JPS6097020A - Purification of carbon monoxide in gaseous mixture containing carbon monoxide, carbon dioxide and nitrogen gas by using adsorbing method - Google Patents

Abstract

PURPOSE:To obtain high purity CO by purification, by removing CO2 by pressure variation type adsorptive separation as a first stage while using the waste gas of a N2-removal stage as regeneration pure gas during the desorptive operation of CO. CONSTITUTION:Stock gas is successively introduced into adsorbing towers A, B to adsorb CO2 and the other gases are exhausted. After an adsorbing process is finished, the adsorbing towers are released under reduced pressure. When pressure in the towers is reduced to the vicinity of atmospheric pressure, the heated waste gas of a N2-removal stage is introduced to raise the temp. of an adsorbent and, thereafter, evacuating exhausion is performed to desorb CO2 while purging the same by the above mentioned waste gas. The gas, from which CO2 is removed, is introduced into an adsorbing tower C to adsorb CO and CO2 while waste gas is used as the above mentioned purge gas. After the adsorbing process is finished, the adsorbing tower C is evacuated and discharged gas is adsorbed with an adsorbing tower D and, after a purge process is performed, said tower D is exhausted under reduced pressure to recover CO as product gas.

Description

DETAILED DESCRIPTION OF THE INVENTION Steel mill byproduct gas, especially converter gas, contains a large amount of carbon monoxide and is attracting attention as a chemical raw material gas. The present invention primarily focuses on the composition of converter gas, i.e. at least GO1C.
High purity - using gas containing 02 and N2 as raw materials
The present invention relates to a method for purifying carbon oxide gas using a pressure swing adsorption method (PSA method).

There are two methods for concentrating and separating carbon monoxide: a cryogenic separation method and a common liquid absorption method.

The cold separation method is a method in which carbon oxide is separated by cooling it to -165°C to -210°C and liquefying it. If carbon monoxide and nitrogen, which has a boiling point close to each other, coexist in large quantities, it is difficult to separate it. The disadvantage is that the liquefaction equipment is expensive because it requires low temperature and high pressure.

Solution absorption methods include the liquid preparation method and the C08ORB method.The liquid preparation method uses an ammonia water bath solution of cuprous formate as an absorbent, and is carried out at 20°C and a high pressure of 150 to 200 kg/crn2G.

The C08ORB method uses a toluene bath solution of cupric tetrachloroaluminate as an absorbent, and the temperature is about 40°C.
．． The absorption rate is 4 kg/cIn2G, but since the absorption liquid reacts with water, the water content in the source gas must be reduced to 1 ppm or less. Although these methods are considered to be optimal for producing highly concentrated gas for mass production, they have the disadvantage that the equipment is complicated and the equipment is expensive.

However, the method of separating and purifying carbon monoxide by adsorption is considered to be one of the preferable methods from the viewpoint of the economic efficiency of the equipment used and the possibility of regenerating the adsorbent packed in the adsorption column.

Adsorption separation using the adsorption method (PSA method) for mixed gases is well known, and was developed in Japanese Patent Publication No. 38-239 for the purpose of recovering gas components that are difficult to adsorb to adsorbents (hereinafter referred to as difficult-to-adsorb components).
28 and Japanese Patent Publication No. 43-15045, various basic inventions have been announced or filed as basic inventions.In addition, gas components that are easily adsorbed to an adsorbent (hereinafter referred to as easily adsorbed components) are adsorbed onto an adsorbent, desorbed, and separated and recovered. A method of separating easily adsorbable components with high purity has also 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 components easily adsorbed onto an adsorbent in a mixed gas 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, carbon monoxide, a gas component that is easily co-adsorbed, is removed from the mixed gas to recover and purify it as highly concentrated carbon monoxide, as in the present mixed gas.

The present applicant previously filed an application for a method for separating GO from a raw material gas containing a small amount of CO, N2, and GO by the PSA method (Ijj Application No. 58-110.61.
(See No. 6).

