Cement clinker manufacturing system and cement clinker manufacturing method

Abstract

This invention provides a cement clinker manufacturing system that can produce carbon dioxide-containing material with a high concentration of carbon dioxide. [Solution] A cement clinker manufacturing system 1 comprising a cyclone-type preheating device 2, a rotary kiln 3, a calcination furnace 4 for promoting the decarbonation of cement clinker raw materials, a clinker cooler 5, a kiln exhaust gas discharge passages 6a to 6e, a combustion-supporting gas supply device 7 for supplying combustion-supporting gas with a higher oxygen concentration than air, a combustion-supporting gas supply passage 8, a carbon dioxide purification device 13 for purifying carbon dioxide-containing exhaust gas generated in the calcination furnace 4, a first calcination furnace exhaust gas supply passage 9 for guiding the exhaust gas from the calcination furnace 4 to the carbon dioxide purification device 13, a cement clinker raw material recovery device 18 for returning the decarbonated cement clinker raw materials, and a first oxygen-containing residual gas supply passage 24 for guiding oxygen-containing residual gas to at least one of the rotary kiln 3 and the calcination furnace 4.

Description

Technical Field

[0001] The present invention relates to a cement clinker production system and a cement clinker production method.

Background Art

[0002] In recent years, in order to suppress global warming, reduction of carbon dioxide emissions has become an important issue. On the other hand, the cement industry is one of the industries with a large amount of carbon dioxide emissions. Among the total amount of carbon dioxide gas (gaseous carbon dioxide) emitted when manufacturing cement, the proportion of carbon dioxide gas emitted by decarbonization of limestone used as a raw material for cement is about 60%, and the proportion of carbon dioxide gas emitted by combustion of fuel used during manufacturing is about 40%. As a method for reducing carbon dioxide gas generated by combustion of fuel, there are methods such as improving energy efficiency and using biomass fuel as fuel. For example, as a cement firing apparatus capable of reducing the amount of carbon dioxide gas generated by combustion of fuel, Patent Document 1 describes a cement firing apparatus characterized by including a main burner that blows a combustible gas as a main fuel and a combustible waste as an auxiliary fuel into a cement kiln.

[0003] On the other hand, since it is difficult to use a calcium-containing raw material with a low amount of carbon dioxide generation instead of limestone, which has a large amount of carbon dioxide generation, as a raw material for cement, it is difficult to reduce the amount of carbon dioxide gas generated by decarbonization of limestone by reducing the amount of limestone used. As a method for reducing carbon dioxide emissions, there is a method of separating the generated carbon dioxide gas, recovering it, and then storing, isolating, or effectively using it. As a method for separating and recovering generated carbon dioxide, for example, Patent Document 2 describes a method for separating and recovering carbon dioxide from by-product gas generated at a steel mill by a chemical absorption method, characterized in that the process of absorbing carbon dioxide from the gas with a chemical absorbent, and then heating the chemical absorbent to separate the carbon dioxide, utilizes or takes advantage of low-grade waste heat of 500°C or less generated at the steel mill. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-52746 [Patent Document 2] Japanese Patent Publication No. 2004-292298 [Overview of the project] [Problems that the invention aims to solve]

[0005] The exhaust gas generated during the manufacture 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 amine compounds or the like. If the concentration of carbon dioxide in the exhaust gas can be increased, the separation, recovery, storage, and storage of carbon dioxide (CCS) will become easier. Furthermore, by reducing the amount of nitrogen and other elements in the exhaust gas, the relative volume of the generated exhaust gas can be reduced, and the equipment required for separating, recovering, and storing carbon dioxide can be reduced. The object of the present invention is to provide a cement clinker manufacturing system that can efficiently obtain a carbon dioxide-containing substance containing a high concentration of carbon dioxide that is easily usable for carbon dioxide storage, etc., from a portion of the exhaust gas when manufacturing cement clinker, effectively utilize the residual gas generated when increasing the carbon dioxide concentration, and reduce the amount of exhaust gas emitted. [Means for solving the problem]

[0006] The inventors have diligently studied to solve the above problems and have found a cyclone-type preheating device, a rotary kiln for firing preheated cement clinker raw materials to obtain cement clinker, a calcination furnace for promoting decarboxylation of cement clinker raw materials, a clinker cooler for cooling cement clinker, a kiln exhaust gas discharge passage for discharging exhaust gas generated in the rotary kiln, a combustion-supporting gas supply device for supplying combustion-supporting gas with increased oxygen concentration, a combustion-supporting gas supply passage for guiding the combustion-supporting gas to the calcination furnace, and a carbon dioxide-containing gas-containing gas-containing gas-containing gas generated in the calcination furnace. We have found that the above objective can be achieved by a cement clinker manufacturing system that includes a carbon dioxide purification device for purifying exhaust gas to obtain a high-concentration carbon dioxide-containing substance and an oxygen-containing residual gas, a first calcination furnace exhaust gas supply passage for guiding exhaust gas from the calcination furnace to the carbon dioxide purification device, a cement clinker raw material recovery device for returning the decarboxylated cement clinker raw material to a cyclone-type preheating device, and a first oxygen-containing residual gas supply passage for guiding the oxygen-containing residual gas to at least one of a rotary kiln and a calcination furnace, and have completed the present invention. In other words, the present invention provides the following [1] to [5].

[0007] [1] A cyclonic preheating device including two or more cyclonic heat exchangers for preheating cement clinker raw materials; a rotary kiln for firing the cement clinker raw materials preheated in the cyclonic preheating device to obtain cement clinker; a calcination furnace including a heating means, disposed upstream of the rotary kiln together with the cyclonic preheating device, for promoting decarboxylation of the cement clinker raw materials using the heating means; a clinker cooler disposed downstream of the rotary kiln for cooling the cement clinker; and a system for passing exhaust gas generated in the rotary kiln through the cyclonic preheating device. A cement clinker manufacturing system including a kiln exhaust gas discharge channel for discharging after the process, comprising: a combustion-supporting gas supply device for supplying a combustion-supporting gas with a higher oxygen concentration than air; a combustion-supporting gas supply channel for guiding the combustion-supporting gas from the combustion-supporting gas supply device to the kiln; a carbon dioxide purification device for purifying the carbon dioxide-containing exhaust gas produced in the kiln to obtain a high-concentration carbon dioxide-containing substance and an oxygen-containing residual gas; and a first kiln exhaust gas supply channel (limited to one different from the kiln exhaust gas discharge channel) for guiding the carbon dioxide-containing exhaust gas from the kiln to the carbon dioxide purification device. A cement clinker manufacturing system characterized by including a cement clinker raw material recovery device installed in the middle of the exhaust gas supply path of the first calcination furnace for recovering decarbonated cement clinker raw materials and returning them to the cyclone-type preheating device, and a first oxygen-containing residual gas supply path for guiding the oxygen-containing residual gas to at least one of the rotary kiln and the calcination furnace.

[0008] [2] The cement clinker manufacturing system according to [1], wherein the combustion-supporting gas supply passage is arranged in the middle of the first calcinerator exhaust gas supply passage to exchange heat between the carbon dioxide-containing exhaust gas flowing through the first calcinerator exhaust gas supply passage and the combustion-supporting gas, and a second calcinerator exhaust gas supply passage is provided to merge a portion of the carbon dioxide-containing exhaust gas flowing through the first calcinerator exhaust gas supply passage with the combustion-supporting gas flowing through the combustion-supporting gas supply passage. [3] The cement clinker manufacturing system according to [1] or [2], further comprising a second oxygen-containing residual gas supply channel for guiding the oxygen-containing residual gas to the combustion-supporting gas supply device.

