JP2005052762A - Method and system for treating gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a system for treating gas, by which carbon dioxide is removed and hydrogen is produced efficiently and stably at a low cost. <P>SOLUTION: The system for treating the gas is provided with a gas treatment apparatus 1 which is provided with an electrolyte 10 through which sodium ions are permeated, an anode 11 which is arranged in the electrolyte 10 and to which an aqueous solution of a sodium compound is supplied, and a cathode 12 which is arranged in the electrolyte 10 and to which the gas to be treated where water or a sodium hydroxide aqueous solution is mixed, is supplied, and separates/removes the carbon dioxide in the gas as a carbonate and produces hydrogen gas on the cathode 12 side by applying DC voltage between the cathode 12 and the anode 11, and the system is provided with a means 14 for injecting water into a supplying line of the gas to be treated in the apparatus 1 by means of carrier gas, solubilizing the carbonate produced on the cathode 12, and discharging the solubilized carbonate to the outside of this system. When the gas to be treated is supplied to the apparatus 1, the sodium hydroxide aqueous solution can be injected together with water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a gas processing method and system, and more particularly, to a method for removing carbon dioxide in a gas and generating hydrogen gas.

  In December 1997, Kyoto City hosted the Third Conference of the Parties to the Climate Change Framework Convention (Global Warming Prevention Council, COP3) to determine a new international framework for the prevention of global warming since 2000 It was. At the Kyoto Conference, the “Kyoto Protocol” was adopted, including numerical targets for reducing greenhouse gases in developed countries as a whole by more than 5% from 1990 to 2008. Among them, the numerical targets for Japan are The reduction is 6%.

Carbon dioxide (CO ₂ ) generated by the combustion of energy accounts for most of the anthropogenic emissions of greenhouse gases. As a result of Japan's active energy conservation efforts since the oil crisis, the energy efficiency of the industrial sector is at the highest level in the world, and the primary energy consumption per GDP is about one-third that of the United States and about two-minutes that of Germany. It is at a low level compared with 1 and other developed countries.

  However, with the remarkable growth in energy consumption, especially in the transportation and consumer sectors in recent years, the amount of carbon dioxide emissions resulting from energy has increased significantly by more than 8% in 1995 compared to 1990. For this reason, it is necessary to immediately undertake the maximum possible measures to achieve the Kyoto Protocol goals.

Under the Kyoto Protocol, greenhouse gases are carbon dioxide (CO ₂ ), methane gas (CH ₄ ), nitrous oxide (N ₂ O), hydrofluorocarbon (HFC), perfluorocarbon (PFC), sulfur hexafluoride (SF ₆ ) However, greenhouse gas emissions in Japan increased by 8.6% in 1995 compared to 1990 levels. Of these, carbon dioxide, which accounts for nearly 90% of the total, and is closely related to the overall economic and social activities, is generated by the combustion of energy. The proportion of CO ₂ in various exhaust gases is about 10% for diesel engine exhaust, about 13% for boiler exhaust, and about 40% for sludge digestion gas discharged from sewage treatment plants and food factories. It is known that there is.

  Currently, development of methods and apparatuses for decomposing and recovering carbon dioxide is underway in many fields. In particular, a pressure swing method in which adsorption / desorption is performed using a zeolite catalyst or the like near room temperature (Non-patent Document 1), a membrane separation method using a polymer membrane (Patent Document 1), a method of dissolving in water, an alkaline aqueous solution, or the like. (Non-Patent Document 2) and the like have been developed, and these have become mainstream.

  In the pressure swing method, carbon dioxide adsorbing substance such as zeolite is filled and carbon dioxide is adsorbed. And after adsorption | saturation is saturated, it hold | maintains to a low pressure or high temperature state, and discharge | releases the adsorbed carbon dioxide.

  In the membrane separation method, a pressurized gas is introduced into one of carbon dioxide selectively permeable membranes (poly ([1-trimethylsilyl]) propylene, polydimethylsiloxane, etc.) to selectively permeate carbon dioxide. This is a method for increasing the concentration.