The present invention relates to an improvement of the invention disclosed in Japanese Patent Application No. 58-110,646. That is, in the present invention, the first step is a carbon dioxide removal step by adsorption method (hereinafter referred to as de-CO2PSA).
During the desorption operation, the waste gas from the denitrification stage (hereinafter referred to as deN2PSA) is used as a regenerated purge gas, and in order to facilitate the desorption of carbon dioxide, the waste gas from the denitrification stage (hereinafter referred to as deN2PSA) is used as a regeneration purge gas.
It has been found that by combining the A adsorption tank with heating using the de-N2PSA waste gas, it is possible to purify high purity carbon oxide with a low carbon dioxide content.

The present invention will be explained in detail below.

The present invention provides a method for purifying carbon monoxide from a raw material gas containing at least carbon monoxide, carbon dioxide, nitrogen, etc., including (a) an adsorbent having selective adsorption properties for 002 in the raw material gas as a first stage treatment; For example, two or more adsorption towers containing adsorbents made of any one or a combination of synthetic or natural zeolites such as activated alumina, activated carbon, molecular seeds, and cation-substituted zeolides are used, and the method is such that each adsorption tower The second stage adsorption operation consists of removing carbon dioxide from the raw material gas by pressure fluctuation adsorption separation that repeats adsorption and desorption at fbl. Using two or more adsorption columns filled with synthetic or natural zeolites, such as activated carbon, molecular sheets, and cation-substituted zeolites, which are selective for carbon monoxide in the stage product gas), The method includes at least four steps consisting of (1) pressurization and adsorption of the adsorption tower with the first stage product gas, (11) depressurization of the adsorption tower, (ll+1 nozzle of the adsorption tower), and (1v) desorption of the product gas. It is characterized by periodically changing the flow between adsorption towers and repeating the process, heating the waste gas with low carbon dioxide content in the second stage and using it for the regeneration process of the adsorption tower in the first stage treatment. The present invention relates to a method for producing high-purity carbon oxide.

The step of removing carbon dioxide gas 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. It's okay. A preferred method of removing carbon dioxide is as follows.

Two or more adsorption towers filled with an adsorption material having selectivity for carbon dioxide are used, and the method includes (1) pressurizing the adsorption tower with the first stage ceramic gas, preferably in a countercurrent direction; (II) An adsorption step in which the raw material gas is passed through an adsorption tower and mainly carbon dioxide is adsorbed onto the adsorbent material, preferably in a countercurrent direction followed by adsorption. (1) Next, the waste gas from the N2 deN2 PSA device is heated (preferably in the range of 40 to 100°C) and introduced into the adsorption tower, where it is removed from the adsorbent. (v) an evacuation step in which the adsorption column is evacuated below atmospheric pressure, preferably in a countercurrent direction; Purge while performing ノξ−
In the second step, the waste gas may be heated to a temperature in the range of 40 to 100°C.

This method consists of repeating the above operation by periodically changing the flow between the adsorption towers.

The preferred second stage of the invention is as follows.

Two or more adsorption towers filled with an adsorption material that is selective to carbon monoxide in the gas discharged from the first stage adsorption process (hereinafter referred to as the first stage ceramic product gas) are used. The method is (1) a pressurizing step of pressurizing the adsorption tower with the first-stage ceramic product gas, (11) the first-stage ceramic product gas is further passed through the adsorption tower, and the concentration of easily adsorbable components at the outlet of the adsorption tower is person (8).

Adsorption (1) step in which the easily adsorbable component is adsorbed on the adsorbent until the concentration of the easily adsorbable component in the mouth is reached, or for an appropriate amount of time or amount after reaching the concentration, or until a little before the point where both concentrations become equal, fil++ adsorption ( 1) After the process is completed, the pressure of the adsorption tower is reduced to an arbitrary pressure between the adsorption pressure and atmospheric pressure, (1)
v) After the pressure reduction process is completed, connect the adsorption tower with the adsorption tower that has undergone vacuum desorption, introduce gas from the former adsorption tower into the latter adsorption tower, and reduce the pressure of the former adsorption tower to atmospheric pressure or near atmospheric pressure. In this case, the former pressure may be reduced until both pressures become approximately the same pressure, or the former pressure may be stopped at atmospheric pressure or higher.

