Method for utilizing cement exhaust gas and equipment utilizing cement exhaust gas

Abstract

Provided are a method and equipment for utilizing exhaust gas by which exhaust gas from a cement manufacturing plant can be efficiently utilized.　This method for utilizing cement exhaust gas comprises a step (step a) of adding nitric acid to CaCO3 to allow reaction and produce carbon dioxide and Ca(NO3)2 aqueous solution, and recovering the carbon dioxide; a step (step b) of heating and dehydrating the Ca(NO3)2 aqueous solution by utilizing the heat of the cement exhaust gas, producing CaO and NOx and discharging the NOx outside the system; a step (step c) of adding H2O to CaO to allow reaction and prepare Ca(OH)2; a step (step d) of bringing Ca(OH)2 into contact with the cement exhaust gas to allow reaction of carbon dioxide in the exhaust gas with Ca(OH)2 to prepare CaCO3 and recycling the CaCO3 as CaCO3 in the step a; and a step (step e) of bringing NOx produced in the step b into contact with water to prepare nitric acid and recycling the nitric acid as nitric acid in the (step a).

Description

Cement exhaust gas utilization method and cement exhaust gas utilization equipment

[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.

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

[0003] Generally, in cement plants, exhaust gas generated by burning coal, heavy oil, or recycled fuel is used to dry cement raw materials, and then the dust contained in the gas is collected in a dust collection process and then discharged outside the system. However, since the exhaust gas after dust collection contains large amounts of water vapor and carbon dioxide derived from coal, etc., and trace amounts of chlorides and nitrogen oxides (hereinafter referred to as NOx), there is a concern that the purity will decrease when carbon dioxide is separated and collected, and therefore, technology for separating trace components is also being investigated.

[0004] Currently, pretreatment for separating and recovering carbon dioxide from cement exhaust gas typically involves collecting dust using an electrostatic precipitator or a bag filter, condensing water vapor using heat recovery, and using urea or alcohol as a denitrification technique for NOx. Patent No. 5,100,432 (Patent Document 1), for example, discloses a method for removing NOx from exhaust gas, specifically a flue gas treatment method for denitrifying exhaust gas containing nitrogen oxides by contacting the exhaust gas with a denitrifying agent, in which the denitrifying agent is a mixture of urea and one or more waste liquids selected from the group consisting of water-soluble waste liquids containing oil, waste liquids produced by washing ash, waste liquids containing alcohols, and waste liquids produced in cement or concrete factories, and the type of waste liquid and the mass ratio of the waste liquid to the urea are determined 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. Furthermore, the optimum temperature for the denitration reaction is said to be 800°C or higher, and the hot gas that has passed 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 is used as a carbon dioxide capture technology, 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 amines for carbon dioxide capture would be high for a typical cement factory, making this method unrealistic.

[0008] Japanese Patent No. 5100432 Japanese Patent Application Laid-Open No. 2009-160565

[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.

[0010] (1) The method for utilizing cement waste gas of the present invention is to ３ Nitric acid is added to react with carbon dioxide and Ca(NO ３ ) ２ a step (a) of generating an aqueous solution of Ca(NO) and recovering the carbon dioxide; ３ ) ２ a step (b) of heating the aqueous solution to dehydrate it, thereby generating CaO and NOx, and discharging the NOx from the system; ２ O is added and reacted to give Ca(OH) ２ (c) a step of preparing the Ca(OH) ２ The cement waste gas containing carbon dioxide is brought into contact with the Ca(OH) ２ and carbon dioxide in the exhaust gas to produce CaCO ３ and the CaCO ３ CaCO in the above (step a) ３ 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).

[0011] (2) A 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), further comprising the step of: ３ ) ２ This method for utilizing cement exhaust gas is characterized by comprising a step (f) of adjusting the aqueous solution to a pH of 6 to 8 and subjecting the insoluble matter to solid-liquid separation.

[0012] (3) Another preferred method for utilizing cement waste gas of the present invention is the method for utilizing cement waste gas of the present invention described above in (1) or (2), wherein 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 The present invention relates to a method for utilizing cement waste gas, characterized in that:

[0013] (4) Another preferred method for utilizing cement waste gas of the present invention is the method for utilizing cement waste gas of the present invention described above in (1) or (2), wherein H in the (c) step is 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 The present invention relates to a method for utilizing cement waste gas, characterized in that:

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

[0015] (6) A further preferred method for utilizing cement exhaust gas of the present invention is any of the above-mentioned methods for utilizing cement exhaust gas of the present invention, further comprising the step of: ３ The method for utilizing cement exhaust gas is characterized by comprising a step (h step) of recovering a portion of the above.

