SNCR (selective non-catalytic reduction) steam denitration process applied to boiler flue gas treatment

Abstract

The invention discloses an SNCR (selective non-catalytic reduction) steam denitration process applied to boiler flue gas treatment, and belongs to the technical field of boiler flue gas treatment. An SNCR (selective non-catalytic reduction) steam denitration process applied to boiler flue gas treatment is characterized in that premixed gas is formed by preparing a modified reducing agent and superheated steam, and injection denitration treatment is performed in a boiler hearth, so that the denitration efficiency is remarkably improved. The process comprises the following steps: preparing a biodegradable reducing agent, carrying out superheated steam heating treatment, carrying out atomized denitration, adding a reaction promoting additive, carrying out tail gas adsorption treatment, separating and recycling carbon dioxide and the like. The method is characterized in that the reaction temperature window, the spray droplet particle size and the spraying parameters are optimized, the effect of keeping efficient denitration in a wide temperature interval is achieved, it is ensured that the NOx concentration is reduced by 70% or above, and ammonia escape is controlled to be 3 ppm or below. The process not only improves the denitration efficiency of the boiler flue gas, but also reduces environmental pollution, and has good environmental protection and economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of boiler flue gas treatment, and more particularly to an SNCR steam denitrification process applied to boiler flue gas treatment. Background Art

[0002] Nitrogen oxides (NOx) are one of the main harmful pollutants in boiler flue gas. Their emissions can cause atmospheric acidification, photochemical smog, and PM2.5 pollution, posing a serious threat to the environment and human health. Selective non-catalytic reduction (SNCR) technology, a mature denitrification method, has been widely used for NOx treatment in coal-fired boilers, waste incinerators, and biomass boilers due to its low cost, simple process, and strong adaptability. Traditional SNCR processes typically use ammonia or urea as a reducing agent to reduce NOx to N2 in a high-temperature range of 850-1100°C. However, these processes suffer from problems such as a narrow temperature window, high ammonia slip, and unstable denitrification efficiency.

[0003] To improve denitrification efficiency and broaden the reaction temperature window, researchers have recently explored improvements such as multi-component reducing agents, auxiliary spray systems, and reaction accelerators. Among these, steam-assisted urea pyrolysis denitrification shows promising application potential due to its stable release of NH3 and HNCO and reduced injection zone temperature requirements. However, this technology currently faces challenges in terms of synergistic reactant utilization, dynamic flue gas regulation, and carbon byproduct utilization. In particular, limited research has been conducted on the relationship between denitrification efficiency and intelligent system control.

[0004] Therefore, the development of a new SNCR denitrification process based on the synergistic effect of multi-component modified urea and superheated steam, combined with temperature window expansion, tail gas resource recovery and intelligent feedback control, has become an important direction of research and engineering technology development in this field. Summary of the Invention

[0005] The object of the present invention is to provide an SNCR steam denitrification process for boiler flue gas treatment, which improves the boiler flue gas denitrification efficiency, reduces environmental pollution, and has good environmental and economic benefits.

[0006] An SNCR steam denitrification process for boiler flue gas treatment comprises the following steps:

[0007] S1. Preparation of modified reducing agent: Add 50% of the total amount of deionized water solvent to the reaction vessel, turn on the stirring system, the speed is 300-500 rpm, heat to 40-50 ° C, slowly add 25-35% of the total amount of industrial-grade granular urea, stir and dissolve for 10-18 minutes to disperse evenly, slowly add 2-5% of the total amount of hydroxylamine hydrochloride, stir and dissolve for 8-12 minutes to disperse evenly, slowly add 5-10% of the total amount of bio-based organic amine triethanolamine, stir and dissolve for 12-20 minutes to disperse evenly, slowly add 0.5-1.5% of the total amount of complexing agent sodium citrate, stir and dissolve for 6-10 minutes to disperse evenly, replenish deionized water to 100%, continue stirring for 12-20 minutes, use a precision pH meter to monitor the pH, the target control is 7.5-9.0, if the pH is too low, add a small amount of triethanolamine, if the pH is too high, add a small amount of 5% citric acid aqueous solution, and finally filter with a 0.45um filter membrane to obtain a modified reducing agent;

[0008] S2. The reducing agent and superheated steam of step S1 are mixed in a volume ratio of 2-4:1 to form a premixed gas, which is heated to 200-240° C. in a pyrolysis chamber for 1-3 seconds.

