Method for circularly absorbing NO in flue gas of rotary kiln by using neutral potassium permanganate solution

Abstract

The invention discloses a method for circularly absorbing nitric oxide (NO) in flue gas of a rotary kiln by using a neutral potassium permanganate (KMnO4) solution, and belongs to the technical field of flue gas purification. The method comprises the following steps: introducing flue gas containing NO into a neutral KMnO4 solution added with EDTA (Ethylene Diamine Tetraacetic Acid) for absorption; after the absorption tail liquid is subjected to evaporation treatment, NO2 returns to the rotary kiln to be subjected to high-temperature reduction into a mixture of N2, MnO2 and KOH, the mixture is fused by utilizing flue gas of the rotary kiln, oxygen is introduced, the mixture is converted into K2MnO4, and K2MnO4 is dissolved and electrolyzed into KMnO4 to be recycled. The method is simple in process, low in operation cost and high in NO removal rate.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial flue gas purification, and particularly relates to a method for treating nitrogen monoxide in rotary kiln flue gas. Background Art

[0002] Nitrogen oxides (NO x As the primary pollutant in rotary kiln flue gas, its emission control has become a critical issue in the environmental protection field. Nitric oxide (NO) accounts for over 90% of this pollutant, and its treatment faces the following technical challenges: NO's extremely low water solubility (Henry's constant at 20°C is only 1.9×10⁻³ mol / L·atm) severely limits the efficiency of traditional wet absorption processes. While strong oxidants (such as NaClO₂, H₂O₂, or O₃) can convert NO to NO₂ or HNO₂, they suffer from low efficiency, high oxidant consumption, and high operating costs. Currently, mainstream industrial NOx treatment technologies include selective catalytic reduction (SCR) and non-selective catalytic reduction (SNCR). While SCR technology achieves high denitrification efficiency, it relies on precious metal catalysts (such as V₂O₅-WO₃ / TiO₂), resulting in high initial investment costs and susceptibility to poisoning and deactivation by flue gas components such as sulfides and alkali metals. SNCR technology, on the other hand, is limited by a narrow temperature window of 900-1100°C, making it difficult to maintain stable denitrification efficiency in practice. In addition, both technologies have the risk of causing secondary pollution. With the increasingly stringent environmental protection standards, many regions have already x The emission limit has been reduced to below 50mg / m³, which poses a severe challenge to existing technologies. Specifically, traditional SCR / SNCR technology is difficult to meet the new emission standards economically and efficiently; in addition, the by-products produced by the wet absorption process lack economic value, resulting in a waste of resources; and the existing technology has high energy consumption and complex operation and maintenance, which increases the environmental protection costs of enterprises. Therefore, it is necessary to develop a new NO2 ionizer that can overcome the limitation of NO2 solubility and realize the resource utilization of by-products. x Treatment technology is of great significance to promoting the progress of industrial flue gas treatment technology. Summary of the Invention

[0003] In response to technical problems such as low NO solubility in industrial flue gas, insufficient efficiency of traditional treatment methods, high operating costs and serious secondary pollution, the present invention provides a neutral potassium permanganate solution circulation absorption-regeneration system and method based on the synergistic effect of EDTA-Mn (II). By constructing an EDTA-Mn (II) complex solubilization system, the solubility of NO in the aqueous phase is increased to achieve efficient recovery of NO, and at the same time, the high-temperature heat energy in the rotary kiln is used to achieve the regeneration of the absorbent. This technology breaks through the technical bottlenecks of low NO solubility and high oxidant consumption in traditional denitrification processes, and provides a new method for the recovery of NO from industrial flue gas. x Governance provides innovative solutions.

[0004] The technical solution of the present invention is:

[0005] A method for absorbing NO in rotary kiln flue gas by circulating a neutral potassium permanganate solution comprises the following steps:

[0006] (1) NO absorption

[0007] When the flue gas from the rotary kiln is introduced into a neutral KMnO4 solution containing EDTA, the following oxidation reaction occurs:

[0008] MnEDTA+NO=Mn(NO)EDTA

[0009] Mn(NO)EDTA+KMnO4→KNO3+MnO2+MnEDTA

[0010] (2) Evaporation of absorption liquid and NO2 treatment

[0011] The tail liquid after absorption is evaporated through the high-temperature flue gas of the rotary kiln. The NO2 decomposed by KNO3 returns to the rotary kiln along with the water vapor. Under high temperature, NO2 reacts with the carbon (C) in the kiln and is reduced to nitrogen (N2) and carbon dioxide (2CO2), achieving harmless treatment. The remaining MnO2 and KOH after evaporation remain in the evaporator in the form of powder:

