Carbon dioxide recovery device and carbon dioxide recovery method

Abstract

The present invention addresses the problem of providing a carbon dioxide recovery device and a carbon dioxide recovery method by a method of calcium looping that permits calcination by heat in a low temperature region, for example, exhaust heat.　This carbon dioxide recovery device is characterized by comprising a thermal decomposition device that thermally decomposes calcium carbonate into calcium oxide and carbon dioxide under reduced pressure and a carbonation device that generates calcium carbonate by reacting calcium oxide received from the thermal decomposition device and carbon dioxide supplied from the outside.

Description

Carbon dioxide capture device and carbon dioxide capture method

[0001] The present invention relates to a carbon dioxide capture device and a carbon dioxide capture method.

[0002] In recent years, the issue of carbon dioxide has become a major cause of global warming, and reducing carbon dioxide emissions into the environment has become an urgent issue worldwide. In particular, carbon dioxide separation using carbon dioxide capture and storage (CCS) is essential for carbon dioxide emission sources such as fossil fuel-based thermal power plants. One method for storing separated and captured carbon dioxide is to contain it underground in a reservoir beneath a shielding layer such as mudstone. It is believed that carbon dioxide remains in the reservoir but dissolves in formation water, reacts with surrounding rocks to become mineralized, and can be stably contained for a long period of time. When storing carbon dioxide in a geological formation, high purity carbon dioxide is preferred, taking into account factors such as transportation to the storage site and injection into the formation.

[0003] The calcium looping technique, in which calcium oxide reacts to fix carbon dioxide, is an effective candidate technology for carbon dioxide fixation. In the calcium looping technique, calcium carbonate and calcium oxide are used. Because calcium carbonate is generated from calcium oxide and carbon dioxide, it has the effect of fixing carbon dioxide, and is therefore sometimes called an adsorbent. Calcium carbonate is decomposed into calcium oxide and carbon dioxide through thermal decomposition, and this calcium oxide can be used again as a carbon dioxide adsorbent. The term calcium looping derives from the use of this reversible reaction. Because the carbon dioxide obtained by thermal decomposition of calcium carbonate is highly pure, it can also be used for industrial purposes. Patent Document 1 discloses an energy recovery method that utilizes the exothermic nature of the carbon dioxide capture process in which calcium oxide is converted into calcium carbonate.

[0004] Special Publication No. 2016-530983

[0005] The calcium looping method aims to capture carbon dioxide by utilizing the reversible reaction between calcium carbonate, a carbonate salt of calcium, and calcium oxide, an oxide of calcium. To separate carbon dioxide from calcium carbonate, a stable substance, a thermal decomposition technique called calcination is used, which typically requires high temperatures of 800°C or higher. Calcination here refers to a heat treatment process in which a solid, such as ore, is heated to cause thermal decomposition or phase transition, or to remove volatile components. This is typically carried out at a temperature below the melting point of the substance. Patent Document 1 also states that calcium carbonate is heated to 800°C to 950°C, regenerating calcium oxide and simultaneously releasing carbon dioxide.

[0006] Waste heat recovery, which leads to energy savings, is also an important means of reducing carbon dioxide emissions into the environment. Waste heat recovery reduces not only the demand for fossil fuels but also greenhouse gases, helping to provide a more sustainable society for the future. However, the thermal energy required in the calcination process of calcium looping, at 800°C to 950°C, falls into the high-temperature range and is of a quality that cannot normally be obtained through waste heat recovery.

[0007] Therefore, an object of the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a carbon dioxide recovery apparatus and a carbon dioxide recovery method using a calcium looping method that enables calcination using heat in a lower temperature range, such as exhaust heat, rather than high-temperature heat of 800°C or higher, by enabling thermal decomposition of calcium carbonate in a lower temperature range.

[0008] As a result of intensive research into the above-mentioned problems, the present inventors have found that since the calcination temperature for thermally decomposing calcium carbonate can be lowered under reduced pressure, it is possible to realize a calcium looping method that utilizes waste heat, for example, below 800°C, and have completed the present invention. That is, the present invention relates to the following carbon dioxide recovery apparatus and carbon dioxide recovery method.

[0009] The carbon dioxide recovery system of the present invention, which solves the above-mentioned problems, is characterized by comprising a thermal decomposition device that thermally decomposes calcium carbonate into calcium oxide and carbon dioxide under reduced pressure, and a carbonation device that produces calcium carbonate by reacting calcium oxide received from the thermal decomposition device with carbon dioxide supplied from an external source. By reducing the pressure, the temperature range required for calcining and thermally decomposing calcium carbonate can be lowered, so that, for example, exhaust heat from a gas turbine can be used as a heat source for the thermal decomposition of calcium carbonate. This enables energy-saving carbon dioxide recovery using exhaust heat.