[0009] S3, spraying the mixed pyrolysis gas described in step S2 into the denitration temperature zone of the boiler furnace after being atomized by a nozzle, wherein the spraying parameters are as follows: the nozzle type is a swirl atomizing nozzle made of 316L stainless steel, the nozzle aperture is 0.8-1.5mm, the spraying pressure is 0.3-0.6MPa, the spraying temperature range is 600-1160°C, the spraying time is 0.6-2 seconds, the spraying layer is set to 3-5 layers, each layer contains 2-4 nozzles, and the nozzles are distributed in the vertical direction of the furnace;

[0010] S4. Adding a reaction-promoting additive to expand the temperature window into the spraying area, wherein the additive is hydrogen peroxide, and the amount added is 1-3% of the total volume of the reducing agent;

[0011] S5. The flue tail gas is passed through a cooling adsorption system to absorb unreacted ammonia and residual reducing agent liquid, and the residual liquid is recycled to the reducing agent preparation unit after liquid phase purification;

[0012] S6. The by-product carbon dioxide is collected and compressed and stored through the carbon dioxide separation module installed at the tail gas outlet for subsequent carbon resource utilization;

[0013] S7. Set up a flue gas online analysis feedback control system to monitor the flue gas temperature, NOx concentration, oxygen concentration, and ammonia escape concentration in real time, and adjust the nozzle switch state, nozzle injection flow rate and additive ratio according to the feedback signal to achieve intelligent closed-loop operation of the system.

[0014] Preferably, the modified reducing agent in step S1 is a biodegradable material with a COD lower than 2000 mg / L and a toxicity level of non-hazardous goods.

[0015] Preferably, the superheated steam in step S2 is superheated water vapor with a temperature of 200-240° C. and a pressure of 0.2-0.5 MPa.

[0016] Preferably, the spray droplet particle size of the atomizing nozzle in step S3 is controlled to be 20-50 μm.

[0017] Preferably, the temperature window of the reaction zone in step S4 is widened to 600-1160°C, and the denitrification efficiency is optimal in the temperature range of 750-1050°C.

[0018] Preferably, the boiler is a 35-75 t / h coal-fired, waste incineration or biomass boiler.

[0019] Preferably, the ammonia escape concentration is controlled to be less than 3 ppm, and the denitrification efficiency is greater than 70%.

[0020] Preferably, the tail gas treatment system includes an integrated condensation absorption tower, the absorption liquid of which is a dilute sulfuric acid solution, and the pH value is controlled at 3-5.

[0021] Preferably, the carbon dioxide recovered in step S6 has a purity of more than 95% after compression, and can be used in application scenarios such as mineral carbon solidification, cement clinker reaction, greenhouse crop fertilization or microalgae cultivation.

[0022] Reaction principle:

[0023] (a) Urea thermal decomposition reaction:

[0024] (NH2)2CO→NH3+NHCO;

[0025] (b) Ammonia selective reduction reaction:

[0026] 4NH3+4NO+O2→4N2+6H2O;

[0027] (c) HNCO hydrolysis reaction:

[0028] HNCO+H2O→NH3+CO2;

[0029] (d) Hydroxylamine reduction reaction:

[0030] NH2OH+NO→N2+H2O.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] (1) High-efficiency and low-temperature denitrification reaction

[0033] The modified reducing agent is prepared using urea, bio-based amines, hydroxylamines, and a chelating agent as raw materials. Their synergistic effect enhances the rate of the NOx selective reduction reaction, while reducing side reactions and improving nitrogen conversion. Premixing the modified reducing agent with superheated steam for pyrolysis improves the efficiency of active substance generation in the reducing agent and optimizes the reduction reaction conditions. The addition of a reaction-promoting additive expands the temperature window to 600-1160°C, with 750-1050°C as the high-efficiency reaction zone. This effectively expands the SNCR process's reaction temperature window, achieving a denitrification efficiency exceeding 70% and ammonia slip concentration below 3 ppm, meeting stringent emission control requirements and effectively reducing secondary pollution. Furthermore, the modified reducing agent is biodegradable, with a COD of less than 2000 mg / L and a non-hazardous toxicity rating, significantly reducing hazards to the environment and operators.

