Method for utilizing cement exhaust gas and facility for utilizing cement exhaust gas

Abstract

To provide a method and equipment for effectively utilizing exhaust gas from cement manufacturing equipment.SOLUTION: The method for utilizing the cement exhaust gas comprises a step (a step) of adding nitric acids to CaCO3 and reacting them to form carbon dioxide and a Ca (NO3) 2 aqueous solution and recovering the carbon dioxide, and a step (b step) of heating and dehydrating the Ca (NO3) 2 aqueous solution. A step (b step) of generating CaO and NOx and discharging the NOx to the outside of the system, a step (c step) of adding H2O to CaO and reacting them to prepare Ca (OH) 2, and a step (d step) of bringing cement exhaust gas into contact with Ca (OH) 2 and reacting it with carbon dioxide in the Ca (OH) 2 exhaust gas; The method includes a step (d step) of preparing CaCO3 and circulating and using the CaCO3 as the CaCO3 in the step (a), and a step (e step) of bringing NOx produced in the step (b) into contact with water to prepare nitrate and circulating and using the nitrate as the nitrate in the step (a).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for utilizing exhaust gas generated from a cement manufacturing plant or the like and an equipment for utilizing said exhaust gas, and in particular to a method for utilizing cement exhaust gas and an equipment for utilizing cement exhaust gas that can recover high-purity carbon dioxide by utilizing the exhaust gas generated from the cement manufacturing plant and the heat of the exhaust gas. [Background technology]

[0002] In recent years, amid growing concerns about changes in the global environment due to the effects of global warming, various carbon dioxide separation and capture methods have been investigated with the aim of reducing carbon dioxide emissions. Cement production is no exception, and since a large amount of carbon dioxide is generated by heating calcium carbonate, a raw material for cement, methods for recovering and utilizing the generated carbon dioxide are being considered in order to reduce carbon dioxide emissions.

[0003] In general, in cement plants, exhaust gas generated by burning coal, heavy oil, and recycled fuel is used to dry cement raw materials, and then the dust contained in the gas is collected in a dust collection process before being discharged outside the system. However, the exhaust gas after dust collection contains a large amount of water vapor and carbon dioxide derived from coal, as well as trace amounts of chlorides and nitrogen oxides (hereinafter referred to as NOx). As there are concerns that the purity may decrease when carbon dioxide is separated and collected, research is also being conducted into technologies to separate trace components.

[0004] Currently, the most common pretreatment methods for separating and recovering carbon dioxide from cement exhaust gas involve collecting dust using electrostatic precipitators or bag filters, condensing water vapor using heat recovery, and using urea or alcohol as a denitrification technology for NOx. As a method for removing NOx from exhaust gas in particular, for example, Japanese Patent No. 5100432 (Patent Document 1) discloses a method for treating exhaust gas in which a denitrifying agent is brought into contact with exhaust gas containing nitrogen oxides to denitrify the exhaust gas, wherein the denitrifying agent is a mixture of urea and one or more types of waste liquid selected from the group consisting of water-soluble waste liquid containing oil, waste liquid produced by washing ash with water, waste liquid containing alcohols, and waste liquid produced in cement or concrete factories, and the type of waste liquid and the mass ratio of the waste liquid to urea are determined so as to satisfy specific conditions.

[0005] However, conventional methods require large initial costs for installing the above-mentioned equipment, as well as running costs for the electricity required for cooling and the amine and other materials used for denitration.In addition, the optimum temperature for the denitration reaction is said to be 800°C or higher, and the hot gas that passes through the urea spray area is not denitrified, so currently it is released from the flue with approximately 400 ppm of residual NOx, raising concerns about a decrease in purity during carbon dioxide capture.

[0006] Furthermore, Japanese Patent Laid-Open Publication No. 2009-160565 (Patent Document 2) discloses a method for removing carbon dioxide from exhaust gas, in which an ammonia solution is used as a substance that absorbs carbon dioxide, and the ammonia solution is brought into contact with carbon dioxide in a mist state to cause an absorption reaction to produce an aqueous ammonium carbonate solution, and then the temperature of the aqueous ammonium carbonate solution is raised to obtain urea, a useful substance.

[0007] However, as mentioned above, if an amine method using ammonia or other carbon dioxide capture technology is used, NOx can also be captured and used at the same time. However, there are concerns that costs will increase due to amine consumption, and furthermore, the procurement costs of amine for carbon dioxide capture would be high for a typical cement factory, making this method unrealistic. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 5100432 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-160565 Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide a method for utilizing exhaust gas, preferably exhaust gas from a cement manufacturing facility, which is equipped with a circulation system that effectively utilizes the exhaust gas and is capable of preparing high-purity carbon dioxide and an energy storage material. [Means for solving the problem]

