Energy-saving and emission-reducing scr flue gas denitration process

Abstract

This invention discloses an energy-saving and emission-reducing SCR flue gas denitrification process in the field of flue gas denitrification technology. The process first mixes dust-removed industrial flue gas with ammonia, and adjusts the flue gas temperature and humidity through water atomization. Then, the flue gas undergoes a denitrification reaction in a reactor loaded with a ruthenium-cerium multi-active-center catalyst supported on a nitrogen-cerium modified zirconium-titanium composite oxide porous support. After the reaction, the flue gas undergoes gas-liquid separation, and the residual ammonia concentration is monitored. The entire process is automatically monitored and regulated by an intelligent control system. The core of this process lies in the catalyst preparation method, which constructs a high specific surface area nitrogen-cerium modified zirconium-titanium composite oxide porous support using sol-gel and freeze-drying technologies, followed by intermediate-temperature nitriding and bimetallic active-center loading steps, ultimately yielding a spherical catalyst with excellent low-temperature activity. This invention achieves highly efficient denitrification under low-temperature conditions, significantly reduces system energy consumption, has a simple process flow, and operates stably, making it suitable for nitrogen oxide emission reduction and treatment in various industrial scenarios.

Description

Technical Field

[0001] This invention belongs to the field of flue gas denitrification technology, specifically relating to an energy-saving and emission-reducing SCR flue gas denitrification process. Background Technology

[0002] With rapid industrialization and continuous growth in energy consumption, the environmental problems caused by nitrogen oxide emissions are becoming increasingly serious, and their harm to the atmospheric environment and human health has attracted widespread global attention. Selective catalytic reduction (SCR) technology, currently the most mature flue gas denitrification technology internationally, has been widely applied in industrial sectors such as coal-fired power plants, chemical plants, and cement kilns. This technology, under the action of a specific catalyst, selectively reduces nitrogen oxides in flue gas to harmless nitrogen and water using reducing agents such as ammonia, thereby achieving the purpose of purifying the flue gas.

[0003] Traditional selective catalytic reduction (SCR) processes commonly employ conventional vanadium-based catalysts, which face multiple challenges in practical applications. First, these catalysts require a relatively high temperature range to maintain ideal catalytic activity, typically between 300 and 400 degrees Celsius. This temperature requirement significantly increases system energy consumption and operating costs. When the flue gas temperature falls below this range, catalyst activity rapidly declines, resulting in a substantial reduction in denitrification efficiency and an inability to meet increasingly stringent emission standards. Second, traditional catalysts are susceptible to the effects of sulfur dioxide and water vapor in the flue gas at low temperatures, leading to catalyst poisoning and pore blockage, resulting in deactivation of active sites and a shortened lifespan. Furthermore, vanadium-based active components may sublimate at high temperatures, causing not only catalyst activity degradation but also posing a risk of secondary pollution. More importantly, traditional processes require the SCR reactor to be located in high-temperature zones, limiting its flexibility in complex operating conditions such as industrial kilns and hindering the full utilization of flue gas waste heat, resulting in energy waste. These technical bottlenecks severely restrict the wider application of SCR technology and impede further improvements in overall energy conservation and emission reduction.

[0004] To overcome the limitations of traditional technologies, research institutions both domestically and internationally have been dedicated to developing novel low-temperature selective catalytic reduction catalyst systems in recent years. Research focuses primarily on transition metal oxides, molecular sieve catalysts, and noble metal catalysts. While transition metal oxide catalysts, such as manganese-based and cerium-based catalysts, exhibit good activity at low temperatures, their resistance to sulfur and water is generally poor, leading to deactivation in real-world flue gas environments. Molecular sieve catalysts possess regular pore structures and tunable acidic sites, but they are prone to hydrothermal aging under high humidity conditions, resulting in structural collapse and decreased activity. Although noble metal catalysts exhibit excellent low-temperature activity, they are expensive and have a strong tendency to over-oxidize ammonia, easily generating the byproduct nitrous oxide, causing secondary pollution. Therefore, developing a novel catalyst system that combines excellent low-temperature activity, good resistance to poisoning, long service life, and reasonable cost, and then constructing an efficient and energy-saving denitrification process based on this system, has become an important development direction in this field and is key to achieving the dual goals of deep purification of industrial flue gas and energy conservation and emission reduction. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide an energy-saving and emission-reducing SCR flue gas denitrification process.

[0006] In a first aspect, the present invention provides an energy-saving and emission-reducing SCR flue gas denitrification process, comprising the following steps:

[0007] S1. The dust-removed industrial flue gas is introduced into the pretreatment tower and mixed with ammonia. The flue gas temperature is adjusted to 80-150℃ through a water spray atomization system, and the flue gas humidity is increased at the same time to obtain pretreated flue gas.

