbon monoxide and carbon dioxide, which are easily adsorbed components, are adsorbed by the adsorbent, and other gases pass through the adsorption tower and some are desorbed.
Used as barge gas for CO ₂ PSA equipment. Since the remaining gas still contains a considerable amount of hydrogen and carbon monoxide, it is collected in the tank 43 for reuse as fuel gas or the like. After completion of the adsorption process for a certain period of time or a certain amount, the raw material supply valve 18 and the outlet valve 17 are closed, and the adsorption tower D
The valve 19 in the connecting pipe is opened to release the internal pressure of the adsorption tower C to near atmospheric pressure, and the adsorbent of the adsorption tower D adsorbs the gas that has been depressurized and released. When the adsorption tower C reaches near atmospheric pressure, the valve 19 is closed and the valve 20 is opened from the product gas tank 42 to expel the separated adsorbed component gas accumulated in the voids (spaces between adsorbents) inside the adsorption tower. 1
7 is opened and the purge process is performed from the lower part of the adsorption tower C. When the purge step is completed, valves 17 and 20 are closed, and valve 21 is opened from the bottom of the adsorption tower to perform vacuum exhaust using a vacuum pump to desorb easily adsorbable components adsorbed on the adsorbent. The exhaust pressure at this time is 300 Torr or less, preferably 30 Torr, and CO, which is an easily adsorbed component, is recovered as a product gas. By sequentially repeating the above operations in each adsorption tower, CO gas, which is an easily adsorbed component, can be continuously adsorbed onto the adsorbent for separation and purification. Note that 43 is a waste gas tank. As mentioned above, CO 2 removal can be achieved by combining the first stage CO ₂ removal PSA equipment and the second stage N ₂ removal PSA equipment.
The _{concentration} of CO ₂ can be significantly reduced compared to when carbon monoxide is concentrated and separated using the N ₂ PSA device alone, and the waste gas from the N ₂ PSA device can be used as the purge gas for the CO 2 PSA device. By doing so, the recovery rate of carbon monoxide was also improved compared to when the product gas from the CO ₂ PSA device was used for the purge process. According to the invention, CO ₂ is 0.5%,
_N2 can be reduced to less than 1%. Example 1 Below, in order to explain the present invention more specifically, converter exhaust gas (CO = 85% CO ₂ = 2.7% N ₂ = 4.9%
An attempt was made to purify H ₂ =9.3% O ₂ =0.1%). As mentioned above, the first stage of the purification process is
The CO ₂ PSA equipment's "adsorption - depressurization, pressure release - exhaust - purge - product pressurization" and the second stage _deN2 PSA equipment's "first stage product gas pressurization - adsorption () - vacuum adsorption () - The purification was carried out based on the purification cycle of "purge-evacuate-pressurize". The first stage CO ₂ PSA device is a steel adsorption tower (12 ^B x 1.7 m) filled with activated zeoherb (50Kg 1/8″ pellets).The second stage N ₂ PSA device is also active. Zeoherb (166Kg 1/8″ pellets)
After evacuating a steel adsorption tower (16 ^B x 2.4 m) filled with gas to 100 Torr and 60 Torr, the above mixed gas was introduced from the bottom of the tower at a linear velocity of 6 cm/sec to purify the mixed gas. did. The amount of purified carbon monoxide gas was 19.3 m ³ for the supplied gas amount of 32.8 m ³ , and the amount of waste gas from the N ₂ PSA device at this time was 13.5 m ³ , and the recovery rate of carbon monoxide was 68%. The gas composition after purification was as follows. Gas composition C = 98.6% CO ₂ = 0.5% N ₂ = 0.9% H ₂ = 0% O ₂ = 0% Example 2 Using the same equipment as Example 1, purification using converter exhaust gas under the following experimental conditions. This is the result of separation. Experimental conditions Gas composition CO=86% CO ₂ = 4% N ₂ = 4%
H ₂ = 6% Operating temperature 25℃ Adsorbent ZE-501 Adsorption rate 6.5cm/sec Adsorption pressure 1.0Kg/cm ² G Vacuum exhaust was performed at 100 Torr and desorption at 60 Torr to concentrate and purify carbon monoxide in the product gas. . The amount of purified carbon monoxide gas is 25.7 m3 for the supplied gas amount of 42.9 ^m3 .
The recovery rate of carbon monoxide in m ³ was 68.6%. The gas composition after purification is CO = 98.7% CO ₂ = 0.5% N ₂ = 0.8% Example 3 Purification of converter exhaust gas was attempted. As mentioned above, in the purification process, the first step is "adsorption - depressurization - vacuum evacuation - purge - product pressurization" of the CO ₂ removal equipment, and the second stage is "first stage product gas pressurization" of the N ₂ removal PSA equipment. Adsorption () - Depressurization/Relief - Purge/
It was carried out based on the purification cycle of release-evacuation-decompression/adsorption (). A steel adsorption tower (12 B x 1.7 m) filled with activated zeoherb (50Kg 1/16″ pellets) is used for the first stage CO ₂ removal PSA equipment, and an activated steel adsorption tower (12 ^B × 1.7 m) is used for the second stage N ₂ removal equipment. Activated alumina (30Kg, Sumitomo KHD-
A steel adsorption tower (16 ^B × 2.4
m) was used. <Experimental conditions> Converter exhaust gas composition: CO = 86% CO ₂ = 3% N ₂ = 4% H ₂ = 7% Operating temperature: 30℃ Adsorption pressure: 1.0Kg/cm ² G Vacuum exhaust: CO ₂ PSA ~ 120Torr N removal ₂ PSA~80Torr Supply gas amount is ^30.2m3 , double contact CO gas amount is
The CO gas recovery rate was 51.58% at ^13.5m3 . At this time, the gas composition after replication is CO = 99.0% CO ₂ =
0.3% N ₂ =0.7% Example 4 Using the same equipment as in Example 3, purification using converter exhaust gas was attempted under the following experimental conditions. <Experimental conditions> Converter exhaust gas composition: CO = 85% CO ₂ = 3% N ₂ = 5% H ₂ = 7% Operating temperature: 35°C Adsorption pressure: 0.5Kg/cm ² G Vacuum exhaust: CO ₂ PSA ~ 120Torr N removal ₂ PSA~80Torr Supply gas amount is ^36.2m3 , while purified CO gas amount is 15.3
The recovery rate of CO gas in m ³ was 49.4%. Gas composition after purification is CO = 99.4% CO ₂ = 0.4%
_N2 =0.2%

