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

Abstract

The present invention is a method for manufacturing ammonium nitrate, which simply and efficiently treats nitrogen dioxide in cement exhaust gas and reduces environmental load, the method including: a nitrogen dioxide recovery step in which nitrogen dioxide in cement exhaust gas is brought into contact with water to produce a liquid containing NOx; a reduction reaction step in which a reducing catalyst is brought into contact with the liquid containing NOx to produce ammonia; an ammonia recovery step in which the ammonia is vaporized using waste heat gas; a solid-liquid separation step in which a remaining portion after the ammonia recovery is subjected to solid-liquid separation and Fe(OH)2 is separated from unused NOx in the remaining portion; a neutralization step in which a liquid containing nitric nitrogen and / or nitrous nitrogen, which is separated, and a liquid containing NOx are brought into contact with the vaporized and recovered ammonia to produce ammonium nitrate; and a catalyst manufacturing step in which a magnetite used in the reduction reaction step is obtained by reacting iron sulfate with an aqueous sodium hydroxide solution and subjecting the solution to solid-liquid separation, the aqueous sodium sulfate solution in the solid-liquid separation is separated into sodium hydroxide and sulfuric acid by electrodialysis, and the sodium hydroxide is recycled in the production of the magnetite.

Description

Technical Field

[0001] This invention relates to a method for manufacturing ammonium nitrate utilizing nitrogen dioxide from cement waste gas, and more particularly to a method for manufacturing ammonium nitrate utilizing nitrogen dioxide from cement waste gas that can efficiently recover nitrogen dioxide generated in cement plants, simply and effectively reduce environmental load, and also suppress environmental load in the preparation of catalysts used in the preparation of the ammonium nitrate. Background Technology

[0002] Typically, in cement manufacturing, the exhaust gases generated from the combustion of coal, heavy oil, or recycled fuels are used for drying cement raw materials. The dust contained in these gases is then collected during the dust collection process and discharged outside the system.

[0003] In addition to carbon dioxide and trace amounts of chlorides, the exhaust gas discharged from the system also contains a large amount of nitrogen oxides (hereinafter referred to as "NOx") caused by fuel combustion and other factors. NOx leads to environmental burdens such as acid rain and has adverse effects on the respiratory system and other human health conditions.

[0004] Based on this problem, suggestions have been made to reduce NOx emissions by selecting fuels with low nitrogen content in cement plants and using denitrification agents to limit NOx emissions.

[0005] In Japanese Patent No. 5100432 (Patent Document 1), an SCR method using urea or alcohol was proposed as a NOx denitrification technology in cement plants. Specifically, a waste gas treatment method was proposed, which is a method for treating waste gas containing nitrogen oxides by contacting the waste gas with a denitrification agent to denitrify the waste gas. In this method, the denitrification agent is a mixture of one or more waste liquids selected from the group consisting of water-soluble waste liquid containing oil, waste liquid generated from washing ash, waste liquid containing alcohol, and waste liquid generated in cement or concrete plants, and urea. The type of waste liquid and the mass ratio of the waste liquid to urea are set to meet specific conditions.

[0006] However, in this method, the optimal temperature for the denitrification reaction is set above 800°C. The hot gas passing through the urea spray zone will not be denitrified, so it can be inferred that about 400 ppm of NOx is discharged into the atmosphere.

[0007] Furthermore, Japanese Patent Application Publication No. 2003-175315 (Patent Document 2) discloses a nitrogen oxide absorbent, which is a nitrogen oxide absorbent for absorbing nitrogen oxides in high-temperature gases containing oxygen and nitrogen oxides. The absorbent is characterized by containing a mixture of oxides or hydroxides of alkaline earth elements and oxides of transition elements, wherein the alkaline earth elements are barium (Ba) and / or strontium (Sr), and the transition elements are copper (Cu) and / or iron (Fe).

[0008] Furthermore, Japanese Patent No. 5963405 (Patent Document 3) discloses a method for denitrifying a NOx-containing gas. This method involves ozone oxidation of the NOx component in the gas being treated. The NOx component in the ozone-oxidized gas then reacts with an absorbent to produce nitrous acid. Ozone pre-added to the absorbent suppresses or prevents the diffusion of NOx generated by the nitrous acid reaction into the gas phase. The method is characterized by setting the molar ratio of ozone supplied to the gas to the gas component to be between 0.1 and 2, and pre-adding ozone at a concentration of 1 ppm or more and below saturation to the absorbent absorbing the gas component. The mixing and contacting of the gas supplied with ozone and the absorbent with added ozone takes place within a fibrous porous body with gas-liquid separation capabilities, with the gas-liquid separation occurring below the porous body.

