Calcium oxide manufacturing method

Abstract

To provide a method for producing calcium oxide capable of inexpensively increasing the concentration of carbon dioxide generated in producing calcium oxide with a simple structure.SOLUTION: The method comprises an air combustion step for combining oxygen contained in air with an oxygen carrier in a reduced state in an environment of an oxidation temperature or higher to change the oxygen carrier to an oxidized state, a calcination reaction step for decomposing calcium carbonate into calcium oxide and carbon dioxide by thermal energy of the oxygen carrier, a fuel reaction step for mixing hydrocarbons and water to burn with oxygen combined with the oxygen carrier to bring the oxygen carrier to a reduced state in an environment of a reduction temperature below the oxidation temperature, a first supply step for supplying the oxygen carrier in an oxidized state from an air combustion part to a calcination reaction part and a fuel reaction part, and a second supply step for supplying the oxygen carrier in a reduced state from the fuel reaction part to the air combustion part.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing calcium oxide from a raw material containing calcium carbonate. [Background technology]

[0002] Quicklime (CaO) is used in a wide range of fields, including steelmaking, cement manufacturing, papermaking, agriculture, and construction. When producing quicklime on an industrial level, it is generally done by calcining and pyrolyzing limestone (CaCO3) (see the reference formula below). CaCO3→CaO+CO2 (reference formula) Thus, when limestone is thermally decomposed to produce quicklime, a large amount of carbon dioxide (CO2) is generated. For this reason, from the perspective of preventing global warming, it is becoming increasingly important to capture the carbon dioxide generated during the production of quicklime without releasing it into the atmosphere.

[0003] The captured carbon dioxide can be widely reused, for example, by storing it underground, cultivating plants and algae, or using it as liquid carbon dioxide as a food ingredient or industrial raw material. On the other hand, in order to effectively use the captured carbon dioxide industrially, it is necessary to increase the purity of the carbon dioxide to a high purity, for example, 95 to 100 vol%. For example, the carbon dioxide contained in the exhaust gas generated in the cement manufacturing process is higher than that of general combustion gases, because it contains carbon dioxide generated from limestone contained in the cement raw material refined powder in addition to that generated by the combustion of coal, petroleum coke, and combustible waste. In addition, when using the captured carbon dioxide for cultivating plants and algae or as a food ingredient, it is also important that it does not contain harmful components.

[0004] As a concentration method for increasing the concentration of carbon dioxide in exhaust gas that contains gas components other than carbon dioxide generated when limestone is thermally decomposed to produce quicklime, for example, there is the amine absorption method (see, for example, Patent Document 1). In the amine absorption method, a gas containing carbon dioxide is brought into contact with an alkaline aqueous solution (absorption liquid) of an amine or the like to selectively absorb carbon dioxide, and then the absorption liquid is heated to separate and recover high-concentration carbon dioxide.

[0005] Also known is a method of preventing contact between the combustion gas and the limestone during calcination of limestone, and increasing the purity of carbon dioxide contained in the exhaust gas produced by calcination of limestone through indirect heating, and then recovering the carbon dioxide (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2011-194388 A [Patent Document 2] Special Publication No. 2014-522802 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when concentrating carbon dioxide to a high concentration by the amine absorption method as in Patent Document 1, a large amount of absorption solution is required, and a large amount of energy is required to desorb carbon dioxide from the absorption solution, resulting in high costs. Therefore, this method has not yet been put to practical use as an industrial-level concentration method for increasing the concentration of carbon dioxide in exhaust gas at low cost.

[0008] Furthermore, in the method of indirectly heating the limestone by separating the combustion gas from the limestone as in Patent Document 2, heat is supplied to the limestone only by thermal conduction, and a large heat transfer surface is required to raise the temperature of the limestone to its decomposition temperature, which poses the problem of high equipment costs, such as the need for a large device.