[0008] S2. The pretreated flue gas is introduced into an SCR reactor filled with a ruthenium-cerium multi-active-center catalyst supported on a nitrogen-cerium modified zirconium-titanium composite oxide porous support to obtain denitrified flue gas; the SCR reactor adopts a vertical arrangement design, and the flue gas flows from top to bottom; a catalyst bed is set inside the SCR reactor, and a rotary soot blower is installed between the beds;

[0009] S3. The denitrified flue gas is fed into a gas-liquid separator, and a laser ammonia analyzer is used to monitor the residual ammonia concentration in the flue gas in real time. The separated liquid is processed and recycled, while the gas enters the air preheater and dust removal system.

[0010] S4. A PLC / DCS control system is used to automatically monitor the entire denitrification process, and sensors collect data on temperature, pressure, and NO in real time. x The concentration and ammonia flow rate are automatically adjusted, and the amount of ammonia and water sprayed are also automatically adjusted.

[0011] In this invention, the energy-saving and emission-reducing SCR flue gas denitrification process is based on the unique performance of a novel catalyst. In the pretreatment stage, flue gas temperature and humidity are precisely controlled through water atomization. Water molecules form a thin adsorption film on the catalyst surface, effectively promoting mass transfer of reactant molecules at active sites. In the core catalytic reaction stage, ammonia molecules preferentially adsorb onto Lewis acid sites formed by cerium species, while nitrogen oxide molecules are activated at ruthenium active centers. Both react rapidly at the dual active centers constructed on the catalyst surface, following the Eley-Rideal mechanism. Gaseous or weakly adsorbed nitrogen oxide molecules react with strongly adsorbed ammonia species to generate harmless nitrogen and water. The mesoporous structure of the catalyst provides ample mass transfer channels for the reaction, while its surface properties effectively suppress side reactions, enabling the denitrification reaction to proceed efficiently at low temperatures. The entire process system optimizes reaction conditions in real time through an intelligent control unit, dynamically adjusting the dosage of reducing agent according to flue gas parameters to ensure high denitrification efficiency while minimizing ammonia slip and energy consumption. This low-temperature operation process, designed based on the characteristics of a novel catalyst, eliminates the necessary flue gas reheating step in traditional processes, fundamentally reducing energy consumption and achieving dual optimization of denitrification efficiency and operating costs.

[0012] As a preferred embodiment of the present invention, in step S1, ammonia reacts with NO in industrial flue gas. x The molar ratio is (0.8-1.0):1.

[0013] As a preferred embodiment of the present invention, in step S2, the catalyst bed consists of 2-3 layers.

[0014] As a preferred embodiment of the present invention, in step S3, the operating pressure of the gas-liquid separator is 0.1 MPa.

[0015] As a preferred technical solution of the present invention, in step S4, the PLC / DCS control system is also equipped with remote monitoring and fault diagnosis functions.

[0016] As a preferred embodiment of the present invention, the preparation steps of the ruthenium-cerium multi-active-center catalyst supported on the nitrogen-cerium modified zirconium-titanium composite oxide porous support include:

[0017] A1. Dissolve zirconium oxychloride and tetraisopropyl titanate in anhydrous ethanol to form solution A; dissolve glycerol and urea in deionized water to form solution B; add solution B dropwise to solution A while stirring at 13-17℃ to obtain a mixed solution; transfer the mixed solution to a high-pressure reactor and age it at 84-86℃ to form a transparent gel; freeze-dry the transparent gel to obtain zirconium-titanium composite oxide aerogel.

[0018] A2. The zirconium-titanium composite oxide aerogel was placed in a tube furnace and heated to 395-405℃ under nitrogen protection and held. The atmosphere was then switched to ammonia and the temperature was raised to 445-455℃ and held. After natural cooling, the powder was obtained. The powder was immersed in cerium ammonium nitrate solution and oscillated at a constant temperature of 68-72℃. After filtration, it was washed with deionized water and dried at 80-100℃ to obtain the treated nitrogen-cerium modified zirconium-titanium composite oxide porous carrier.

[0019] A3. The treated nitrogen-cerium modified zirconium-titanium composite oxide porous carrier was dispersed in a reactor containing deionized water. Ruthenium trichloride and cerium nitrate aqueous solution were added dropwise to adjust the pH value to 7.4-7.6. After the addition was completed, stirring was continued, and then sodium borohydride aqueous solution was added. The reaction was carried out under nitrogen protection to obtain solid material.

[0020] A4. Filter the solid material, wash it alternately with ethanol and deionized water, and then dry it in a vacuum drying oven at 78-82℃ to obtain the dried material. Place the dried material in a muffle furnace and heat it to 345-355℃ in an air atmosphere and hold it thereafter. Then switch to an argon atmosphere and heat it to 445-455℃ and hold it thereafter to obtain the material. Press the material into spherical particles.

