JP7761475B2 - How to store carbon dioxide - Google Patents

Description

One embodiment of the present invention relates to a system and method for storing carbon dioxide.

Adsorbents containing iron and carbon-based carbides prepared from biomass are capable of adsorbing phosphate ions derived from phosphoric acid. Therefore, they are known to be useful for improving the water quality of bodies of water such as rivers, lakes, and oceans, and for recovering phosphorus from sludge dewatering separation liquid at sewage treatment plants. Furthermore, adsorbents that have adsorbed phosphate ions can also be used as fertilizer. Therefore, by spreading the adsorbent on soil after adsorbing phosphate ions, it is possible to effectively utilize the carbon dioxide fixed by plants and store the carbon dioxide in the soil. Therefore, adsorbents obtained from biomass play a central role in carbon sequestration, which fixes greenhouse gases in the atmosphere (see Patent Document 1 and Non-Patent Document 1).

Japanese Patent Application Laid-Open No. 2007-75706

Akira Shibata, "Simple carbonization of biomass and carbon storage vegetables for regional development: COOL VEGETM," Journal of the High Temperature Society, March 2011, Vol. 37, No. 2, pp. 37-42

An object of one embodiment of the present invention is to provide a system and method for storing carbon dioxide. Alternatively, an object of one embodiment of the present invention is to provide a system and method for storing carbon dioxide using a purification material that can improve water quality and air quality.

One embodiment of the present invention is a method for storing carbon dioxide. The method includes carbonizing biomass to produce a carbonized material and a dry distillation gas, mixing the carbonized material with iron powder and/or iron oxide powder to produce an iron-containing carbonized material, contacting the iron-containing carbonized material with a gas containing nitrogen oxides and/or sulfur oxides and carbon dioxide, and contacting the iron-containing carbonized material with water containing a phosphorus compound.

1 is a conceptual diagram illustrating a system for storing carbon dioxide according to one embodiment of the present invention. 1 is a flow chart illustrating a method for producing a purification material that can be used in a system and method according to one embodiment of the present invention. 1 is a schematic perspective view of a cartridge for adsorbing phosphorus compounds in a system and method according to one embodiment of the present invention.

Each embodiment of the present invention will be described below with reference to the drawings, etc. However, the present invention can be embodied in various forms without departing from the spirit of the invention, and should not be construed as being limited to the description of the embodiments exemplified below.

One embodiment of the present invention is a system and method for improving water and air quality while storing carbon dioxide. A conceptual diagram of the system is shown in Figure 1. The system uses biomass as a starting material to generate energy and remove pollutants from water and the air. Furthermore, the system promotes plant growth through soil improvement and aims to reduce greenhouse gases such as carbon dioxide. The grown plants are used as food or materials, and biomass is regenerated as residue. This series of steps completes the cycle shown in Figure 1. A more detailed explanation is provided below.

1. Carbonization: This system uses biomass as a raw material to produce charcoal, which serves as a substrate for iron-containing charcoal (described below), which functions as a purification material. Biomass refers to a type of organic matter, including biologically derived substances and their metabolites. Examples of biomass include wood-derived materials. Specific examples include planks and columns of wood, thinnings, pruning waste, construction waste, powdered sawdust, and wooden molded products such as particle boats. There are no restrictions on the type of wood, and cedar, cypress, and bamboo are also acceptable. Other examples of biomass include agricultural waste such as rice husks, bagasse, corn cobs, and leaves, as well as agricultural by-products such as straw, wheat straw, and hay. Other examples include plants that are used to produce fibers, such as hemp, flax, cotton, sisal, abaca, and palm hair. Seaweed and other algae are also acceptable. Other examples include food waste and silage made from animal waste.