[0010] Furthermore, one embodiment of the carbon dioxide recovery system of the present invention is characterized in that exhaust gas from a gas turbine of a combined cycle power generation system is used as a heat source for a thermal decomposition system that thermally decomposes calcium carbonate, and the exhaust gas used for thermal decomposition of calcium carbonate is heated by heat generated in a carbonation system and supplied as a heat source for steam generation in a steam turbine. This allows for the use of exhaust gas from a gas turbine in combined cycle power generation as a heat source for decomposing calcium carbonate, and further, the exhaust gas therefrom can be heated by using the heat generated during calcium carbonate production from calcium oxide and carbon dioxide and supplied as a heat source for steam turbine power generation, thereby enabling multi-stage utilization of thermal energy. Heat utilization using calcium oxide as a heat storage material makes it possible to control the calorific value of exhaust heat, expanding the scope of uses for exhaust heat utilization.

[0011] The carbon dioxide recovery method of the present invention, which solves the above-mentioned problems, is characterized by comprising a thermal decomposition step of thermally decomposing calcium carbonate into calcium oxide and carbon dioxide under reduced pressure, and a carbonation step of producing calcium carbonate by reacting calcium oxide received from a thermal decomposition device with carbon dioxide supplied from outside. The reduced pressure makes it possible to lower the temperature at which calcium carbonate is calcined and thermally decomposed, enabling energy-saving carbon dioxide recovery using exhaust heat.

[0012] Furthermore, one embodiment of the carbon dioxide recovery method of the present invention is characterized in that exhaust gas from a gas turbine of a combined cycle power generation system is used as a heat source for a thermal decomposition step of thermally decomposing the calcium carbonate, and the exhaust gas used for thermally decomposing the calcium carbonate is heated by heat generated in a carbonation step and supplied as a heat source for steam generation in a steam turbine. This makes it possible to use the exhaust gas from the gas turbine power generation as a heat source for decomposing calcium carbonate, and further to heat the exhaust gas therefrom in the heat utilization step and supply it as a heat source for steam turbine power generation, thereby providing a carbon dioxide recovery method that enables multi-stage utilization of thermal energy and further improves power generation efficiency.

[0013] According to the present invention, it is possible to provide a carbon dioxide recovery apparatus and a carbon dioxide recovery method using a calcium looping method that enables thermal decomposition of calcium carbonate at a lower temperature range and enables calcination even with exhaust heat of, for example, below 800°C.

[0014] It is a conceptual diagram of calcium looping. It is a schematic explanatory diagram of a carbon dioxide capture device according to a first embodiment of the present invention. It is a schematic explanatory diagram of a carbon dioxide capture device according to a second embodiment of the present invention.

[0015] The following describes in detail the embodiments of the present invention, but the present invention is not limited to these, and various modifications are possible within the scope of the description. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0016] Carbon dioxide (CO ) is produced by the repeated thermal decomposition and carbonation of calcium carbonate (CaCO ). ２The absorption and desorption of carbon dioxide is generally called calcium looping. Calcium carbonate, which is used as an adsorbent or carrier for carbon dioxide, is widely found in nature, is inexpensive, and is highly safe. Figure 1 shows the concept of calcium looping used in an embodiment of the present invention. The carbonate looping method using carbonate is generally called calcium looping. Calcium looping consists of two reactions: carbonation, which produces calcium carbonate by the reaction of calcium oxide with carbon dioxide, and thermal decomposition, which separates calcium carbonate into calcium oxide and carbon dioxide by thermal decomposition. The reaction formula is as follows: Carbonation CaO + CO ２ → CaCO3 ΔH = -178 kJ ... (Reaction formula 1) Decarbonation CaCO3 → CaO + CO ２ ΔH = +178 kJ... (Reaction Formula 2) Carbonation is an exothermic reaction in the reaction temperature range of 600 to 700°C. Decarbonization is an endothermic reaction in the reaction temperature range of 800 to 900°C. These reactions to produce calcium carbonate from calcium oxide and carbon dioxide, and to separate calcium carbonate into calcium oxide and carbon dioxide, are reversible, and in theory, these reactions can be repeated any number of times.