[0009] The method described in the previous patent document 2 is carried out under high-temperature gas conditions (300-600°C). When applied in cement plants, it is difficult to treat because dust is mixed in with the cement combustion exhaust gas.

[0010] Furthermore, the method in the aforementioned prior patent document 3 is a method for recovering NOx with water at room temperature, but it requires the use of ozone or the like to oxidize the recovered nitrous acid, making the process complex and costly, and difficult to implement in actual cement plants.

[0011] Thus, in previous methods, the denitrification of NOx in the exhaust gas generated in cement plants could only be carried out within a limited temperature range, or the process became too complex, making it impossible to effectively reuse the recovered NOx. Furthermore, a method for manufacturing ammonium nitrate that utilizes NOx from exhaust gas to significantly reduce environmental impact is anticipated.

[0012] Existing technical documents

[0013] Patent documents

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

[0015] Patent Document 2: Japanese Patent Application Publication No. 2003-175315

[0016] Patent Document 3: Japanese Patent No. 5963405 Summary of the Invention

[0017] The problem the invention aims to solve

[0018] The purpose of this invention is to solve the above-mentioned problems and provide a method for manufacturing ammonium nitrate that utilizes nitrogen dioxide in cement waste gas. This method can simply and efficiently denitrify nitrogen dioxide in the waste gas generated during cement manufacturing in cement plants, thereby inhibiting its emission into the atmosphere and reducing environmental impact.

[0019] Furthermore, a cycle is provided that is suitable for cement plants and the like, and has excellent environmental impact reduction: by using the waste heat gas discharged during the cement manufacturing process to produce ammonium nitrate from nitrogen dioxide in the cement waste gas, and also to reduce the environmental impact in the production of the catalyst used in the production of ammonium nitrate, and to effectively use the obtained residue during cement manufacturing.

[0020] Solution for solving the problem

[0021] (I) The method for manufacturing ammonium nitrate utilizing nitrogen dioxide from cement waste gas of the present invention is characterized by comprising:

[0022] 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.

[0023] In the reduction reaction step (2), the reduced iron and magnetite are then brought into contact with all or part of the liquid containing nitrate nitrogen and / or nitrite nitrogen obtained in the nitrogen dioxide recovery step (1) under acidic conditions to generate Fe(OH)2 and ammonia.

[0024] 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.

[0025] The solid-liquid separation process (4) performs solid-liquid separation on the remaining portion after the ammonia recovery process (3), and separates the Fe(OH)2 from the reduction reaction process (2) and the unused remaining portion of nitrate nitrogen and / or nitrite nitrogen from the ammonia recovery process (3).

[0026] 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

[0027] 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.

[0028] (II) Preferably, in the above-described (I) method of manufacturing ammonium nitrate utilizing nitrogen dioxide in cement waste gas, the sulfuric acid obtained in the catalyst manufacturing step (7) is used to set the reduction reaction step (2) under acidic conditions; and / or reacts with unreacted sodium hydroxide after the preparation of magnetite to produce sodium sulfate, and is recycled together with the sodium sulfate aqueous solution that has undergone solid-liquid separation in the catalyst manufacturing step (7) in the electrodialysis.

[0029] (III) Further preferred in the above-described (I) or (II) method of manufacturing ammonium nitrate that utilizes nitrogen dioxide in cement waste gas, the hydrogen generated during the preparation of magnetite in the catalyst manufacturing step (7) is recycled as a combustion raw material during cement manufacturing.

[0030] (IV) Further preferred in the above-described (I) or (II) method for manufacturing ammonium nitrate utilizing nitrogen dioxide in cement waste gas, the method is characterized by further comprising: a granulation step (6) for granulating the ammonium nitrate prepared in the neutralization step (5).

[0031] (V) Further preferred in the above-described (I) or (II) method of manufacturing ammonium nitrate using nitrogen dioxide in cement waste gas, characterized in that the Fe(OH)2 separated in the solid-liquid separation step (4) becomes iron hydroxyl oxide by being exposed to air, which is used as a cement raw material.

