JP7748812B2 - Cement clinker manufacturing system and cement clinker manufacturing method - Google Patents

Description

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

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 cement production, approximately 60% is emitted by decarbonation of limestone, which is used as a raw material for cement, and approximately 40% is emitted by 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.

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.

JP 2018-52746 A Japanese Patent Application Laid-Open No. 2004-292298

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, separation and recovery of carbon dioxide becomes easier. Furthermore, by reducing the amount of nitrogen and other substances contained in the exhaust gas, the volume of the generated exhaust gas can be relatively reduced, and the equipment for separating and recovering carbon dioxide can be made smaller.
An object of the present invention is to provide a cement clinker production system that, when producing cement clinker, can increase the carbon dioxide concentration in part of exhaust gas to obtain gas containing a high concentration of carbon dioxide that is easily usable for producing methane, and that can efficiently produce methane using the carbon dioxide.

As a result of intensive research by the present inventors to solve the above problems, they have come up with a system for supplying a combustion-stimulating gas (hydrogen gas, as described later) having 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 for promoting decarbonation of the cement clinker raw materials, a clinker cooler for cooling the cement clinker, which is disposed downstream of the rotary kiln, and a kiln exhaust gas discharge path for discharging exhaust gas generated in the rotary kiln after passing through the cyclone-type preheating device. The inventors have found that the above-mentioned object can be achieved by a cement clinker production system including a combustion-supporting gas supply line for guiding the combustion-supporting gas to a calciner, a mixer for mixing carbon dioxide-containing exhaust gas with hydrogen gas, a hydrogen gas supply device for supplying hydrogen gas, a hydrogen gas supply line for guiding hydrogen gas to the mixer, a calciner exhaust gas supply line for guiding the carbon dioxide-containing exhaust gas to the mixer, a methane generator for reacting carbon dioxide and hydrogen gas contained in the mixed gas to produce methane, and a mixed gas supply line for guiding the mixed gas to the methane generator, and have completed the present invention.
That is, the present invention provides the following [1] to [7].

[1] A cement clinker production system including a cyclone preheating device for preheating cement clinker raw materials, a rotary kiln for burning the cement clinker raw materials preheated in the cyclone preheating device to obtain cement clinker, a calciner disposed upstream of the rotary kiln together with the cyclone 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 kiln exhaust gas discharge path for discharging exhaust gas generated in the rotary kiln after passing through the cyclone preheating device, the system including a combustion-supporting gas supplying device for supplying a combustion-supporting gas having a higher oxygen concentration than air, and a combustion-supporting gas supplying device for supplying the combustion-supporting gas from the combustion-supporting gas supplying device. a mixing device for mixing carbon dioxide-containing exhaust gas generated in the calciner with hydrogen gas to prepare a mixed gas of the carbon dioxide-containing exhaust gas and the hydrogen gas and for adjusting the temperature of the mixed gas; a hydrogen gas supply device for supplying the hydrogen gas; a hydrogen gas supply path for guiding the hydrogen gas from the hydrogen gas supply device to the mixing device; a calciner exhaust gas supply path for guiding the carbon dioxide-containing exhaust gas from the calciner to the mixing device; a methane generator for reacting the carbon dioxide and hydrogen gas contained in the mixed gas using a catalyst to produce methane and steam; and a mixed gas supply path for guiding the mixed gas from the mixing device to the methane generator.

[2] The cement clinker production system according to [1], further comprising a methane supply line for supplying methane-containing gas containing methane produced in the methane production device to the calciner.
[3] The cement clinker production system according to [1] or [2], wherein the combustion-supporting gas supply device and the hydrogen gas supply device are water electrolysis devices for electrolyzing water to obtain hydrogen gas and oxygen gas.
[4] The cement clinker production system according to any one of [1] to [3], 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.

[5] The cement clinker production system according to any one of [1] to [4], further comprising a confluence passage for confluence of a part of the exhaust gas flowing through the calciner exhaust gas supply passage with the combustion-supporting gas flowing through the combustion-supporting gas supply passage.
[6] A method for producing cement clinker using the cement clinker production system according to any one of [1] to [5], 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.
[7] The method for producing cement clinker according to [6] , wherein the temperature of the mixed gas is adjusted to 200 to 300°C in the mixing device .