[0010] (1) The method for utilizing cement waste gas of the present invention includes a step (a) of adding nitric acid to CaCO3 and reacting them to generate carbon dioxide and an aqueous solution of Ca(NO3)2, and recovering the carbon dioxide; a step (b) of heating and dehydrating the Ca(NO3)2 aqueous solution using the heat of the cement exhaust gas to generate CaO and NOx, and discharging the NOx outside the system; A step (c) of adding HO to the CaO and reacting to prepare Ca(OH), A step (d) of contacting the Ca(OH)2 with cement exhaust gas containing carbon dioxide to react the Ca(OH)2 with the carbon dioxide in the exhaust gas to prepare CaCO3, and recycling the CaCO3 as the CaCO3 in the above step (a); and A step (e) of contacting the NOx produced in the above step (b) with water to prepare nitric acid, and circulating and using the nitric acid as the nitric acid in step (a). The present invention relates to a method for utilizing cement exhaust gas, the method comprising the steps of:

[0011] (2) A preferred method of utilizing cement exhaust gas of the present invention is the method of utilizing cement exhaust gas of the present invention described above in (1), characterized in that it further comprises, between the above (step a) and (step b), a step (step f) of adjusting the pH of the generated Ca(NO3)2 aqueous solution to 6 to 8 and subjecting the insoluble matter to solid-liquid separation.

[0012] (3) Another preferred method for utilizing cement exhaust gas of the present invention is the method for utilizing cement exhaust gas of the present invention described above in (1), characterized in that when heating the Ca(NO3)2 aqueous solution in (step b) above, cement exhaust gas containing carbon dioxide is directly brought into contact with the Ca(NO3)2 aqueous solution, thereby simultaneously carrying out (step b), (step c), and (step d) to prepare CaCO3.

[0013] (4) Another preferred method of utilizing cement exhaust gas of the present invention is the method of utilizing cement exhaust gas of the present invention described above in (1), characterized in that the addition of H2O in the (c) step is performed by contacting exhaust gas containing water vapor and carbon dioxide with CaO, thereby allowing (c) step and (d) step to proceed simultaneously to prepare CaCO3.

[0014] (5) A further preferred method for utilizing cement exhaust gas of the present invention is a method for utilizing cement exhaust gas of the present invention described above in any one of (1) to (4), characterized in that it further comprises a step (g) of recovering a portion of the CaO obtained in (b) step.

[0015] (6) An even more preferable method for utilizing cement exhaust gas of the present invention is a method for utilizing cement exhaust gas of the present invention described above in any one of (1) to (4), characterized in that it further comprises a step (h step) of recovering a portion of the CaCO3 obtained in (d step).

[0016] (7) The cement exhaust gas utilization equipment of the present invention comprises a means for adding nitric acid to CaCO3 to cause a reaction and generate carbon dioxide and an aqueous solution of Ca(NO3)2, a means for recovering the generated carbon dioxide, a means for transporting the cement exhaust gas and using the heat of the exhaust gas to heat and dehydrate the aqueous solution of Ca(NO3)2 to generate CaO and NOx, a means for discharging the generated NOx to the outside of the system, a means for adding H2O to the CaO to cause a reaction and prepare Ca(OH)2, and a means for converting the cement containing carbon dioxide into Ca(OH)2. means for introducing NOx discharged from the system into contact with the exhaust gas, reacting Ca(OH)2 with carbon dioxide in the exhaust gas to prepare CaCO3, means for circulating and transporting the produced CaCO3 to means for adding nitric acid to the CaCO3 and reacting them to produce carbon dioxide and an aqueous Ca(NO3)2 solution, and means for contacting NOx discharged outside the system with water to prepare nitric acid, and means for circulating the produced nitric acid to means for adding nitric acid to the CaCO3 and reacting them to produce carbon dioxide and an aqueous Ca(NO3)2 solution. The cement exhaust gas utilization equipment is characterized by comprising:

[0017] (8) Another cement exhaust gas utilization facility of the present invention includes a means for adding nitric acid to CaCO3 to cause a reaction and generate carbon dioxide and a Ca(NO3)2 aqueous solution, a means for recovering the generated carbon dioxide, a means for transporting cement exhaust gas containing carbon dioxide and introducing the exhaust gas directly into the Ca(NO3)2 aqueous solution to generate CaCO3 and NOx using steam obtained by heating and dehydrating the Ca(NO3)2 aqueous solution and the carbon dioxide in the exhaust gas, a means for discharging the generated NOx to the system, a means for circulating and transporting the generated CaCO3 to a means for adding nitric acid to the CaCO3 to cause a reaction and generate carbon dioxide and a Ca(NO3)2 aqueous solution, and a means for contacting the NOx discharged to the system with water to prepare nitric acid, and a means for circulating the generated nitric acid to a means for adding nitric acid to the CaCO3 to cause a reaction and generate carbon dioxide and a Ca(NO3)2 aqueous solution. The cement exhaust gas utilization equipment is characterized by comprising:

[0018] (9) Another cement exhaust gas utilization facility of the present invention includes a means for adding nitric acid to CaCO3 to cause a reaction and generate carbon dioxide and a Ca(NO3)2 aqueous solution, a means for recovering the generated carbon dioxide, a means for transporting the cement exhaust gas and utilizing the heat of the exhaust gas to heat and dehydrate the Ca(NO3)2 aqueous solution to generate CaO and NOx, a means for discharging the generated NOx to the outside of the system, a means for introducing cement exhaust gas containing water vapor and carbon dioxide into the CaO to cause contact and generate CaCO3 from the water vapor and carbon dioxide in the exhaust gas, a means for generating CaCO3 from the water vapor and carbon dioxide in the exhaust gas, a means for circulating and transporting the generated CaCO3 to a means for adding nitric acid to the CaCO3 to cause a reaction and generate carbon dioxide and a Ca(NO3)2 aqueous solution, a means for contacting the NOx discharged to the outside of the system with water to prepare nitric acid, a means for circulating the generated nitric acid to a means for adding nitric acid to the CaCO3 to cause a reaction and generate carbon dioxide and a Ca(NO3)2 aqueous solution, The cement exhaust gas utilization equipment is characterized by comprising: [Effects of the Invention]