[0032] (VI) Preferably, in the above-described (I) method of manufacturing ammonium nitrate using nitrogen dioxide from cement waste gas, the ammonium nitrate prepared in the neutralization step (5) is characterized in that the ammonium nitrate is contained in ammonium nitrate and a liquid containing nitrate nitrogen and / or nitrite nitrogen, the resulting liquid is heated and distilled to 170-180°C using waste heat gas to concentrate the ammonium nitrate, and the residual nitrate nitrogen and / or nitrite nitrogen is vaporized and circulated in the neutralization step (5), a portion of the ammonia vaporized in the ammonia recovery step (3) is added to the concentrated ammonium nitrate to react with the unreacted nitrate nitrogen and / or nitrite nitrogen mixed in the concentrated ammonium nitrate to improve the purity of the ammonium nitrate, and then cooled to obtain crystallized ammonium nitrate.

[0033] The effects of the invention

[0034] The method for manufacturing ammonium nitrate according to the present invention can produce a recycling cycle with the following excellent environmental benefits: it can efficiently denitrify nitrogen dioxide in the exhaust gas discharged from cement plants, which is also environmentally excellent; and the recovered nitrate nitrogen and / or nitrite nitrogen can be reduced without special oxidation treatment. The ammonium nitrate obtained as the final product can be effectively utilized as an blasting agent in limestone mines, which are used as raw materials for cement manufacturing.

[0035] Furthermore, the waste heat gases emitted during the cement manufacturing process can be used as a heat source for manufacturing magnetite as a reducing catalyst and for gasifying ammonia, thus making effective use of the waste heat gases from the cement manufacturing process.

[0036] Furthermore, it is possible to form a cycle that is suitable for cement plants and the like, with excellent environmental impact reduction: the environmental impact can also be reduced in the manufacture of the reducing catalyst used in the manufacture of ammonium nitrate, and the residue obtained can be effectively used in the manufacture of cement. Attached Figure Description

[0037] Figure 1 This is a flowchart illustrating an example of a method for manufacturing ammonium nitrate utilizing nitrogen dioxide from cement waste gas, according to the present invention.

[0038] Figure 2 It means Figure 1 A schematic diagram of an example of the catalyst manufacturing process (7) in the process. Detailed Implementation

[0039] refer to Figure 1 and Figure 2 The present invention will be described through the following preferred examples, but is not limited thereto.

[0040] The present invention provides a method for manufacturing ammonium nitrate utilizing nitrogen dioxide from cement waste gas, comprising:

[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 brought into contact with all or part of the liquid containing nitrate nitrogen and / or nitrite nitrogen obtained in the nitrogen dioxide recovery step (1) under acidic conditions to generate Fe(OH)2 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) performs solid-liquid separation on the remaining portion after the ammonia recovery process (3), and separates the Fe(OH)2 from the reduction reaction process (2) and the unused remaining portion of nitrate nitrogen and / or nitrite nitrogen from the ammonia recovery process (3).

[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 perspective of effectively utilizing waste, household waste, sewage sludge, waste acid / alkali, waste plastics, dried sludge, waste clay, wood chips, recycled oil, ASR, PKS, and other wastes are used as fuels to burn, and the resulting heat source is used as the heat source for the cement clinker calcination process.

[0050] Furthermore, as a cement raw material, nitrogen-containing wastes, such as coal ash, general combustion ash, construction soil, combustion residue, sludge, casting sand, steelmaking dust, and slow-cooling slag, can also be used as raw materials.

[0051] Here, waste gas refers to the waste gas emitted during the calcination of these wastes, such as the gas used in the clinker calcination process that contains a large amount of dust such as cement dust or CO2.

[0052] The exhaust gas contains various dust particles. For example, the dust in the exhaust gas can be recovered using an electrostatic precipitator, and the exhaust gas can be cooled, for example, to about 30°C.

[0053] The amount of NOx in the cooled exhaust gas is, for example, 300 to 400 ppm. However, in this invention, by recovering NOx in the exhaust gas in the NOx recovery process (1) described below, for example, if 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 NOx recovery process (1) can be reduced to 28 ppm.