[0021] In this invention, the preparation reaction mechanism of the ruthenium-cerium multi-active-center catalyst supported on a nitrogen-cerium modified zirconium-titanium composite oxide porous support involves a complex material synthesis and modification process. First, in the aerogel framework construction stage, the zirconium and titanium sources undergo synergistic hydrolysis and condensation reactions in an alcohol-water mixture. Ammonia released from the thermal decomposition of urea, along with glycerol in the system, acts as a structure-directing agent, guiding the formation of a zirconium-titanium composite hydroxide aerogel with a three-dimensional structure. This aerogel undergoes freeze-drying to maximize the preservation of its nanoporous framework, resulting in a zirconium-titanium composite oxide aerogel with an ultra-high specific surface area. Subsequently, in the carrier modification stage, during the high-temperature nitriding treatment, ammonia gas undergoes a displacement reaction with oxygen atoms on the carrier surface, introducing nitrogen into the lattice in the form of nitrogen doping. This significantly enhances the density of basic sites and electron-donating ability on the carrier surface. Simultaneously, by precisely controlling the heat treatment temperature, the porous framework of the material is preserved while achieving nitriding. In the active center construction stage, the cerium species introduced in step A2 through cerium ammonium nitrate solution impregnation are mainly anchored on the carrier framework and pore surface, enhancing carrier stability and initial surface modification, together forming a nitrogen-cerium modified zirconium-titanium composite oxide porous carrier. In step A3, the cerium nitrate loaded synergistically with ruthenium trichloride to form closely adjacent ruthenium-cerium bimetallic active centers under a mild reducing environment. At these active centers, the cerium component, with its excellent oxygen storage and release capacity, promotes the activation and adsorption of ammonia molecules, while the ruthenium component utilizes its unique d-electron orbital characteristics to efficiently activate nitrogen and oxygen molecules. Through a significant electronic synergistic effect, both components significantly reduce the activation energy barrier of the selective catalytic reduction reaction of nitrogen oxides.

[0022] As a preferred technical solution of the present invention, in step A1, the mass ratio of zirconium oxychloride, tetraisopropyl titanate, glycerol and urea is 1 : (1.1-1.3) : (0.7-0.8) : (0.2-0.3).

[0023] As a preferred embodiment of the present invention, in step A2, the temperature is raised to 395-405℃ and held for 2-4 hours; the temperature is raised to 445-455℃ and held for 4-6 hours.

[0024] As a preferred embodiment of the present invention, in step A3, the reaction time under nitrogen protection is 2-4 hours.

[0025] As a preferred embodiment of the present invention, in step A4, the temperature is raised to 345-355℃ and held for 4-6 hours; the temperature is raised to 445-455℃ and held for 2-4 hours.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) This invention achieves a breakthrough in the efficient removal of nitrogen oxides under low-temperature conditions by innovatively developing a novel catalyst and combining it with an optimized process flow. Compared with traditional selective catalytic reduction technology, the most significant technical effect of this process lies in its excellent low-temperature catalytic activity. It can stably maintain extremely high denitrification efficiency in a low-temperature range significantly lower than that of traditional processes, completely overcoming the technical bottleneck of the sharp decline in activity of traditional catalysts at low temperatures. This characteristic allows the reaction system to operate efficiently without additional heating of the flue gas, significantly reducing energy consumption. At the same time, the catalyst, through its unique dual-active-center design combined with the three-dimensional mesoporous structure of the composite support material, creates abundant active sites and excellent reactant mass transfer channels, which not only significantly improves the reaction rate but also effectively suppresses the occurrence of side reactions, keeping the ammonia escape concentration at a level far below the current environmental protection standards, thus avoiding the risk of secondary pollution.

[0028] (2) In terms of energy conservation and emission reduction, this process demonstrates comprehensive advantages. Due to the adoption of the low-temperature operation concept, the system completely eliminates the flue gas reheating device required in traditional processes, directly reducing equipment investment and operating costs, and significantly reducing energy consumption. The entire system achieves precise automated operation through an intelligent control unit, which can adjust process conditions in real time according to the inlet flue gas parameters, ensuring that the system is always in the optimal operating state, which not only guarantees denitrification efficiency but also minimizes the consumption of reducing agent. The separated liquid generated in the process is recycled after appropriate treatment, realizing water conservation and wastewater reduction. In addition, the catalytic reactor adopts a reasonable layout and multi-bed design, combined with an effective dust removal device, which effectively prevents dust accumulation and system blockage, reduces maintenance frequency and intensity, and extends the service life of the catalyst, achieving synergistic effects of energy conservation and pollutant emission reduction from multiple dimensions.

[0029] (3) Another outstanding technical effect of this invention lies in the comprehensive performance of the catalyst and the wide applicability of the process. The novel catalyst developed not only has excellent low-temperature activity, but also exhibits excellent resistance to poisoning and long-term operational stability. In complex and harsh industrial flue gas environments, the catalyst can maintain stable operation for a long time with slow activity decay, which is far superior to the performance of traditional catalysts under similar conditions. This strong environmental adaptability greatly expands the applicable scenarios of the process, enabling it to adapt to a variety of complex and changing industrial environments. At the same time, the modular system design and the introduction of intelligent monitoring functions make the process easy to install and simple to operate. It is suitable for new projects and can also be easily upgraded to existing facilities, providing a reliable and economical technical solution for the deep treatment of nitrogen oxides in a wide range of industrial fields, with significant environmental and economic benefits. Detailed Implementation

[0030] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0031] The sources of some components in the examples and comparative examples are as follows:

[0032] The zirconium oxychloride was purchased from Zhejiang Zirconium Valley Technology Co., Ltd.

