Manganese nitride catalyst, preparation method and enamelled wire waste gas comprehensive treatment system

Abstract

The invention relates to a manganese nitride catalyst, a preparation method and an enamelled wire waste gas comprehensive treatment system, the manganese nitride catalyst contains an active component, the active component is a Mn3N2-CeO2-Fe2O3 ternary heterostructure, and the molar ratio of a manganese element to a cerium element to an iron element is 5: 3: 2. The manganese nitride catalyst has a good catalytic oxidation effect on NO in waste gas, and an enameled wire waste gas comprehensive treatment system using the manganese nitride catalyst can effectively reduce the content of VOCs in the waste gas and improve the conversion rate of nitrogen oxides.

Description

Technical Field

[0001] The present invention relates to the field of waste gas treatment, and in particular to a manganese nitride catalyst, a preparation method and a comprehensive waste gas treatment system for enameled wires. Background Art

[0002] During the enameled wire production process, high-temperature exhaust gases containing nitrogen oxides (NOx), volatile organic compounds (VOCs), and particulate matter are emitted. To reduce these environmental pollutants and prevent harm to human health, these exhaust gases must be effectively purified.

[0003] Currently, selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR) are the most widely used denitrification technologies in industry. SNCR reduces NOx to nitrogen by injecting a reducing agent (such as ammonia or urea) into a high-temperature region (850-1100°C). However, the SNCR process relies on a precise temperature window, and the complex temperature distribution of actual flue gas makes it difficult to ensure that the reducing agent fully reacts within the optimal reaction range. This results in large fluctuations in denitrification efficiency (typically below 60%) and is prone to problems such as ammonia slip and the deposition of secondary pollutants (such as ammonium bisulfate). In contrast, SCR technology achieves efficient and selective NOx reduction using a catalyst at moderate temperatures and is currently one of the most mature and efficient industrial denitrification technologies. However, SCR also has limitations, such as insufficient catalytic activity at low temperatures, susceptibility to catalyst deactivation due to sulfur poisoning, a strong dependence on precious metals or rare earth materials, and high operating costs. Furthermore, SCR systems primarily target NOx removal and are difficult to simultaneously treat VOCs. These systems typically require the integration of additional treatment processes, resulting in increased equipment investment, complex system architecture, and increased operational and maintenance burdens. On the other hand, if the NOx absorption method is adopted, the waste liquid after NOx absorption contains a large amount of soluble salts. In order to reduce the processing volume, facilitate resource recovery or meet emission standards, it needs to be treated by evaporation and concentration. This process has high energy consumption and also increases the system operating cost to a certain extent. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the first object of the present invention is to provide a manganese nitride catalyst that has a good catalytic oxidation effect on NO in exhaust gas.

[0005] The second object of the present invention is to provide a method for preparing the manganese nitride catalyst, which can effectively prepare the manganese nitride catalyst.

[0006] A third object of the present invention is to provide a method for denitrifying exhaust gas using the manganese nitride catalyst.

[0007] The fourth object of the present invention is to provide an enameled wire exhaust gas comprehensive treatment system using the manganese nitride catalyst, which can effectively reduce the VOCs content in the exhaust gas and improve the removal rate of nitrogen oxides.

[0008] To achieve the first object of the present invention, the present invention provides a manganese nitride catalyst containing an active ingredient, wherein the active ingredient is a Mn3N2-CeO2-Fe2O3 ternary heterostructure, wherein the molar ratio of manganese element, cerium element and iron element is 5:3:2.

[0009] In some embodiments of the present invention, the manganese nitride catalyst further contains a carrier, the carrier is a honeycomb ceramic, the honeycomb ceramic is cordierite, and the mesh number of the honeycomb ceramic is 1500 mesh; the active ingredient accounts for 20-30% by mass in the manganese nitride catalyst.

[0010] In some embodiments of the present invention, the specific surface area of the manganese nitride catalyst is ≥120m 2 / g, and the pore size distribution is 3 to 8 nm.

[0011] To achieve the second purpose of the present invention, the present invention provides a method for preparing a manganese nitride catalyst as described in any of the above schemes, which comprises the following steps: step 1: immersing the honeycomb ceramic in an aluminum nitrate solution; step 2: mixing a mixed solution of manganese nitrate, cerium nitrate, and ferric nitrate with ammonia water, and immersing the honeycomb ceramic into the mixed solution for co-precipitation; step 3: calcining the solid obtained in step 2 under a mixed atmosphere of NH3 and N2; step 4: reducing in nitrogen containing H2.