[0054] The dust in the exhaust gases such as combustion gases discharged from the cement manufacturing process is recovered and cooled, for example, the exhaust gases are cooled to below 40°C and introduced into the NOx (nitrogen dioxide, etc.) recovery process (1), and then brought into contact with water.

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

[0056] Specifically, the exhaust gas cooled after dust collection is brought into contact with water, and the NOx contained in the exhaust gas is brought into contact with water, thereby absorbing the NOx into the water and recovering the NOx as a liquid containing nitrate nitrogen and / or nitrite nitrogen.

[0057] For example, heat recovery can be performed indirectly using a heat exchanger, and NOx can be reacted with water to convert NOx into nitrate nitrogen and / or nitrite nitrogen.

[0058] The NOx in the cement waste gas that is to be recycled has the equilibrium relationship represented by the following equation (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) will be 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 as follows: the catalyst with reducing effect is brought into contact with a liquid containing nitrate nitrogen and / or nitrite nitrogen under acidic conditions, for example, by adding sulfuric acid generated by bipolar membrane electrodialysis in the catalyst manufacturing step (7) described below, and the reaction is carried out so that the nitrate nitrogen and / or nitrite nitrogen in the liquid containing nitrate nitrogen and / or nitrite nitrogen becomes ammonia.

[0070] As the catalyst with reducing effect used in the reduction reaction step (2), a commercially available magnetic material capable of reducing nitrate nitrogen to ammonia can be used. Examples include spinel ferrite system (R1-Fe2O4) and hexagonal ferrite (R2-Fe2O4). 12 O 19 ), Garnet iron oxide system (R3-Fe5O) 12 ), R3-MB, etc.

[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 a catalyst with a reducing effect, magnetite and / or reduced iron powder (e.g., JIP 300R, manufactured by JFE Steel Corporation) in magnetic materials can be preferably used. The magnetite and reduced iron powder can also be any magnetite and reduced iron powder that are commercially available, or for example, magnetite prepared by effectively utilizing waste heat gas discharged from a cement plant can also be used. In this invention, the magnetite preferably used is magnetite prepared by utilizing waste gas from the cement plant (catalyst manufacturing step (7)).

[0077] Here, waste heat gas is different from waste gas, and refers to hot gases such as air that are heated outside the cement kiln during the cement manufacturing process and do not contain cement dust.

[0078] In order to prepare the reducing catalyst used in this invention, namely magnetite, it can be prepared by solid-liquid separation of magnetite obtained by reacting ferric sulfate with sodium hydroxide (reaction formulas (d) to (e)) and sodium sulfate aqueous solution (catalyst manufacturing step (7)).

[0079] Ferric sulfate can be any commercially available ferric sulfate, such as industrial ferrous sulfate monohydrate (manufactured by SAKAI CHEMICAL INDUSTRY CO., LTD.).

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

[0081] Na2SO4+2H2O→2NaOH+H2SO4……(c)

[0082] Bipolar membrane electrodialysis is performed on an aqueous solution containing sodium sulfate (reaction (c) above) to produce sulfuric acid and sodium hydroxide. This sodium sulfate is the same sodium sulfate that is recycled during the preparation of magnetite via reaction (d) below for bipolar membrane electrodialysis.

[0083] Furthermore, the sulfuric acid obtained by this bipolar membrane electrodialysis can be used to set the reduction reaction step (2) under acidic conditions and / or react with unreacted sodium hydroxide after the preparation of magnetite to produce sodium sulfate, and can be recycled together with the sodium sulfate aqueous solution that was separated into solid and liquid in the catalyst manufacturing step (7) in the above electrodialysis.

[0084] Furthermore, sodium hydroxide obtained by bipolar membrane electrodialysis is used to prepare magnetite that reacts with ferric sulfate as shown in the following reaction formula (d).

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

[0086] Magnetite is produced using ferric sulfate and sodium hydroxide generated in reaction (c) above, via the ferrite process described in reactions (d) to (e).

[0087] In this manufacturing process, for example, waste heat gas is used to react ferric sulfate and sodium hydroxide at 200–250°C, for example, at pH 8–13.

[0088] FeSO4+2NaOH→Fe(OH)2+Na2SO4……(d)

[0089] 3Fe(OH)2→Fe3O4+H2+2H2O……(e)

[0090] The obtained magnetite can be used as a catalyst with reducing effect in the reduction reaction step (2).