Carbonization is carried out by heating biomass under conditions of low oxygen concentration. For example, carbonization is carried out by heating biomass under an inert gas atmosphere such as nitrogen gas or argon gas, an oxygen-free atmosphere, a low-oxygen atmosphere, a reducing atmosphere, or a reduced-pressure atmosphere. When carbonization is carried out under a reduced-pressure atmosphere, it can be carried out under a low vacuum state of 10 ² Pa to 10 ⁵ Pa, a medium vacuum state of 10 ⁻¹ Pa to 10 ² Pa, a high vacuum state of 10 ⁻⁵ Pa to 10 ⁻¹ Pa, or an ultra-high vacuum state of 10 ⁻⁵ Pa or less. When carbonization is carried out under a low-oxygen atmosphere, it can be carried out at an oxygen concentration of 0.01% to 3% or 0.1% to 2%. The heating temperature for carbonization may be 400°C to 1200°C, 500°C to 1100°C, 600°C to 1000°C, or 600°C to 900°C. The heating time may be from 10 minutes to 10 days, or from 10 minutes to 5 hours.

Carbonization can be carried out using an internal combustion or external heat carbonization furnace. Examples of carbonization furnaces include batch-type sealed charcoal kilns, continuous rotary kilns, rocking carbonization furnaces, and screw furnaces.

Carbonization of biomass generates pyrolysis gas, and a porous carbonized material is produced in which pores of various shapes and sizes are formed, with pores resulting from the structure of the biomass and pores formed by desorption of the pyrolysis gas being a complex mixture. The carbonized material has a large specific surface area due to the pores formed inside. Specifically, the specific surface area of the carbonized material may be 100 m ² /g or more and 900 m ² /g or less, 100 m ² /g or more and 800 m ² /g or less, or 150 m ² /g or more and 400 m ² /g or less. The specific surface area is measured using a gas adsorption method such as mercury porosimetry or the BJH method or the HK method.

2. Energy Generation Using Carbonized Gas The carbonized gas produced by carbonization contains mainly flammable or reducing gases, such as hydrogen, carbon monoxide, and alkanes, such as methane, propane, and butane. Furthermore, the carbonized gas is extracted from the carbonization furnace at high temperatures (700°C to 1300°C). Therefore, the thermal energy and flammability of the carbonized gas can be used as an energy source for hot water supply and power generation. For example, the carbonized gas can be introduced into a heat exchanger to extract thermal energy and use it to generate hot water. Alternatively, the thermal energy obtained by burning the carbonized gas can be used to generate power. In this case, the carbonized gas can be used as fuel for gas turbine, gas engine, or dual-fuel engine power generation systems.

3. Preparation of Iron-Containing Carbide (1) Mixing and Kneading In this system, iron (zero-valent iron) and/or an iron compound is further mixed with the carbide obtained by carbonization to prepare an iron-containing carbide. The flow for preparing iron-containing carbide is shown in Figure 2. As shown in Figure 2, first, the carbide obtained by carbonizing biomass, a binder, and iron powder and/or iron oxide powder are mixed, and the resulting mixture is kneaded (kneaded).

The iron powder may be iron powder that does not contain iron compounds, or iron powder that has iron compounds formed on its surface with divalent, trivalent, and/or mixed-valence iron compounds (a mixture of divalent and trivalent iron compounds) formed by the oxidation of iron. In the latter case, the iron-containing carbide contains iron compounds, and examples of iron compounds include iron hydroxide and iron oxide with divalent, trivalent, or mixed valences.

As the iron oxide powder, powder of divalent, trivalent, or mixed valence iron oxide can be used. The iron oxide powder may also contain iron hydroxide of divalent, trivalent, or mixed valence. As in the case of using iron powder with an oxidized surface, when iron oxide powder is used, the iron-containing carbide contains the above-mentioned divalent, trivalent, or mixed valence iron oxide as the iron compound.