[0009] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a method for producing calcium oxide that can highly concentrate carbon dioxide generated when calcium oxide is produced by thermally decomposing a calcium-containing raw material, with a simple configuration and at low cost. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention proposes the following means. That is, the method for producing calcium oxide of the present invention includes an air combustion step of mixing the oxygen carrier in a reduced state with air, and binding oxygen contained in the air to the oxygen carrier in an environment at or above an oxidation temperature, thereby changing the oxygen carrier to an oxidized state; a calcination reaction step of decomposing calcium carbonate into calcium oxide and carbon dioxide by thermal energy of the oxygen carrier in an oxidized state heated in the air combustion step; a fuel reaction step of mixing hydrocarbons and water, burning them with oxygen bound to the oxygen carrier in an oxidized state heated in the air combustion step, and reducing the number of bound oxygen atoms in the oxygen carrier in an environment at a reduction temperature below the oxidation temperature, thereby changing the oxygen carrier to a reduced state; a first supply step of supplying the oxygen carrier in an oxidized state from the air combustion step to the calcination reaction step and the fuel reaction step; and a second supply step of supplying the oxygen carrier in a reduced state from the fuel reaction step to the air combustion step. death, The calcination reaction step and the fuel reaction step are carried out in separate reactors. It is characterized by:

[0011] According to the present invention, when calcium carbonate is thermally decomposed, calcium carbonate is directly contacted with an oxygen carrier heated to a temperature equal to or higher than the thermal decomposition temperature, thereby making it possible to produce highly concentrated calcium oxide efficiently and at low cost with a simple configuration. Moreover, the carbon dioxide produced at the same time has a high purity with few impurities, and therefore can be used as a low-cost, high-purity carbon dioxide source without a post-process such as concentration processing.

[0013] The present invention may further include a separation step of separating calcium oxide and carbon dioxide produced by decomposition in the calcination reaction step.

[0014] In addition, the present invention may further include a carbon dioxide absorption step of mixing the calcium oxide separated in the separation step with an exhaust gas containing carbon dioxide outside the system, and reacting the carbon dioxide in the exhaust gas with the calcium oxide to generate calcium carbonate and supply the calcium carbonate to the calcination reaction step.

[0015] In the present invention, the oxygen carrier may contain at least one of iron oxide, nickel oxide, copper oxide, manganese oxide, and calcium sulfate.

[0016] In the present invention, the air combustion step may change the oxygen carrier from a reduced state to an oxidized state in a temperature range of 1000° C. or higher and a sintering temperature of the oxygen carrier or lower.

[0017] In the present invention, in the calcination reaction step, in addition to the oxygen carrier in an oxidized state, another heat medium may be further supplied.

[0018] An example of a calcium oxide production system for carrying out the calcium oxide production method of the present invention is characterized by having an oxygen carrier containing a metal oxide that can change between an oxidized state and a reduced state depending on the number of bonds of oxygen elements to metal elements; an air combustion section that mixes the oxygen carrier in a reduced state with air and bonds oxygen contained in the air to the oxygen carrier in an environment at or above the oxidation temperature to change the oxygen carrier to an oxidized state; a calcination reaction section that decomposes calcium carbonate into calcium oxide and carbon dioxide by thermal energy of the oxygen carrier in an oxidized state heated in the air combustion section; a fuel reaction section that mixes hydrocarbons and water, combusts them by thermal energy of the oxygen carrier in an oxidized state heated in the air combustion section, and reduces the number of bonds of oxygen in the oxygen carrier in an environment at a reduction temperature lower than the oxidation temperature to reduce the oxygen carrier to a reduced state; a first supply section that supplies the oxygen carrier in an oxidized state from the air combustion section to the calcination reaction section and the fuel reaction section; and a second supply section that supplies the oxygen carrier in a reduced state from the fuel reaction section to the air combustion section.

[0019] The calcination reaction section and the fuel reaction section may be integrally formed.

[0020] The apparatus may further include a separation section for separating calcium oxide and carbon dioxide produced by decomposition in the calcination reaction section.