[0009] [4] A cement clinker manufacturing method using the cement clinker manufacturing system described in any of [1] to [3] above, characterized in that the oxygen concentration of the combustion-supporting gas is adjusted so that the carbon dioxide concentration of the carbon dioxide-containing exhaust gas generated in the above-mentioned furnace is 80% by volume or more with respect to 100% by volume excluding water vapor. [5] A cement clinker manufacturing method using the cement clinker manufacturing system described in any of [1] to [3] above, wherein the carbon dioxide purifying apparatus purifies the carbon dioxide-containing exhaust gas using a cryogenic separation method at a temperature that is above the boiling point of oxygen contained in the carbon dioxide-containing exhaust gas and above the boiling point of nitrogen contained in the carbon dioxide-containing exhaust gas, and below the boiling point of carbon dioxide contained in the carbon dioxide-containing exhaust gas. [Effects of the Invention]

[0010] According to the cement clinker manufacturing system of the present invention, when manufacturing cement clinker, it is possible to efficiently obtain a carbon dioxide-containing substance containing a high concentration of carbon dioxide that is easily usable for carbon dioxide storage, etc., from a portion of the exhaust gas, and to reduce the amount of exhaust gas emitted. Furthermore, the residual gas with a high oxygen content, which is generated when increasing the concentration of carbon dioxide, can be effectively utilized as a combustion-supporting gas, thereby reducing fuel consumption. [Brief explanation of the drawing]

[0011] [Figure 1] This figure schematically illustrates an example of the cement clinker manufacturing system of the present invention. [Figure 2] This figure schematically illustrates an example of the cement clinker manufacturing system of the present invention. [Modes for carrying out the invention]

[0012] Figures 1 and 2 schematically represent examples of embodiments of the cement clinker manufacturing system of the present invention. An example of the cement clinker manufacturing system of the present invention will be described in detail below with reference to Figure 1. The cement clinker manufacturing system 1 in Figure 1 includes a cyclone-type preheating device 2 containing two or more cyclone-type heat exchangers 2a to 2d for preheating the cement clinker raw material, a rotary kiln 3 for firing the cement clinker raw material preheated in the cyclone-type preheating device 2 to obtain cement clinker, a calcination furnace 4 including a heating means 20 disposed upstream of the rotary kiln 3 together with the cyclone-type preheating device 20 to promote decarboxylation of the cement clinker raw material using the heating means 20, a clinker cooler 5 disposed downstream of the rotary kiln 3 for cooling the cement clinker, and a kiln exhaust gas discharge passage 6 for discharging the exhaust gas generated in the rotary kiln 3 after passing through the cyclone-type preheating device 2. The cement clinker manufacturing system 1 further includes a combustion-supporting gas supply device 7 for supplying a combustion-supporting gas with 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 7 to the calcination furnace 4, an exhaust gas compressor 12 for compressing the carbon dioxide-containing exhaust gas produced in the calcination furnace 4 to obtain compressed exhaust gas, a carbon dioxide purification device 13 for purifying the carbon dioxide-containing exhaust gas or compressed exhaust gas produced in the calcination furnace 4 to obtain a high-concentration carbon dioxide-containing substance and an oxygen-containing residual gas, and a carbon dioxide-containing exhaust gas from the calcination furnace 4. The system includes a first calcination furnace exhaust gas supply passage 9 (limited to one different from the kiln exhaust gas discharge passage 6) for leading to a carbon dioxide purification device 13, a cement clinker raw material recovery device 18 installed in the middle of the first calcination furnace exhaust gas supply passage 9 for recovering decarbonized cement clinker raw materials and returning them to a cyclone-type preheating device 2, a first oxygen-containing residual gas supply passage 24 for leading the oxygen-containing residual gas to at least one of the rotary kiln 3 and the calcination furnace 4, and a second oxygen-containing residual gas supply passage 25 for leading the oxygen-containing residual gas to a combustion-supporting gas supply device 7.

[0013] The cyclone-type preheating device 2 consists of two or more cyclone-type heat exchangers 2a to 2d. The multiple cyclone-type heat exchangers 2a to 2d are connected by a flow path for moving cement clinker raw materials and kiln exhaust gas discharge passages 6a to 6e for discharging exhaust gas generated in the rotary kiln 3 after it has passed through the multiple cyclone-type heat exchangers 2a to 2d. The kiln exhaust gas discharge passages 6a to 6e may also serve as a flow path for moving cement clinker raw materials. The number of cyclone-type heat exchangers is two or more, usually four to five. The multiple cyclone-type heat exchangers are usually arranged vertically. The cement clinker raw material is fed into a cyclone-type heat exchanger 2a located at the very front of the cyclone-type preheating device 2. Within the cyclone-type heat exchanger 2a, it is centrifuged while exchanging heat with the kiln exhaust gas and then fed from the bottom of the cyclone-type heat exchanger 2a to a cyclone-type heat exchanger 2b located downstream. There, it is again centrifuged while exchanging heat with the exhaust gas and then fed into a cyclone-type heat exchanger 2c located further downstream. In this way, the cement clinker raw material is preheated (heated) by the exhaust gas and moves sequentially to the cyclone-type heat exchangers 2b to 2c located downstream.

[0014] By preheating the cement clinker raw material in the cyclone-type preheating device 2, the amount of fuel used to promote decarbonation in the calcination furnace 4 can be reduced. In the cyclone-type preheating device 2, the cement clinker raw material is preheated to preferably 400-750°C, more preferably 500-725°C, and particularly preferably 600-700°C. If the temperature is 400°C or higher, the amount of fuel used to promote decarbonation in the calcination furnace 4 can be reduced. If the temperature is 750°C or lower, decarbonation of the cement clinker raw material is less likely to be promoted in the cyclone-type preheating device 2, thereby preventing an increase in the carbon dioxide concentration in the kiln exhaust gas.

[0015] The cement clinker raw materials are not particularly limited, and those commonly used as raw materials for cement clinker can be used. Specifically, natural raw materials such as limestone, soil, clay, silica, iron raw materials, etc., and waste materials or by-products such as coal ash, steel slag, municipal waste incineration ash, sewage sludge incineration ash, fresh sludge, waste concrete powder, etc. can be mentioned. Further, as the cement clinker raw material, calcium-containing waste materials (described later) that have absorbed carbon dioxide gas may be used. The cement clinker raw materials are pulverized and mixed at appropriate ratios using a raw material mill, and then fed into the cyclone preheating device 2. From the viewpoint of making the production of cement clinker easier, the particle size of the cement clinker raw materials is preferably 100 μm or less. Also, a part of the cement clinker raw materials (for example, contaminated soil containing a large amount of organic matter) may be directly fed into the rotary kiln 3 without being fed into the cyclone preheating device 2.

[0016] The preheated cement clinker raw materials are fed from the preheated raw material supply path 19 connected to any one of two or more cyclone heat exchangers 2a to 2d constituting the cyclone preheating device 2 into the calcination furnace 4. In FIG. 1, the preheated raw material supply path 19 is connected to the cyclone heat exchanger 2c disposed second or more from the last flow side of the cyclone preheating device 2. The cement clinker raw materials preheated through the cyclone heat exchangers 2a to 2c are fed from the cyclone heat exchanger 2c through the preheated raw material supply path 19 into the calcination furnace 4. By connecting the preheated raw material supply path 19 to the cyclone heat exchanger 2c located second from the last flow side, the sufficiently preheated cement clinker raw materials can be fed into the calcination furnace 4. Also, by returning the cement clinker raw materials decarbonated in the calcination furnace 4 to the cyclone heat exchanger 2d located on the last flow side without directly feeding them into the rotary kiln 3, the temperature of the kiln exhaust gas can be increased by the high-temperature cement clinker raw materials.

[0017] The calciner 4 is disposed on the upstream side of the rotary kiln 3 together with the cyclone preheater 2 for the purpose of promoting the decarbonation of the cement clinker raw material by burning fuel using the heating means 20. Here, the decarbonation of the cement clinker raw material means decomposing calcium carbonate (CaCO3), which is the main component of limestone contained in the cement clinker raw material, into quicklime (CaO) and carbon dioxide gas (CO2) by heating. When heating the cement clinker raw material using a combustion-supporting gas with a higher oxygen concentration than air in the calciner 4, the carbon dioxide partial pressure increases. For this reason, since the temperature required to promote decarbonation becomes higher, it is necessary to increase the temperature compared to the case of using air as the combustion-supporting gas. The heating in the calciner 4 is preferably carried out so that the temperature of the heated cement clinker raw material is 850 to 1,100 °C, more preferably 880 to 1,080 °C, still more preferably 900 to 1,050 °C, still more preferably 950 to 1,025 °C, and particularly preferably 975 to 1,000 °C. If the above temperature is 850 °C or higher, the decarbonation of the cement clinker raw material can be further promoted even in an atmosphere with a high carbon dioxide partial pressure, and even if the decarbonated cement clinker raw material is directly charged into the rotary kiln 3, it is possible to prevent the temperature in the rotary kiln 3 from decreasing excessively. If the above temperature is 1,100 °C or lower, it is possible to prevent blockage of pipes, etc. due to sintering of the raw materials.