There are two main dissolution methods. The first method uses a phenomenon in which carbon dioxide is absorbed into an aqueous sodium hydroxide solution to form carbonate (Na ₂ CO ₃ ).

2NaOH + CO ₂ → Na ₂ CO ₃ + H ₂ O
The second method uses a thermal decomposition / absorption method of sodium hydrogen carbonate (NaHCO ₃ ).

2NaHCO ₃ → Na ₂ CO ₃ + CO ₂ + H ₂ O (above 65 ° C.)
Na ₂ CO ₃ + CO ₂ + H ₂ O → 2NaHCO ₃ (room temperature to 50 ° C.)
In the automobile industry, development of fuel cell vehicles has been promoted in recent years as one of the measures against global warming, and the demand for hydrogen gas used as the fuel is increasing. The following methods are mainly known as industrial methods for producing hydrogen gas (Non-patent Document 2).

  1) Water electrolysis method In this method, 15 to 20% caustic soda solution is electrolyzed using a nickel plating electrode to obtain by-product oxygen along with pure hydrogen.

  2) Gasification of coke This is a method for producing water gas using coke as a raw material. Normally, intermittent hydrogen generation furnaces have been known for a long period of time in which air is blown into red-hot coke and burned, and blows that raise the furnace temperature and steam that feeds steam to generate gas have been known for a long time. In addition, a continuous water gas generation furnace that introduces a mixture of oxygen and water vapor has appeared. Here, the water gas undergoes purification steps such as dust removal, water washing, and desulfurization, and carbon monoxide in the gas is converted to hydrogen using a water gas conversion reaction, and carbon dioxide produced at the same time is removed by adsorption. Except for a small amount of carbon monoxide, it is hydrogen without impurities.

  3) Full gasification of coal This is a method of gasification by sending oxygen and water vapor into fine coal or pulverized coal, and the main reaction is a reaction of hydrocarbon, oxygen and water vapor, so that hydrogen, carbon monoxide, or A gas mainly composed of methane is produced. Most recently developed methods such as winker gas generator, copper soot gas generator, and Otto-Rummel gas generator belong to this. The properties of the product gas, the purification method, and the modification method are almost the same as the method 2).

  4) Gasification of petroleum, natural gas, coke oven gas, petroleum refining waste gas, etc. Gasification is used when the raw material is liquid fuel, and it is called metamorphism when it is a gaseous fuel. Are the same in that a gas having the same property is obtained by the reaction of hydrocarbon and oxygen or water vapor. Moreover, the above-mentioned complete gasification of coal can be said to be the same reaction using coal, which is a solid hydrocarbon, as a raw material. In contrast to normal pressure gas generators such as copper soot check gas generators and fauser-Montecatini gas generators, the development of pressurized gas generators such as texaco gas generators and shell gas generators has been remarkable recently. Catalytic catalytic cracking methods are widely used to transform gaseous hydrocarbons.

  5) Separation from coke gas This is a method in which gas from a coke gas generator is compressed and cooled to liquefy and remove all gas other than hydrogen to separate hydrogen. Remove sulfur compounds from the furnace gas in a conventional manner, compress to about 12 atmospheres, wash with water and caustic soda solution, remove carbon dioxide, water at -40 ° C, methane and other hydrocarbons at -60 ° C, monoxide Carbon is condensed and removed, and hydrogen is separated.

6) Reaction between iron and water vapor This method is called the Methaschmitt method. That is, rye oresite (FeCO ₃ ) is baked to Fe ₃ O ₄ , further reduced with water gas (CO + H ₂ ) or the like to FeO, and by reacting this with H ₂ O, FeO is oxidized, Along with this, pure hydrogen is obtained.
Saburo Nagakura et al. “Science and chemistry dictionary”, Iwanami Shoten Japanese Patent No. 2521884 (pages 2 to 4) "Chemical Dictionary" edited by the Editorial Committee of the Chemical Dictionary, Kyoritsu Publishing

  In the pressure swing method, water components are adsorbed in addition to carbon dioxide, so a dehydrator must be provided in the previous stage. Further, continuous processing is impossible, and at least two processing towers are required, and additional equipment such as heating equipment and vacuum equipment equipment is required, resulting in a large-scale equipment.