[0021] The system may further include a carbon dioxide absorption section that mixes the calcium oxide separated in the separation section with exhaust gas containing carbon dioxide outside the system, reacts the carbon dioxide in the exhaust gas with the calcium oxide to generate calcium carbonate, and supplies the calcium carbonate to the calcination reaction section. Effect of the Invention

[0022] According to the present invention, it is possible to provide a method for producing calcium oxide that can highly concentrate carbon dioxide generated when producing calcium oxide by thermal decomposition of a calcium-containing raw material, with a simple configuration and at low cost. [Brief description of the drawings]

[0023] [Figure 1] 1 is a schematic configuration diagram showing a calcium oxide production system according to a first embodiment of the present invention. FIG. [Diagram 2] FIG. 2 is a schematic configuration diagram showing a calcium oxide production system according to a second embodiment of the present invention. [Diagram 3] FIG. 1 is a schematic configuration diagram showing a calcium oxide production system according to a third embodiment of the present invention. [Figure 4] FIG. 1 is a schematic configuration diagram showing a calcium oxide production system according to a fourth embodiment of the present invention. [Diagram 5] 4 is a graph showing the composition of exhaust gas discharged from a fuel reactor in an example. [Figure 6] 1 is a graph showing the composition of the exhaust gas discharged from the air combustion tower of the embodiment. [Figure 7] 1 is a graph showing a simulation result of the equilibrium temperature and composition of CaCO3 and CaO. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, a method for producing calcium oxide according to one embodiment of the present invention will be described with reference to the drawings. Note that each embodiment shown below is specifically described to better understand the gist of the invention, and does not limit the present invention unless otherwise specified. Furthermore, the drawings used in the following description may show essential parts in an enlarged scale for the sake of convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of each component may not necessarily be the same as in reality.

[0025] (First embodiment) FIG. 1 is a schematic diagram showing a calcium oxide production system according to a first embodiment of the calcium oxide production method of the present invention. The calcium oxide manufacturing system 10 of this embodiment uses an oxygen carrier containing a metal oxide, which can change between an oxidized state and a reduced state depending on the number of bonds between oxygen elements and metal elements, by circulating it as an oxygen supply medium and a heat supply medium.

[0026] In this embodiment, iron oxide is used as the oxygen carrier. While circulating within the calcium oxide production system 10, the iron oxide changes into two states: Fe2O3 (iron oxide (III)), which is an oxygen carrier in an oxidized state in which the number of oxygen atoms bonded to the iron element is large (hereinafter referred to as the oxygen carrier in an oxidized state), and FeO (iron oxide (II)), which is an oxygen carrier in a reduced state in which the number of oxygen atoms bonded to the iron element is smaller (hereinafter referred to as the oxygen carrier in a reduced state).

[0027] The calcium oxide production system 10 comprises an air combustion section 11, a calcination / fuel reaction section 12 in which a calcination reaction section and a fuel reaction section are integrally formed, a first supply path 13 and a second supply path 14 for transferring an oxygen carrier between the air combustion section 11 and the calcination / fuel reaction section 12, and a separation section 15 connected to the calcination / fuel reaction section 12.

[0028] The air combustion section 11 is composed of, for example, a reaction tower. FeO, which is an oxygen carrier in a reduced state, is introduced into the air combustion section 11 through a second supply line 14 connected to the calcination / fuel reaction section 12. Air (outside air) or the like is introduced into the air combustion section 11 by, for example, a fan.

[0029] The air combustion unit 11 binds oxygen contained in the air to FeO in a temperature environment of an oxidation temperature, for example, 900°C or higher, and a temperature lower than the sintering temperature of the oxygen carrier (for example, 1200°C or lower), and converts it to Fe2O3, which is an oxygen carrier in an oxidized state (air combustion process). That is, FeO reacts with oxygen in the air to generate Fe2O3 as shown in formula (1). 4FeO+O2→2Fe2O3(-577kJ / mol)...(1)

[0030] The above-mentioned reaction from FeO to Fe2O3 is an exothermic reaction, and the air combustion section 11 is maintained at an oxidation temperature of 1000°C to 1200°C by the thermal energy generated by this exothermic reaction. Then, the oxidized oxygen carrier Fe 2 O 3 produced in the air combustion section 11 is supplied to the calcination and fuel reaction section 12 via the first supply passage 13 .