[0033] The tetraisopropyl titanate was purchased from Anhui Taigexiang New Materials Co., Ltd.

[0034] The glycerol was purchased from Zibo Guangtong Chemical Co., Ltd.

[0035] The urea was purchased from Sinochem Fertilizer Co., Ltd.

[0036] The cerium ammonium nitrate was purchased from Shandong Chengxin Materials Co., Ltd. in Leshan.

[0037] The ruthenium trichloride was purchased from Heraeus Precious Metals Technologies (China) Co., Ltd.

[0038] The cerium nitrate was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0039] The sodium borohydride was purchased from Yudan Chemical Technology Co., Ltd.

[0040] Example 1: This example provides an energy-saving and emission-reducing SCR flue gas denitrification process, including the following steps:

[0041] S1. The dust-removed industrial flue gas is introduced into the pretreatment tower and mixed with ammonia. Multiple nozzles are used through a water spray atomization system to spray the gas evenly, and the flue gas temperature is precisely adjusted to 120℃. At the same time, the flue gas humidity is increased to 60% relative humidity to obtain pretreated flue gas. The molar ratio of ammonia to NOx in the industrial flue gas is 0.9.

[0042] S2. The pretreated flue gas is introduced into an SCR reactor loaded with a ruthenium-cerium multi-active-center catalyst supported on a porous carrier of nitrogen-cerium modified zirconium-titanium composite oxide. The reactor is 5m high and 2m in diameter. The flue gas flows from top to bottom at a flow rate of 0.5m / s to obtain denitrified flue gas. The SCR reactor is equipped with two catalyst beds, each with a catalyst height of 0.5m. A rotary soot blower is installed between the bed layers, with a soot blower rotation speed of 10rpm.

[0043] S3. The denitrified flue gas is fed into a gas-liquid separator. The separator operates at a pressure of 0.1 MPa. At the same time, a laser ammonia analyzer is used to monitor the residual ammonia concentration in the flue gas in real time. The residual ammonia concentration is 2 ppm. The separated liquid is filtered and pH adjusted before being recycled, while the gas enters the air preheater and dust removal system.

[0044] S4. The entire denitrification process is automatically monitored by a PLC / DCS control system. Data is collected in real time through temperature sensors, pressure sensors, NOx sensors and ammonia flow sensors, with a sampling frequency of 1 time / second. The system automatically adjusts the ammonia injection rate and water injection rate with a control accuracy of ±1%. The PLC / DCS control system is also equipped with remote monitoring and fault diagnosis functions, and transmits data in real time through the network.

[0045] The preparation steps of the ruthenium-cerium multi-active-site catalyst supported on a nitrogen-cerium modified zirconium-titanium composite oxide porous support include:

[0046] A1. Dissolve 10g zirconium oxychloride and 12g tetraisopropyl titanate in 200mL of anhydrous ethanol and stir at 300rpm for 30min using a magnetic stirrer to form a homogeneous solution A. Dissolve 7.5g glycerol and 2.5g urea in 100mL of deionized water and stir under the same conditions to form solution B. In a 15℃ constant temperature water bath, add solution B dropwise to solution A at a rate of 1 drop per second using a dropping funnel while stirring at 500rpm. After the addition is complete, continue stirring for 30min to obtain a mixed solution. Transfer the mixed solution to a 50mL high-pressure reactor and age it at 85℃ for 4h to form a transparent gel. Place the transparent gel in a freeze dryer and pre-freeze it at -50℃ for 4h. Then freeze-dry it for 24h under conditions of condenser temperature of -60℃ and vacuum degree below 10 Pa to obtain zirconium-titanium composite oxide aerogel.

[0047] A2. Place 10g of zirconium-titanium composite oxide aerogel in a tube furnace and heat it to 400℃ at 5℃ / min for 3h under nitrogen protection. Then switch to an ammonia atmosphere at a flow rate of 100mL / min and heat it to 450℃ at 5℃ / min for 5h. After naturally cooling to room temperature, obtain powder. Immerse the powder in 100mL of an aqueous solution containing 1g of cerium ammonium nitrate and shake it at 150rpm for 2h in a constant temperature shaker at 70℃. After filtration, wash it three times with 100mL of deionized water each time and dry it in an 80℃ drying oven for 4h to obtain the treated nitrogen-cerium modified zirconium-titanium composite oxide porous carrier.