[0018] The decarbonation of the cement clinker raw material is promoted by burning fuel using the heating means 20 and the combustion-supporting gas in the calciner 4 to directly heat the cement clinker raw material. The combustion-supporting gas is supplied as at least one of the primary air and the secondary air of the heating means 20. Examples of the heating means 20 include burners and the like. The fuel used in a calcination furnace is not particularly limited and includes, for example, fossil fuels such as coal, heavy oil, and natural gas; biomass such as coconut husks; biogas produced by gasifying biomass; and methane produced by methanation using carbon dioxide as a raw material. These may be used individually or in combination of two or more. In particular, using carbon-free fuels such as biomass can substantially reduce carbon dioxide emissions in cement clinker production.

[0019] The combustion-supporting gas used in the calcination furnace 4 has a higher oxygen concentration than air. By using such a combustion-supporting gas, the carbon dioxide concentration in the calcination furnace exhaust gas can be increased. Furthermore, because the combustion efficiency of the fuel is improved by using the above-mentioned combustion-supporting gas, fuels that were previously difficult to use because they were difficult to finely grind can now be used. From the viewpoint of increasing the carbon dioxide concentration of the combustion-supporting gas in the furnace exhaust gas, the oxygen concentration of the above combustion-supporting gas is preferably 21% by volume or more (higher than the oxygen concentration in the atmosphere), more preferably 25% by volume or more, and particularly preferably 30% by volume or more, based on 100% by volume including water vapor. Furthermore, from the viewpoint of making combustion easier to 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.

[0020] The combustion-supporting gas used in the calcination furnace 4 is supplied from the combustion-supporting gas supply device 7 and guided to the calcination furnace 4 through the combustion-supporting gas supply path 8. In Figure 1, the combustion-supporting gas supply passage 8 is arranged such that the combustion-supporting gas passing through the combustion-supporting gas supply passage 8 is indirectly heated and warmed by the air flowing through the air passage 23, which is used to circulate air heated by heat exchange with the cement clinker in the clinker cooler 5. The air passage 23 can be arranged arbitrarily. Alternatively, the combustion-supporting gas may be heated by the heat of the cement clinker by passing it through a combustion-supporting gas supply passage 8 in a portion of the downstream side of the cement cooler (outlet side of the clinker cooler) (not shown). By raising the temperature of the combustion-supporting gas, the amount of fuel used in the combustion furnace 4 can be reduced.

[0021] Examples of combustion-supporting gas supply devices 7 include an oxygen tank, an air separation unit (ASU) for separating oxygen from air, and a water electrolysis device for generating oxygen by electrolysis of water. Methods for separating oxygen from air include cryogenic separation, adsorption separation, and membrane separation. Among these, cryogenic separation is preferred from the viewpoint of obtaining a large amount of oxygen.

[0022] The combustion-supporting gas supplied from the combustion-supporting gas supply device 7 has a higher oxygen concentration than air. The combustion-supporting gas may be used as is in the furnace 4, but its composition may be adjusted as appropriate before being used in the furnace 4. For example, to prevent the oxygen concentration of the combustion-supporting gas used in the calcination furnace 4 from becoming excessively high, making it difficult to control combustion, and to prevent carbon dioxide-containing exhaust gas generated in the calcination furnace (hereinafter referred to as "calcination furnace exhaust gas") Also known as ), in order to increase the carbon dioxide concentration and reduce the amount of oxygen remaining in the combustion furnace exhaust gas, the combustion-supporting gas supplied from the combustion-supporting gas supply device 7 may be mixed with carbon dioxide, and the resulting mixed gas may be used as the combustion-supporting gas in the combustion furnace 4. Furthermore, from the viewpoint of effectively utilizing the residual gas generated when increasing the concentration of carbon dioxide, the combustion-supporting gas supplied from the combustion-supporting gas supply device 7 may be mixed with the oxygen-containing residual gas (described later), and the resulting mixed gas may be used as the combustion-supporting gas in the calcination furnace 4. Furthermore, in order to lower the temperature necessary to promote decarbonation by lowering the partial pressure of carbon dioxide, 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 calcination furnace 4. The carbon dioxide concentration of the above 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 and water vapor) is preferably 10 to 79% by volume, more preferably 20 to 75% by volume, and even more preferably 30 to 70% by volume, based on 100% by volume including water vapor.

[0023] Furthermore, from the viewpoint of reducing the volume of the furnace exhaust gas and increasing the carbon dioxide concentration of the furnace exhaust gas, it is preferable that the combustion-supporting gas used in the furnace 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 above 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.

[0024] An example of a method for mixing the combustion-supporting gas supplied from the combustion-supporting gas supply device 7 with carbon dioxide is to mix the combustion-supporting gas supplied from the combustion-supporting gas supply device 7 with the exhaust gas from the calcination furnace. Since the temperature of the exhaust gas discharged from the calcination furnace 4 is high, around 800°C, the combustion-supporting gas can be heated up by using the calcination furnace exhaust gas. When mixing combustion-supporting gas and furnace exhaust gas, for example, by providing a confluence passage 11 to combine a portion of the furnace exhaust gas flowing through the first furnace exhaust gas supply passage 9, which leads the furnace exhaust gas generated in the furnace 4 to the carbon dioxide purification device 13, with the combustion-supporting gas (combustion-supporting gas supplied from the combustion-supporting gas supply device 7) flowing through the combustion-supporting gas supply passage 8, the combustion-supporting gas and furnace exhaust gas flowing through the combustion-supporting gas supply passage 8 can be mixed. From the viewpoint of being able to mix higher temperature furnace exhaust gas with combustion-supporting gas, it is preferable that the confluence passage 11 be arranged to connect with the first furnace exhaust gas supply passage 9 at a location upstream of the dust collector 14 and the acid gas removal device 15 of the first furnace exhaust gas supply passage 9. Furthermore, if the combustion-supporting gas supply passage 8 is arranged such that the combustion-supporting gas passing through the combustion-supporting gas supply passage 8 is indirectly heated and warmed by air heated by heat exchange with the cement clinker in the clinker cooler 5, it is preferable that the confluence passage 11 is arranged so that a portion of the combustion-supporting gas and furnace exhaust gas merge downstream of the location where the combustion-supporting gas is indirectly heated using the air (further away from the combustion-supporting gas supply device 7). When mixing a combustion-supporting gas and an oxygen-containing residual gas, for example, by connecting the first oxygen-containing residual gas supply channel 24 (described later) to the combustion-supporting gas supply channel 8, the oxygen-containing residual gas flowing through the first oxygen-containing residual gas supply channel 24 can be combined with the combustion-supporting gas (combustion-supporting gas supplied from the combustion-supporting gas supply device 7) flowing through the combustion-supporting gas supply channel 8, thereby mixing the combustion-supporting gas and the furnace exhaust gas.

[0025] The cement clinker raw materials decarbonated in the calcination furnace 4 and the carbon dioxide-containing exhaust gas (calcination furnace exhaust gas) generated in the calcination furnace are discharged into the first calcination furnace exhaust gas supply passage 9 and are guided through the first calcination furnace exhaust gas supply passage 9 to the carbon dioxide purification device 13 (described later). Furthermore, the first calcination furnace exhaust gas supply channel 9 is different from the kiln exhaust gas discharge channels 6a to 6e, which are used to discharge the exhaust gas generated in the rotary kiln 3. By completely separating the first calcination furnace exhaust gas supply channel 9 from the kiln exhaust gas discharge channels 6a to 6e, only the calcination furnace exhaust gas with a high carbon dioxide concentration can be recovered.

[0026] The cement clinker raw material decarbonated in the calcination furnace 4 is recovered in a cement clinker raw material recovery device 18 located in the middle of the first calcination furnace exhaust gas supply path 9, and is returned (supplied) to the cyclone-type preheating device 2 via the decarbonated raw material supply path 22 while maintaining its high temperature after heating. Examples of cement clinker raw material recovery equipment 18 include cyclones, bag filters, and electrostatic precipitators. The decarbonation raw material supply channel 22 is typically arranged to supply decarbonated cement clinker raw material into a cyclone-type heat exchanger 2d located downstream of the cyclone-type heat exchanger 2c, which is connected to the preheating raw material supply channel 19. Alternatively, at least a portion of the decarbonated cement clinker raw material may be directly fed into the rotary kiln 3 from the decarbonation raw material supply channel 22.

[0027] Since the exhaust gas from a calcination furnace has a high concentration of carbon dioxide, it is easy to separate and recover carbon dioxide from the exhaust gas. The carbon dioxide concentration of the exhaust gas from the calcination furnace 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 above carbon dioxide concentration can be adjusted by adjusting the oxygen concentration of the combustion-supporting gas. Specifically, the above carbon dioxide concentration can be increased by increasing the oxygen concentration of the combustion-supporting gas, or by decreasing the concentration of gases other than oxygen, carbon dioxide, and water vapor (e.g., nitrogen) in the combustion-supporting gas. Furthermore, since the exhaust gas from the furnace is at a high temperature, it is also possible to generate steam by heating water using this exhaust gas, and then generate electricity using this steam and a steam turbine.

