Denitration catalyst with high specific surface area as well as preparation method and application thereof
By using a titanium-silicon composite oxide support and the modified component Ce0.6Zr0.4O2 in the SCR denitrification catalyst, combined with a supercritical drying process, the problem of low specific surface area of the TiO2 support was solved, achieving efficient medium- and low-temperature denitrification and sulfur resistance performance, which is suitable for flue gas denitrification systems in thermal power and steel industries.
Patent Information
- Application Number
- CN202511980942.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-25
- Publication Date
- 2026-05-12
AI Technical Summary
The TiO2 support of existing SCR denitration catalysts has a low specific surface area, resulting in poor dispersion of active components, insufficient low-temperature activity and resistance to sulfur poisoning. In addition, the traditional modified support preparation process is complex and costly, making it difficult to apply industrially.
Using titanium-silicon composite oxide as a carrier, V2O5, WO3 and modified component Ce0.6Zr0.4O2 are loaded and prepared by stepwise sol-gel method combined with supercritical drying process to ensure uniform dispersion of active components and improve specific surface area and sulfur resistance.
A catalyst with a specific surface area ≥220m2/g was prepared, which has a denitrification efficiency ≥95% in the temperature range of 200℃ to 400℃, excellent sulfur resistance, and is suitable for denitrification of flue gas at medium and low temperatures. The preparation process was simplified and the cost was reduced.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of environmental catalysis technology, specifically a high specific surface area denitrification catalyst and its preparation method, as well as the application of this high specific surface area denitrification catalyst in medium and low temperature flue gas denitrification. Background Technology
[0002] Nitrogen oxides (NO) x Nitrogen oxides (NOx) are major air pollutants emitted by industries such as thermal power, steel, and chemicals, leading to environmental problems such as acid rain and photochemical smog. Selective catalytic reduction (SCR) technology is currently the most mature and widely used denitrification technology, and its core lies in the denitrification catalyst.
[0003] Chinese patent document CN103586017A discloses a method for preparing titanium-tungsten powder for flue gas denitrification catalyst and the product prepared therefrom. Specifically, it provides a titanium-tungsten powder for flue gas denitrification catalyst. The method includes: (1) preparing metatitanic acid: adding titanium oxysulfate solution and dispersant I to a constant temperature reactor, adding carbonate aqueous solution dropwise to the constant temperature reactor under stirring conditions, adjusting the solid matter in the mixed solution in the constant temperature reactor, washing and drying the solid matter to obtain metatitanic acid particles; (2) preparing composite particles: crushing the metatitanic acid particles prepared in step 1, dissolving them in a second reactor containing tungsten solution, adding Tween 80 to the tungsten solution, raising the temperature to 80-90℃, until the water in the second reactor is basically evaporated to obtain composite particles; (3) post-treatment: drying the composite particles, and then calcining them at 500-600℃ for 3-5 hours to obtain the product. Chinese patent document CN102166514A discloses a method for preparing a structured flue gas denitrification catalyst, the prepared catalyst, and its application. The method involves preparing titanium dioxide powder containing WO3 by premixing TiO2 powder with an oxalic acid solution containing ammonium metatungstate; then mixing the prepared titanium dioxide powder, inorganic binder, plasticizer, glass fiber, and guar gum powder in a specific mass ratio, adding an oxalic acid solution containing ammonium metavanadate and a cerium nitrate aqueous solution, adjusting the pH to 9-10 with ammonia, and aging for 5-10 days; finally, coating the aged material onto a stainless steel mesh, rolling it into shape, and then drying and calcining it to obtain a plate-type structured V2O5 / TiO2-based denitrification catalyst.
[0004] Currently, most existing SCR denitrification catalysts use TiO2 as a support, loaded with components such as V2O5 and WO3. Traditional TiO2 supports have a relatively low specific surface area (typically ≤150 m²). 2The presence of a specific surface area ( / g) leads to poor dispersion of the active component, resulting in insufficient low-temperature activity (200℃ to 300℃) and resistance to sulfur poisoning. Furthermore, while some modified supports can increase the specific surface area, their preparation processes are complex and costly, hindering industrial application. Therefore, developing a denitrification catalyst with high specific surface area, high activity, excellent sulfur resistance, and simple preparation is of great significance. Summary of the Invention
[0005] This invention provides a high specific surface area denitrification catalyst and its preparation method, which overcomes the shortcomings of the prior art. By optimizing the support composition and preparation process, and combining the introduction of modified components, the specific surface area, activity and sulfur resistance of the catalyst are improved.