The cement clinker production system of the present invention increases the carbon dioxide concentration in part of the exhaust gas when producing cement clinker, thereby obtaining gas containing a high concentration of carbon dioxide that is easily usable for methane production, and can then use this carbon dioxide to efficiently produce methane.

1 is a diagram schematically illustrating an example of a cement clinker production system according to the present invention.

The cement clinker production system of the present invention will be described in detail below 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-type preheating device 2 for preheating cement clinker raw materials, a rotary kiln 3 for burning the cement clinker raw materials preheated in the cyclone-type preheating device 2 to obtain cement clinker, a calciner 4 for accelerating decarbonation of the cement clinker raw materials, which is disposed upstream of the rotary kiln 3 together with the cyclone-type preheating device 2, a clinker cooler 5 for cooling the cement clinker, which is disposed downstream of the rotary kiln 3, and kiln exhaust gas discharge paths 6a to 6e for discharging exhaust gas (hereinafter sometimes abbreviated as "kiln exhaust gas") generated in the rotary kiln 3 after passing through the cyclone-type preheating device 2, and a combustion-supporting gas supplying device (water electrolysis device in FIG. 1 ) for supplying a combustion-supporting gas having a higher oxygen concentration than air. a mixing device 8 for mixing the carbon dioxide-containing exhaust gas (hereinafter sometimes abbreviated as "calciner exhaust gas") produced in the calciner 4 with hydrogen gas to prepare a mixed gas of carbon dioxide-containing exhaust gas and hydrogen gas and for adjusting the temperature of the mixed gas; a hydrogen gas supply device (water electrolysis device 9 in FIG. 1) for supplying hydrogen gas; a hydrogen gas supply path 10 for guiding the hydrogen gas from the hydrogen gas supply device to the mixing device 8; a calciner exhaust gas supply path 11 for guiding the carbon dioxide-containing exhaust gas from the calciner 4 to the mixing device 8; a methane generator 12 for reacting the carbon dioxide and hydrogen gas contained in the mixed gas using a catalyst to produce methane and water vapor; and a mixed gas supply path 13 for guiding the mixed gas from the mixing device 8 to the methane generator 12.

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 transporting 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 charged 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 charged from the bottom of cyclone heat exchanger 2a into cyclone heat exchanger 2b, which is disposed downstream, and then again centrifuged while exchanging heat with the exhaust gas, and then charged 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 successively through cyclone heat exchangers 2b to 2c, which are disposed downstream, before being charged into calciner 4.

In the cyclone preheating device 2, the cement clinker raw materials are preheated preferably to 400 to 750°C, more preferably 500 to 725°C, and especially 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 less likely to be promoted in the cyclone preheating device 2, preventing the carbon dioxide concentration in the kiln exhaust gas from increasing.

The cement clinker raw material is not particularly limited, and may be any of the common raw materials for cement clinker, such as natural raw materials such as limestone, soil, clay, silica stone, and iron raw materials, as well as waste materials 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.
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 resulting 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 .

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.

Here, decarbonation of cement clinker raw materials means decomposing calcium carbonate (CaCO ₃ ), which is the main component of limestone contained in the cement clinker raw materials, into quicklime (CaO) and carbon dioxide (CO ₂ ) 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 a higher temperature is required 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.

The decarbonation of the cement clinker raw material is promoted by directly heating the cement clinker raw material in the calciner 4 using the heating means 15a by burning a fuel and a combustion-supporting gas.
An example of the heating means 15a is a burner.
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; methane produced by methanation using carbon dioxide as a raw material; etc. These may be used alone or in combination of two or more.
Among these, from the viewpoint of reducing carbon dioxide emissions in cement clinker production and reducing fuel costs, methane produced by methanation using carbon dioxide contained in the carbon dioxide-containing exhaust gas produced in the calciner 4 as a raw material in the methane generator 12 described below is preferred.
Furthermore, if carbon-free fuels such as biomass are used, carbon dioxide emissions in cement clinker production can be substantially reduced.

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.
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 of the calciner exhaust gas including water vapor, from the viewpoint of increasing the carbon dioxide concentration in the calciner exhaust gas. 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.

