Method for producing ammonium nitrate using nitrogen dioxide in cement exhaust gas

Abstract

In order to simply and efficiently treat nitrogen dioxide in cement exhaust gas and reduce environmental burden by a method for producing ammonium nitrate, the present invention comprises: a nitrogen dioxide recovery step for bringing nitrogen dioxide in cement exhaust gas into contact with water to form a liquid containing NOx; a reduction reaction step in which ammonia is generated by bringing a reducing catalyst into contact with the NOx-containing liquid; an ammonia recovery step in which the ammonia is gasified using the waste heat gas; a solid-liquid separation step in which the remaining part after ammonia recovery is subjected to solid-liquid separation and iron hydroxide is separated from the remaining part of NOx that is not used; a neutralization step for producing ammonium nitrate by bringing the separated liquid containing nitrate nitrogen and / or nitrite nitrogen and the separated liquid containing NOx into contact with ammonia recovered by gasification; and a catalyst production step in which the magnetite used in the reduction reaction step is obtained by reacting ferric sulfate with an aqueous sodium hydroxide solution and performing solid-liquid separation, and the aqueous sodium sulfate solution during the solid-liquid separation is separated into sodium hydroxide and sulfuric acid by electrodialysis, the sodium hydroxide is recycled in the preparation of the magnetite.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for producing ammonium nitrate using nitrogen dioxide in cement exhaust gas, and more particularly, to a method for producing ammonium nitrate using nitrogen dioxide in cement exhaust gas, which can efficiently recover nitrogen dioxide generated in a cement plant, simply and effectively reduce environmental load, and also suppress environmental load in the production of a catalyst used in the production of the ammonium nitrate. BACKGROUND

[0002] Generally, in cement production, exhaust gas generated by burning coal, heavy oil, and recycled fuel is discharged to the outside of the system after dust contained therein is recovered in a dust collection process after drying of cement raw materials.

[0003] In the exhaust gas discharged to the outside of the system, in addition to carbon dioxide and a small amount of chloride, a large amount of nitrogen oxides (hereinafter, referred to as "NOx") caused by the combustion of fuel or the like is contained, and NOx causes environmental load such as acid rain and adverse effects on the human body such as the respiratory system.

[0004] Based on this problem, it has been proposed to reduce the amount of NOx discharged by selecting a fuel with a small amount of nitrogen component in a cement plant, using a denitration agent for NOx discharge restriction, and the like.

[0005] In Japanese Patent No. 5100432 (Patent Document 1), as a denitration technology for NOx in a cement plant, an SCR method using urea or alcohol is proposed, and specifically, a method for treating exhaust gas, which is a method for denitrifying exhaust gas containing nitrogen oxides by bringing the exhaust gas into contact with a denitration agent, is proposed, in which, as the denitration agent, a denitration agent formed by mixing one or two or more kinds of waste liquid selected from the group consisting of water-soluble waste liquid containing oil, waste liquid generated by water washing of ash, waste liquid containing alcohol, and waste liquid generated in a cement or concrete plant, and urea is used, and the kind of the waste liquid and the mass ratio of the waste liquid to urea are set to satisfy a specific condition.

[0006] However, in this method, the optimum temperature of the denitration reaction is set to 800°C or higher, and hot gas passing through a urea spray area is not denitrated, so it can be inferred that about 400 ppm of NOx is discharged into the atmosphere.

[0007] Further, in Japanese Patent No. 5963405 (Patent Document 3), there is disclosed a method for removing NOx from a treated gas containing NOx, which method subjects NOx, a treated gas component in the treated gas, to ozone oxidation, generates nitrous acid by mixing and contacting the NOx component in the treated gas after the ozone oxidation with an absorption liquid, and suppresses or prevents diffusion of NOx generated by conversion of the nitrous acid into the gas phase using ozone added in advance to the absorption liquid, the method for removing NOx from a treated gas containing NOx being characterized in that a molar ratio of ozone supplied to the treated gas to the treated gas component is set to a range of 0.1 to 2 times, and ozone is added in advance to the absorption liquid absorbing the treated gas component at 1 ppm or more and less than a saturated concentration, and mixing and contacting of the treated gas to which the ozone is supplied and the absorption liquid to which the ozone is added is performed in a fibrous porous body having a gas-liquid separation function, and the gas-liquid separation is performed below the porous body.

[0008] Further, in Japanese Patent No. 5963405 (Patent Document 3), there is disclosed a method for removing NOx from a treated gas containing NOx, which method subjects NOx, a treated gas component in the treated gas, to ozone oxidation, generates nitrous acid by mixing and contacting the NOx component in the treated gas after the ozone oxidation with an absorption liquid, and suppresses or prevents diffusion of NOx generated by conversion of the nitrous acid into the gas phase using ozone added in advance to the absorption liquid, the method for removing NOx from a treated gas containing NOx being characterized in that a molar ratio of ozone supplied to the treated gas to the treated gas component is set to a range of 0.1 to 2 times, and ozone is added in advance to the absorption liquid absorbing the treated gas component at 1 ppm or more and less than a saturated concentration, and mixing and contacting of the treated gas to which the ozone is supplied and the absorption liquid to which the ozone is added is performed in a fibrous porous body having a gas-liquid separation function, and the gas-liquid separation is performed below the porous body.