[0006] One of the technical solutions of the present invention is achieved through the following measures: a high specific surface area denitrification catalyst, comprising the following components by mass percentage: 55% to 80% titanium-silicon composite oxide support, 1.5% to 5.0% active component, 5% to 15% co-catalyst, and 8% to 25% modified component; wherein the molar ratio of Si to Ti in the titanium-silicon composite oxide support is 0.05 to 0.15:1.
[0007] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions: The specific surface area of the aforementioned titanium-silicon composite oxide carrier is 280 m². 2 / g to 350m 2 / g.
[0008] The active component mentioned above is V2O5.
[0009] The aforementioned co-catalyst is WO3.
[0010] The modified component mentioned above is Ce 0.6 Zr 0.4 O2, Ce 0.6 Zr 0.4 The particle size of O2 ranges from 15 nm to 30 nm.
[0011] The above-mentioned high specific surface area denitration catalyst was prepared according to the following steps: Step 1: The titanium-silicon composite sol is dried under supercritical CO2 conditions. After calcination of the dried product, a titanium-silicon composite oxide carrier is obtained. Step 2: Dissolve ammonium metavanadate in oxalic acid solution, then add ammonium tungstate and Ce. 0.6 Zr 0.4 O2 powder is dispersed to obtain an impregnation solution; Step 3: Impregnate the titanium-silicon composite oxide support in the impregnation solution. After impregnation, the product is dried and calcined to obtain a high specific surface area denitrification catalyst.
[0012] In step one above, the titanium-silicon composite sol is prepared according to the following steps: Tetrabutyl titanate was dissolved in ethanol, added to citric acid solution, and stirred until homogeneous to obtain titanium sol; Tetraethyl orthosilicate was dissolved in ethanol and then added dropwise to titanium sol. The pH was adjusted to 3.5 to 4.5 with ammonia and stirred until homogeneous to obtain a composite sol.
[0013] The volume ratio of tetrabutyl titanate to ethanol is 1:3 to 1:5, the mass concentration of citric acid solution is 10% to 15%, and the amount of citric acid solution used is 0.5 to 1.5 times that of ethanol.
[0014] The volume ratio of tetraethyl orthosilicate to ethanol is 1:20 to 1:30.
[0015] In step one above, the supercritical conditions for CO2 are: drying at a temperature of 31℃ to 35℃ and a pressure of 7.5mPa to 8.0mPa for 3h to 6h; and calcination at a temperature of 550℃ to 600℃ for 4h to 6h.
[0016] In step two above, Ce 0.6 Zr 0.4 O2 was prepared by a co-precipitation method, with ammonium bicarbonate as the precipitant. The co-precipitated product was calcined to obtain Ce. 0.6 Zr 0.4 O2; roasting temperature is 500℃ to 550℃, roasting time is 3h to 4h.
[0017] In step two above, the molar ratio of ammonium metavanadate, ammonium tungstate, and oxalic acid is (1.5 to 2.5): (2 to 2.5): (3.5 to 4.5).
[0018] In step three above, the immersion temperature is 50℃ to 70℃, and the immersion time is 3 to 5 hours.
[0019] In step three above, drying is performed at 100℃ to 120℃ for 10 to 15 hours, and calcination is performed at 450℃ to 500℃ for 5 to 8 hours.
[0020] The second technical solution of the present invention is achieved through the following measures: a method for preparing a high specific surface area denitration catalyst, comprising the following steps: Step 1: The titanium-silicon composite sol is dried under supercritical CO2 conditions. After calcination of the dried product, a titanium-silicon composite oxide carrier is obtained. Step 2: Dissolve ammonium metavanadate in oxalic acid solution, then add ammonium tungstate and Ce. 0.6 Zr 0.4 O2 powder is dispersed to obtain an impregnation solution; Step 3: Impregnate the titanium-silicon composite oxide support in the impregnation solution. After impregnation, the product is dried and calcined to obtain a high specific surface area denitrification catalyst.