[0012] In some embodiments of the present invention, in step 2, the mixed solution of manganese nitrate, cerium nitrate and ferric nitrate is mixed with ammonia water, the pH is adjusted to within the range of 9.0 to 10.0, and the mixture is stirred and aged at 60° C. for 6 hours; the immersion time is 24 hours.

[0013] In some embodiments of the present invention, in step three, the volume ratio of NH3 to N2 is 1:4, the calcination temperature is 650°C, and the calcination time is 4 hours.

[0014] In some embodiments of the present invention, in step 4, the volume content of H2 in the H2-containing nitrogen is 5%, the reduction temperature is 300°C, and the reduction time is 2 hours.

[0015] To achieve the third object of the present invention, the present invention provides a method for denitrifying exhaust gas, wherein nitrogen oxides are catalytically oxidized using the manganese nitride catalyst described in any of the above schemes, and the catalytic oxidation temperature is 250-300°C.

[0016] To achieve the fourth objective of the present invention, the present invention provides a comprehensive treatment system for enameled wire exhaust gas, which includes: an oxygen content adjustment unit for inputting air into the exhaust gas to increase the oxygen volume content of the resulting mixed gas to 16-18%; a two-stage catalytic reaction unit, arranged downstream of the oxygen content adjustment unit, the two-stage catalytic reaction unit comprising a primary non-catalytic oxidation section and a secondary catalytic oxidation section arranged in sequence; wherein the temperature of the primary non-catalytic oxidation section is 250-300°C, and the secondary catalytic oxidation section uses a manganese nitride catalyst, the manganese nitride catalyst is the manganese nitride catalyst according to any one of claims 1 to 3, or the manganese nitride catalyst obtained by the preparation method according to claim 4 or 5; a spray absorption unit, arranged downstream of the secondary catalytic oxidation section, the spray absorption unit comprising an alkaline solution spray circulation system.

[0017] In some embodiments of the present invention, the enameled wire waste gas comprehensive treatment system further includes: a waste heat collection unit for collecting heat from the waste gas; and a waste heat evaporation unit for evaporating the waste liquid from the spray absorption unit using the collected heat.

[0018] In some embodiments of the present invention, the comprehensive treatment system for enameled wire waste gas also includes a main exhaust pipe and an outlet cooling end exhaust pipe respectively coming out of the drying furnace; the oxygen content adjustment unit inputs air from the outlet cooling end exhaust pipe, so that the temperature of the outlet cooling end exhaust pipe drops to 100-150°C, and the mixed gas of the outlet cooling end exhaust pipe is passed to the main exhaust pipe; the main exhaust pipe leads to the first-level non-catalytic oxidation section.

[0019] In some embodiments of the present invention, the first end of the waste heat collection unit is connected to the outlet cooling end discharge pipe, the main discharge pipe, the oxygen content adjustment unit, the primary non-catalytic oxidation section, the secondary catalytic oxidation section, the spray absorption unit or at least one point between two adjacent ones; the second end of the waste heat collection unit is connected to the waste heat evaporation unit; the waste heat collection unit uses air, exhaust gas or other media to transfer heat.

[0020] In some embodiments of the present invention, the spray absorption unit further includes a pH online monitoring system, which is used to detect the pH value of the alkaline solution. When the pH value is greater than or equal to a preset value, the spray absorption unit uses the alkaline solution for spray circulation; when the pH value is less than the preset value, the spray absorption unit transports the alkaline solution to the waste heat evaporation unit.

[0021] In some embodiments of the present invention, the waste heat evaporation unit evaporates the waste liquid at a temperature above 200° C., and the gauge pressure of the waste heat evaporation unit is -15 kPa.

[0022] In some embodiments of the present invention, the comprehensive treatment system for enameled wire exhaust gas also includes a PLC control system, which is respectively connected to and controls the oxygen content adjustment unit, the two-stage catalytic reaction unit, the spray absorption unit, the waste heat collection unit and the waste heat evaporation unit.

[0023] In some embodiments of the present invention, the average residence time of the exhaust gas in the primary non-catalytic oxidation section is 2 to 3 seconds.