[0034] (2) Advanced spray system

[0035] 316L stainless steel swirl atomizing nozzles are used, and the spray droplet size is controlled at 20-50um, which significantly improves the spatial distribution uniformity and reaction efficiency of the reducing agent in the furnace. The spray layer is set to 3-5 layers, and each layer is equipped with multiple nozzles, which are evenly arranged in the vertical direction of the furnace, which helps to achieve sufficient reaction in different temperature zones and improve the overall denitrification efficiency.

[0036] (3) The condensation absorption tower efficiently absorbs residual ammonia and the closed-loop recycling of waste liquid reduces emissions

[0037] An integrated condensation absorption tower, using dilute sulfuric acid with a pH controlled at 3-5, efficiently removes unreacted ammonia, helping to improve tail gas emission standards. Furthermore, residual liquid from the tail gas adsorption system can be reused in reducing agent preparation after liquid phase purification, forming a recycling system that reduces wastewater discharge and operating costs.

[0038] (4) Centralized treatment and resource utilization of by-product CO2

[0039] The recovered carbon dioxide is compressed and purified (purity can reach 95%) to avoid direct emission of greenhouse gases into the atmosphere, thereby improving the overall carbon emission reduction effect. It can be used for applications such as mineral carbon solidification, cement clinker reaction, greenhouse fertilization or microalgae cultivation, promoting resource recycling and carbon capture and utilization (CCU). BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a process flow chart of the SNCR steam denitrification process for treating boiler flue gas according to the present invention. DETAILED DESCRIPTION

[0041] Example 1:

[0042] S1. Preparation of modified reducing agent: Add 50% of the total amount of deionized water solvent to the reaction vessel, turn on the stirring system, the speed is 300 rpm, heat to 40°C, slowly add 25% of the total amount of industrial-grade granular urea, stir and dissolve for 10 minutes and disperse evenly, slowly add 2% of the total amount of hydroxylamine hydrochloride, stir and dissolve for 8 minutes and disperse evenly, slowly add 5% of the total amount of bio-based organic amine triethanolamine, stir and dissolve for 12 minutes and disperse evenly, slowly add 0.5% of the total amount of complexing agent sodium citrate, stir and dissolve for 6 minutes and disperse evenly, replenish deionized water to 100%, continue stirring for 12 minutes, use a precision pH meter to monitor the pH, the target control is 7.5, if the pH is too low, add a small amount of triethanolamine, if the pH is too high, add a small amount of 5% citric acid aqueous solution, and finally filter with a 0.45um filter membrane to obtain a modified reducing agent;

[0043] S2. The reducing agent described in step S1 and superheated steam at a temperature of 200° C. and a pressure of 0.2 MPa are mixed in a volume ratio of 2:1 to form a premixed gas, which is heated to 200° C. in a pyrolysis chamber. The premixed pyrolysis time is 1 second.

[0044] S3, spraying the mixed pyrolysis gas described in step S2 into the denitration temperature zone of the boiler furnace after being atomized by a nozzle, wherein the spraying parameters are as follows: the nozzle type is a swirl atomizing nozzle made of 316L stainless steel, the nozzle aperture is 0.8 mm, the spraying pressure is 0.3 MPa, the spraying temperature zone is 600° C., the spraying time is 0.6 seconds, the spraying layer is set to 3 layers, each layer contains 2 nozzles, the nozzles are distributed in the vertical direction of the furnace, and the spray droplet particle size of the atomizing nozzle is controlled at 20 μm;

[0045] S4, adding a reaction-promoting additive for expanding the temperature window to the injection area, wherein the additive is hydrogen peroxide, and the amount added is 1% of the total volume of the reducing agent;

[0046] S5. The flue gas is passed through a cooling adsorption system to absorb unreacted ammonia and residual reducing agent. The tail gas treatment system includes an integrated condensation absorption tower. The absorption liquid is a dilute sulfuric acid solution with a pH value controlled at 5. The residual liquid is purified in the liquid phase and then recycled to the reducing agent preparation unit.