[0021] The third technical solution of the present invention is achieved through the following measures: the application of a high specific surface area denitrification catalyst in flue gas denitrification.
[0022] The above application conditions are: flue gas temperature 200℃ to 400℃, space velocity 15000h. -1 Up to 30000h -1 NH3 and NO in flue gas x The molar ratio is 0.9 to 1.1, and the NO inlet of the flue gas denitrification system is... x Concentration of 500 mg / m 3 Up to 1500 mg / m 3 .
[0023] This invention provides a high specific surface area denitrification catalyst and its preparation method. The catalyst uses a titanium-silicon composite oxide as a support, loading the active component vanadium oxide, the co-catalyst tungsten oxide, and the modifying component cerium-zirconium solid solution. The support is prepared by a stepwise sol-gel method combined with supercritical drying, and then the active and co-catalyst components are loaded using an impregnation method, ultimately yielding a catalyst with a specific surface area ≥220 m². 2 A denitrification catalyst with a denitrification efficiency of ≥95% in the temperature range of 200℃ to 400℃ and excellent resistance to sulfur poisoning, which can be widely used in flue gas denitrification scenarios in industries such as thermal power and steel. Detailed Implementation
[0024] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.
[0025] The present invention will be further described below with reference to embodiments: Example 1: The high specific surface area denitrification catalyst comprises the following components by mass percentage: 55% to 80% titanium-silicon composite oxide support, 1.5% to 5.0% active component, 5% to 15% co-catalyst, and 8% to 25% modified component; in the titanium-silicon composite oxide support, the molar ratio of Si to Ti is 0.05 to 0.15:1.
[0026] Example 2: As an optimization of the above example, the specific surface area of the titanium-silicon composite oxide carrier is 280 m². 2 / g to 350m 2 / g.
[0027] Example 3: As an optimization of the above example, the active component is V2O5.
[0028] Example 4: As an optimization of the above examples, the co-catalyst is WO3.
[0029] Example 5: As an optimization of the above examples, the modified component is Ce. 0.6 Zr 0.4 O2, Ce 0.6 Zr 0.4 The particle size of O2 ranges from 15 nm to 30 nm.
[0030] Example 6: The preparation method of this high specific surface area denitration catalyst includes the following steps: Step 1: The titanium-silicon composite sol is dried under supercritical CO2 conditions. After calcination of the dried product, a titanium-silicon composite oxide carrier is obtained. Step 2: Dissolve ammonium metavanadate in oxalic acid solution, then add ammonium tungstate and Ce. 0.6 Zr 0.4 O2 powder is dispersed to obtain an impregnation solution; Step 3: Impregnate the titanium-silicon composite oxide support in the impregnation solution. After impregnation, the product is dried and calcined to obtain a high specific surface area denitrification catalyst.
[0031] Example 7: As an optimization of the above examples, in step one, the titanium-silicon composite sol is prepared according to the following steps: Tetrabutyl titanate was dissolved in ethanol, added to citric acid solution, and stirred until homogeneous to obtain titanium sol; Tetraethyl orthosilicate was dissolved in ethanol and then added dropwise to titanium sol. The pH was adjusted to 3.5 to 4.5 with ammonia and stirred until homogeneous to obtain a composite sol.
[0032] The volume ratio of tetrabutyl titanate to ethanol is 1:3 to 1:5, the mass concentration of citric acid solution is 10% to 15%, and the amount of citric acid solution used is 0.5 to 1.5 times that of ethanol.
[0033] The volume ratio of tetraethyl orthosilicate to ethanol is 1:20 to 1:30.
[0034] Example 8: As an optimization of the above example, in step one, the supercritical conditions for CO2 are: drying at a temperature of 31°C to 35°C and a pressure of 7.5mPa to 8.0mPa for 3 to 6 hours; and calcination at a temperature of 550°C to 600°C for 4 to 6 hours.
