JPH10130009A - Method and apparatus for purifying carbon dioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon dioxide gas purification method and a carbon dioxide gas purification apparatus capable of obtaining high purity carbon dioxide gas by preventing nitrogen oxide and propylene from being mixed into purified carbon dioxide gas. provide. SOLUTION: A compression step of compressing crude carbon dioxide containing impurities obtained by an alkanolamine absorption method by a carbon dioxide compressor, and a first adsorption step of absorbing and removing impurities such as a small amount of water and acetaldehyde. , A catalytic reaction step of decomposing nitrogen oxides by a catalytic reaction in the presence of hydrogen, a second adsorption step of adsorbing and removing impurities such as moisture generated in the catalytic reaction step, and trace amounts of oxygen and nitrogen by liquefied fractionation. And a liquefaction and purification step of separating low boiling components such as hydrogen, thereby removing a small amount of impurities from the crude carbon dioxide gas to obtain a product liquefied carbon dioxide gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for purifying carbon dioxide gas, and more particularly to a nitrogen oxidation method for further purifying and containing a crude carbon dioxide gas obtained by concentrating a raw material gas by an alkanolamine absorption method carbon dioxide concentrator. The present invention relates to a method and an apparatus for obtaining high-purity liquefied carbon dioxide by removing trace impurities such as substances, acetaldehyde, oxygen, and nitrogen.

[0002]

2. Description of the Related Art High-purity carbon dioxide gas used as a raw material gas for the food industry and the chemical industry is generally used as a by-product gas in the synthesis of ammonia, an off-gas for hydrolysis of naphtha and the like in oil refining, a combustion gas such as a boiler, or the like. First, a crude carbon dioxide gas is obtained from an exhaust gas from steelmaking and refining by using an alkanolamine absorption method carbon dioxide gas concentrator or a pressure fluctuation type adsorption separator (PSA device), and then the crude carbon dioxide gas is purified to remove trace impurities. High purity carbon dioxide gas is obtained by removing.

As an example of a conventional apparatus and method for purifying crude carbon dioxide gas from the above-mentioned alkanolamine absorption method carbon dioxide gas enrichment apparatus, a case in which combustion gas is used as a raw material and monoethanolamine is used as an absorbing solution will be described with reference to FIG. I do.

A source gas from a source gas source 1 is supplied to a monoethanolamine absorption type carbon dioxide concentrator (MEA absorption type C).
(O ₂ concentrator) 2 to obtain crude carbon dioxide gas. The MEA absorption type CO ₂ concentrating apparatus 2 includes a step of introducing the raw material gas into a washing tower and bringing the raw material gas into contact with an aqueous caustic soda solution flowing down from the top to separate impurities such as sulfur compounds contained in the raw material gas, A step of bringing the monoethanolamine solution and the like into countercurrent gas-liquid contact in an absorption tower to absorb carbon dioxide gas, a step of stripping the solution having absorbed the carbon dioxide gas in a regeneration tower to remove concentrated carbon dioxide gas, and washing with water. And washing and removing the residual amine in a tower to obtain a crude carbon dioxide gas.

[0005] The crude carbon dioxide gas obtained by the MEA absorption type CO ₂ concentrating apparatus 2 usually contains 99.0% or more of carbon dioxide gas, and contains 10 ppm to 1.0% of nitrogen and 0.11 ppm to It contains hundreds of ppm of oxygen, saturated water, 1 to several ppm of nitric oxide, and 0.01 ppm or less of nitrogen dioxide. In addition, although usually lower than the detection limit, depending on the operating conditions, trace amounts of carbon monoxide, odor components, and the like may be contained as impurities. Further, when the absorption solution is monoethanolamine, the crude carbon dioxide gas is accompanied by about 4 to 5 ppm of acetaldehyde.

[0006] Of the nitrogen oxides mixed in the raw material gas, nitrogen dioxide is removed in the step of producing the crude carbon dioxide gas and in the subsequent step of purification, but the amount of nitrogen monoxide is reduced to about a fraction. Is reduced but not completely removed, and a small amount of nitric oxide of about several ppm passes through a dryer and a deodorizer, reaches a liquefier / purifier (rectification tower), and is discharged at the inlet of the rectification tower. It was confirmed that when the concentration was 0.5 ppm or more, the presence of oxygen changed to nitrogen dioxide. The nitrogen dioxide may be mixed into the product liquefied carbon dioxide on the liquid phase side, and may exceed the product specification value, for example, 0.01 ppm.

