Method for circularly absorbing nitric oxide in flue gas of industrial furnace through potassium manganate

Abstract

The invention discloses a method for circularly absorbing nitric oxide in flue gas of an industrial furnace through potassium manganate. The method comprises the following steps: introducing NO-containing flue gas into a mixed solution of KOH and K2MnO4 for absorption, and converting NO into nitrate by using Mn (II) complexation and K2MnO4 oxidation; filtering the absorption tail liquid to obtain MnO2, and crystallizing the filtrate to obtain sylvite; mnO2 and sylvite are fused, oxygen is introduced, K2MnO4 is regenerated, and K2MnO4 is recycled; nOx generated in the regeneration process returns to the hearth and is reduced into N2. According to the method, an absorption-oxidation-regeneration-reduction closed-loop system is formed, the technical problems of low NO mass transfer efficiency, high oxidant / complexing agent consumption, high operation cost, secondary pollution and the like in the existing denitration technology are solved, efficient removal (the efficiency is greater than 95%) and resource circulation of NOx are realized, and the method has the advantages of low cost and no secondary pollution.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of industrial flue gas purification, and particularly relates to a method for cyclically absorbing nitrogen monoxide in industrial furnace flue gas by using potassium manganate. BACKGROUND

[0002] Nitrogen oxides (NO x ) are one of the main atmospheric pollutants in kiln and boiler flue gas, and its deep treatment is a major challenge in the field of environmental protection. Among the NOx produced in high-temperature processes, more than 90% is nitrogen monoxide (NO), which has a stable molecular structure and extremely low water solubility, directly leading to very low direct removal efficiency of NO by traditional wet absorption technology.

[0003] At present, the treatment technology for NO mainly includes wet and dry methods, but both have significant technical bottlenecks:

[0004] (1) Wet denitration technology faces the dilemma of oxidant or complexing agent failure. The core of the wet technology is how to convert the insoluble NO into a component that is easy to absorb. The existing methods mainly include oxidation absorption method and complex absorption method. The oxidation absorption method usually uses strong oxidants such as ozone to oxidize NO in gas phase to NO2, which is then absorbed by alkaline solution. However, ozone itself has poor stability and low utilization rate, which limits the conversion rate of NO oxidation; at the same time, the escape of unreacted ozone will cause secondary pollution. Complex absorption method: transition metal complexing agents (such as Fe 2+ -EDTA, Co 2+ , etc.) are used to generate complexes with NO to improve its solubility. However, a large amount of oxygen in the flue gas will irreversibly oxidize the active center (such as Fe 2+ ) to an inactive form (such as Fe 3+ ), resulting in rapid failure of the complexing agent, which needs to be regenerated or supplemented frequently, and the operation cost is high, which makes it difficult to achieve stable industrial operation. If NO is not pre-oxidized or complexed, only strong alkali and strong oxidant solution is used to directly absorb NO, due to the huge mass transfer resistance, the absorption efficiency is usually not higher than 20%, which cannot meet the requirement of deep removal.

[0005] (2) The mainstream dry denitrification technology has high cost, poor adaptability and secondary pollution risk. The mainstream technology currently used in industry is dry method, including selective catalytic reduction (SCR) and non-selective catalytic reduction (SNCR). Although the SCR technology can achieve high denitrification efficiency, it relies on noble metal catalysts (such as V2O5-WO3 / TiO2), which not only has high initial investment cost, but also the catalyst is easily poisoned and deactivated by sulfides, alkali metals and other components in the flue gas. The SNCR technology does not rely on expensive catalysts, but it is limited to a narrow temperature window of 900-1100℃ and is very sensitive to the temperature distribution of the furnace, making it difficult to maintain stable denitrification efficiency in actual operation. In addition, both of these technologies using ammonia (NH3) as a reducing agent have the problem of secondary pollution of ammonia escape.