  The membrane separation method using a polymer membrane is difficult and expensive to optimize the gas pressure and carbon dioxide permeability received by the membrane itself. Furthermore, in general, gases such as nitrogen and oxygen permeate in addition to carbon dioxide, so that complete separation becomes difficult. In addition, additional equipment such as a gas pressurizer is also large.

The first dissolution method is a very simple method, but the post-treatment of the produced carbonate (Na ₂ CO ₃ ) is difficult (neutralization with hydrochloric acid), so far it has been disposed of after heating and drying. This is the current situation. Moreover, in the 2nd melt | dissolution method, since the absorption amount and absorption rate with respect to a carbon dioxide of sodium hydrogencarbonate are very slow with respect to sodium hydroxide aqueous solution, it becomes inefficient.

  On the other hand, in the method for producing hydrogen gas, the method 1) has advantages in using water as a raw material, but has the following disadvantages. In other words, it requires pure water, requires a large number of electrolytic cells, is not sufficiently adaptable to excess or shortage of current, has many problems in aging due to carbonation of the electrolyte, floor area, initial cost, Economic disadvantage. Therefore, in recent years, waste gas such as heavy oil and natural gas has been used as a hydrogen source, and therefore, the method 2-5) has become the mainstream.

  However, in the methods 2 to 6), the facility becomes large, which causes an increase in initial cost and running cost. Further, in the hydrogen gas production process, carbon dioxide such as carbon monoxide and carbon dioxide is by-produced, and a process for removing this must be provided, and the production efficiency of hydrogen gas is not increased.

  As described above, the conventional carbon dioxide removal technology and hydrogen production technology have problems that a large-scale apparatus is required, initial cost and running cost are high, and carbon dioxide removal rate and hydrogen generation efficiency are low. In particular, since most of the sources of carbon dioxide, which account for the majority of greenhouse gases, are sewage treatment plants and factories, it is necessary to establish a method for carbon dioxide removal and hydrogen generation that takes into account the running costs of these facilities. Necessary.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a gas processing method and system for performing carbon dioxide removal and hydrogen generation more inexpensively and efficiently and more stably.

In order to solve the above problems, the gas treatment method of the present invention is provided with an anode and a cathode in an electrolyte that transmits sodium ions, an aqueous solution of a sodium compound is brought into contact with the anode, and a gas to be treated is provided to the cathode. A step of separating and removing the carbon dioxide component in the gas in the form of carbonate on the cathode side by applying a DC voltage between the two electrodes, and converting the water component into hydrogen gas;
And a step of injecting water or an aqueous sodium hydroxide solution into the supply line of the gas to be treated with a carrier gas to make the carbonate produced on the cathode into a solution and to discharge it out of the system.

The gas treatment system of the present invention includes an electrolyte that permeates sodium ions, an anode that is provided in the electrolyte and is provided with an aqueous solution of a sodium compound, and a cathode that is provided in the electrolyte and is provided with a gas to be treated. A gas treatment device that applies a DC voltage between the two electrodes to separate and remove carbon dioxide in the gas in the form of a carbonate on the cathode side and generate hydrogen gas;
And a means for injecting water or an aqueous sodium hydroxide solution into the gas supply line of the gas processing apparatus by a carrier gas to make the carbonate produced on the cathode into a solution and to discharge it from the system. To do.

  According to the gas processing method and the gas processing system of the present invention, the carbonate formed by injecting water into the gas supply line to be processed with the carrier gas to make the carbonate occluded at the cathode into an aqueous solution and the carrier gas flow. The aqueous solution is forcibly excluded. Thus, the occluded carbonate is easily removed from the system, and a new reaction surface with the gas to be treated is secured on the cathode. Therefore, efficient and continuous carbon dioxide removal and hydrogen generation are possible. In addition, by injecting water into the gas to be treated, carbon dioxide can be removed and hydrogen can be generated at room temperature, so that energy costs can be suppressed and an electrolyte membrane having a low heat-resistant temperature can be used. it can. Therefore, the electrolyte membrane used in the present invention does not need to consider the heat-resistant temperature and may be any one that allows sodium ions to migrate. And if sludge digestion gas and biogas are used as gas to be treated, these gases can be converted into high energy gas rich in methane and hydrogen. The carrier gas includes air or nitrogen gas. Biogas means gas generated by the activities of humans and other animals.

