Quicklime manufacturing method

Abstract

To provide a quick lime manufacturing system capable of reducing an exhaust amount of carbon dioxide generated when quick lime is produced from lime stone and capable of preventing deterioration of a catalyst used in a methane manufacturing apparatus.SOLUTION: A quick lime manufacturing system 1a comprises: a lime stone firing furnace 2 for producing quick lime by decarbonation of lime stone by heating; a lime stone feed path 3 for feeding the lime stone to the lime stone firing furnace 2; a quick lime discharge path 4 for discharging the quick lime from the lime stone firing furnace; a methane generation apparatus 5 for reacting carbon dioxide gas and hydrogen gas with a catalyst 6 to generate methane; an exhaust gas discharge path 7 for guiding waste gas containing carbon dioxide gas generated by decarbonation in the lime stone firing furnace 2 to the methane generation apparatus 5; a hydrogen gas feed path 8 for guiding the hydrogen gas to the methane generation apparatus 5; and a methane feed path 9 for feeding the methane generated by the methane generation apparatus 5 to heating means 13a for using as an energy source in the lime stone firing furnace 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In recent years, reducing carbon dioxide emissions has become an important issue in order to prevent global warming. In the production of cement, limestone, which is a raw material for cement, is heated to undergo a decarbonation process to turn it into quicklime, during which a large amount of carbon dioxide is generated. Known methods for reducing carbon dioxide emissions include separating and capturing the generated carbon dioxide (gaseous carbon dioxide) and then storing, isolating, or effectively utilizing the carbon dioxide. As a method for separating and recovering the generated carbon dioxide gas, for example, Patent Document 1 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 method for separating and recovering carbon dioxide is characterized by utilizing or making use of low-grade exhaust heat of 500°C or less generated in the steelworks.

[0003] Also, as a method for effectively utilizing carbon dioxide, methanation using carbon dioxide as a raw material is known. For example, Patent Document 2 describes a methanation method for obtaining methane by a methanation reaction using a catalyst using hydrogen and carbon dioxide contained in the combustion exhaust gas of a carbon-containing fuel as raw materials, the method including: a) a step of bringing the combustion exhaust gas into contact with a carbon dioxide absorbent to absorb carbon dioxide in the combustion exhaust gas; b) a step of heating the carbon dioxide absorbent that has absorbed carbon dioxide to extract a first gas mainly composed of carbon dioxide; c) a step of adding a first hydrogen, which is a first amount of hydrogen, to the first gas to obtain a second gas, passing the second gas through a desulfurizer filled with a desulfurizing agent to remove sulfur compounds in the second gas; and d) a step of adding a second hydrogen, which is a second amount of hydrogen, to the third gas that has been subjected to the step of removing the sulfur compounds, and converting the third gas into methane by a methanation reaction through a methanation catalyst. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-292298 A [Patent Document 2] JP 2019-172595 A Summary of the Invention [Problem to be solved by the invention]

[0005] When limestone is heated and decarbonated to obtain quicklime, exhaust gas containing carbon dioxide is generated. The exhaust gas is usually diluted with air, and then dust-removed before being discharged into the atmosphere. In addition, when limestone is heated and decarbonated using a shaft furnace, a rotary kiln, or the like, a fossil-derived thermal energy source such as coal, coke, or heavy oil (a thermal energy source derived from a fossil resource; hereinafter, abbreviated as "fossil thermal energy source") is usually used. However, since the fossil thermal energy source contains sulfur, the exhaust gas generated during the decarbonation process contains sulfur oxides (SOx). The gasified sulfur oxides react with the quicklime that has completed the decarbonation and are fixed to the quicklime as CaSO4, or the exhaust gas is cooled and then collected as dust by a dust collector, but a small amount of sulfur oxides ultimately remains in the exhaust gas. In addition, nitrogen oxides (NOx) are also generated when the fossil thermal energy source is burned. When producing methane using a methanation device using carbon dioxide contained in exhaust gas as a raw material, if the exhaust gas contains sulfur oxides or nitrogen oxides, there is a problem that the catalyst used to methanate the carbon dioxide is prone to deterioration. An object of the present invention is to provide a quicklime production system that can reduce the amount of carbon dioxide emitted when producing quicklime from limestone and can prevent deterioration of the catalyst used in the methane generation device. [Means for solving the problem]

[0006] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned objects can be achieved by a quicklime production system including a limestone calcination furnace for producing quicklime by heating and decarbonating limestone by burning a thermal energy source using a heating means, a limestone supply passage for supplying limestone to the limestone calcination furnace, a quicklime discharge passage for discharging the quicklime from the limestone calcination furnace, a methane generation device for generating methane, an exhaust gas discharge passage for guiding exhaust gas generated by decarbonation in the limestone calcination furnace to the methane generation device, a hydrogen gas supply passage for guiding hydrogen gas to the methane generation device, and a methane supply passage for supplying methane generated in the methane generation device to the heating means so as to use it as a thermal energy source in the limestone calcination furnace, and have completed the present invention.

