JPH07187606A - Method for recovering hydrogen from gaseous hydrogen containing much carbon dioxide - Google Patents

Abstract

PURPOSE:To operate a PSA device by a two-tower system not requiring a complicated sequence while saving the energy required for pressure rise and the consumption of raw fuel. CONSTITUTION:Of gaseous hydrogen contg. much carbon dioxide discharged without performing pressure equalizing operation after adsorption operation in a pressure swing adsorption method, the gaseous hydrogen holding 10 to 30 atm of gas pressure is subjected to decarbonation treatment to trun it into gas contg. much hydrogen from which hydrogen is recovered. And also a part of the gaseous hydrogen is subjected to pressure rise and cicrculating by a compressor of one stage, and a part of the circulated gas is fed to the pressure rise of a PSA device. Thus, hydrogen is recovered from gaseous hydrogen contg. much carbon dioxide by the PSA device operated by a two-tower system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering hydrogen, while reducing energy consumption required for pressurization and saving raw materials and fuels (hereinafter referred to as raw fuels) supplied to a reaction system, PSA. An object of the present invention is to provide a method for recovering hydrogen from hydrogen gas containing a large amount of carbon dioxide, which can be operated in two towers without requiring a complicated sequence.

[0002]

2. Description of the Related Art As an example of a process for generating hydrogen gas containing a large amount of carbon dioxide, a methanol reformer using steam reforming, partial oxidation and shift reaction using hydrocarbons such as methane, natural gas, butane and naphtha as raw materials. There is quality. The composition of hydrogen gas containing carbon dioxide generated varies depending on the process, but is generally in the following range. That is, carbon dioxide: 10 to 25 m0l% hydrogen: 65 to 75 m0l% carbon monoxide: 2 to 5 m0l% hydrocarbon: 2 to 10 m0l%.

As an example of recovering hydrogen from hydrogen gas containing a large amount of carbon dioxide, a pressure swing adsorption method (hereinafter referred to as PS
This is called method A. )It has been known. The PSA method is one of the methods for separating and separating a specific gas from a mixed gas.
A method of adsorbing an adsorbent on an adsorbent at a high pressure, and then desorbing the adsorbent adsorbed on the adsorbent by lowering the pressure of the adsorbent to separate the adsorbate from the adsorbent. , Industrially, a plurality of towers filled with adsorbents are provided, and in each of the adsorption towers, a series of operations of pressurization → adsorption → washing → degassing (regeneration) is repeated to continuously separate the entire apparatus. The PSA device having a treatment scale of 1000 Nm ³ / Hr or more has four or more towers in view of the recovery rate of the supplied hydrogen in spite of the complicated sequence. An adsorption tower is used.

In the PSA method, stopping the adsorption operation before one of the various components other than the non-adsorbed component, hydrogen, breaks through and leaks into the product hydrogen is to prevent the leakage of impurities into the product hydrogen. This is to prevent this, and after removing hydrogen gas at the same concentration as the product hydrogen gas from the top of the adsorption tower, perform pressure equalization operation and sequentially equalize pressure to the tower with lower pressure while also performing the washing operation. It is also well known that the effective use of the stored pressure is to increase the recovery rate of the supplied hydrogen. Usually, the adsorption-completed column is pressure-equalized with another adsorption column that is increasing the pressure in order to start the adsorption operation, and the residual pressure (hereinafter referred to as page gas) is the adsorption-completed column. Then, it is transferred to a tower that performs a washing operation at low pressure, and the pressure is lowered while washing. Here, the purge gas is lowered to a pressure near atmospheric pressure, and the column lowered to a pressure near atmospheric pressure is a column which is finally washed with the product hydrogen and the pressure is increased to start the adsorption operation. The hydrogen used for cleaning causes a production loss.

In the above series of operations, the exhaust gas containing a large amount of carbon dioxide immediately after the end of the adsorption operation is used for the pressure equalizing operation of the tower whose pressure is increased to enter the adsorption operation, and then to near the normal pressure. It is discharged as a purge gas whose pressure is reduced. The pressure of the purge gas after being subjected to the pressure equalization operation a plurality of times also serving as cleaning is about half of the gas pressure immediately before the pressure equalization operation is performed, and each component exceeds the adsorption amount of each component corresponding to the pressure. Will be removed. In this case, since hydrogen is a non-adsorption component, the desorption amount of the adsorption component increases as the pressure decreases, and the hydrogen concentration decreases as the pressure equalization operation is repeated.

As described above, the purge gas is carbon dioxide in the case of steam reforming using hydrocarbons such as methane, natural gas, butane and naphtha as raw materials, and methanol reforming involving partial oxidation and shift reaction. An external combustion reformer that is used to reform hydrocarbon raw materials in upstream processes, and is composed of carbon monoxide, methane, hydrogen as a refining loss, etc. in addition to carbon dioxide. It is used as a part of the fuel required in the (hereinafter referred to as reforming furnace).