[0035] Example 9: As an optimization of the above embodiment, in step two, Ce 0.6 Zr 0.4 O2 was prepared by a co-precipitation method, with ammonium bicarbonate as the precipitant. The co-precipitated product was calcined to obtain Ce.0.6 Zr 0.4 O2; roasting temperature is 500℃ to 550℃, roasting time is 3h to 4h.
[0036] Example 10: As an optimization of the above example, in step two, the molar ratio of ammonium metavanadate, ammonium tungstate, and oxalic acid is (1.5 to 2.5): (2 to 2.5): (3.5 to 4.5).
[0037] Example 11: As an optimization of the above example, in step three, the immersion temperature is 50°C to 70°C, and the immersion time is 3 to 5 hours.
[0038] Example 12: As an optimization of the above example, in step three, drying is performed at 100°C to 120°C for 10 to 15 hours, and calcination is performed at 450°C to 500°C for 5 to 8 hours.
[0039] Example 13: Application of the high specific surface area denitrification catalyst in flue gas denitrification.
[0040] Example 14: As an optimization of the above examples, the application conditions are: flue gas temperature 200°C to 400°C, space velocity 15000 h⁻¹. -1 Up to 30000h -1 NH3 and NO in flue gas x The molar ratio is 0.9 to 1.1, and the NO inlet of the flue gas denitrification system is... x Concentration of 500 mg / m 3 Up to 1500 mg / m 3 .
[0041] Example 15: (1) Preparation of titanium-silicon composite oxide carrier: Dissolve 10 mL of tetrabutyl titanate in 30 mL of ethanol, add 20 mL of 12% citric acid solution, and stir for 1 h to obtain titanium sol. Dissolve 0.8 mL of tetraethyl orthosilicate in 10 mL of ethanol, add it dropwise to the titanium sol, adjust the pH of the system to 4.0 with ammonia, and stir for 2 h to obtain a titanium-silicon composite sol; The titanium-silicon composite sol was placed in a supercritical drying apparatus and dried at 32℃ and 7.8 mPa for 4 h. The dried product was then calcined at 580℃ for 5 h to obtain a titanium-silicon composite oxide carrier with a measured specific surface area of 295 m². 2 / g.
[0042] (2) Preparation of impregnation solution: Dissolve 0.004 mol ammonium metavanadate (NH4VO3) in 10 mL of oxalic acid solution (containing 0.008 mol oxalic acid), then add 0.004 mol ammonium tungstate ((NH4)2WO4) and 2.0 g Ce. 0.6 Zr0.4 O2 (calcined at 520℃ for 3.5h, particle size 22nm) was ultrasonically dispersed for 30min to obtain the impregnation solution.
[0043] (3) Load and molding: 5g of carrier was immersed in impregnation solution, impregnated in water bath at 60℃ for 4h, dried at 110℃ for 12h, calcined at 480℃ for 6h, and pressed into Φ5×5mm particles to obtain a high specific surface area denitrification catalyst.
[0044] Example 16: The difference from Example 15 is that in step (1), the amount of tetraethyl orthosilicate used is 0.4 mL, and in step (2), Ce... 0.6 Zr 0.4 The amount of O2 added is 2.0g.
[0045] Example 17: The difference from Example 15 is that in step (1), the amount of tetraethyl orthosilicate used is 0.6 mL, and in step (2), Ce... 0.6 Zr 0.4 The amount of O2 added is 1.5g.
[0046] Example 18: The difference from Example 15 is that in step (1), the amount of tetraethyl orthosilicate used is 0.4 mL, and in step (2), Ce... 0.6 Zr 0.4 The amount of O2 added is 1.0g.
[0047] Comparative Example: The difference from Example 15 is that a pure TiO2 support (specific surface area 142 m²) was used. 2 / g) Replace the titanium-silicon composite oxide carrier. The remaining components and preparation steps are the same as in Example 15.
[0048] Performance testing: The specific surface area of the catalysts in Examples 15 to 18 and the comparative examples was tested, and the results are shown in Table 1.
[0049] Referring to GB / T 33104-2024 "Test Method for Marine SCR Cellular Denitrification Catalysts", a specific standard for marine cellular SCR catalysts is established. Testing is conducted at 350℃ under specific flue gas composition conditions (500ppm NO, 500ppm NH3, 5% O2, N2 equilibrium). The standard requires that NO levels under these conditions be [not specified in the original text]. x A conversion rate of ≥90% is used as the basis for determining the denitrification efficiency.