Therefore, in order to remove the trace impurities, the crude carbon dioxide gas obtained by the MEA absorption type CO ₂ concentrator 2 is hydrogenated before or after the CO ₂ compressor 3 as shown in FIG. While adding hydrogen by means 4, CO 2
_{(2) After} compressing to a predetermined pressure by the compressor 3 and heating to 80 to 100 ° C., the mixture is introduced into the catalytic reaction tube 5 filled with a noble metal catalyst, and nitrogen oxides (NOx) are decomposed into nitrogen and water by hydrogenation reduction. Catalytic reaction step, moisture removal step by dryer 6, odor component and remaining NOx by deodorizer 7
, And then purified by rectifying and separating low-boiling components such as oxygen, nitrogen and hydrogen contained in the liquefied purifier (rectification tower) 8 to obtain the product liquefied carbon dioxide gas. The product is stored in the liquefied carbon dioxide gas storage tank 9.

[0008]

As described above, when a crude carbon dioxide gas is produced by the solution absorption method using monoethanolamine, a small amount of acetaldehyde accompanying the solution absorption / separation step in the MEA absorption type CO ₂ concentrator 2 is used. Is mixed into the crude carbon dioxide gas. A part of this acetaldehyde may be converted to propylene, though it is very small, in a catalytic reaction step for removing nitrogen oxides in the purification step.

The generated propylene is not removed by the dryers 6 and deodorizers 7 in the subsequent process, but goes to the next rectification / separation step by the liquefier / purifier (rectification tower) 8 where it is separated into the liquid phase. As a result, it is mixed into the product liquefied carbon dioxide gas at a concentration of about 1 to several tens of ppb, which causes a decrease in the purity of the product liquefied carbon dioxide gas.

It has been confirmed that this reaction proceeds not only when a specific catalyst such as a noble metal is used, but also when various catalysts are used.

Accordingly, the present invention provides a method for purifying carbon dioxide gas and a carbon dioxide gas purifying apparatus capable of obtaining high-purity carbon dioxide gas by preventing nitrogen oxide and propylene from being mixed into purified carbon dioxide gas. It is intended to be.

[0012]

In order to achieve the above object, a first method of the present invention is a method for removing carbon dioxide from a crude carbon dioxide gas containing at least trace amounts of nitrogen oxides, water and acetaldehyde as impurities. In the gas purification method, after removing the water and impurities such as acetaldehyde from the crude carbon dioxide gas by adsorption, the nitrogen oxide is decomposed by a catalytic reaction in the presence of a small amount of hydrogen, and then the decomposition products and the like are removed. It is characterized by removing impurities.

A second method is a method for purifying carbon dioxide gas for removing a trace amount of impurities from crude carbon dioxide gas obtained by an alkanolamine absorption method, wherein the crude carbon dioxide gas containing the impurities is removed by a carbon dioxide gas compressor. A compression step of compressing to a predetermined pressure, and then a first adsorption step of removing impurities such as water and acetaldehyde contained in trace amounts by adsorption,
A catalytic reaction step of decomposing nitrogen oxides contained by the catalytic reaction in the presence of a small amount of hydrogen, a second adsorption step of removing impurities such as moisture generated in the catalytic reaction step by adsorption, and then liquefaction rectification separation And a liquefaction / purification step of separating low-boiling-point component impurities such as oxygen, nitrogen and hydrogen by a small amount to remove trace impurities from the crude carbon dioxide gas to obtain a product liquefied carbon dioxide gas.

Further, in the second method, a small amount of hydrogen used in the catalytic reaction step is added in a hydrogenation step before or after the compression step, and is removed in the second adsorption step. The impurities are water generated in the catalytic reaction step, an odor component such as hydrogen sulfide and a trace amount of sulfur compounds, and the catalyst used in the catalytic reaction step is a noble metal catalyst. , 50-100
° C, preferably 60 to 90 ° C.

