Cement clinker production system

Abstract

To provide a cement clinker production system capable of obtaining gas containing carbon dioxide gas of a high concentration by increasing a carbon dioxide gas concentration of a part of exhaust gas.SOLUTION: A cement clinker production system 1 includes: a cyclone type pre-heating device 2 for pre-heating a cement clinker raw material; a rotary kiln 3 for burning the pre-heated cement clinker raw material so as to obtain cement clinker; a calcining furnace 4 for accelerating decarbonation of the cement clinker raw material; a clinker cooler 5 for cooling the cement clinker; kiln exhaust gas discharge passages 6a to 6e for discharging exhaust gas generated in the rotary kiln 3; a combustion supporting gas supply device for supplying combustion supporting gas increased in an oxygen concentration compared to air; a combustion supporting gas supply passage 8 for guiding combustion supporting gas to the furnace; and a furnace exhaust gas discharge passage 9 for discharging exhaust gas generated in the calcining furnace 4 (limited to being different from the kiln exhaust gas discharge passage 6).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cement clinker production system. [Background technology]

[0002] In recent years, reducing carbon dioxide emissions has become an important issue in order to curb global warming. Meanwhile, the cement industry is one of the industries that emits large amounts of carbon dioxide. Of the total amount of carbon dioxide (gaseous carbon dioxide) emitted during the production of cement, approximately 60% is emitted by the decarbonation of limestone, which is used as a raw material for cement, and approximately 40% is emitted by the combustion of fuel used during production. Methods for reducing carbon dioxide gas generated by fuel combustion include improving energy efficiency, using biomass fuel as fuel, etc. For example, Patent Document 1 describes a cement calcination apparatus that can reduce the amount of carbon dioxide gas generated by fuel combustion, which is characterized by having a main burner that injects combustible gas as the main fuel and combustible waste as the auxiliary fuel into a cement kiln.

[0003] On the other hand, it is difficult to use calcium-containing raw materials that generate less carbon dioxide as a cement raw material instead of limestone, which generates a lot of carbon dioxide, so it is difficult to reduce the amount of carbon dioxide generated by decarbonation of limestone. Known methods for reducing carbon dioxide emissions include separating and recovering the generated carbon dioxide gas, and then storing, isolating, or effectively utilizing the gas. As a method for separating and recovering the generated carbon dioxide gas, for example, Patent Document 2 describes a method for separating and recovering carbon dioxide from by-product gas generated in a steelworks by a chemical absorption method, in which carbon dioxide is absorbed from the gas by a chemical absorption liquid, and then the chemical absorption liquid is heated to separate the carbon dioxide, and the carbon dioxide separation and recovery method is characterized by utilizing or making use of low-grade exhaust heat of 500°C or less generated in the steelworks. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-52746 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-292298 Summary of the Invention [Problem to be solved by the invention]

[0005] The exhaust gas generated during the production of cement clinker contains large amounts of nitrogen, oxygen, and other elements in addition to carbon dioxide. Therefore, in order to separate and recover carbon dioxide from the exhaust gas, it is necessary to use a chemical absorption method using an amine compound, for example. If the concentration of carbon dioxide contained in the exhaust gas can be increased, it will be easier to separate and recover the carbon dioxide. 。 An object of the present invention is to provide a cement clinker production system that increases the carbon dioxide concentration in part of exhaust gas when producing cement clinker, thereby obtaining gas containing high concentrations of carbon dioxide that can be easily used for carbon dioxide fixation, etc. [Means for solving the problem]