[0016] (7) The cement waste gas utilization equipment of the present invention is 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 ) ２A 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 and a means for circulating the cement exhaust gas to a means for producing an aqueous solution.

[0017] (8) Another cement waste gas utilization facility of the present invention is 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 ) ２a 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 and a means for circulating the cement exhaust gas to a means for producing an aqueous solution.

[0018] (9) Another cement waste gas utilization facility of the present invention is 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 generating CaCO by using 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 and a means for circulating the cement exhaust gas to a means for producing an aqueous solution.

[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, it makes it possible to effectively utilize the raw materials used in cement production in the cement manufacturing facility, and further makes effective use of the exhaust gas generated from the cement manufacturing facility. In this specification, the term "energy storage material" refers to a material that can store all heat, including sensible heat, heat of hydration, and heat of neutralization, within a substance, and that allows heat recovery even after the substance has cooled.

[0020] 1 is a diagram showing an outline of an example of a method for utilizing cement exhaust gas according to the present invention. FIG. 2 is a diagram showing a schematic view of an example of a facility for utilizing cement exhaust gas according to the present invention.

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

[0022] The method for utilizing cement waste gas of the present invention is to ３ Nitric acid is added to react with carbon dioxide and Ca(NO ３ ) ２ a step (a) of generating an aqueous solution of Ca(NO) and recovering the carbon dioxide; ３ ) ２ a step (b) of heating the aqueous solution to dehydrate it, thereby generating CaO and NOx, and discharging the NOx from the system; ２ O is added and reacted to give Ca(OH) ２ (c) a step of preparing 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) ３and 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).

[0023] The raw materials used in the present invention are not particularly limited, and commercially available products, recycled waste products, and the like can be used. Furthermore, 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 calcination in cement calcination 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). Furthermore, when heat recovery from the exhaust gas is not performed, cooled exhaust gas can also be used.

[0024] (Step a) In the step a of the present invention, nitric acid is added to calcium carbonate such as limestone powder, which is a cement raw material, while stirring the calcium carbonate, to produce carbon dioxide and Ca(NO) through the neutralization reaction shown in the following formula (1): ３ ) ２ The process involves producing an aqueous solution and recovering the high-purity carbon dioxide. ３ +2HNO ３ → Ca(NO ３ ) ２ +CO ２ +H ２ 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, and the like.

[0025] CaCO ３ The calcium carbonate may be, but is not limited to, waste materials containing calcium carbonate or limestone that is generally produced or excavated.３ It is also possible to use limestone (CaCO) as a cement raw material in cement factories. ３ Since the method for utilizing cement exhaust gas of the present invention uses limestone, which is used in cement production, to recover carbon dioxide from cement exhaust gas, it is convenient for cement production facilities because limestone used in cement production can be used to recover carbon dioxide. Preferably, limestone containing calcium carbonate with a purity of 90% or more is used.

[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 to be 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 and having a nitric acid concentration of 60 to 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 to 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, 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 or the like.

[0029] (Step f) Preferably, between the above (Step a) and the following (Step b), the generated Ca(CO ３ ) ２The aqueous solution is adjusted to a pH of 6 to 8, and the insoluble matter is subjected to solid-liquid separation (step f). ３ ) ２ ) is highly soluble in water and therefore dissolved in the aqueous solution, but if insoluble matter such as dust is contained, it is preferable to remove it by solid-liquid separation and to provide a method for removing the insoluble residue (step f). In such solid-liquid separation, it is preferable to adjust the pH to 6 to 8 and then perform solid-liquid separation of the insoluble residue. In particular, when recovering and utilizing CaO obtained in the following step b), it is preferable to provide such a separation step. The recovered insoluble solid matter can be recycled and used as a cement raw material.

[0030] (Step b) of the present invention is a step of preparing the Ca(NO ３ ) ２ An aqueous solution, preferably Ca(NO) that has undergone the solid-liquid separation step (step f) described above. ３ ) ２ This is a process in which the aqueous solution is heated and dehydrated using the heat of the cement exhaust gas (represented by the following formula (2)) to produce CaO and NOx, and the NOx is discharged outside the system. ３ ) ２ →CaO+NO ２ +NO+O (2) The reaction of the above formula (2) in the step b is an endothermic reaction, and heat is stored in the produced CaO.