An apparatus for purifying carbon dioxide to achieve the object of the present invention removes trace impurities from crude carbon dioxide obtained by an alkanolamine absorption method from a combustion gas from a boiler or the like or an exhaust gas from steelmaking and refining. In a carbon dioxide gas purifying apparatus, a hydrogen addition means for adding a small amount of hydrogen to the crude carbon dioxide gas, a carbon dioxide gas compressor for compressing the crude carbon dioxide gas to a predetermined pressure, and a water content slightly contained in the pressurized crude carbon dioxide gas And a first adsorber for removing impurities such as acetaldehyde, a catalytic reaction tube for decomposing nitrogen oxides contained therein into nitrogen and water by a catalytic reaction, and a second adsorber for removing impurities such as moisture generated in the catalytic reaction tube. (2) equipped with an adsorber and a liquefaction purifier for separating low-boiling-point components such as oxygen, nitrogen and hydrogen contained therein by liquefaction rectification separation, and To remove objects, characterized in that to obtain a product liquefied carbon dioxide.

Further, in the carbon dioxide gas purifying apparatus,
The first adsorber is filled with an adsorbent mainly containing silica gel and / or alumina gel, and the second adsorber is an adsorbent mainly containing silica gel and / or alumina gel; Activated carbon is filled in this order, the hydrogenation means is for adding hydrogen to the crude carbon dioxide gas after the carbon dioxide gas compressor, and the catalyst filled in the catalyst reaction tube is a platinum catalyst. And / or a palladium catalyst.

[0017]

According to the method for purifying carbon dioxide gas and the apparatus for purifying carbon dioxide gas of the present invention described above, a small amount of acetaldehyde mixed in the absorption step for obtaining crude carbon dioxide gas is adsorbed and removed by the adsorbent. After that, a catalytic reaction for decomposing nitrogen oxides is performed, so that propylene is not generated, and it is possible to prevent propylene and nitrogen oxides from being mixed into the purified carbon dioxide gas. Hereinafter, the purification apparatus and method will be described in more detail with reference to FIG.

The embodiment of the apparatus for purifying carbon dioxide shown in FIG. 1 uses a source gas (combustion gas, etc.) from a source gas source 11.
Monoethanolamine absorption carbon dioxide concentrator (MEA absorption CO ₂ concentrator) to obtain crude carbon dioxide gas
Subsequent to 12, a hydrogenation means 14 for adding a small amount of hydrogen to the crude carbon dioxide gas is provided, and a CO ₂ compressor 13 for compressing the crude carbon dioxide gas to a predetermined pressure is provided. Also, CO
_{(2) In} the latter stage of the compressor 13, a first adsorber 15 for removing impurities such as a small amount of water and acetaldehyde contained in the pressurized crude carbon dioxide gas, and a catalytic reaction of nitrogen oxides contained in the pressurized crude carbon dioxide gas And a second adsorber 17 for removing impurities such as moisture generated in the catalyst reaction tube 16;
Liquefaction purifier (rectification tower) 18 for separating low-boiling component impurities such as nitrogen and hydrogen by liquefaction rectification separation, and liquefaction purifier 1
The product liquefied carbon dioxide gas storage tank 19 for storing the purified product liquefied carbon dioxide gas obtained in 8 is provided in this order.

The addition of hydrogen by the hydrogen adding means 14 is performed before the catalytic reaction tube 16 because it is used for the catalytic reaction. Therefore, not only before the CO ₂ compressor 13 but also before the first adsorber 15 or the catalytic reaction tube 16, hydrogen is added by the hydrogen adding means 14.

The first adsorber 15 is filled with an adsorbent mainly composed of silica gel and / or alumina gel. The second adsorber 17 has an adsorbent mainly composed of silica gel and / or alumina gel at the inlet side of the container, and an adsorbent suitable for removing odorous components such as activated carbon at the outlet side, which is the upper layer of the container. Each is filled. In this case, since the amount of water is small, the order of filling the adsorbent may be reversed. Further, the second adsorber 1
7 may be formed by connecting an adsorber filled with an adsorbent mainly composed of silica gel and / or alumina gel and an adsorber filled with activated carbon or the like in series. The catalyst filled in the catalyst reaction tube 16 is a platinum catalyst and / or a palladium catalyst.