[0031] Furthermore, the nitrogen remaining after oxygen has been removed from the air by the air combustion step may be discharged directly from the reaction tower of the air combustion section 11, and may also be utilized as a nitrogen source or a heat source.

[0032] The calcination / fuel reaction section 12 is an integrated calcination reaction section and a fuel reaction section, and is composed of, for example, a reaction tower. Oxidized oxygen carrier Fe2O3 is introduced into the calcination / fuel reaction section 12 through a first supply line 13 connected to the air combustion section 11.

[0033] Also, calcium carbonate (CaCO3), which is a raw material for producing calcium oxide (CaO), for example in a powder state, is supplied to the calcination / fuel reaction section 12. Furthermore, for example, coal and steam are supplied to the calcination / fuel reaction section 12 as a hydrocarbon source, which is the fuel.

[0034] The calcination / fuel reaction section 12 thermally decomposes calcium carbonate in a temperature environment of, for example, 850°C to less than 1000°C by supplying an oxygen carrier in an oxidized state heated in the air combustion section 11, to generate calcium oxide and carbon dioxide as shown in formula (2) (calcination reaction step). CaCO3→CaO+CO2(+178kJ / mol)···(2)

[0035] The carbon dioxide generated by such a calcination reaction step is produced by thermally decomposing calcium carbonate, and therefore has a high purity, for example, carbon dioxide of 95 to 100 vol % purity.

[0036] In addition, the calcination / fuel reaction section 12 is supplied with an oxidized oxygen carrier heated in the air combustion section 11, and in a temperature environment at a reduction temperature lower than the oxidation temperature of the air combustion section 11, for example, a temperature of less than 850 to 1000°C, reacts the carbon contained in the coal fuel with water vapor to produce carbon monoxide and hydrogen as shown in formula (3), and further reacts this carbon monoxide and hydrogen with the oxidized oxygen carrier Fe2O3 to produce the reduced oxygen carrier FeO and carbon dioxide as shown in formula (4) (fuel reaction process). C+H2O→CO+H2(+131kJ / mol)...(3) 2Fe2O3+CO+H2→4FeO+CO2+H2O(+52kJ / mol)...(4)

[0037] The calcination reaction process and fuel reaction process occurring in the calcination / fuel reaction section 12 are large endothermic reactions as shown in the above formula 2. Therefore, in order to maintain the reaction continuously and appropriately, it is preferable to circulate more of the oxidized oxygen carrier (Fe2O3), which serves as the reaction heat source, than the theoretical value. For example, about 8 moles of Fe2O3, which serves as the reaction heat source, are supplied for 1 mole of the input raw material CaCO3. An example of the heat balance in such a calcination reaction process is shown in formula (5). CaCO3 (raw material: 800°C) + 8Fe2O3 (reaction heat source: 1100°C) + 0.5C (43°C) = CaO + 2FeO + 7Fe2O3 + 1.5CO2 (total product: 850°C) (5)

[0038] FeO, which is a reduced oxygen carrier generated in the fuel reaction step of the calcination / fuel reaction section 12, is supplied to the air combustion section 11 via the second supply path 14 (second supply step). In this second supply step, in addition to FeO, Fe2O3 that has not reacted in the calcination / fuel reaction section 12 is also returned to the air combustion section 11.

[0039] The separation section 15 connected to the calcination / fuel reaction section 12 introduces CaO and CO2 produced by thermal decomposition of CaCO3 in the calcination reaction process of the calcination / fuel reaction section 12, and CO2 produced in the fuel reaction process, and separates the CaO and CO2 into solid and gas. For example, a cyclone-type solid-gas separator or a filter-type solid-gas separator can be used for the separation section 15.

[0040] High-purity CaO is produced through this separation section 15. The separated CO2 has a high purity (for example, 95 to 100 vol%) and can be used as it is as an industrial carbon dioxide source without any special concentration treatment.