[0031] In this (step b), the heat of cement exhaust gas discharged from a cement factory is directly or indirectly converted into Ca(NO ３ ) ２ Heat is transferred to the aqueous solution and heated to dehydrate. Ca(NO ３ ) ２ The temperature to which the aqueous solution is heated 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 water contained therein evaporates, and Ca(NO) is obtained as shown in the above formula (2). ３ ) ２is decomposed to give CaO. Generally, CaCO ３ To obtain CaO from CaCO3, it is necessary to perform the reaction at a temperature of 850°C or higher. ３ However, the present invention provides a method for decomposing Ca(NO ３ ) ２ Since CaO is obtained via ３ This method allows CaO to be obtained at a lower temperature than when CaO is obtained from the endothermic reaction of formula (2). Furthermore, it is possible to effectively utilize the heat of exhaust gas from cement production facilities. A portion of the CaO obtained by the endothermic reaction of formula (2) above can also be recovered and used as an energy storage material.

[0032] (Step e) Ca(NO ３ ) ２ The NOx generated by the thermal decomposition of the above can be cooled to room temperature and then wet recovered using, for example, an apparatus manufactured by Pollution Prevention Equipment Research Institute Co., Ltd., and the NOx can be brought into contact with water to produce nitric acid. As described above, the produced nitric acid can be used as the nitric acid in the above (step a), and a circulation system can be constructed. The NOx generated in the above formula (2) contains NO and NO ２ Contains, but mainly NO ２ is.

[0033] (Step g) The CaO produced in (Step b) is subjected to the following (Step c), 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 can be heated by heat exchange with sufficiently dried exhaust heat air. Furthermore, the obtained CaO can store heat as an energy storage material, but even after the CaO has cooled, it can also be stored at room temperature as an energy storage material.

[0034] In addition, in (step b), Ca(NO ３ ) ２ When heating the aqueous solution, the cement waste gas itself containing carbon dioxide is directly converted into Ca(NO ３ ) ２By contacting with the aqueous solution, the (b) step, the (c) step, and the (d) step proceed simultaneously, resulting in Ca(OH) ２ In this way, by directly injecting high-temperature cement exhaust gas instead of utilizing the heat of the cement exhaust gas, not only CaO is produced but also the production of CaCO in the following (step d) can be achieved. ３ The reaction proceeds until the formation of CaCO ３ is the CaCO used in the above (step a) ３ This allows for the construction of a circulation system. ３ It is also possible to recover a portion of this and use it as an energy storage material.

[0035] (Step c) In the (step c) of the present invention, H is added to the CaO obtained in the above step (b). ２ O is added and reacted as shown in the following formula (3) to give Ca(OH) ２ This is a process for preparing CaO+H ２ O → Ca(OH) ２ The reaction of the above formula (3) in the (c) step is an exothermic reaction.

[0036] The water added in (step c) is used to convert CaO into Ca(OH) ２ The amount of water required to make the CaO solution is sufficient, and it is not necessarily required to make the CaO solution, but the CaO solution or gel can be obtained. For example, the CaO solution can be obtained by adding water dropwise to the CaO solution, or by bringing the CaO solution into contact with the water in a mist state to convert the CaO into Ca(OH). ２ The reaction of 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, and the like.

[0037] In addition, H used in (c) ２As long as O is moisture, any water can be used, for example, exhaust gas containing moisture. In (step c), exhaust gas containing moisture (water vapor) and carbon dioxide is brought into contact with CaO, which enables the simultaneous progression of (step c) and (step d) described below. In this case, the moisture content in the exhaust gas is preferably 5% by mass or more, more preferably 10% by mass or more. Furthermore, in order to smoothly proceed with the reaction of the above formula (3) using such exhaust gas, it is preferable to spray water on the CaO as needed before injecting the exhaust gas into contact with CaO.

[0038] (Step d) of the present invention is a step of reacting Ca(OH) produced in the (step c) ２ The cement waste gas is brought into contact with the Ca(OH) ２ and carbon dioxide in the exhaust gas to produce CaCO by the reaction of the following formula (4): ３ and the CaCO ３ CaCO in the above (step a) ３ This is a process in which the product is recycled as Ca(OH) ２ +CO ２ →CaCO ３ + H ２ O...(4) Said Ca(OH) ２ As a method for contacting exhaust gas, such as cement exhaust gas, with Ca(OH) ２ Aqueous solution and gel-like Ca(OH) ２ There is a method of injecting cement exhaust gas containing carbon dioxide into the combustion chamber. The exhaust gas is not particularly limited as long as it contains carbon dioxide, but as described above, for example, cement calcination bleed gas bled from the rising duct of the preheater of a cement production facility can be suitably used.