[0024] In some embodiments of the present invention, the space velocity of the manganese nitride catalyst in the secondary catalytic oxidation section is controlled at 8000 h-1.

[0025] In some embodiments of the present invention, the alkaline solution is a NaOH solution, and the pH value of the alkaline solution is above 8.5.

[0026] In some embodiments of the present invention, the comprehensive treatment system for enameled wire waste gas also includes an online pollutant monitoring system and an exhaust gas return system. The online pollutant monitoring system is arranged downstream of the spray absorption unit to detect whether the treated exhaust gas meets the exhaust standards. The exhaust gas return system is used to transport the exhaust gas that does not meet the exhaust standards after detection by the online pollutant monitoring system back to the upstream of the first-level non-catalytic oxidation section.

[0027] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0028] The Mn3N2-CeO2-Fe2O3 ternary catalyst provided by the present invention is formed through the synthesis process of the present invention. It has a ternary heterogeneous structure composed of Mn3N2 with high charge transfer efficiency, CeO2 with excellent oxygen storage capacity, and Fe2O3 with stable structure. It exhibits excellent low-temperature activity at 250-300°C and is suitable for catalytic oxidation of nitrogen oxides in exhaust gas, with a high conversion rate to NO. The comprehensive enameled wire exhaust gas treatment system provided by the present invention achieves a total NOx removal rate of >90%, a VOCs removal rate of >85%, and a catalyst poisoning rate of <5% through a process combination of oxygen content adjustment, graded catalysis, and alkaline solution absorption. In addition, the comprehensive enameled wire exhaust gas treatment system can also include waste heat recovery and waste heat evaporation processes. The process of using waste gas waste heat to evaporate and concentrate waste liquid can reduce treatment costs by 45%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a scanning electron microscope morphology image of a catalyst embodiment of the present invention;

[0030] Figure 2 This is a process flow chart of an embodiment of the comprehensive treatment system for enameled wire waste gas of the present invention.

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. DETAILED DESCRIPTION

[0032] An embodiment of the present invention provides a manganese nitride catalyst containing an active ingredient, which is a Mn3N2-CeO2-Fe2O3 ternary heterostructure, wherein the molar ratio of manganese element, cerium element and iron element is 5:3:2.

[0033] The novel catalyst provided in this embodiment is particularly suitable for the catalytic oxidation reaction of nitrogen oxides. This embodiment innovatively uses manganese nitride as a catalyst. Unlike conventional oxide catalysts, the metal-nitrogen covalent bond strength of the manganese nitride catalyst is lower than that of conventional metal oxides, and it has better electronic conductivity, which is conducive to the rapid migration of electrons in the surface redox reaction and accelerates the oxidation reaction rate of NO. At the same time, the nitride is more stable to SO2, which can maintain more stable catalytic performance and extend the service life; cerium oxide has excellent oxygen storage / release capacity, which can continuously provide active oxygen species to the reaction system and accelerate the catalytic cycle reaction; iron oxide has good thermal stability and structural support performance while assisting the electron transfer process on the catalyst surface, which can improve the mechanical strength and high temperature resistance of the overall catalyst. These three active components can form a heterojunction at the contact interface, forming a built-in electric field through charge rearrangement to further promote the charge transfer process inside the material, significantly improving the catalyst's oxidation activity and conversion efficiency for NO.

[0034] In some examples, the manganese nitride catalyst of this embodiment also contains a carrier, which is a honeycomb ceramic made of cordierite. In addition to several active components, the cordierite substrate has a weak binding affinity with SO2, which can inhibit SO2 poisoning reactions. The honeycomb ceramic has a mesh size of 1500, which facilitates the adhesion and dispersion of the active components. The active components account for 20-30% by weight of the manganese nitride catalyst.

[0035] In some examples, the manganese nitride catalyst of this embodiment consists of a carrier and an Mn3N2-CeO2-Fe2O3 active component, and no other substances are added except the carrier and the active component.

[0036] In some examples, the specific surface area of the manganese nitride catalyst is ≥120 m 2 / g, pore size distribution is 3~8nm. The morphology of manganese nitride catalyst is as follows Figure 1 The above specific surface area and pore size are beneficial to improving the catalytic efficiency of the manganese nitride catalyst.