[0009] The method of the above-described conventional Patent Document 2 is performed under a high-temperature gas condition (300 to 600°C), and in a cement plant, it is difficult to perform the treatment because dust is mixed in a cement combustion exhaust gas.

[0010] Further, the method of the above-described conventional Patent Document 3 is a method for recovering NOx with water at normal temperature, but it is necessary to oxidize the recovered nitrous acid with ozone or the like, the process becomes complicated and the cost is high, and it is difficult to introduce into an actual cement plant.

[0011] Thus, in the conventional methods, denitration of NOx in an exhaust gas generated in a cement plant can be performed only in a limited temperature range, or the process becomes complicated, and it is not possible to effectively reuse the recovered NOx. Further, a method for producing ammonium nitrate using NOx in an exhaust gas, which achieves sufficient reduction of environmental load, is expected.

[0012] Prior Art Documents

[0013] Patent Documents

[0014] Patent Document 1: Japanese Patent No. 5100432

[0015] Patent Literature 2: Japanese Patent Application Laid-Open No. 2003-175315

[0016] Patent Literature 3: Japanese Patent No. 5963405 SUMMARY

[0017] PROBLEMS TO BE SOLVED BY THE INVENTION

[0018] The present application has an object to solve the above problems and provide a method for producing ammonium nitrate using nitrogen dioxide in cement exhaust gas, which can simply and efficiently perform denitration treatment of nitrogen dioxide in exhaust gas generated when cement is produced in a cement plant, can suppress discharge into the atmosphere, and reduce environmental load.

[0019] Further, there is provided a cycle period suitable for a cement plant or the like, which is excellent in reduction of environmental load, in which nitrogen dioxide in cement exhaust gas is produced into ammonium nitrate using exhaust heat gas discharged in a cement production process, reduction of environmental load can be achieved in production of a catalyst used in the process of producing ammonium nitrate, and the obtained residue can be effectively used when cement is produced.

[0020] SOLUTION TO THE PROBLEMS

[0021] (I) A method for producing ammonium nitrate using nitrogen dioxide in cement exhaust gas according to the present application is characterized by comprising:

[0022] a nitrogen dioxide recovery step (1) in which nitrogen dioxide in cement exhaust gas is brought into contact with water, and the nitrogen dioxide is recovered as a liquid containing nitric nitrogen and / or nitrous nitrogen by allowing the water to absorb the nitrogen dioxide;

[0023] a reduction reaction step (2) in which, subsequently, reduced iron and magnetite are brought into contact with all or a part of the liquid containing nitric nitrogen and / or nitrous nitrogen obtained in the nitrogen dioxide recovery step (1) under acidic conditions to generate iron hydroxide and ammonia;

[0024] an ammonia recovery step (3) in which, subsequently, the ammonia generated in the reduction reaction step (2) is distilled and gasified using exhaust heat gas from a cement production step to recover;

[0025] a solid-liquid separation step (4) in which the remaining portion after the ammonia is recovered in the ammonia recovery step (3) is subjected to solid-liquid separation, and the iron hydroxide from the reduction reaction step (2) and the nitric nitrogen and / or nitrous nitrogen of the remaining portion which is not used, which have passed through the ammonia recovery step (3), are subjected to solid-liquid separation;

[0026] a neutralization step (5) of bringing into contact with ammonia gasified and recovered in the ammonia recovery step (3) a liquid containing nitric nitrogen and / or nitrous nitrogen separated in the solid-liquid separation step (4) and a liquid containing nitric nitrogen and / or nitrous nitrogen remaining in the nitrogen dioxide recovery step (1) and not introduced into the reduction reaction step (2) to produce ammonium nitrate; and

[0027] a catalyst manufacturing step (7) in which the magnetite used in the reduction reaction step (2) is produced by subjecting a reaction product of ferric sulfate and an aqueous sodium hydroxide solution to solid-liquid separation to produce an aqueous sodium sulfate solution, and the aqueous sodium hydroxide solution is separated into sodium hydroxide and sulfuric acid by electrodialysis, and the obtained sodium hydroxide is recycled for use in the production of the magnetite for the reaction with the ferric sulfate.

[0028] (II) In the production method of ammonium nitrate using nitrogen dioxide in cement exhaust gas according to the present invention of the above (I), preferably, in the catalyst manufacturing step (7), the sulfuric acid obtained is used to set the reduction reaction step (2) to an acidic condition; and / or the unreacted sodium hydroxide after the production of the magnetite is reacted to produce sodium sulfate, and is recycled together with the aqueous sodium sulfate solution subjected to the solid-liquid separation in the catalyst manufacturing step (7) for use in the electrodialysis.