[0048] A3. Disperse 10g of the treated nitrogen-cerium modified zirconium-titanium composite oxide porous carrier in a reactor containing 500mL of deionized water. Stir at 400rpm using a mechanical stirrer. Add an aqueous solution containing 0.5g of ruthenium trichloride and 0.5g of cerium nitrate dropwise over 30min. Adjust the pH to 7.5 using 1mol / L NaOH solution. After the addition is complete, continue stirring for 1h. Then add 100mL of an aqueous solution containing 0.5g of sodium borohydride. Stir at 200rpm for 3h under nitrogen protection to obtain a solid material.

[0049] A4. Filter the solid material and wash it three times alternately with ethanol and deionized water, 50 mL each time. Then dry it in a vacuum drying oven at 80°C for 6 hours to obtain the dried material. Place the dried material in a muffle furnace and heat it to 350°C at 5°C / min under an air atmosphere and hold it for 5 hours. Then switch to an argon atmosphere at a flow rate of 200 mL / min and heat it to 450°C at 5°C / min and hold it for 3 hours to obtain the material. Use a tablet press to compress the material into spherical particles with a diameter of 3 mm under a pressure of 10 MPa.

[0050] Example 2: This example provides an energy-saving and emission-reducing SCR flue gas denitrification process, including the following steps:

[0051] S1. The dust-removed industrial flue gas is introduced into the pretreatment tower and mixed with ammonia. The mixture is then sprayed evenly through multiple nozzles using a water atomization system. The flue gas temperature is precisely adjusted to 100℃, and the flue gas humidity is increased to a relative humidity of 55%, resulting in pretreated flue gas. The molar ratio of ammonia to NOx in the industrial flue gas is 0.8.

[0052] S2. The pretreated flue gas is introduced into an SCR reactor loaded with a ruthenium-cerium multi-active-center catalyst supported on a nitrogen-cerium modified zirconium-titanium composite oxide porous support. The reactor is 5m high and 2m in diameter. The flue gas flows from top to bottom at a flow rate of 0.5m / s to obtain denitrified flue gas. The SCR reactor is equipped with a catalyst bed with 3 layers. Each layer is filled with catalyst to a height of 0.5m. A rotary soot blower is installed between the bed layers with a rotation speed of 10rpm.

[0053] S3. The denitrified flue gas is fed into a gas-liquid separator. The separator operates at a pressure of 0.1 MPa. At the same time, a laser ammonia analyzer is used to monitor the residual ammonia concentration in the flue gas in real time. The residual ammonia concentration is 1 ppm. The separated liquid is filtered and pH adjusted before being recycled, while the gas enters the air preheater and dust removal system.

[0054] S4. The entire denitrification process is automatically monitored by a PLC / DCS control system. Data is collected in real time through temperature sensors, pressure sensors, NOx sensors and ammonia flow sensors, with a sampling frequency of 1 time / second. The system automatically adjusts the ammonia injection rate and water injection rate with a control accuracy of ±1%. The PLC / DCS control system is also equipped with remote monitoring and fault diagnosis functions, and transmits data in real time through the network.

[0055] The preparation steps of the ruthenium-cerium multi-active-site catalyst supported on a nitrogen-cerium modified zirconium-titanium composite oxide porous support include:

[0056] A1. Dissolve 10g of zirconium oxychloride and 11g of tetraisopropyl titanate in 200mL of anhydrous ethanol and stir at 300rpm for 30min using a magnetic stirrer to form a homogeneous solution A. Dissolve 7g of glycerol and 2g of urea in 100mL of deionized water and form solution B under the same stirring conditions. In a constant temperature water bath at 13℃, add solution B dropwise to solution A at a rate of 1 drop per second using a dropping funnel while stirring at 500rpm. After the addition is complete, continue stirring for 30min to obtain a mixed solution. Transfer the mixed solution to a 50mL high-pressure reactor and age it at 84℃ for 5h to form a transparent gel. Place the transparent gel in a freeze dryer and pre-freeze it at -45℃ for 5h. Then freeze-dry it for 26h under conditions of condenser temperature of -55℃ and vacuum degree below 15Pa to obtain zirconium-titanium composite oxide aerogel.

[0057] A2. Place 10g of zirconium-titanium composite oxide aerogel in a tube furnace and heat it to 395℃ at 5℃ / min under nitrogen protection and hold for 4h. Switch to an ammonia atmosphere with a flow rate of 100mL / min and heat it to 445℃ at 5℃ / min and hold for 6h. After naturally cooling to room temperature, obtain powder. Immerse the powder in 100mL of an aqueous solution containing 1g of cerium ammonium nitrate and shake it at 150rpm for 3h in a constant temperature shaker at 68℃. After filtration, wash it three times with 100mL of deionized water each time and dry it in an 80℃ drying oven for 4h to obtain the treated nitrogen-cerium modified zirconium-titanium composite oxide porous carrier.

