JP2003103235A - Method and apparatus for removing carbon dioxide by using biomass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for removing carbon dioxide by using biomass, whereby carbon dioxide can be effectively removed from the atmospheric air in an energetically self-sufficient manner. SOLUTION: Biomass B in which carbon dioxide in the atmospheric air has been fixed is ground into an organic matter slurry S, the organic slurry S is subjected to methane fermentation by using methanogens kept at the activation temperature. While the methane gas produced by the fermentation is heated to the decomposition temperature, it is decomposed into hydrogen and solid carbon by contact with a catalyst 14. The carbon dioxide in the atmospheric air is removed in an energetically self-sufficient manner as solid carbon by covering the energy necessary to keep the grinding and activation temperatures and to heat the methane to the decomposition temperature by the combustion energy of the hydrogen. Desirably, the power necessary for the entire system is supported by the system itself by maintaining the methane decomposition reaction by using part of the hydrogen and transforming another part of the hydrogen into electric power and high-temperature water, which keep the temperature of the slurry S, by a fuel battery 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for removing carbon dioxide using biomass, and more particularly to a method and apparatus for removing carbon dioxide in the air or water as solid carbon by mediating biomass.

[0002]

2. Description of the Related Art Carbon dioxide (CO) that causes global warming
Concentrations of greenhouse gases such as ₂ ) in the atmosphere have increased with the increase in fossil fuel consumption since the Industrial Revolution. If current economic growth continued without curbing emissions, atmospheric CO
_{2 The} concentration is currently around 360ppm, while it will be 450ppm in 2030.
ppm, it is expected to reach 700 ppm in 2100. C in the atmosphere
When the O ₂ concentration reaches 700 ppm, the average temperature on the earth is about 2 ° C (1
It is thought that there will be immeasurable effects in various fields such as abnormal weather occurrence, ecosystem disruption and changes in food production, land land loss (reduction of national land) due to sea level rise, etc. . Therefore, for the purpose of reducing the CO ₂ concentration in the atmosphere, the removal of CO ₂ in the atmosphere with emissions of CO ₂ are required.

[0003] Conventionally, as the elemental technology relating to the removal of CO ₂ , a method of membrane separation from the air with a polymer membrane or a ceramic membrane, an adsorption / recovery method such as PSA (Pressure Swing Adsorption), and storage in the deep sea or underground There have been proposed physical and chemical methods such as a method for absorption, a method for absorbing in an organic solvent, a method for reducing and immobilizing to methanol, solid carbon or the like by a catalyst.

FIG. 6 schematically shows a system for reducing and fixing CO ₂ to solid carbon using natural gas (methane, CH ₄ ) as a reducing agent. In the figure, in the one-stage reactor 26
CH ₄ is decomposed into solid carbon and hydrogen by a catalyst (Ni / SiO ₂ catalyst) (endothermic reaction), and the hydrogen and CO ₂ are separated into a two-stage reactor 27
Is converted into CH ₄ and water (steam) at (exothermic reaction),
After this CH ₄ is separated from water in the condenser 28, it is returned to the one-stage reactor 26 together with CH ₄ supplied from the outside and reused as a reducing agent. After all, the net reaction in Figure 6 is CH ₄ + C.
O ₂ → 2C + 2H ₂ O (Equation (3) below).

Further, Japanese Patent Laid-Open No. 2000-271472 discloses that CH ₄ generated by anaerobic treatment of organic waste as shown in FIG.
We have proposed a CO ₂ fixation device that uses Conventional physical and chemical CO ₂ removal methods mainly use high-concentration CO _{2 at the} source.
However, the concentration of CO _{2 in} the atmosphere is extremely dilute, about 360 ppm, and it is necessary to utilize the photosynthetic action of living organisms in order to efficiently remove dilute CO ₂ . Figure 7
The device (A) is proposed from such a viewpoint.

In the apparatus shown in FIG. 7A, CO _{2 in} the atmosphere and biogas (mixed gas of CH ₄ and CO ₂ ) generated in the organic waste treatment section 31 are mixed in a gas mixing / condensing unit 32. Then, in the reaction tank 34, solid carbon and water are produced by causing the reactions of the following formulas (1) and (2) using a catalyst. The net reaction in this case is also the following equation (3) as in the case of FIG. Although the conversion rate of CO ₂ to solid carbon in the equation (2) is not high, as shown in FIG. 7B, the unreacted CO ₂ is circulated and the reaction tank 34
All of the CO ₂ in the gas mixer / condenser 32 is converted into solid carbon and water by being fed into the gas mixer / condenser 32. The apparatus includes a CO ₂ both the atmospheric CH ₄ and CO ₂ in the biogas immobilized as solid carbon, by suppressing the discharge to the outside of the CO _2, the CO ₂ removal rate of the atmosphere It is aimed at improvement.