[0047] S6. The by-product carbon dioxide is collected and compressed and stored through the carbon dioxide separation module installed at the tail gas outlet for subsequent carbon resource utilization;

[0048] S7. Set up a flue gas online analysis feedback control system to monitor the flue gas temperature, NOx concentration, oxygen concentration, and ammonia escape concentration in real time, and adjust the nozzle switch state, nozzle injection flow rate and additive ratio according to the feedback signal to achieve intelligent closed-loop operation of the system.

[0049] Example 2:

[0050] S1. Preparation of modified reducing agent: Add 50% of the total amount of deionized water solvent to the reaction vessel, turn on the stirring system, the speed is 350 rpm, heat to 42 ° C, slowly add 27.5% of the total amount of industrial-grade granular urea, stir and dissolve for 12 minutes to disperse evenly, slowly add 2.75% of the total amount of hydroxylamine hydrochloride, stir and dissolve for 9 minutes to disperse evenly, slowly add 6.25% of the total amount of bio-based organic amine triethanolamine, stir and dissolve for 14 minutes to disperse evenly, slowly add 0.75% of the total amount of complexing agent sodium citrate, stir and dissolve for 7 minutes to disperse evenly, replenish deionized water to 100%, continue stirring for 14 minutes, use a precision pH meter to monitor the pH, the target control is 7.8, if the pH is too low, add a small amount of triethanolamine, if the pH is too high, add a small amount of 5% citric acid aqueous solution, and finally filter with a 0.45um filter membrane to obtain a modified reducing agent;

[0051] S2. The reducing agent described in step S1 and superheated steam at a temperature of 210° C. and a pressure of 0.275 MPa are mixed in a volume ratio of 2.5:1 to form a premixed gas, which is heated to 210° C. in a pyrolysis chamber. The premixed pyrolysis time is 1.5 seconds.

[0052] S3, spraying the mixed pyrolysis gas described in step S2 into the denitration temperature zone of the boiler furnace after being atomized by a nozzle, wherein the spraying parameters are as follows: the nozzle type is a swirl atomizing nozzle made of 316L stainless steel, the nozzle aperture is 0.9 mm, the spraying pressure is 0.375 MPa, the spraying temperature zone is 740°C, the spraying time is 0.8 seconds, the spraying layer is set to 3 layers, each layer contains 2 nozzles, the nozzles are distributed in the vertical direction of the furnace, and the spray droplet particle size of the atomizing nozzle is controlled at 27 μm;

[0053] S4, adding a reaction-promoting additive to expand the temperature window in the injection area, wherein the additive is hydrogen peroxide, and the amount added is 1.5% of the total volume of the reducing agent;

[0054] S5. The flue gas is passed through a cooling adsorption system to absorb unreacted ammonia and residual reducing agent. The tail gas treatment system includes an integrated condensation absorption tower. The absorption liquid is a dilute sulfuric acid solution with a pH value controlled at 4.5. The residual liquid is purified in the liquid phase and then recycled to the reducing agent preparation unit.

[0055] S6. The by-product carbon dioxide is collected and compressed and stored through the carbon dioxide separation module installed at the tail gas outlet for subsequent carbon resource utilization;

[0056] S7. Set up a flue gas online analysis feedback control system to monitor the flue gas temperature, NOx concentration, oxygen concentration, and ammonia escape concentration in real time, and adjust the nozzle switch state, nozzle injection flow rate and additive ratio according to the feedback signal to achieve intelligent closed-loop operation of the system.

[0057] Example 3:

[0058] S1. Preparation of modified reducing agent: Add 50% of the total amount of deionized water solvent to the reaction vessel, turn on the stirring system, the speed is 400 rpm, heat to 45 ° C, slowly add 30% of the total amount of industrial-grade granular urea, stir and dissolve for 14 minutes to disperse evenly, slowly add 3.5% of the total amount of hydroxylamine hydrochloride, stir and dissolve for 10 minutes to disperse evenly, slowly add 7.5% of the total amount of bio-based organic amine triethanolamine, stir and dissolve for 16 minutes to disperse evenly, slowly add 1% of the total amount of complexing agent sodium citrate, stir and dissolve for 8 minutes to disperse evenly, replenish deionized water to 100%, continue stirring for 16 minutes, use a precision pH meter to monitor the pH, the target control is 8.2, if the pH is too low, add a small amount of triethanolamine, if the pH is too high, add a small amount of 5% citric acid aqueous solution, and finally filter with a 0.45um filter membrane to obtain a modified reducing agent;

[0059] S2. The reducing agent described in step S1 is mixed with superheated steam at a temperature of 220° C. and a pressure of 0.35 MPa in a volume ratio of 3:1 to form a premixed gas, which is heated to 220° C. in a pyrolysis chamber. The premixed pyrolysis time is 2 seconds.