[0058] A3. Disperse 10g of the treated nitrogen-cerium modified zirconium-titanium composite oxide porous carrier in a reactor containing 500mL of deionized water. Stir at 400rpm using a mechanical stirrer. Add an aqueous solution containing 0.5g of ruthenium trichloride and 0.5g of cerium nitrate dropwise over 30min. Adjust the pH to 7.4 using 1mol / L NaOH solution. After the addition is complete, continue stirring for 1h. Then add 100mL of an aqueous solution containing 0.5g of sodium borohydride. Stir at 200rpm for 2h under nitrogen protection to obtain a solid material.

[0059] A4. Filter the solid material and wash it three times alternately with ethanol and deionized water, 50 mL each time. Then dry it in a vacuum drying oven at 78°C for 8 hours to obtain the dried material. Place the dried material in a muffle furnace and heat it to 345°C at 5°C / min under an air atmosphere and hold it for 6 hours. Then switch to an argon atmosphere at a flow rate of 200 mL / min and heat it to 445°C at 5°C / min and hold it for 4 hours to obtain the material. Use a tablet press to compress the material into spherical particles with a diameter of 3 mm under a pressure of 10 MPa.

[0060] Example 3: This example provides an energy-saving and emission-reducing SCR flue gas denitrification process, including the following steps:

[0061] S1. The dust-removed industrial flue gas is introduced into the pretreatment tower and mixed with ammonia. The mixture is then sprayed evenly through multiple nozzles using a water atomization system. The flue gas temperature is precisely adjusted to 140℃, while the flue gas humidity is increased to a relative humidity of 65%, resulting in pretreated flue gas. The molar ratio of ammonia to NOx in the industrial flue gas is 1.0.

[0062] S2. The pretreated flue gas is introduced into an SCR reactor loaded with a ruthenium-cerium multi-active-center catalyst supported on a porous carrier of nitrogen-cerium modified zirconium-titanium composite oxide. The reactor is 5m high and 2m in diameter. The flue gas flows from top to bottom at a flow rate of 0.5m / s to obtain denitrified flue gas. The SCR reactor is equipped with two catalyst beds, each with a catalyst height of 0.5m. A rotary soot blower is installed between the bed layers, with a soot blower rotation speed of 10rpm.

[0063] S3. The denitrified flue gas is fed into a gas-liquid separator. The separator operates at a pressure of 0.1 MPa. At the same time, a laser ammonia analyzer is used to monitor the residual ammonia concentration in the flue gas in real time. The residual ammonia concentration is 3 ppm. The separated liquid is filtered and pH adjusted before being recycled, while the gas enters the air preheater and dust removal system.

[0064] S4. The entire denitrification process is automatically monitored by a PLC / DCS control system. Data is collected in real time through temperature sensors, pressure sensors, NOx sensors and ammonia flow sensors, with a sampling frequency of 1 time / second. The system automatically adjusts the ammonia injection rate and water injection rate with a control accuracy of ±1%. The PLC / DCS control system is also equipped with remote monitoring and fault diagnosis functions, and transmits data in real time through the network.

[0065] The preparation steps of the ruthenium-cerium multi-active-site catalyst supported on a nitrogen-cerium modified zirconium-titanium composite oxide porous support include:

[0066] A1. Dissolve 10g of zirconium oxychloride and 13g of tetraisopropyl titanate in 200mL of anhydrous ethanol and stir at 300rpm for 30min using a magnetic stirrer to form a homogeneous solution A. Dissolve 8g of glycerol and 3g of urea in 100mL of deionized water and stir under the same conditions to form solution B. In a 17℃ constant temperature water bath, add solution B dropwise to solution A at a rate of 1 drop per second using a dropping funnel while stirring at 500rpm. After the addition is complete, continue stirring for 30min to obtain a mixed solution. Transfer the mixed solution to a 50mL high-pressure reactor and age it at 86℃ for 3h to form a transparent gel. Place the transparent gel in a freeze dryer and pre-freeze it at -55℃ for 3h. Then freeze-dry it for 22h under conditions of -65℃ condenser temperature and vacuum degree below 8Pa to obtain zirconium-titanium composite oxide aerogel.

[0067] A2. Place 10g of zirconium-titanium composite oxide aerogel in a tube furnace and heat it to 405℃ at 5℃ / min for 2h under nitrogen protection. Then switch to an ammonia atmosphere at a flow rate of 100mL / min and heat it to 455℃ at 5℃ / min for 4h. After naturally cooling to room temperature, obtain powder. Immerse the powder in 100mL of an aqueous solution containing 1g of cerium ammonium nitrate and shake it at 150rpm for 1h in a constant temperature shaker at 72℃. After filtration, wash it three times with 100mL of deionized water each time and dry it in an 80℃ drying oven for 4h to obtain the treated nitrogen-cerium modified zirconium-titanium composite oxide porous carrier.

[0068] A3. Disperse 10g of the treated nitrogen-cerium modified zirconium-titanium composite oxide porous carrier in a reactor containing 500mL of deionized water. Stir at 400rpm using a mechanical stirrer. Add an aqueous solution containing 0.5g of ruthenium trichloride and 0.5g of cerium nitrate dropwise over 30min. Adjust the pH to 7.6 using 1mol / L NaOH solution. After the addition is complete, continue stirring for 1h. Then add 100mL of an aqueous solution containing 0.5g of sodium borohydride. Stir at 200rpm for 4h under nitrogen protection to obtain a solid material.