[0037] In some examples, the method for preparing the manganese nitride catalyst includes the following steps:

[0038] Step 1: Immerse the honeycomb ceramic in an aluminum nitrate solution. Use the aluminum nitrate solution to pretreat the substrate or carrier, which is beneficial to the subsequent precipitation of manganese, cerium and iron compounds. After pretreatment, the aluminum nitrate solution can be filtered out and then the step 2 reaction can be carried out.

[0039] Step 2: Mix a solution of manganese nitrate, cerium nitrate, and iron nitrate with ammonia water. Immerse the honeycomb ceramic in the mixture for co-precipitation, loading the active ingredient onto the honeycomb ceramic. After co-precipitation, the liquid can be filtered to remove the solid, and the solid can be dried to proceed to step 3.

[0040] Step 3: calcining the solid obtained in step 2 in a mixed atmosphere of NH3 and N2 for nitriding treatment.

[0041] Step 4: Reduce in nitrogen containing H2 to activate the catalyst.

[0042] As can be seen from the above, the preparation method of the manganese nitride catalyst of this embodiment has simple and controllable steps, and can effectively load the Mn3N2-CeO2-Fe2O3 active components onto the honeycomb ceramic to obtain a manganese nitride catalyst with good oxidation catalysis for NO.

[0043] In some examples, in step 2, the pH is adjusted to a range of 9.0 to 10.0, the mixing includes stirring and aging at 60° C. for 6 hours, and the impregnation time is 24 hours, so that manganese, cerium and iron form hydroxide precipitates.

[0044] In some examples, in step three, the volume ratio of NH3 to N2 is 1:4, the calcination temperature is 650°C, and the calcination time is 4 hours, so as to fully react to form manganese nitride, cerium oxide, and iron oxide.

[0045] In some examples, in step 4, the H 2 content in the H 2 -containing nitrogen is 5% by volume, the reduction temperature is 300° C., and the reduction time is 2 hours.

[0046] In some examples, this embodiment also provides a method for denitrifying exhaust gas, using the above-mentioned manganese nitride catalyst to catalytically oxidize nitrogen oxides at a temperature of 250 to 300°C. The manganese nitride catalyst of this embodiment exhibits excellent low-temperature activity at 250 to 300°C.

[0047] In some examples, this embodiment also provides a comprehensive treatment system for enameled wire exhaust gas, such as Figure 2 As shown, the system includes an oxygen content adjustment unit 1, a two-stage catalytic reaction unit and a spray absorption unit 4.

[0048] Among them, the oxygen content adjustment unit 1 is used to input air into the exhaust gas to increase the oxygen volume content of the obtained mixed gas to 16-18%. The air uses ordinary air with an oxygen content of 21 vol%. By mixing with air, the oxygen content (volume content) of the waste gas can be adjusted from 12-14% to 16-18%.

[0049] The two-stage catalytic reaction unit is located downstream of the oxygen content adjustment unit 1. In this embodiment, the term "downstream" refers to the downstream direction of the waste flow. The two-stage catalytic reaction unit includes a primary non-catalytic oxidation section 2 and a secondary catalytic oxidation section 3, which are arranged in sequence. The secondary catalytic oxidation section 3 is located downstream of the primary non-catalytic oxidation section 2.

[0050] The temperature of the primary non-catalytic oxidation stage 2 is 250-300°C. This temperature can be maintained by utilizing the heat released by the oxidation of VOCs and NO. The temperature can be controlled by adjusting the waste gas flow rate. The secondary catalytic oxidation stage 3 utilizes the manganese nitride catalyst of this embodiment. In other words, the catalytic reaction unit of this embodiment comprises two stages of catalytic oxidation.

[0051] The spray absorption unit 4 is located downstream of the secondary catalytic oxidation stage 3 and includes an alkaline solution spray circulation system. Exhaust gas can enter the spray absorption unit 4 from the bottom and exit from the top. The alkaline solution is sprayed downward from the top to absorb NO2 contained in the exhaust gas itself and the NO2 obtained after the oxidation of NO.

[0052] This embodiment addresses the existing issues of low NOx catalytic oxidation efficiency and the difficulty in simultaneously treating VOCs, thereby providing a comprehensive enameled wire exhaust gas treatment system capable of treating VOCs and achieving a high NOx conversion rate. This system achieves synergistic NO and VOC oxidation through oxygen content regulation technology, and achieves a high NOx conversion rate through hierarchical catalysis technology and a novel, highly efficient catalyst.