[0007]

[Chemical 1] CH ₄ → C + 2H ₂ …………………………………………………… (1) CO ₂ ＋ 2H ₂ → C ＋ 2H ₂ O ……………………………… ……………… (2) CH ₄ + CO ₂ → 2C + 2H ₂ O …………………………………………… (3)

[0008]

However, the above-mentioned CO ₂
Each of the fixed removal systems of the above has a problem that energy must be supplied from the outside to remove CO ₂ . The net reaction (equation (3)) in FIGS. 6 and 7 is an exothermic reaction with a small reaction heat. For example, in the system of FIG. 6, the heat recovery from the two-stage reactor 27 and the first-stage reaction of the recovered heat are performed. Considering heat loss in the transfer process to the reactor 26, heat required for reheating CH ₄ separated from water in the condenser 28, and the like, it is presumed that external heat supply is indispensable. Further, in the system of FIG. 7, it is necessary to supply heat necessary for heating the organic waste treatment unit 31, the reaction tank 34, the catalyst regenerator 36 and the like, and drive power of the system.

In the system of FIG. 7, in order to reduce energy supply from the outside, unreacted hydrogen in the reaction tank 34 is recovered by the hydrogen separator 38, and a part of the recovered hydrogen is converted into thermal energy by the hydrogen combustor 40. Converted to organic waste treatment department
It has been proposed that the surplus hydrogen be supplied to the reactor 31, the reaction tank 34, and the catalyst regenerator 36 and the surplus hydrogen be used for power generation (see FIG. 7A). However, the hydrogen produced by Eq. (1) is a substrate necessary for CO ₂ conversion, and the more hydrogen consumed by Eq. (2), the less hydrogen can be recovered.・ There is a limit to power generation. If the amount of hydrogen recovered by the hydrogen separator 38 is increased, the self-sufficiency of energy is improved, but the hydrogen concentration in the reaction tank 34 is reduced, which may lead to a reduction in CO ₂ removal efficiency. That is, in the system of FIG. 7, it is difficult for the energy of the entire system to be self-sufficient.

Consumption of new fossil fuels to remove atmospheric CO ₂ should be avoided as much as possible, and development of a system capable of efficiently removing CO ₂ without external energy supply is desired. There is. Therefore, an object of the present invention is to provide a carbon dioxide removal method and device using biomass that can efficiently remove carbon dioxide in the atmosphere and energy itself.

[0011]

[Means for Solving the Problems] The present inventor
As a result of examining the method of reforming CH ₄ in this biogas into hydrogen by producing methane by subjecting the organism (hereinafter referred to as biomass) to which ₂ is fixed and can be used as an energy resource to methane fermentation, It was concluded that the method of reforming only CH _{4 in} gas to hydrogen without generating CO ₂ would solve the difficult problem of achieving self-sufficiency in removing CO _{2 from} the atmosphere.

CO ₂ in the atmosphere is fixed as an organic substance in the body of plants living on the earth by photosynthesis and the like, and carbon based on CO ₂ is also an organic substance in the body of animals through feeding of the plant. It is stored. Carbon fixed in organisms does not cause a global CO ₂ imbalance even if it becomes CO ₂ again by combustion and diffuses into the atmosphere. For this reason, biomass is drawing attention as an environmentally friendly alternative energy source that does not disturb the global CO ₂ balance even when burned.

[0013] In the reforming reaction to the conventional CH ₄ hydrogen, by adding water vapor to CH ₄ at a high temperature to generate hydrogen and carbon monoxide (CO) (steam reforming reaction, (4)), Furthermore, steam is added to CO to generate hydrogen and CO ₂ (shift reaction,
(Equation (5)). The net reaction is as shown in equation (6) (hereinafter this reaction is called steam reforming). In this reaction, H ₂ O also serves as an H ₂ source, so a large amount of hydrogen is generated, but at the same time CO ₂ is generated.
This CO ₂ does not disturb the global CO ₂ balance as described above, but CO ₂ generation in the system is not preferable for the purpose of removing CO ₂ from the atmosphere. In steam reforming, it is difficult to avoid carbon monoxide (CO) by-product from Eq. (4), but when CO is mixed with H ₂ gas and enters the fuel cell, the electrode catalyst is poisoned, so selective catalytic oxidation is performed. It is necessary to remove it beforehand by the method etc.

[0014]

[Chemical formula 2] CH ₄ + H ₂ O → 2CO + 3H ₂ …………………………………… (4) CO + H ₂ O → CO ₂ + H ₂ ………………………………… ………………… (5) CH ₄ + 2H ₂ O → CO ₂ + 4H ₂ …………………………………………… (6)

CH_FourThat directly decomposes carbon into solid carbon and hydrogen
By the way, there is the above formula (1). According to equation (1), steam reforming
CO or CO like the law₂Is not discharged, so after disassembling
Can be used directly as fuel for fuel cells and the like. Well
CO fixed in biomass ₂Diffused back into the atmosphere
It can be taken out as solid carbon instead of being made to cause it.
CO fixed in biomass₂Take out as solid carbon
As a result, the atmospheric CO₂The concentration can be reduced.

Referring to the embodiment of FIG. 1, the method for removing carbon dioxide using biomass according to the present invention is to pulverize the biomass B having carbon dioxide in the atmosphere fixed into an organic slurry S to activate the organic slurry S at an activation temperature. The methane is fermented by the group of methanogens, and the methane gas from the fermentation is heated to the decomposition temperature to bring it into contact with the catalyst 14 to decompose it into hydrogen and solid carbon. By supplying the energy required for heating with the energy conversion of hydrogen, carbon dioxide in the atmosphere is self-sufficiently removed as solid carbon.