[Brief explanation of the drawing]

The figure is a flow sheet showing a preferred embodiment for carrying out the invention.

Claims (1)

[Scope of Claims] 1. A method for concentrating carbon monoxide in a raw material gas containing at least carbon dioxide, carbon monoxide, and nitrogen by a two-stage adsorption operation, including: (a) the first stage adsorption operation The method uses two or more adsorption towers filled with an adsorbent material that is selective to (b) The second stage adsorption operation increases the selectivity to carbon monoxide in the gas discharged from the first stage adsorption process (hereinafter referred to as the first stage product gas). The method includes (i) pressurizing the adsorption tower with the first stage product gas; and (ii) further flowing the first stage product gas into the adsorption tower. an adsorption () step in which the easily adsorbable component is adsorbed on the adsorbent until the concentration of the easily adsorbable component at the outlet of the adsorption tower reaches the concentration of the easily adsorbable component at the inlet of the adsorption tower, or until slightly before the point where both concentrations become equal; (iii) After the adsorption () process is completed, the adsorption tower is connected to the adsorption tower where vacuum desorption has been completed, and gas is introduced from the former adsorption tower to the latter adsorption tower to reduce the pressure in the former adsorption tower. (iv) A purge step in which the second-stage product gas is introduced into the depressurized adsorption tower to purge the difficult-to-adsorb components; (v) After the purge step, the adsorption tower is evacuated to below atmospheric pressure and the adsorption begins. A recovery process in which easily adsorbable components adsorbed by the agent are desorbed and product gas is recovered;
and (vi) adsorption tower and adsorption after product gas recovery ().
The process consists of an adsorption () process in which the gas from the latter adsorption tower is introduced into the former adsorption tower by connecting the adsorption tower after the process has been completed, and the flow between the adsorption towers is changed periodically.
A method characterized by repeating the above operations. 2. The first stage adsorption operation includes (i) a pressurizing step in which the adsorption tower is pressurized by the first stage product gas, (ii) an adsorption step in which the raw material gas is passed through the adsorption tower and mainly carbon dioxide is adsorbed on the adsorbent material; (iii) Next, there is a depressurization process in which the adsorption is depressurized to near atmospheric pressure, (iv) Next, there is an exhaust process in which the adsorption tower is evacuated by a vacuum pump, etc., and (v) Next, there is a purge process in which the waste gas from the second stage is used. Claim 1 consists of repeating the above operation by periodically changing the flow between the adsorption towers.
The method described in section.