[0019] The method for utilizing exhaust gas of the present invention makes it possible to construct a circulation system that can effectively utilize exhaust gas (referred to as cement exhaust gas) from, for example, a cement manufacturing facility and the heat of the exhaust gas to produce high-purity carbon dioxide and prepare an energy storage material that effectively recovers (stores) the exhaust heat from the exhaust gas. In particular, raw materials used in cement production in cement production facilities can be effectively utilized, and further, exhaust gases generated from cement production facilities can be effectively utilized. In this specification, an energy storage material refers to a material that can store all heat, including sensible heat, heat of hydration, and heat of neutralization, and that can recover heat even after the material has cooled. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram showing an outline of an example of a method for utilizing cement waste gas according to the present invention. [Figure 2] 1 is a diagram schematically illustrating an example of a facility for utilizing cement exhaust gas according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described below with reference to the following preferred examples with reference to Fig. 1, but is not limited thereto. Furthermore, although the exhaust gas is not limited to cement exhaust gas, the preferred embodiment will be described using cement exhaust gas as an example.

[0022] The method for utilizing cement waste gas of the present invention includes a step (a) of adding nitric acid to CaCO3 and reacting them to generate carbon dioxide and an aqueous solution of Ca(NO3)2, and recovering the carbon dioxide; a step (b) of heating and dehydrating the Ca(NO3)2 aqueous solution using the heat of the cement exhaust gas to generate CaO and NOx, and discharging the NOx outside the system; A step (c) of adding HO to the CaO and reacting to prepare Ca(OH), A step (d) of contacting the Ca(OH) with cement exhaust gas containing carbon dioxide to react the Ca(OH) with the carbon dioxide in the exhaust gas to prepare CaCO3, and recycling the CaCO3 as the CaCO3 in the above step (a); and a step (e) of contacting the NOx produced in the step (b) with water to prepare nitric acid, and circulating and using the nitric acid as the nitric acid in the step (a); This is a method for utilizing cement exhaust gas.

[0023] The raw materials used in the present invention are not particularly limited, and commercially available products, recycled waste products, etc. can be used. The exhaust gas applicable to the method for utilizing exhaust gas of the present invention can be exhaust gas discharged from any factory, etc., and an example thereof is hot gas used in clinker burning in cement burning equipment and extracted from the rising duct of a preheater (extracted hot gas temperature: 800 to 1000°C, moisture concentration in extracted hot gas: 10 to 15%, carbon dioxide concentration in extracted hot gas: 10 to 15%, NOx amount in extracted hot gas: 500 to 700 ppm).In addition, when heat recovery is not performed from the exhaust gas, cooled exhaust gas can also be used.

[0024] (Step a) The process (a) of the present invention is a process in which calcium carbonate such as limestone powder, which is a cement raw material, is stirred while nitric acid is added to generate carbon dioxide and a Ca(NO) aqueous solution through the neutralization reaction shown in the following formula (1), and the high-purity carbon dioxide is recovered. CaCO3+2HNO3→Ca(NO3)2+CO2+H2O····(1) The neutralization reaction of the above formula (1) in the step (a) is an exothermic reaction, and the generated heat can be recovered and utilized. The use of the recovered heat is not particularly limited, and depending on the temperature range of the recovered heat, it can be utilized for, for example, boiler power generation, drying of raw materials, TSA of adsorbents, various reactions, etc.

[0025] There are no particular limitations on the CaCO3, and for example, waste materials containing calcium carbonate or commonly produced or excavated limestone can be used. It is also possible to use CaCO3 obtained in the process (d) described below. Since limestone (CaCO3) is used as a cement raw material in cement factories, the method for utilizing cement exhaust gas of the present invention is convenient for cement manufacturing facilities in that the limestone used in manufacturing cement can be used to recover carbon dioxide from cement exhaust gas. It is preferable to use limestone containing calcium carbonate with a purity of 90% or more.

[0026] In the present invention, nitric acid is used as the acid for generating carbon dioxide by acid treatment of the calcium carbonate. The concentration of the nitric acid used is not particularly limited, but it is desirable to use nitric acid having a concentration of preferably 30% by mass or more, more preferably 50% by mass or more, in order to improve the heat recovery efficiency in the next step (b).

[0027] The nitric acid may be a commercially available product, a product conforming to JIS K8541 for research and testing purposes with a nitric acid concentration of 60-61% by mass, or nitric acid prepared by wet recovery of NOx present in cement flue gas using, for example, the apparatus described in JP 2017-051899 A. The nitric acid obtained by the wet recovery may have a nitric acid concentration of approximately 20-30% by mass, taking into account the recovery efficiency of NOx in cement flue gas. It is also possible to use nitric acid prepared from NOx obtained in (step b) described below (step e).