[0007] That is, the present invention provides the following [1] to [6]. [1] A quicklime production system including a limestone calcination furnace including a heating means, the heating means being used to burn a thermal energy source to heat and decarbonate limestone to produce quicklime, a limestone supply passage for supplying the limestone to the limestone calcination furnace, a quicklime discharge passage for discharging the quicklime from the limestone calcination furnace, and a methane generation device for reacting carbon dioxide gas and hydrogen gas using a catalyst to produce methane, the quicklime production system including an exhaust gas discharge passage for guiding carbon dioxide-containing exhaust gas produced by decarbonation in the limestone calcination furnace to the methane generation device, a hydrogen gas supply passage for guiding the hydrogen gas to the methane generation device, and a methane supply passage for supplying the methane produced in the methane generation device to the heating means for use as the thermal energy source in the limestone calcination furnace. [2] The quicklime production system according to [1], further comprising a methanation inhibitor separation device provided in the exhaust gas discharge path for separating inhibitors of the catalyst from the carbon dioxide-containing exhaust gas.

[0008] [3] The quicklime production system described in [1] above, wherein the limestone calcination furnace includes the heating means, a calcination furnace body for accommodating the limestone, and an indirect heating appendage arranged to accommodate the calcination furnace body, the heating means of the limestone calcination furnace includes indirect heating means for indirectly heating and decarbonating the limestone in the calcination furnace body by burning the thermal energy source in the indirect heating appendage, and the exhaust gas discharge path is composed of a first exhaust gas discharge path and a second exhaust gas discharge path, the first exhaust gas discharge path is for guiding a carbon dioxide-containing exhaust gas generated in the calcination furnace body to the methane generation device, and the second exhaust gas discharge path is for discharging a carbon dioxide-containing exhaust gas generated in the indirect heating appendage. [4] The quicklime production system according to [3], further comprising a methanation inhibitor separation device provided in the first exhaust gas discharge path for separating inhibitors of the catalyst from the carbon dioxide-containing exhaust gas.

[0009] [5] The quicklime production system described in [4], wherein the second exhaust gas discharge passage is arranged so that the exhaust gas flowing through the second exhaust gas discharge passage merges with the exhaust gas flowing through the first exhaust gas discharge passage at the methanation inhibition component separation device or at a point upstream of the device. [6] The quicklime production system described in any of [3] to [5], wherein the methane generation apparatus comprises a methane generation apparatus main body for causing the reaction and an auxiliary means for indirect heating arranged to accommodate the methane generation apparatus main body, and the auxiliary means for indirect heating is arranged midway through the second exhaust gas exhaust passage and uses the exhaust gas circulating through the second exhaust gas exhaust passage to indirectly heat the internal space of the methane generation apparatus main body. Effect of the Invention

[0010] According to the quicklime production system of the present invention, it is possible to reduce the amount of carbon dioxide discharged in the production of quicklime, and to prevent deterioration of the catalyst used in the methane generation device. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating a schematic diagram of an example (first embodiment) of a quicklime producing system according to the present invention. [Diagram 2] FIG. 2 is a diagram showing a schematic diagram of another example (second embodiment) of the quicklime producing system of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The quicklime producing system of the present invention will be described in detail below with reference to Figs. FIG. 1 is a schematic diagram showing an example (first embodiment) of a quicklime producing system according to the present invention. The quicklime production system 1a includes a limestone calcination furnace 2 including a heating means 13a, which heats and decarbonates limestone by burning a thermal energy source using the heating means 13a to produce quicklime, a limestone supply passage 3 for supplying limestone to the limestone calcination furnace 2, a quicklime discharge passage 4 for discharging the quicklime from the limestone calcination furnace 2, and a methane generation device 5 for reacting carbon dioxide gas and hydrogen gas using a catalyst 6 to produce methane, and includes an exhaust gas discharge passage 7 for guiding carbon dioxide-containing exhaust gas generated by decarbonation in the limestone calcination furnace 2 to the methane generation device 5, a hydrogen gas supply passage 8 for guiding hydrogen gas to the methane generation device 5, and a methane supply passage 9 for supplying the methane generated in the methane generation device 5 to the heating means 13a so that it can be used as a thermal energy source in the limestone calcination furnace 2.