[0041] As described above, according to the method for producing calcium oxide of the present embodiment, when calcium carbonate is thermally decomposed, calcium carbonate is directly contacted with an oxygen carrier heated to a temperature equal to or higher than the thermal decomposition temperature, whereby high-concentration calcium oxide can be produced efficiently and at low cost with a simple configuration. In addition, the carbon dioxide produced at the same time is highly pure with few impurities, and can therefore be used as a low-cost source of carbon dioxide for industrial use without the need for post-processing such as concentration.

[0042] In this embodiment, iron oxide is used as the oxygen carrier, but the oxygen carrier is not limited to this. For example, nickel oxide, copper oxide, and manganese oxide can be used as the oxygen carrier. Nickel oxide: NiO (reduced oxygen carrier), Ni2O3 (oxidized oxygen carrier) Copper oxide: Cu2O (reduced oxygen carrier), CuO (oxidized oxygen carrier) Manganese oxide: MnO (reduced oxygen carrier), MnO2 (oxidized oxygen carrier)

[0043] In this embodiment, coal is used as the hydrocarbon source, which is the fuel, but the present invention is not limited thereto, and for example, solid fuel, liquid fuel, gas fuel, etc. can be used. In addition to coal, examples of solid fuel include biomass, waste plastic, and combustible garbage. Examples of liquid fuel include alcohol, light oil, and heavy oil. Examples of gas fuel include natural gas and methane gas.

[0044] In addition, calcium carbonate used as a raw material for producing calcium oxide in this embodiment includes limestone and dolomite, which are natural ores, and CaCO3, which is produced by recombining CaO and CO2 during the process.

[0045] Second embodiment FIG. 2 is a schematic diagram showing a calcium oxide production system according to a second embodiment of the present invention for carrying out the calcium oxide production method. The same components as those in the first embodiment are given the same reference numbers, and duplicated explanations will be omitted. The calcium oxide manufacturing system 20 of this embodiment includes an air combustion section 11, a calcination reaction section 21, a fuel reaction section 22, first supply passages 13A, 13B for transferring oxidized oxygen carriers between the air combustion section 11 and the calcination reaction section 21, and between the calcination reaction section 21 and the fuel reaction section 22, respectively, a second supply passage 14 for transferring reduced oxygen carriers between the fuel reaction section 22 and the air combustion section 11, and a separation section 15 connected to the calcination reaction section 21.

[0046] The calcination reaction section 21 is composed of, for example, a reaction tower. Fe2O3, which is an oxygen carrier in an oxidized state, is introduced into the calcination reaction section 21 from the first supply line 13A connected to the air combustion section 11. In addition, calcium carbonate (CaCO3), which is a raw material for producing calcium oxide (CaO), is supplied to the calcination reaction section 21 in, for example, a powder state.

[0047] In the calcination reaction section 21, calcium carbonate is thermally decomposed in a temperature environment of, for example, 900°C to 1050°C by supplying an oxygen carrier in an oxidized state heated in the air combustion section 11, to generate calcium oxide and carbon dioxide as shown in the above-mentioned formula (2) (calcination reaction process). CaO and CO2 produced by thermal decomposition of CaCO3 in the calcination reaction step of the calcination reaction section 21 are introduced into the separation section 15 and then separated into CaO and CO2.

[0048] The fuel reaction section 22 is composed of, for example, a reaction tower. Fe2O3, which is an oxygen carrier in an oxidized state, is introduced into the fuel reaction section 22 through the first supply line 13B connected to the calcination reaction section 21. In addition, for example, coal and steam are supplied to the fuel reaction section 22 as a hydrocarbon source, which is a fuel.