Preferably, a part of the hydrogen supplies heating energy to the decomposition temperature, and another part of the hydrogen is converted into electric power and high temperature water by the fuel cell 17,
The high temperature water from 17 supplies the holding energy of the activation temperature, and the electric power from the fuel cell 17 supplies the grinding energy. More preferably, the main component of the catalyst 14 is nickel, iron,
Alternatively, cobalt is used, and the methane gas is heated to 200 to 900 ° C. and brought into contact with the catalyst 14.

Further, referring to the embodiment of FIG. 1, in the carbon dioxide removing apparatus using biomass of the present invention, the biomass B in which atmospheric carbon dioxide is fixed is mixed with the organic slurry S.
Crushing means 2 and 3 for crushing into a mixture, a fermentation chamber 20 for holding a group of methanogens at a high concentration, and a slurry S introduced into the fermentation chamber 20
Bioreactor 6 having a heat-retaining means 7 for keeping the methane-producing bacteria at the activation temperature, a reaction chamber 16 in which a catalyst 14 for decomposing methane gas from the bioreactor 6 into hydrogen and solid carbon is present, and methane gas in a part of the hydrogen. A methane decomposition means 13 having a heating means 15 for heating the hydrogen gas to a decomposition temperature, and a fuel cell 17 for converting another part of the hydrogen into electric power and high temperature water. Is kept warm and the pulverizing means 2 and 3 are driven by the electric power from the fuel cell 17 to remove carbon dioxide in the atmosphere as solid carbon by energy self-sufficiency.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the embodiment shown in FIG. 1, plants are grown as biomass B in a land or water carbon dioxide (CO ₂ ) immobilization facility 1, and the grown biomass B is used as a unit by crushing means 2 and 3. Grind to a high-concentration organic matter slurry that produces a large amount of methane gas (CH ₄ ) per weight. As the biomass B, terrestrial sugar cane and corn having high CO ₂ utilization efficiency, soybeans and sesame having a high oil content, seagrass having a high growth rate, and other seaweed algae can be used. Is not limited to plants. According to the present invention, many animals and plants inhabiting the earth or a part thereof (vegetables, fruits, vegetable oils, fish and shellfish, meats, etc.) or those of them are provided under the condition that they can be pulverized into the organic matter slurry S. CO for processed products, residues (garbage, etc.), animal excrement, etc.
₂ Can be used as biomass B for removal.

Typical organic substances in the biomass B in which CO ₂ has been converted are polysaccharides, fats, proteins and the like. When these organic substances are crushed into a slurry and methane-fermented by a methanogen group, Along with that, it is gradually decomposed into a simple substance. First, in the first step, the hydrolyzing bacteria in the methanogen group convert polysaccharides into monosaccharides and proteins into amino acids. Next, these compounds are decomposed into lower fatty acids such as acetic acid, butyric acid and propionic acid, and small amounts of alcohols and aldehydes by the acid-producing bacteria in the methanogenic bacteria group. Finally, the methanogens in the group of methanogens produce a gaseous product containing CH ₄ and CO ₂ as main components. The gaseous products are referred to as biogas, CH ₄ and 60% to 70%, contains CO ₂ 30 to 40%.

In order to efficiently remove CO ₂ in the atmosphere, it is necessary to efficiently recover as much biogas G as possible from biomass B. In order to increase the recovery amount of the biogas G, it is effective to grind the biomass B into a slurry having a small particle size, preferably to a particle size of 1 mm or less. In the embodiment shown in FIG. 1, the crusher 2 with a foreign matter separating function separates the non-slurryable portion in the biomass B and crushes the slurryable portion into a predetermined size.
Further, the average number of parts that can be slurried by the fine pulverizer 3 is 100.
Finely pulverize to about micron. In the present invention, since the pulverizers 2 and 3 are driven by energy conversion of a part of hydrogen from the methane decomposition means 13 described later, it is not necessary to supply drive energy for foreign matter separation and pulverization from the outside.

The crushed slurry S is diluted with an amount of water such that the fluidity is improved, for example, an equal amount of water, and temporarily stored in the slurry tank 4 or the like. Not only diluting the slurry S to a high concentration of organic matter can reduce the cost of dilution water, but also reduce the volume of the bioreactor 6 and reduce the heating energy of the reactor, thus improving the energy self-sufficiency of the system. Is effective in. For example, the concentration of organic matter (CODcr value, chemical oxygen demand) of the diluted slurry S is set to 150,000 to 200,000 mg / L (L represents liter, the same applies hereinafter) or more. The stored organic slurry S is gradually fed into the bioreactor 6 by the slurry pump 5.

Since the methane fermentation in the bioreactor 6 is carried out in an anaerobic state, it is not necessary to supply oxygen and energy consumption is small. However, bioreactor 6
In order to efficiently perform methane fermentation, (1) maintaining the organic matter slurry S at a pH of about 6.5 to 8.0, (2) maintaining the slurry S at the activation temperature of the methanogen group,
(3) Maintaining a high concentration of methanogens in the fermentation chamber 20 of the bioreactor 6, (4) No clogging due to a large amount of solid content (SS) contained in the slurry S, etc. Conditions are required.