The combustion-sustaining gas used in the calciner 4 is supplied from a combustion-sustaining gas supply device (water electrolysis device 9 in FIG. 1) and is introduced into the calciner 4 through a combustion-sustaining gas supply line 7 .
The combustion-supporting gas supply passage 7 may be disposed so that the temperature of the combustion-supporting gas passing through the combustion-supporting gas supply passage 7 is indirectly heated by air heated by heat exchange with the cement clinker in the clinker cooler 5. Alternatively, the combustion-supporting gas may be heated by the heat of the cement clinker by passing the combustion-supporting gas through the combustion-supporting gas supply passage 7 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.

Examples of the combustion-stimulating gas supply device for supplying the combustion-stimulating gas to the calciner 4 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.
Furthermore, when a water electrolysis device is used as the combustion-supporting gas supply device, the combustion-supporting gas supply device also serves as a hydrogen gas supply device, which will be described later.

The combustion-sustaining gas supplied from the combustion-sustaining gas supply device 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, which would make 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 may be mixed with carbon dioxide, 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 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 and at least one of carbon dioxide gas and water vapor) is preferably 10 to 79 vol%, more preferably 20 to 75 vol%, and even more preferably 30 to 70 vol%, relative to 100 vol% of the volume including water vapor.

Furthermore, from the perspective of reducing the volume of 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 (e.g., 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.

An example of a method for mixing the combustion-supporting gas supplied from the combustion-supporting gas supply device with carbon dioxide gas is a method for mixing the combustion-supporting gas supplied from the combustion-supporting gas supply device 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 mixing the calciner exhaust gas, a confluence passage 18 is provided for merging a portion of the calciner exhaust gas flowing through the calciner exhaust gas supply passage 11 for leading the gas to the mixer 8 described below with the combustion-sustaining gas flowing through the combustion-sustaining gas supply passage 7 (the combustion-sustaining gas supplied from the combustion-sustaining gas supply device), and the combustion-sustaining gas flowing through the combustion-sustaining gas supply passage 7 and a portion of the calciner exhaust gas are mixed together.
Furthermore, when the combustion-supporting gas supply passage 7 is arranged so that the combustion-supporting gas passing through the combustion-supporting gas supply passage 7 is indirectly heated and heated by air heated by heat exchange with the cement clinker in the clinker cooler 5, the confluence flow passage 18 is preferably arranged so that the combustion-supporting gas and a portion of the exhaust gas are confluent at a point after the combustion-supporting gas has been indirectly heated by the air.

The carbon dioxide-containing exhaust gas produced in the calciner 4 is led from the calciner 4 through a calciner exhaust gas supply line 11 to the mixer 8 .
The calciner exhaust gas supply line 11 is different from the kiln exhaust gas discharge lines 6a to 6e, which are used to discharge the exhaust gas generated in the rotary kiln 3. By completely separating the calciner exhaust gas supply line 11 from the kiln exhaust gas discharge lines 6a to 6e, it is possible to recover only the calciner exhaust gas with a high carbon dioxide concentration.

The carbon dioxide-containing exhaust gas discharged from the calciner 4 has a high carbon dioxide concentration and a low nitrogen content, which allows the size of the methane generator and other equipment to be reduced, and is suitable as a raw material for methane generation. In addition, because the temperature of the carbon dioxide-containing exhaust gas is high, the amount of heat supplied from an external source can be reduced to keep the temperature inside the methane generator 12 within a temperature range suitable for methane generation (for example, 200°C to 800°C).
The carbon dioxide concentration of the carbon dioxide-containing 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.
The temperature of the carbon dioxide-containing exhaust gas varies depending on the decarbonation conditions in the calciner 4, but is usually 700 to 900° C. Since the carbon dioxide-containing exhaust gas has a high temperature, the exhaust gas may be used to heat water to generate steam, and the steam may be used with a steam turbine to generate electricity.

The mixer 8 mixes the carbon dioxide-containing exhaust gas generated in the calciner 4 with hydrogen gas to prepare a mixed gas of carbon dioxide-containing exhaust gas and hydrogen gas, and also adjusts the temperature of the mixed gas.
In the mixing device 8, by appropriately adjusting the mixing ratio of the carbon dioxide-containing exhaust gas and hydrogen gas and adjusting the temperature of the mixed gas, methane can be produced more efficiently in the methane generation device 12 (details of which will be described later).