[0049] The fuel reaction section 22 reacts the carbon contained in the coal fuel with steam in an environment of a reduction temperature lower than the oxidation temperature of the air combustion section 11, for example, 800°C to 900°C, by supplying an oxidized oxygen carrier after supplying heat for the thermal decomposition of calcium carbonate (CaCO3) in the calcination reaction section 21, to generate carbon monoxide and hydrogen as shown in the above formula (3), and further reacts the carbon monoxide and hydrogen with the oxidized oxygen carrier Fe2O3 to generate the reduced oxygen carrier FeO and carbon dioxide as shown in the above formula (4) (fuel reaction step). The reduced oxygen carrier (FeO) generated in the fuel reaction section 32 is introduced into the air combustion section 11 via the second supply passage 14.

[0050] In the second embodiment having such a configuration, the calcination reaction section 21 and the fuel reaction section 22 are provided independently, and the oxidized oxygen carrier heated in the air combustion section 11 is first supplied to the calcination reaction section 21, where an endothermic reaction (equation (2)) with a larger amount of heat absorption occurs, and then the oxidized oxygen carrier whose temperature has been slightly reduced in the calcination reaction section 21 is supplied to the fuel reaction section 22 and used as a heat source for the endothermic reaction (equations (3) and (4)) with a smaller amount of heat absorption. With this configuration, the efficiency of calcium carbonate (CaCO3) treatment can be improved, and the heat of the oxygen carrier in an oxidized state heated in the air combustion section 11 can be utilized more effectively.

[0051] Third embodiment FIG. 3 is a schematic diagram showing a calcium oxide production system according to a third embodiment of the present invention. The same components as those in the first embodiment are given the same reference numbers, and duplicated explanations will be omitted. The calcium oxide manufacturing system 30 of this embodiment comprises an air combustion section 11, a calcination reaction section 31, a fuel reaction section 32, first supply passages 13C, 13D, 13E for transferring oxidized oxygen carriers between the air combustion section 11 and the calcination reaction section 31, and between the air combustion section 11 and the fuel reaction section 32, respectively, a second supply passage 14 for transferring reduced oxygen carriers between the fuel reaction section 32 and the air combustion section 11, and a separation section 15 connected to the calcination reaction section 31.

[0052] The calcination reaction section 31 is composed of, for example, a reaction tower. An oxygen carrier, Fe2O3, in an oxidized state is introduced into the calcination reaction section 31 from the first supply path 13C connected to the air combustion section 11. In this embodiment, the oxygen carrier supplied to the calcination reaction section 31 is a heat medium (heat source) that does not contribute to the reaction, and the composition of the oxygen carrier (heat medium) does not change until it is supplied from the air combustion section 11 to the calcination reaction section 31 via the first supply path 13C and returned from the calcination reaction section 31 to the air combustion section 11 via the first supply path 13D.

[0053] Such a heat medium may have a different composition from the oxygen carrier supplied to the calcination reaction section 31. For example, as the heat medium supplied to the calcination reaction section 31, other than iron oxide, aluminum oxide, silicon oxide, or other materials having a large heat capacity can be used. In addition, when the heat transfer medium flowing through the calcination reaction section 31 and the oxygen carrier flowing through the fuel reaction section 32 are made of different substances, a separator that classifies the materials according to particle size can be provided at the outlet of the air combustion section 11 to separate the heat transfer medium and the oxygen carrier.

[0054] Calcium carbonate (CaCO3), which is a raw material for producing calcium oxide (CaO), is supplied, for example, in a powder state, to the calcination reaction section 31. Then, in the calcination reaction section 31, calcium carbonate is thermally decomposed in a temperature environment of, for example, 900°C to 1050°C by supplying an oxygen carrier as a heat medium heated in the air combustion section 11, to produce calcium oxide and carbon dioxide as shown in the above-mentioned formula (2) (calcination reaction step). CaO and CO2 produced by thermal decomposition of CaCO3 in the calcination reaction step of the calcination reaction section 31 are introduced into the separation section 15 and then separated into CaO and CO2.

[0055] The fuel reaction section 32 is composed of, for example, a reaction tower. Fe2O3, which is an oxygen carrier in an oxidized state, is introduced into the fuel reaction section 32 from a first supply passage 13E connected to the air combustion section 11. In addition, for example, coal and steam are supplied to the fuel reaction section 32 as a hydrocarbon source, which is a fuel.