[0029] (III) In the production method of ammonium nitrate using nitrogen dioxide in cement exhaust gas according to the present invention of the above (I) or (II), further preferably, in the catalyst manufacturing step (7), the hydrogen generated in the production of the magnetite is recycled as a combustion raw material in the production of cement.

[0030] (IV) In the production method of ammonium nitrate using nitrogen dioxide in cement exhaust gas according to the present invention of the above (I) or (II), further preferably, it further comprises a granulation step (6) of granulating the ammonium nitrate produced in the neutralization step (5).

[0031] (V) In the production method of ammonium nitrate using nitrogen dioxide in cement exhaust gas according to the present invention of the above (I) or (II), further preferably, the ferric hydroxide separated in the solid-liquid separation step (4) is exposed to air to become ferric oxyhydroxide, and the ferric oxyhydroxide is used as a cement raw material.

[0032] (VI) In the production method of ammonium nitrate using nitrogen dioxide in cement exhaust gas according to the present application of (I) above, preferably, the ammonium nitrate produced in the neutralization step (5) is concentrated by heating and distilling the resultant liquid containing ammonium nitrate and liquid containing nitrogen in nitric acid form and / or nitrogen in nitrous acid form using waste heat gas to 170 to 180°C, and the residual nitrogen in nitric acid form and / or nitrogen in nitrous acid form is vaporized and recycled in the neutralization step (5), and a part of the ammonia vaporized in the ammonia recovery step (3) is added to the concentrated ammonium nitrate, and the unreacted nitrogen in nitric acid form and / or nitrogen in nitrous acid form existing in the concentrated ammonium nitrate is reacted to increase the purity of ammonium nitrate, and the resultant is cooled to obtain crystallized ammonium nitrate.

[0033] Effects of the Invention

[0034] The production method of ammonium nitrate according to the present application can produce a recycling regeneration cycle which is excellent in environmental aspects, in which nitrogen dioxide in exhaust gas discharged from a cement plant is denitrated efficiently, is excellent in environmental aspects, and the recovered nitrogen in nitric acid form and / or nitrogen in nitrous acid form can be reduced without special oxidation treatment, and the obtained ammonium nitrate as a final product can be effectively used as a blasting agent for a limestone mine which is a raw material for cement production, and the like.

[0035] Further, the waste heat gas discharged in the cement production step can be used as a heat source for producing magnetite which is a reductive catalyst and for vaporizing ammonia, and thus the waste heat gas in the cement production step can also be effectively used.

[0036] Further, a recycling cycle which is excellent in reduction of environmental load for a cement plant and the like can be formed, in which reduction of environmental load can be achieved in the production of a reductive catalyst used in the process of producing ammonium nitrate, and the obtained residue can be effectively used in the production of cement. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a flow chart showing an example of an outline of the production method of ammonium nitrate using nitrogen dioxide in cement exhaust gas according to the present application.

[0038] Figure 2 is a schematic diagram showing an example of the catalyst production step (7) in Figure 1 DETAILED DESCRIPTION

[0039] Reference Figure 1 and Figure 2 The present application will be described by the following preferred examples, but is not limited to these.

[0040] The production method of ammonium nitrate using nitrogen dioxide in cement exhaust gas according to the present application comprises:​

[0041] In the nitrogen dioxide recovery process (1), nitrogen dioxide in cement waste gas is brought into contact with water, and the water absorbs nitrogen dioxide and recovers the nitrogen dioxide as a liquid containing nitrate nitrogen and / or nitrite nitrogen.

[0042] In the reduction reaction step (2), the reduced iron and magnetite are then contacted under acidic conditions with all or part of the liquid containing nitrate nitrogen and / or nitrite nitrogen obtained in the nitrogen dioxide recovery step (1) to generate ferric hydroxide and ammonia.

[0043] In the ammonia recovery process (3), the ammonia generated in the reduction reaction process (2) is then distilled and vaporized using waste heat gas from the cement manufacturing process.

[0044] The solid-liquid separation process (4) separates the remaining portion after the ammonia recovery process (3) from the iron hydroxide from the reduction reaction process (2) and the unused remaining portion of nitrate nitrogen and / or nitrite nitrogen.

[0045] Neutralization step (5) involves contacting the liquid containing nitrate nitrogen and / or nitrite nitrogen separated in the solid-liquid separation step (4) and the remaining liquid containing nitrate nitrogen and / or nitrite nitrogen obtained in the nitrogen dioxide recovery step (1) but not introduced into the reduction reaction step (2) with ammonia recovered by vaporization in the ammonia recovery step (3) to prepare ammonium nitrate; and

[0046] In the catalyst manufacturing process (7), the magnetite used in the reduction reaction process (2) is prepared by solid-liquid separation of magnetite and sodium sulfate aqueous solution generated by reacting ferric sulfate with sodium hydroxide aqueous solution. The sodium sulfate aqueous solution is separated into sodium hydroxide and sulfuric acid by electrodialysis, and the obtained sodium hydroxide is recycled in the preparation of magnetite reacting with the ferric sulfate.