[0007]

The above-mentioned conventional techniques have the following problems to be improved. (1) When four or more adsorption towers are industrially used in the methanol method, when one of the towers has a failure, it is confirmed which one has a failure, and after the confirmation, the operation is performed with the remaining towers. There was a problem of so-called trouble countermeasures due to the complicated sequence such as mode switching. (2) In order to avoid the above problems, there is a problem that when the operation with two towers that requires a simpler sequence is performed, the recovery rate of hydrogen supplied to the PAS device is worse than when four or more towers are used. Despite the problem of 1), it is used in 4 or more towers. In addition, while high-purity hydrogen is obtained by the PSA method, degassing (regeneration) operation of the adsorbent leaves hydrogen containing a large amount of carbon dioxide close to normal pressure as purge gas, which is close to normal pressure. When attempting to boost the pressure of the purge gas and recover hydrogen, the power required to boost the pressure becomes large. Therefore, from the viewpoint of energy consumption for the above reasons, an appropriate usage method other than using it as a part of the fuel in the reforming furnace. It was a long time ago. (3) Furthermore, for the sake of explanation, the following simple reaction formula for steam reforming of methane is shown as an example. Even if hydrogen gas containing a large amount of carbon dioxide is returned to the reaction system after pressurization, the following reaction formula (1) Since (2) and (2) were difficult to proceed, the raw materials supplied to the reaction system as a whole were not saved. CH ₄ + H ₂ 0 → C0 + 3H ₂ ··· (1) CH ₄ + H ₂ 0 → C0 ₂ + H ₂ ··· (2) Part of fuel in the reformer from the viewpoint of energy consumption There was no suitable usage other than as. The present invention is to provide a method for solving the aforementioned problems at the same time. That is, the present invention aims to reduce the energy consumption required for pressurization, which is a problem of the above-mentioned prior art, and the saving of raw materials and fuels (hereinafter referred to as raw fuels) supplied to the reaction system, while reducing PS.
It is an object of the present invention to provide a method for recovering hydrogen from hydrogen gas containing a large amount of carbon dioxide, which can operate the apparatus A in two towers without requiring a complicated sequence.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method for recovering hydrogen from hydrogen gas containing a large amount of carbon dioxide.
In the SA method, the hydrogen gas containing a large amount of carbon dioxide after the adsorption operation is introduced into the decarboxylation method step without performing the pressure equalization operation, and the pressure of the hydrogen gas before and after the decarboxylation process is substantially changed. The present invention has been made paying attention to the fact that it is not present. That is, the present invention provides (1) a hydrogen gas containing a large amount of carbon dioxide, which is maintained at a gas pressure of 10 to 30 atm, among hydrogen gas containing a large amount of carbon dioxide discharged after an adsorption operation in a pressure swing adsorption method. Decarburization is performed by the decarbonation method to obtain a gas containing a large amount of hydrogen, (2)
Configuration of a method for recovering hydrogen from hydrogen gas containing a large amount of carbon dioxide, characterized in that a part of the hydrogen gas containing a large amount of hydrogen gas is returned to an upstream reaction system by a one-stage compressor to recover hydrogen Is. In the present invention, the hydrogen gas containing a large amount of carbon dioxide discharged after the end of the adsorption operation in the PSA device is decarbonated and becomes a main gas containing a large amount of hydrogen, and the upstream PSA device or reactor, preferably the reaction Although it is circulated in the vessel, if the circulated amount exceeds 50% of the gas amount discharged after decarbonation, the consumption amount of the raw fuel increases as shown in Example 3 and Comparative Example 2 described later, which is not preferable. (3) The gas containing a large amount of circulated hydrogen is circulated to the reactor, the two-column PSA device, and the two-column PS.
It is used for boosting the pressure of another column that is preparing to enter the adsorption process in the A unit. That is, the configuration of the present invention is to remove the carbon dioxide having a gas pressure of 10 to 30 atm from the hydrogen gas containing a large amount of carbon dioxide discharged without performing the pressure equalizing operation after the adsorption operation in the pressure swing adsorption method. A large amount of hydrogen gas is decarburized by a decarbonation method to recover hydrogen as a gas containing a large amount of hydrogen, and a portion of this hydrogen gas is circulated under pressure by a single-stage compressor to reduce the amount of this circulating gas. Is a method for recovering hydrogen from hydrogen gas containing a large amount of carbon dioxide, which is characterized in that the PAS device can be operated in two columns by supplying a part to the pressure rising of the PAS device. In the present invention, the hydrogen gas containing a large amount of carbon dioxide discharged after the end of the adsorption operation in the PSA device is decarbonated,
It becomes a main gas containing a large amount of hydrogen and is circulated to the upstream PSA device or reaction tower, preferably the reaction tower, but when the circulation amount exceeds 50% of the gas amount discharged after decarbonation,
As shown in Example 3 and Comparative Example 2 described later, the consumption of raw fuel increases, which is not preferable.