[0006] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned objects can be achieved by a cement clinker production system including a cyclone-type preheating device for preheating cement clinker raw materials, a rotary kiln for burning the preheated cement clinker raw materials to obtain cement clinker, a calciner arranged upstream of the rotary kiln for accelerating the decarbonation of the cement clinker raw materials, a clinker cooler arranged downstream of the rotary kiln for cooling the cement clinker, and a kiln exhaust gas discharge path for discharging exhaust gas generated in the rotary kiln after passing through the cyclone-type preheating device, and the system also includes a combustion-supporting gas supply device for supplying a combustion-supporting gas having a higher oxygen concentration than air, a combustion-supporting gas supply path for guiding the combustion-supporting gas to the calciner, and a calciner exhaust gas discharge path (limited to being different from the kiln exhaust gas discharge path) for discharging exhaust gas generated in the calciner (limited to being different from the kiln exhaust gas discharge path). That is, the present invention provides the following [1] to [7]. [1] A cyclone type preheating device for preheating cement clinker raw materials, a rotary kiln for burning the cement clinker raw materials preheated by the cyclone type preheating device to obtain cement clinker, a calciner disposed upstream of the rotary kiln together with the cyclone type preheating device to promote decarbonation of the cement clinker raw materials, a clinker cooler disposed downstream of the rotary kiln to cool the cement clinker, and a clinker cooler disposed downstream of the rotary kiln to cool the exhaust gas generated in the rotary kiln. A cement clinker production system including a kiln exhaust gas discharge path for discharging the exhaust gas after passing through a cyclone-type preheating device, the cement clinker production system comprising: a combustion-supporting gas supply device for supplying a combustion-supporting gas having an oxygen concentration higher than that of air; a combustion-supporting gas supply path for guiding the combustion-supporting gas from the combustion-supporting gas supply device to the calciner; and a calciner exhaust gas discharge path (limited to being different from the kiln exhaust gas discharge path) for discharging carbon dioxide-containing exhaust gas generated in the calciner.

[0007] [2] The cement clinker production system according to [1], further comprising a chlorine bypass device for extracting and cooling a portion of the exhaust gas generated in the rotary kiln without passing through the cyclone preheating device, removing solids, discharging the exhaust gas from which the solids have been removed, and classifying the solids into coarse powder and fine powder, using the coarse powder as part of the cement clinker raw material, and recovering the fine powder. [3] The cement clinker production system according to [1] or [2], further comprising a confluence passage for confluence of a portion of the exhaust gas flowing through the calciner exhaust gas discharge passage with the combustion-supporting gas flowing through the combustion-supporting gas supply passage. [4] A method for producing cement clinker using the cement clinker production system according to any one of [1] to [3], characterized in that the oxygen concentration of the combustion-supporting gas is adjusted so that the carbon dioxide concentration of the exhaust gas generated in the calciner is 80% by volume or more relative to 100% by volume excluding water vapor.

[0008] [5] A method for producing cement clinker using the cement clinker production system according to any one of [1] to [3], characterized in that the exhaust gas generated in the calciner is recovered and carbon dioxide gas in the exhaust gas is used. [6] The method for producing cement clinker according to [5], wherein methane is produced from hydrogen gas and carbon dioxide gas in the recovered exhaust gas using a catalyst, and the produced methane is used as fuel for at least one of the rotary kiln and the calciner. [7] A method for producing cement clinker according to [5] or [6], wherein the recovered exhaust gas is brought into contact with calcium-containing waste, carbon dioxide contained in the exhaust gas is absorbed by the calcium-containing waste, and the calcium-containing waste that has absorbed the carbon dioxide is then used as a cement clinker raw material. [Effects of the Invention]