[0028] In the first calcination furnace exhaust gas supply line 9, an exhaust gas compressor 12 is optionally provided between the cement clinker raw material recovery unit 18 and the carbon dioxide purification unit 13 to compress the carbon dioxide-containing exhaust gas and obtain compressed exhaust gas (which is obtained by compressing the carbon dioxide-containing exhaust gas). In the exhaust gas compressor 12, the carbon dioxide-containing exhaust gas generated in the calcination furnace 4 is compressed, and compressed exhaust gas (obtained by pressurizing the carbon dioxide-containing exhaust gas) that is pressurized (increased in pressure) compared to before it was supplied to the compressed exhaust gas compressor 12 can be obtained. By compressing the carbon dioxide-containing exhaust gas, the carbon dioxide-containing exhaust gas can be efficiently purified in the carbon dioxide purification device 13 (described later). Examples of exhaust gas compressors 12 include turbo compressors such as centrifugal compressors and positive displacement compressors such as reciprocating compressors. The resulting compressed exhaust gas is led from the exhaust gas compressor 12 through the first furnace exhaust gas supply passage 9 to the carbon dioxide purification device 13. Furthermore, when compressing the exhaust gas from the incinerator, water (water vapor) contained in the exhaust gas may be recovered. By recovering the water contained in the exhaust gas from the incinerator, the concentration of carbon dioxide in the compressed exhaust gas can be increased, thereby increasing the concentration of carbon dioxide in the high-concentration carbon dioxide-containing product purified by the carbon dioxide purification device 13.

[0029] In the carbon dioxide purification device 13, carbon dioxide-containing exhaust gas or compressed exhaust gas (if an exhaust gas compressor 12 is provided) is purified to obtain a carbon dioxide-containing substance with a higher (larger) carbon dioxide concentration compared to the exhaust gas of the incineration furnace, as well as an oxygen-containing residual gas. Examples of methods for purifying carbon dioxide-containing exhaust gas or compressed exhaust gas in the carbon dioxide purification apparatus 13 (to increase the carbon dioxide concentration by removing oxygen, nitrogen, etc. contained in the carbon dioxide-containing exhaust gas or compressed exhaust gas) include cryogenic separation, membrane separation, and physical adsorption. These may be used individually or in combination of two or more. Among these, cryogenic separation is preferred from the viewpoint of obtaining carbon dioxide-containing material with a higher carbon dioxide concentration. An example of purification using cryogenic separation is a method in which, in a carbon dioxide purification apparatus 12, the carbon dioxide-containing exhaust gas or compressed exhaust gas is heated to a temperature above the boiling point of oxygen and nitrogen contained in the carbon dioxide-containing exhaust gas or compressed exhaust gas, and below the boiling point of carbon dioxide contained in the carbon dioxide-containing exhaust gas or compressed exhaust gas, thereby removing the oxygen and nitrogen contained in the carbon dioxide-containing exhaust gas or compressed exhaust gas and obtaining a carbon dioxide-containing substance with a higher carbon dioxide concentration compared to the exhaust gas of a combustion furnace. The obtained carbon dioxide-containing substance is usually in liquid form.

[0030] An example of purification using membrane separation is a method in which carbon dioxide-containing exhaust gas or compressed exhaust gas is passed through a membrane such as an amine-containing polymer membrane, thereby separating the gas into one containing a high concentration of carbon dioxide and another containing no carbon dioxide or only a low concentration of carbon dioxide. Physical adsorption is a method of separating carbon dioxide from other gases using at least one of a pressure difference or a temperature difference. Examples include the pressure swing adsorption method (PSA), in which carbon dioxide is adsorbed onto an adsorbent such as zeolite or activated carbon under high pressure, and then desorbed and recovered by lowering the pressure; the thermal swing adsorption method (TSA), in which carbon dioxide is adsorbed onto the above adsorbent at a low temperature, and then desorbed and recovered by raising the temperature; and PTSA, which combines the pressure swing method and the thermal swing method.

[0031] Furthermore, in the carbon dioxide purification apparatus 13, the oxygen concentration of the residual gas (oxygen-containing residual gas) remaining after obtaining a carbon dioxide-containing substance with a high carbon dioxide concentration is 21% or more of the volume relative to 100% of the volume of the oxygen-containing residual gas (higher than atmospheric concentration). Other components besides oxygen in the oxygen-containing residual gas include nitrogen. Additionally, the oxygen-containing residual gas may contain some of the carbon dioxide-containing exhaust gas or compressed exhaust gas that remained unpurified during the purification process. This oxygen-containing residual gas may be used as primary and secondary air for combustion in rotary kiln 3, or as combustion-supporting gas (primary and secondary air) for calcination furnace 4. In particular, using it as primary or secondary air for rotary kiln 3 improves the combustibility of the fuel, allowing the use of waste-derived fuels, biomass fuels, ammonia, etc., which are difficult to combust under conditions where air is used as primary or secondary air. Furthermore, because there are fewer components that do not contribute to combustion, such as nitrogen, compared to air, the amount of energy required to raise the temperature of these materials can be reduced, leading to a reduction in the amount of energy input and a reduction in the amount of kiln exhaust gas. As a result, the total energy input is reduced, and the exhaust gas treatment equipment can be made more compact. In addition, as the carbon dioxide concentration in the kiln exhaust gas increases, the carbon dioxide in the kiln exhaust gas is more easily adsorbed by waste concrete, which is part of the raw material for cement clinker, in cyclone-type preheating devices, etc., making it easier to effectively utilize the carbon dioxide in the kiln exhaust gas. Furthermore, when using oxygen-containing residual gas as secondary air for rotary kiln 3, the low temperature of the oxygen-containing residual gas allows it to cool the clinker, improving the cooling rate of the clinker and enhancing the combustibility of the kiln burner.

[0032] The oxygen-containing residual gas is supplied to at least one of the rotary kiln 3 and the calcination furnace 4 as primary air or secondary air through a first oxygen-containing residual gas supply passage 24 for guiding the oxygen-containing residual gas to at least one of the rotary kiln 3 and the calcination furnace 4. In Figure 1, the first oxygen-containing residual gas supply channel 24 branches off from a single pipe connected to the carbon dioxide purification device 13 and is arranged to supply oxygen-containing residual gas to the heating means of the rotary kiln 3, the vicinity of the inlet side of the clinker cooler 5 (near the connection point with the rotary kiln 3), and the combustion-supporting gas supply channel 8. The oxygen-containing residual gas supplied near the inlet of the clinker cooler 5 passes through the clinker cooler 5 and is supplied to the rotary kiln 3 as secondary air. Furthermore, the residual oxygen-containing gas supplied to the combustion-supporting gas supply line 8 is supplied to the furnace 4 as part of the combustion-supporting gas circulating within the combustion-supporting gas supply line 8. Alternatively, oxygen-containing residual gas may be supplied to the rotary kiln 3 and the calcination furnace 4 using two separate pipes connected to the carbon dioxide purification device 13. This configuration is also included in the first oxygen-containing residual gas supply channel 24. The oxygen-containing residual gas may be used in place of, or as part of, the air supplied to the combustion-supporting gas supply device 7. This reduces the load on the combustion-supporting gas supply device 7, such as the amount of electricity required, compared to supplying a combustion-supporting gas with a higher concentration from air. Furthermore, the oxygen-containing residual gas is supplied to the combustion-supporting gas supply device 7 through an optional second oxygen-containing residual gas supply passage 25, which is provided for the purpose of leading to the combustion-supporting gas supply device 7. In Figure 1, the second oxygen-containing residual gas supply channel 25 is connected to the first oxygen-containing residual gas supply channel 24 by branching off from it midway through the channel. The channel is arranged so that a portion of the oxygen-containing residual gas flowing through the first oxygen-containing residual gas supply channel 24 passes through the second oxygen-containing residual gas supply channel 25 and is supplied to the combustion-supporting gas supply device 7. Alternatively, the second oxygen-containing residual gas supply channel may be directly connected to the carbon dioxide purification device 13 without being connected to the first oxygen-containing residual gas supply channel 24, and configured to supply oxygen-containing residual gas from the carbon dioxide purification device 13 to the combustion-supporting gas supply device 7 (not shown).