[0017] Calcium looping has two technical functions. One is a technology that captures carbon dioxide derived from the combustion of fossil fuels. Calcium oxide binds with carbon dioxide to produce calcium carbonate, which fixes the carbon dioxide. In this case, calcium oxide functions as a carbon dioxide adsorbent. Furthermore, the gaseous carbon dioxide obtained by thermally decomposing the calcium carbonate produced by decarbonization has few impurities and is suitable for refinement, storage, or use. The other is a technology that functions as an energy storage material for renewable energy power generation. Taking advantage of the fact that the carbonation reaction between calcium oxide and carbon dioxide is an exothermic reaction, calcium oxide is used as a chemical heat storage material. This chemical heat storage function can be applied to create a chemical heat pump function that outputs at a temperature different from the input temperature level.

[0018] [First Embodiment] FIG. 2 is a diagram showing the schematic configuration of a carbon dioxide capture system 10a according to an embodiment of the present invention. The carbon dioxide capture system 10a includes a thermal decomposition device 101 and a carbonation device 201. The thermal decomposition device 101 calcines calcium carbonate under a predetermined reduced pressure to produce solid calcium oxide and gaseous carbon dioxide. The calcium oxide is returned to the carbonation device 201 and reused for reaction with carbon dioxide. The carbonation device 201 contains solid calcium oxide returned from the thermal decomposition device 101 and comes into contact with exhaust gas containing carbon dioxide. The calcium oxide reacts with the carbon dioxide in the exhaust gas to produce calcium carbonate. This reduces the carbon dioxide concentration in the exhaust gas. The produced calcium carbonate is returned to the thermal decomposition device 101. The carbon dioxide emitted from the thermal decomposition device 101 contains few impurities and can be stored and used as a chemical raw material. Therefore, it is convenient to have a device to temporarily store this carbon dioxide. The carbon dioxide retention device 301 retains the carbon dioxide produced by thermal decomposition in the thermal decomposition device 201. The temporarily held carbon dioxide is stored or used as a chemical raw material. The thermal decomposition device 101, the carbonation device 201, and the carbon dioxide holding device 301 will be described below.

[0019] (Thermal Decomposition Apparatus) The thermal decomposition apparatus 101 decomposes calcium carbonate into calcium oxide and carbon dioxide. In the thermal decomposition apparatus 101 according to an embodiment of the present invention, the thermal decomposition temperature is lowered by reducing the pressure inside the thermal decomposition apparatus 101. For example, when the pressure inside the thermal decomposition apparatus 101 is reduced to 40 Pa, decarbonation is possible in a reaction temperature range of 500 to 600°C. The thermal decomposition apparatus 101 may be any apparatus capable of thermally decomposing calcium carbonate, and its configuration is not particularly limited. As long as it is capable of reducing the pressure, it may be a fluidized-bed type thermal decomposition apparatus commonly used in calcination. Furthermore, a vacuum heat treatment furnace can more effectively achieve thermal decomposition of calcium carbonate under reduced pressure while preventing oxidation reactions. Since decarbonation is possible in a reaction temperature range of 500 to 600°C, the heat source supplied to the thermal decomposition apparatus 101 can be, for example, exhaust heat from exhaust gas from a carbon dioxide emission source such as a boiler. This is advantageous as a carbon dioxide capture device installed next to a carbon dioxide emission source.

[0020] The calcium oxide produced in the thermal decomposition device 101 is recycled to the carbonation device 201 and used again as a carbon dioxide adsorbent. Furthermore, calcium oxide that has been repeatedly regenerated and whose carbon dioxide adsorption performance has deteriorated is discharged outside the carbon dioxide recovery device 10a, and new calcium oxide raw material is replenished. The deteriorated calcium oxide discharged outside the carbon dioxide recovery device 10a can be used for a variety of purposes other than as a chemical thermal storage material, such as raw material for building materials such as bricks, mortar, and plaster, glass, paper, the production of sodium carbonate by the ammonia-soda process (Solvay process), the refining of steel, aluminum, and magnesium, the production of various calcium salts and industrial chemical products, the decolorization of sucrose and beet sugar solution, insecticides and fungicides, and sewage treatment.

[0021] (Carbonation Device) The carbonation reaction between calcium oxide contained in carbonation device 201 and carbon dioxide introduced into the device along with the exhaust gas proceeds in a reaction temperature range of 600 to 700°C. If the temperature of the exhaust gas is higher than this reaction temperature range, the exhaust gas is cooled before being introduced into carbonation device 101. Conversely, if the temperature of the exhaust gas is lower than this reaction temperature range, the temperature is raised before being introduced into carbonation device 101. The heat to be input into pyrolysis device 101 can be used as a heat source for raising the temperature. Calcium carbonate produced by the carbonation reaction is refluxed to pyrolysis device 101 and subjected to separation into calcium oxide and carbon dioxide. After refluxing to pyrolysis device 201, calcium oxide produced by pyrolysis is refluxed to carbonation device 201 and used as an adsorbent for carbon dioxide.