[0053] Specifically, this embodiment can precisely adjust the oxidation rate of NO to NO2 by controlling the oxygen concentration in the reaction system and using a graded catalytic strategy, and promote the oxidation of VOCs by controlling the oxygen-rich environment. In addition, the introduction of the non-catalytic section can also basically separate the oxidation process of VOCs and NO, allowing the decomposition process of VOCs to be concentrated in the non-catalytic section, avoiding the decomposition of VOCs on the catalyst surface to form a surface carbon layer, resulting in a decrease in catalytic activity; at the same time, precise control of the oxygen content can prevent excessive oxygen from causing excessive accumulation of NO2 or oxidation poisoning of the catalyst surface, thereby ensuring stable operation of the catalytic section and catalyst life. This embodiment, combined with oxygen concentration control and a graded catalytic strategy, achieves a total NO conversion rate of over 90%, a VOCs removal rate of over 85%, and a catalyst poisoning rate of less than 5%.

[0054] In some examples, the comprehensive enameled wire waste gas treatment system also includes: a waste heat collection unit 5 for collecting waste gas heat; and a waste heat evaporation unit 6 for using the collected heat to evaporate the waste liquid from the spray absorption unit 4. This embodiment also introduces a heat exchange device to recover sensible heat from the high-temperature waste gas for use in the waste liquid evaporation process, significantly reducing equipment energy consumption, achieving effective utilization of waste heat resources, significantly reducing energy consumption, and lowering waste gas treatment costs by 45%.

[0055] In some examples, the comprehensive waste gas treatment system for enameled wire also includes a main exhaust pipe 8 and an outlet cooling end exhaust pipe 9, each exiting from the drying furnace 7. The main exhaust pipe 8 is the primary channel for exhaust gas discharge, while the outlet cooling end exhaust pipe 9 is the channel for cooling and discharging the enameled wire. The outlet cooling end exhaust pipe 9 also contains some exhaust gas. The oxygen content adjustment unit 1 inputs air from the outlet cooling end exhaust pipe 9, lowering the temperature of the outlet cooling end exhaust pipe 9 to 100-150°C, thereby cooling the wire. The mixed gas from the outlet cooling end exhaust pipe 9 is then passed to the main exhaust pipe 8, where it is mixed with the exhaust gas from the main exhaust pipe 8 and treated together. The main exhaust pipe 8 leads to the primary non-catalytic oxidation stage 2.

[0056] In some examples, the first end of the waste heat collection unit 5 is connected to the outlet cooling end discharge pipe 9, the main discharge pipe 8, the oxygen content adjustment unit 1, the primary non-catalytic oxidation section 2, the secondary catalytic oxidation section 3, the spray absorption unit 4, or at least one location between two adjacent ones thereof, to collect heat from the aforementioned components or pipes. The second end of the waste heat collection unit 5 is connected to the waste heat evaporation unit 6, which releases the collected heat to the waste heat evaporation unit 6 for waste liquid evaporation. The waste heat collection unit 5 transfers heat using air, exhaust gas, or other media, and can utilize the sensible heat or latent heat of the aforementioned media for heat transfer. The aforementioned media can circulate between the first and second ends of the waste heat collection unit 5.

[0057] In some examples, the spray absorption unit 4 further includes an online pH monitoring system 12 for detecting the pH value of the alkaline solution. For example, the online pH monitoring system 12 can be connected in series to the spray circulation pipeline of the alkaline solution spray circulation system of the spray absorption unit 4. When the pH value is greater than or equal to a preset value, the spray absorption unit 4 uses the alkaline solution for spray circulation. When the pH value is less than the preset value, the spray absorption unit 4 transfers the alkaline solution to the waste heat evaporation unit 6 for treatment or recovery. The preset value can be, for example, 8.5.

[0058] In some examples, the waste heat evaporation unit 6 evaporates the waste liquid at a temperature above 200° C., and the gauge pressure of the waste heat evaporation unit 6 is −15 kPa, which can improve the evaporation concentration efficiency.

[0059] In some examples, the comprehensive treatment system for enameled wire waste gas also includes a PLC control system, which respectively connects and controls the oxygen content adjustment unit 1, the two-stage catalytic reaction unit, the spray absorption unit 4, the waste heat collection unit 5 and the waste heat evaporation unit 6 to precisely control the entire system.