Next, an embodiment of a method for purifying carbon dioxide using this apparatus for purifying carbon dioxide will be described. First,
A raw material gas (combustion gas and the like) from a raw material gas source 11 is introduced into a monoethanolamine absorption type carbon dioxide gas concentration device (MEA absorption type CO ₂ concentration device) 12 to obtain a crude carbon dioxide gas. In this step, the raw material gas is introduced into the washing tower and brought into contact with an aqueous solution of caustic soda flowing down from the top of the column to separate impurities such as sulfur compounds contained in the raw material exhaust gas. Next, the solution is introduced into the absorption tower and brought into countercurrent gas-liquid contact with the monoethanolamine solution to absorb carbon dioxide gas. The solution absorbing the carbon dioxide gas is stripped by the regeneration tower to remove the concentrated carbon dioxide gas. Then, the remaining amine is washed with a washing tower to obtain crude carbon dioxide gas.

As described above, the crude carbon dioxide gas obtained by the MEA absorption type CO ₂ concentrating apparatus 12 usually has 99.0% or more of carbon dioxide gas and 10 ppm as a trace impurity.
0.1 to 1.0% nitrogen, 0.1 ppm to several hundred ppm oxygen, saturated water, 1 to several ppm nitric oxide
Contains less than 01 ppm nitrogen dioxide. Also,
Depending on operating conditions, trace amounts of carbon monoxide, odor components, and the like may be included as impurities. Further, when the absorption solution is monoethanolamine, about 4 to 5 ppm of acetaldehyde is introduced into the crude carbon dioxide gas.

Next, the MEA absorption type CO ₂ concentrator 12
The process enters a purification step for removing trace impurities from the crude carbon dioxide gas obtained in the above. A small amount of hydrogen, which decomposes nitrogen oxides in the catalytic reaction step, is added to the crude carbon dioxide gas entering the purification step by the hydrogenation means 14. The hydrogenation means 14 may be optional, and the hydrogenation site is not necessarily limited to the CO ₂ compressor 13.
Need not be before the CO ₂ compressor 13 or the first
What is necessary is just before the catalyst reaction tube 16, such as after the adsorber 15.
Further, a hydrogen compressor may be used as the hydrogen addition means,
The choice is free.

The amount of hydrogen added may be greater than the stoichiometric amount relative to the amount of nitrogen oxides contained, but the excess is preferably smaller. Further, when the crude carbon dioxide gas contains oxygen, the stoichiometric amount required for the reaction is added.

Next, the crude carbon dioxide gas is to compress the pressure required for this purification step, a CO ₂ compressor 13 28 kg
/ Cm ² G. The compression pressure in this compression step may be any pressure required for all steps of the purification step, and is usually in the range of about 5 to 30 kg / cm ² G, and
Particularly preferred is a range of from 30 kg / cm ² G to 30 kg / cm ² G.

Subsequently, the pressurized crude carbon dioxide gas is supplied to the first adsorber 1.
5 to perform the first adsorption step. That is, in the first adsorption step, a saturated amount of water and a small amount of acetaldehyde which are condensed by the aftercooler after the compression step and are not separated by the water separator are removed together with the crude carbon dioxide gas production step. In this step, the water content is adjusted to a dew point of −60 ° C. using an adsorbent mainly composed of silica gel and / or alumina gel.
Acetaldehyde is below the detection limit (0.5pp
m) is removed to the following.

Thereafter, the pressurized crude carbon dioxide gas is heated to 80 ° C., introduced into a catalytic reaction tube 16 filled with a noble metal catalyst, and reduces nitrogen oxides to decompose them into nitrogen and moisture.
The nitrogen oxides contained are rendered harmless by the following reaction in this catalytic reaction step. The catalytic reaction temperature at this time is 50 to 100 ° C, preferably 60 to 90 ° C. 2NO + H ₂ → N ₂ + 2H ₂ O 2NO + 4H ₂ + O ₂ → N ₂ + 4H ₂ O (NO ₂ + 2H ₂ → 1 / 2N ₂ + 2H ₂ O)