  In addition to water, an aqueous sodium hydroxide solution may be injected with a carrier gas. By injecting a sodium hydroxide aqueous solution into the gas supply line to be treated, carbon dioxide in the gas to be treated is absorbed to some extent, so that the amount of carbon dioxide reacted at the cathode of the gas treatment device can be reduced, Power consumption can be further reduced. Further, by introducing a sodium hydroxide aqueous solution or a carbonate aqueous solution generated by absorbing carbon dioxide into the gas processing apparatus, the conductivity of the interface between the electrolyte membrane and the cathode in the gas processing apparatus can be maintained. At the same time, the concentration of sodium ions on the cathode increases, and the operating characteristics (carbon dioxide removal ability and hydrogen production ability) of the gas treatment apparatus are stabilized and improved. If a pipe for supplying the gas to be processed to the gas processing apparatus is provided with a mixing pipe for mixing the gas to be processed and sodium hydroxide, the contact time between the gas to be processed and sodium hydroxide is secured, It will increase even more.

  According to the gas processing method and system of the present invention, carbonate is formed by injecting water into the supply line of the gas to be processed with the carrier gas to make the carbonate occluded at the cathode into an aqueous solution and by the carrier gas flow. The aqueous solution is forcibly excluded. As a result, the occluded carbonate is easily removed from the system, and a new reaction surface with the gas to be treated is secured on the cathode, so that efficient and continuous removal of carbon dioxide and generation of hydrogen are achieved. Can be done. In addition, by injecting water into the gas to be treated, carbon dioxide can be removed and hydrogen can be generated at room temperature, so that energy costs can be reduced and the heat resistant temperature of the electrolyte used in the present invention is taken into consideration. This is unnecessary, and the initial cost of the device system can be reduced. If sludge digestion gas or biogas is used as the gas to be treated, these gases can be efficiently converted into high energy gas rich in methane and hydrogen.

  In addition, by injecting an aqueous sodium hydroxide solution in addition to water, carbon dioxide in the gas to be treated is absorbed to some extent, and the amount of carbon dioxide reacted at the cathode of the gas treatment device can be reduced. Electric power can be further reduced. Further, by introducing a sodium hydroxide aqueous solution or a carbonate aqueous solution obtained by absorbing carbon dioxide into the gas treatment device, the conductivity of the interface between the electrolyte membrane and the cathode in the gas treatment device can be maintained. At the same time, the concentration of sodium ions on the cathode increases, and the operating characteristics (carbon dioxide removal ability and hydrogen production ability) of the gas treatment apparatus are stabilized and improved.

  As described above, according to the present invention, carbon dioxide can be removed and hydrogen can be generated more inexpensively and efficiently.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic view of a gas processing system of the present embodiment. The gas processing system includes a water injection unit 14 in a gas supply system to be processed in the gas processing apparatus 1.

The illustrated gas processing apparatus 1 includes an electrolyte 10 provided with an anode 11 to which a sodium compound aqueous solution (referred to as Na ⁺ source in FIG. 1) is supplied and a cathode 12 to which a gas to be processed is supplied. And a power source 13 for applying a DC voltage therebetween.

The electrolyte 10 is a polymer electrolyte membrane having a sodium ion exchange function. Examples thereof include those based on fluororesin or vinyl chloride resin. Furthermore, it is formed by including a sulfonic acid resin, a perfluorocarbon sulfonic acid resin, a polytrifluorostyrene sulfonic acid resin, a polystyrene sulfonic acid resin, a phenol sulfonic acid resin, or the like based on a copolymer of styrene and divinylbenzene. Are illustrated. Other electrolytes include β-alumina (Na ₂ O · 11Al ₂ O ₃ ), NASICON (Na _{1 + X} Zr ₂ P _3-X Si _X O ₁₂ , X is a real number, 0 <X <3), etc. Is exemplified.