[0069] A4. Filter the solid material and wash it three times alternately with ethanol and deionized water, 50 mL each time. Then dry it in a vacuum drying oven at 82°C for 4 hours to obtain the dried material. Place the dried material in a muffle furnace and heat it to 355°C at 5°C / min under an air atmosphere and hold it for 4 hours. Then switch to an argon atmosphere at a flow rate of 200 mL / min and heat it to 455°C at 5°C / min and hold it for 2 hours to obtain the material. Use a tablet press to compress the material into spherical particles with a diameter of 3 mm under a pressure of 10 MPa.

[0070] Comparative Example 1

[0071] The difference between this comparative example and Example 1 is that glycerol is omitted in catalyst preparation step A1.

[0072] Comparative Example 2

[0073] The difference between this comparative example and Example 1 is that urea is omitted in catalyst preparation step A1.

[0074] Comparative Example 3

[0075] The difference between this comparative example and Example 1 is that cerium ammonium nitrate is omitted in catalyst preparation step A2, and deionized water is used instead of cerium ammonium nitrate solution.

[0076] In accordance with national and industry standard testing specifications, the energy-saving and emission-reducing SCR flue gas denitrification processes provided in the above embodiments and comparative examples were tested using the following methods:

[0077] The ruthenium-cerium multi-active-center catalyst samples prepared in Examples 1-3 and Comparative Examples 1-3, supported on porous carriers of nitrogen-cerium modified zirconium-titanium composite oxides, were pressed into spherical particles with a diameter of 3 mm using a tablet press at 10 MPa. 5.00 g of the sample was accurately weighed and packed into a quartz fixed-bed reactor with an inner diameter of 20 mm and a length of 500 mm. The reactor was equipped with a three-stage independently temperature-controlled heating furnace to ensure uniform axial temperature. The mixed gas simulating industrial flue gas was precisely controlled by a mass flow meter, with a composition of 500 ppm NO, 500 ppm NH3, 5% O2, and 10% H2O (volume fraction), with the remainder being high-purity N2 as a balance gas. The total gas flow rate was controlled at 1.67 L / min. The reactor temperature was precisely controlled at 120 °C using a PID temperature control system and a K-type thermocouple, the reaction pressure was atmospheric pressure (101.325 kPa), and the gas hourly space velocity (GHSV) was set to 10000 h⁻¹. -1 Gas sampling points were set up at the reactor inlet and outlet, and NO was measured every 5 minutes using a Testo 350 flue gas analyzer. x The concentration was measured with an accuracy of ±1 ppm. Simultaneously, a Horiba VA-5000 laser ammonia analyzer was used to continuously monitor the ammonia slip concentration in the outlet gas with an accuracy of ±0.1 ppm. Each sample was pretreated under reaction conditions for 1 hour before testing to reach a stable state. The formal test lasted 2 hours. All experimental data were automatically recorded through a data acquisition system. Each sample was tested three times, and the final result was the arithmetic mean. After the test, the catalyst was weighed to assess its mechanical stability.

[0078] The performance test data above are shown in Table 1.

[0079] Table 1 Performance Test Results

[0080] ;

[0081] As can be seen from the above, Examples 1-3 effectively solve two key technical problems existing in the current SCR technology compared with Comparative Examples 1-3: First, NO under low temperature conditions x The problem of insufficient conversion efficiency, NO in Examples 1-3 xThe conversion rates all reached over 97.8%, significantly higher than the 85.4-90.3% of Comparative Examples 1-3. This was mainly due to the complete catalyst preparation system. Glycerol, as a pore-forming agent, formed a well-developed hierarchical pore structure. The nitrogen species generated during the heat treatment of urea enhanced the acidity of the support. The pretreatment of cerium ammonium nitrate introduced cerium species, enhancing the redox capacity. The synergistic effect of these three factors significantly improved the number of low-temperature active sites and mass transfer efficiency of the catalyst. Secondly, there was the secondary pollution problem caused by poor control of ammonia slip concentration. The ammonia slip concentration in Examples 1-3 was controlled within the range of 1.3-3.0 ppm. Within the range, it is far lower than the 5.3-7.2 ppm of comparative examples 1-3. This is because the complete catalyst composition forms a synergistic effect of multiple active centers of ruthenium and cerium, which optimizes the adsorption-activation-reaction pathway of ammonia and improves ammonia utilization efficiency. Among them, the mesoporous structure constructed by glycerol promotes reactant diffusion, the basic sites derived from urea enhance the activation ability of ammonia, and the cerium species introduced by cerium ammonium nitrate promotes the rapid conversion of intermediate products. Thus, while ensuring high denitrification efficiency, it significantly reduces the risk of ammonia escape and solves the technical problem of traditional SCR catalysts being unable to balance activity and selectivity under low temperature conditions.