[0022] In this way, if the performance of calcium carbonate deteriorates due to the repeated alternating carbonation and thermal decomposition reactions, calcium carbonate may be introduced from the outside as necessary. Calcium carbonate with deteriorated performance may be stored as solid calcium carbonate with carbon dioxide fixed, without being refluxed to the thermal decomposition apparatus 101. Furthermore, calcium carbonate may be used as a raw material for building materials and cement, as a filler in the fields of paper, plastics, rubber, adhesives, sealants, and paints, as an additive for foods such as salt and cosmetics, as a raw material for producing carbon dioxide gas, and for various other purposes.

[0023] (Carbon dioxide retention device) The carbon dioxide retention device 301 is a device that temporarily retains the gaseous carbon dioxide generated in the thermal decomposition device 201. The carbon dioxide may be retained in its gaseous state, or may be retained in a state in which it is adsorbed onto an adsorbent material such as zeolite. In the carbon dioxide capture device 10a of this embodiment, carbon dioxide is captured by adsorbing carbon dioxide onto calcium oxide and then thermally decomposing the calcium carbonate. Therefore, the captured carbon dioxide has a high purity and is therefore suitable for industrial applications. Carbon dioxide has a variety of industrial uses, including as a coolant, refrigerant, and fire extinguisher. It is also used for welding, cutting, paint stripping, chemical reactions, and other applications. It can also be retained using a retention method appropriate for the industrial application.

[0024] According to the carbon dioxide capture device 10a of this embodiment, decarbonation can be performed at a lower reaction temperature range of 500 to 600°C, rather than the reaction temperature range of 800 to 900°C. This makes it possible to perform calcium looping decarbonation, which previously required high-temperature input, with a wider range of heat sources, such as exhaust gas, thereby providing a carbon dioxide capture device with higher thermal efficiency. The effect of high thermal efficiency is that carbon dioxide emissions from the heat source can also be reduced.

[0025] [Second embodiment] A carbon dioxide capture device 10b according to a second embodiment of the present invention will be described below. FIG. 3 is a schematic explanatory diagram of a carbon dioxide capture device according to a second embodiment of the present invention. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof will be omitted. The same applies to the third embodiment hereinafter. The carbon dioxide capture device 10b includes a thermal decomposition device 101 and a carbonation device 201.

[0026] The calcium carbonate built into the carbonation device 201 reacts with carbon dioxide introduced into the carbonation device 201 along with the exhaust gas from the gas turbine of combined cycle power generation, to produce calcium carbonate. Similar to the first embodiment, the carbonation device 201 introduces the exhaust gas and produces gas from which carbon dioxide has been removed. Because the reaction from which calcium carbonate is produced between calcium carbonate and carbon dioxide is an exothermic reaction, the gas from which carbon dioxide has been removed can be heated to a temperature higher than before being introduced into the carbonation device 201. The heated gas from which carbon dioxide has been removed can be used as a heat source for the waste heat recovery boiler of the steam turbine of combined cycle power generation.

[0027] A carbon dioxide capture device 10b according to a second embodiment of the present invention is a carbon dioxide capture device that uses calcium oxide as a heat storage material and has the function of a so-called chemical heat pump. A chemical heat pump uses a specific chemical material as a chemical heat storage material to reversibly store heat and generate heat. It is also a system that recovers exhaust heat generated from various industrial processes without requiring the input of electrical energy or the like. The carbon dioxide capture device 10b according to the second embodiment uses calcium oxide / calcium carbonate chemical heat storage. It is possible to release heat generated when calcium oxide in the chemical heat storage material reacts with carbon dioxide, and conversely, it is possible to store heat as a chemical heat storage material by heating the calcium carbonate produced by the carbonation of calcium oxide and separating it from carbon dioxide.

[0028] The function of a chemical heat pump is explained using Figure 2. Unlike mechanical heat pumps, chemical heat pumps use specific chemical materials to reversibly store and output heat. They are systems that recover waste heat generated from various industrial processes without requiring the input of electrical energy. Chemical heat pumps have the following advantages: high heat storage density, little heat loss during heat storage, the ability to store heat at room temperature, and the ability to release heat at a temperature higher than the temperature during heat storage.