As the sodium compound aqueous solution, a sodium hydroxide (NaOH) aqueous solution, a sodium carbonate (Na ₂ CO ₃ ) aqueous solution, a sodium hydrogen carbonate (NaHCO ₃ ) aqueous solution, or the like is employed.

  Examples of the anode 11 and the cathode 12 include Pt, Au, Cr, Cu, Ni, and oxides thereof, and porous electrodes are used. The electrode can be formed in the electrolyte 10 by screen printing, brushing, vapor deposition, thermal spraying, dip coating, or the like, or by pressing a metal fiber (porous body).

  As the power source 13, a power source having a function of applying a DC voltage is adopted, and a known one may be used. As a power source for applying the voltage, a general constant potential power source (potentiostat or the like) can be used, but a power source having a variable current density is preferably used. One means for adjusting the current density is adjustment of the applied voltage.

  Here, FIGS. 3 and 4 show an embodiment of the gas processing apparatus 1.

The gas processing apparatus shown in FIG. 3A is a cell 50 configured by sandwiching an electrolyte 50 including an anode 11 and a cathode 12 between an anode side frame 51 and a cathode side frame 52. At this time, the anode side frame 51 is provided with a flow path for temporarily retaining a sodium compound aqueous solution (referred to as Na ⁺ source in the figure), a supply pipe 511 for supplying this aqueous solution, and this aqueous solution. And a discharge pipe 512 for discharging the gas. Similarly, the cathode side frame body 52 is provided with a flow path for temporarily retaining the gas to be processed, a supply pipe 521 for supplying the gas to be processed, and a discharge pipe 522 for discharging the processing gas. Is connected. A bypass plate 523 is provided in the flow path of the anode side frame 51 and the cathode side frame 52. In the cathode side frame body disclosed in FIG. 3A, a single bypass plate 523 is provided, but the present invention is not limited to this, and the frame bodies 51 and 52 shown in FIG. A plurality of them may be provided. With such a configuration, the introduced gas to be treated and the water or sodium compound aqueous solution contained therein can be uniformly supplied to the anode surface and the cathode surface of the electrolyte 10, so that the carbon dioxide removal efficiency and the hydrogen concentration can be reduced. Production efficiency increases.

  Further, as shown in FIG. 3C, a plurality of gas processing apparatuses having a cell structure are installed according to the load amount of the gas to be processed. The gas processing apparatus according to this embodiment has a configuration in which three cells 50 are installed. At this time, manifolds 53, 54, 55, and 56 are installed on the side surfaces of the apparatus. A supply pipe 121 for supplying a gas to be processed is connected to the manifold 53. A discharge pipe 122 for discharging the processing gas is connected to the manifold 54. A supply pipe 111 for supplying a sodium compound aqueous solution is connected to the manifold 55. A discharge pipe 121 for discharging the sodium compound aqueous solution is connected to the manifold 56.

FIG. 4A shows a configuration example when two electrolytes 10 are laminated. The number of stacked layers is determined by the load amount of the gas to be processed. As shown in the drawing, two electrolytes 10 are laminated via a separator 62, and plates 61 and 63 are provided from above and below, respectively. At this time, the plate 61 is provided with a flow path of a sodium compound aqueous solution (Na ⁺ source in the figure). A flow path for the gas to be processed is provided on the upper surface of the separator 62, and a flow path for the sodium compound aqueous solution is provided on the lower surface. The separator 53 is provided with a flow path for the gas to be processed. 4C, a manifold 64 provided with a supply pipe 121 is provided on the inflow side of the gas to be processed, and a manifold 65 provided with a discharge pipe 122 is provided on the exhaust side of the process gas. The A manifold 66 provided with an inflow pipe 111 is installed on the inflow side of the sodium compound aqueous solution, and a manifold 67 provided with a discharge pipe 112 is installed on the discharge side. Note that, like the partition plate 621 in the separator 62 illustrated in FIG. 4B, a plurality of partition plates may be provided in the flow paths provided in the plates 61 and 63 and the separator 62. With such a configuration, the introduced gas to be treated and the water contained therein or the sodium compound aqueous solution described later (Embodiment 2) can be uniformly supplied to the anode surface and the cathode surface of the electrolyte 10. In addition, the carbon dioxide removal efficiency and the hydrogen generation efficiency are increased.