[0050] Referring to EN12952-12: the EU certification standard for SCR denitrification equipment in boiler systems, it is required that the catalyst operate for 72 hours under standard flue gas containing SO2 and water vapor, and NO... xThe conversion rate should be ≥90%; after 4000 hours of simulated operation, the decrease in denitrification efficiency should be ≤5%, while the ammonia slip concentration should be limited to ≤3ppm (dry basis, standard state) to assist in verifying the stability of catalyst performance. The denitrification efficiency of the catalysts in Examples 15 to 18 and the comparative examples was maintained at 1000 mg / m³ in both the denitrification efficiency and the denitrification efficiency in an SO2 atmosphere. 3 (The system was continuously operated in an SO2 atmosphere for 100 hours). The results are shown in Table 1.
[0051] The present invention has the following beneficial effects: Regarding catalyst structure design: First, this invention selects titanium-silicon composite oxide as the support. The introduction of Si element can inhibit TiO2 grain growth and increase the specific surface area of the support. By controlling the Si to Ti molar ratio to be 0.05 to 0.15:1, the stability of the support is ensured while avoiding excessive Si from covering the active sites. Second, V2O5 is used as the core active component, with a mass percentage of 1.5% to 5.0%. Too high a percentage can easily lead to NH3 oxidation, while too low a percentage results in insufficient activity. The co-catalyst WO3 can improve the thermal stability of the catalyst and inhibit V2O5 agglomeration, with a mass percentage of 5% to 15%. Modifying component Ce... 0.6 Zr 0.4 O2 has excellent oxygen storage capacity, can promote the oxidation of NO to NO2, improve low-temperature activity, and enhance resistance to sulfur poisoning.
[0052] Regarding the preparation process: This invention employs a stepwise sol-gel method combined with supercritical drying. Compared to traditional drying, supercritical drying avoids gel network shrinkage and significantly increases the specific surface area of the carrier (≥280m²). 2 / g); uniform dispersion of the titanium-silicon component is ensured through citric acid chelation and pH adjustment. The impregnation method employed in this invention ensures uniform loading of the active component onto the carrier surface, while controlling the drying temperature at 110℃ and the calcination temperature at 450℃ to 500℃ to prevent sintering of the active component.
[0053] In terms of performance: The high specific surface area denitrification catalyst of this invention has a specific surface area ≥220m². 2 / g, with good dispersibility of the active component and excellent low-temperature activity, achieving a denitrification efficiency of ≥95% at 200℃ to 400℃, making it suitable for medium and low temperature flue gas scenarios; in addition, it has strong sulfur resistance, and the modified component Ce 0.6 Zr 0.4 O2 can inhibit the deposition of ammonium sulfate on the catalyst surface, so that the denitrification efficiency of the catalyst decreases by ≤5% when it runs continuously for 100 hours under 1000 mg / m³ SO2 conditions.
[0054] In summary, the high specific surface area denitrification catalyst of the present invention has a simple preparation process and controllable cost. It has a high specific surface area, excellent low-temperature activity and sulfur resistance. It can be directly applied to medium and low temperature flue gas denitrification systems in industries such as thermal power and steel. The molding method can also be adjusted according to actual needs (such as honeycomb type or plate type), and it has broad prospects for industrial application.
[0055] The above technical features constitute various embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.
Claims
1. A high specific surface area denitration catalyst, characterized in that... The product comprises, by mass percentage, 55% to 80% titanium-silicon composite oxide support, 1.5% to 5.0% active component, 5% to 15% co-catalyst, and 8% to 25% modified component; wherein the molar ratio of Si to Ti in the titanium-silicon composite oxide support is 0.05 to 0.15:
1.
2. The high specific surface area denitration catalyst according to claim 1, characterized in that... The specific surface area of the titanium-silicon composite oxide carrier is 280 m². 2 / g to 350m 2 / g.