[0047] like Figure 1 As shown, the cement manufacturing process in a cement plant typically involves several steps: a raw material crushing process to pulverize the raw materials, a clinker calcination process to calcine the pulverized raw materials to produce cement clinker, and a cement refining process to pulverize the cement clinker and mix the pulverized cement clinker with gypsum.

[0048] In order to produce cement clinker, the fuel is calcined at a temperature of about 1300 to 1500°C, and cement raw materials are calcined in a cement kiln to produce cement clinker.

[0049] From the viewpoint of effectively utilizing waste, waste such as household garbage, sewage sludge, waste acid / waste alkali, waste plastic, dry sludge, waste white clay, wood chips, reclaimed oil, ASR, PKS, etc. is combusted in fuel, and the heat source obtained is used as a heat source for a cement clinker calcination process.

[0050] Also, as a cement raw material, waste containing nitrogen such as coal ash, general combustion ash, construction generated soil, combustion residue, sludge, foundry sand, steelmaking dust, slow cooling slag, etc. can be used as a raw material.

[0051] Here, the exhaust gas refers to exhaust gas or the like discharged by calcining these waste, and for example, refers to a gas used in a clinker calcination process and containing a large amount of dust such as cement dust or CO2 or the like.

[0052] Various dusts are contained in the exhaust gas, and for example, the dust in the exhaust gas is recovered with an electric dust collector, and the exhaust gas is cooled, for example, to about 30°C.

[0053] The amount of NOx in the cooled exhaust gas is, for example, 300 to 400 ppm, but in the present application, by recovering NOx in the exhaust gas in the following NOx recovery process (1), for example, in the case where the amount of NOx contained in the exhaust gas before the NOx recovery process is 350 ppm, the amount of NOx contained in the exhaust gas after the application of the NOx recovery process (1) can be reduced to 28 ppm.

[0054] The exhaust gas, for example, the exhaust gas cooled to 40°C or less, in which the dust in the combustion gas or the like discharged from the cement manufacturing process is recovered and cooled, is introduced into the NOx (nitrogen dioxide or the like) recovery process (1), and is brought into contact with water.

[0055] The NOx recovery process (1) is a recovery process using a water-based NOx absorption removal process.

[0056] Specifically, the exhaust gas cooled after the dust is recovered is brought into contact with water, and the NOx contained in the exhaust gas is brought into contact with water, whereby the NOx is absorbed into the water, and the NOx is recovered as a liquid containing nitric acid nitrogen and / or nitrous acid nitrogen.

[0057] For example, heat recovery can be performed indirectly using a heat exchanger, and the NOx is reacted with water to be nitric acid nitrogen and / or nitrous acid nitrogen.

[0058] The NOx in the cement exhaust gas that becomes the recovery target has the following equilibrium relationship represented by formula (a).

[0059] 2NO→2NO2←→N2O4... (a)

[0060] Furthermore, as shown in the following reaction formula (b), nitrate nitrogen and / or nitrite nitrogen are generated by contacting NO2 with water.

[0061] 2NO2 + H2O → HNO3 + HNO2……(b)

[0062] (N₂O₄ + H₂O → HNO₃ + HNO₂)

[0063] The volume ratio of ((HNO3+HNO2) / containing liquid) in the obtained liquid containing nitrate nitrogen and / or nitrite nitrogen is not particularly limited, but for example, 0.01 to 0.15 can be exemplified, and 0.01 to 0.08 can be preferably exemplified.

[0064] As described above, this NOx recovery process uses water as the NOx absorbent and does not use chemicals or other reagents, thus keeping costs low and enabling the absorbent to be recovered / reused as a nitric acid solution.

[0065] Furthermore, in this invention, there is no need to reset the process for oxidizing nitrous acid to nitric acid, such as the process for converting nitrous acid to nitric acid by means of ozone, etc. Both nitrous acid and nitric acid can be reduced in the subsequent reduction process (2), thus shortening the reaction process.

[0066] Next, all or part of the liquid containing nitrate nitrogen and / or nitrite nitrogen generated in the above NOx recovery step (1) is introduced into the subsequent reduction reaction step (2). Figure 1 (The arrows indicate the main manufacturing process) and then proceed with the processing.

[0067] The liquid containing nitrate nitrogen and / or nitrite nitrogen introduced into the reduction reaction step (2) can be all or part of the liquid containing nitrate nitrogen and / or nitrite nitrogen generated in the NOx recovery step (1) above. If it is part, the remaining liquid containing nitrate nitrogen and / or nitrite nitrogen can be introduced into the neutralization step (5) below.