[0060] In some examples, the average residence time of the exhaust gas in the primary non-catalytic oxidation section 2 is 2 to 3 seconds, which means that the treatment time is short and the treatment efficiency is high.

[0061] In some examples, the space velocity of the manganese nitride catalyst in the secondary catalytic oxidation section 3 is controlled at 8000 h -1 , which is beneficial to the complete oxidation of NO and improves the treatment efficiency.

[0062] In some examples, the alkaline solution is a NaOH solution, and the pH value of the alkaline solution is above 8.5, for example, above 10, or above 13, to achieve efficient absorption of NO2.

[0063] In some examples, the comprehensive treatment system for enameled wire waste gas also includes an online pollutant monitoring system 10 and an exhaust gas return system 11. The online pollutant monitoring system 10 is arranged downstream of the spray absorption unit 4 to detect whether the treated exhaust gas meets the exhaust standards. The exhaust gas return system 11 is used to transport the exhaust gas that does not meet the exhaust standards after detection by the online pollutant monitoring system 10 back to the upstream of the first-level non-catalytic oxidation section 2.

[0064] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0065] Example 1

[0066] The preparation method of the catalyst of this embodiment adopts the following steps:

[0067] Manganese nitrate, cerium nitrate, and iron nitrate were dissolved in deionized water at a molar ratio of 5:3:2. Ammonia was added to adjust the pH to 9.2 and the mixture was aged at 60°C for 6 hours with stirring. A cordierite honeycomb (1500 mesh), pre-treated by impregnation with aluminum nitrate, was immersed in the resulting solution for 24 hours. After drying at 120°C, the mixture was calcined at 650°C in a muffle furnace for 4 hours. The mixture was then nitrided in a mixed atmosphere of NH3 / N2 (volume ratio 1:4), and finally activated in a 5% H2 atmosphere.

[0068] The process flow of the comprehensive treatment system for enameled wire waste gas in this embodiment is as follows: Figure 1As shown, the factory exhaust gas is discharged from the drying furnace 7 in two directions, namely the main exhaust pipe 8 and the outlet cooling end exhaust pipe 9. The outlet cooling end exhaust pipe 9 is connected to the main exhaust pipe 8 through the oxygen content regulating unit 1 to complete the adjustment of the oxygen content in the pipeline. The oxygen content is adjusted from about 13% to about 17%. The oxygen-enriched air is mixed with the exhaust gas and enters the primary non-catalytic oxidation section 2. The primary oxidation is completed at 300°C, VOCs are oxidized, and the NO conversion rate reaches 50%. The exhaust gas then enters the secondary catalytic oxidation section 3. NO is further oxidized under the action of the catalyst. The exhaust gas after the secondary oxidation is mainly NO2 and enters the spray absorption unit 4 to achieve efficient NOx control. The waste heat collection unit 5 collects the heat of the pipeline. After the spray tower absorbs the waste liquid, it enters the waste heat evaporation unit 6 and is evaporated and concentrated using the pipeline temperature of 200°C. The space velocity of the catalyst in this embodiment is controlled at 8000h -1 . In the catalytic reaction tower, the exhaust gas will stay in the first-level non-catalytic oxidation section 2 for 2-3 seconds. During this process, about 50% of NO will be oxidized to NO2. At the same time, VOCs will be fully oxidized and removed in an atmosphere with a high oxygen content to avoid decomposition in the catalytic oxidation section and covering the catalyst surface, causing the catalyst to be deactivated. After leaving the first-level non-catalytic oxidation section 2, the exhaust gas reaches the second-level catalytic oxidation section 3 filled with Mn3N2-CeO2-Fe2O3 / honeycomb ceramic catalyst for further full oxidation. Subsequently, the exhaust gas enters the spray tower of the spray absorption unit 4 for absorption and conversion of nitrogen oxides. Sodium hydroxide solution is used to convert all NO2 into sodium nitrate and sodium nitrite. The reaction principle is as follows:

[0069] 2NO2+2NaOH→NaNO2+NaNO3+H2O

[0070] The concentration of the NaOH solution used in this example is 0.5 mol / L.

[0071] Since there may still be a small amount of NO in the exhaust gas that is difficult to absorb, the exhaust gas after spraying treatment enters the pollutant online monitoring system 10 to determine whether it meets the emission standards. If it meets the requirements, it can be discharged.