3. The high specific surface area denitration catalyst according to claim 2, characterized in that... The active component is V2O5; Or / and, the co-catalyst is WO3; Or / and, the modified component is Ce 0.6 Zr 0.4 O2, Ce 0.6 Zr 0.4 The particle size of O2 ranges from 15 nm to 30 nm.
4. The high specific surface area denitrification catalyst according to any one of claims 1 to 3, characterized in that... The high specific surface area denitration catalyst was prepared according to the following steps: Step 1: The titanium-silicon composite sol is dried under supercritical CO2 conditions. After calcination of the dried product, a titanium-silicon composite oxide carrier is obtained. Step 2: Dissolve ammonium metavanadate in oxalic acid solution, then add ammonium tungstate and Ce. 0.6 Zr 0.4 O2 powder is dispersed to obtain an impregnation solution; Step 3: Impregnate the titanium-silicon composite oxide support in the impregnation solution. After impregnation, the product is dried and calcined to obtain a high specific surface area denitrification catalyst.
5. The high specific surface area denitration catalyst according to claim 4, characterized in that... In step one, the titanium-silicon composite sol is prepared according to the following steps: Tetrabutyl titanate was dissolved in ethanol, added to citric acid solution, and stirred until homogeneous to obtain titanium sol; Tetraethyl orthosilicate was dissolved in ethanol and then added dropwise to titanium sol. The pH was adjusted to 3.5 to 4.5 with ammonia and stirred until homogeneous to obtain a composite sol.
6. The high specific surface area denitration catalyst according to claim 5, characterized in that... The volume ratio of tetrabutyl titanate to ethanol is 1:3 to 1:5, the mass concentration of citric acid solution is 10% to 15%, and the amount of citric acid solution used is 0.5 to 1.5 times that of ethanol. Or / and, the volume ratio of tetraethyl orthosilicate to ethanol is 1:20 to 1:
30.
7. The high specific surface area denitrification catalyst according to any one of claims 4 to 6, characterized in that... In step one, the supercritical conditions for CO2 are: drying at a temperature of 31℃ to 35℃ and a pressure of 7.5mPa to 8.0mPa for 3h to 6h; and calcination at a temperature of 550℃ to 600℃ for 4h to 6h. Or / and, in step two, Ce 0.6 Zr 0.4 O2 was prepared by a co-precipitation method, with ammonium bicarbonate as the precipitant. The co-precipitated product was calcined to obtain Ce. 0.6 Zr 0.4 O2; roasting temperature is 500℃ to 550℃, roasting time is 3h to 4h; Or / and, in step two, the molar ratio of ammonium metavanadate, ammonium tungstate, and oxalic acid is (1.5 to 2.5):(2 to 2.5):(3.5 to 4.5); Or / and, in step three, the immersion temperature is 50°C to 70°C, and the immersion time is 3 to 5 hours; Or / and, in step three, drying is performed at 100°C to 120°C for 10 to 15 hours, and calcination is performed at 450°C to 500°C for 5 to 8 hours.
8. A method for preparing a high specific surface area denitration catalyst according to claim 1, 2, 3, 5, 6, or 7, characterized in that... Includes the following steps: Step 1: The titanium-silicon composite sol is dried under supercritical CO2 conditions. After calcination of the dried product, a titanium-silicon composite oxide carrier is obtained. Step 2: Dissolve ammonium metavanadate in oxalic acid solution, then add ammonium tungstate and Ce. 0.6 Zr 0.4 O2 powder is dispersed to obtain an impregnation solution; Step 3: Impregnate the titanium-silicon composite oxide support in the impregnation solution. After impregnation, the product is dried and calcined to obtain a high specific surface area denitrification catalyst.
9. The application of a high specific surface area denitrification catalyst according to any one of claims 1 to 7 in flue gas denitrification.
10. The application of the high specific surface area denitrification catalyst according to claim 9 in flue gas denitrification, characterized in that... The application conditions are: flue gas temperature 200℃ to 400℃, space velocity 15000h. -1 Up to 30000h -1 NH3 and NO in flue gas x The molar ratio is 0.9 to 1.1, and the NO inlet of the flue gas denitrification system is... x Concentration of 500 mg / m 3 Up to 1500 mg / m 3 .