[0068] As an example, about 40% by volume, preferably 38% by volume, and more preferably 35% by volume of the liquid containing nitrate nitrogen and / or nitrite nitrogen generated in the above-mentioned NOx recovery step (1) can be separated from the subsequent reduction reaction step (2) and introduced into the neutralization step (5) below.

[0069] The reduction reaction step (2) is a step in which a catalyst having a reduction function is brought into contact with a liquid containing nitric nitrogen and / or nitrous nitrogen under acidic conditions, for example, by adding sulfuric acid produced by the bipolar membrane electrodialysis of the following catalyst production step (7) to make the conditions acidic, and the nitric nitrogen and / or nitrous nitrogen in the liquid containing nitric nitrogen and / or nitrous nitrogen is reduced to ammonia.

[0070] As the catalyst having a reduction function used in the reduction reaction step (2), a commercially available magnetic material capable of reducing nitric nitrogen to ammonia can be used, for example, spinel ferrite (R1-Fe2O4), hexagonal ferrite (R2-Fe 12 O 19 ), garnet ferrite (R3-Fe5O 12 ), R3-M-B, and the like.

[0071] In the above structural formula, R1, R2, R3, and M can be exemplified as follows.

[0072] R1: Fe, Mn, Ni, Cu, Zn,

[0073] R2: Ba, Sr, Pb,

[0074] R3: Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu,

[0075] M: Fe, Fe-Co

[0076] In particular, as the catalyst having a reduction function, a magnetite and / or a reduced iron powder (example: JIP 300R, manufactured by JFE Steel Corporation) and the like can be preferably used, and the magnetite and the reduced iron powder can also be used by using any of the commercially available magnetite and reduced iron powder, or for example, a magnetite produced by effectively using waste heat gas discharged from a cement plant can also be used, and in the present application, the magnetite is preferably a magnetite produced using the waste gas from the cement plant (catalyst production step (7)).

[0077] Here, the waste heat gas is different from the waste gas, and refers to a hot gas such as air heated outside a cement kiln in a cement production step, and not containing cement dust or the like.

[0078] In order to produce the reduction catalyst, i.e., the magnetite, used in the present application, a magnetite obtained by reacting iron sulfate with sodium hydroxide (reaction formulas (d) to (e)) can be produced by solid-liquid separation with a sodium sulfate aqueous solution (catalyst production step (7)).

[0079] The ferric sulfate can use a commercially available ferric sulfate, for example, an industrial ferrous sulfate monohydrate (manufactured by SAKAI CHEMICAL INDUSTRY CO., LTD.) or the like can be exemplified.

[0080] Also, the sodium hydroxide can use a commercially available sodium hydroxide, but in the present application, for example, a sodium hydroxide obtained by bipolar membrane electrodialysis (reaction formula (c)) described below is used. Also, as described above, the sulfuric acid can be used in the reduction reaction process (2).

[0081] Na2SO4+ 2H2O → 2NaOH + H2SO4... (c)

[0082] The bipolar membrane electrodialysis is performed on an aqueous solution containing sodium sulfate (reaction formula (c) described above), and generates sulfuric acid and sodium hydroxide. The sodium sulfate is sodium sulfate generated by the following reaction formula (d) in the preparation of magnetite, and is recycled for the bipolar membrane electrodialysis.

[0083] Also, the sulfuric acid obtained by the bipolar membrane electrodialysis can be used for setting the reduction reaction process (2) under acidic conditions and / or can be reacted with unreacted sodium hydroxide after the preparation of magnetite to produce sodium sulfate, and is recycled together with the sodium sulfate aqueous solution solid-liquid separated in the catalyst manufacturing process (7) for the above-mentioned electrodialysis.

[0084] Also, the sodium hydroxide obtained by the bipolar membrane electrodialysis is used for the preparation of magnetite which is reacted with the ferric sulfate as shown in the following reaction formula (d).

[0085] Thus, in the catalyst manufacturing process (7), the sodium hydroxide can be recycled.

[0086] The magnetite is manufactured by the ferrite method of the following reaction formulae (d) to (e) using the ferric sulfate and the sodium hydroxide generated in the above-mentioned reaction formula (c).

[0087] In this manufacturing process, for example, the ferric sulfate and the sodium hydroxide are reacted at 200 to 250°C using waste heat gas, for example, at pH 8 to 13.

[0088] FeSO4+ 2NaOH → Fe(OH)2+ Na2SO4... (d) 3Fe(OH)2→ Fe3O4+ H2+ 2H2O... (e)

[0089] The obtained magnetite can be used as a catalyst having a reducing action in the reduction reaction process (2).

[0090] Further, in a case where sodium hydroxide is not reacted after the production of magnetite by the above-described reaction formulae (d) to (e), sulfuric acid obtained by the above-described bipolar membrane electrodialysis (reaction formula (c)) can be added to the unreacted sodium hydroxide and reacted to produce sodium sulfate, and the sodium sulfate can be subjected to bipolar membrane electrodialysis treatment together with the sodium sulfate produced by the above-described reaction formula (d).