[0056] The fuel reaction section 32 reacts the carbon contained in the coal fuel with steam in an environment of a reduction temperature lower than the oxidation temperature of the air combustion section 11, for example, 800°C to 900°C, by supplying the oxidized oxygen carrier Fe2O3 from the air combustion section 11, to generate carbon monoxide and hydrogen as shown in the above formula (3), and further reacts the carbon monoxide and hydrogen with the oxidized oxygen carrier Fe2O3 to generate the reduced oxygen carrier FeO and carbon dioxide as shown in the above formula (4) (fuel reaction step). The reduced oxygen carrier (FeO) generated in the fuel reaction section 32 is introduced into the air combustion section 11 via the second supply passage 14.

[0057] In the third embodiment having such a configuration, the calcination reaction section 31 and the fuel reaction section 32 are provided independently, and an oxygen carrier is supplied to the calcination reaction section 31 as a heat medium whose composition does not change, while an oxidized oxygen carrier is supplied to the fuel reaction section 32 and converted into a reduced oxygen carrier which is then returned to the air combustion section 11. This configuration improves the processing efficiency of calcium carbonate (CaCO3) and makes more effective use of the heat of the oxygen carrier heated in the air combustion section 11.

[0058] (Fourth embodiment) FIG. 4 is a schematic diagram showing a calcium oxide production system according to a fourth embodiment of the present invention. The same components as those in the first embodiment are given the same reference numbers, and duplicated explanations will be omitted. The calcium oxide production system 40 of this embodiment includes an air combustion section 11, a calcination / fuel reaction section 12 in which a calcination reaction section and a fuel reaction section are integrally formed, a first supply path 13 and a second supply path 14 for transferring an oxygen carrier between the air combustion section 11 and the calcination / fuel reaction section 12, a separation section 15 connected to the calcination / fuel reaction section 12, and a carbon dioxide absorption section 41.

[0059] The carbon dioxide absorption section 41 is composed of, for example, a reaction tower. Calcium oxide (CaO) produced in the calcination / fuel reaction section 12 and carbon dioxide (CO2) are separated from each other in the separation section 15, and CaO is introduced into the carbon dioxide absorption section 41. Furthermore, exhaust gas containing CO2 is introduced into the carbon dioxide absorption section 41.

[0060] The carbon dioxide absorption unit 41 binds CO2 contained in the exhaust gas to CaO in a temperature environment of, for example, 400 to 600° C., and converts it to calcium carbonate (CaCO3) (carbon dioxide absorption step). That is, CaO reacts with CO2 to generate CaCO3 as shown in formula (6). CaO+CO2→CaCO3(-178kJ / mol)···(6)

[0061] The CaCO3 produced in the carbon dioxide absorption section 41 is supplied to the calcination / fuel reaction section 12, where it is thermally decomposed again into CaO and CO2 by the heat of Fe2O3, an oxygen carrier in an oxidized state supplied from the air combustion section 11.

[0062] In the fourth embodiment having such a configuration, the generated CaO is used to absorb CO2 contained in exhaust gas, so that the CO2 in the exhaust gas containing a large amount of CO2 can be removed and released into the atmosphere as clean gas with reduced greenhouse gas emissions.

[0063] Although the embodiment of the present invention has been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. This embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. This embodiment and its modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and gist of the invention. EXAMPLES

[0064] The effects of the present invention were verified below. The internal temperature of the fuel reactor (volume: 0.02 m) was set to 950°C. 3 ) and an air combustion tower (with an internal volume of 0.03 m) with the internal temperature set to 1100°C. 3 An oxygen carrier made of iron oxide (oxidized Fe2O3, reduced FeO) was circulated between the fuel reactor and the air combustion tower. Coal and steam were introduced into the fuel reactor, and air was introduced into the air combustion tower.