[0033] In the first calcinerator exhaust gas supply path 9, a dust collector 14 for removing soot from the calcinerator exhaust gas is optionally installed between the cement clinker raw material recovery device 18 and the carbon dioxide purification device 13 (or the exhaust gas compressor 12 if one is installed). In the dust collector 14, methods for removing soot include a wet treatment method, an electrostatic precipitator method, and a bag filter method. Among these, the method using a bag filter is preferred from the viewpoint of dust collection efficiency. The dust removed and collected by the dust collector 14 is discharged through the dust discharge passage 21. The dust removed and recovered by the dust collector 14 is typically fine powder containing quicklime. This fine powder may be used as a quicklime-containing raw material, as part of the raw materials for cement clinker. The quicklime-containing raw material (fine powder containing quicklime) recovered by the dust collector 14 may be supplied directly to the rotary kiln 3 or to the cyclone-type preheating device 2.

[0034] In the first calcinerator exhaust gas supply line 9, an acid gas removal device 15 is optionally installed between the cement clinker raw material recovery device 18 and the carbon dioxide purification device 13 (or the exhaust gas compressor 12 if one is installed), for the purpose of removing acidic gases (except carbon dioxide) from the calcinerator exhaust gas (carbon dioxide-containing exhaust gas). Examples of methods for removing acidic gases from the furnace exhaust gas in the acidic gas removal device 15 include using a wet scrubber to dissolve and remove the acidic gases in a solution such as caustic soda or magnesium hydroxide solution, or passing the furnace exhaust gas through a tower filled with an adsorbent such as activated carbon to remove the acidic gases. These methods may be used individually or in combination of two or more. Examples of acidic gases (excluding carbon dioxide) include sulfur oxides (SOx) such as sulfur dioxide (SO2) and sulfur trioxide (SO3), nitrogen oxides (NOx) such as nitric oxide (NO) and nitrogen dioxide (NO2), and hydrogen chloride (HCl).

[0035] The order of the dust collector 14 and the acid gas removal device 15 is not particularly limited. The acid gas removal device may be placed upstream of the dust collector (closer to the furnace 4), or downstream of the dust collector (further away from the furnace 4). In particular, from the viewpoint of more efficient dust collection and removal of acid gases, it is preferable to place the acid gas removal device downstream of the dust collector. Furthermore, the dust collector may also function as an acidic gas removal device. For example, in a dust collector using a bag filter, an acidic gas treatment agent such as slaked lime or baking soda may be added to the exhaust gas of the incinerator before the dust collector. This agent can then capture the acidic gases contained in the exhaust gas, and the bag filter can then simultaneously remove both dust and acidic gases.

[0036] Furthermore, a furnace exhaust gas temperature reduction device (not shown) may be installed in the middle of the first furnace exhaust gas supply passage 9, and upstream of the location where the dust collector 14 and the acid gas removal device 15 are installed, to reduce the temperature of the furnace exhaust gas circulating in the furnace exhaust gas supply passage 9. The furnace exhaust gas temperature reduction device is not particularly limited as long as it can reduce the temperature of the furnace exhaust gas. Examples include a device for heat exchange between air and furnace exhaust gas, or a device for heat exchange between liquid and furnace exhaust gas. By lowering the temperature of the incinerator exhaust gas to, for example, 100-400°C, the dust collector 14 and the acid gas removal device 15 can more efficiently collect dust and remove acid gases. In addition, the adverse effects on various devices caused by the high temperature of the incinerator exhaust gas can be reduced.

[0037] The high-concentration carbon dioxide-containing material purified in the carbon dioxide purification device 13 is discharged through the high-concentration carbon dioxide-containing material discharge channel 17. The resulting high-concentration carbon dioxide-containing material is either a liquid or a gas, depending on the purification method and conditions. Of these, liquid is preferred from the viewpoint of easier handling, such as storage. In the above-mentioned high-concentration carbon dioxide-containing material, which is in a gaseous state, the proportion of carbon dioxide (CO2) is preferably greater than 95 mol%, and more preferably greater than 98 mol%. In the above-mentioned high-concentration carbon dioxide-containing substance in gaseous form, the proportion of nitrogen (N2) is preferably less than 2 mol%, the proportion of hydrogen (H2) is preferably less than 0.75 mol%, and the proportion of carbon monoxide (CO) is preferably less than 0.2 mol%. In the above-mentioned high-concentration carbon dioxide-containing substance, which is in a gaseous state, the total proportion of nitrogen (N2), hydrogen (H2), carbon monoxide (CO), and oxygen (O2) is preferably less than 4 mol%.

[0038] In the above-mentioned high-concentration carbon dioxide-containing material, which is in a gaseous state, the proportion of oxygen (O2) (by volume) is preferably less than 10 ppm. In the above-mentioned high-concentration carbon dioxide-containing material, which is in a gaseous state, the proportion of hydrogen sulfide (H2S) (by volume) is preferably less than 200 ppm. In the above-mentioned high-concentration carbon dioxide-containing substance in a gaseous state, the proportion of sulfur dioxide (SO2) (by volume) is preferably less than 100 ppm from a safety and health viewpoint, and more preferably less than 50 ppm from the viewpoint of preventing corrosion of the equipment. In the above-mentioned high-concentration carbon dioxide-containing material in gaseous form, the proportion of nitrogen dioxide (NO2) (by volume) is preferably less than 100 ppm from a safety and health viewpoint, and more preferably less than 50 ppm from the viewpoint of preventing corrosion of the equipment. High-concentration carbon dioxide-containing materials in a gaseous state in which the proportion of carbon dioxide (CO2), etc., satisfies the above-mentioned numerical range are suitable for storage and use as a raw material for methane, etc.

[0039] The resulting high-concentration carbon dioxide-containing material may be transported to a storage tank (not shown) in its liquid state and stored there. Alternatively, the carbon dioxide contained in the obtained high-concentration carbon dioxide-containing material may be used. One example of carbon dioxide utilization is the production of methane or methanol from hydrogen gas and carbon dioxide contained in the exhaust gas using a catalyst. Hydrogen gas can be obtained by electrolyzing water, etc. If renewable energy sources such as hydropower, wind power, geothermal energy, or solar energy are used as the electrical energy for electrolyzing water, carbon dioxide emissions can be further reduced. Oxygen is also produced during this process, and this oxygen may be used as the oxygen contained in the combustion-supporting gas mentioned above.

[0040] Examples of catalysts for conversion to methane include Rh / Mn, Rh, Ni, Pd, and Pt-based catalysts. A support material may also be used to support the catalyst. Examples of such supports include CeO2, ZrO2, Y2O3, Al2O3, MgO, and TiO2. These can be selected and used as appropriate. The methane produced can be used as fuel for at least one of the rotary kiln 3 and the calcination furnace 4, with the aim of reducing carbon dioxide emissions. Alternatively, the methane produced may be used separately as fuel for power generation. Examples of catalysts for converting methanol include Re-based, Pt-based, Ir-based, Cu-based, and Zn-based catalysts. The resulting methanol can be further converted into valuable fuels or chemical substances such as olefins and aromatics using solid acid catalysts. Furthermore, marine fuel and aviation fuel (SAF: Sustainable Aviation Fuel) may be produced by reacting a high-concentration carbon dioxide-containing substance with hydrogen or the like.

[0041] Another example of carbon dioxide utilization is the carbonation of calcium-containing waste. Specifically, this method involves bringing a high-concentration carbon dioxide-containing material into contact with calcium-containing waste, allowing the calcium-containing waste to absorb the carbon dioxide (usually in gaseous form) contained in the high-concentration carbon dioxide-containing material. By absorbing and fixing the carbon dioxide in the calcium-containing waste, the amount of carbon dioxide released into the atmosphere can be reduced. Examples of calcium-containing waste include waste concrete. Calcium-containing waste that has absorbed carbon dioxide may be used as a cement raw material in the cement clinker manufacturing system described above. Furthermore, calcium-containing waste that has absorbed carbon dioxide may be crushed, classified, etc., and used as roadbed material or concrete aggregate. In addition, if the calcium-containing waste is waste concrete, only the paste component from the waste concrete that has absorbed carbon dioxide may be separated and recovered and used as a cement raw material.

