JP2009189929A - Gas separation method and gas separation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit the performance deterioration of a porous membrane due to the clogging of its pores with included solid particles, when the gas of an absorbing liquid is dissipated into a vacuum space by injecting the absorbing liquid into the vacuum space through micropores of the porous membrane. <P>SOLUTION: A gas to be separated and the absorbing liquid are brought into gas-liquid contact with each other through a gas permeable membrane. Through this process, the absorption of a specific component gas of the gas to be separated by the absorbing liquid can be achieved without including the solid particle in the gas to be separated into the absorbing liquid. Following this procedure, the absorbing liquid which has absorbed the specific component gas is brought into contact with the more pressure-reduced space than the absorbing liquid side through the liquid permeable porous membrane, and the absorbing liquid is jetted into the vacuum space through the fine pores of the porous membrane. Thus the specific component gas contained in the absorbing liquid is dissipated into the vacuum space to achieve the separation of the specific component gas. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for separating a specific component gas such as carbon dioxide from combustion gas discharged by thermal power generation and gas generated in a reaction process such as iron making, cement manufacturing, chemical industry, and fermentation. is there.

A large amount of carbon dioxide (CO ₂ ) is contained in combustion exhaust gas and reaction process gas. Since carbon dioxide brings about global warming due to the greenhouse effect, it is desired to recover carbon dioxide from these gases.

  There is an absorption method as a method of separating the specific component gas in the gas to be separated. The absorption method consists of an absorption step in which a gas to be separated and an absorption liquid are brought into contact with each other in an absorption tower packed with a packing to absorb the specific component gas in the gas to be separated into the absorption liquid, and then the specific component is heated by heating the absorption liquid. A method for recovering a specific component gas, and the most common method.

  As an absorption tower used in the absorption process, in addition to the absorption tower packed with packing, the gas-liquid contact efficiency is improved by making the liquid-liquid contact through a hydrophobic porous membrane in order to reduce the size of the absorption tower. The method of making it known is also known (see Patent Document 1).

  On the other hand, in the general chemical absorption method in the absorption method, it is necessary to heat the entire absorption liquid that has absorbed the specific component gas in the diffusion process to a high temperature so as to boil, so that the energy and cost required for separation increase. was there.

  Therefore, in order to improve the diffusion process, the present inventors bring the absorbing liquid that has absorbed the specific component gas into contact with the reduced pressure space from the absorbing liquid side to release the specific component gas in the absorbing liquid to the reduced pressure space. Thus, a diffusion process using a gas vacuum separator filled with a filler has been proposed (see Patent Document 2). The proposed diffusion process, in which the specific component gas in the absorption liquid is diffused into the decompression space using the gas decompression separator, is separated compared to the method in which the specific component gas in the absorption liquid is diffused by heating the absorption liquid to a high temperature. Energy and cost can be reduced.

  And in the proposal, as the first stage of the gas decompression separation device, the absorbing liquid that has absorbed the specific component gas is brought into contact with the decompression space through the liquid permeable membrane, thereby separating the absorbing liquid from the gas other than the specific component gas. In addition, it is proposed that a step of ejecting the specific component gas from the absorbing liquid may be provided while being injected into the reduced pressure space through the liquid permeable membrane.

JP-A-3-296413 JP 2005-270814 A

  In order to further improve the proposed method using the gas decompression separation method in the diffusion step, the absorption liquid that has absorbed the specific component gas is removed through the liquid permeable membrane without using a gas decompression separation device filled with a filler. A gas separation method was studied in which the diffusion process brought into contact with the gas was the main diffusion process.

  However, if an absorption tower packed with a packing is used as an absorption step in this gas separation method, and if a diffusion device using a porous membrane is used as a liquid permeable membrane in the diffusion step, the function of the diffusion device is increased with the use time. There was a significant problem.