[0028] The high-purity carbon dioxide obtained by the neutralization reaction of the above formula (1) can be recovered and utilized. The recovered carbon dioxide can be used for agricultural purposes or after methanation. For example, it can be used as a raw material for agricultural fertilizer, or as a fuel by synthesizing methane, the main component of city gas, from hydrogen and carbon dioxide, or by producing methane from hydrogen and carbon dioxide produced from renewable energy sources.

[0029] (f process) Preferably, between the above (step a) and the following (step b), a step (step f) of adjusting the pH of the produced Ca(CO3)2 aqueous solution to 6 to 8 and subjecting the insoluble matter to solid-liquid separation is provided. Calcium nitrate (Ca(NO3)2) obtained by the neutralization reaction of the above formula (1) is dissolved in the aqueous solution due to its high solubility in water, but if it contains insoluble matter such as dust, it is preferable to remove it by solid-liquid separation, and it is desirable to provide a method for removing the insoluble residue (step f), and in such solid-liquid separation, it is desirable to adjust the pH to 6 to 8 before performing solid-liquid separation. In particular, when recovering and utilizing CaO obtained in the following step (step b), it is preferable to provide such a separation step. The recovered insoluble solids can be recycled and reused as a cement raw material.

[0030] (b process) The (b) step of the present invention is a step in which the Ca(NO3)2 aqueous solution obtained in the (a) step above, preferably the Ca(NO3)2 aqueous solution that has been subjected to the solid-liquid separation step (f) above, is heated and dehydrated using the heat of the cement exhaust gas (following formula (2)) to produce CaO and NOx, and the NOx is discharged outside the system. Ca(NO3)2 → CaO + NO2 + NO + O (2) The reaction of the above formula (2) in the (b step) is an endothermic reaction, and heat is stored in the produced CaO.

[0031] In this (step b), the heat of the cement exhaust gas emitted from the cement factory is transferred directly or indirectly to a Ca(NO3)2 aqueous solution to heat and dehydrate it. The temperature to which the Ca(NO3)2 aqueous solution is heated using the heat of the cement exhaust gas is preferably 470 to 1000°C, more preferably 470 to 850°C, even more preferably 550 to 800°C, and even more preferably 550 to 650°C. As a result, the contained water evaporates and Ca(NO3)2 decomposes as shown in the above formula (2), thereby obtaining CaO. Generally, to obtain CaO from CaCO3, it is necessary to heat and decompose CaCO3 at a temperature of 850°C or higher, but in the present invention, CaO is obtained via Ca(NO3)2, so CaO can be obtained at a lower temperature than when obtained from CaCO3. In addition, the heat of exhaust gas from cement manufacturing facilities can be effectively utilized. A portion of the CaO obtained by the endothermic reaction of the above formula (2) can be recovered and used as an energy storage material.

[0032] (e process) The NOx generated by the thermal decomposition of Ca(NO3)2 in the above formula (2) can be cooled to room temperature and then wet-recovered using, for example, an apparatus manufactured by Pollution Prevention Equipment Research Institute Co., Ltd. The NOx can be brought into contact with water to produce nitric acid, and as described above, the produced nitric acid can be used as the nitric acid in the above (step a), thereby constructing a circulation system. The NOx generated in the above formula (2) contains NO and NO2, but is mainly NO2.

[0033] (g process) The CaO produced in the step (b) is subjected to the step (c) described below, but if necessary, a portion of the CaO can be recovered and used as an energy storage material. When used as an energy storage material, it is possible to heat the air by heat exchange with sufficiently dried exhaust air. Furthermore, the obtained CaO can store heat as an energy storage material, and even after the CaO has cooled, it can also be stored at room temperature as an energy storage material.

[0034] Furthermore, in (step b), when heating the Ca(NO3)2 aqueous solution, the cement exhaust gas containing carbon dioxide is directly brought into contact with the Ca(NO3)2 aqueous solution, so that (step b) and the following (step c) and (step d) proceed simultaneously, making it possible to prepare Ca(OH)2. In this way, by directly injecting high-temperature cement exhaust gas instead of using the heat of the cement exhaust gas, the reaction not only produces CaO but also progresses to the production of CaCO3 in the following (step d), and the resulting CaCO3 can be used as the CaCO3 used in the above (step a). This makes it possible to build a circulation system. If necessary, it is also possible to recover a portion of the CaCO3 and use it as an energy storage material.

[0035] (c process) The (c) step of the present invention is a step of adding H2O to the CaO obtained in the (b) step and causing a reaction as shown in the following formula (3) to prepare Ca(OH)2. CaO+H2O→Ca(OH)2·····(3) The reaction of the above formula (3) in the (c) step is an exothermic reaction.

[0036] The amount of water added in (step c) is sufficient to convert CaO to Ca(OH)2, and is not necessarily sufficient to form an aqueous solution, but the CaO can be in the form of an aqueous solution or a gel. For example, water can be added dropwise to CaO, or mist-like water is brought into contact with the CaO to convert the CaO to Ca(OH)2. The reaction of the above formula (3) is an exothermic reaction, and the generated heat can be recovered and utilized. The use of the recovered heat is not particularly limited, and depending on the temperature range of the recovered heat, it can be utilized for, for example, boiler power generation, drying of raw materials, TSA of adsorbents, various reactions, etc.