Next, the crude carbon dioxide gas after the catalytic reaction step is introduced into the second adsorber 17 and enters the second adsorption step.
Moisture is removed by an adsorbent mainly composed of silica gel and / or alumina gel, and odor components are removed by an adsorbent suitable for removing odor components such as activated carbon. In the second adsorption step, water generated in the catalytic reaction step and impurities that could not be removed in the first adsorption step, that is, trace amounts (less than or equal to several ppm) mixed under operating conditions below the detection limit in normal operation. Removal of sulfur compounds such as nitrogen oxides (NOx) and odor components is performed. When no odor component or the like is contained, it is natural that there is no need to fill an adsorbent for deodorization such as activated carbon. Further, the first adsorber 15 and the second adsorber 17 are each of a two-tube switching type, and perform continuous operation by switching one cylinder to the adsorption step and the other cylinder to the regeneration step.

The crude carbon dioxide gas after the completion of the second adsorption step is
A heat exchanger (not shown) exchanges heat with the released gas, cools to a predetermined temperature (for example, 10 ° C.), liquefies in a liquefier (not shown), and liquefies and purifies in a rectification separation step (rectification column). ), And low-boiling components such as oxygen, nitrogen and hydrogen contained therein are rectified and separated, collected at the top of the column and discharged. The liquefied carbon dioxide gas separated at the tower bottom is led out of a liquefier / purifier (rectification tower) 18 and stored in a product liquefied carbon dioxide gas storage tank 19.

The product liquefied carbon dioxide purified and separated in this manner has the product purity shown in the following examples, and a product of high purity greatly exceeding the value of the Food Sanitation Law standards (food additive standard value) is obtained. Can be

[0031]

EXAMPLE Table 1 shows the results of measuring the concentration of impurities contained in the conventional method according to FIG. 2 in the case of producing a product liquefied carbon dioxide gas by purifying a combustion gas. Table 2 shows the results of measuring the concentrations.

The sampling position of the sample gas to be analyzed in the conventional method according to FIG. 2 is as follows: sampling position a: outlet of the CO ₂ compressor 3 (crude carbon dioxide) sampling position c: outlet of the catalytic reaction tube 5 (carbon dioxide) sampling position d : 3 outlets of liquefied refiner (rectification tower) 8 outlet (product liquefied carbon dioxide).

[0033]

[Table 1]

The sampling position of the sample gas to be analyzed in the method of the present embodiment according to FIG. 1 is as follows: sampling position a: outlet of CO ₂ compressor 13 (crude carbon dioxide) sampling position b: outlet of first adsorber 15 (carbon dioxide) ) Sampling position c: Catalytic reaction tube 16 outlet (carbon dioxide) Sampling position d: liquefaction refiner (rectification tower) 18 outlet (product liquefied carbon dioxide).

[0035]

[Table 2]

As is clear from the above analysis values, the provision of the first adsorption step before the catalytic reaction step allows a trace amount of acetaldehyde to be removed from the crude carbon dioxide gas before the catalytic reaction step. Propylene which was produced in a very small amount in the reaction step and mixed in the product liquefied carbon dioxide gas was not detected. Nitric oxide was also removed to 0.001 ppm or less in the catalytic reaction step. The reason why the concentration of nitrogen monoxide varies after the first adsorption step is that the switching time of the first adsorber 15 is set based on the breakthrough time of water and acetaldehyde. That is, the concentration is 0 ppm before the breakthrough time of nitric oxide, and is higher than the inlet concentration after the breakthrough time.

As described above, according to the purification method of this embodiment,
It is possible to obtain carbon dioxide gas of extremely high purity, and the carbon dioxide gas thus obtained is used not only as a source gas for producing carbonated beverages and as a raw material gas for producing dry ice for food cooling, but also as a source gas for welding gas and steelmaking. It can be used as a stirring gas.

[0038]

As described above, according to the method for purifying carbon dioxide gas and the apparatus for purifying carbon dioxide gas of the present invention, the liquefaction of a product is achieved by decomposing nitrogen oxides in crude carbon dioxide gas into nitrogen and water. 0.001 concentration of nitrogen oxides in carbon dioxide
ppm or less. At the same time, the acetaldehyde entrained in the conventional process of absorbing carbon dioxide gas becomes propylene in the catalytic reaction process, and the amount of propylene mixed in the liquefied carbon dioxide gas can be reduced to 0.01 ppm or less.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a method and an apparatus for purifying carbon dioxide gas of the present invention.