  While investigating the cause, it was found that the absorbing solution was injected through the micropores of the porous membrane in the diffusion device, so that solid particles were mixed in the absorbing solution and the porous membrane was clogged. . Especially when absorbing carbon dioxide gas in combustion exhaust gas, the dust contained in the combustion exhaust gas is often mixed in the absorption liquid in the absorption tower packed with packing, and the porous membrane is used in a short time. I can't. Such clogging of the porous membrane does not occur even if the gas-liquid contact is made through the porous membrane unless the gas-phase side is depressurized. It was also found that this was caused by reducing the pressure on the gas phase side of the porous membrane. Up to now, no gas separation method employing a gas vacuum separation method using a porous membrane as a main diffusion step has been performed, and therefore, there was no problem that the porous membrane was clogged.

  Therefore, the present invention aims to adopt a gas vacuum separation method using a porous membrane as a main diffusion step, and to enable continuous operation by preventing clogging of the porous membrane.

  The inventors of the present invention have not only the effect of reducing the size of the absorption tower but also the absorption liquid as a method called a membrane contactor by contacting a gas and liquid through a membrane instead of an absorption tower filled with a conventional packing. It is thought that it is effective in avoiding the mixing of fixed particles into the inside, and by adopting this as an absorption process, the absorption liquid is injected into the reduced pressure space through the micropores of the porous membrane, and the gas in the absorption liquid is Even if the diffusion process to diffuse was adopted, it came to solve the problem of the above-mentioned function fall.

  That is, the gas separation method of the present invention comprises an absorption step in which a specific component gas in the separation gas is absorbed by the absorption liquid by bringing the separation gas and the absorption liquid into gas-liquid contact via a gas permeable membrane. Then, the absorption liquid is brought into contact with the reduced-pressure space from the absorption liquid side through the liquid-permeable porous membrane, and the absorption liquid is jetted into the reduced-pressure space through the micropores of the porous film. A gas separation method including a diffusion step of diffusing the specific component gas therein to a reduced pressure space.

  In the absorption step of absorbing the specific component gas in the gas to be separated into the absorption liquid by bringing the gas to be separated and the liquid absorption into contact with each other through a gas permeable membrane, solid particles are contained in the gas to be separated. Even in the case where the absorption liquid is present, the solid particles hardly enter the absorption liquid, so that the porous film used in the subsequent process is greatly reduced from being clogged even if the absorption liquid is sprayed from the fine pores. There is an advantage that the lifetime of the film is prolonged. As described above, the present invention overcomes the problem by utilizing the membrane in the absorption step, which is the previous step, in adopting the method of injecting the absorbing liquid through the fine pores of the porous membrane in the diffusion step of the normal absorption method. Furthermore, there is an advantage that the absorption tower is downsized along with the improvement of the gas-liquid contact efficiency by the membrane.

  Since the gas permeable membrane in the absorption step of the gas separation method of the present invention plays a role of absorbing the specific component gas in the gas to be separated into the absorption liquid through gas-liquid contact therewith, It is required that the property is good and the absorbing solution does not leak. Therefore, the gas permeable membrane used in the absorption process of the present invention is a non-porous membrane or a hydrophobic porous membrane having good gas permeability.

  In the case of a non-porous membrane, the absorbing liquid cannot leak out, but a thin film formed on the surface of the support is preferably used in order to improve gas permeability. Examples of the material of the non-porous film include silicone rubber having good gas permeability, polytrimethylsilylpropyne and the like. Examples of the material of the hydrophobic porous membrane include fluororesins such as polytetrafluoroethylene and polyvinylidene fluoride, and polyolefins such as polypropylene and polyethylene.

  Since the hydrophobic porous membrane is required to prevent the absorption liquid from leaking out, the hydrophobic porous membrane preferably has a pore diameter in the range of 0.01 μm to 10 μm, and more preferably has a pore diameter in the range of 0.01 μm to 1 μm. is there.

  The shape of the membrane is not particularly limited, such as a flat membrane, a tubular membrane, or a hollow fiber membrane, as long as the gas can flow on one side separated by the membrane and the absorbing solution can flow on the other side. In the case of a tubular membrane or a hollow fiber membrane, gas flows through one of the inside and outside of the membrane and the absorbing solution flows through the other, but there is no particular limitation on which one flows inside. When a large amount of gas is processed, the operation is facilitated by flowing the gas so that the gas is on the outside and the absorbing liquid is on the inside. Practically, it is used in the form of a membrane module in which the membrane is housed in a container and provided with a gas and absorbent inlet / outlet.