[0037] Furthermore, the H2O used in (step c) is not particularly limited as long as it is water, and any water can be used, for example, exhaust gas containing water. In (c) step, exhaust gas containing moisture (water vapor) and carbon dioxide is brought into contact with CaO, thereby making it possible to simultaneously carry out (c) step and (d) step described below. In this case, the water content in the exhaust gas is preferably 5% by mass or more, more preferably 10% by mass or more. In order to smoothly proceed with the reaction of the above formula (3) using such exhaust gas, it is preferable to spray water onto the CaO as needed before injecting the exhaust gas into contact with CaO.

[0038] (d process) The process (d) of the present invention is a process in which the Ca(OH)2 produced in the process (c) is brought into contact with cement exhaust gas to react with carbon dioxide in the exhaust gas, thereby preparing CaCO3 by the reaction of the following formula (4), and the CaCO3 is recycled and reused as the CaCO3 in the process (a). Ca(OH)2+CO2→CaCO3+ H2O·····(4) One method for contacting Ca(OH) with exhaust gas, such as cement exhaust gas, is to inject cement exhaust gas containing carbon dioxide into an aqueous Ca(OH) solution or gel-like Ca(OH)2 solution. The exhaust gas is not particularly limited as long as it contains carbon dioxide, but as mentioned above, for example, cement calcination bleed gas bled from the rising duct of a preheater in a cement manufacturing facility can be suitably used.

[0039] Cement exhaust gas containing carbon dioxide may contain NOx, but NOx reacts with Ca(OH)2 to form Ca(NO3)2, so there is no problem when recycling and implementing the method of the present invention. Dust may also be contained, but the dust is alkaline, and the alkali components such as Na and K contained in the dust are dissolved by the nitric acid added in the above (step a), so the presence of dissolved alkali components does not pose any particular problem. If necessary, separation and removal as described above can also be preferably carried out. Furthermore, the insoluble dust contained in the dust can be removed by solid-liquid separation as described above (step f). The removed solid content can be used as a cement raw material.

[0040] The temperature of the cement exhaust gas to be injected into the Ca(OH)2 aqueous solution or gel-like Ca(OH)2 is desirably 5 to 600°C, preferably 200 to 500°C, and more preferably 350 to 450°C, so that the carbonation of Ca(OH)2 occurs and the reverse reaction to CaO, as shown in the above formula (4), does not occur.

[0041] Considering the efficiency of the carbon dioxide carbon dioxide carbon dioxide carbonation reaction with calcium, the carbon dioxide concentration in the exhaust gas is preferably 5% by mass or more, more preferably 10% by mass or more. In the present invention, when the objective is to recover and utilize calcium in addition to storing energy (heat) and recovering carbon dioxide, it is preferable to remove dust, NOx, etc. from the exhaust gas.

[0042] Furthermore, if excessive carbonation is allowed to proceed in the (d) step, the Ca(HCO3)2 will become Ca(HCO3)2 and re-dissolve. However, if the generated Ca(HCO3)2 is circulated to the (a) step, the Ca(HCO3)2 will become Ca(NO3)2 through acid extraction with nitric acid in the (a) step, so there is no need to adjust the pH, and this is not a particular problem. Similarly, even if a small amount of Ca(OH)2 remains after (step d), if it is recycled to (step a), there is no problem because the reaction proceeds through acid extraction with nitric acid in (step a) to form Ca(NO3)2.

[0043] (h process) The CaCO3 obtained in (step d) can be partially recovered and reused without being recycled to the above (step a). In this case, it is preferable to adjust the pH to 6 to 8. When the obtained CaCO3 is recovered and reused, it is desirable to separate it into solid and liquid and wash it with water to prevent contamination with potassium and sodium components.

[0044] Preferred examples of the apparatus and facility for carrying out the method for utilizing cement exhaust gas of the present invention are shown below. A preferred facility for utilizing cement exhaust gas of the present invention comprises: a means for adding nitric acid to CaCO3 to cause a reaction and generate carbon dioxide and an aqueous solution of Ca(NO3)2; a means for recovering the generated carbon dioxide; a means for transporting cement exhaust gas and utilizing the heat of the exhaust gas to heat and dehydrate the aqueous solution of Ca(NO3)2 to generate CaO and NOx; a means for discharging the generated NOx to the outside of the system; a means for adding H2O to the CaO to cause a reaction and prepare Ca(OH)2; and a means for introducing cement exhaust gas containing carbon dioxide into the Ca(OH)2 and contacting it with the Ca(OH). The facility for utilizing cement exhaust gas (not shown) comprises: a means for reacting Ca(OH)2 with carbon dioxide in the exhaust gas to prepare CaCO3; a means for circulating and transporting the produced CaCO3 to a means for adding nitric acid to the CaCO3 and causing a reaction to produce carbon dioxide and a Ca(NO3)2 aqueous solution; a means for contacting NOx discharged outside the system with water to prepare nitric acid; and a means for circulating the produced nitric acid to a means for adding nitric acid to the CaCO3 and causing a reaction to produce carbon dioxide and a Ca(NO3)2 aqueous solution.