[0091] As an example of an outline of the production process of magnetite, the following can be exemplified.

[0092] After the precipitate produced by the above-described reaction formulae (d) to (e) is filtered with a filter press while the aqueous sodium hydroxide solution containing iron sulfate, the water is evaporated and dried using waste heat gas from a cement plant, for example, dried at 70°C for about 30 minutes, and then, pulverized with a hammer mill or the like, the magnetite is recovered by magnetic separation, and sieved with a vibrating screen to set the particle size to 0.5 mm to 2 mm, whereby a magnetite pulverized product can be produced.

[0093] The chemical composition of the obtained magnetite can be analyzed using a fluorescent X-ray measuring device (PRIMUS IV, manufactured by Rigaku Corporation), and for example, a magnetite pulverized product having the following composition can be produced.

[0094] Fe: 68.3%, O: 28.6%, C: 1.2%, Mn: 1.1%, Al: 0.3%, S: 0.3%, Si: 0.2%

[0095] Further, after the obtained magnetite pulverized product is further finely pulverized, X-ray diffraction measurement is performed using a powder X-ray diffractometer (manufactured by PANalytical, X'Part Powder) with the measurement conditions set to measurement range: 2θ = 10 to 70°, step size: 0.017°, scanning speed: 0.1012° / s, voltage: 45 kV, current: 40 mA, whereby it can be confirmed that it is magnetite.

[0096] Specifically, for the X-ray diffraction pattern, it can be confirmed that it is magnetite using a crystal structure analysis software (manufactured by PANalytical, X'Part High Score Plus version 2.1b) provided in the above-described powder X-ray diffractometer.

[0097] Further, hydrogen produced by the above-described reaction formulae (d) to (e) can be recycled as a heat source for a burner in the production of cement.

[0098] In the above reduction reaction step (2), as described above, nitrate nitrogen and / or nitrite nitrogen is allowed to react with the magnetite or the like having a reduction action, which is produced in the above catalyst production step (7), under acidic conditions to produce ammonia.

[0099] For example, the above magnetite or the like having a reduction action is put into the liquid containing nitrate nitrogen and / or nitrite nitrogen introduced from the NOx recovery step, and reduction reaction is performed under acidic conditions, whereby all or a part of the nitrate nitrogen and / or nitrite nitrogen is converted into ammonia.

[0100] As an example, "a part" can be exemplified by conversion of 90% by volume, preferably 93% by volume, of the nitrate nitrogen and / or nitrite nitrogen into ammonia.

[0101] Further, in order to efficiently perform the reduction reaction, it is preferable to maintain an equilibrium state so that oxygen does not enter the liquid containing nitrate nitrogen and / or nitrite nitrogen, and for example, it can be exemplified by performing under a closed state or under an inactive atmosphere.

[0102] As an example, for example, the magnetite and reduced iron obtained in the above catalyst production step (7) are put into the liquid containing nitrate nitrogen and / or nitrite nitrogen introduced in the reduction reaction step at a mass ratio of 2: 1, the pH of the liquid containing nitrate nitrogen and / or nitrite nitrogen is set to 1.0 to 6.0 under normal temperature and acidic conditions, preferably the pH is set to 1.0 to 4.0, more preferably the pH is set to 1.0 to 2.0, and the following reduction reaction is performed for 1 to 10 hours, preferably 3 hours to 10 hours, while stirring.

[0103] The reduction reaction is represented by the following formulas (f) to (g).

[0104] HNO3+ 4Fe + 5H2O → NH3+ 4Fe(OH)2... (f)

[0105] HNO2+ 3Fe + 4H2O → NH3+ 3Fe(OH)2... (g)

[0106] As an additive for promoting the reduction reaction of the above formulas (f) to (g) under acidic conditions, any additive can be used as long as it can adjust the pH of an aqueous solution to be acidic and does not affect the treatment of the present application, and for example, hydrochloric acid, sulfuric acid, nitric acid, or the like can be used, and nitric acid can be preferably used, and sulfuric acid obtained by electrodialysis in the above catalyst production step (7) can be used, which is preferable from the viewpoint of recycling.

[0107] Further preferably, in the above reduction treatment, in order to effectively perform the reduction treatment, it is preferable to continuously measure using an ORP electrode and adjust the ORP to -500 mV to -200 mV, preferably -500 mV to -400 mV.

[0108] Next, the liquid containing nitric nitrogen and / or nitrous nitrogen obtained in the above reduction reaction step (2) is introduced into an ammonia recovery step (3) (arrow of the main manufacturing step of Figure 1

[0109] Next, after adjusting the ammonia and the liquid containing nitric nitrogen and / or nitrous nitrogen to pH 8.0 to 14.0, preferably pH 10.0 to 14.0 using an alkali agent, distillation is performed using waste heat gas from a cement plant to heat and vaporize the ammonia to recover it (ammonia recovery step (3)).