  The flow direction of the gas and the absorbing liquid is selected from a parallel flow type, a counter flow type, a cross flow type (a method in which the flow directions are orthogonal to each other), and the like. preferable.

The gas to be separated in the present invention is a mixed gas containing a specific component gas to be separated. The type of the specific component gas is not limited, but an example thereof is an acidic gas, and the absorbent in that case is preferably an alkaline aqueous solution. Examples of the acid gas include carbon dioxide gas (CO ₂ ) and sulfur dioxide gas (SO ₂ ). Acid gas absorption liquids include aqueous solutions of amines represented by alkanolamines such as monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA), as well as carbonates, amino acids, amino acid salts, and the like. Is suitably used in the form of a single or a mixture of aqueous solutions.

  In the gas separation method of the present invention, following the above absorption step, the absorption liquid that has absorbed the specific component gas is brought into contact with the space under reduced pressure from the absorption liquid side through the liquid-permeable porous membrane, and the absorption liquid is The specific component gas is separated and recovered by providing a diffusion step of diffusing the specific component gas in the absorption liquid into the reduced pressure space by spraying it into the reduced pressure space through the micropores of the porous membrane. Further, the diffusion step is a step of regenerating the absorbing solution.

  Since the liquid permeable porous membrane in the diffusion step of the gas separation method of the present invention is for injecting the absorbing liquid into the reduced pressure space through its fine pores, it is required that the absorbing liquid has good permeability. Is done. For this reason, the membrane used in the diffusion process of the present invention is a porous membrane having good liquid permeability.

  As the material of the liquid permeable porous membrane in the diffusion process of the gas separation method of the present invention, various organic materials such as various ceramics, metals, inorganic materials, polyethylene, polypropylene, polyvinylidene fluoride, polysulfone, polyethersulfone, cellulose acetate, etc. Molecular materials.

  A preferable fine pore diameter of the liquid permeable porous membrane is 0.01 to 200 μm.

  An example of this liquid-permeable porous membrane is formed in a channel shape, in which the absorbing liquid flows in the channel and the outside of the channel is decompressed. The shape of the membrane is not particularly limited, such as a flat membrane, a tubular membrane, and a hollow fiber membrane, but in order to dissipate a large amount of gas, an absorbing liquid is supplied to the inside of the tubular membrane or the hollow fiber membrane and the outside is decompressed. Easy to operate. Practically, it is used in the form of a membrane module in which the membrane is housed in a container and an inlet / outlet port for the absorbing liquid and a connection port for a vacuum pump are provided.

  The gas separation device for realizing the gas separation method of the present invention includes an absorption part and a diffusion part. The absorption unit includes a first container, a gas permeable membrane disposed in the first container and brought into gas-liquid contact, a gas supply port for supplying a gas to be separated to one surface of the gas permeable membrane, An absorption liquid supply port for supplying an absorption liquid to an absorption liquid flow path along the other surface of the gas permeable membrane, and the absorption liquid that has absorbed a specific component gas in the gas to be separated through the gas permeable film. An absorption liquid outlet for taking out the first container from the first container and a gas outlet for letting out residual gas from the first container are provided.

  The diffusion part is disposed on the one surface of the second container, the liquid-permeable porous membrane that is disposed inside the container and contacts the absorbing liquid taken out from the first container, and the liquid-permeable porous membrane. An absorption liquid supply port for supplying the absorption liquid taken out from the first container to the absorption liquid flow path, and a reduced pressure from the absorption liquid side through the liquid permeable porous membrane in the second container A decompression device for forming the space is provided, and is provided at the rear stage of the absorption unit.

  In the gas separation device of the present invention, the absorption liquid supplied to the second container based on such a configuration is injected into the reduced pressure space through the micropores of the liquid-permeable porous membrane, thereby The specific component gas in the absorption liquid supplied to the container is diffused into the decompression space and recovered from the gas outlet of the decompression device.

  Preferred forms of the gas permeable membrane in the first container and the liquid permeable porous membrane in the second container in the gas separation apparatus of the present invention are the same as those described for the gas separation method of the present invention.