[0012] 2NO2+2C→N2+2CO2

[0013] (3) Regeneration of KMnO4

[0014] ① Melting reaction: The remaining MnO2 and KOH in (2) are melted with oxygen at high temperature to produce potassium manganate (K2MnO4) and water:

[0015] 2MnO2+4KOH+O2 2K2MnO4+2H2O

[0016] ② Electrolysis reaction: The generated K2MnO4 solution is electrolyzed to obtain KMnO4, KOH and hydrogen. The KMnO4 generated by electrolysis can be reused to absorb NO and recycled:

[0017] 2K2MnO4+2H2O 2KMnO4+2KOH+H2

[0018] Furthermore, the pH of the reaction system in step (1) should be controlled at 6-8, and the Mn(II) / EDTA molar ratio should be maintained in the range of 1:1 to 1:2.

[0019] Furthermore, the temperature in the rotary kiln in step (2) should be controlled at 600-1200°C (preferably 800-1000°C).

[0020] Furthermore, in step ①, the melting temperature should be controlled at 300-500°C, the KOH / MnO2 molar ratio should be controlled at 2:1, and the oxygen flow rate should be 1.2-1.5 times the theoretical demand.

[0021] Furthermore, the electrolysis in step ② should be controlled at a current density of 10-50 mA / cm 2 .

[0022] The beneficial effects of the present invention are:

[0023] (1) High-efficiency denitrification performance: The complex formed by EDTA and Mn(II) significantly improves the solubility of NO in the liquid phase. Combined with the strong oxidizing effect of KMnO4, NO is efficiently converted into nitrate ions. The denitrification efficiency can reach more than 90%, effectively solving the technical problem of low NO mass transfer efficiency.

[0024] (2) Operation under neutral conditions: A neutral KMnO4 solution with a pH of 6-8 is used as the absorbent to avoid corrosion of the equipment by strong acid / alkaline environments, while reducing the generation of harmful by-products. The system operates stably and reliably.

[0025] (3) Absorbent recycling: The high-temperature flue gas of the rotary kiln is used to evaporate and concentrate the absorption liquid, and the residual potassium manganese salt is melted and converted into potassium manganate, which is then regenerated into KMnO4 through an electrolytic process. This realizes the recycling of the absorbent, greatly reduces the operating cost, and solves the industry pain points of high oxidant consumption and difficult solid waste disposal in traditional wet denitrification.

[0026] (4) Advantages of synergistic emission reduction: The high temperature reducing environment in the rotary kiln can convert nitrogen oxides entering the kiln head into N2, avoiding the increase of NO at the kiln tail. x Emissions, achieving NO x The coordinated control is particularly suitable for the treatment of rotary kiln flue gas with complex composition and large temperature fluctuations.

[0027] (5) Green environmental protection and economical: The whole process forms a closed-loop system of "absorption-oxidation-regeneration", which uses the waste heat in the kiln to achieve energy recovery. It has the comprehensive advantages of low operating cost, high resource utilization rate, and environmental friendliness, and is a new energy source for industrial rotary kiln NO x Ultra-low emissions offer an economically viable solution.

[0028] By utilizing the above technical advantages, the present invention improves the denitrification efficiency while achieving the recycling of the absorbent and optimizing energy consumption, and has significant industrial application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a process flow diagram of the present invention DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited thereto.

[0031] Example 1: Standard process verification (EDTA-KMnO4 absorption + thermal energy regeneration full process)

[0032] Weigh 3.16g of KMnO4 and 1.86g of EDTA disodium salt, add them to 200mL of distilled water, and adjust the pH to 7 with 10% KOH solution to prepare an absorption solution. Pour the prepared absorption solution into a 250mL glass reaction bottle and place it in a constant temperature water bath maintained at 25°C. Then, introduce NO at a concentration of 500mg / m 3 The simulated flue gas was controlled at a gas flow rate of 5 L / min. After 30 minutes of reaction, the NO concentration at the outlet was measured by a flue gas analyzer and dropped to 38 mg / m 3 The reaction solution was transferred to a rotary evaporator and concentrated to 50 mL in an 85°C water bath. The concentrate was then placed in a muffle furnace set to 400°C while oxygen was introduced at a rate of 50 mL / min. After heating for 2 hours, a dark green potassium manganate solid was obtained. Finally, this solid was dissolved in 100 mL of water and electrolyzed using a platinum electrode for 2 hours, at which point the solution returned to its purple-red color.