[0060] S3, spraying the mixed pyrolysis gas described in step S2 into the denitration temperature zone of the boiler furnace after being atomized by a nozzle, wherein the spraying parameters are as follows: the nozzle type is a swirl atomizing nozzle made of 316L stainless steel, the nozzle aperture is 1.1 mm, the spraying pressure is 0.45 MPa, the spraying temperature zone is 880°C, the spraying time is 1.2 seconds, the spraying layer is set to 4 layers, each layer contains 3 nozzles, the nozzles are distributed in the vertical direction of the furnace, and the spray droplet size of the atomizing nozzle is controlled at 35 μm;

[0061] S4, adding a reaction-promoting additive for expanding the temperature window to the injection area, wherein the additive is hydrogen peroxide, and the amount added is 2% of the total volume of the reducing agent;

[0062] S5. The flue gas is passed through a cooling adsorption system to absorb unreacted ammonia and residual reducing agent. The tail gas treatment system includes an integrated condensation absorption tower. The absorption liquid is a dilute sulfuric acid solution with a pH value controlled at 4. The residual liquid is purified in the liquid phase and then recycled to the reducing agent preparation unit.

[0063] S6. The by-product carbon dioxide is collected and compressed and stored through the carbon dioxide separation module installed at the tail gas outlet for subsequent carbon resource utilization;

[0064] S7. Set up a flue gas online analysis feedback control system to monitor the flue gas temperature, NOx concentration, oxygen concentration, and ammonia escape concentration in real time, and adjust the nozzle switch state, nozzle injection flow rate and additive ratio according to the feedback signal to achieve intelligent closed-loop operation of the system.

[0065] Example 4:

[0066] S1. Preparation of modified reducing agent: Add 50% of the total amount of deionized water solvent to the reaction vessel, turn on the stirring system, the speed is 450 rpm, heat to 47.5 ° C, slowly add 32.5% of the total amount of industrial-grade granular urea, stir and dissolve for 16 minutes to disperse evenly, slowly add 4.25% of the total amount of hydroxylamine hydrochloride, stir and dissolve for 11 minutes to disperse evenly, slowly add 8.75% of the total amount of bio-based organic amine triethanolamine, stir and dissolve for 18 minutes to disperse evenly, slowly add 1.25% of the total amount of complexing agent sodium citrate, stir and dissolve for 9 minutes to disperse evenly, replenish deionized water to 100%, continue stirring for 18 minutes, use a precision pH meter to monitor the pH, the target control is 8.8, if the pH is too low, add a small amount of triethanolamine, if the pH is too high, add a small amount of 5% citric acid aqueous solution, and finally filter with a 0.45um filter membrane to obtain a modified reducing agent;

[0067] S2. The reducing agent described in step S1 is mixed with superheated steam at a temperature of 230° C. and a pressure of 0.425 MPa in a volume ratio of 3.5:1 to form a premixed gas, which is heated to 230° C. in a pyrolysis chamber for 2.5 seconds.

[0068] S3, spraying the mixed pyrolysis gas described in step S2 into the denitration temperature zone of the boiler furnace after being atomized by a nozzle, wherein the spraying parameters are as follows: the nozzle type is a swirl atomizing nozzle made of 316L stainless steel, the nozzle aperture is 1.3mm, the spraying pressure is 0.525MPa, the spraying temperature zone is 1020°C, the spraying time is 1.6 seconds, the spraying layer is set to 4 layers, each layer contains 3 nozzles, the nozzles are distributed in the vertical direction of the furnace, and the spray droplet particle size of the atomizing nozzle is controlled at 42μm;

[0069] S4, adding a reaction-promoting additive to expand the temperature window in the injection area, wherein the additive is hydrogen peroxide, and the added amount is 2.5% of the total volume of the reducing agent;

[0070] S5. The flue gas is passed through a cooling adsorption system to absorb unreacted ammonia and residual reducing agent. The tail gas treatment system includes an integrated condensation absorption tower. The absorption liquid is a dilute sulfuric acid solution with a pH value controlled at 3.5. The residual liquid is purified in the liquid phase and then recycled to the reducing agent preparation unit.