[0072] After absorbing nitrogen oxides, the wastewater passes through an online pH monitoring system 12. If the wastewater pH does not drop to 8.5, a spray solution is circulated to improve alkali utilization. In this embodiment, the spray solution circulation rate is 8 m³ / h. If the wastewater pH drops below 8.5, the wastewater is discharged into the waste heat evaporation unit 6. Heat from the waste heat collection unit 5 is used for evaporation, producing a concentrated solution. In this embodiment, the evaporator operating pressure is -15 kPa (gauge pressure).

[0073] This embodiment uses a PLC control system to realize real-time analysis and processing of parameters during operation, thereby performing fully automatic control.

[0074] Comparative Example 1

[0075] The ternary catalyst used in Example 1 was replaced with a conventional V2O5-WO3 / TiO2 catalyst, and the other process flows were the same as in Example 1.

[0076] Comparative Example 2

[0077] The graded catalytic unit in Example 1 was replaced with a separate catalytic oxidation section, and the other process flows were the same as in Example 1.

[0078] Comparative Example 3

[0079] The oxygen content of the waste gas was controlled at 14%, and the other process flows were the same as those in Example 1.

[0080] The harmful substances in the waste gas after treatment in the above examples and comparative examples were analyzed, and the catalyst poisoning was tested. The above tests were all performed using conventional methods and equipment in the art.

[0081] The harmful substances in the exhaust gas and the catalyst poisoning rate after treatment with different catalysts are shown in Table 1.

[0082] Table 1 Results of harmful substances in exhaust gas and catalyst poisoning rates in different experiments

[0083] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 NO conversion rate (%) 95.3 65.1 75.6 70.8 VOCs removal rate (%) 96.2 93.6 46.8 31.7 <![CDATA[SO2 poisoning rate (%)]]> ＜5 ＞30 ＜5 ＜5

[0084] After adopting the above technical solution, the beneficial effects of this embodiment are:

[0085] The new three-way catalyst prepared in the embodiment of the present invention has a significantly higher NO conversion rate than the control sample. In comparative example 1, a conventional catalyst is used, and its NO conversion rate is significantly lower than that of the embodiment. The simultaneous use of a graded catalytic strategy and oxygen content control can effectively improve the NO conversion rate and reduce the VOCs content. Comparative example 2 uses a single catalytic strategy and is inferior to the embodiment in both exhaust gas VOCs content and NO conversion rate. The oxygen content of comparative example 3 does not reach the design range, and the exhaust gas pollutant removal efficiency is also significantly poor. In addition to the above advantages, the use of waste heat from exhaust gas to evaporate the absorption waste liquid can significantly reduce the energy consumption of the device, achieving a 45% reduction in energy consumption.

[0086] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A manganese nitride catalyst, characterized in that It contains active ingredients, which are a ternary heterogeneous structure of Mn3N2-CeO2-Fe2O3, wherein the molar ratio of manganese element, cerium element and iron element is 5:3:

2.

2. A manganese nitride catalyst according to claim 1, characterized in that The catalyst further comprises a carrier, which is a honeycomb ceramic, which is cordierite, and has a mesh size of 1500 meshes; and the active component accounts for 20 to 30% by mass in the manganese nitride catalyst.

3. A manganese nitride catalyst according to claim 2, characterized in that The specific surface area of the manganese nitride catalyst is ≥120 m2 / g, and the pore size distribution is 3-8 nm.

4. The method for preparing a manganese nitride catalyst according to any one of claims 2 to 3, characterized in that The following steps are involved: Step 1: Immerse the honeycomb ceramic in aluminum nitrate solution; Step 2: mixing a mixed solution of manganese nitrate, cerium nitrate and iron nitrate with ammonia water, and immersing the honeycomb ceramic into the mixed solution for co-precipitation; Step 3: calcining the solid obtained in step 2 under a mixed atmosphere of NH3 and N2; Step 4: Reduction in nitrogen containing H2.

5. The method for preparing a manganese nitride catalyst according to claim 4, characterized in that In the second step, a mixed solution of manganese nitrate, cerium nitrate and iron nitrate is mixed with ammonia water, the pH value is adjusted to 9.0 to 10.0, and the mixture is stirred and aged at 60° C. for 6 hours; the immersion time is 24 hours; In the step 3, the volume ratio of NH3 to N2 is 1:4, the calcination temperature is 650°C, and the calcination time is 4 hours; In the step 4, the volume content of H2 in the H2-containing nitrogen is 5%, the reduction temperature is 300°C, and the reduction time is 2 hours.