The operating pressure for decarbonation varies depending on the partial pressure of carbon dioxide in hydrogen gas containing a large amount of carbon dioxide,
It is preferably 10 atm or more and 30 atm or less. If it is less than 10 atm, the efficiency of decarboxylation may decrease, and if it exceeds 30 atm, there is no change in the efficiency of decarboxylation as in the case of 30 atm or less. The decarboxylation method used in the present invention may be either a physical absorption method or a chemical absorption method as an absorption method, but an amine method, a potassium carbonate method and the like which are chemical absorption methods are usually used.

[0010]

The operation will be further described with reference to the drawings of an example of steam reforming of methane, but the present invention is not limited thereto. In the steam reforming using methane as the raw material 30, the raw material 30 and the steam required for the reaction are supplied to the reactor 1 through the line 5. The pressure in the reactor 1 is about 2
The pressure is 0 atm or more and 60 atm or less, and in the present invention, it is preferable that the pressure condition is less than 45 atm.

Hydrogen gas containing a large amount of carbon dioxide generated in the reactor 1 is supplied to the PSA apparatus 2 through a line 6, a cooler 20 and a line 7. Usually line 6
The temperature at 700 ° C. to 850 ° C., and the inlet temperature of the PSA apparatus 2 is 30 to 40 ° C. The PSA unit 2 is operated at a pressure of 10 to 30 atm,
Hydrogen of 9.9% or higher purity is obtained from line 8. In this case, since the carbon dioxide that suppresses the reaction formula (2) in the steam reforming of methane described above is removed, the reaction formula (2) easily proceeds, while the reaction formula (2) is circulated in the reaction system. Although (1) is suppressed, Example 1 described later
3 to 3 and Comparative Example 1, the raw material 30 and the fuel 40
The sum of raw fuel consumption is improved. On the other hand, pressure 10
Hydrogen gas containing a large amount of carbon dioxide at 30 to 30 atm is introduced to the carbon dioxide removal device 3 through the line 9. The decarbonation device 3 employs an amine method, a hot potassium carbonate method, or the like. By the way, the purge gas whose pressure is less than the pressure required for decarbonation in the PSA apparatus 2 merges with the line 17 to which the fuel 40 is supplied through the line 14 and is used as a part of the fuel.

A large amount of hydrogen obtained by decarboxylation in the decarbonation device 3 is introduced into the compressor-4 through lines 10 and 19 and is pressurized and circulated. When it is circulated in the reaction system, it is supplied to the reactor 1 through lines 21, 11 and 13, 23. In this case, since the carbon dioxide that suppresses the reaction formula (2) in the steam reforming of methane described above is removed, the reaction formula (2) easily proceeds, while the reaction formula (2) is circulated in the reaction system. Although (1) is suppressed, the raw fuel consumption, which is the sum of the raw material 30 and the fuel 40, is improved as shown in Examples 1 to 3 and Comparative Example 1 described later.

When it is circulated to the PSA device 2, it is circulated through lines 21, 11 and 12. Although any place may be adopted as the place to be circulated, it is preferably circulated to the reaction system in order to simplify the process.
It is also possible to raise the pressure up to the operating pressure of the column which is branched from the line 18 and is preparing to enter the adsorption step in the PSA apparatus 2. The following examples are provided to explain the present invention in more detail, but the present invention is not limited thereto.

[0014]