[0013] In the quicklime production system 1a, limestone, which is the raw material of quicklime, is fed into a limestone calciner 2 through a limestone supply line 3. In the limestone calciner 2, a thermal energy source is combusted using a heating means 13a, whereby the fed limestone is directly heated and decarbonated, thereby producing quicklime. Examples of the limestone calcination furnace 2 include vertical calcination furnaces such as a Beckenbach furnace, a Merz furnace, and a top-type furnace, and rotary calcination furnaces such as a rotary kiln. An example of the heating means 13a is a burner. As the thermal energy source, methane generated by the methane generator 5 using carbon dioxide gas generated when limestone is heated and decarbonated as a raw material is used from the viewpoint of reducing carbon dioxide emissions. Furthermore, since methane and limestone do not contain sulfur, the exhaust gas generated when limestone is heated and decarbonated using methane as a thermal energy source does not contain sulfur oxides, which are inhibitors of the catalyst used to generate methane. Therefore, the amount of sulfur oxides in the exhaust gas can be reduced by the amount of methane used as the thermal energy source, and deterioration of the catalyst 6 used in the methane generator 5 can be further prevented. As part of the thermal energy source, fossil thermal energy sources such as coal, coke, heavy oil, and natural gas may be used.

[0014] Here, decarbonation of limestone refers to the decomposition of calcium carbonate (CaCO3), the main component of limestone, into quicklime (CaO) and carbon dioxide (CO2) by heating. Quicklime can be obtained by decarbonating limestone. In the limestone calcination furnace 2, the temperature at which limestone is heated is preferably 600 to 1,050°C, more preferably 700 to 1,000°C, and particularly preferably 800 to 950°C. If the temperature is 600°C or higher, the decarbonation of limestone can be further promoted. If the temperature is 1,000°C or lower, clogging of the limestone calcination furnace 2 due to sintering of the raw materials can be prevented.

[0015] The quicklime obtained by decarbonating the limestone is discharged from a quicklime discharge passage 4. The discharged limestone may be cooled in a cooler, or may be used as a cement clinker raw material while maintaining the high temperature after heating. Carbon dioxide-containing exhaust gas (exhaust gas containing carbon dioxide) generated by decarbonation in the limestone calciner 2 passes through an exhaust gas exhaust passage 7 and is led to the methane generator 5. An exhaust gas inducer 15 for sucking in the carbon dioxide-containing exhaust gas may be provided in the exhaust gas exhaust passage 7. A part of the carbon dioxide-containing exhaust gas may be discharged to the outside.

[0016] The methane generator 5 uses a catalyst 6 filled in its internal space to react carbon dioxide gas with hydrogen gas to generate methane. Examples of the catalyst include Rh / Mn-based, Rh-based, Ni-based, Pd-based, and Pt-based catalysts. A carrier may be used to support the catalyst. Examples of the carrier include CeO2, ZrO2, Y2O3, Al2O3, MgO, and TiO2. These may be appropriately selected and used. The reaction of producing methane from carbon dioxide and hydrogen gas using a catalyst (so-called methanation reaction) is an exothermic reaction, but the methanation reaction does not proceed unless a certain level of energy is applied. For this reason, it is necessary to supply thermal energy from the outside in order to promote the reaction. For example, a heating means 18 may be provided around the methane generator 5 to indirectly heat the internal space of the methane generator 5.

[0017] The carbon dioxide gas is contained in the carbon dioxide-containing exhaust gas produced by decarbonation in the limestone calciner 2. The hydrogen gas is introduced from the hydrogen storage tank 10 through a hydrogen gas supply line 8 to the methane generator 5. A hydrogen gas attractor 16 for sucking in hydrogen gas may be provided in the hydrogen gas supply line 8. The hydrogen stored in the hydrogen storage tank 10 can be obtained by electrolyzing water. If the electrical energy used for electrolyzing water is derived from renewable energy sources such as hydroelectric power, wind power, geothermal power, or solar power, the amount of carbon dioxide emissions can be further reduced.