(■) A purge process in which the second-stage ceramic product gas is introduced in parallel flow into the depressurized adsorption tower to remove the difficult-to-adsorb components.In this case, the gas flowing out from the top of the adsorption tower is It may be introduced into the finished adsorption tower and used to pressurize the adsorption tower.

[vl] A recovery process in which the adsorption tower after the purge process is evacuated to below atmospheric pressure to desorb easily adsorbed components adsorbed by the adsorbent and product gas is recovered; (vlli) an adsorption step in which the tower is connected to the adsorption tower that has completed the adsorption (1) step or the decompression step, and gas from the latter adsorption tower is introduced into the former adsorption tower; (vlli) a purge step for the other adsorption tower; adsorption (I) step using gas from the adsorption column, and is characterized in that the above operation is repeated by periodically changing the flow between the adsorption towers.

A preferred embodiment of the second stage of the present invention will be described.

Step (1) of this embodiment is an adsorption tower pressurization step in which the raw material gas is introduced into the adsorption tower.
g/can 2.0 or more, and generally an adsorption pressure of about 1 to 9/cIrL2.G is sufficient, and a lower adsorption pressure may be used.

Step (11) is the adsorption (1) step, which is the point at which the concentration of easily adsorbed components (-carbon oxide gas, carbon dioxide 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 the breakthrough point of the adsorbent. 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 this aspect,
Since the component to be recovered is a component that is easily adsorbed, adsorption is carried out until the breakthrough point or just before the breakthrough point is reached. Further, seven adsorption operations may be performed until the breakthrough point is exceeded.

In step fl), after the adsorption step is completed, the pressure is reduced preferably in the parallel flow direction to an arbitrary pressure between the adsorption pressure and atmospheric pressure, and the hardly adsorbable components remaining near the outlet of the adsorption tower are discarded. This step does not necessarily have to be performed.

Step (1) connects the adsorption tower that has undergone the adsorption (1) step or the depressurization step with the adsorption tower that has undergone vacuum desorption, and preferably flows the gas from the former adsorption tower to the latter adsorption tower in a cocurrent direction. The pressure in the former adsorption tower is reduced to atmospheric pressure or near atmospheric pressure. Alternatively, the pressure of the former may be lowered until the pressures of both adsorption towers become approximately equal. In this step, the gas in the space between the adsorbents housed in the adsorption tower is released and is used to pressurize the adsorption (Il) 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 (v), the product gas is cocurrently introduced into the depressurized 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, etc. (Purge is performed by connecting the product gas tank and the adsorption tower. Also, at this time, the purge gas concentration at the outlet of the adsorption tower is only slightly lower than the product gas concentration due to the addition of the difficult-to-adsorb components remaining in the adsorption tower to the product gas concentration, and is sufficiently rich in carbon monoxide than the raw material mixed gas concentration. This is the purge gas (the part close to the product gas concentration). When this part is recovered and used to continuously concentrate carbon monoxide gas, the pressurizing gas (adsorption (nil) in other towers is used. This purge gas is You don't have to use it.

The adsorption tower after the process (vO is .
The gas is evacuated to a range of Torr, and components adsorbed by the adsorbent (-carbon oxide gas, etc.) are desorbed and recovered as a product gas.

In the step (viD), the adsorption tower that has completed product recovery is connected to the adsorption tower that has completed the adsorption (1) step or the pressure reduction step, and the former adsorption tower is pressurized and adsorbed by the gas from the latter adsorption tower.

In this step, the pressure in the former adsorption tower does not reach atmospheric pressure.

The step (viril) can also be adsorption (Ill) with gas from the purge step of another adsorption column. This step (vtl) is optional.

The present invention will be described 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 oxide. It is not limited to specific examples.

The figure is a flow sheet in which carbon dioxide and nitrogen are continuously removed from converter exhaust gas using an adsorption method, and -carbon oxide gas is separated and concentrated.

Adsorption towers A and B house adsorbents that selectively adsorb carbon dioxide. After the adsorption towers A and B are evacuated to 300 Torr, preferably 60 Tprr, using a vacuum pump, the adsorption tower A is pressurized to normal pressure with raw material gas.