Claims

1. An energy-saving and emission-reducing SCR flue gas denitrification process, characterized in that, Includes the following steps: S1. The dust-removed industrial flue gas is introduced into the pretreatment tower and mixed with ammonia. The flue gas temperature is adjusted to 80-150℃ through a water spray atomization system, and the flue gas humidity is increased at the same time to obtain pretreated flue gas. S2. The pretreated flue gas is introduced into an SCR reactor filled with a ruthenium-cerium multi-active-center catalyst supported on a nitrogen-cerium modified zirconium-titanium composite oxide porous support to obtain denitrified flue gas; the SCR reactor adopts a vertical arrangement design, and the flue gas flows from top to bottom; a catalyst bed is set inside the SCR reactor, and a rotary soot blower is installed between the beds; S3. The denitrified flue gas is fed into a gas-liquid separator, and a laser ammonia analyzer is used to monitor the residual ammonia concentration in the flue gas in real time. The separated liquid is processed and recycled, while the gas enters the air preheater and dust removal system. S4. A PLC / DCS control system is used to automatically monitor the entire denitrification process, and sensors collect data on temperature, pressure, and NO in real time. x The concentration and ammonia flow rate are automatically adjusted, and the amount of ammonia and water sprayed is also automatically adjusted. The preparation steps of the ruthenium-cerium multi-active-center catalyst supported on the nitrogen-cerium modified zirconium-titanium composite oxide porous support include: A1. Dissolve zirconium oxychloride and tetraisopropyl titanate in anhydrous ethanol to form solution A; Glycerol and urea were dissolved in deionized water to form solution B; solution B was added dropwise to solution A under stirring at 13-17℃ to obtain a mixed solution; the mixed solution was transferred to a high-pressure reactor and aged at 84-86℃ to form a transparent gel; the transparent gel was freeze-dried to obtain zirconium-titanium composite oxide aerogel. A2. The zirconium-titanium composite oxide aerogel was placed in a tube furnace and heated to 395-405℃ under nitrogen protection and held. The atmosphere was then switched to ammonia and the temperature was raised to 445-455℃ and held. After natural cooling, the powder was obtained. The powder was immersed in cerium ammonium nitrate solution and oscillated at a constant temperature of 68-72℃. After filtration, it was washed with deionized water and dried at 80-100℃ to obtain the treated nitrogen-cerium modified zirconium-titanium composite oxide porous carrier. A3. The treated nitrogen-cerium modified zirconium-titanium composite oxide porous carrier was dispersed in a reactor containing deionized water. Ruthenium trichloride and cerium nitrate aqueous solution were added dropwise to adjust the pH value to 7.4-7.

6. After the addition was completed, stirring was continued, and then sodium borohydride aqueous solution was added. The reaction was carried out under nitrogen protection to obtain solid material. A4. Filter the solid material, wash it alternately with ethanol and deionized water, and then dry it in a vacuum drying oven at 78-82℃ to obtain the dried material. Place the dried material in a muffle furnace and heat it to 345-355℃ in an air atmosphere and hold it thereafter. Then switch to an argon atmosphere and heat it to 445-455℃ and hold it thereafter to obtain the material. Press the material into spherical particles.

2. The energy-saving and emission-reducing SCR flue gas denitrification process according to claim 1, characterized in that, In step S1, ammonia reacts with NO in industrial flue gas. x The molar ratio is (0.8-1.0):

1.

3. The energy-saving and emission-reducing SCR flue gas denitrification process according to claim 1, characterized in that, In step S2, the catalyst bed consists of 2-3 layers.

4. The energy-saving and emission-reducing SCR flue gas denitrification process according to claim 1, characterized in that, In step S3, the operating pressure of the gas-liquid separator is 0.1 MPa.

5. The energy-saving and emission-reducing SCR flue gas denitrification process according to claim 1, characterized in that, In step S4, the PLC / DCS control system is also equipped with remote monitoring and fault diagnosis functions.

6. The energy-saving and emission-reducing SCR flue gas denitrification process according to claim 1, characterized in that, In step A1, the mass ratio of zirconium oxychloride, tetraisopropyl titanate, glycerol and urea is 1 : (1.1-1.3) : (0.7-0.8) : (0.2-0.3).

7. The energy-saving and emission-reducing SCR flue gas denitrification process according to claim 1, characterized in that, In step A2, the temperature is raised to 395-405℃ and held for 2-4 hours; the temperature is raised to 445-455℃ and held for 4-6 hours.

8. The energy-saving and emission-reducing SCR flue gas denitrification process according to claim 1, characterized in that, In step A3, the reaction time under nitrogen protection is 2-4 hours.

9. The energy-saving and emission-reducing SCR flue gas denitrification process according to claim 1, characterized in that, In step A4, the temperature is raised to 345-355℃ and held for 4-6 hours; the temperature is raised to 445-455℃ and held for 2-4 hours.