[0006] With the emission limit of NO x As the emission limit of NO

[0007] In summary, the existing technologies either have low efficiency and unstable operation due to the low solubility of NO and the consumption and failure of key reagents (oxidizing agent, complexing agent), or are difficult to be economically and efficiently promoted due to high investment and operating costs and poor adaptability to complex flue gas. Therefore, it has become a key problem in the field to develop an economic, efficient and resourceful NO deep treatment technology that can break through the mass transfer limitation of NO, achieve efficient circulation of the absorbent, and adapt to the complex conditions of kiln / boiler. SUMMARY

[0008] In view of the low solubility of NO in the flue gas of industrial kiln (kiln, boiler, etc.), the insufficient efficiency of traditional treatment methods, high operating cost and serious secondary pollution, the present application provides a method for recycling potassium permanganate to absorb nitrogen monoxide in the flue gas of industrial kiln, which is based on Mn(II) complexation to absorb NO, and then uses potassium permanganate to oxidize the complexed and dissolved NO to soluble NO3 -The method comprises the following steps of: absorbing NO in the industrial furnace flue gas by using a mixed solution containing potassium hydroxide and potassium manganate; filtering out manganese dioxide precipitate from the tail liquid after absorption; precipitating potassium salt crystals containing potassium nitrate and potassium hydroxide from the filtrate by reducing the temperature; melting the manganese dioxide and the potassium salt crystals and introducing oxygen to prepare potassium manganate; and recycling the potassium manganate for absorbing NO. Nitrogen oxides released in the melting process of the manganese dioxide and the potassium salt are sent to a furnace chamber, so that the NO is reduced to nitrogen by using the high-temperature atmosphere and the reducing agent such as carbon monoxide in the furnace chamber. The industrial furnace equipment resources are fully utilized, the technical bottleneck of low NO solubility and large oxidant consumption in the traditional denitration process is broken, and an innovative solution is provided for deep treatment of flue gas NO.

[0009] The technical scheme of the present application is as follows:

[0010] A method for recycling potassium manganate to absorb nitrogen monoxide in industrial furnace flue gas, comprising the following steps:

[0011] S1, absorbing: introducing the industrial furnace flue gas containing nitrogen monoxide into a mixed solution containing potassium hydroxide and potassium manganate to perform an absorption reaction, so that the nitrogen monoxide is oxidized and absorbed;

[0012] The flue gas is introduced into the K2MnO4 solution to occur the following absorption and oxidation reactions:

[0013] NO+K2MnO4→KNO3+Mn(NO3) 2，

[0014] Mn(NO3)2+NO→Mn(NO)(NO3) 2， ‌‌

[0015] Mn(NO)(NO3)2+K2MnO4→KNO3+MnO2+KOH,

[0016] Overall, the reaction is as follows:

[0017] 3K2MnO4+2NO+2H2O=2KNO3+3MnO2+4KOH.

[0018] When the flue gas containing NO just contacts the potassium manganate solution, a small amount of NO is dissolved into the solution and reacts with the potassium manganate to generate potassium nitrate and manganese nitrate, and the manganese nitrate immediately plays a role of a complexing absorbent to dissolve a large amount of NO to generate a complexed dissolved substance; the NO absorbed by the complexing is immediately oxidized to potassium nitrate by the potassium manganate, and the manganese is converted into manganese dioxide.

[0019] S2, separating: performing solid-liquid separation on the absorption tail liquid obtained in the step S1 to obtain a solid containing manganese dioxide and a filtrate containing potassium nitrate and potassium hydroxide;

[0020] S3, crystallization: the filtrate obtained in step S2 is subjected to temperature reduction crystallization, and potassium salt crystals are separated out, and the obtained mother liquor is returned to step S1 for preparation of a mixed solution; since the solubility of potassium nitrate changes significantly with temperature, the filtrate is reduced to 0-5℃ to precipitate more than 80% of potassium nitrate, and the solubility of potassium hydroxide is not sensitive to temperature, so when the absorption solution is initially prepared, a certain proportion of potassium hydroxide is added to ensure that part of the potassium hydroxide is precipitated synchronously with potassium nitrate as mixed potassium salt to meet the material requirements for compounding with manganese dioxide to regenerate potassium manganate. The mother liquor is directly returned for preparation of a mixed solution, and the material circulates in the system without causing loss.