In the methanogenic bacteria group, the medium temperature range (35-40 ° C)
There is a mesophilic bacterium that exhibits activity in 1. and a thermophilic bacterium that exhibits activity in a high temperature range (52 to 58 ° C). Preferably, thermophilic bacteria having a faster decomposition rate than mesophilic bacteria are used, and required biogas is recovered in a short time. In the present invention, the heat retention means 7 provided in the bioreactor 6 is intended to hold the slurry S at the activation temperature of the methane-producing bacteria group by energy conversion of a part of hydrogen from the methane decomposition means 13 described later. An example of the heat retaining means 7 is
For example, as shown in the embodiment of FIG. 2, it is a heat exchanger of high temperature water heated by combustion of hydrogen and the slurry S in the fermentation chamber 20. The slurry circulation pump 9 shown in FIG. 2 can also be driven by a part of the electric power from the fuel cell 17, which will be described later.

As a method for increasing the concentration of the methanogens in the fermentation chamber 20, the UASB method (Upflow Anaerobic Sludge Blanket) for granulating microorganisms, a fixed bed for filling the fermentation chamber 20 with a carrier to which microorganisms adhere There are laws etc. In the fermentation chamber 20 of the bioreactor 6 shown in FIG. 2, a hollow cylindrical body 22 having an inner diameter of 50 to 70 mm and having a porous peripheral wall 23 made of a nonwoven fabric of glass fiber or carbon fiber as shown in FIG. The supported microorganism carriers 21 are vertically and regularly filled.
By attaching methanogens to the carrier 21, the fermentation chamber
The concentration of microorganisms in 20 can be increased. Further, since the hollow cylindrical carrier 21 is vertically and regularly filled, the biogas G can be prevented from blocking the carrier 21 due to SS or the like by passing through the cylindrical carrier 21.

CH ₄ in the biogas G generated in the bioreactor 6 contains carbon constituting the organic matter in the biomass B, that is, carbon of CO _{2 in} the atmosphere. In the present invention, the carbon atom of CH ₄ in the biogas G is taken out as solid carbon by the methane decomposition means 13 (see the formula (1)). Conventionally, a plurality of catalysts 14 for decomposing CH ₄ into solid carbon and hydrogen, for example, a catalyst containing nickel, cobalt, iron or the like as a main component is known, and such a catalyst 14 is used as a methane decomposition means of the present invention. It can be used by being present in 13 reaction chambers 16.

1 and 4, the reaction system is a gas-solid system, the reactor is a fixed bed reactor, and the catalyst 14 is a solid having a state, size, shape, etc. that can be used in the fixed bed reactor. Although illustrated, the reaction system, the reactor, and the catalyst are not limited to the gas-solid system, the fixed bed reactor, and the fixed bed catalyst, respectively. The reaction system may be, for example, a gas-liquid-solid system. The reactor may be, for example, a fluidized bed reactor, a moving bed reactor or the like. The state of the catalyst may be liquid or gas, and the size and shape of the catalyst may be fine powder, fine particles, powder, small diameter particles, or the like.

In FIGS. 1 and 4, the catalyst is present in the reaction chamber.
One method is to put the catalyst in the reaction chamber in advance.
The method was exemplified, but the catalyst or catalyst precursor was used as a reactant.
CH _FourHow to introduce into the reaction chamber together with gas, beforehand
Reactant CH_FourPut gas in there, and there is a catalyst or
The method of introducing a catalyst precursor can also be adopted.

The catalyst is usually composed of a main catalyst component, a co-catalyst component, and a carrier, and is officially called a supported catalyst, but the catalyst used in the present invention is not limited to the supported catalyst. For example, the catalyst precursor itself is heated in a CH ₄ gas atmosphere to be activated and used as it is as a catalyst, or the catalyst precursor is made into a fluid such as a solution, a sol or a slurry and blown into the heated CH ₄ gas. It can be activated and used as it is as a catalyst.

Since the reaction of the formula (1) is an endothermic reaction, it is necessary to heat CH ₄ by the heating means 15 to a temperature at which the decomposition reaction occurs. The energy required for heating the CH ₄ gas can be covered by a part of hydrogen generated by the methane decomposition means 13. For example, CH ₄ is heated to the decomposition temperature by introducing a part of the hydrogen generated by the methane decomposition means 13 to the heating means 15 and burning it.

In the methane decomposition means 13 of FIG. 4, the main component of the catalyst 14 is nickel, cobalt, iron or the like. In the illustrated example, the shape of the catalyst 14 is spherical (see (A) and (B) in the same figure) or quadrangular pyramid (see (D) in the same figure), but the shape of the catalyst 14 is not limited to the illustrated example. Various shapes such as a cylindrical shape, a honeycomb shape, a granular shape, a spiral shape, a pellet shape, and a ring shape can be adopted. The quadrangular pyramid catalyst shown in FIG. 3D is used when carbon is used and then used as it is as a heat-resistant electromagnetic wave absorber.