[0039] Cement exhaust gas containing carbon dioxide may contain NOx, which is a compound of Ca(OH) ２ It reacts with Ca(NO ３ ) ２Therefore, there is no problem when carrying out the method of the present invention by recycling the waste. Furthermore, although dust may be contained, 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. Furthermore, if necessary, separation and removal as described above can also be preferably carried out. Furthermore, insoluble dust contained in the dust can be removed by solid-liquid separation in the above (step f). The removed solid components can be used as cement raw materials.

[0040] Ca(OH) ２ Aqueous solution and gel-like Ca(OH) ２ The temperature of the cement exhaust gas injected into the furnace is determined by the Ca(OH) ２ In order to allow the carbonation of the slag to occur and prevent the reverse reaction to form CaO, the temperature is desirably 5 to 600°C, preferably 200 to 500°C, and more preferably 350 to 450°C.

[0041] Considering the efficiency of the carbon dioxide carbon dioxide carbon dioxide carbon dioxide carbon dioxide carbon dioxide carbon dioxide carbon dioxide calcium carbonate ...

[0042] In addition, if carbonation is excessively promoted in the (d) step, Ca(HCO ３ ) ２ It becomes and re-dissolves, but the generated Ca(HCO ３ ) ２ When circulating to the above (step a), Ca(HCO ３ ) ２ is Ca(NO ３ ) ２ Therefore, there is no particular need to adjust the pH, and this is not a particular problem. Similarly, after (step d), Ca(OH) ２ Even if a small amount of Ca remains, when circulating it to (step a), the reaction proceeds by acid extraction with nitric acid in (step a) and Ca(NO３ ) ２ Therefore, there is no problem.

[0043] (H step) The CaCO obtained in (D step) ３ is not recycled to the above (step a), and a part of CaCO ３ In this case, it is preferable to adjust the pH to 6 to 8. ３ When recovering and reusing the product, it is desirable to separate the product into solid and liquid form and wash it with water to prevent contamination with potassium and sodium components.

[0044] Preferred examples of the apparatus and equipment for carrying out the method for utilizing cement waste gas of the present invention are shown below. 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 The cement waste gas utilization facility is equipped with a means for circulating the waste gas to a means for producing an aqueous solution (not shown).

[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, such as the above (1).

[0046] Another suitable utilization facility for cement waste gas of the present invention is 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 The cement waste gas utilization facility is equipped with a means for circulating the waste gas to a means for producing an aqueous solution (not shown).

[0047] 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, such as the above (3).

[0048] Another suitable utilization facility for cement waste gas of the present invention is 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 generating CaCO by using 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 The cement waste gas utilization facility is equipped with a means for circulating the waste gas to a means for producing an aqueous solution (not shown).

[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, such as the above (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] An example of a batch-type utilization facility for cement exhaust gas of the present invention is shown in Figure 2. In Figure 2, (a), (b), (c), and (d) indicate examples of raw materials used in each of the steps (step a), (step b), (step c), and (step d) in the above-mentioned method for utilizing exhaust gas of the present invention.

[0052] As shown in Figure 2, CaCO ３ and HNO ３ The CaCO3 solution is introduced into the apparatus through an inlet at the top of the apparatus, and the inlet is closed. ３ and HNO ３ The above (step a) is carried out while stirring.２ Since CO is heavier than air, it accumulates in the lower part of the space above the device. ２ As the CO2 is generated, the pressure in the space inside the device increases, and by opening a valve at another outlet, the generated CO2 is released. ２ The air inside the device can be discharged to the outside of the device by opening a relief valve depending on the amount of carbon dioxide generated.

[0053] When the generated 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 needed. Furthermore, the generated carbon dioxide can be recovered depending on the recovery standard for the desired concentration of carbon dioxide; for example, in the case of a cement factory, it is desirable to discharge and recover carbon dioxide once the carbon dioxide concentration reaches 15% or more. Furthermore, the air containing the recovered carbon dioxide can be concentrated separately and used as needed.

[0054] The Ca(NO) obtained in the above (step a) ３ ) ２ When it is desired to remove solid impurities from an aqueous solution containing Ca(NO ３ ) ２ The aqueous solution can be taken out and subjected to solid-liquid separation. As a separation method, there is a method of discharging only the solid matter precipitated in the device, or a method of discharging the entire amount of Ca(NO ３ ) ２ It is also possible to separate the aqueous solution containing the compound by discharging the aqueous solution and performing solid-liquid separation using, for example, a filter press using an MF membrane (step f).