[0021] S4, regeneration: the manganese dioxide solid obtained in step S2 and the potassium salt crystals obtained in step S3 are mixed, and a melting reaction is carried out in the presence of oxygen to regenerate potassium manganate, and the reaction formula is as follows:

[0022] MnO2+ KNO3+ KOH+ O2 K2MnO4+ NO+ NO2+ H2O.

[0023] At high temperature, the NOx decomposed returns to the furnace and reacts with carbon (C) and carbon monoxide (CO) in the furnace to be reduced to nitrogen (N2) and carbon dioxide (CO2), achieving harmless treatment, and the reaction formula is as follows:

[0024] NO2+ C→ N2+ CO2.

[0025] S5, harmless treatment: the nitrogen oxides released in the melting reaction process of step S4 are returned to the furnace of the industrial furnace, and are reduced to nitrogen by using the reducing atmosphere therein.

[0026] Further, in step S1, the industrial furnace is a kiln or / and a boiler, and the mass fraction of potassium manganate in the mixed solution is 1%-20%, and the initial mass ratio of potassium hydroxide to potassium manganate is 8-10:1.

[0027] Further, in step S1, the manganese nitrate generated by the reaction is used as an intermediate to complex and absorb nitrogen monoxide in the absorption reaction to form Mn(NO)(NO3)2, which is then oxidized by potassium manganate to generate potassium nitrate and manganese dioxide.

[0028] Further, in step S3, the temperature for temperature reduction crystallization is controlled at 0-5℃.

[0029] Further, in step S4, the temperature for melting reaction is 400-600℃.

[0030] Further, in step S4, the regenerated potassium manganate is dissolved in the mother liquor and returned to step S1 for recycling, forming a closed loop of materials.

[0031] Further, in step S5, the reducing atmosphere in the hearth is provided by carbon monoxide and / or carbon produced by incomplete combustion of the fuel, and the nitrogen oxides are reduced to nitrogen and carbon dioxide by reacting with the carbon monoxide and / or carbon.

[0032] Further, the potassium salt crystals are a mixture of potassium nitrate and potassium hydroxide, and the molar ratio is controlled by the initial amount of potassium hydroxide added in step S1 to meet the stoichiometric requirement of regenerating potassium permanganate in step S4.

[0033] The device used in the above method includes an absorption device, a solid-liquid separation device, a crystallization device, a melting regeneration device, and a reflux pipeline, the solid-liquid separation device is connected with the absorption device, the crystallization device is connected with the solid-liquid separation device, the melting regeneration device is connected with the solid-liquid separation device and the crystallization device respectively, and the reflux pipeline is used to introduce the nitrogen oxides generated by the melting regeneration device into the hearth of the industrial furnace; the absorption device is used for the absorption step; the solid-liquid separation device is used for the separation step; the crystallization device is used for the crystallization step; and the melting regeneration device is used for the regeneration step.

[0034] Further, the melting regeneration device is a high-temperature melting furnace, and is provided with an oxygen introduction interface.

[0035] The beneficial effects of the present application are:

[0036] (1) Breaking the NO mass transfer bottleneck, realizing efficient and deep denitrification: The present application creatively uses the in-situ generated Mn(II) as a complexing medium during the reaction process, significantly improving the dissolution rate and capacity of the poorly soluble NO in the liquid phase, and breaking through the mass transfer limitation of the traditional wet denitrification. Combined with the strong oxidation of K2MnO4, the complexed NO can be efficiently and quickly converted into nitrate, thereby realizing the deep removal of nitrogen monoxide. Experiments have proved that the denitrification efficiency of this method can reach more than 95%, which can meet the increasingly stringent ultra-low emission standard (such as <50mg / m 3 ), effectively solving the technical problem of low NO mass transfer efficiency.