  In the gas separation method and gas separation apparatus of the present invention, the gas to be separated and the absorption liquid are brought into gas-liquid contact with each other through the gas permeable membrane, so that the specific component gas in the separation gas is absorbed by the absorption liquid. Even if solid gas is contained in the gas to be separated, it hardly enters the absorption liquid, and the clogging of the porous membrane used in the subsequent diffusion process can be reduced, and the great effect of extending its life is achieved. is there. Furthermore, the absorption of gas-liquid contact through the gas-permeable membrane increases the gas-liquid contact area compared to the absorption by a packed tower having the normal packing surface as the gas-liquid contact surface. In addition, by using a porous membrane to dissipate due to a pressure difference, the required energy can be greatly reduced, and the cost required for gas separation can also be reduced.

  The present invention is a widely applicable technique that can be applied to various gas separations by selecting an absorbing liquid according to a specific component gas to be separated. An example of the specific component gas to be separated is carbon dioxide gas, and an appropriate absorbent in that case is as described above.

An embodiment of the present invention will be described below.
FIG. 1 is a schematic cross-sectional view of a gas separation apparatus, and represents an outline of one embodiment in which the present invention is applied to a carbon dioxide separation apparatus. In this embodiment diagram, carbon dioxide-containing gas is used as the gas to be separated, and carbon dioxide is taken up as the specific component gas.

The absorption device 1 composed of a membrane module introduces a CO ₂ -containing gas on one side with respect to a gas permeable membrane provided therein, and flows an absorption liquid on the other side, and CO ₂ is passed through the membrane. Absorbed in the absorbent. The absorption liquid that has absorbed CO ₂ is sent from the absorption device 1 to the diffusion device 3 including the second membrane module by the pump 2. In addition, the upper part of the absorption apparatus 1 in FIG. 1 is an absorption liquid supply part, and a lower part is an absorption liquid extraction part.

The diffusion device 3 introduces an absorbing solution that absorbs CO ₂ into one side of the liquid-permeable porous membrane provided therein, and draws the other side with a decompression device (vacuum pump) 4 to reduce the pressure. Put it in a state. The absorbing liquid is injected into the reduced pressure space through the micropores of the porous membrane, whereby CO ₂ in the absorbing liquid is diffused and the absorbing liquid is regenerated. The diffused CO ₂ is cooled by the heat exchanger 5 via the decompression device 4, and water coexisting with CO ₂ is separated and removed to recover CO ₂ .

On the other hand, the absorption liquid regenerated by the diffusion device 3 is sent by the pump 6 and introduced into the absorption device 1 to be used again for absorbing CO ₂ . In this way, the absorption liquid is circulated between the absorption device 1 and the diffusion device 3.

  FIG. 2 schematically shows an absorption device 10 as an example of the absorption device 1 in the gas separation device of FIG. 1, and a membrane module having a structure in which a gas and an absorption liquid are in gas-liquid contact via a hollow fiber membrane 12. It is a vertical sectional view of the absorption device consisting of. In FIG. 2, only one hollow fiber membrane is shown for simplification. However, in reality, a large number of hollow fiber membranes 12 are bundled to form a module, and the modularized product is stored in the absorption device 10. Is provided.

  The gas flow path 10a outside the hollow fiber membrane 12 has a gas inlet 13a at the lower end and a gas outlet 13b serving as a gas outlet at the upper end, and the gas flows from the lower side to the upper side of the absorber 10. Supplied as The absorbent channel 10b inside the hollow fiber membrane 12 has an absorbent inlet 14a at the upper end and an absorbent outlet 14b as an absorbent outlet at the lower end. Supplied to flow toward the side.

  1 and 2, the gas is supplied so as to flow from the upper side to the lower side of the absorption device 10, and the absorption liquid is supplied so as to flow from the lower side to the upper side of the absorption device 10. In addition, the flow direction of the gas and the absorbing liquid may be reversed.

  FIG. 3 schematically shows a diffusion device 30 as an example of the diffusion device 3 in the gas separation device of FIG. 1, in order to inject the absorbing liquid from the micropores 33 of the porous hollow fiber membrane 32 into the reduced pressure space. It is a vertical sectional view of a diffusion device comprising the membrane module. Although only one porous hollow fiber membrane is shown in FIG. 3 for the sake of simplification, in reality, a number of hollow fiber membranes 32 are bundled into a module, and the modularized one is the diffusion device 30. It is provided within.