The average particle size of the iron powder and iron oxide powder may be 20 μm or more and 500 μm or less, or 50 μm or more and 200 μm or less. The average particle size of the iron powder and iron oxide powder may be the same or substantially the same. Furthermore, iron powder having a particle size distribution in which 1) the proportion of iron particles having a particle size in the range of 1 μm or more and less than 150 μm is 3% by mass to 70% by mass, 2) the proportion of iron particles having a particle size in the range of 1 μm or more and less than 75 μm is 0% by mass to 25% by mass, 3) the proportion of iron particles having a particle size in the range of 1 μm or more and less than 45 μm is 0% by mass to 15% by mass, 4) the proportion of iron particles having a particle size in the range of 150 μm or more and less than 2000 μm is 30% by mass to 99% by mass, and 5) the proportion of iron particles having a particle size in the range of 600 μm or more and less than 2000 μm is 0% by mass to 15% by mass, and the sum of the proportion of iron particles in at least one of 1) to 3) and the proportion of iron particles in 4) or 5) is 100% by mass. Here, the average particle size of the iron powder is the average value obtained by analyzing an image obtained by observing the iron powder under a microscope and determining the particle sizes of a plurality of iron particles. The particle size of each iron particle can be, for example, the diameter of a circle inscribed in the projection of each iron particle in a microscope image, or the length of one side of a square. Since the particle size of carbide is often larger than the particle size of iron powder or iron oxide powder, the carbide may be crushed and/or classified to have a particle size approximately the same as that of iron powder or iron oxide powder before mixing and kneading. The particle size distribution and circularity of the iron oxide powder may be the same as those of the iron powder.

There are no restrictions on the shape of the iron powder or iron oxide powder. For example, iron powder or iron oxide powder with an average circularity of 50 to 100, 70 to 95, or 80 to 90 may be used. Here, average circularity is one of the parameters that describe the shape of each particle contained in the powder, and is calculated by analyzing images obtained by observing the powder under a microscope, determining the circularity of multiple particles, and averaging these values. Circularity can be calculated, for example, by dividing the perimeter of a circle with an area equal to the area of the projection surface of each particle in the microscope image by the perimeter of the projection surface. Alternatively, the circularity can be calculated by dividing the area of the projection surface by the area of a circle inscribed in the projection surface.

There are no restrictions on the type of binder, and organic and/or inorganic binders can be used. Examples of organic binders include one or more selected from the group consisting of molasses, blackstrap molasses, starch, dextrin, corn starch, rice bran, polyvinyl alcohol, vinyl acetate-ethylene copolymers or their saponified forms, pulp waste liquor, lignin sulfonate, carboxymethyl cellulose, hydroxypropyl methyl cellulose, sodium alginate, phenolic resin, and tar pitch. Molasses is particularly inexpensive, contains few harmful components, and has a high solid content, making it easy to mold the purification material. Examples of inorganic binders include cement, ground granulated blast furnace slag, fly ash, gypsum (calcium sulfate), calcined gypsum obtained by heating and dehydrating gypsum, and sodium silicate.

The amounts of carbide, binder, iron powder, and iron oxide powder can be adjusted appropriately so that the carbide content in the resulting iron-containing carbide is within the range of 20% by mass to 80% by mass, 40% by mass to 80% by mass, or 60% by mass to 80% by mass; the iron and iron compound content is within the range of 5% by mass to 35% by mass, 5% by mass to 25% by mass, or 5% by mass to 20% by mass; and the binder content is within the range of 5% by mass to 50% by mass, 15% by mass to 50% by mass, or 20% by mass to 50% by mass.

When mixing or kneading, water is added to the carbide, binder, and iron powder and/or iron oxide powder as needed. Adding water prevents dust from being generated and allows the carbide, iron powder, and iron oxide powder to be mixed more uniformly.

A kneader can be used to mix and knead these raw materials. Examples of kneaders that can be used include single-screw kneaders, twin-screw kneaders, mixing rolls, kneaders, and Banbury mixers. A kneader with both mixing and kneading functions can also be used. In this case, the carbide, iron powder and/or iron oxide powder, and binder are added to the kneader, followed by mixing and kneading. Alternatively, mixing and kneading can be performed continuously. For example, the carbide and iron powder and/or iron oxide powder are added to the kneader and mixed, and then the binder is added to the kneader and kneaded. The binder can be added all at once, intermittently, or continuously. By mixing the carbide and iron powder and/or iron oxide powder and then adding the binder and kneading, aggregation of the carbide and iron powder and/or iron oxide powder can be prevented, and foaming can be suppressed.

The kneading temperature can be set at any temperature, for example, between 0°C and 50°C, or between 10°C and 40°C. The kneading time can also be set appropriately taking into account the mixing ratio and amount of raw materials, the type of binder, the capacity of the kneader, etc., and can be set within the range of, for example, between 1 second and 1 hour, between 1 minute and 30 minutes, or between 1 minute and 15 minutes.