In the embodiment of FIG. 4, CH ₄ is added at 200 to 900 ° C.
To contact the catalyst 14. When the temperature is lower than 200 ° C, the conversion rate (hydrogen generation amount) in the decomposition reaction becomes low. On the other hand, if the temperature exceeds 900 ° C, the catalyst life will be shortened and the conversion rate will not decrease, but the final hydrogen generation amount will decrease as a result. The present inventor has experimentally confirmed that by heating CH ₄ to the decomposition temperature and bringing it into contact with the catalyst 14, hydrogen in an amount substantially the same as the theoretical calculated value based on the equation (1) can be produced.

By heating to the decomposition temperature and then contacting with the catalyst 14, CH ₄ is decomposed into solid carbon and hydrogen,
Solid carbon accumulates on the catalyst 14. The crystal structure and shape of the accumulated carbon may vary depending on the type of the catalyst 14, but in the case of the nickel catalyst 14, the accumulated carbon structure can be a hollow graphite filament structure useful as a functional material. When a powder or particulate catalyst is used for a long period of time, the catalyst is subdivided and buried in solid carbon as the solid carbon is produced and grown. Therefore, the catalyst and solid carbon can be separated by a usual method. It will be difficult. In this case, the catalyst content in solid carbon is extremely low because the catalyst is widely dispersed in a large amount of solid carbon. Depending on the application, it can be effectively used as it is as a functional carbon material. On the other hand, when it is desired to recover the catalyst, the catalyst metal component is removed from the solid carbon by an appropriate method and used for catalyst regeneration. In the present invention, the energy required for taking out the catalytic metal component and regenerating the catalyst 14 can be covered by a part of the hydrogen generated by the methane decomposition means 13.

The gas discharged from the reaction chamber 16 of the methane decomposition means 13 is separated into unreacted CH ₄ and hydrogen by an appropriate method such as adsorption or membrane separation. Unreacted CH ₄ is returned to the methane decomposition means 13.
Hydrogen is not only a clean energy source that does not release CO ₂ even when it burns, but also has three times as much heat generation energy per unit weight as petroleum, and can be converted into electric energy by a fuel cell. In the present invention,
A large amount of biogas G is efficiently recovered from the biomass B in the crushing means 2 and 3 and the bioreactor 6, and almost the same amount of theoretically calculated hydrogen is produced from CH ₄ in the biogas G in the methane decomposition means 13. By crushing
It is possible to take out from the methane decomposition means 13 an amount of hydrogen capable of supplying all the energy required for fermentation / decomposition and other systems. Moreover, since CO _{2 in} the atmosphere fixed in the biomass B is taken out as solid carbon and is not returned to the atmosphere, the CO ₂ concentration in the atmosphere can be reduced as a result.

Thus, the object of the present invention is to provide the "method and apparatus for removing carbon dioxide in the atmosphere, which can efficiently remove carbon dioxide in the atmosphere and energy itself".

[0036]

[Example] Organic slurry S obtained by pulverizing biomass B
In the bioreactor 6, 80 to 90% of organic matter is decomposed by methanogens to become biogas G and fermented liquid E. When the organic matter slurry S having a CODcr value of about 210 g / L is decomposed by the high temperature methane fermentation bioreactor 6, about 200 Nm ³ of biogas is generated per ton of the slurry. On the other hand, since the fermentation liquor E remaining in the bioreactor 6 also contains a small amount (10 to 20%) of organic matter, the fermentation liquor E is sent to the final treatment facility 8 in the embodiment of FIG. It is discharged to sewers and rivers as treated water. In the final treatment facility 8, usually, activated sludge treatment using aerobic microorganisms is performed. However, it is also possible to use the fermentation liquid E remaining in the bioreactor 6 as it is as liquid fertilizer.

Further, in the embodiment shown in FIG. 1, a desulfurization and denitrification refining device 10 and a methane concentration device 12 are provided between the bioreactor 6 and the methane decomposition means 13. Biogas G is mainly
Although it is a mixed gas of CH ₄ and CO _2, it contains tens of ppm to hundreds of ppm of impurities such as hydrogen sulfide and ammonia. Since these impurities deteriorate the catalyst 14 of the methane decomposition means 13 or shorten the life thereof, they are removed in the desulfurization denitrification refining apparatus 10. In the desulfurization and denitrification refining apparatus 10 of the illustrated example, the biogas G is refined by removing hydrogen sulfide with iron oxide pellets or the like and removing ammonia with activated carbon or the like. The methane concentrator 12 removes CO ₂ from the purified biogas G to concentrate CH ₄ to, for example, 98% or more. In the methane concentrator 12 of the illustrated example, CH ₄ in the biogas G is concentrated by adsorbing and removing CO ₂ with the PSA device.

The CO ₂ removed from the biogas G in the methane concentrator 12 can be returned to the atmosphere, for example.
CO ₂ in the biogas G is a native of CO ₂ fixed in the air in the biomass B, it does not break the balance of CO ₂ on a global scale even when returning to the atmosphere. Moreover, even if CO ₂ contained in the biogas G in an amount of 30 to 40% is returned to the atmosphere, if CH ₄ contained in the biogas in an amount of 60 to 70% is taken out as solid carbon, CO fixed in the biomass B is reduced. Since it can remove more than half of ₂ (carbon equivalent), it does not hinder the removal of CO _{2 in} the atmosphere. The CO ₂ removed from the biogas G can also be used by reacting it with solid carbon obtained from CH ₄ to convert it to CO as a chemical raw material.