[0018] In addition, a methanation inhibition component separation device 11 may be provided in the exhaust gas discharge path 7 to separate inhibiting components of the catalyst used in the methane generation device 5 (components that inhibit the action of the catalyst and reduce its performance as a catalyst) from the carbon dioxide-containing exhaust gas. Examples of the above-mentioned inhibitory components include sulfur oxides (SOx), nitrogen oxides (NOx), and hydrogen chloride (HCl). The methanation-inhibiting component separation device 11 is an appropriate combination of known methods and devices for removing the above-mentioned inhibiting components such as sulfur oxides, nitrogen oxides, and hydrogen chloride. In the quicklime manufacturing system 1a of the present invention, when the thermal energy source of the heating means is entirely methane, the carbon dioxide-containing exhaust gas does not contain the above-mentioned inhibiting components, or even if it does contain them, the amount is very small, so that the methanation inhibiting component separation device 11 does not need to be provided.

[0019] Examples of methods for removing sulfur oxides include a method in which carbon dioxide-containing exhaust gas is brought into contact with an aqueous alkali solution such as caustic soda to convert the sulfur oxides into sulfate ions and then removed; and a method in which quicklime or slaked lime is sprayed onto carbon dioxide-containing exhaust gas to convert the sulfur oxides into gypsum, which is then recovered and removed using a dust collector. Methods for removing nitrogen oxides include a method in which ammonia or urea is sprayed into exhaust gas containing carbon dioxide to convert the nitrogen oxides into nitrogen (N2) and then removed; a method in which the exhaust gas containing carbon dioxide is brought into contact with activated coke, whereby the nitrogen oxides are adsorbed onto the activated coke and then removed; and a method in which a strong oxidizing agent is added to exhaust gas containing carbon dioxide to convert NO to NO2, which is then absorbed in water.

[0020] Furthermore, in the methanation inhibition component separation device 11, water may be removed as necessary. For example, when a method for removing sulfur oxides or nitrogen oxides is carried out by a dry means, the water vapor in the carbon dioxide-containing exhaust gas can be separated and removed as liquid water by cooling the temperature of the carbon dioxide-containing exhaust gas until the temperature is below the condensation temperature of water. Also, when the method for removing sulfur oxides or nitrogen oxides is carried out by a wet means, water is naturally removed.

[0021] In addition, oxygen (O2) in the carbon dioxide-containing exhaust gas reacts with hydrogen gas used in producing methane in the methane generator 5, resulting in the problem of excessive consumption of hydrogen gas. Nitrogen (N2) in the carbon dioxide-containing exhaust gas is a useless gas that does not participate in methanation. Therefore, from the viewpoint of efficient methanation, oxygen and nitrogen may be removed from the carbon dioxide-containing exhaust gas, and carbon dioxide may be separated, recovered, and introduced into the methane generator 5. Examples of methods for separating and recovering carbon dioxide from carbon dioxide-containing exhaust gas include a method of physically adsorbing and recovering carbon dioxide using a zeolite membrane with a controlled pore size, and physical absorption methods such as the Selexol method and the Rectisol method. In addition, a chemical absorption method using an amine-based absorbing liquid or the like is an example of a highly reliable method, although it has the drawback of consuming excessive energy for regeneration. According to this method, carbon dioxide is selectively absorbed in the amine-based absorbing liquid, and then the amine-based absorbing liquid is heated in a regeneration tower to obtain a high concentration of carbon dioxide.

[0022] The methane generated in the methane generator 5 is discharged as a methane-containing gas containing methane, moisture, and unreacted CO2 and H2. After removing at least moisture, the methane passes through the methane supply passage 9 and is supplied to the heating means 13a of the limestone calciner 2 as a thermal energy source. A methane storage tank 12 for temporarily storing methane and a methane gas inducer 17 for sucking in methane and adjusting the amount of methane supplied may be provided along the methane supply path 9.

[0023] By using methane as a thermal energy source for the heating means 13a of the limestone calciner 2, it is possible to obtain the thermal energy required to heat and decarbonate the limestone, thereby reducing the amount of carbon dioxide emitted during combustion. Here, the amount of carbon dioxide emission in the quicklime manufacturing system 1a is calculated as follows. Note that in an actual quicklime manufacturing system, the amount of carbon dioxide emission varies due to various factors, so it does not necessarily correspond to the calculated value. For example, assuming that 1,880 kg of limestone with a CaCO3 purity of 95% by mass is used to produce 1 ton of quicklime, and that heavy oil is used in an amount that results in a combustion heat of 5,440 MJ as the only thermal energy source, then calculated amounts of carbon dioxide emitted will be 1,949 kg (1,163 kg from the combustion of heavy oil, and 786 kg from decarbonation). Instead of heavy oil with a combustion heat of 5,440 MJ, 152 Nm3 of methane was generated in the methane generator 5. 3 When this system is used, the amount of carbon dioxide generated by the combustion of the thermal energy source is reduced by approximately 79 kg. In addition, the same mole of carbon dioxide as methane supplied to the heating means 13a of the limestone calciner 2 is guided to the methane generator 5 through the exhaust gas exhaust line 7 and is re-methanized. As a result, the amount of carbon dioxide emitted in the quicklime production system 1a is 1,571 kg, which is approximately 20% less than when heavy oil is used as the thermal energy source.