The above procedure allows for the production of a paste-like precursor containing a mixture of carbide, binder, and iron powder and/or iron oxide powder. Note that if iron oxide powder is not used and iron powder that does not contain iron compounds is used, some of the iron powder may be oxidized during this process, resulting in the iron-supported carbide containing compounds containing divalent, trivalent, or mixed-valent iron. As mentioned above, examples of iron compounds include iron hydroxide and iron oxide.

(2) Granulation As an optional step, the mixture of the obtained carbide, iron powder and/or iron oxide powder, and binder may be granulated and molded into a certain shape. The mixture can be molded using a granulator. Examples of granulators include a compression granulator, an extrusion granulator, a roll granulator, a blade granulator, a melt granulator, and a spray granulator.

When using an extrusion granulator, a paste-like mixture formed into a predetermined shape is extruded from a die attached to the granulator. The extruded mixture is cut to a predetermined length and formed into pellets with the extrusion direction as the height direction. The length of the precursor (the height of the pellet shape) can be adjusted by adjusting the extrusion speed and cutting speed of the mixture in the extrusion granulator (or the rotation speed of the cutter if a rotary cutting method is used). In addition, the diameter of the mixture (or the diameter if the cross-sectional shape is circular) can be adjusted by adjusting the opening diameter of the die. Therefore, by using an extrusion granulator, it is possible to obtain a mixture having a pellet shape with a controlled size (for example, an approximately cylindrical shape).

The size of the pellet shape can be set as desired. For example, the length of each pellet can be 1 mm to 20 mm, 3 mm to 15 mm, or 6 mm to 12 mm. If the cross-sectional shape is circular, the diameter of the pellet can be 1 mm to 20 mm, 2 mm to 10 mm, or 3 mm to 8 mm.

The cross-sectional shape of the mixture after molding (a cross section perpendicular to the longitudinal direction) is not limited to a circle. The cross-sectional shape of the mixture may be, for example, an ellipse or a polygon. In other words, the mixture after molding may be in the shape of a pellet, not just a cylinder, but also an elliptical cylinder or a polygonal cylinder. The cross-sectional shape of the mixture can be changed by changing the shape of the die opening. This granulation process may be performed after the drying process described below.

(3) Drying As an optional step, the mixture after molding may be dried. The drying temperature and time are also appropriately selected depending on the amount of the mixture and the amount of water contained. For example, the drying temperature may be selected from the range of 30°C or higher but lower than 400°C, 50°C or higher but lower than 300°C, or 100°C or higher but lower than 300°C. The humidity during drying may be 20% or higher but lower than 95%, or 50% or higher but lower than 90%. The drying time may also be appropriately selected from the range of 1 minute or higher but lower than 1 week, 1 hour or higher but lower than 3 days, or 3 hours or higher but lower than 1 day. The atmosphere during drying may also be, for example, air, nitrogen, a rare gas such as argon, or a mixture of these. Biomass may be carbonized in a separate batch, and drying may be performed using the thermal energy of the resulting dry distillation gas.

The above steps allow for the production of iron-containing carbide. This method does not require high-temperature firing. In other words, it is not necessary to heat the binder to the temperature required to carbonize it (e.g., 400°C or higher). This eliminates the time and energy required for firing, making it possible to provide iron-containing carbide at lower cost.

4. Nitrogen Oxide Removal In this system, air pollutants such as nitrogen oxides ( _NOx ) (e.g., nitric oxide and nitrogen dioxide) and sulfur oxides ( _SOx ) are removed using iron-containing carbides. Specifically, gas containing nitrogen oxides and/or sulfur oxides is brought into contact with the iron-containing carbide to remove the air pollutants. The gas may further contain carbon dioxide. The carbides and binders used as raw materials for the iron-containing carbide contain oxides and salts (hydroxides, halides, sulfates, nitrates) of alkali metals and alkaline earth metals. When contacted with a gas containing carbon dioxide, at least a portion of these oxides and salts is converted to carbonates or bicarbonates (carbonation). In general, carbonates and bicarbonates of alkali metals and alkaline earth metals have lower solubility in water than hydroxides, halides, sulfates, and nitrates. Therefore, by promoting carbonation, when the water to be treated is treated with the iron-containing carbide described below, the alkali metals and alkaline earth metals remain as carbonates or bicarbonates, thereby improving the shape stability of the iron-containing carbide in water and preventing it from collapsing in water.