[0091] Furthermore, if unreacted sodium hydroxide remains after preparing magnetite via the above reaction formulas (d) to (e), sulfuric acid obtained by the above bipolar membrane electrodialysis (reaction formula (c)) can be added to the unreacted sodium hydroxide and reacted to generate sodium sulfate. The sodium sulfate generated by the above reaction formula (d) can then be subjected to bipolar membrane electrodialysis treatment.

[0092] As a general example of the manufacturing process of magnetite, the following can be illustrated.

[0093] After filtration of the precipitate generated by the above reactions (d) to (e) through a filter press into an aqueous sodium hydroxide solution containing ferric sulfate, the water is evaporated and dried using waste heat gas from a cement plant. For example, the water is dried at 70°C for about 30 minutes. Then, the precipitate is crushed using a coarse pulverizer such as a hammer mill, recovered by magnetic separation, and sieved using a vibrating screen to set the particle size to 0.5 mm to 2 mm, thereby producing magnetite pulverized material.

[0094] The chemical composition of the obtained magnetite can be analyzed using a fluorescence X-ray diffraction apparatus (PRIMUS IV, manufactured by Rigaku Corporation), and for example, magnetite pulverizers with the following composition can be prepared.

[0095] Fe: 68.3%, O: 28.6%, C: 1.2%, Mn: 1.1%, Al: 0.3%, S: 0.3%, Si: 0.2%

[0096] Furthermore, after further micro-pulverizing the obtained magnetite powder, X-ray diffraction was performed using a powder X-ray diffractometer (PANalytical, X'Part Powder) with the following conditions set: measurement range: 2θ = 10–70°, step size: 0.017°, scan speed: 0.1012° / s, voltage: 45kV, current: 40mA. This confirmed that the material was magnetite.

[0097] Specifically, the X-ray diffraction pattern can be confirmed as magnetite using the crystal structure analysis software (PANalytical, X'Part High Score Plusversion 2.1b) provided in the powder X-ray diffraction apparatus.

[0098] Furthermore, the hydrogen generated by the above reactions (d) to (e) can be recycled as a heat source for the burner during cement production.

[0099] In the reduction reaction step (2) described above, nitrate nitrogen and / or nitrite nitrogen are reacted with a catalyst such as magnetite, which has a reducing effect, manufactured in the catalyst manufacturing step (7) described above, under acidic conditions to generate ammonia.

[0100] For example, a reducing catalyst such as magnetite is introduced into a liquid containing nitrate nitrogen and / or nitrite nitrogen introduced from a NOx recovery process, and a reduction reaction is carried out under acidic conditions, thereby converting all or part of the nitrate nitrogen and / or nitrite nitrogen into ammonia.

[0101] As an example, "a portion" can exemplify the conversion of 90% by volume, preferably 93% by volume, of nitrate nitrogen and / or nitrite nitrogen into ammonia.

[0102] Furthermore, in order to carry out the reduction reaction efficiently, it is preferable to maintain an equilibrium state so that oxygen does not enter the liquid containing nitrate nitrogen and / or nitrite nitrogen, for example, by carrying out the reaction in a closed state or under an inactive atmosphere.

[0103] As an example, magnetite and reduced iron obtained in the catalyst manufacturing step (7) are added to a 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, preferably 1.0 to 4.0, and more preferably 1.0 to 2.0, under acidic conditions at room temperature. The following reduction reaction is carried out for, for example, 1 to 10 hours, preferably 3 to 10 hours, while stirring.

[0104] The reduction reaction is represented by the following equations (f) to (g).

[0105] HNO3+4Fe+5H2O→NH3+4Fe(OH)2……(f)

[0106] HNO2+3Fe+4H2O→NH3+3Fe(OH)2……(g)

[0107] As an additive used to promote the reduction reaction of the above reaction formulas (f) to (g) under acidic conditions, any additive can be used as long as the pH of the aqueous solution can be adjusted to acidic and the processing of the present invention is not affected. For example, hydrochloric acid, sulfuric acid, nitric acid, etc. are suitable. Nitric acid is preferred. Sulfuric acid obtained by electrodialysis in the above catalyst manufacturing process (7) can be used, which is preferred from the point of view of recycling.