[0024] Fig. 2 is a schematic diagram showing another embodiment (second embodiment) of the quicklime production system of the present invention using a limestone calciner. In Fig. 2, the same reference numerals as those in Fig. 1 are used for the parts having the same names as those in Fig. 1. The quicklime production system 1b is a limestone calciner including heating means 13b, 14, and includes a limestone calciner 2 for heating and decarbonating limestone by burning a thermal energy source using the heating means 13b, 14 to produce quicklime, a limestone supply passage 3 for supplying limestone to the limestone calciner 2, a quicklime discharge passage 4 for discharging the quicklime from the limestone calciner 2, a methane generator 5 for reacting carbon dioxide gas with hydrogen gas using a catalyst 6 to produce methane, an exhaust gas discharge passage 7a for guiding carbon dioxide gas-containing exhaust gas generated by decarbonation in the limestone calciner to the methane generator 5, a hydrogen gas supply passage 8 for guiding hydrogen gas to the methane generator 5, and a gas supply passage 9 for supplying methane generated in the methane generator 5 to the limestone calciner 2 as a thermal energy source for the limestone calciner 2. and a methane supply passage 9 for supplying methane to the heating means for use in the calcination furnace 2; the limestone calcination furnace 2 includes a heating means, a calcination furnace body 2a for accommodating limestone, and an indirect heating appendage 2b arranged to accommodate the calcination furnace body 2a; the heating means of the limestone calcination furnace 2 includes an indirect heating means 14 for indirectly heating and decarbonating the limestone in the calcination furnace body 2a by burning a thermal energy source in the indirect heating appendage 2b; the exhaust gas discharge passage is composed of a first exhaust gas discharge passage 7a and a second exhaust gas discharge passage 7b, the first exhaust gas discharge passage 7a is for guiding the carbon dioxide-containing exhaust gas generated in the calcination furnace body 2a to the methane generation device 5, and the second exhaust gas discharge passage 7b is for discharging the carbon dioxide-containing exhaust gas generated in the indirect heating appendage 2b.

[0025] In the second embodiment, the limestone calcination furnace 2 includes heating means (indirect heating means 14, heating means 13b), a calcination furnace body 2a for accommodating limestone, and an indirect heating attachment 2b arranged to accommodate the calcination furnace body 2a. An example of a calcination furnace having such a structure is a double-cylindrical rotary kiln. The limestone calcination furnace 2 in FIG. 2 shows a double-cylindrical rotary kiln cut vertically along its axis. The indirect heating attachment 2b may be any attachment capable of heating the limestone in the calcination furnace main body 2a, and may be disposed so as to house (cover) a part of the calcination furnace main body 2a. The indirect heating means 14 is capable of indirectly heating and decarbonating the limestone in the calciner main body 2a by burning a thermal energy source in the indirect heating auxiliary body 2b.

[0026] Since the kiln body 2a and the indirect heating attachment 2b are completely separated, catalyst inhibitors such as sulfur oxides generated when a thermal energy source is burned in the indirect heating means 14 (especially when a fossil thermal energy source such as coal, coke, heavy oil, or natural gas is burned) are not mixed into the carbon dioxide-containing exhaust gas generated in the kiln body 2a, so that the carbon dioxide-containing exhaust gas is less likely to deteriorate the catalyst of the methane generation device. In addition, since the carbon dioxide-containing exhaust gas does not contain nitrogen or oxygen derived from combustion-supporting gases such as air used when burning the thermal energy source, the carbon dioxide-containing exhaust gas has a high carbon dioxide concentration. For this reason, the carbon dioxide-containing exhaust gas generated in the kiln body 2a is preferable as a raw material for generating methane.