The gas containing air pollutants can therefore be the atmosphere, or exhaust gas from facilities that emit large amounts of carbon dioxide (such as chemical plants, waste incineration facilities, thermal power plants, and various other factories). The exhaust gas does not need to be denitrified or desulfurized. Alternatively, exhaust gas from vehicles can be used, or, as shown in Figure 1, exhaust gas produced when carbonized gas is burned to generate electricity. By using such gases, not only can substances that cause air pollution be removed, but carbon dioxide, which acts as a greenhouse gas, can also be efficiently fixed.

5. Fixation of Phosphorus Compounds: This system uses iron-containing carbides that have been treated with gases containing air pollutants to adsorb and fix phosphorus compounds contained in water (water to be treated) from various bodies of water, thereby improving water quality. The contact between the iron-containing carbides and the water to be treated can be carried out continuously or batchwise. In the latter case, as shown in FIG. 3, for example, a cartridge 100 having a mesh-shaped housing 102 filled with iron-containing carbides 106 can be used to bring the water to be treated into contact with the iron-containing carbides 106. The mesh size can be, for example, 0.1 mm to 50 mm, or 0.5 mm to 20 mm. If the housing 102 does not have sufficient weight, a weight 104 can be attached to the housing 102 to ensure that the housing 102 is securely placed in the water to be treated. Instead of the weight 104, an anchor (not shown) can be attached to the housing 102 to secure it to the bottom of a river or lake, a septic tank, or an advanced treatment tank. In this way, by filling the cartridge 100 with the iron-containing carbide 106 and bringing the water to be treated into contact with the iron-containing carbide 106, it becomes easier to handle the iron-containing carbide 106. Furthermore, as described above, when the gas containing air pollutants contains carbon dioxide, carbonation can prevent the iron-containing carbide 106 from collapsing in water, and therefore the collapsed iron-containing carbide 106 does not flow out of the mesh-like casing 102, and the iron-containing carbide 106 can be reliably collected.

Although not shown in Figure 1, the water to be treated may be treated before treating the gas containing air pollutants with iron-containing carbides. Alternatively, after treating the gas containing air pollutants with iron-containing carbides and the water to be treated, the gas containing air pollutants may be treated again.

5. Fertilizer Production: Phosphorus compounds function as nutrients that promote the growth of various plants, so iron-containing carbides with immobilized phosphorus compounds can function as fertilizers. Therefore, iron-containing carbides can be used as phosphorus-containing fertilizers after purifying air containing air pollutants and treating water to be treated. Furthermore, when carbon dioxide is present in the gas containing air pollutants, the alkali metal and alkaline earth salts contained in the carbide are carbonated, and the alkali metal and alkaline earth salts contained in the binder are also carbonated. In particular, when cement or ground granulated blast furnace slag is used as a binder, these contain large amounts of calcium hydroxide and calcium oxide. Therefore, applying iron-containing carbides to soil without carbonation increases the soil pH. However, when iron-containing carbides come into contact with carbon dioxide, the calcium hydroxide and calcium oxide are converted to calcium carbonate or calcium bicarbonate. Furthermore, residual basic salts such as calcium hydroxide and calcium oxide can be removed during treatment with the water to be treated, thereby preventing an increase in soil pH.

When producing fertilizer from iron-containing carbide, the iron-containing carbide is first crushed. Crushing can be carried out using a crusher. There are no restrictions on the structure or type of crusher, and examples include vibration mills, jet mills, ball mills, roller mills, rod mills, hammer mills, impact mills, rotary mills, pin mills, pin-disk mills, and planetary mills. Crushing the iron-containing carbide using a crusher increases the surface area, which in turn promotes the release of phosphorus compounds fixed on the iron-containing carbide.

The crushed iron-containing carbide may be classified to adjust its particle size to suit its intended use as fertilizer. There are no restrictions on the structure or type of classifier, and either a dry or wet classifier may be used. Examples of classifiers include air classifiers, gravity field classifiers, inertial field classifiers, and centrifugal field classifiers.