[0045] The facility for utilizing cement exhaust gas can be suitably applied to carrying out the method for utilizing cement exhaust gas according to the present invention described above in (1).

[0046] Another preferred facility for utilizing cement exhaust gas according to the present invention is a facility for utilizing cement exhaust gas (not shown), comprising: means for adding nitric acid to CaCO3 to cause a reaction and thereby generate carbon dioxide and a Ca(NO3)2 aqueous solution; means for recovering the generated carbon dioxide; means for transporting carbon dioxide-containing cement exhaust gas and directly introducing the exhaust gas into the Ca(NO3)2 aqueous solution, thereby heating and dehydrating the Ca(NO3)2 aqueous solution to generate CaCO3 and NOx using the resulting steam and the carbon dioxide in the exhaust gas; means for discharging the generated NOx to the system; means for circulating and transporting the generated CaCO3 to means for adding nitric acid to the CaCO3 to cause a reaction and generate carbon dioxide and a Ca(NO3)2 aqueous solution; means for contacting the NOx discharged to the system with water to prepare nitric acid; and means for circulating the generated nitric acid to the means for adding nitric acid to the CaCO3 to cause a reaction and generate carbon dioxide and a Ca(NO3)2 aqueous solution.

[0047] The facility for utilizing cement exhaust gas can be suitably applied to carrying out the method for utilizing cement exhaust gas according to the present invention described above in (3).

[0048] Another preferred facility for utilizing cement exhaust gas of the present invention comprises a means for adding nitric acid to CaCO3 to cause a reaction and generate carbon dioxide and an aqueous solution of Ca(NO3)2, a means for recovering the generated carbon dioxide, a means for transporting the cement exhaust gas and utilizing the heat of the exhaust gas to heat and dehydrate the aqueous solution of Ca(NO3)2 to generate CaO and NOx, a means for discharging the generated NOx to the outside of the system, a means for introducing the cement exhaust gas containing water vapor and carbon dioxide into the CaO to bring it into contact with the CaO, and a means for converting CaCO3 into water vapor and carbon dioxide in the exhaust gas. The facility for utilizing cement exhaust gas (not shown) comprises: a means for generating CaCO3 from the exhaust gas; a means for generating CaCO3 from water vapor and carbon dioxide in the exhaust gas; a means for circulating and transporting the generated CaCO3 to a means for adding nitric acid to the CaCO3 to cause a reaction and generate carbon dioxide and a Ca(NO3)2 aqueous solution; a means for contacting NOx discharged outside the system with water to prepare nitric acid; and a means for circulating the generated nitric acid to a means for adding nitric acid to the CaCO3 to cause a reaction and generate carbon dioxide and a Ca(NO3)2 aqueous solution.

[0049] The facility for utilizing cement exhaust gas can be suitably applied to carrying out the method for utilizing cement exhaust gas of the present invention described above in (4).

[0050] Furthermore, the reactions and raw materials in each means in the above-mentioned cement exhaust gas utilization facilities are the same as the reactions in the exhaust gas utilization method of the present invention, and the same raw materials can be used.

[0051] FIG. 2 shows an example of a batch-type utilization facility for utilizing cement waste gas according to the present invention. In Figure 2, (a), (b), (c), and (d) show examples of raw materials used in each of the steps (step a), (step b), (step c), and (step d) in the method for utilizing exhaust gas of the present invention.

[0052] As shown in Figure 2, CaCO3 and HNO3 are introduced into the device through an inlet at the top of the device, and the inlet is then closed. Next, the above (step a) is carried out while stirring the CaCO3 and HNO3 introduced into the device. The CO2 generated in this step is heavier than air and therefore accumulates in the lower part of the space above the device. As CO2 is generated, the pressure in the space within the device increases, and by opening a valve at another outlet, the generated CO2 can be discharged and recovered. In addition, the air within the device is discharged to the outside of the device by opening a relief valve depending on the amount of carbon dioxide generated.

[0053] When the produced carbon dioxide is discharged and recovered, for example, it can be discharged until the pressure inside the device reaches equilibrium with atmospheric pressure, and further, carbon dioxide remaining in the device can be recovered using a fan or the like, as necessary. Also, the produced carbon dioxide can be recovered depending on the recovery standard for the desired concentration of carbon dioxide, and for example, in the case of a cement factory, it is desirable to discharge and recover carbon dioxide after the carbon dioxide concentration reaches 15% or more. Furthermore, the recovered carbon dioxide-containing air can be concentrated separately and used as needed.

[0054] If it is desired to remove solid impurities from the aqueous solution containing Ca(NO3)2 obtained in the above (step a), solid-liquid separation can be performed by removing the aqueous solution of Ca(NO3)2 from the bottom of the apparatus shown in Figure 2. Separation methods include discharging only the solids that have precipitated in the apparatus, or discharging the entire aqueous solution containing Ca(NO3)2 and performing solid-liquid separation using, for example, a filter press with an MF membrane (step f).