[0009] According to the cement clinker production system of the present invention, when producing cement clinker, the carbon dioxide concentration of part of the exhaust gas can be increased to obtain gas containing a high concentration of carbon dioxide that is easily usable for the fixation of carbon dioxide, etc. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram schematically illustrating an example of a cement clinker production system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the cement clinker production system of the present invention will be described in detail with reference to FIG. FIG. 1 is a schematic diagram showing an example of an embodiment of a cement clinker production system according to the present invention. The cement clinker production system 1 includes a cyclone preheating device 2 for preheating cement clinker raw materials, a rotary kiln 3 for burning the cement clinker raw materials preheated by the cyclone preheating device 2 to obtain cement clinker, a calciner 4 disposed upstream of the rotary kiln 3 together with the cyclone preheating device 2 for promoting decarbonation of the cement clinker raw materials, a clinker cooler 5 disposed downstream of the rotary kiln 3 for cooling the cement clinker, and an exhaust gas (hereinafter referred to as "kiln exhaust") generated in the rotary kiln 3. The cement clinker production system includes kiln exhaust gas discharge paths 6a to 6e for discharging the exhaust gas (hereinafter sometimes abbreviated as "calciner exhaust gas") generated in the calciner 4 after passing through a cyclone-type preheating device 2, and further includes a combustion-supporting gas supply device 7 for supplying a combustion-supporting gas having a higher oxygen concentration than air, a combustion-supporting gas supply path 8 for guiding the combustion-supporting gas from the combustion-supporting gas supply device to the calciner 4, and a calciner exhaust gas discharge path 9 (limited to a path different from the kiln exhaust gas discharge path 6) for discharging the exhaust gas (hereinafter sometimes abbreviated as "calciner exhaust gas") generated in the calciner 4.

[0012] The cyclone preheating device 2 comprises a plurality of cyclone heat exchangers 2a to 2d. The plurality of cyclone heat exchangers 2a to 2d are connected by a flow path for moving the cement clinker raw material and kiln exhaust gas discharge paths 6a to 6e for discharging the exhaust gas generated in the rotary kiln 3 after passing through the plurality of cyclone heat exchangers 2a to 2d. The number of cyclone heat exchangers is not particularly limited, but is typically four to five. The plurality of cyclone heat exchangers are typically arranged vertically. The cement clinker raw materials are fed into cyclone heat exchanger 2a, which is disposed at the forefront of cyclone preheating device 2, where they are centrifuged while exchanging heat with the kiln exhaust gas, and then fed from the bottom of cyclone heat exchanger 2a into cyclone heat exchanger 2b, which is disposed downstream, and then centrifuged again while exchanging heat with the exhaust gas, before being fed into cyclone heat exchanger 2c, which is disposed downstream. In this way, the cement clinker raw materials are preheated (heated) by the exhaust gas and move sequentially through cyclone heat exchangers 2b to 2c, which are disposed downstream, before being fed into calciner 4.

[0013] In the cyclone preheating device 2, the cement clinker raw materials are preheated to preferably 400 to 750°C, more preferably 500 to 725°C, and particularly preferably 600 to 700°C. If the temperature is 400°C or higher, the amount of fuel used to promote decarbonation in the calciner can be reduced. If the temperature is 750°C or lower, decarbonation of the cement clinker raw materials is not promoted as easily in the cyclone preheating device 2, and an increase in the carbon dioxide concentration in the kiln exhaust gas can be prevented.

[0014] The cement clinker raw material is not particularly limited, and any common raw material for cement clinker can be used. Specific examples include natural raw materials such as limestone, soil, clay, silica stone, and iron raw materials, as well as waste or by-products such as coal ash, steel slag, municipal waste incineration ash, sewage sludge incineration ash, raw concrete sludge, and finely divided waste concrete. Calcium-containing waste (described below) that has absorbed carbon dioxide may also be used as the cement clinker raw material. The cement clinker raw materials are prepared by pulverizing and mixing various raw materials in an appropriate ratio using a raw material mill, and then the mixture is fed into the cyclone preheating device 2. The particle size of the cement clinker raw materials is preferably 100 μm or less, from the viewpoint of facilitating the production of cement clinker. Furthermore, a portion of the cement clinker raw materials (for example, contaminated soil containing a large amount of organic matter) may be directly charged into the rotary kiln 3 without being charged into the cyclone preheating device 2.

[0015] The calciner 4 is disposed upstream of the rotary kiln 3 together with the cyclone preheater 2 for the purpose of promoting decarbonation of the cement clinker raw material. In Fig. 1, calciner 4 is disposed between cyclone heat exchanger 2c, which is disposed second downstream of cyclone preheating device 2, and cyclone heat exchanger 2d, which is disposed last downstream, and the cement clinker raw material preheated by passing through cyclone heat exchangers 2a to 2c is fed from cyclone heat exchanger 2c to calciner 4. The cement clinker raw material fed into calciner 4 is heated in calciner 4, which promotes decarbonation of the cement clinker raw material.