Further, in the embodiment shown in FIG. 1, a fuel cell 17 is provided to convert a part of hydrogen taken out from the methane decomposition means 13 into high temperature water and electric power. The power generation efficiency of the fuel cell 17
Although it is about 40 to 50%, high-temperature water (or steam) is discharged from the fuel cell 17, so if this high-temperature heat is effectively used, a total energy efficiency of about 80% can be obtained (Kenichi Hirose "Fuel Cell Story" Japanese Standards Association, 1992
July 5, 1st edition, p56). The high temperature water which is the exhaust heat of the fuel cell 17 is effectively used for the heat retaining means 7 of the bioreactor 6. In addition, due to a part of the electric power from the fuel cell 17, FIG.
The electric power required to drive the crushing means 2 and 3 shown in FIG. 2, the slurry circulation pump 9 of the bioreactor 6 (FIG. 2), the final treatment facility 8, the desulfurization and denitrification refiner 10, the methane concentrator 12 and the like.

In the embodiment shown in FIG. 1, the heating means 15 is heated by a part of the hydrogen generated in the methane decomposition means 13, and the other part of the hydrogen is converted into electric power and high temperature water by the fuel cell 17. At least a part of the high temperature water from the fuel cell 17 can be used to keep the heat insulating means 7 warm, and at least a part of the electric power from the fuel cell 17 can drive the crushing means 2, 3, etc., so that CO ₂ in the atmosphere can be self-sufficient. To be removed as solid carbon.

One of the grounds for determining that the present invention is energy self-sufficiency will be described with reference to FIG. FIG. 8 is a graph showing the relationship between the power generation amount and system power consumption of the system using the above-described methane steam reforming reactor in place of the methane decomposition means 13 in FIG. 1 (clean energy (November 2000)). , P34-38, Yoshitaka Togo, "Metacles and Fuel Cells"). The graph α in the figure shows the amount of power generation according to the amount of processed biomass (garbage in FIG. 8), and the graph β shows the change in power consumption required to drive the system. According to the graph, the amount of power generated when processing 5 tons of biomass a day is approximately 3 × 10 ³ kWh / day, which exceeds the power consumption required to drive the system of approximately 1 × 10 ³ kWh / day. . Moreover, it can be seen that the difference between the amount of power generation and this system power consumption widens as the amount of biomass processed increases.

Comparing the case of using the methane steam reforming reactor as shown in FIG. 8 for producing hydrogen from CH ₄ with the case of using the methane decomposition means 13 as in the present invention, the formula (6) and ( 1)
As is clear from the comparison with the equation, the amount of hydrogen generated when the methane decomposition means 13 is used is half that when the methane steam reforming reactor is used. Considering this point and looking at FIG. 8, about 1.5 × 10 ³ kWh / day can be expected as the amount of power generation when the methane decomposition means 13 is used to process 5 tons of biomass per day.

On the other hand, comparing the power consumption required to drive the system, the enthalpy change of the reaction when using the methane decomposition means 13 and when using the methane steam reforming reaction device, the reaction temperature is 500 per mol of hydrogen. Almost the same at ℃ and 800 ℃. Furthermore, the reaction temperature range is 20 due to methane decomposition.
There is a region that overlaps with 0-900 ℃ and 600-850 ℃ by methane steam reforming. The reaction pressures are normal pressure and 20-30 atm, respectively, and methane decomposition is slightly more advantageous (reference data of methane steam reforming: Miki Sato, Petrotech, vol. 24, 54
3 (2001)). From the above comparison, the system power consumption in the case of using the methane decomposition means 13 as in the present invention is the power consumption in the case of using the methane steam reforming reactor as shown in FIG. 8 (about 1.0 × 10 ³ kWh / It is estimated to be less than (day). That is, when using the methane decomposition means 13, 5.0 × 10 ² kWh /
It is possible to expect surplus power of about a day (= 1.5 × 10 ³ −1.0 × 10 ³ ), and this surplus power increases as the amount of biomass processed increases. That is, the present invention can be said to be self-sufficient in energy.

FIG. 5 shows a specific example of the mass balance and the energy balance in the case of treating 5 tons of biomass B having CO ₂ in the atmosphere fixed therein per day. Prior to fermentation, 5 tons of biomass B is pulverized by a pulverizer 2 having a foreign substance separating function to remove foreign substances, and finely pulverized by a fine pulverizer 3 to obtain an organic substance slurry S. Further, in order to improve the fluidity of the slurry S, 5 tons of dilution water is added to dilute it twice. The CODcr value at this time is about 210.
The g / L and BOD value (biological oxygen demand) are about 160 g / L. When this slurry S is subjected to methane fermentation by thermophilic bacteria in the bioreactor 6 while being kept at 55 ° C. which is the activation temperature of thermophilic bacteria, about 85% of CODcr is decomposed and biogas G is generated at 1,000 Nm ³ per day. The average concentration of CH ₄ in this biogas G is 65%, and the amount of CH ₄ is 650 Nm ³ per day. Impurities in biogas G are removed by desulfurization and denitrification refining device 10, and CH ₄ is concentrated by a methane concentrating device 12 to 98% or more.