In this embodiment, the sodium compound aqueous solution (Na ⁺ source) is introduced from the adjustment tank 3 by the pump P1. The surplus sodium compound aqueous solution is returned to the adjustment tank 3 through the discharge pipe 112. The adjustment tank 3 includes a tank 30 for temporarily storing a sodium compound aqueous solution to be supplied to the anode 11. At this time, the sodium ion concentration of the liquid phase in the tank 30 is adjusted to be constant. For this purpose, the tank 30 includes an ion concentration measuring means 31 for measuring the sodium ion concentration, and a pipe 32 for supplying a high-concentration sodium ion source and water. Valve means that opens and closes based on the liquid phase ion concentration is provided. As the ion concentration measurement means, for example, a pH measurement function is provided, and the concentration of sodium ions is calculated based on the pH value.

  Further, the gas to be processed is introduced into the gas processing apparatus 1 through the pipe 100. The pipe 100 is provided with water injection means 14.

  FIG. 5 is a schematic view showing an embodiment of the water injection means. The water injection means 14 injects water into the pipe 100 with a carrier gas. Further, water is appropriately continuously or intermittently injected according to the amount of carbonate occluded in the cathode 12 in the gas treatment apparatus 1. The water injection means 14 includes a tank 140 that stores water, a pipe 141 that is introduced into the liquid phase in the tank 140 and supplies a carrier gas, and a pipe 142 that discharges the water in the tank 140 together with the carrier gas. Is provided. Examples of the carrier gas include air and nitrogen gas. The air may contain a carbon dioxide component. The flow rate of water is preferably set to a level that does not hinder the supply of the gas to be processed and a level at which the aqueous carbonate solution is generated at the cathode 12. In order to prevent the backflow of water, the pipe 142 may be provided with a check valve, and the connection position between the pipe 100 and the pipe 142 may be set higher than the installation position of the supply pipe 121.

  On the other hand, the processing gas is supplied to the gas-liquid separation tank 2 together with the carbonate aqueous solution generated at the cathode 12 and subjected to gas-liquid separation processing. The gas-liquid separation tank 2 retains an aqueous carbonate solution.

Next, an operation example of the gas processing system of the present embodiment will be described with reference to FIG. Here, a case where the sodium ion source is a sodium hydroxide aqueous solution (hereinafter referred to as NaOH aqueous solution) and the gas to be treated is a gas containing CH ₄ and CO ₂ will be described.

Carbon dioxide gas removal and hydrogen generation in the gas treatment system are performed by applying a DC voltage between the anode 11 and the cathode 12. That is, as shown in FIG. 1, an aqueous NaOH solution is supplied from the supply pipe 111 to the anode 11 side, and the anode 11 is immersed in this sodium ion source. Further, the gas to be processed is supplied from the supply pipe 121 to the cathode 12 side. The gas to be treated contains water (H ₂ O) by the water injection means 14. Here, when a DC voltage is applied from the power source 13 between the anode 11 and the cathode 12, the following reaction occurs on the surface of the anode 11 in contact with NaOH.

NaOH → Na ⁺ + OH ⁻ (1)
2OH ⁻ → 1 / 2O ₂ + H ₂ O + 2e ⁻ (2)
At this time, sodium ions (Na ⁺ ) pass through the anode 11, migrate through the electrolyte 10, and reach the cathode 12. On the other hand, electrons (e ⁻ ) released on the anode 11 side reach the cathode 12 via the power source 13.

Here, when carbon dioxide (CO ₂ ) and moisture (H ₂ O) in the gas phase come into contact with the surface of the cathode 12, the following reaction occurs.