[0016] Here, decarbonation of cement clinker raw materials means decomposing calcium carbonate (CaCO3), the main component of limestone contained in cement clinker raw materials, into quicklime (CaO) and carbon dioxide (CO2) by heating. When the cement clinker raw materials are heated in the calciner 4 using a combustion-supporting gas with a higher oxygen concentration than air, the carbon dioxide partial pressure increases. Therefore, a higher temperature is required to promote decarbonation, and the temperature must be higher than when air is used as the combustion-supporting gas. Therefore, the temperature at which the cement clinker raw materials are heated is preferably 850 to 1,050°C, more preferably 880 to 1,000°C, and particularly preferably 900 to 980°C. A temperature of 850°C or higher can further promote decarbonation of the cement clinker raw materials even in an atmosphere with a high carbon dioxide partial pressure. A temperature of 1,050°C or lower can prevent clogging due to sintering of the raw materials, etc.

[0017] Decarbonation of the cement clinker raw material is facilitated in the calciner 4 by burning fuel with a combustion-supporting gas to directly heat the cement clinker raw material. The fuel used in the calciner is not particularly limited, and examples thereof include fossil fuels such as coal, heavy oil, and natural gas; biomass such as coconut husks; biogas obtained by gasifying biomass; and methane produced by methanation using carbon dioxide as a raw material. The use of carbon-free fuels such as biomass can substantially reduce carbon dioxide emissions in cement clinker production.

[0018] The combustion-supporting gas used in the calciner 4 has a higher oxygen concentration than air. By using such a combustion-supporting gas, the carbon dioxide concentration of the calciner exhaust gas can be increased. Furthermore, by using the combustion-supporting gas, the combustibility of the fuel is improved, so that even fuels that have been difficult to use in the past because they are difficult to pulverize can be used. From the viewpoint of increasing the carbon dioxide concentration in the calciner exhaust gas, the oxygen concentration of the combustion-supporting gas is preferably 21% by volume or more, more preferably 25% by volume or more, and particularly preferably 30% by volume or more, based on 100% by volume including steam. Also, from the viewpoint of facilitating combustion control, the oxygen concentration is preferably 90% by volume or less, more preferably 80% by volume or less, and particularly preferably 70% by volume or less.

[0019] The combustion-sustaining gas used in the calciner 4 is supplied from a combustion-sustaining gas supply device 7 and is led to the calciner 4 through a combustion-sustaining gas supply path 8 . The combustion-supporting gas supply passage 8 may be disposed so that the temperature of the combustion-supporting gas passing through the combustion-supporting gas supply passage 8 is indirectly heated by air heated by heat exchange with the cement clinker in the clinker cooler 5. Alternatively, the temperature of the combustion-supporting gas may be raised by the heat of the cement clinker by passing the combustion-supporting gas through the combustion-supporting gas supply passage 8 through a part of the downstream side of the cement cooler (the outlet side of the clinker cooler). By increasing the temperature of the combustion-supporting gas, the amount of fuel input used in the calciner 4 can be reduced.

[0020] Examples of the combustion-supporting gas supply device 7 include an oxygen tank, an air separation unit (ASU) that separates oxygen from air, and a water electrolysis device that generates oxygen by electrolysis of water. Methods for separating oxygen from air include cryogenic separation, adsorption separation, membrane separation, etc. Among these, cryogenic separation is preferred from the viewpoint of obtaining a large amount of oxygen.