[0029] The reaction of calcium carbonate produced by calcium oxide and carbon dioxide in the carbonation device 201 is an exothermic reaction. In this case, from the perspective of a heat pump function, the carbonation device 201 contains calcium oxide, a heat storage material. The produced calcium carbonate is returned to the thermal decomposition device 101, where carbon dioxide is separated and calcium oxide is regenerated as a heat storage material. Because the thermal decomposition of calcium carbonate in the thermal decomposition device 101 is an endothermic reaction, heat input is required for the reaction. Calcium oxide, a heat storage material, is regenerated by the input heat and returned to the carbonation device 201 for the exothermic reaction. The chemical heat pump is one of the energy-recycling heat pump technologies that uses chemical heat storage to store heat, reform the heat, and reuse it as hot and cold energy. Chemical heat storage is a method of converting heat into a substance using a reversible chemical reaction, storing the heat, and extracting and utilizing the heat through a reverse reaction.

[0030] A chemical heat pump is composed of two reaction systems: a main reaction system and a working medium storage system. In this embodiment, the carbonation device 201 acts as the main reaction system, and the thermal decomposition device 101 acts as the working medium storage system.

[0031] Chemical heat pumps that use calcium oxide / calcium carbonate chemical heat storage are characterized by being non-toxic and non-corrosive, having excellent reversibility of the reaction, not producing any by-products, and being readily available as raw materials for the heat storage material.

[0032] Inorganic calcium compounds include calcium carbonate, "CaCO ３ ”, slaked lime “Ca(OH) ２ ", quicklime "CaO", and dolomite "Ca·Mg(CO ３ ) ２ The particle size of the inorganic calcium compound is preferably 200 μm to 500 μm.

[0033] The carbon dioxide recovery device 10b of this embodiment can further improve the power generation efficiency of combined cycle power generation. The action of the chemical heat pump can accommodate heat sources in various temperature ranges required by users. Ultimately, the heat utilization efficiency can be improved, enabling effective use of heat. Furthermore, the effect of high thermal efficiency can also reduce carbon dioxide emissions from the heat source itself.

[0034] [Third Embodiment] The third embodiment of the present invention is a carbon dioxide recovery method that utilizes a reaction to produce calcium carbonate from calcium oxide and carbon dioxide, and a reaction to thermally decompose calcium carbonate into calcium oxide and carbon dioxide under reduced pressure. The configuration of the third embodiment is the same as the configuration of the apparatus of the first embodiment. Therefore, the description of the carbon dioxide recovery method in this embodiment can be replaced with the description of the features and operation of the carbon dioxide recovery apparatus of the first embodiment.

[0035] [Fourth Embodiment] A fourth embodiment of the present invention is a carbon dioxide recovery method in which exhaust gas from a gas turbine power generation system is used as a heat source for a thermal decomposition step of thermally decomposing calcium carbonate, and the exhaust gas used for thermally decomposing calcium carbonate is heated by heat generated in the carbonation step and supplied as a heat source for steam generation in a steam turbine power generation system. Regarding the configuration of the fourth embodiment of the present invention, the configuration of the apparatus in the second embodiment should be read as a method. Therefore, the description of the carbon dioxide recovery method in this embodiment can be replaced with the description of the features and operation of the carbon dioxide recovery apparatus in the second embodiment.

[0036] 10a, 10b Carbon dioxide recovery device, 101 Pyrolysis device, 201 Carbonation device, 301 Carbon dioxide retention device

Claims

1. A carbon dioxide recovery system comprising: a thermal decomposition device that thermally decomposes calcium carbonate into calcium oxide and carbon dioxide under reduced pressure; and a carbonation device that produces calcium carbonate by reacting the calcium oxide received from the thermal decomposition device with carbon dioxide supplied from an external source.

2. The carbon dioxide recovery system according to claim 1, characterized in that exhaust gas from a gas turbine of a combined cycle power generation system is used as a heat source for a thermal decomposition device that thermally decomposes the calcium carbonate, and the exhaust gas used to thermally decompose the calcium carbonate is heated by heat generated by the carbonation device and supplied as a heat source for generating steam for a steam turbine.

3. A carbon dioxide recovery method comprising: a thermal decomposition step of thermally decomposing calcium carbonate into calcium oxide and carbon dioxide under reduced pressure; and a carbonation step of producing calcium carbonate by reacting the calcium oxide received from the thermal decomposition device with carbon dioxide supplied from an outside source.

4. A method for recovering carbon dioxide as described in claim 3, characterized in that exhaust gas from a gas turbine of a combined cycle power generation system is used as a heat source for a thermal decomposition process in which the calcium carbonate is thermally decomposed, and the exhaust gas used for thermally decomposing the calcium carbonate is heated by heat generated in the carbonation process and supplied as a heat source for generating steam for a steam turbine.

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