Na ⁺ + e ⁻ + CO ₂ + H ₂ O → NaHCO ₃ + ½H ₂ (3)
2Na ⁺ + CO ₂ + H ₂ O + 2e ⁻ → Na ₂ CO ₃ + H ₂ (4)
In this way, carbon dioxide contained in the gas to be treated is fixed to the surface of the cathode 12 in the form of carbonate, so that it is separated and removed and hydrogen gas is generated. Further, the carbonate produced at the cathode 12 is easily made into an aqueous solution by the water supplied from the water injection means 14. Then, the carbonate aqueous solution is forcibly discharged out of the apparatus 1 by the introduced carrier gas flow, and a reaction surface with the gas to be treated is newly secured on the cathode 12. Therefore, continuous carbon dioxide removal and hydrogen generation are possible. Further, by supplying the gas to be treated mixed with water to the gas processing apparatus 1, it becomes possible to remove carbon dioxide and generate hydrogen at room temperature. The carbonate aqueous solution is supplied to the gas-liquid separation tank 2 together with the processing gas and subjected to gas-liquid separation processing. At this time, the carbon dioxide component remaining in the gas is absorbed and removed by the aqueous carbonate solution. The carbonate aqueous solution collected in the gas-liquid separation tank 2 is converted into a sodium hydroxide aqueous solution in the regeneration tank 4 and then returned to the adjustment tank 3 by the pump P2. An example of the regeneration tank 4 is disclosed in Japanese Patent Application No. 2002-343508 (paragraph numbers (0060) to (0077) and FIG. 5).

  As described above, according to the gas processing system according to the present embodiment, it is possible to efficiently remove carbon dioxide and generate hydrogen by injecting water into the gas to be processed. In addition, since carbon dioxide can be removed and hydrogen can be generated at room temperature, the operating temperature is low, such as an electrolyte membrane based on vinyl chloride resin, fluororesin, or perfluorinated sulfonic acid polymer. An electrolyte can be suitably used. Therefore, energy costs can be suppressed, and inexpensive carbon dioxide can be removed and hydrogen can be generated.

  Furthermore, when the gas to be treated is a gas containing methane such as sludge digestion gas or biogas, a high energy gas can be obtained by supplying this gas to the gas treatment system of this embodiment. For example, sludge digestion gas generated in sewage treatment plants and biogas generated in livestock manure facilities can be used as useful energy sources, but the conventional technology can only be used as a heat source particularly in small and medium-capacity treatment plants. I couldn't find it. One reason is that the methane gas concentration is low. Therefore, by supplying sludge digestion gas and biogas to the gas treatment system, these gases can be converted into high energy gas rich in methane and hydrogen. This high energy gas can be used effectively such as sold as fuel for fuel cells, gas turbines, or other fuels.

(Embodiment 2)
FIG. 2 shows a schematic diagram of the gas processing system of the present embodiment. Components having the same configuration as the means disclosed in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted as appropriate.

  The gas processing system of this embodiment includes a sodium hydroxide aqueous solution injection means 15 for injecting a sodium hydroxide aqueous solution into a gas supply line to be processed to the gas processing apparatus 1 using a carrier gas. Similar to the water injection means 14 shown in FIG. 5, the sodium hydroxide aqueous solution injection means 15 supplies the carrier gas introduced into the tank 150 storing a sodium hydroxide aqueous solution having a constant concentration and the liquid phase in the tank 150. And a pipe 152 for discharging water in the tank 150 together with the carrier gas. Examples of the carrier gas include air and nitrogen gas. For example, an aqueous sodium hydroxide solution adjusted to about 0.1 to 10 mol / l is used.