The concentrated CH ₄ is supplied to the methane decomposition means 13. The reaction chamber 16 of the methane decomposition means 13 has a catalyst 14 and is maintained at a decomposition temperature of 500 ° C. 650 Nm to methane decomposition means 13
Supplying ³ / day of CH ₄ produces 348 kg of carbon and 116
Can extract kg of hydrogen. The amount of heat of hydrogen taken out is 3,35
It is 7 × 10 ³ kcal / day, and part of the hydrogen is used as fuel for the heating means 15 of the methane decomposition means 13. 650Nm ³ / day CH ₄ 500
Decomposition at ℃ requires 622 × 10 ³ kcal / day (21 kg-hydrogen / day), so the remaining heat of hydrogen is 2,735 × 10 ³
It becomes kcal / day (95kg-equivalent to hydrogen / day). When the rest of the hydrogen is used as the fuel for the phosphoric acid fuel cell 17, the power generation efficiency of the fuel cell 17 when hydrogen is used as the fuel is about 45%, so the power that can be generated is 1,431 kwh / day.

Since the power consumption required to drive the entire system shown in FIG. 5 is about 1,000 to 1,200 kwh / day, the fuel cell 17
It is possible to fully cover the power consumption of the entire system with the power from the. Even when the decomposition temperature is raised to 800 ° C, the reaction heat is 688 × 10 ³ kcal / day (equivalent to 24 kg-hydrogen / day), so the power generation is 1,397 kwh / day, which exceeds the system power consumption. Further, assuming that about 45% of the reaction heat of hydrogen can be recovered, exhaust heat of 1,231 × 10 ³ kcal / day is generated from the fuel cell 17, so it is recovered as hot water or steam. The amount of heat required to heat biomass and dilution water from 20 ° C to 55 ° C
Since the amount of heat released from the bioreactor 6 is about 350 × 10 ³ kcal / day and the amount of heat released from the bioreactor 6 is about 150 × 10 ³ kcal / day, the amount of heat for keeping the bioreactor 6 at 55 ° C. is 500 × 10 ³ kcal.
/ Day is enough, and the hot water from the fuel cell 17 can be sufficiently covered.

From the flow chart of FIG. 5, according to the present invention, 348 kg of CO ₂ (converted to carbon) can be removed as solid carbon by treating the biomass B in which atmospheric CO ₂ is fixed at 5 tons / day. Further, it is possible to cover all the energy conversion of hydrogen to recover the energy required for the removal of CO ₂ in the system, it is possible to remove the energy self-sufficient manner CO _2. Furthermore, surplus power of about 231 kwh / day (= 1,431-1,200) and 731 × 10 ³ kcal / day (= 1,231 × 10 ³ −500)
It is possible to generate excess hot water of approximately 10 ³ ), and it is expected that the economical efficiency of a power generation facility will be obtained while removing CO ₂ from the atmosphere.

[0048]

INDUSTRIAL APPLICABILITY As described above, the method and apparatus for removing carbon dioxide using biomass of the present invention is to pulverize the biomass in which atmospheric carbon dioxide is fixed into an organic slurry and maintain the active temperature to generate methane. Fermented methane by the bacterial group, decomposed into hydrogen and solid carbon by contacting with the catalyst while heating methane gas by fermentation to the decomposition temperature, the energy required for the crushing and maintaining the activation temperature and heating to the decomposition temperature Since it is covered by the energy conversion of hydrogen, the following remarkable effects are achieved.

(A) Since hydrogen generated in the system can be used as a fuel to drive the system, it is not necessary to replenish energy from the outside, and carbon dioxide in the atmosphere can be self-sufficiently removed as solid carbon. (B) Since carbon dioxide in the atmosphere is removed using biomass as a medium, extremely dilute carbon dioxide in the atmosphere can be efficiently removed. (C) By using readily available biomass such as garbage, it is possible to construct a facility to remove carbon dioxide in the atmosphere from anywhere. (D) Since the anaerobic treatment, which consumes a small amount of energy, is used, it is expected that the amount of energy consumed in the system can be minimized to supply surplus energy as heat and electricity to the outside. (E) By using a highly active high-temperature methanogen or the like, a device such as a bioreactor becomes compact, which is economically advantageous. (F) By using a catalyst whose main component is nickel, cobalt, iron, etc., solid carbon having a structure and shape useful as a functional material can be taken out, and it is used as a battery electrode material and an electromagnetic wave absorber loss material. For example, it is possible to effectively use solid carbon.

[Brief description of drawings]

FIG. 1 is a schematic flow diagram of one embodiment of the present invention.

FIG. 2 is an explanatory diagram of a bioreactor according to the present invention.

FIG. 3 is an explanatory diagram of an example of a microbial carrier used in the present invention.

FIG. 4 is an explanatory diagram of an example of methane decomposition means.

FIG. 5 is a diagram showing an example of a material balance and an energy balance in the present invention.

FIG. 6 is an explanatory diagram of an example of a conventional method for removing carbon dioxide in the atmosphere.

FIG. 7 is an explanatory diagram of another example of a conventional method for removing carbon dioxide in the atmosphere.