[0065] Then, the exhaust gas discharged from the fuel reactor and the exhaust gas discharged from the air combustion tower were collected and their compositions were analyzed. The composition of the exhaust gas discharged from the fuel reactor is shown in Figure 5, and the composition of the exhaust gas discharged from the air combustion tower is shown in Figure 6. In the example, the amount of coal fed per unit time was doubled one hour after the start of the experiment.

[0066] From the results shown in Figures 5 and 6, it can be seen that the exhaust gas composition from the fuel reactor is mostly CO2, and that the oxygen in the exhaust gas from the air combustion tower decreases as the amount of coal fed increases. These results confirm that the oxidized oxygen carrier (Fe2O3) reacts with the carbon and hydrogen in the coal (see formulas (3) and (4)), and that the reduced oxygen carrier (FeO) is reoxidized by oxygen in the air in the air combustion tower (see formula (1)).

[0067] Next, a simulation was performed on the equilibrium temperature and composition of CaCO3 and CaO for the calcination / fuel reaction section shown in the first embodiment. The results are shown in FIG. According to the results shown in Figure 7, CaCO3 and CaO reach equilibrium at around 750°C. It is preferable to set the temperature of the calcination / fuel reaction section to a temperature above 850°C, where the partial pressure ratio of CaCO3 and CaO becomes 2:8, and below the temperature of the air combustion section. [Industrial Applicability]

[0068] The present invention can be widely applied to various manufacturing plants that require calcium oxide, such as cement manufacturing plants. In addition, since the manufactured calcium oxide can be used to absorb carbon dioxide, the present invention can also be applied to the purification of exhaust gas from various manufacturing plants that emit exhaust gas containing carbon dioxide. Therefore, the present invention has industrial applicability.

Claims

1. using an oxygen carrier including a metal oxide that can change between an oxidized state and a reduced state depending on the number of bonds of an oxygen element to a metal element; an air combustion process in which the oxygen carrier in a reduced state is mixed with air, and oxygen contained in the air is bound to the oxygen carrier in an environment at or above an oxidation temperature, thereby changing the oxygen carrier to an oxidized state; a calcination reaction step in which calcium carbonate is decomposed into calcium oxide and carbon dioxide by thermal energy of the oxygen carrier in an oxidized state heated in the air combustion step; a fuel reaction step of mixing hydrocarbon and water, burning them with oxygen bound to the oxygen carrier in an oxidized state heated in the air combustion step, and reducing the number of bound oxygen atoms in the oxygen carrier in an oxidized state in an environment of a reducing temperature lower than the oxidation temperature to bring the oxygen carrier into a reduced state; a first supply step of supplying the oxygen carrier in an oxidized state from the air combustion step to the calcination reaction step and the fuel reaction step; A second supply step of supplying the oxygen carrier in a reduced state from the fuel reaction step to the air combustion step, The method for producing calcium oxide, wherein the calcination reaction step and the fuel reaction step are carried out in separate reactors.

2. 2. The method for producing calcium oxide according to claim 1, further comprising a separation step of separating calcium oxide and carbon dioxide produced by decomposition in the calcination reaction step from each other.

3. 3. The method for producing calcium oxide according to claim 2, further comprising a carbon dioxide absorption step of mixing the calcium oxide separated in the separation step with an exhaust gas containing carbon dioxide outside the system, and reacting the calcium oxide with the carbon dioxide in the exhaust gas to produce calcium carbonate, which is then supplied to the calcination reaction step.

4. 4. The method for producing calcium oxide according to claim 1, wherein the oxygen carrier contains at least one of iron oxide, nickel oxide, copper oxide, manganese oxide, and calcium sulfate.

5. 5. The method for producing calcium oxide according to claim 1, wherein the air combustion step changes the oxygen carrier from a reduced state to an oxidized state in a range of 1000° C. or higher and a sintering temperature of the oxygen carrier or lower.

6. The method for producing calcium oxide according to any one of claims 1 to 5, characterized in that, in the calcination reaction step, in addition to the oxygen carrier in an oxidized state, another heat medium is further supplied.

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