[0108] Further preferably, in order to effectively carry out the reduction treatment, continuous measurement is preferably performed using an ORP electrode, and the ORP is adjusted to -500mV to -200mV, preferably -500mV to -400mV.

[0109] Next, the liquid containing nitrate nitrogen and / or nitrite nitrogen obtained in the above reduction reaction step (2) is introduced into the ammonia recovery step (3). Figure 1 (Arrows indicating the main manufacturing process).

[0110] Next, the ammonia and the liquid containing nitrate nitrogen and / or nitrite nitrogen are adjusted to pH 8.0 to 14.0, preferably pH 10.0 to 14.0, using an alkaline agent. Then, waste heat gas from the cement plant is used for distillation to heat and vaporize the ammonia for recovery (ammonia recovery step (3)).

[0111] Regarding the waste heat gas, it can also be used to recycle the waste heat gas from the heating and concentration of ammonium nitrate prepared in the neutralization process (5) to precipitate crystals, and applied to the vaporization of ammonia in the ammonia recovery process (3).

[0112] In the recovery of ammonia by heating and vaporizing, for example, the stripping method is preferred, and the heating temperature is set to 50-70°C.

[0113] Furthermore, a portion of the vaporized ammonia is introduced into the neutralization process (5) described below, and the remaining vaporized ammonia reacts with the nitrate nitrogen and / or nitrite nitrogen remaining in the ammonium nitrate obtained by heating and concentrating the ammonium nitrate obtained in the neutralization process (5) described below, thereby improving the purity of the ammonium nitrate.

[0114] As the above-mentioned alkaline agent, any additive can be used as long as the pH of the aqueous solution can be adjusted to alkaline and the processing of the present invention is not affected. For example, sodium hydroxide, calcium hydroxide, potassium hydroxide, and magnesium hydroxide can be used. Sodium hydroxide is preferred. For example, sodium hydroxide obtained by electrodialysis in the above-mentioned catalyst manufacturing process (7) can be used, which is preferred from the point of view of recycling.

[0115] Furthermore, the residue Fe(OH)2 generated by the above reaction formulas (f) and (g) is introduced into the ammonia recovery process (3) together with ammonia and liquid containing nitrate nitrogen and / or nitrite nitrogen. After the above ammonia recovery process (3), the remaining part is subjected to solid-liquid separation. The Fe(OH)2 from the above reduction reaction process (2) and the unused remaining part of nitrate nitrogen and / or nitrite nitrogen are subjected to solid-liquid separation (solid-liquid separation process (4)).

[0116] The Fe(OH)2 separated in the above-mentioned solid-liquid separation process (4) becomes iron hydroxy oxide (reaction formula (h) below) by being exposed to air, and the iron hydroxy oxide can be reused as a cement raw material.

[0117] 4Fe(OH)2+O2→4FeO(OH)+2H2O……(h)

[0118] Next, a portion of the ammonia recovered by vaporization in the ammonia recovery step (3), the liquid containing nitrate nitrogen and / or nitrite nitrogen separated in the solid-liquid separation step (4), and the remaining portion of the 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) are introduced into the neutralization step (5) and a contact reaction is carried out to produce ammonium nitrate (e.g., with a purity of 78%).

[0119] In the neutralization process (5), a solution containing the generated ammonium nitrate and excess nitrate nitrogen and / or nitrite nitrogen not used to generate ammonium nitrate can be obtained.

[0120] For example, the reaction of nitrate nitrogen with ammonia is represented by the following formula (i), which can produce an ammonium nitrate solution with a concentration of about 78%.

[0121] HNO3+NH3→NH4NO3……(i)

[0122] The ammonium nitrate-containing liquid thus obtained is heated and distilled using waste heat gas, for example, adjusted to 170–180°C and distilled to obtain a suspension that concentrates the ammonium nitrate (e.g., with a purity of 98%), and to volatilize any residual nitrate nitrogen and / or nitrite nitrogen (HNO3 + HNO2). The volatilized HNO3 and HNO2 are preferably recycled in the neutralization step (5) described above.

[0123] Vaporized ammonia gas, which was not introduced into the neutralization step (5) above, is added to the concentrated ammonium nitrate suspension. By adding this ammonia gas, the suspension (concentrated ammonium nitrate) becomes weakly alkaline, and the purity of the ammonium nitrate (e.g., about 100%) can be increased by neutralization reaction with the residual nitrate nitrogen and / or nitrite nitrogen (HNO3 + HNO2) in the concentrated ammonium nitrate. The ammonium nitrate crystals are then precipitated and separated by cooling.