[0021] The combustion-sustaining gas supplied from the combustion-sustaining gas supply device 7 has an oxygen concentration higher than that of air. The combustion-sustaining gas may be used in the calciner 4 as is, or its composition may be appropriately adjusted before being used in the calciner 4. For example, from the viewpoint of preventing the oxygen concentration of the combustion-supporting gas used in the calciner 4 from becoming excessively high, making it difficult to control combustion, increasing the carbon dioxide concentration of the calciner exhaust gas, and reducing the amount of oxygen remaining in the calciner exhaust gas, the combustion-supporting gas supplied from the combustion-supporting gas supply device 7 may be mixed with carbon dioxide gas, and the resulting mixed gas may be used as the combustion-supporting gas used in the calciner 4. Furthermore, in order to lower the temperature required to promote decarbonation by lowering the carbon dioxide partial pressure, the combustion-supporting gas supplied from the combustion-supporting gas supply device 7 may be mixed with water vapor, and the resulting mixed gas may be used as the combustion-supporting gas in the calciner 4. The carbon dioxide concentration of the mixed gas (a mixture of the combustion-supporting gas supplied from the combustion-supporting gas supply device 7 and at least one of carbon dioxide gas and water vapor) is preferably 10 to 79 volume %, more preferably 20 to 75 volume %, and even more preferably 30 to 70 volume %, relative to 100 volume % including water vapor.

[0022] Furthermore, from the viewpoint of reducing the volume of the exhaust gas generated in the calciner 4 and increasing the carbon dioxide concentration of the exhaust gas, it is preferable that the combustion-supporting gas used in the calciner 4 does not contain gases other than oxygen, carbon dioxide, and water vapor (for example, nitrogen). The concentration of gases other than oxygen, carbon dioxide, and water vapor in the combustion-supporting gas is preferably 10% by volume or less, more preferably 5% by volume or less, and particularly preferably 2% by volume or less, based on 100% by volume including water vapor.

[0023] An example of a method for mixing the combustion-supporting gas supplied from the combustion-supporting gas supply device 7 with carbon dioxide gas is a method for mixing the combustion-supporting gas supplied from the combustion-supporting gas supply device 7 with calciner exhaust gas. Since the temperature of the calciner exhaust gas discharged from the calciner 4 is as high as about 800°C, the temperature of the combustion-supporting gas can be increased by using the exhaust gas. When calciner exhaust gas is mixed, a confluence flow passage 11 is provided to allow a portion of the exhaust gas flowing through the calciner exhaust gas discharge passage 9 (which must be different from the kiln exhaust gas discharge passages 6a to 6e) for discharging the exhaust gas generated in the calciner 4 to merge with the combustion-sustaining gas (the combustion-sustaining gas supplied from the combustion-sustaining gas supply device 7) flowing through the combustion-sustaining gas supply passage 8, and the combustion-sustaining gas flowing through the combustion-sustaining gas supply passage 8 and the exhaust gas are mixed. Furthermore, when the combustion-supporting gas supply passage 8 is arranged so that the combustion-supporting gas passing through the combustion-supporting gas supply passage 8 is indirectly heated and heated by air heated by heat exchange with the cement clinker in the clinker cooler 5, the confluence flow passage 11 is preferably arranged so that the combustion-supporting gas and a part of the exhaust gas are confluent at a point after the combustion-supporting gas has been indirectly heated by the air.

[0024] The calciner exhaust gas is discharged from a calciner exhaust gas discharge passage 9. After the calciner exhaust gas is subjected to dust removal using a cyclone, a bag filter, an electrostatic precipitator, or the like, moisture is further removed, and then carbon dioxide gas is separated and recovered. The calciner exhaust gas discharge path 9 is different from the kiln exhaust gas discharge paths 6a to 6e, which are used to discharge exhaust gas generated in the rotary kiln 3. By completely separating the calciner exhaust gas discharge path 9 from the kiln exhaust gas discharge paths 6a to 6e, it is possible to recover only the calciner exhaust gas with a high carbon dioxide concentration.

[0025] Since the calciner exhaust gas has a high carbon dioxide concentration, it is easy to separate and recover the carbon dioxide from the calciner exhaust gas. The carbon dioxide concentration of the calciner exhaust gas is preferably 80% by volume or more, more preferably 85% by volume or more, and particularly preferably 90% by volume or more, based on 100% by volume excluding water vapor. The carbon dioxide concentration can be increased by adjusting the oxygen concentration of the combustion-supporting gas. Specifically, the carbon dioxide concentration can be increased by increasing the oxygen concentration of the combustion-supporting gas or decreasing the concentrations of gases other than oxygen, carbon dioxide, and water vapor (e.g., nitrogen) in the combustion-supporting gas. Furthermore, since the calciner exhaust gas has a high temperature, the exhaust gas may be used to heat water to generate steam, which may then be used to generate electricity using a steam turbine.