【Example】

Example 1 An example of a method for recovering hydrogen from hydrogen gas containing a large amount of carbon dioxide according to the present invention will be described below with reference to the drawings. Table 1 below shows the conditions of the gas supplied to the PSA device 2. As the PSA device 2, one having an inner diameter of 43 mm and a height of 2 m, which was filled with a molecular sieve and activated carbon as an adsorbent at a ratio of 4: 6, was used, and the supply gas flow rate was 15 liter / min. At the bottom of the PSA apparatus 2, the purified gas is fed from the top of the PSA apparatus 2 at 99.9%.
Hydrogen from line 8 and purge gas from line 1
Ejected from 4. The pressure of the gas containing a large amount of carbon dioxide in the reactor 1 and the line 9 was 20 atm and 10 atm, respectively. The gas containing a large amount of carbon dioxide was supplied to the decarbonation device 3 through the line 9 and decarbonated. In the decarboxylation device 3, the monoethanolamine method (MEA), which is one of the amine methods, is used.
Law) was adopted. After decarboxylation, 10% of the decarbonated gas was circulated back to the bottom of the reactor 1 through the line 11 and the line 13 by the compressor-4. In addition, the pressure-increasing gas was introduced into one column of the PSA apparatus 2 through the line 18. The calculated raw fuel consumption is shown in Table 2 below. Example 2 The amount of circulating gas in Example 1 was changed from 10% to 30%, and the same procedure as in Example 1 was carried out. The calculated raw fuel consumption is also shown in Table 2. Example 3 The procedure of Example 1 was repeated except that the amount of circulating gas in Example 1 was changed from 10% to 50%. The calculated raw fuel consumption is also shown in Table 2. Comparative Example 1 The circulating gas amount of Example 1 was changed from 10% to 0%.
I went as well. The calculated raw fuel consumption is also shown in Table 2. Comparative Example 2 The same procedure as in Example 1 was carried out by changing the circulating gas amount in Example 1 from 10% to 70%. The calculated raw fuel consumption is also shown in Table 2. Example 4 10% of the gas after decarboxylation was circulated back to the bottom of the reactor 1 through the line 13 of Example 1 and returned to the bottom of the PSA apparatus 2 through the lines 12 and 7. The same procedure as in Example 1 was carried out except that the circulation was performed. The calculated raw fuel consumption is also shown in Table 3 below. Example 5 The cycle gas amount of Example 4 was changed from 10% to 30%, and the same procedure as in Example 4 was carried out. Table 3 shows the calculated raw fuel consumption. Example 6 The amount of circulating gas in Example 4 was changed from 10% to 50%, and the same procedure as in Example 4 was carried out. Table 3 shows the calculated raw fuel consumption. Comparative Example 3 Example 4 in which the circulating gas amount in Example 4 was changed from 10% to 0%
I went as well. Table 3 shows the calculated raw fuel consumption. Comparative Example 4 The same procedure as in Example 4 was carried out by changing the circulating gas amount in Example 4 from 10% to 70%. Table 3 shows the calculated raw fuel consumption.

[0015]

The method of recovering hydrogen from hydrogen gas containing a large amount of carbon dioxide according to the present invention has the following effects because it has the above-described structure. (1) Since a gas containing a large amount of hydrogen obtained after decarbonation is returned to the reaction system or the inlet of the PSA device, it is effective in reducing the raw fuel consumption. (2) PSA is a gas containing a large amount of hydrogen obtained after decarboxylation.
Since it is used for boosting the pressure of the device, without reducing the hydrogen recovery rate,
Moreover, it can be operated with two towers, and the control by a complicated sequence is unnecessary. (3) Since the gas is decarbonated at a pressure of 10 atm or more to produce a hydrogen-rich gas, which is circulated and returned, the amount to be returned is relatively small, and a single-stage compressor is sufficient. Therefore, since the power of the compressor is small and the size is small,
This has the effect of reducing the cost of machinery and equipment required for operating the compressor. (4) The above is more effective as the pressure in the reaction system is higher. (5) When the conventional methanol method is industrially used with four or more adsorption towers, if one of them fails, it is confirmed which one fails, and after confirmation, the remaining towers are operated. There is a problem of so-called trouble countermeasures due to the complicated sequence such as switching the operating mode
Since there are two towers, the number of issues for those trouble countermeasures has decreased.

[Brief description of drawings]

FIG. 1 is an explanatory view of a process flow of an embodiment of a method for recovering hydrogen from hydrogen gas containing a large amount of carbon dioxide according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactor 2 ... PSA device 3 ... Decarbonation device 4 ... Compressor 5 to 19 ... Line 21 to 23 ... Line 20 ... Cooler 30 ... raw material 40 ... fuel 50 ... high-purity hydrogen 60 ... carbon dioxide 70 ... pressure equalizing gas _{V 1, V 2, V 3} , V 4 ··· adjustment valve

Claims (2)

[Claims] 1. A hydrogen gas containing a large amount of carbon dioxide discharged without performing a pressure equalizing operation after an adsorption operation in a pressure swing adsorption method contains a large amount of the carbon dioxide having a gas pressure of 10 to 30 atm. The hydrogen gas is decarburized by a decarbonation method to recover the hydrogen as a gas containing a large amount of hydrogen, and a part of this hydrogen gas is pressure-circulated by a one-stage compressor to partly circulate this PAS gas. A method for recovering hydrogen from hydrogen gas containing a large amount of carbon dioxide, characterized in that the PAS device can be operated in two columns by supplying pressure to the device. 2. The circulating gas is used as a reaction system and / or PA.
The method for recovering hydrogen from hydrogen gas containing a large amount of carbon dioxide according to claim 1, which is circulated through the S device.