[0124] Preferably, this treatment is performed before the granulation process (6) described below.

[0125] Furthermore, the aforementioned waste heat gas can be used for the vaporization of ammonia in the aforementioned ammonia recovery process (3) after the ammonium nitrate is concentrated and precipitated.

[0126] Next, after separating the above-mentioned ammonium nitrate, granulated ammonium nitrate is manufactured using any commercially available granulator (granulation step (6)).

[0127] In the granulation process (6), it can be set up as a process of mixing light oil and the like with solid ammonium nitrate to manufacture explosives or blasting materials, for example.

[0128] The treatment method of this invention can convert nitrogen dioxide contained in cement waste gas into ammonium nitrate for utilization, effectively reduce the nitrogen dioxide content in cement waste gas to achieve denitrification, and reduce the environmental impact in the manufacturing of the reducing catalyst used in the manufacturing of ammonium nitrate. It can also utilize the waste heat gas from cement manufacturing and effectively utilize the residue obtained by the treatment method of this invention during cement manufacturing, thereby forming an environmentally excellent cycle.

[0129] Industrial availability

[0130] The present invention can efficiently denitrify nitrogen dioxide in the exhaust gas from cement plants, forming an excellent environmental cycle. Therefore, the treatment method of the present invention can be effectively applied in cement plants that manufacture cement.

Claims

1. A method for manufacturing ammonium nitrate utilizing nitrogen dioxide from cement waste gas, characterized in that, have: 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. In the reduction reaction step (2), the reduced iron and magnetite are then brought into contact with all or part of the liquid containing nitrate nitrogen and / or nitrite nitrogen obtained in the nitrogen dioxide recovery step (1) under acidic conditions to generate Fe(OH)2 and ammonia. 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. The solid-liquid separation process (4) performs solid-liquid separation on the remaining portion after the ammonia recovery process (3), and separates the Fe(OH)2 from the reduction reaction process (2) and the unused remaining portion of nitrate nitrogen and / or nitrite nitrogen from the ammonia recovery process (3). 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 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.

2. The method for manufacturing ammonium nitrate utilizing nitrogen dioxide from cement waste 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 acidic conditions; and / or reacts with unreacted sodium hydroxide after the preparation of magnetite to produce sodium sulfate, which is then recycled together with the aqueous sodium sulfate solution that has undergone solid-liquid separation in the catalyst manufacturing step (7) for the electrodialysis.

3. The method for manufacturing ammonium nitrate utilizing nitrogen dioxide from cement waste gas according to claim 1 or 2, characterized in that, In the catalyst manufacturing process (7), the hydrogen generated during the preparation of magnetite is recycled as a combustion raw material in the manufacture of cement.

4. The method for manufacturing ammonium nitrate utilizing nitrogen dioxide from cement waste gas according to claim 1 or 2, characterized in that, It also has: Granulation step (6) granulates the ammonium nitrate prepared in the neutralization step (5).

5. The method for manufacturing ammonium nitrate utilizing nitrogen dioxide from cement waste gas according to claim 1 or 2, characterized in that, The Fe(OH)2 separated in the solid-liquid separation process (4) becomes iron hydroxyl oxide by being exposed to air, and this iron hydroxyl oxide is used as a cement raw material.

6. The method for manufacturing ammonium nitrate utilizing nitrogen dioxide from cement waste gas according to claim 1, characterized in that, The ammonium nitrate prepared in the neutralization step (5) is contained in ammonium nitrate and a liquid containing nitrate nitrogen and / or nitrite nitrogen. The resulting liquid is heated and distilled to 170-180°C using waste heat gas to concentrate the ammonium nitrate. The residual nitrate nitrogen and / or nitrite nitrogen are vaporized and recycled in the neutralization step (5). A portion of the ammonia vaporized in the ammonia recovery step (3) is added to the concentrated ammonium nitrate to react with the unreacted nitrate nitrogen and / or nitrite nitrogen mixed in the concentrated ammonium nitrate to improve the purity of the ammonium nitrate. The mixture is then cooled to obtain crystallized ammonium nitrate.

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