[0055] Next, by introducing the cement waste gas containing carbon dioxide into the apparatus containing the Ca(NO3)2 aqueous solution through an inlet other than the above inlet and opening the valve of the inlet, steps (b) to (d) of the method for utilizing exhaust gas of the present invention can be carried out simultaneously. In this case, when the method for utilizing exhaust gas of the present invention is carried out using the apparatus of Figure 2, the cement waste gas is directly injected into the facility (apparatus), and the method for utilizing exhaust gas of the present invention described above in (3) can be preferably carried out.

[0056] The water in the calcium nitrate aqueous solution produced in step (a) above is preferably evaporated by introducing exhaust gas at 100-200°C to prevent steam explosion, or by using a heating element such as an electric heater. Using the heat of the water vapor and exhaust gas remaining in the apparatus and the carbon dioxide in the exhaust gas, steps (b) to (d) of the exhaust gas utilization method of the present invention proceed simultaneously to obtain CaCO3. Furthermore, although baffles may or may not be installed in the apparatus, it is preferable to install baffles in the apparatus while stirring to increase contact so that calcium nitrate tetrahydrate after evaporation and Ca(OH)2 during step (d) can react efficiently with carbon dioxide in the exhaust gas. It is also preferable to thoroughly remove dust from the exhaust gas using a cyclone or the like.

[0057] The generated NOx is heavier than air, so it accumulates in the lower part of the space above the device. As NOx and evaporated water vapor are generated, the pressure in the space inside the device increases, and by opening a valve at another outlet, the generated NOx is discharged and collected. The generated NOx can be discharged and collected until the pressure inside the device reaches equilibrium with atmospheric pressure. If necessary, the NOx remaining inside the device can be collected using a fan or the like.

[0058] Alternatively, using the apparatus of Figure 2, following the above (step a), instead of directly introducing cement exhaust gas, it is possible to carry out (step b) of the above-mentioned method of utilizing exhaust gas of the present invention by opening the valve of the inlet and introducing heat from the cement exhaust gas (exhaust heat air) into the apparatus containing the Ca(NO3)2 aqueous solution.

[0059] The generated NOx is heavier than air, so it accumulates in the lower part of the space above the device. As NOx is generated and water vapor is produced, the pressure in the space inside the device increases, and by opening a valve at another outlet, the generated NOx is discharged and collected. The generated NOx can be discharged and collected in the same manner as above, for example, until the pressure inside the device reaches equilibrium with atmospheric pressure. In addition, the NOx and water vapor remaining in the device can be collected using a fan or the like, as necessary. It is also possible to recover some of the CaO produced within the device and use it as an energy storage material.

[0060] Next, to carry out (step c), water or steam is introduced into the CaO in the apparatus by spraying or the like to generate Ca(OH)2 (step c), and then exhaust gas containing carbon dioxide is introduced to generate CaCO3 (step d). Alternatively, exhaust gas containing steam and carbon dioxide can be introduced into the CaO generated in the apparatus, and (step c) and (step d) can be carried out simultaneously to generate CaCO3. The produced CaCO3 can be recycled and reused as the CaCO3 in the above (step a), and a portion of it can also be recovered and used as an energy storage material. In this way, the device of Figure 2 can be applied even when the exhaust gas utilization method (1) of the present invention is carried out in the order of (a) followed by (b), (c), and (d), or when the exhaust gas utilization method (4) is carried out.

[0061] As in the above, a baffle plate may or may not be installed in the apparatus, but it is preferable to install a baffle plate in the apparatus to increase contact while stirring so that Ca(OH)2 can react efficiently with carbon dioxide gas in the exhaust gas as (step d) progresses.

[0062] As described above, the carbon dioxide and NOx generated in the present invention are preferably collected and concentrated after being retained in the lower part of the device, taking advantage of the fact that they have a higher specific gravity than air. For example, the timing for collecting carbon dioxide can be determined by the carbon dioxide concentration in the air pushed out from the relief valve at the top.

[0063] The exhaust gas utilization method and utilization equipment of the present invention make it possible to effectively utilize cement exhaust gas and the heat of the exhaust gas, recover high-purity carbon dioxide, and generate energy storage materials by utilizing the heat of the exhaust gas.Furthermore, it becomes possible to form a circulating cycle for the utilization of exhaust gas, which will be an excellent contribution to the environment. [Industrial Applicability]

[0064] The present invention makes it possible to effectively utilize exhaust gas and cement raw materials emitted from cement production facilities, recover high-purity carbon dioxide, and form an environmentally friendly circulation cycle, so that the method for utilizing exhaust gas of the present invention can be effectively applied to cement factories that produce cement.

Claims

1. CaCO ３ Nitric acid is added to react with carbon dioxide and Ca(NO ３ ) ２ a step of producing an aqueous solution and recovering the carbon dioxide (step a); The heat of the cement exhaust gas is used to ３ ) ２ a step (b) of heating the aqueous solution to dehydrate it, thereby producing CaO and NOx, and discharging the NOx from the system; The CaO is ２ O is added and reacted to give Ca(OH) ２ (step c), The Ca(OH) ２ The cement waste gas containing carbon dioxide is brought into contact with the Ca(OH) ２ is reacted with carbon dioxide in the exhaust gas to produce CaCO ３ and the CaCO ３ CaCO in the above (step a) ３ a step (step d) of recycling the product as a recycled product; and A step (e) of contacting the NOx produced in the step (b) with water to prepare nitric acid, and circulating the nitric acid for use as the nitric acid in the step (a). A method for utilizing cement exhaust gas, comprising:

2. In the method for utilizing cement exhaust gas according to claim 1, the generated Ca(NO ３ ) ２ A method for utilizing cement exhaust gas, comprising a step (f) of adjusting the pH of the aqueous solution to 6 to 8 and subjecting the insoluble matter to solid-liquid separation.