[0110] As for the waste heat gas, a waste heat gas cycle for heating and concentrating ammonium nitrate produced in the above neutralization step (5) to precipitate crystals can also be applied to the vaporization of ammonia in this ammonia recovery step (3).

[0111] In the recovery of ammonia by heating and vaporization, for example, it is preferable to apply a stripping method and set the heating temperature to 50 to 70°C.

[0112] Further, a part of the vaporized ammonia is introduced into the above neutralization step (5), and the remaining vaporized ammonia reacts with the nitric nitrogen and / or nitrous nitrogen remaining in the ammonium nitrate obtained by heating and concentrating the ammonium nitrate produced in the above neutralization step (5), and the purity of the ammonium nitrate can be improved.

[0113] As the above alkali agent, any additive can be used as long as it can adjust the pH of an aqueous solution to be alkaline and does not affect the treatment of the present application, and for example, sodium hydroxide, calcium hydroxide, potassium hydroxide, magnesium hydroxide can be exemplified, and sodium hydroxide can be preferably used, and for example, sodium hydroxide obtained by electrodialysis in the above catalyst manufacturing step (7) can be used, which is preferable from the viewpoint of recycling.

[0114] Further, the residue, i.e., iron (II) hydroxide, generated by the above reaction formulae (f), (g) is introduced into the ammonia recovery step (3) together with the ammonia and the liquid containing nitric nitrogen and / or nitrous nitrogen, and after passing through the above ammonia recovery step (3), the remaining part is subjected to solid-liquid separation, and the iron hydroxide from the above reduction reaction step (2) and the nitric nitrogen and / or nitrous nitrogen of the remaining part which is not used are subjected to solid-liquid separation (solid-liquid separation step (4)).

[0115] ​The iron hydroxide separated in the above-mentioned solid-liquid separation step (4) becomes iron oxyhydroxide (reaction formula (h) below) by being exposed to air, and this iron oxyhydroxide can be reused as a cement raw material.

[0116] 4Fe(OH)2+ O2→ 4FeO(OH) + 2H2O... (h)

[0117] Next, a part of the ammonia gasified and recovered in the above-mentioned ammonia recovery step (3), the liquid containing nitric nitrogen and / or nitrous nitrogen separated in the solid-liquid separation step (4), and the remaining part of the liquid containing nitric nitrogen and / or nitrous nitrogen obtained in the above-mentioned nitrogen dioxide recovery step (1) and not introduced into the above-mentioned reduction reaction step (2) are introduced into a neutralization step (5) and subjected to a contact reaction to produce ammonium nitrate (for example, purity of 78%).

[0118] In this neutralization step (5), a solution containing the produced ammonium nitrate and the excess nitric nitrogen and / or nitrous nitrogen not used for the production of ammonium nitrate can be obtained.

[0119] For example, the reaction of nitric nitrogen and ammonia is represented by formula (i) below, and for example, ammonium nitrate liquid with a concentration of about 78% can be produced.

[0120] HNO3 + NH3→ NH4NO3... (i)

[0121] For the liquid containing ammonium nitrate thus obtained, heating distillation is performed as necessary using waste heat gas, for example, distillation is performed at 170 to 180°C, whereby a suspension of concentrated ammonium nitrate (for example, purity of 98%) is obtained, and the remaining nitric nitrogen and / or nitrous nitrogen (HNO3 + HNO2) is volatilized. The volatilized HNO3 and HNO2 are preferably recycled in the above-mentioned neutralization step (5).

[0122] In the concentrated ammonium nitrate suspension, the remaining part of the gasified ammonia gas not introduced into the above-mentioned neutralization step (5) is added. By adding this ammonia gas, the suspension (concentrated ammonium nitrate) becomes weakly alkaline, and the purity of the ammonium nitrate (for example, about 100%) can be increased by a neutralization reaction with the remaining nitric nitrogen and / or nitrous nitrogen (HNO3 + HNO2) in the concentrated ammonium nitrate, and the crystals of ammonium nitrate are precipitated by cooling and separated.

[0123] Preferably, this treatment is performed before the following granulation step (6).

[0124] Also, the above-mentioned waste heat gas can be used for the gasification of ammonia in the above-mentioned ammonia recovery step (3) after the concentration and precipitation of ammonium nitrate.

[0125] Next, after the above ammonium nitrate is separated, granulated ammonium nitrate is produced using any granulator available on the market (granulation step (6)).

[0126] In this granulation step (6), a step of mixing light oil or the like with solid ammonium nitrate to produce, for example, explosives or blasting materials or the like can be provided.