  The sodium hydroxide aqueous solution injection means 15 injects water continuously or intermittently as appropriate according to the amount of carbonate occluded in the cathode 12 in the gas treatment device 1. When the aqueous sodium hydroxide solution is injected into the pipe 100, a certain amount of carbon dioxide component in the gas flowing through the pipe 100 is absorbed and removed by the aqueous sodium hydroxide solution. Further, in the gas processing apparatus 1, the aqueous solution is easily made into an aqueous solution by the sodium hydroxide aqueous solution supplied with the carbonate generated at the cathode 12. Further, the carbonate aqueous solution is forcibly discharged out of the apparatus 1 by the introduced carrier gas flow, and a reaction surface with the gas to be treated is newly secured on the cathode 12. In addition, the conductivity of the interface between the electrolyte 10 and the cathode 12 is maintained by the sodium hydroxide aqueous solution or the generated carbonate aqueous solution, and the dynamic characteristics (carbon dioxide removal ability and hydrogen production ability) of the gas treatment apparatus are stabilized. Further, since the sodium ion concentration on the surface of the cathode 12 is increased, the carbon dioxide component in the gas is easily absorbed when the gas to be treated comes into contact with the cathode 12, and the carbon dioxide removal efficiency and the hydrogen generation efficiency are further increased. An amount of sodium carbonate or sodium hydrogen carbonate aqueous solution corresponding to the amount of sodium hydroxide aqueous solution introduced is discharged from the gas treatment device 1. If these aqueous solutions are supplied to the regeneration tank 4, the sodium ion source to the anode 11 is discharged. Can be reused as Further, as in the first embodiment, a check valve may be provided in the pipe 102 in order to prevent the back flow of the sodium hydroxide aqueous solution. At this time, the connection position between the pipe 100 and the pipe 152 is preferably set higher than the installation position of the supply pipe 121. The pipe 100 may be provided with a mixing pipe 103 that mixes the gas to be treated and the aqueous sodium hydroxide solution. Although a spiral pipe is disclosed in FIG. 2, the mixing pipe 103 is not limited to the illustrated form as long as the gas to be treated and the sodium hydroxide aqueous solution can be mixed.

Schematic which shows the embodiment example of the gas processing system of this invention. Schematic which shows the embodiment example of the gas processing system of this invention. Schematic which shows the embodiment example of a gas processing apparatus. Schematic which shows the embodiment example of a gas processing apparatus. Schematic which shows the embodiment example of a water injection | pouring means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Gas processing apparatus, 10 ... Electrolyte membrane, 11 ... Anode, 12 ... Cathode, 100 ... Pipe, 103 ... Mixing pipe, 111, 121 ... Supply pipe, 112, 122 ... Discharge pipe, 13 ... Power supply 14 ... Water injection means 15 ... Sodium hydroxide aqueous solution injection means, 140, 150 ... Tank, 141, 142, 151, 152 ... Pipe 2 ... Gas-liquid separation tank 3 ... Adjustment tank, 30 ... Tank, 31 ... Ion concentration meter, 32 ... Pipe

Claims (4)

An anode and a cathode are provided on an electrolyte that transmits sodium ions, an aqueous solution of a sodium compound is brought into contact with the anode and a gas to be treated is provided to the cathode, and a DC voltage is applied between the two electrodes, whereby the cathode side is Separating and removing the carbon dioxide component in the gas in the form of a carbonate and converting the water component to hydrogen gas;
And a step of injecting water or a sodium hydroxide aqueous solution into the supply line of the gas to be treated by a carrier gas to make the carbonate produced on the cathode into a solution and discharging it out of the system. . The gas treatment method according to claim 1, wherein the gas to be treated is sludge digestion gas or biogas. An electrolyte that permeates sodium ions, an anode that is provided in the electrolyte and is provided with an aqueous solution of a sodium compound, and a cathode that is provided in the electrolyte and is provided with a gas to be treated are provided, and a DC voltage is applied between the two electrodes. A gas processing device for separating and removing carbon dioxide in the gas in the form of carbonate on the cathode side and generating hydrogen gas;
And a means for injecting water or an aqueous sodium hydroxide solution into the gas supply line of the gas processing apparatus by a carrier gas to make the carbonate produced on the cathode into a solution and to discharge it from the system. Gas processing system. 4. The gas according to claim 3, wherein, when the sodium hydroxide aqueous solution is injected, a pipe for supplying the gas to be processed to the gas processing apparatus is provided with a mixing pipe for mixing the gas to be processed and sodium hydroxide. Processing system.

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