The crushed and classified iron-containing carbide may be mixed with other fertilizer components. Such fertilizer components may include one or more selected from nitrogen, potassium, calcium, magnesium, manganese, silica, and boron. Specific examples of materials include oil cake, flavored chicken manure, fish meal, bone meal, rice bran, bat guano, compost, wood ash, lime, and chemical fertilizer. These fertilizer components are mixed with the iron-containing carbide using a mixer. There are no restrictions on the structure or type of mixer, and any of a free-fall mixer, forced mixer, Y-branch mixer, agitator mixer, or paddle mixer can be selected.

6. Soil Improvement and Plant Growth The obtained fertilizer is spread on the soil and used for plant growth. There are no restrictions on the method of spreading the fertilizer into the soil; for example, a gravity-drop spreader such as a ground sower or a diffusion-type spreader that uses compressed air may be used. There are also no restrictions on the application method; either a stripe-type spreader or an all-over spreader may be used. The fertilizer is preferably spread within 30 cm of the soil surface. Spreading the fertilizer promotes plant growth. In other words, carbon dioxide from the atmosphere is fixed by plant photosynthesis, creating resources that can be used as food or materials.

As described above, in this system, atmospheric carbon dioxide is fixed by plant photosynthesis to form organic matter, and the biomass generated through its utilization and metabolism is carbonized to produce char and pyrolysis gas (Figure 1, (1)). The pyrolysis gas is used as an energy source (2), while the char is converted into iron-containing carbides that function as a purification material (3). This purification material can remove air pollutants from the atmosphere or exhaust gases generated by burning pyrolysis gas (4) and can also fix phosphorus compounds in water (5). The purification material is converted into fertilizer, contributing to plant growth (7), and is ultimately returned to the ground as carbon, thereby storing carbon dioxide underground. Through this series of processes, this system contributes to purifying the air and reducing carbon dioxide emissions.

As mentioned above, iron-containing carbides can remove or fix water and air pollutants, so this system can be said to contribute to environmental conservation by improving water and air quality. Furthermore, when producing the carbide that serves as the raw material for iron-containing carbides, thermal energy and electrical energy are generated from the dry distillation gas produced by carbonizing biomass, and the exhaust gas generated during this process can be purified using iron-containing carbides. Therefore, this system can be said to contribute to energy generation without placing a significant burden on the environment. In addition, iron-containing carbides that remove or fix water and air pollutants also function as fertilizer to promote plant growth without increasing soil pH. For these reasons, this system can also be said to contribute to the development of agriculture and forestry.

The above-described embodiments of the present invention can be implemented in any suitable combination, provided they are not mutually inconsistent. Any product in which a person skilled in the art appropriately adds, deletes, or modifies components based on each embodiment is also included within the scope of the present invention, as long as it maintains the essence of the present invention.

Even if there are other effects and advantages different from those provided by the above-described embodiments, those that are clear from the description in this specification or that would be easily predicted by a person skilled in the art are naturally understood to be provided by the present invention.

100: Cartridge, 102: Housing, 104: Weight, 106: Iron-containing carbide

Claims (7)

carbonizing the biomass to produce char and carbonization gas;
mixing the carbide with iron powder and/or iron oxide powder to produce an iron-containing carbide;
A method for storing carbon dioxide, comprising: contacting the iron-containing carbide with a first gas containing nitrogen oxides and/or sulfur oxides, and carbon dioxide; and contacting the iron-containing carbide with water containing a phosphorus compound. The method of claim 1, further comprising generating electricity using the dry distillation gas. The method of claim 2 , wherein the first gas is an exhaust gas produced in the power generation. The method of claim 1, further comprising spreading the iron-containing carbide that has been contacted with water on soil. The method of claim 1 , wherein said contacting with said water occurs after said contacting with said first gas. 6. The method of claim 5, further comprising contacting the iron-containing carbide with a second gas comprising nitrogen oxides and carbon dioxide after contacting the iron-containing carbide with the water containing the phosphorus compound . The method of claim 1, wherein the mixing with the iron powder and/or iron oxide powder is carried out by mixing the carbide, the binder, and the iron powder and/or iron oxide powder.