[0027] An example of the indirect heating means 14 is a burner. Examples of the thermal energy source used in the indirect heating means 14 include fossil thermal energy sources such as coal, coke, heavy oil, and natural gas. In addition, methane generated by using a methane generator using carbon dioxide gas generated when limestone is heated and decarbonated as a raw material may be used as the thermal energy source. By using the methane as a thermal energy source, it is possible to reduce the amount of carbon dioxide emissions. In addition, since methane does not contain sulfur, the carbon dioxide-containing exhaust gas generated when methane is burned does not contain sulfur oxides, which are methanation inhibitors. Therefore, the amount of sulfur oxides in the carbon dioxide-containing exhaust gas generated when the thermal energy source is burned can be reduced by the amount of methane used as the thermal energy source, and when methane is generated using the exhaust gas, it is possible to prevent deterioration of the catalyst 6 used in the methane generator 5.

[0028] In addition, from the viewpoint of accelerating the heating and decarbonation of limestone, a heating means 13b may be provided in the calcination furnace body 2 for directly heating and decarbonating the limestone in the calcination furnace body 2a by burning a thermal energy source in the calcination furnace body 2. As the heating means 13b and the thermal energy source used for the heating means 13b, the same ones as those for the indirect heating means 14 can be used.

[0029] The temperature to which the limestone is heated in the calcination furnace body 2a is preferably 600 to 1,050°C, more preferably 700 to 1,000°C, and particularly preferably 800 to 950°C. If the temperature is 600°C or higher, the decarbonation of the limestone can be further promoted. If the temperature is 1,000°C or lower, clogging of the limestone calcination furnace 2 due to sintering of the raw materials can be prevented. The temperature inside the indirect heating appendage 2b is preferably 900° C. or higher, more preferably 950 to 1,050° C., and particularly preferably 980 to 1,020° C. If the temperature is 900° C. or higher, the limestone inside the calciner body 2a can be sufficiently heated.

[0030] In the second embodiment, the exhaust gas discharge path is made up of a first exhaust gas discharge path 7a and a second exhaust gas discharge path 7b. The first exhaust gas discharge passage 7a is for guiding the carbon dioxide-containing exhaust gas generated in the calciner main body 2a to the methane generator 5. The exhaust gas generated in the calciner body 2a contains almost no sulfur oxides or nitrogen oxides, but if necessary, a methanation inhibition component separation device 11 may be provided in the first exhaust gas discharge path 7a. Further, an exhaust gas inducer 15 for sucking in the exhaust gas containing carbon dioxide may be provided in the middle of the first exhaust gas discharge passage 7a. Further, a part of the exhaust gas containing carbon dioxide may be discharged to the outside.

[0031] The second exhaust gas exhaust passage 7b is for discharging the carbon dioxide-containing exhaust gas generated in the indirect heating appendage 2b. In addition, an exhaust gas inducer 15 for sucking the carbon dioxide-containing exhaust gas may be provided in the middle of the second exhaust gas exhaust passage 7b. The carbon dioxide-containing exhaust gas produced in the indirect heating appendage 2b may be used as a feedstock for producing methane in the methanator 5. In the case where the carbon dioxide gas contained in the carbon dioxide-containing exhaust gas generated in the indirect heating appendage 2b is used as a raw material for generating methane, the second exhaust gas discharge passage may be arranged so as to merge with the above-mentioned exhaust gas flowing through the first exhaust gas discharge passage 7a at the methanation inhibition component separation device 11 or at a point upstream thereof. In particular, when a fossil thermal energy source such as coal, coke, heavy oil, or natural gas is used as the thermal energy source for the indirect heating means 14, the carbon dioxide-containing exhaust gas generated in the indirect heating appendage 2b contains catalyst inhibiting components such as sulfur oxides, so it is preferable to separate the above-mentioned inhibiting components using the methanation inhibiting component separation device 11. Furthermore, for the purpose of reducing the burden on the methanation inhibition component separation device 11, the above-mentioned exhaust gas flowing through the second exhaust gas discharge passage 7b may be subjected to desulfurization and denitrification treatment and then discharged to the outside from the chimney, without being used as a raw material for generating methane, for example.

[0032] The methane generator 5 used is the same as that used in the quicklime production system 1a described above. In addition, for the purpose of promoting the reaction of generating methane from carbon dioxide and hydrogen gas, the methane generator 5 may be composed of a methane generator main body 5a for generating the reaction and an auxiliary means for indirect heating 5b arranged to accommodate the methane generator main body 5a, and the auxiliary means for indirect heating 5b may be arranged in the middle of the second exhaust gas discharge passage 7b, and the internal space of the methane generator main body 5a may be indirectly heated using the exhaust gas flowing through the second exhaust gas discharge passage 7b. The exhaust gas used to indirectly heat the internal space of the methane generator main body 5a may pass through the second exhaust gas discharge passage 7b and merge with the exhaust gas flowing through the first exhaust gas discharge passage 7a at the methanation inhibition component separation device 11 or at a point upstream of the device, or may be discharged to the outside. The indirect heating auxiliary means 5b may be any means capable of increasing the temperature inside the methane generation device main body 5a, and may be disposed so as to house (cover) a part of the methane generation device main body 5a.