The hydrogen gas used in the mixer 8 is supplied to the mixer 8 through a hydrogen gas supply path 10 for guiding hydrogen gas from a hydrogen gas supply device (water electrolysis device 9 in FIG. 1) to the mixer 8.
The hydrogen gas supply device may be any device capable of supplying hydrogen gas, and examples thereof include hydrogen gas cylinders; hydrogen gas storage tanks; and water electrolysis devices such as alkaline water electrolysis devices, solid polymer water electrolysis devices, and steam electrolysis devices.
Among these, from the viewpoint of constructing an efficient cement clinker production system, a water electrolysis device capable of electrolyzing water to obtain hydrogen gas and oxygen gas is preferred.
Furthermore, when a steam electrolysis device is used, steam generated in the methane generation device 12 or steam generated in a heat exchanger appropriately provided in the cement clinker production system can be used as a raw material.

When the water electrolysis device 9 is used as the hydrogen gas supply device, oxygen gas is also generated along with hydrogen gas, and this oxygen gas may be used as the oxygen gas contained in the combustion-supporting gas. In this case, the water electrolysis device 9 also serves as the combustion-supporting gas supply device. The oxygen gas generated by the water electrolysis device 9 is supplied to the combustion-supporting gas supply path 7.
Furthermore, a hydrogen gas supply device such as a hydrogen gas tank may be prepared separately from the water electrolysis device, and hydrogen gas may be supplied separately from the hydrogen gas supply device to the hydrogen gas supply path 10 .
Furthermore, carbon dioxide emissions can be further reduced by using electrical energy derived from renewable energy sources such as hydropower, wind power, geothermal power, or solar power as the electrical energy used for electrolyzing water, or by using electricity generated using methane produced in the methane generation device 12 as fuel.

The carbon dioxide-containing exhaust gas generated in the calciner 4 contains a small amount of oxygen gas, and when the carbon dioxide-containing exhaust gas and hydrogen gas are mixed in the mixer 8, the oxygen gas reacts with the hydrogen gas to form water vapor.
In the mixer 8 , the mixed gas is usually prepared by increasing or decreasing the amount of hydrogen gas supplied from the hydrogen gas supply line 10 .

The temperature of the mixed gas is preferably 200 to 600°C, more preferably 220 to 500°C, even more preferably 240 to 400°C, and particularly preferably 250 to 300°C. If the mixed gas is at 200°C or higher, the efficiency of methane production in the methane generator 12 can be improved. Since the temperature of the hydrogen gas to be mixed is usually room temperature (20°C), it is difficult to obtain a mixed gas with a temperature exceeding 600°C. Furthermore, if the temperature is 600°C or lower, the burden on equipment such as the mixer 8 and the mixed gas supply channel 13 can be reduced.
The mixed gas may be heated or cooled in the mixer 8 so that the temperature of the mixed gas falls within the above-mentioned range.

The mixed gas mixed in the mixer 8 is supplied to the methane generator 12 through a mixed gas supply path 13 for guiding the mixed gas from the mixer 8 to the methane generator 12 .
When the mixed gas has a high dust concentration, the dust may be collected by providing a cyclone, a bag filter, an electrostatic precipitator, or the like in the mixed gas supply path 13, from the viewpoint of more efficiently generating methane and reducing the burden on the methane generator 12. The dust concentration in the mixed gas is preferably 1 ^g /m3N or less, more preferably 0.5 g/ ^m3 or less.

Furthermore, a methanation-inhibiting component separation device may be provided in the mixed gas supply path 13 to separate inhibitory components of the catalyst used in the methane generation device 12 (components that inhibit the action of the catalyst and reduce its performance as a catalyst).
Examples of the inhibiting components include sulfur oxides (SOx), nitrogen oxides (NOx), hydrogen chloride (HCl), etc. The methanation inhibiting component separation device may be an appropriate combination of known methods and devices for removing the inhibiting components such as sulfur oxides, nitrogen oxides, and hydrogen chloride.
Furthermore, in the methanation-inhibiting component separation device, water (water vapor) may be removed as necessary.
Furthermore, nitrogen (N ₂ ) in the carbon dioxide-containing exhaust gas is a useless gas that does not contribute to the production of methane, and therefore, from the viewpoint of efficient methane production, nitrogen may be removed from the mixed gas.