6. A method for denitrifying waste gas, characterized in that Nitrogen oxides are catalytically oxidized using a manganese nitride catalyst, wherein the manganese nitride catalyst is the manganese nitride catalyst according to any one of claims 1 to 3, or the manganese nitride catalyst obtained by the preparation method according to claim 4 or 5, and the catalytic oxidation temperature is 250-300°C.

7. A comprehensive treatment system for enameled wire waste gas, characterized in that include: An oxygen content regulating unit is used to input air into the exhaust gas to increase the oxygen content of the resulting mixed gas to 16-18% by volume; A two-stage catalytic reaction unit is provided downstream of the oxygen content regulating unit, the two-stage catalytic reaction unit comprising a primary non-catalytic oxidation section and a secondary catalytic oxidation section arranged in sequence; wherein the temperature of the primary non-catalytic oxidation section is 250-300° C., and the secondary catalytic oxidation section uses a manganese nitride catalyst, the manganese nitride catalyst being the manganese nitride catalyst according to any one of claims 1 to 3, or the manganese nitride catalyst obtained by the preparation method according to claim 4 or 5; The spray absorption unit is arranged downstream of the secondary catalytic oxidation section, and the spray absorption unit comprises an alkaline solution spray circulation system.

8. The comprehensive treatment system for enameled wire waste gas according to claim 7 is characterized in that Also includes: a waste heat collection unit, configured to collect heat from the waste gas; The waste heat evaporation unit uses the collected heat to evaporate the waste liquid from the spray absorption unit.

9. The comprehensive treatment system for enameled wire waste gas according to claim 8 is characterized in that The enameled wire exhaust gas comprehensive treatment system also includes a main exhaust pipe and an outlet cooling end exhaust pipe respectively exiting the drying furnace; the oxygen content regulating unit inputs air through the outlet cooling end exhaust pipe, so that the temperature of the outlet cooling end exhaust pipe is reduced to 100-150°C, and the mixed gas from the outlet cooling end exhaust pipe is passed to the main exhaust pipe; the main exhaust pipe is connected to the primary non-catalytic oxidation section; The first end of the waste heat collection unit is connected to the outlet cooling end discharge pipe, the main discharge pipe, the oxygen content adjustment unit, the primary non-catalytic oxidation section, the secondary catalytic oxidation section, the spray absorption unit, or at least one point between two adjacent ones; the second end of the waste heat collection unit is connected to the waste heat evaporation unit; the waste heat collection unit transfers heat using air, exhaust gas, or other media; The spray absorption unit further includes a pH online monitoring system, which is used to detect the pH value of the alkaline solution. When the pH value is greater than or equal to a preset value, the spray absorption unit uses the alkaline solution for spray circulation. When the pH value is less than the preset value, the spray absorption unit transports the alkaline solution to the waste heat evaporation unit. The waste heat evaporation unit evaporates the waste liquid at a temperature above 200° C., and the gauge pressure of the waste heat evaporation unit is -15 kPa; The enameled wire exhaust comprehensive treatment system also includes a PLC control system, which is respectively connected to and controls the oxygen content adjustment unit, the two-stage catalytic reaction unit, the spray absorption unit, the waste heat collection unit and the waste heat evaporation unit.

10. The comprehensive treatment system for enameled wire waste gas according to claim 9, characterized in that The average residence time of the exhaust gas in the primary non-catalytic oxidation section is 2 to 3 seconds; The space velocity of the manganese nitride catalyst in the secondary catalytic oxidation section is controlled at 8000 h -1 ; The alkaline solution is a NaOH solution, and the pH value of the alkaline solution is above 8.5; The comprehensive treatment system for enameled wire waste gas also includes an online pollutant monitoring system and an exhaust gas return system. The online pollutant monitoring system is arranged downstream of the spray absorption unit to detect whether the treated exhaust gas meets the exhaust standards. The exhaust gas return system is used to transport the exhaust gas that does not meet the exhaust standards after detection by the online pollutant monitoring system back to the upstream of the first-level non-catalytic oxidation section.

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