[0033] 2, methane generated in the methane generator 5 is discharged as a methane-containing gas containing methane, moisture, and unreacted CO2 and H2. After removing at least moisture, the methane is passed through the methane supply passage 9 and supplied as a thermal energy source to at least one of the heating means 13b of the calciner body 2a and the indirect heating means 14 of the indirect heating attachment 2b. Further, a methane storage tank 12 for temporarily storing methane and a methane gas inducer 17 for sucking methane and adjusting the amount of methane supplied may be provided midway along the methane supply line 9.

[0034] The hydrogen gas supply path 8, the hydrogen storage tank 10, the methanation inhibition component separation device 11, the methane storage tank 12, and the hydrogen gas induction machine 16 in Figure 2 are similar to the hydrogen gas supply path 8, the hydrogen storage tank 10, the methanation inhibition component separation device 11, the methane storage tank 12, and the hydrogen gas induction machine 16 in Figure 1 described above, respectively.

[0035] The amount of carbon dioxide emission in the quicklime production system 1b is calculated as follows. Note that in actual cement clinker production, the amount of carbon dioxide emission varies due to various factors, so it does not necessarily correspond to the calculated value. For example, in order to obtain 1 ton of quicklime, 1,880 kg of limestone with a CaCO3 purity of 95% by mass is used, and heavy oil is burned in an amount that results in a combustion heat of 1,088 MJ in the indirect heating means 14, and methane is burned in an amount that results in a combustion heat of 4,354 MJ in the heating means 13b, respectively, in the indirect heating means 14 and the heating means 13b. In this case, the amount of carbon dioxide generated in the calcination furnace body 2a is calculated to be 1,811 kg. Of this, 240 kg of carbon dioxide is used as a raw material for methane production. On the other hand, the amount of carbon dioxide generated in the indirect heating attachment 2b by the combustion of heavy oil is calculated to be 862 kg. Therefore, the total amount of carbon dioxide emitted from the entire quicklime production system 1b is calculated to be 2,433 kg. The exhaust gas generated within the indirect heating attachment 2b contains a high concentration (about 4,400 ppm) of sulfur oxides. On the other hand, instead of heavy oil with a combustion heat of 1,088 MJ, 30 Nm3 of methane generated in the methane generator 5 was used. 3 When using this system, the amount of carbon dioxide generated by the combustion of the thermal energy source is reduced by approximately 17 kg. Also, the same mole of carbon dioxide as methane supplied to the indirect heating means 14 and the heating means 13b is guided to the methane generator 5 through the exhaust gas exhaust path and is re-methanized. Therefore, the amount of carbon dioxide emitted in the quicklime production system 1b is 2,357 kg, which is approximately 3% less than the amount of 2,433 kg when heavy oil is used as the thermal energy source. The above estimate of carbon dioxide emissions was based on the assumption that only the amount of carbon dioxide that can be used as a thermal energy source in the quicklime production system 1b is methanated. However, if there is a use for methane other than in the quicklime production system 1b, a larger amount of carbon dioxide can be methanated and used, thereby enabling further reduction in carbon dioxide emissions.

[0036] In the quicklime production system, the supply amount of the fossil thermal energy source used auxiliary in the heating means may be controlled based on the supply amount and composition of the methane-containing gas produced in the methane generator. Since methanation in a methane generator is an equilibrium reaction, it is not possible to produce gas with a methane concentration of 100% by volume. In addition, if the methanation conditions change, the composition and heat value of the resulting methane-containing gas also change, so even if the flow rate of the gas is kept constant and it is supplied to the heating means of the limestone calciner, it is difficult to keep the combustion heat value in the heating means constant. By increasing or decreasing the amount of the fossil heat energy source supplied to the heating means as an auxiliary based on the supply amount and composition of the methane-containing gas, it is possible to stably produce quicklime. One method for controlling the supply amount of fossil thermal energy sources is to subtract the amount of heat that can be compensated for by burning the methane-containing gas produced in the methane generation device from the amount of heat required for the limestone calciner, and then supply a fossil thermal energy source equivalent to the shortfall in heat.