The methane generator 12 uses a catalyst to cause a reaction between carbon dioxide gas and hydrogen gas contained in the mixed gas to generate methane and water vapor.
Examples of the catalyst include Rh/Mn-based, Rh-based, Ni-based, Pd-based, and Pt-based catalysts. A carrier for supporting the catalyst may also be used. Examples of the carrier include CeO ₂ , ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , MgO, TiO ₂ , and SiO ₂ . These may be appropriately selected and used.
The temperature of the internal space of the methane generator 12 (the space where carbon dioxide gas and hydrogen gas react to produce methane) is preferably 200 to 800°C, more preferably 250 to 700°C.

The reaction to produce methane from carbon dioxide and hydrogen using a catalyst (the so-called methanation reaction) is an exothermic reaction, but the methanation reaction will not proceed unless a certain level of energy is applied. In the present invention, the high-temperature carbon dioxide-containing exhaust gas generated in the calciner 4 is used, and the temperature of the mixed gas is adjusted in the mixer 8, so that the temperature of the internal space of the methane generator 12 can be easily kept within the above temperature range.
Furthermore, in order to promote the reaction, thermal energy may be supplied from an external source. For example, a heating means may be disposed around the methane generator 12 to indirectly heat the internal space of the methane generator 12.
Furthermore, if the temperature of the internal space exceeds 800°C due to an exothermic reaction, the methanation reaction may suddenly decrease. In this case, a refrigerant may be introduced for cooling. The heat recovered using the refrigerant may be used for power generation, etc.
The methane generator 12 is not particularly limited as long as it can fill its internal space with a catalyst and cause a methanation reaction, and examples thereof include a fixed-bed reactor.

The methane and water vapor generated in the methane generator 12 are discharged as a methane-containing gas containing the methane, the water vapor, and carbon dioxide gas and hydrogen gas that remain unreacted.
From the viewpoint of reducing carbon dioxide emissions in cement clinker production and reducing fuel costs, the methane-containing gas may be supplied to the calciner 4 through the methane supply path 14. The methane contained in the methane-containing gas supplied to the calciner 4 is used as fuel for the heating means 15a of the calciner 4.
The methane-containing gas supplied to the calciner 4 may contain water vapor generated in the methane generator 12. When the methane-containing gas contains water vapor, the carbon dioxide partial pressure in the calciner 4 decreases, and decarbonation can be performed at a temperature 10 to 50°C lower than when a methane-containing gas not containing water vapor is supplied.
In addition, from the viewpoint of increasing the calorific value of the methane-containing gas, water vapor may be removed from the methane-containing gas.

Furthermore, the methane-containing gas supplied to the calciner 4 may contain hydrogen gas that remains unreacted in the methane generator 12. This hydrogen gas can be used as fuel for the heating means 15a of the calciner 4.
If the proportion of hydrogen gas in the methane-containing gas exceeds 15 mass %, it becomes difficult to control the temperature of the calciner 4, and problems such as the generation of NOx may arise, so that a heating means suitable for using hydrogen as fuel may be required.

The methane-containing gas may also be supplied to the heating means 15b of the rotary kiln 3 and used as fuel for the heating means 15b.
The methane-containing gas has a high temperature (for example, 200 to 800°C), and by supplying the gas to the calciner 4 or the rotary kiln 3 while maintaining the high temperature, the temperature inside the calciner 4 or the rotary kiln 3 can be adjusted to a desired value with a smaller amount of gas than when a methane-containing gas is supplied at room temperature.
Furthermore, the methane generated in the methane generator 12 may be used separately as fuel for power generation.

After the decarbonation of the cement clinker raw material is promoted in the calciner 4, the raw material is charged into the cyclone heat exchanger 2d disposed at the rear end of the cyclone preheating device 2 while maintaining the high temperature after heating, 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).

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 for burning 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-type preheating device 2, and is then discharged from the top of the cyclone-type preheating device 2. After dust is removed using a cyclone, a bag filter, an electric dust collector, or the like, the exhaust gas is discharged to the outside through a chimney.

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.

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 17 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 base bypass device 17 is usually disposed at the connection between the cyclone preheating device 2 and the rotary kiln 3. By providing the chlorine bypass device 17, 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 17 is usually returned to the kiln exhaust gas discharge path 6a.