  The absorption liquid flow path 30b inside the porous hollow fiber membrane 32 has an absorption liquid inlet 34a at the lower end, and the absorption liquid is supplied so as to flow from the lower side toward the upper side. A space 30a outside the porous hollow fiber membrane 32 has a gas discharge port 35 at the upper end and an absorbent discharge port 34b at the lower end, and the gas discharge port 35 is connected to the decompression device (vacuum pump) 4 to 30a is kept in a reduced pressure state.

  In the embodiment, an example is shown in which carbon dioxide is separated and recovered as a specific component gas to be separated from the gas to be separated, but the specific component gas to be separated is not limited to carbon dioxide.

In this case, the absorbing liquid selectively absorbs other specific component gases, for example, sulfur dioxide can be separated by using an aqueous solution of sulfite with respect to a sulfur dioxide (SO ₂ ) -containing gas. it can. Thus, the present invention can be similarly applied to specific component gases other than carbon dioxide.

  The present invention relates to gas discharged from thermal power generation, steelmaking, cement industry or incinerators, biogas and digestion gas generated in sewage and environmental treatment, gas separation process and gas purification process in petrochemical industry, etc. It can be used to separate and recover carbon dioxide gas or other target gas from the generated gas or gas generated in the semiconductor industry.

It is a schematic sectional drawing of the gas separation apparatus of one Example. It is a schematic sectional drawing which shows an example of the absorber in the Example. It is a schematic sectional drawing which shows an example of the diffusion apparatus in the Example.

Explanation of symbols

1,10 Absorption device 2,6 Pump 3,30 Dissipation device 4 Pressure reducing device (vacuum pump)
5 Heat exchanger 10a Gas flow path 10b Absorption liquid flow path 12 Hollow fiber membrane 13a Gas inlet 13b Gas discharge port 14a Absorption liquid inlet 14b Absorption liquid discharge port 30a Porous hollow fiber membrane outer space 30b Absorption liquid flow path 32 Porous hollow Thread membrane 33 Fine hole 34a Absorbent inlet 34b Absorbent outlet 35 Gas outlet

Claims (4)

An absorption step in which the absorption liquid absorbs the specific component gas in the separation gas by bringing the separation gas and the absorption liquid into gas-liquid contact through a gas permeable membrane;
Subsequently, the absorption liquid is brought into contact with the reduced pressure space from the absorption liquid side through the liquid-permeable porous membrane, and the absorption liquid is sprayed into the reduced pressure space through the micropores of the porous film, thereby absorbing the absorption liquid. A gas separation method including a diffusion step of diffusing the specific component gas therein to a reduced pressure space.   The gas separation method according to claim 1, wherein the specific component gas is carbon dioxide, and the absorption liquid is a solution containing at least one of amine, amino acid, amino acid salt, and carbonate. A first container, a gas permeable membrane disposed in the container and brought into gas-liquid contact, a gas supply port for supplying a gas to be separated to one surface of the membrane, and an absorbing liquid along the other surface of the membrane An absorption liquid supply port for supplying an absorption liquid to the flow path, an absorption liquid extraction port for taking out the absorption liquid that has absorbed the specific component gas in the gas to be separated through the membrane, and the remainder from the container An absorption part having a gas outlet for discharging gas to the outside;
A second container, a liquid-permeable porous membrane disposed in the second container and in contact with the absorbent taken out of the first container, and an absorbent along one surface of the porous membrane An absorption liquid supply port for supplying the absorption liquid taken out from the first container to the flow path, and a space for forming a reduced pressure space in the second container from the absorption liquid side through the porous membrane A pressure reducing device, and a dissipating part provided at a subsequent stage of the absorbing part,
The specific component gas in the absorption liquid supplied to the second container is diffused into the reduced pressure space by injecting the absorption liquid supplied to the second container to the reduced pressure space through the micropores of the porous membrane. A gas separation device that recovers from the gas outlet of the decompression device.   The gas separation device according to claim 3, wherein the gas permeable membrane of the absorption part is a gas permeable non-porous membrane or a hydrophobic porous membrane.

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