[0026] Carbon dioxide gas may be purified by removing oxygen, nitrogen, water vapor, etc. from the calciner exhaust gas. When the concentration of carbon dioxide gas in the calciner exhaust gas is high, the carbon dioxide gas can be purified by directly compressing and cooling it to liquefy it, without using a chemical absorbent such as an amine to separate and recover the carbon dioxide gas.

[0027] After the decarbonation of the cement clinker raw material is promoted in the calciner 4, the raw material is fed, while still at a high temperature after heating, into a cyclone heat exchanger 2d disposed at the rear end of the cyclone preheating device 2, and then into the rotary kiln 3. Alternatively, a calciner may be disposed between the cyclone preheater and the rotary kiln, and the cement clinker raw material may be directly charged into the rotary kiln after decarbonation has been promoted in the calciner (not shown).

[0028] Cement clinker can be obtained by burning the cement clinker raw materials in the rotary kiln 3. The burning temperature of the cement clinker raw materials may be a general temperature used in cement clinker production, and is usually 1,400°C or higher. In the rotary kiln 3, the fuel used to burn the raw materials for cement clinker can be the same as the fuel used in the calciner 4. In addition, fuels that are difficult to crush, such as contaminated soil containing a large amount of organic components or waste tires, can be directly charged into the rotary kiln 3 through the raw material charging port. The exhaust gas generated in the rotary kiln 3 flows through kiln exhaust gas discharge paths 6a to 6e, which are used to discharge the exhaust gas after passing through the cyclone preheating device 2, and is then discharged from the top of the cyclone preheating device 2. After dust is removed using a cyclone, a bag filter, an electrostatic precipitator, or the like, the exhaust gas is discharged to the outside through a chimney.

[0029] From the viewpoint of further reducing the amount of carbon dioxide emissions, carbon dioxide may be separated and recovered from the kiln exhaust gas. Examples of methods for separating and recovering carbon dioxide from kiln exhaust gas include chemical absorption using monoethanolamine or the like as a carbon dioxide absorbent, calcium looping using quicklime as a carbon dioxide absorbent, solid adsorption, and membrane separation. The quicklime used in calcium looping may be obtained by decarbonation of limestone. The repeatedly used limestone can ultimately be used as a cement clinker raw material.

[0030] Alternatively, a portion of the kiln exhaust gas may be extracted and cooled without passing through the cyclone preheating device 2, and after the solids have been removed, the exhaust gas from which the solids have been removed may be discharged. At the same time, the solids may be classified into coarse and fine powders, and the coarse powder may be used as part of the cement clinker raw material. A chlorine bypass device 10 may be provided to recover the fine powder. It should be noted that "coarse powder" tends to have a high content of cement clinker raw material components and a low content of chlorine, while "fine powder" tends to have a high content of chlorine. The chlorine bypass unit 10 is usually installed at the connection between the cyclone preheater 2 and the rotary kiln 3. By installing the chlorine bypass unit 10, chlorine-containing waste such as municipal waste incineration ash can be used in larger quantities as a cement clinker raw material or fuel for the rotary kiln. The kiln exhaust gas discharged from the chlorine bypass device 10 is usually returned to the kiln exhaust gas discharge path 6a.