FIG. 8 is an explanatory diagram of a relationship between a power generation amount of a fuel cell including a conventional methane steam reforming reaction device and system power consumption.

[Explanation of symbols]

1… Carbon dioxide fixation facility 2. Crusher with a foreign matter separation function (crushing means) 3 ... Fine crusher (crushing means) 4 ... Slurry tank 5 ... Slurry pump 6 ... Bioreactor 7 ... Heat insulation means 8 ... Final treatment facility 9 ... Slurry circulation pump 10 ... Desulfurization denitrification refining equipment 12 ... Methane concentrator 13 ... Methane decomposition means 14 ... Catalyst 15 ... Heating means 16 ... Reaction chamber 17 ... Fuel cell 20 ... Fermentation room 21 ... Microbial carrier 22 ... Hollow cylinder 23 ... Porous peripheral wall 24 ... Frame 26 ... Primary reactor 27 ... Secondary reactor 28 ... Condenser 31 ... Organic waste treatment unit 32 ... Gas mixing / condenser 33 ... Pump 34 ... Reaction tank 35 ... Catalyst / carbon separator 36 ... Catalyst regenerator 37 ... Pump 38 ... Hydrogen separator 39 ... Pump 40 ... Hydrogen combustor E ... Fermentation liquid G ... Biogas S ... Organic slurry

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) C12M 1/107 C12N 1/00 P C12N 1/00 B09B 3/00 CD (72) Inventor Togo Yoshitaka Tokyo Kashima Construction Co., Ltd., 1-2-7 Moto-Akasaka, Minato-ku, Tokyo (72) Inventor Masahiro Tada 1-2-7 Moto-Akasaka, Minato-ku, Tokyo Kashima Construction Co., Ltd. F-term (reference) 4B065 AA01X AA57X AC14 BB22 CA01 CA55 4D004 AA02 AA03 AA04 AA50 BA03 BA04 CA04 CA18 CB04 CB31 CC08 DA06 4D059 AA07 AA08 AA30 BA14 BA15 BA27 BA34 BK11 BK12 BK17 CA01 CA27 CC01 CC03 4G040 DA03 DC02 4G046 CA01 CC01 CC03 CC03 CC03 CC03 CC03 CC03 CC03 CC03 CC03

Claims (9)

[Claims] 1. A biomass in which carbon dioxide in the atmosphere is fixed is pulverized into an organic matter slurry, the organic matter slurry is maintained at an active temperature and methane-fermented by a methanogen group, and methane gas produced by the fermentation is heated to a decomposition temperature. While contacting with the catalyst to decompose into hydrogen and solid carbon, the energy required for the crushing and maintaining the activation temperature and heating to the decomposition temperature is covered by the energy conversion of hydrogen to convert carbon dioxide in the atmosphere into energy. A method for removing carbon dioxide using biomass, which is self-sufficiently removed as solid carbon. 2. The removal method according to claim 1, wherein a part of the hydrogen covers heating energy to the decomposition temperature, and another part of the hydrogen is converted into electric power and high temperature water by a fuel cell, The method for removing carbon dioxide using biomass, wherein the high temperature water is used to cover the energy held at the activation temperature, and the electric power from the fuel cell is used to cover the grinding energy. 3. The removal method according to claim 1 or 2, wherein the biomass is an organism having high utilization efficiency of carbon dioxide,
A method for removing carbon dioxide using biomass, which comprises crushing the organism into a high-concentration organic matter slurry that produces a large amount of methane gas per unit weight. 4. The removal method according to claim 1, wherein the main component of the catalyst is nickel, iron, or cobalt, and the methane gas is heated to 200 to 900 ° C. and brought into contact with the catalyst. Carbon dioxide removal method using biomass. 5. The method for removing carbon dioxide using biomass according to any one of claims 1 to 4, wherein the organic slurry is held at 52 to 58 ° C. and methane-fermented by a methanogen group. 6. A pulverizing means for pulverizing biomass in which atmospheric carbon dioxide is fixed into an organic matter slurry, a fermentation chamber for holding a high concentration of methanogens, and a slurry for introducing the slurry into the fermentation chamber. A bioreactor having a heat-retaining means for keeping the methane gas from the bioreactor, and a heating means for heating the methane gas to a decomposition temperature in a reaction chamber in which a catalyst for decomposing methane gas from the bioreactor into hydrogen and solid carbon is present. And a fuel cell for converting another part of the hydrogen into electric power and high-temperature water, the high-temperature water from the fuel cell keeps the heat-retaining means warm, and the electric power from the fuel cell Carbon dioxide using biomass produced by driving the crushing means to self-sufficiently remove carbon dioxide in the atmosphere as solid carbon Removed by the device. 7. The carbon dioxide removing device according to claim 6, wherein the main component of the catalyst is nickel, iron, or cobalt, and the methane gas is heated to 200 to 900 ° C. by the heating means. 8. The carbon dioxide removing device using biomass according to claim 6 or 7, wherein a desulfurizing and denitrifying refining device and a methane concentrating device are provided between the bioreactor and the methane decomposing means. 9. The carbon dioxide removing device according to claim 6, wherein the pulverizing means finely pulverizes the biomass into a high-concentration organic substance slurry having a large amount of methane gas generated per unit weight. .