[0037] (2) Realizing the internal circulation of the absorbent, and fundamentally solving the problems of solid waste and cost: Unlike the traditional wet method which needs to continuously add oxidizing agents or complexing agents, the present application constructs an "absorption-regeneration" internal circulation system with potassium permanganate as the core. The reaction by-products MnO2 and potassium salt can be efficiently regenerated into K2MnO4 through a simple melting process, and are recycled for the absorption process. The manganese-based material is stable in nature and has no degradation loss, which fundamentally eliminates the secondary pollutants such as waste absorbents or deactivated catalysts generated by the traditional wet method, and greatly reduces the high operating cost caused by reagent consumption and solid waste disposal.

[0038] (3) Coupled end-of-pipe treatment to achieve synergistic resource utilization of pollutants: This invention ingeniously utilizes the unique high-temperature reducing conditions of industrial furnaces (kilns / boilers) to utilize the NO generated in the regeneration process. x The byproducts are returned to the furnace, where they are used as "fuel" and reduced to harmless N2 by the C / CO present in the furnace. This design cleverly integrates the pollutant treatment process with the existing end of the process, eliminating the need for additional complex NO treatment facilities. x The treatment facilities do not increase the end-of-pipe emission load, but instead transform pollutants into harmless components, achieving a synergistic resource utilization effect of "treating waste with waste".

[0039] (4) Constructing a closed-loop technology system that combines economic efficiency and environmental friendliness: The entire process forms a complete closed loop of "complexation absorption-oxidation-separation-regeneration-reduction," with materials recycled within the system and no pollutants discharged externally. This system does not require precious metal catalysts, is unaffected by sulfide poisoning, and is highly adaptable to the complex operating conditions of industrial furnaces. Compared to the high investment and operating costs of SCR / SNCR technology, this invention provides an economically feasible solution with low energy consumption, low material consumption, and high resource utilization for NO2 in industrial furnace flue gas. x Ultra-low emissions provide a new path that combines environmental and economic benefits. Attached Figure Description

[0040] Figure 1 This is a flowchart of the process flow of the present invention. Detailed Implementation

[0041] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited thereto.

[0042] Example 1

[0043] Weigh 10 g of K₂MnO₄ and 100 g of KOH, add them to 100 mL of distilled water to prepare an absorption solution. Pour the prepared absorption solution into a 250 mL glass absorption bottle and place it in a constant temperature water bath at 25°C. Then, pass NO with a concentration of 500 mg / mL through the solution. 3 Simulated flue gas was used, with a flow rate controlled at 5 L / min. After 5 seconds of reaction, the NO concentration at the outlet dropped to 37 mg / m³. 3 The concentration remained at 20 mg / m² for the next 400 minutes. 3 -30mg / m 3mg / m3, the initial denitration efficiency was as high as 93% or more, and the continuous denitration efficiency was stabilized at 94%-96%. 3 -30mg / m 3 , the initial denitration efficiency was as high as 93% or more, and the continuous denitration efficiency was stabilized at 94%-96%.

[0044] Example 2

[0045] Take 10 grams of K2Mn04, 80 grams of KOH, add 100 mL of distilled water to prepare the absorption solution. Pour the prepared absorption solution into a 250 mL glass absorption bottle, and keep it in a constant temperature water bath at 20°C. Then, the simulated flue gas with a NO concentration of 500 mg / m3is introduced, and the gas flow is controlled at 5 L / min. After 5 seconds of reaction, the outlet NO concentration is reduced to 32 mg / m3. In the following 400 min, the outlet NO concentration is maintained at 15 mg / m3-25 mg / m3. 3 3 3 -25mg / m 3 The solution after reaction is filtered, and the filter cake is dried to obtain 4.62 grams. The filtrate is placed in a constant temperature water bath at 5°C, and the potassium salt is precipitated and dried to obtain 7.1 grams. Then, the filter cake and the potassium salt are transferred to a crucible, mixed uniformly, and placed in a muffle furnace at 500°C. Oxygen is introduced at a flow rate of 50 mL / min, and after 1 hour of heating, a dark green potassium permanganate solid is obtained. The potassium permanganate solid is cooled, dissolved in the aforementioned filtered filtrate, and then transferred to a glass absorption bottle for cyclic absorption of NO. Under the same conditions, the outlet NO concentration is still maintained at 15 mg / m3-25 mg / m3after 400 min. 3 -25mg / m 3 The initial denitration efficiency was as high as 94% or more, and the continuous denitration efficiency was stabilized at 95%-97%.