[0031] The cement clinker obtained in the rotary kiln 3 is fed into a clinker cooler 5, which is disposed downstream of the rotary kiln and is used to cool the cement clinker, and is cooled there. In order to perform heating in the calciner 4 and the rotary kiln 3 more efficiently, the air used to cool the cement clinker may be divided into an upstream side and a downstream side of the clinker cooler 5, and the downstream side air after cooling the cement clinker may be used to indirectly heat the combustion-supporting gas passing through the combustion-supporting gas supply path 8. Also, different gases may be used for cooling the upstream side and the downstream side. Specifically, air may be used as the gas for cooling the upstream side of the clinker cooler 5, and the combustion-supporting gas passing through the combustion-supporting gas supply passage 8 may be used as the gas for cooling the downstream side. The gas that cools the upstream side exchanges heat with high-temperature cement clinker, and is then used as a combustion-supporting gas for burning fuel in the rotary kiln 3. Note that the gas that cools the upstream side exchanges heat at the inlet side of the clinker cooler 5, and therefore becomes hotter after heat exchange than the gas that cools the downstream side.

[0032] Electric energy may also be used to heat the air and combustion-supporting gas used when burning fuel in the rotary kiln, and to supplement the heating of the rotary kiln and calciner. Examples of heating methods using electric energy include plasma heating, resistance heating, and microwave heating. Using renewable energy as the electric energy can further reduce carbon dioxide emissions.

[0033] In the method for producing cement clinker using the above-described cement clinker production system, the carbon dioxide-containing exhaust gas generated in the calciner 4 may be recovered and the carbon dioxide gas in the exhaust gas may be utilized. One example of the use of carbon dioxide is methanation, which is the reaction of hydrogen and carbon dioxide to produce methane and water. Specifically, there is a method of producing methane from hydrogen gas and carbon dioxide gas contained in the exhaust gas using a catalyst. Hydrogen gas can be obtained by electrolyzing water, etc. If the electrical energy used for electrolyzing water is derived from renewable energy sources such as hydraulic power, wind power, geothermal power, or solar power, carbon dioxide emissions can be further reduced. In this process, oxygen is also produced, and this oxygen may be used as the oxygen contained in the combustion-supporting gas described above.

[0034] Examples of the catalyst include Rh / Mn-based, Rh-based, Ni-based, Pd-based, and Pt-based catalysts. A carrier may also be used to support the catalyst. Examples of the carrier include CeO2, ZrO2, Y2O3, Al2O3, MgO, and TiO2. These may be selected appropriately. From the viewpoint of further reducing carbon dioxide emissions, the produced methane can be used as fuel for at least one of the rotary kiln 3 and the calciner 4. The produced methane may also be used separately as fuel for power generation.

[0035] Another example of the use of carbon dioxide gas is the carbonation of calcium-containing waste. Specifically, this method involves bringing the exhaust gas into contact with calcium-containing waste, and allowing the calcium-containing waste to absorb the carbon dioxide contained in the exhaust gas. By absorbing and immobilizing the carbon dioxide in the calcium-containing waste, it is possible to reduce the amount of carbon dioxide emitted into the atmosphere. Examples of calcium-containing waste include waste concrete. The calcium-containing waste that has absorbed carbon dioxide may be used as a cement clinker raw material in the above-mentioned cement clinker production system. The calcium-containing waste that has absorbed carbon dioxide may be crushed, classified, etc., and used as roadbed material, concrete aggregate, etc. Furthermore, when the calcium-containing waste is waste concrete, only the paste component in the waste concrete that has absorbed carbon dioxide may be separated and recovered and used as a cement raw material.

[0036] In the above-mentioned methanation and carbonation of calcium-containing waste, by using the carbon dioxide-containing exhaust gas directly at a high temperature for methanation or carbonation of calcium-containing waste without purifying it (without separating or removing the carbon dioxide), methanation and carbonation of waste concrete can be carried out more efficiently. In addition, the carbon dioxide-containing exhaust gas generated in the calciner 4 during the production of cement clinker using the above-described cement clinker production system may be stored and isolated as it is. [Explanation of symbols]

[0037] 1. Cement clinker production system 2 Cyclone preheating device 2a, 2b, 2c, 2d Cyclone heat exchanger 3. Rotary Kiln 4 Calciner 5 Clinker Cooler 6a, 6b, 6c, 6d, 6e Kiln exhaust gas exhaust duct 7. Combustion-supporting gas supply device 8. Combustion-supporting gas supply line 9 Calciner exhaust gas discharge channel 10 Chlorine Bypass Device 11 Merging flow path