[0042] In rotary kiln 3, cement clinker can be obtained by firing the cement clinker raw materials. The firing temperature of the cement clinker raw materials can be the typical temperature used in cement clinker production, usually 1,400°C or higher. In rotary kiln 3, the same fuel used in calcination furnace 4 can be used for firing the raw materials for cement clinker. In addition, fuels that are difficult to crush, such as contaminated soil containing a large amount of organic components or waste tires, may be directly fed into the raw material inlet of rotary kiln 3. Furthermore, the exhaust gas generated in the rotary kiln 3 flows through kiln exhaust gas discharge passages 6a to 6e, which are used to discharge the exhaust gas after it has passed through the cyclone-type preheating device 2. After being de-dusted using a cyclone, bag filter, or electrostatic precipitator, it is discharged to the outside through the chimney.

[0043] From the perspective of further reducing carbon dioxide emissions, carbon dioxide may be separated and recovered from 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 decarboxylation of limestone. The limestone, which has been used repeatedly, can ultimately be used as a raw material for cement clinker.

[0044] Alternatively, a portion of the kiln exhaust gas may be extracted and cooled without passing through the cyclone-type preheating device 2 to remove solid components. After removing the solid components, the exhaust gas is discharged, and the solid components are classified into coarse and fine powders. The coarse powder is used as part of the cement clinker raw material, and a chlorine bypass device 10 is installed to recover the fine powder. Furthermore, "coarse powder" tends to have a higher concentration of cement clinker raw material components and a lower concentration of chlorine, while "fine powder" tends to have a higher concentration of chlorine. The base bypass device 10 is typically installed at the connection point between the cyclone-type preheating device 2 and the rotary kiln 3. By installing the chlorine bypass device 10, larger quantities of chlorine-containing waste, such as municipal solid waste incineration ash, can be used as raw materials for cement clinker or as fuel for the rotary kiln. The kiln exhaust gas discharged from the chlorine bypass device 10 is normally returned to the kiln exhaust gas discharge channel 6a.

[0045] The cement clinker obtained in rotary kiln 3 is fed into clinker cooler 5, which is located downstream of the rotary kiln, and cooled there. From the viewpoint of more efficiently heating in the calcination furnace 4 and the rotary kiln 3, the air used to cool the cement clinker may be divided into a forward and a backward side of the clinker cooler 5, and the air on the backward side after the cement clinker has been cooled may be used for indirect heating of the combustion-supporting gas passing through the combustion-supporting gas supply passage 8. Furthermore, different gases may be used for cooling the forward and downstream sides. Specifically, air may be used as the cooling gas for the forward side of the clinker cooler 5, and a combustion-supporting gas passing through the combustion-supporting gas supply passage 8 may be used as the cooling gas for the downstream side. The gas used to cool the forward flow is used as a combustion-supporting gas for burning fuel inside the rotary kiln 3 after heat exchange with the high-temperature cement clinker. Since the gas used to cool the forward flow undergoes heat exchange at the inlet of the clinker cooler 5, it becomes hotter after heat exchange compared to the gas used to cool the downstream flow.

[0046] Furthermore, electrical energy may be used to heat the air and combustion-supporting gases used when burning fuel in the rotary kiln, as well as to assist in heating the rotary kiln and the calcination furnace. Examples of heating methods using electrical energy include plasma heating, resistance heating, and microwave heating. Using renewable energy as the electrical energy source can further reduce carbon dioxide emissions.

[0047] An example of the cement clinker manufacturing system of the present invention will be described in detail below with reference to Figure 2. The cement clinker manufacturing system 31 in Figure 2 includes a cyclonic preheating device 32 containing two or more cyclonic heat exchangers 32a to 32d, a rotary kiln 33, a calcination furnace 34 including a heating means 50, a clinker cooler 35, kiln exhaust gas discharge passages 36, 36a to 36e, a combustion-supporting gas supply device 37, a combustion-supporting gas supply passage 38 located in the middle of the first calcination furnace exhaust gas supply passage 39, upstream of the dust collector 44 and the acid gas removal device 45, and arranged to exchange heat between carbon dioxide-containing exhaust gas flowing through the first calcination furnace exhaust gas supply passage 39 and combustion-supporting gas flowing through the combustion-supporting gas supply passage 38, an exhaust gas compressor 42, a carbon dioxide purification device 43, and the first calcination furnace exhaust gas supply passage 39. The system includes a cement clinker raw material recovery device 48, a dust collector 44, an acid gas removal device 45, a second calcinerator exhaust gas supply channel 53 located in the middle of the first calcinerator exhaust gas supply channel 39, downstream of the dust collector 44 and the acid gas removal device 45, which is connected to the first calcinerator exhaust gas supply channel 39 and allows a portion of the carbon dioxide-containing exhaust gas flowing through the first calcinerator exhaust gas supply channel 39 to be merged with the combustion-supporting gas flowing through the combustion-supporting gas supply channel 38, a first oxygen-containing residual gas supply channel 60 for guiding the oxygen-containing residual gas to at least one of the rotary kiln 33 and the calcinerator 34, and a second oxygen-containing residual gas supply channel 61 for guiding the oxygen-containing residual gas to the combustion-supporting gas supply device 37.

[0048] The cyclone heat exchangers 32a-32d, the cyclone preheating device 32, the rotary kiln 33, the calcination furnace 34, the clinker cooler 35, the kiln exhaust gas discharge passages 36, 36a-36e, the combustion-supporting gas supply device 37, the chlorine bypass device 40, the exhaust gas compressor 42, the carbon dioxide purification device 43, the dust collector 44, the acid gas removal device 45, the high-concentration carbon dioxide discharge passage 47, the cement clinker raw material recovery device 48, the preheating raw material supply passage 49, the heating means 50, the soot discharge passage 51, and the decarbonation supply passage 52 are each The same applies to the cyclone heat exchangers 2a-2d, cyclone preheating device 2, rotary kiln 3, calcination furnace 4, clinker cooler 5, kiln exhaust gas discharge passages 6, 6a-6e, combustion-supporting gas supply device 7, chlorine bypass device 10, exhaust gas compressor 12, carbon dioxide purification device 13, dust collector 14, acid gas removal device 15, high-concentration carbon dioxide discharge passage 17, cement clinker raw material recovery device 18, preheating raw material supply passage 19, heating means 20, soot discharge passage 21, and decarbonation supply passage 22 described above.

[0049] In the cyclone-type preheating device 32, among the two or more cyclone-type heat exchangers 32a to 32d that constitute the cyclone-type preheating device 32, the cement clinker raw material is preheated to a temperature of preferably 600 to 900°C, more preferably 700 to 900°C, in the cyclone-type heat exchanger 32c to which the preheating raw material supply passage 49 is connected. Preheating in this temperature range makes it easier to fix (carbonize) the carbon dioxide contained in the kiln exhaust gas as it passes through the cyclone-type preheating device 32 (especially the cyclone-type heat exchanger 32c to which the preheating raw material supply passage 49 is connected) into the quicklime-containing raw material (described in detail later) introduced into the cyclone-type preheating device 32 from the quicklime-containing raw material supply passage 54. This reduces the amount of carbon dioxide in the kiln exhaust gas and increases the concentration of carbon dioxide in the calcination furnace exhaust gas.

[0050] The oxygen-containing residual gas is supplied to at least one of the rotary kiln 33 and the calcination furnace 34 as primary air or secondary air through a first oxygen-containing residual gas supply passage 60 for guiding the oxygen-containing residual gas to at least one of the rotary kiln 33 and the calcination furnace 34. In Figure 2, the first oxygen-containing residual gas supply channel 60 branches off from a single pipe connected to the carbon dioxide purification device 43 and is arranged to supply oxygen-containing residual gas to the heating means of the rotary kiln 33, the vicinity of the inlet side of the clinker cooler 35 (near the connection point with the rotary kiln 33), and the combustion-supporting gas supply channel 38. The oxygen-containing residual gas supplied near the inlet of the clinker cooler 35 passes through the clinker cooler 35 and is supplied to the rotary kiln 33 as secondary air. Alternatively, oxygen-containing residual gas may be supplied to the rotary kiln 33 and the calcination furnace 34, respectively, using two separate pipes connected to the carbon dioxide purification device 43. Furthermore, the oxygen-containing residual gas is supplied to the combustion-supporting gas supply device 37 through a second oxygen-containing residual gas supply path 61, which leads to the combustion-supporting gas supply device 37.