[0046] Example 3

[0047] Take 10 grams of K2Mn04, 80 grams of KOH, add 100 mL of distilled water to prepare the absorption solution. Pour the prepared absorption solution into a 250 mL glass absorption bottle, and keep it in a constant temperature water bath at 20°C. Then, the simulated flue gas with a NO concentration of 500 mg / m3is introduced, and the gas flow is controlled at 5 L / min. After 5 seconds of reaction, the outlet NO concentration is reduced to 32 mg / m3. In the following 400 min, the outlet NO concentration is maintained at 15 mg / m3-25 mg / m3. 3 3 ​​​After 400 min, the concentration of NO at the outlet is maintained at 5 mg / m 3 - 15 mg / m 3 The solution after the reaction is filtered to obtain 4.71 g of filter cake, and the filtrate is placed in a constant-temperature water bath at 5°C to precipitate potassium salt, which is dried to obtain 7.6 g. Then, the filter cake and the potassium salt are transferred to a crucible, mixed uniformly, and placed in a muffle furnace at 600°C, while oxygen is introduced at a flow rate of 40 mL / min. After 1 hour of heating, dark green potassium manganate solid is obtained. After the potassium manganate solid is cooled, it is dissolved in the aforementioned filtered filtrate and then transferred to a glass absorption bottle for cyclic absorption of NO. Under the same conditions, the concentration of NO at the outlet is maintained at 10 mg / m 3 - 20 mg / m 3 The initial denitration efficiency is as high as 98%, and the continuous denitration efficiency is stably maintained at 96%-98%.

[0048] Example 4 Verification of closed-loop circulation and long-term stability

[0049] 10 g of K2MnO4 and 90 g of KOH are weighed and dissolved in 100 mL of distilled water to prepare an absorption solution. The absorption solution is placed in a reactor at a constant temperature of 25°C, and simulated flue gas with a NO concentration of 500 mg / m 3 is introduced at a gas flow rate of 5 L / min. After 5 seconds of reaction, the concentration of NO at the outlet is reduced to 35 mg / m 3 , and is stably maintained at 20-30 mg / m 3 for the next 400 minutes. The initial denitration efficiency is as high as 93%, and the continuous denitration efficiency is stably maintained at 94%-96%.

[0050] The solution after the reaction is filtered to obtain 4.5 g of MnO2 solid. The filtrate is crystallized at 5°C to separate 7.8 g of mixed potassium salt of KNO3 and KOH. The MnO2 and the potassium salt are mixed and subjected to a melting reaction at 400°C in an oxygen atmosphere (50 mL / min) for 1 hour, successfully regenerating dark green K2MnO4 solid, with a manganese element recovery rate of more than 95%.

[0051] The regenerated K2MnO4 is dissolved in the mother liquor to prepare a new absorption solution, and three consecutive cycle experiments are performed. The denitration efficiency of each cycle is maintained at more than 90%, and the concentration of NO at the outlet is stable, proving the long-term effectiveness and stability of the closed-loop circulation of the present application, and no secondary solid waste is generated.

[0052] Comparative Example 1 Traditional alkali solution absorption method

[0053] A 100 g KOH / 100 mL water solution is prepared, and simulated flue gas is introduced under the same conditions as in Example 1. The concentration of NO at the outlet is always higher than 400 mg / m 3, the efficiency of denitration is lower than 20%, which cannot meet the emission requirements.

[0054] Comparative Example 2 Complex absorption method (Fe(II)-EDTA)

[0055] A 0.1 mol / L Fe(II)-EDTA aqueous solution was prepared and the absorption was carried out under the same conditions as in Example 1 (flue gas containing 5% O2). The initial denitration efficiency can reach 75%, but after 30 minutes of operation, the denitration efficiency rapidly decreases to below 30% due to the oxidation of Fe(II) to Fe(III) by O2 in the flue gas, which proves the instability of the traditional complexing agent.