FIG. 2 is a diagram illustrating an example of a conventional method and apparatus for purifying carbon dioxide.

[Explanation of symbols]

12: monoethanolamine absorption method carbon dioxide gas concentrator (MEA absorption CO ₂ concentrator), 13: CO ₂ compressor, 14: hydrogenation means, 15: first adsorber, 16: catalytic reaction tube, 17: first 2 adsorber, 18: liquefaction refiner (rectification tower), 19: liquefied carbon dioxide gas storage tank

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Akio Kajiwara 2-51-3 Akabane, Kita-ku, Tokyo Liquefied Carbonated Inc. (72) Inventor Kaoru Koshibe 2-51-3 Akabane, Kita-ku, Tokyo Liquefaction Carbonated Inc.

Claims (10)

[Claims] 1. A method for purifying carbon dioxide gas for removing impurities from crude carbon dioxide gas containing at least trace amounts of nitrogen oxides, moisture and acetaldehyde as impurities.
After removing impurities such as water and acetaldehyde from the crude carbon dioxide gas by adsorption, decomposing the nitrogen oxides by a catalytic reaction in the presence of a small amount of hydrogen, and then removing impurities such as the decomposition products. Characteristic carbon dioxide purification method. 2. A method of purifying a carbon dioxide gas for removing a trace amount of impurities from a crude carbon dioxide gas obtained by an alkanolamine absorption method, wherein the crude carbon dioxide gas containing the impurities is compressed to a predetermined pressure by a carbon dioxide gas compressor. A first adsorption step for removing impurities such as water and acetaldehyde contained in trace amounts by adsorption; a catalytic reaction step for decomposing nitrogen oxides contained by a catalytic reaction in the presence of a small amount of hydrogen; A crude carbon dioxide gas is obtained by a second adsorption step for removing impurities such as moisture generated in the catalytic reaction step, and a liquefaction and purification step for separating a small amount of low-boiling-point components such as oxygen, nitrogen and hydrogen by liquefied fractionation. A method for purifying carbon dioxide, characterized by obtaining a product liquefied carbon dioxide by removing trace impurities from the product. 3. The method for purifying carbon dioxide according to claim 2, wherein a small amount of hydrogen used in said catalytic reaction step is added in a hydrogenation step before or after said compression step. 4. The purification of carbon dioxide gas according to claim 2, wherein the impurities removed in the second adsorption step are water generated in the catalytic reaction step and a trace amount of odor components. Method. 5. The method for purifying carbon dioxide according to claim 1, wherein the catalytic reaction is a reaction using a noble metal catalyst. 6. An apparatus for purifying a carbon dioxide gas for removing trace impurities from a crude carbon dioxide gas obtained by an alkanolamine absorption method, comprising: hydrogenation means for adding a small amount of hydrogen to the crude carbon dioxide gas; Gas compressor for compressing the water to a predetermined pressure, a first adsorber for removing impurities such as a small amount of water and acetaldehyde contained in the pressurized crude carbon dioxide gas, and nitrogen and water containing nitrogen oxides by catalytic reaction. And a second adsorber for removing impurities such as moisture generated in the catalyst reaction tube, and a low-boiling component impurity such as a small amount of oxygen, nitrogen and hydrogen contained therein by liquid rectification separation. A purifying apparatus for carbon dioxide, comprising: a liquefied purifier that removes trace amounts of impurities from crude carbon dioxide to obtain product liquefied carbon dioxide. 7. The apparatus for purifying carbon dioxide according to claim 6, wherein the first adsorber is filled with an adsorbent mainly composed of silica gel and / or alumina gel. 8. The apparatus for purifying carbon dioxide according to claim 6, wherein the second adsorber is filled with an adsorbent mainly composed of silica gel and / or alumina gel and activated carbon. 9. The apparatus for purifying carbon dioxide according to claim 6, wherein said hydrogen adding means adds hydrogen to the crude carbon dioxide after the carbon dioxide compressor. 10. The apparatus for purifying carbon dioxide according to claim 6, wherein the catalyst filled in the catalyst reaction tube is a platinum catalyst and / or a palladium catalyst.