[0051] The combustion-supporting gas supply passage 38 is located in the middle of the furnace exhaust gas supply passage 39, upstream of the location where the dust collector 44 is installed and the location where the acid gas removal device 45 is installed, and is arranged to exchange heat between the furnace exhaust gas circulating in the first furnace exhaust gas supply passage 39 and the combustion-supporting gas. By arranging the equipment in this manner, the combustion-supporting gas flowing through the combustion-supporting gas supply passage 38 is indirectly heated and its temperature is increased, thereby reducing the amount of fuel that needs to be fed into the calcinerator 34. Furthermore, by lowering the temperature of the calcinerator exhaust gas flowing through the first calcinerator exhaust gas supply passage 39, the efficiency of removing soot from the calcinerator exhaust gas in the dust collector 44 and the efficiency of removing acidic gases from the calcinerator exhaust gas in the acidic gas removal device 45 can be improved. Furthermore, the combustion-supporting gas supply passage 38 may be arranged such that the combustion-supporting gas passing through the combustion-supporting gas supply passage 38 is indirectly heated and warmed by the air that has been warmed by heat exchange with the cement clinker in the clinker cooler 35 (not shown). Alternatively, the combustion-supporting gas supply passage 38 may be passed through a portion of the downstream side of the cement cooler 35 (the outlet side of the clinker cooler) so that the combustion-supporting gas is warmed by the heat of the cement clinker (not shown).

[0052] A second calcinerator exhaust gas supply channel 53 is provided in the middle of the first calcinerator exhaust gas supply channel 39, downstream of the dust collector 44 and the acid gas removal device 45, and is connected to the first calcinerator exhaust gas supply channel 39. This second channel 53 is provided to merge a portion of the calcinerator exhaust gas flowing through the first calcinerator exhaust gas supply channel 39 with the combustion-supporting gas flowing through the combustion-supporting gas supply channel 38. With this arrangement, the combustion-supporting gas flowing through the combustion-supporting gas supply passage 38 can be mixed with the furnace exhaust gas (especially carbon dioxide) to adjust the oxygen concentration of the combustion-supporting gas. Furthermore, since the temperature of the furnace exhaust gas discharged from the furnace 34 is high, around 800°C, the combustion-supporting gas can be heated up by mixing it with the furnace exhaust gas. Furthermore, by using a portion of the calcinerator exhaust gas as part of the combustion-supporting gas and circulating it, the amount of exhaust gas discharged from the first calcinerator exhaust gas supply passage 39 can be reduced. The amount of calcinerator exhaust gas circulating in the first calcinerator exhaust gas supply passage 39 that is used as part of the combustion-supporting gas is preferably 50 to 70% by volume. Furthermore, the carbide furnace exhaust gas that is merged from the first carbide furnace exhaust gas supply passage 39 into the combustion-supporting gas flowing through the combustion-supporting gas supply passage 38 has already had particulate matter and acidic gases recovered by the dust collector 44 and the acidic gas removal device 45. Therefore, it is possible to reduce dust accumulation and adhesion within the carbide furnace 34, adverse effects on fuel combustion, and adverse effects on heat exchange between the carbide furnace exhaust gas and the combustion-supporting gas due to dust accumulation and adhesion within the first carbide furnace exhaust gas supply passage 39.

[0053] A denitrification agent supply device (not shown) may be installed to supply a denitrification agent to the exhaust gas flowing through the kiln exhaust gas discharge passage 36, from the portion of the kiln exhaust gas discharge passage 36 connected to the rotary kiln 33 to the portion of the cyclone-type heat exchanger 32d located at the furthest end of the flow (indicated by a dashed line in Figure 2). By spraying a denitrification agent such as urea into the exhaust gas, the NOx in the exhaust gas can be reduced.

[0054] Typically, spraying a denitrifying agent into the exhaust gas at a temperature of around 900°C can reduce NOx in the exhaust gas. In a typical cement clinker manufacturing system, the exhaust gas temperature reaches around 900°C in the region from the tail of the rotary kiln to the bottom cyclone (a cyclone-type heat exchanger located at the rear of the flow). However, a large amount of fine powder derived from the cement clinker raw materials is present in this region. As a result, the sprayed denitrifying agent is adsorbed by the fine powder, reducing the effectiveness of the denitrifying agent. On the other hand, the cement clinker manufacturing system 31 of the present invention can reduce the amount of fine powder derived from cement clinker raw materials in the exhaust gas in the above-mentioned region (the portion of the kiln exhaust gas discharge passage 36 from the part connected to the rotary kiln 33 to the cyclone-type heat exchanger 32d located at the furthest end of the flow path), thereby efficiently reducing the amount of NOx in the exhaust gas.

[0055] Furthermore, a heating means gas supply passage 58 may be provided at a location closer to the combustion-supporting gas supply device 37 than the portion of the combustion-supporting gas supply passage 38 that exchanges heat between the combustion-supporting gas and the combustion-supporting gas, and at least one of the following locations in the second combustion-supporting gas supply passage 53 (between the connection point between the second combustion-supporting gas supply passage 53 and the first combustion-supporting gas supply passage 39 and the connection point between the second combustion-supporting gas supply passage 53 and the combustion-supporting gas supply passage 38): the heating means gas supply passage 58 may be provided at least one of the following locations: a location closer to the combustion-supporting gas supply device 37 than the portion of the combustion-supporting gas supply passage 38 that exchanges heat between the combustion-supporting gas and the combustion-supporting gas, and a location in the middle of the second combustion-supporting gas supply passage 53 (between the connection point between the second combustion-supporting gas supply passage 53 and the first combustion-supporting gas supply passage 39 and the connection point between the second combustion-supporting gas supply passage 53 and the combustion-supporting gas supply passage 38), and for supplying at least one of the combustion-supporting gas flowing through the combustion-supporting gas supply passage 38 and the combustion-supporting gas flowing through the second combustion-supporting gas supply passage 53 to the heating means 50 of the combustion-supporting gas supply passage 58. In Figure 2, the heating gas supply passage 58 is connected to the combustion-supporting gas supply passage 38 at a position closer to the combustion-supporting gas supply device 37 than the portion of the combustion-supporting gas supply passage 38 that exchanges heat between the furnace exhaust gas and the combustion-supporting gas. By supplying gas to the heating means 50 of the calcination furnace 34 using the gas supply passage 58 for the heating means, the volume of calcination furnace exhaust gas discharged from the calcination furnace 34 can be reduced, and the carbon dioxide concentration in the calcination furnace exhaust gas can be increased.

[0056] A quicklime-containing raw material recovery device 41 may be installed in the middle of the decarbonated raw material supply channel 52 to recover a portion of the decarbonated cement clinker raw material flowing through the decarbonated raw material supply channel 52 as quicklime-containing raw material. The quicklime-containing raw material recovered by the quicklime-containing raw material recovery device 41 is supplied from the quicklime-containing raw material recovery device 41 through the quicklime-containing raw material discharge passage 57 to the quicklime-containing raw material supply passage 54 and then to the cyclone-type preheating device 32 for the purpose of immobilizing (carbonizing) carbon dioxide gas in the kiln exhaust gas onto the quicklime-containing raw material. The quicklime-containing raw material discharge channel 57 may also be connected to the fly ash discharge channel 51. In Figure 2, the quicklime-containing raw material discharge channel 57 is connected to the quicklime-containing raw material supply channel 54 (not shown).

[0057] The quicklime-containing raw material (fine powder containing quicklime, or decarboxylated cement clinker raw material containing quicklime) recovered in the quicklime-containing raw material recovery device 41 and the dust collector 44 is supplied through the quicklime-containing raw material supply passage 54 to either the cyclone-type heat exchanger 32c, which is connected to the preheating raw material supply passage 49, or one of the two or more cyclone-type heat exchangers 32a to 32d that constitute the cyclone-type preheating device 32, or to the cyclone-type heat exchangers 32a to 32b located upstream of the cyclone-type heat exchanger.

[0058] By supplying quicklime-containing raw material to either the cyclone-type heat exchanger 32c, to which the preheating raw material supply passage 49 is connected, or to any of the cyclone-type heat exchangers 32a to 32b located upstream of the cyclone-type heat exchanger, the carbon dioxide contained in the kiln exhaust gas flowing through the kiln exhaust gas discharge passage 36 is fixed (carbonized) in the quicklime-containing raw material as it passes through the cyclone-type preheating device 32. This reduces the amount of carbon dioxide contained in the kiln exhaust gas discharged from the kiln exhaust gas discharge passage 36. The carbon dioxide fixed in the quicklime-containing raw material is fed into the calcinerator 34 along with other cement clinker raw materials, where it is decarbonated and recovered as calcinerator exhaust gas.