[0033] Testing has shown that this process achieves a NOx removal rate of 92.5%. Comparative experiments revealed that the removal rate of the absorbent containing EDTA doubled compared to that without EDTA. During the evaporation and concentration stage, we measured that 83 kJ of heat was recovered for every liter of absorbent processed. The concentration of the potassium permanganate solution after electrolytic regeneration was 0.48 mol / L, with a regeneration efficiency of 91.3%. When the regenerated solution was used again to treat flue gas, the removal rate remained above 90%, demonstrating the stability of this circulation system. Furthermore, only 4.2% of the manganese was lost during the entire process, with the majority being recycled.

[0034] Example 2: Absorption time effect experiment

[0035] This experiment focused on observing the effects of different absorption times. Five identical absorption solutions were prepared according to the method of Example 1, and absorption experiments were conducted for 15 minutes, 30 minutes, 45 minutes, 60 minutes, and 90 minutes, respectively. Each experiment used a new absorption solution and the flue gas conditions were the same. Every 5 minutes, 1 mL of liquid was extracted with a syringe and the NO in it was detected using an ion chromatograph. 3- After the reaction was completed, all samples were evaporated, melted and electrolytically regenerated according to the method of Example 1.

[0036] Experimental data show that the removal rate is 68.3% after 15 minutes of absorption, 92.5% after 30 minutes, and 93% after 60 minutes. The effect is not obvious after extending the time. In the first 15 minutes, NO is mainly absorbed by the EDTA-Mn complex, and then KMnO4 begins to oxidize in large quantities. According to calculations, 3.1 mg of NO can be converted per minute per liter of absorption liquid. x The purity of KMnO4 after regeneration is above 98.7%, indicating that the absorption time has little effect on the regeneration effect. Taking all factors into consideration, 30 minutes is the optimal absorption time.

[0037] Example 3: Melting temperature optimization experiment

[0038] This experiment focused on optimizing the temperature of the regeneration process. The MnO2 precipitate obtained in Example 1 was divided into three portions and mixed with KOH in a 1:2 ratio. The first portion was heated in a furnace at 300°C, the second at 400°C, and the third at 500°C, all with oxygen flowing through them for 2 hours. After heating, the product composition was analyzed using an X-ray diffractometer, and then each portion was prepared into solutions for electrolytic regeneration. Each experiment was repeated three times, and the average value was calculated.

[0039] Experimental results show that the conversion rate of K2MnO4 is only 82.4% at 300°C, increasing to 95.1% at 400°C and reaching 96% at 500°C. However, excessively high temperatures lead to increased energy consumption. Specifically, at 400°C, the heat consumed per kilogram of product was 28% less than at 500°C. During electrolytic regeneration, the solution concentration obtained at 400°C was 0.49 mol / L, and the current efficiency reached 93%. Microscopic observation showed that the particles of the sample treated at 400°C were more uniform, which is very beneficial for subsequent electrolysis. Therefore, we determined that 400°C is the optimal melting temperature.

Claims

1. A method for absorbing NO in rotary kiln flue gas by circulating a neutral potassium permanganate solution, characterized in that: The following steps are involved: (1) The rotary kiln flue gas containing NO is passed into a neutral KMnO4 solution with EDTA added for absorption, so that NO is oxidized to NO2 and MnO2 and KOH are generated at the same time.

2. (2) The absorption tail liquid obtained in step (1) is evaporated using the high-temperature dust-free flue gas at the rotary kiln outlet, so that NO2 returns to the rotary kiln along with the water vapor and reacts with carbon under the high temperature conditions in the kiln to produce N2 and CO2, while recovering solid products MnO2 and KOH; (3) melting the MnO2 and KOH recovered in step (2) using high-temperature flue gas from a rotary kiln and introducing oxygen to generate K2MnO4 and H2O; (4) The K2MnO4 obtained in step (3) is made into a solution and electrolyzed to regenerate a KMnO4 solution, and the regenerated KMnO4 solution is returned to step (1) for recycling.

3. The method according to claim 1, characterized in that The mass concentration of EDTA in step (1) is 0.1%-2%, and the mass concentration of KMnO4 is 5%-30%.

4. The method according to claim 1, wherein The temperature of the melting reaction in step (3) is 300-500°C.

5. The method according to claim 1, characterized in that The current density of the electrolysis reaction in step (4) is 10-50 mA / cm².

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