Claims

1. a cyclone-type preheating device for preheating the cement clinker raw material; a rotary kiln for burning the cement clinker raw material preheated by the cyclone preheating device to obtain cement clinker; a calciner disposed upstream of the rotary kiln together with the cyclone preheating device, for promoting decarbonation of the cement clinker raw material; a clinker cooler disposed downstream of the rotary kiln for cooling the cement clinker; A kiln exhaust gas discharge path for discharging the exhaust gas generated in the rotary kiln after passing through the cyclone type preheating device. A cement clinker production system comprising: a combustion-supporting gas supply device for supplying a combustion-supporting gas having an oxygen concentration higher than that of air; a combustion-sustaining gas supply line for guiding the combustion-sustaining gas from the combustion-sustaining gas supply device to the calciner; a calciner exhaust gas exhaust passage (limited to one different from the kiln exhaust gas exhaust passage) for discharging carbon dioxide-containing exhaust gas generated in the calciner; a cyclone for separating the decarbonated cement clinker raw material and exhaust gas generated in the calciner into a solid component and the carbon dioxide-containing exhaust gas; a solid flow passage for joining the solid matter separated by the cyclone in the middle of the flow path of the kiln exhaust gas discharge passage connected to the rotary kiln, and introducing the solid matter into a cyclone heat exchanger disposed at the rear end of the cyclone preheating device; A cement clinker manufacturing method using a cement clinker manufacturing system including: the combustion-supporting gas supply passage is arranged so that the combustion-supporting gas passing through the combustion-supporting gas supply passage is indirectly heated and heated by air heated by heat exchange with the cement clinker in the clinker cooler, a step of obtaining a mixed gas by mixing the oxygen-containing combustion-supporting gas supplied from the combustion-supporting gas supply device with water vapor, the mixed gas contains oxygen and water vapor, and the concentration of the oxygen in the mixed gas is 25 to 70% by volume relative to 100% by volume of the mixed gas; a method for producing cement clinker, comprising adjusting the concentration of oxygen in the mixed gas so that the concentration of carbon dioxide in the exhaust gas generated in the calciner is 80% by volume or more relative to 100% by volume excluding water vapor.

2. 2. The method for producing cement clinker according to claim 1, wherein the mixed gas contains carbon dioxide gas in addition to the oxygen and the water vapor, the concentration of the carbon dioxide gas in the mixed gas is 20 to 70% by volume relative to 100% by mass of the mixed gas, and the concentrations of gases other than the oxygen, the water vapor, and the carbon dioxide gas in the mixed gas are 5% by volume or less.

3. 3. The method for producing cement clinker according to claim 1 or 2, wherein the cement clinker production system further comprises a chlorine bypass device for extracting and cooling a portion of the exhaust gas generated in the rotary kiln without passing through the cyclone preheating device, removing solids therefrom, discharging the exhaust gas from which the solids have been removed, and classifying the solids into coarse powder and fine powder, using the coarse powder as part of the cement clinker raw materials, and recovering the fine powder.

4. 3. The method for producing cement clinker according to claim 1, wherein the cement clinker production system includes a confluence passage for confluence of a portion of the exhaust gas flowing through the calciner exhaust gas discharge passage with the combustion-supporting gas flowing through the combustion-supporting gas supply passage.

5. 3. The method for producing cement clinker according to claim 1 or 2, further comprising recovering the exhaust gas produced in the calciner, generating methane from hydrogen gas and carbon dioxide gas in the recovered exhaust gas using a catalyst, and using the generated methane as fuel for at least one of the rotary kiln and the calciner.

6. 6. A method for producing cement clinker according to claim 5, wherein the recovered flue gas is brought into contact with calcium-containing waste, carbon dioxide contained in the flue gas is absorbed by the calcium-containing waste, and then the calcium-containing waste having absorbed the carbon dioxide is used as a cement clinker raw material.

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