[0059] The second decarboxylated raw material supply channel 59 is connected to the decarboxylated raw material supply channel 52 and is intended to supply a portion of the decarboxylated cement clinker raw material from the decarboxylated raw material supply channel 52 to the cyclone heat exchanger 32d, which is located on the last-flow side of the two or more cyclone heat exchangers that make up the cyclone-type preheating device 32. The decarboxylated cement clinker raw material flowing through the second decarboxylated raw material supply channel 59 is at a high temperature (for example, 950 to 1,000°C). By supplying this raw material to the cyclone-type heat exchanger 32d located at the furthest end of the flow, the temperature inside the cyclone-type preheating device 32 is increased, allowing for more efficient preheating of the cement clinker raw material and more efficient fixation (carbonation) of carbon dioxide contained in the kiln exhaust gas. The cement clinker raw material supplied to the cyclone-type heat exchanger 32d is subjected to centrifugal separation while exchanging heat with the kiln exhaust gas passing through the cyclone-type heat exchanger 32d, and then fed into the rotary kiln 33. Furthermore, a portion of the second decarbonation raw material supply channel 59 may also serve as the kiln exhaust gas discharge channel 36.

[0060] The decarbonation raw material supply control device 55 adjusts the amount of decarbonated cement clinker raw material supplied from the second decarbonation raw material supply passage 59 to the cyclone-type heat exchanger 32d located at the furthest downstream end. By adjusting the amount of said raw material, it adjusts the temperature inside the cyclone-type heat exchanger 32d and the temperature of the kiln exhaust gas passing through the cyclone-type heat exchanger 32d, thereby adjusting the temperature inside the cyclone-type heat exchanger 32c which is connected to the preheating raw material supply passage 49. The amount of the above-mentioned raw materials is adjusted based on the temperature of the kiln exhaust gas in the kiln exhaust gas discharge passage 36 as it passes through the cyclone-type heat exchanger 32c, which is connected to the preheating raw material supply passage 49. The above temperature may be the temperature near the inlet of the kiln exhaust gas discharge passage 36 (the position where the kiln exhaust gas enters the cyclone-type heat exchanger 32c) which passes through the cyclone-type heat exchanger 32c connected to the preheating raw material supply passage 49, or it may be the temperature near the outlet of the kiln exhaust gas discharge passage 36 (the position where the kiln exhaust gas leaves the cyclone-type heat exchanger 32c). The above temperature is measured by a temperature measuring device 26. The temperature measuring device 26 can be appropriately installed in the cyclone-type heat exchanger 32c, which is connected to the preheating raw material supply passage 49.

[0061] For the purpose of adjusting the temperature inside the cyclone-type heat exchanger 32c, which is connected to the preheating raw material supply passage 49, a moisture supply device (not shown) may be installed to supply water or water-containing waste to the exhaust gas flowing through the kiln exhaust gas discharge passage 36, from the portion of the kiln exhaust gas discharge passage 36a connected to the rotary kiln 33 to the upstream portion of the cyclone-type heat exchanger 32d located at the furthest end (shown as enclosed by a dashed line in Figure 2). By supplying water or water-containing waste to the exhaust gas, the temperature is adjusted. This adjustment may be performed based on the temperature measured by the temperature measuring device 26, and may also be linked to the decarboxylation raw material supply amount control device 55.

[0062] Furthermore, an air supply passage 56 may be provided to guide the air from the clinker cooler 35 into the kiln exhaust gas discharge passage 36a. This air is heated by heat exchange with the cement clinker in the clinker cooler 35. By adjusting the amount of air supplied from the air supply passage 56 to the kiln exhaust gas discharge passage 36a, the temperature and amount of kiln exhaust gas in the kiln exhaust gas discharge passage 36 can be adjusted, and incomplete combustion of waste introduced into the kiln tail can be eliminated. The amount of air can be adjusted based on the temperature measured by the temperature measuring device 26, or it may be adjusted in conjunction with the decarboxylation raw material supply control device 55. [Explanation of symbols]

[0063] 1.31 Cement Clinker Manufacturing System 2.32 Cyclone-type preheating device 2a,2b,2c,2d,32a,32b,32c,32d Cyclone heat exchanger 3.33 Rotary Kiln 4,34 kiln 5.35 Clinka Cooler 6,6a,6b,6c,6d,6e,36a,36,36b,36c,36d,36e Kiln exhaust gas discharge path 7.37 Combustion-supporting gas supply device 8,38 Combustion-supporting gas supply lines 9,39 First Incinerator Exhaust Gas Supply Line 10,40 Chlorine bypass device 11 Merging flow path 12,42 Exhaust gas compressor 13,43 Carbon dioxide purification equipment 14, 44 Dust collector 15,45 Acid Gas Removal Device 17,47 High-concentration carbon dioxide-containing discharge path 18,48 Cement clinker raw material recovery device 19,49 Preheating raw material supply route 20,50 Heating means 21,51 Dust discharge passage 22,52 Decarbonation raw material supply path 23 Airflow passage 24,60 First oxygen-containing residual gas supply channel 25,61 Second oxygen-containing residual gas supply channel 26 Temperature measuring device 41 Quicklime-containing raw material recovery device 53 Second combustion furnace exhaust gas supply channel 54 Quicklime-containing raw material supply route 55 Decarboxylation raw material supply control device 56 Air supply path 57 Quicklime-containing raw material discharge path 58 Gas supply channel for heating means 59 Second supply route for decarboxylated raw materials

Claims

1. A cyclonic preheating device including two or more cyclonic heat exchangers for preheating cement clinker raw materials, A rotary kiln for firing the cement clinker raw material, which has been preheated in the cyclone-type preheating device described above, to obtain cement clinker, A calcination furnace, which includes a heating means and is arranged together with the cyclone-type preheating device on the upstream side of the rotary kiln, for promoting the decarbonation of the cement clinker raw material using the heating means, A clinker cooler for cooling the cement clinker is installed downstream of the rotary kiln mentioned above. A kiln exhaust gas discharge channel for discharging exhaust gas generated in the rotary kiln after passing it through the cyclone-type preheating device. A cement clinker manufacturing system including, A combustion-supporting gas supply device for supplying a combustion-supporting gas with a higher oxygen concentration than air, A combustion-supporting gas supply path for guiding the combustion-supporting gas from the combustion-supporting gas supply device to the furnace, A carbon dioxide purification apparatus for purifying the carbon dioxide-containing exhaust gas produced in the above-mentioned incineration furnace to obtain a high-concentration carbon dioxide-containing substance with increased carbon dioxide concentration, and an oxygen-containing residual gas, A first calcination furnace exhaust gas supply channel (however, limited to one different from the kiln exhaust gas discharge channel) for guiding the carbon dioxide-containing exhaust gas from the calcination furnace to the carbon dioxide purification device, A cement clinker raw material recovery device is installed in the middle of the exhaust gas supply path of the first calcination furnace described above, for recovering the decarbonated cement clinker raw material and returning it to the cyclone-type preheating device described above. A first oxygen-containing residual gas supply channel for guiding the above-mentioned oxygen-containing residual gas to at least one of the above-mentioned rotary kiln and the above-mentioned furnace, A cement clinker manufacturing system characterized by including [the following].

2. The above-mentioned combustion-supporting gas supply passage is arranged in the middle of the above-mentioned first furnace exhaust gas supply passage so as to exchange heat between the carbon dioxide-containing exhaust gas flowing through the above-mentioned first furnace exhaust gas supply passage and the above-mentioned combustion-supporting gas. A second combustion furnace exhaust gas supply channel is provided to merge a portion of the carbon dioxide-containing exhaust gas flowing through the first combustion furnace exhaust gas supply channel with the combustion-supporting gas flowing through the combustion-supporting gas supply channel. A cement clinker manufacturing system according to claim 1, comprising:

3. A cement clinker manufacturing system according to claim 1 or 2, further comprising a second oxygen-containing residual gas supply channel for guiding the above-mentioned oxygen-containing residual gas to the above-mentioned combustion-supporting gas supply device.

4. A method for producing cement clinker using the cement clinker production system described in claim 1 or 2, A method for producing cement clinker, characterized by adjusting the oxygen concentration of the combustion-supporting gas so that the carbon dioxide concentration of the carbon dioxide-containing exhaust gas generated in the above-mentioned furnace is 80% or more by volume, relative to 100% by volume excluding water vapor.

5. A method for producing cement clinker using the cement clinker production system described in claim 1 or 2, A method for producing cement clinker, wherein the carbon dioxide-containing exhaust gas is purified using a cryogenic separation method at a temperature that is above the boiling point of oxygen and nitrogen contained in the carbon dioxide-containing exhaust gas, and below the boiling point of carbon dioxide contained in the carbon dioxide-containing exhaust gas, in the carbon dioxide purification apparatus described above.

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