[0127] By the treatment method of the present application, nitrogen dioxide contained in cement exhaust gas can be converted into ammonium nitrate for use, the content of nitrogen dioxide contained in cement exhaust gas can be sufficiently reduced to effectively perform denitration, and in the production of a reducing catalyst used in the production of ammonium nitrate, environmental load can also be reduced, waste heat gas at the time of cement production can be used, and the residue obtained by the treatment method of the present application can be effectively used at the time of cement production, thus forming an excellent recycling cycle from the environmental aspect.

[0128] Industrial applicability

[0129] Nitrogen dioxide in exhaust gas discharged from a cement plant can be efficiently denitrated, an excellent recycling cycle from the environmental aspect can be formed, and thus the treatment method of the present application can be effectively applied to a cement plant that produces cement.

Claims

1. A method for producing ammonium nitrate using nitrogen dioxide in cement exhaust gas, characterized by, Possessing: a nitrogen dioxide recovery step (1) in which nitrogen dioxide in cement exhaust gas is brought into contact with water, and the water absorbs the nitrogen dioxide to recover the nitrogen dioxide as a liquid containing nitric nitrogen and / or nitrous nitrogen; a reduction reaction step (2) in which, subsequently, reduced iron and magnetite are brought into contact with all or a portion of the liquid containing nitric nitrogen and / or nitrous nitrogen obtained in the nitrogen dioxide recovery step (1) under acidic conditions to generate iron hydroxide and ammonia; an ammonia recovery step (3) in which, subsequently, the ammonia generated in the reduction reaction step (2) is subjected to distillation and gasification using waste heat gas from a cement manufacturing step to recover the ammonia; a solid-liquid separation step (4) in which, after the ammonia is recovered in the ammonia recovery step (3), the remaining portion is subjected to solid-liquid separation, and the iron hydroxide from the reduction reaction step (2) that has passed through the ammonia recovery step (3) and the nitric nitrogen and / or nitrous nitrogen of the remaining portion that has not been used are subjected to solid-liquid separation; a neutralization step (5) in which the liquid containing nitric nitrogen and / or nitrous nitrogen separated in the solid-liquid separation step (4) and the liquid containing nitric nitrogen and / or nitrous nitrogen obtained in the nitrogen dioxide recovery step (1) and not introduced into the reduction reaction step (2) are brought into contact with the ammonia gasified and recovered in the ammonia recovery step (3) to produce ammonium nitrate; and a catalyst manufacturing step (7) in which the magnetite used in the reduction reaction step (2) is produced by subjecting a magnetite generated by reacting iron sulfate with an aqueous sodium hydroxide solution and an aqueous sodium sulfate solution separated by electrodialysis into sodium hydroxide and sulfuric acid to solid-liquid separation, and the obtained sodium hydroxide is recycled in the production of the magnetite that reacts with the iron sulfate.

2. The method of manufacturing ammonium nitrate using nitrogen dioxide in cement exhaust gas according to claim 1, characterized in that: the sulfuric acid obtained in the catalyst manufacturing step (7) is used to set the reduction reaction step (2) to an acidic condition; and / or the unreacted sodium hydroxide after the production of the magnetite is reacted to produce sodium sulfate, and is recycled together with the aqueous sodium sulfate solution subjected to solid-liquid separation in the catalyst manufacturing step (7) and used in the electrodialysis.

3. The method of manufacturing ammonium nitrate using nitrogen dioxide in cement exhaust gas according to claim 1 or 2, characterized in that: in the catalyst manufacturing step (7), hydrogen generated at the time of production of the magnetite is recycled as a combustion raw material at the time of manufacturing cement.

4. The method for producing ammonium nitrate using nitrogen dioxide in cement exhaust gas according to claim 1 or 2, characterized by, Further possessing: a granulation step (6) in which the ammonium nitrate produced in the neutralization step (5) is granulated.

5. The method of manufacturing ammonium nitrate using nitrogen dioxide in cement exhaust gas according to claim 1 or 2, characterized in that: the iron hydroxide separated in the solid-liquid separation step (4) becomes a hydroxyl iron oxide by being exposed to air, and the hydroxyl iron oxide is used as a cement raw material.

6. The method of manufacturing ammonium nitrate using nitrogen dioxide in cement exhaust gas according to claim 1, characterized in that: The ammonium nitrate produced in the neutralization step (5) is contained in ammonium nitrate and a liquid containing nitric nitrogen and / or nitrous nitrogen, the resultant liquid is heated and distilled to 170 to 180°C using waste heat gas to concentrate the ammonium nitrate, and the residual nitric nitrogen and / or nitrous nitrogen is vaporized and recycled in the neutralization step (5), a part of the ammonia vaporized in the ammonia recovery step (3) is added to the concentrated ammonium nitrate, and reacts with the unreacted nitric nitrogen and / or nitrous nitrogen mixed in the concentrated ammonium nitrate to increase the purity of the ammonium nitrate, and is cooled, whereby crystallized ammonium nitrate is obtained.

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