The cement clinker obtained in the rotary kiln 3 is fed into a clinker cooler 5, which is disposed downstream of the rotary kiln, for cooling 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 7.
Furthermore, 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 7 may be used as the gas for cooling the downstream side.
The gas that cools the upstream side is heat exchanged with the high-temperature cement clinker, and then used as a combustion-supporting gas for burning fuel in the rotary kiln 3. Since the gas that cools the upstream side is heat exchanged at the inlet side of the clinker cooler 5, it has a higher temperature after heat exchange than the gas that cools the downstream side.

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

REFERENCE SIGNS LIST 1 Cement clinker production system 2 Cyclone preheater 2a, 2b, 2c, 2d Cyclone heat exchanger 3 Rotary kiln 4 Calciner 5 Clinker cooler 6 Kiln exhaust gas discharge channel 6a, 6b, 6c, 6d, 6e Kiln exhaust gas discharge channel 7 Combustion-supporting gas supply channel 8 Mixing device 9 Water electrolysis device (combustion-supporting gas supply device, hydrogen gas supply device)
REFERENCE SIGNS LIST 10 Hydrogen gas supply channel 11 Calciner exhaust gas supply channel 12 Methane generator 13 Mixed gas supply channel 14 Methane supply channel 15a, 15b Heating means 17 Chlorine bypass device 18 Confluence flow channel

Claims (6)

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 to promote 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 passage connected to the rotary kiln for discharging exhaust gas generated in the rotary kiln after passing through the cyclone-type preheating device,
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 mixer for mixing the carbon dioxide-containing exhaust gas produced in the calciner with hydrogen gas to prepare a mixed gas of the carbon dioxide-containing exhaust gas and the hydrogen gas, and for adjusting the temperature of the mixed gas;
a hydrogen gas supply device for supplying the hydrogen gas;
a hydrogen gas supply path for guiding the hydrogen gas from the hydrogen gas supply device to the mixing device;
a calciner exhaust gas supply line connected to the calciner for guiding the carbon dioxide-containing exhaust gas from the calciner to the mixing device;
a methane generator for reacting carbon dioxide gas and hydrogen gas contained in the mixed gas using a catalyst to generate methane and water vapor;
a mixed gas supply passage for guiding the mixed gas from the mixing device to the methane generator ;
a confluence passage for confluence of a portion of the carbon dioxide-containing exhaust gas flowing through the calciner exhaust gas supply passage with gas flowing through the combustion-supporting gas supply passage;
A cement clinker manufacturing method using a cement clinker manufacturing system including:
the combustion-supporting gas is a gas containing oxygen, carbon dioxide, and water vapor, the oxygen concentration in the combustion-supporting gas is 21 to 80% by volume, the carbon dioxide concentration is 10 to 70% by volume, and the concentration of gases other than the oxygen, carbon dioxide, and water vapor in the combustion-supporting gas is 5% by volume or less;
a step of obtaining the combustion-supporting gas by mixing the oxygen-containing gas supplied from the combustion-supporting gas supply device, a portion of the carbon dioxide-containing exhaust gas, and water vapor;
A method for producing cement clinker, characterized in that the oxygen concentration of the combustion-supporting gas is adjusted so that the concentration of carbon dioxide in the carbon dioxide-containing exhaust gas generated in the calciner is 80 volume % or more per 100 volume % excluding water vapor. 2. The method for producing cement clinker according to claim 1, further comprising a methane supply line for supplying methane-containing gas containing methane produced in the methane generator to the calciner. 3. The method for producing cement clinker according to claim 1, wherein the combustion-supporting gas supply device and the hydrogen gas supply device are water electrolysis devices for electrolyzing water to obtain hydrogen gas and oxygen gas. 4. The method for producing cement clinker according to claim 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 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. 5. The method for producing cement clinker according to claim 1 , wherein the temperature of the mixed gas is adjusted to 200 to 300°C in the mixing device. 6. The method for producing cement clinker according to claim 1, further comprising a methanation inhibitor separation device provided in the mixed gas supply path for separating, from the mixed gas, inhibitors of the catalyst used in the methane generation device and removing water from the mixed gas.