[0037] In addition, in a quicklime manufacturing system, a combustion supporting gas having a higher oxygen concentration than air may be used instead of air as a combustion supporting gas required for combustion of a thermal energy source. By using the combustion supporting gas, the amount of nitrogen (derived from a combustion supporting gas such as air) contained in the generated exhaust gas can be reduced, the absolute amount of exhaust gas to be handled can be reduced, and the equipment can be made compact. The combustion supporting gas is supplied from a combustion supporting gas supply device (not shown) and is led to the heating means of the limestone calciner through a combustion supporting gas supply passage (not shown). Examples of the combustion supporting gas supply device 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.

[0038] For example, in the limestone calcination system 1a, when all the thermal energy source used is methane generated by the methane generator 5 to produce 1 ton of quicklime, the amount of carbon dioxide-containing exhaust gas generated is 2,688 Nm3 when air is used as the combustion supporting gas. 3 When a gas containing 100% oxygen by volume is used as the combustion support gas, the 3It becomes. In addition, when air is used as the combustion supporting gas, the carbon dioxide concentration in the exhaust gas is about 35% by volume, whereas when an oxygen content of 100% by volume is used as the combustion supporting gas, the carbon dioxide concentration in the exhaust gas is about 72% by volume. The higher the carbon dioxide concentration in the exhaust gas, the more preferable the exhaust gas is as a raw material for methanation. In an actual quicklime production system, the exhaust gas emissions and carbon dioxide concentration change due to various factors, so they do not necessarily correspond to the calculated values. [Explanation of symbols]

[0039] 1a,1b Quicklime production system 2 Limestone kiln 2a Firing furnace body 2b Indirect heating attachment 3 Limestone supply route 4 Quicklime discharge channel 5. Methane Generator 5a Methane generator main body 5b Auxiliary means for indirect heating 6. Catalyst 7 Exhaust gas exhaust duct 7a First exhaust gas outlet 7b Second exhaust gas outlet 8 Hydrogen gas supply line 9 Methane supply line 10 Hydrogen storage tank 11 Methanation inhibitor separation device 12 Methane storage tank 13a,13b,18 Heating means 14 Indirect heating means 15 Exhaust gas induction machine 16 Hydrogen gas induction machine 17 Methane gas induction machine

Claims

1. A limestone calciner including a direct heating means for directly heating limestone, the direct heating means being used to combust a thermal energy source to heat and decarbonate the limestone to produce quicklime; a limestone supply passage for supplying the limestone to the limestone calciner; a quicklime discharge passage for discharging the quicklime from the limestone calciner; A quicklime production system including a methane generator for generating methane by reacting carbon dioxide gas with hydrogen gas using a catalyst, an exhaust gas exhaust passage for guiding the carbon dioxide-containing exhaust gas generated by the decarbonation in the limestone calciner to the methane generation device; a hydrogen gas supply line for guiding the hydrogen gas to the methane generator; a methane supply passage for supplying the methane generated in the methane generation device to the heating means so as to use the methane as the thermal energy source in the limestone calciner; A method for producing quicklime using a quicklime production system comprising: all of the thermal energy source is methane, and at least a portion of the methane is produced in the methanator; A method for producing quicklime, comprising the steps of: introducing the carbon dioxide-containing exhaust gas into the methane generation device without subjecting the exhaust gas to a methanation inhibitor separation process for separating inhibitors of the catalyst.

2. The limestone calcination furnace includes the direct heating means, a calcination furnace body for accommodating the limestone, an indirect heating appendage disposed to accommodate the calcination furnace body, and indirect heating means for indirectly heating and decarbonating the limestone in the calcination furnace body by burning the thermal energy source in the indirect heating appendage, The exhaust gas discharge path includes a first exhaust gas discharge path and a second exhaust gas discharge path, The first exhaust gas discharge passage is for guiding a carbon dioxide-containing exhaust gas generated in the combustion furnace body to the methane generation device, 2. The method for producing quicklime according to claim 1, wherein the second exhaust gas exhaust passage is for discharging exhaust gas containing carbon dioxide gas generated within the indirect heating attachment.

3. The methane generator comprises a methane generator body for causing the reaction, and an auxiliary means for indirect heating arranged to accommodate the methane generator body, 3. The method for producing quicklime as described in claim 2, wherein the auxiliary means for indirect heating is arranged in the middle of the second exhaust gas exhaust passage and is for indirectly heating the internal space of the methane generation device main body by using the exhaust gas flowing through the second exhaust gas exhaust passage.

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