At this time, everything except pulp (1) is in a closed state. Adsorption tower B still maintains a vacuum state at this step. Introducing raw material gas into adsorption tower A, adsorption pressure 0.01
kg/cm2・G maybe 3.0 to 9/cm2・G preferably 0.21g7 Cm2・G to 1,, Ok+?
/cyn2- G adsorption pressure is maintained, valve (2) is opened, and part of the gas containing carbon dioxide and carbon monoxide is adsorbed to the adsorbent, while the rest is discharged from the other end of the adsorption tower. do. After completion of the adsorption process for a certain period of time or a certain amount, the raw material supply valve (1) and the output valve (2) are closed, and the valve (
3) is opened and the internal pressure of adsorption tower A is reduced to near atmospheric pressure. When adsorption tower A reaches atmospheric pressure, Pal/(5
) is opened and a certain amount of heated N2PSA waste gas is introduced into the adsorption tower A through the heat exchanger HE-1 which uses low pressure steam as a heat source to raise the temperature of the adsorbent, and then the valve (5) is closed. The valve (4) is opened from the bottom of the adsorption tower, and a vacuum pump is used to perform evacuation under reduced pressure to desorb the carbon dioxide component adsorbed on the adsorbent.The evacuation pressure at this time is 300 Torr, preferably 60 Torr. When the decompression exhaustion is completed, the valve (5) is opened (at this time, the amount of purge gas is adjusted with the manual valve θa). By using the waste gas from the deN2 equipment, the waste gas that has not been completely desorbed to the adsorbent is adsorbed. The carbon dioxide contained in the adsorbent is expelled from the adsorbent by entrainment desorption with the purge gas. At this time, heat exchanger HE-1 may be bypassed. When the exhaust purge is completed, the valves (4) and (5) are closed, and the valve (6) is opened to pressurize the inside of the adsorption tower to the adsorption pressure with the deCO2 gas (gas passing through the adsorption tower B).

The above operation is repeated in each adsorption tower in order to continuously adsorb and remove the adsorbent KCO2. The gas from which carbon dioxide has been removed in the first-stage de-CO2 PSA is subjected to the second-stage de-N2 PSA to remove hydrogen, oxygen, and nitrogen, thereby concentrating and separating the carbon monoxide to a high concentration. The adsorption tower CDEF contains an adsorbent that selectively adsorbs easily adsorbable components (carbon monoxide and carbon dioxide). Adsorption tower CDEF
300 To
rr) is introduced under pressure. This is done by opening the valve (16) to increase the pressure from the regenerated vacuum state. The pressure increase rate at this time is adjusted by the valve (+5).After the pressure increase, the valve aηα is opened at the same time as the valve 06).
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 of them are de-CO
It is used after being heated as a purge gas for 2PSA equipment. The remainder still contains a considerable amount of hydrogen and carbon oxide, so it is collected in a tank (4 tanks) for reuse as fuel gas, etc.

After the adsorption process for a certain time or a certain amount, the raw material supply valve (
II'0 and output valve 07) are closed, and the valve H in the connecting pipe to the adsorption tower is opened to release the internal pressure of the adsorption tower C to near atmospheric pressure, and release the reduced pressure to the adsorbent in the adsorption tower. Adsorbs pressurized gas. When adsorption tower A reaches atmospheric pressure, the product gas tank (42
1) Open the valve (a) and perform the purge process from the bottom of the adsorption tower C. In this purge step, the gas discharged from the adsorption tower is introduced into the adsorption tower, and following the previous depressurization and pressurization step,
Allow the adsorbent to adsorb easily adsorbable components. At this point, the pressure in the adsorption tower is reduced to near atmospheric pressure.

When the purge process is completed, the valve α9 and (21) are closed and the valve (21) is opened from the bottom of the adsorption tower to perform depressurized exhaust using a vacuum pump. The pressure is increased to 300 Torr, preferably 60 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, in the first-stage desorption 002 PSA, the effect of increasing the desorption rate of carbon dioxide can be obtained by applying heat to the adsorption tower and intentionally keeping the adsorbent temperature high before the carbon dioxide desorption operation. , large dynamic adsorption capacity can be ensured in limited time operation. The pressure fluctuation type adsorption separation method is basically an adiabatic operation, and when heat is added from outside the system, the temperature of the adsorption tower increases except for the amount of heat carried away by the passing gas. This temperature increase is balanced by an increase in the amount of heat dissipated from the surface of the adsorption tower.