Claims

1. A method for absorbing nitric oxide from industrial furnace flue gas using potassium manganate via a circulating process, characterized in that, Includes the following steps: S1. Absorption: Industrial furnace flue gas containing nitric oxide is passed into a mixed solution containing potassium hydroxide and potassium manganate to carry out an absorption reaction, so that nitric oxide is oxidized and absorbed. S2. Separation: The absorption tail liquid obtained in step S1 is subjected to solid-liquid separation to obtain a solid containing manganese dioxide and a filtrate containing potassium nitrate and potassium hydroxide. S3. Crystallization: Cool the filtrate obtained in step S2 to crystallize and separate the potassium salt crystals. The resulting mother liquor is returned to step S1 for preparing the mixed solution. S4. Regeneration: The manganese dioxide solid obtained in step S2 and the potassium salt crystals obtained in step S3 are mixed and melted in the presence of oxygen to regenerate potassium manganate. S5. Detoxification: The nitrogen oxides released during the melting reaction in step S4 are returned to the furnace of the industrial furnace and reduced to nitrogen gas using the reducing atmosphere therein.

2. The method for absorbing nitric oxide from industrial furnace flue gas using potassium manganate according to claim 1, characterized in that, In step S1, the industrial furnace is a kiln or / and a boiler, the mass fraction of potassium manganate in the mixed solution is 1%~20%, and the initial mass ratio of potassium hydroxide to potassium manganate is 8~10:

1.

3. The method for absorbing nitric oxide from industrial furnace flue gas using potassium manganate according to claim 1, characterized in that, In step S1, the manganese nitrate generated in the reaction is used as an intermediate to complex and absorb nitric oxide, forming Mn(NO)(NO3)2, which is then oxidized by potassium manganate to produce potassium nitrate and manganese dioxide.

4. The method for absorbing nitric oxide from industrial furnace flue gas using potassium manganate according to claim 1, characterized in that, In step S3, the temperature for cooling crystallization is controlled between 0℃ and 5℃.

5. The method for absorbing nitric oxide from industrial furnace flue gas using potassium manganate according to claim 1, characterized in that, In step S4, the temperature of the melting reaction is 400℃~600℃.

6. The method for absorbing nitric oxide from industrial furnace flue gas using potassium manganate according to claim 1, characterized in that, In step S4, the potassium manganate obtained from regeneration is dissolved in the mother liquor and then returned to step S1 for recycling, forming a closed-loop cycle of materials.

7. The method for absorbing nitric oxide from industrial furnace flue gas using potassium manganate according to claim 1, characterized in that, In step S5, the reducing atmosphere in the furnace is provided by carbon monoxide and / or carbon produced by the incomplete combustion of fuel. Nitrogen oxides react with carbon monoxide and / or carbon and are reduced to nitrogen and carbon dioxide.

8. The method for absorbing nitric oxide from industrial furnace flue gas using potassium manganate according to claim 1, characterized in that, The potassium salt crystals are a mixture of potassium nitrate and potassium hydroxide, and their molar ratio is controlled by the initial addition of potassium hydroxide in step S1 to meet the stoichiometric requirements of regenerated potassium manganate in step S4.

9. The apparatus used in the method according to any one of claims 1 to 8, characterized in that, It includes an absorption device, a solid-liquid separation device, a crystallization device, a melt regeneration device, and a reflux pipeline. The solid-liquid separation device is connected to the absorption device, the crystallization device is connected to the solid-liquid separation device, the melt regeneration device is connected to both the solid-liquid separation device and the crystallization device, and the reflux pipeline is used to introduce the nitrogen oxides generated by the melt regeneration device into the furnace of the industrial furnace.

10. The apparatus according to claim 9, characterized in that, The melting and regeneration device is a high-temperature melting furnace and is equipped with an oxygen inlet.

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