3. In the method for utilizing cement exhaust gas according to claim 1, the Ca(NO ３ ) ２ When heating the aqueous solution, the cement waste gas containing carbon dioxide is directly converted into Ca(NO ３ ) ２ By contacting the aqueous solution, (step b), (step c), and (step d) proceed simultaneously to form CaCO ３ A method for utilizing cement waste gas, characterized in that:

4. 2. The method for utilizing cement waste gas according to claim 1, wherein H in the step (c) ２ The addition of O is carried out by contacting exhaust gas containing water vapor and carbon dioxide with CaO, and (step c) and (step d) proceed simultaneously to produce CaCO ３ A method for utilizing cement waste gas, characterized in that:

5. 4. The method for utilizing cement exhaust gas according to claim 1, further comprising a step (g) of recovering a portion of the CaO obtained in step (b).

6. The method for utilizing cement waste gas according to any one of claims 1 to 4, wherein the CaCO obtained in step d ３ A method for utilizing cement exhaust gas, comprising a step (h) of recovering a portion of the exhaust gas.

7. CaCO ３ Nitric acid is added to react with carbon dioxide and Ca(NO ３ ) ２ a means for recovering the produced carbon dioxide; a means for transporting cement exhaust gas and utilizing the heat of the exhaust gas to produce the Ca(NO ３ ) ２ A means for heating the aqueous solution to dehydrate it and generate CaO and NOx, a means for discharging the generated NOx from the system, and a means for adding H to the CaO. ２ O is added and reacted to give Ca(OH) ２ means for preparing said Ca(OH) ２ A cement waste gas containing carbon dioxide is introduced into the catalyst and brought into contact with the catalyst, thereby producing Ca(OH) ２ and carbon dioxide in the exhaust gas to produce CaCO ３ the resulting CaCO ３ the CaCO ３ Nitric acid is added to react with carbon dioxide and Ca(NO ３ ) ２ a means for circulating and transporting the NOx discharged outside the system to a means for producing an aqueous solution of the NOx and the aqueous solution of the CaCO3; a means for preparing nitric acid by bringing the NOx discharged outside the system into contact with water; ３ Nitric acid is added to react with carbon dioxide and Ca(NO ３ ) ２ a means for circulating the aqueous solution to the means for generating the aqueous solution; A cement exhaust gas utilization facility characterized by comprising:

8. CaCO ３ Nitric acid is added to react with carbon dioxide and Ca(NO ３ ) ２ a means for generating an aqueous solution of Ca(NO), a means for recovering the generated carbon dioxide, a means for transporting a cement exhaust gas containing carbon dioxide, and converting the exhaust gas into the Ca(NO ３ ) ２ By directly introducing it into aqueous solution, Ca(NO ３ ) ２ The aqueous solution was heated and dehydrated to obtain water vapor, and the carbon dioxide in the exhaust gas was used to produce CaCO ３ and NOx generating means, means for discharging the generated NOx to the outside of the system, the generated CaCO ３ the CaCO ３ Nitric acid is added to react with carbon dioxide and Ca(NO ３ ) ２ a means for circulating and transporting the NOx discharged outside the system to a means for producing an aqueous solution of the NOx and the aqueous solution of the CaCO3; a means for preparing nitric acid by bringing the NOx discharged outside the system into contact with water; ３ Nitric acid is added to react with carbon dioxide and Ca(NO ３ ) ２ a means for circulating the aqueous solution to the means for generating the aqueous solution; A cement exhaust gas utilization facility characterized by comprising:

9. CaCO ３ Nitric acid is added to react with carbon dioxide and Ca(NO ３ ) ２ a means for recovering the produced carbon dioxide; a means for transporting cement exhaust gas and utilizing the heat of the exhaust gas to produce the Ca(NO ３ ) ２ A means for heating and dehydrating the aqueous solution to generate CaO and NOx, a means for discharging the generated NOx to the outside of the system, a means for introducing and contacting cement exhaust gas containing water vapor and carbon dioxide with the CaO, and converting CaCO3 into CaO by the water vapor and carbon dioxide in the exhaust gas. ３ means for producing the CaCO ３ the CaCO ３ Nitric acid is added to react with carbon dioxide and Ca(NO ３ ) ２ a means for circulating and transporting the NOx discharged outside the system to a means for producing an aqueous solution of the NOx and the aqueous solution of the CaCO3; a means for preparing nitric acid by bringing the NOx discharged outside the system into contact with water; ３ Nitric acid is added to react with carbon dioxide and Ca(NO ３ ) ２ a means for circulating the aqueous solution to the means for generating the aqueous solution; A cement exhaust gas utilization facility comprising:

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