However, if the amount of heat given is large, the temperature of the adsorption tower will rise significantly, and the decrease in the static adsorption capacity of the adsorbent will outweigh the improvement in the dynamic adsorption capacity, reducing the carbon dioxide adsorption separation effect. Adsorption and desorption start temperature of 20℃
The temperature must be heated to ~50°C, preferably 25-35°C.

Therefore, the effect of the present invention becomes extremely significant in the winter season.

It does not require a large potential as a heating energy source; low-pressure steam, heated waste water, heated waste gas, etc. are sufficient, and it is extremely inexpensive and can be implemented industrially.

Furthermore, in the specific example described above, the temperature of the de-N2PSA waste gas was raised prior to the depressurization operation for desorption, and the adsorption tower was heated with it, or the raw material gas was heated and the adsorption tower was heated with the same effect. It is also possible to remove CO2PSA by increasing the temperature. In this case, the operating time of various adsorption/desorption processes is not limited, and less heating is required, so the objective can be achieved with an energy source with lower potential compared to the above method, but the dynamic adsorption capacity is The improvement does not extend to methods that increase the temperature prior to the desorption operation.

In the de-C02PSA regeneration operation, it is not necessary to wait for the adsorption tower to reach normal pressure before heating and introducing the de-NzPSA waste gas, and the adsorption tower pressure is lower than the waste gas pressure. The introduction amount needs to be optimized within the constraints of the amount of gas heating and the allowable time for the regeneration operation.

The C02PSA and second N2P removal according to the present invention
By combining SA, the first stage can be removed from C○2PSAC0
2 The separation effect can be enhanced, which is the second stage of N2 removal.
By keeping the carbon dioxide concentration in the PSA waste gas low, we were able to obtain an extremely large mutual effect of further enhancing the effect of the CO2 removal PSA regeneration operation using the waste gas. As a result, it was possible to produce high-purity carbon oxide gas with a low carbon dioxide content and improve the recovery rate of carbon monoxide.

Example 1-4 and Comparative Example 1 The C02 PSA operation is "adsorption - vacuum release - normal pressure purge - vacuum evacuation - purge - product pressurization" and the N2 PSA operation is [raw material pressurization - adsorption - vacuum pressurization (- ) - No ξ - Di pressurization (-) - Vacuum evacuation - Depressurization and pressurization (B) - Purge pressurization (G)" We attempted to purify carbon monoxide from the raw material gas with the following composition. .

co N2co2 H2 85.8% 4.0% 3.6% 6.6%As is clear from the table below, the example according to the present invention has a higher CO ray It is clear that the purity and GO yield are high.

[Brief explanation of drawings]

The figure is a flow sheet of a preferred embodiment of the apparatus for carrying out the invention. Patent applicant Osaka Sanso Kogyo Co., Ltd. Kawasaki Steel Corporation (4 others)

Claims (1)

[Scope of Claims] In a method for purifying carbon monoxide from a raw material gas containing at least carbon monoxide, carbon dioxide, nitrogen, etc. the method consists of removing carbon dioxide from the feed gas by pressure swing adsorptive separation with at least repeated adsorption and desorption in each adsorption tower, and ( b) The second stage adsorption operation is carried out using two or more adsorbents filled with adsorbent substances that are selective 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 (1) pressurization of the adsorption tower with the first stage product gas and adsorption step, (11) depressurization of the adsorption tower, Il+1 purging of the adsorption tower, and (1v) purging of the adsorption tower with the product gas. It consists of repeating at least four steps consisting of desorption by periodically changing the flow between the adsorption towers, heating the waste gas with low carbon dioxide content in the second stage, and regenerating the adsorption tower in the first stage treatment. A carbon monoxide purification method characterized by use in a process.