[0055] Next, cement waste gas containing carbon dioxide was introduced into another inlet, and the valve of the inlet was opened to introduce Ca(NO ３ ) ２By introducing the exhaust gas into the apparatus containing the aqueous solution, 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, cement exhaust 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 suitably carried out.

[0056] The water in the aqueous calcium nitrate solution produced in the above (step a) is preferably evaporated by introducing exhaust gas at 100 to 200°C in order 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, (step b) to (step d) of the method for utilizing exhaust gas of the present invention proceed simultaneously, and CaCO ３ Furthermore, a baffle plate may be installed in the apparatus, but it is not necessary to install one, as this may prevent calcium nitrate tetrahydrate from being formed after evaporation and Ca(OH) ２ In order to allow the carbon dioxide gas in the exhaust gas to react efficiently with the catalyst, it is preferable to increase contact by installing a baffle plate in the device while stirring. 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 and therefore 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. When discharging the generated NOx, for example, it can be discharged and collected until the pressure inside the device is equilibrated with atmospheric pressure. Furthermore, NOx remaining in the device can be collected using a fan or the like, as necessary.

[0058] Alternatively, using the apparatus of FIG. 2, following the above (step a), instead of directly introducing the cement exhaust gas, heat from the cement exhaust gas (exhaust heat air) is introduced through an inlet, and the valve of the inlet is opened to generate Ca(NO ３ ) ２By introducing the exhaust gas into a device containing an aqueous solution, it is possible to carry out (step b) of the method for utilizing exhaust gas of the present invention and obtain NOx and CaO.

[0059] The generated NOx is heavier than air and therefore 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 within the device increases, and the generated NOx is discharged and recovered by opening a valve at another exhaust port. In discharging the generated NOx, it can be discharged and recovered, for example, until the pressure within the device reaches equilibrium with atmospheric pressure, as described above. In addition, the NOx and water vapor remaining in the device can be recovered using a fan or the like, as necessary. It is also possible to recover a portion of the CaO generated within the device and use it as an energy storage material.

[0060] Next, in order to carry out the (c) step, water or water vapor is introduced into the CaO in the apparatus by spraying or the like to form Ca(OH). ２ (step c), and then an exhaust gas containing carbon dioxide is introduced to produce CaCO ３ (Step d), or by introducing exhaust gas containing water vapor and carbon dioxide into the CaO produced in the apparatus, (Step c) and (Step d) are carried out simultaneously to produce CaCO ３ It is also possible to produce CaCO ３ is the CaCO ３ 2 can be applied to the case where the exhaust gas utilization method of the present invention (1) is carried out in the order of (b), (c), and (d) after (a), or to the case where the exhaust gas utilization method of the present invention (4) is carried out.

[0061] As in the above, a baffle plate may or may not be installed in the apparatus, but the baffle plate may be installed to prevent the Ca(OH) ２ In order to allow the carbon dioxide gas in the exhaust gas to react efficiently with the catalyst, it is preferable to increase contact by stirring the catalyst and by installing a baffle plate in the apparatus.

[0062] As described above, it is preferable that the carbon dioxide and NOx generated in the present invention are 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 of carbon dioxide collection 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.

[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 (a) of generating an aqueous solution of Ca(NO) and recovering the carbon dioxide; ３ ) ２ a step (b) of heating the aqueous solution to dehydrate it, thereby generating CaO and NOx, and discharging the NOx from the system; ２ O is added and reacted to give Ca(OH) ２ (c) a step of preparing 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 and (e) a step of contacting the NOx produced in (b) with water to prepare nitric acid, and circulating and using the nitric acid as the nitric acid in (a).

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 aqueous solution to a pH of 6 to 8 and subjecting the insoluble matter to solid-liquid separation.

3. In the method for utilizing cement waste 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. In the method for utilizing cement waste gas according to claim 1, 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. A method for utilizing cement exhaust gas as set forth in any one of claims 1 to 3, characterized in that it comprises a step (g) of recovering a portion of the CaO obtained in (b) step.

6. CaCO obtained in step d in the method for utilizing cement waste gas according to any one of claims 1 to 4. 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 and a means for circulating the cement exhaust gas to a means for producing an aqueous solution.

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 and a means for circulating the cement exhaust gas to a means for producing an aqueous solution.

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 and a means for circulating the cement exhaust gas to a means for producing an aqueous solution.

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