[0071] S6. The by-product carbon dioxide is collected and compressed and stored through the carbon dioxide separation module installed at the tail gas outlet for subsequent carbon resource utilization;

[0072] S7. Set up a flue gas online analysis feedback control system to monitor the flue gas temperature, NOx concentration, oxygen concentration, and ammonia escape concentration in real time, and adjust the nozzle switch state, nozzle injection flow rate and additive ratio according to the feedback signal to achieve intelligent closed-loop operation of the system.

[0073] Example 5:

[0074] S1. Preparation of modified reducing agent: Add 50% of the total amount of deionized water solvent to the reaction vessel, turn on the stirring system, the speed is 500 rpm, heat to 50°C, slowly add 35% of the total amount of industrial-grade granular urea, stir and dissolve for 18 minutes to disperse evenly, slowly add 5% of the total amount of hydroxylamine hydrochloride, stir and dissolve for 12 minutes to disperse evenly, slowly add 10% of the total amount of bio-based organic amine triethanolamine, stir and dissolve for 20 minutes to disperse evenly, slowly add 1.5% of the total amount of complexing agent sodium citrate, stir and dissolve for 10 minutes to disperse evenly, replenish deionized water to 100%, continue stirring for 20 minutes, use a precision pH meter to monitor the pH, the target control is 9.0, if the pH is too low, add a small amount of triethanolamine, if the pH is too high, add a small amount of 5% citric acid aqueous solution, and finally filter with a 0.45um filter membrane to obtain a modified reducing agent;

[0075] S2. The reducing agent described in step S1 is mixed with superheated steam at a temperature of 240° C. and a pressure of 0.5 MPa in a volume ratio of 4:1 to form a premixed gas, which is heated to 240° C. in a pyrolysis chamber for 3 seconds.

[0076] S3, spraying the mixed pyrolysis gas described in step S2 into the denitration temperature zone of the boiler furnace after being atomized by a nozzle, wherein the spraying parameters are as follows: the nozzle type is a swirl atomizing nozzle made of 316L stainless steel, the nozzle aperture is 1.5 mm, the spraying pressure is 0.6 MPa, the spraying temperature zone is 1160° C., the spraying time is 2 seconds, the spraying layer is set to 5 layers, each layer contains 4 nozzles, the nozzles are distributed in the vertical direction of the furnace, and the spray droplet size of the atomizing nozzle is controlled at 50 μm;

[0077] S4, adding a reaction-promoting additive to expand the temperature window in the injection area, wherein the additive is hydrogen peroxide, and the amount added is 3% of the total volume of the reducing agent;

[0078] S5. The flue gas is cooled and absorbed by the adsorption system to absorb unreacted ammonia and residual reducing agent. The tail gas treatment system includes an integrated condensation absorption tower. The absorption liquid is a dilute sulfuric acid solution with a pH value controlled at 3. The residual liquid is purified by the liquid phase and then recycled to the reducing agent preparation unit.

[0079] S6. The by-product carbon dioxide is collected and compressed and stored through the carbon dioxide separation module installed at the tail gas outlet for subsequent carbon resource utilization;

[0080] S7. Set up a flue gas online analysis feedback control system to monitor the flue gas temperature, NOx concentration, oxygen concentration, and ammonia escape concentration in real time, and adjust the nozzle switch state, nozzle injection flow rate and additive ratio according to the feedback signal to achieve intelligent closed-loop operation of the system.

[0081] Performance Testing

[0082] Denitrification efficiency and ammonia escape concentration test

[0083] A sampling probe was placed at the outlet of the denitration system. A 55 ton / hour coal-fired boiler was selected. The boiler was started and the denitration process was initiated according to the parameters set in Examples 1-5. A Testo 350 portable flue gas analyzer was used to continuously collect NOx and NH3 data. The NOx concentrations before and after the reaction were recorded. The denitration efficiency was calculated according to the formula η = (C0 - C1) / C0 × 100%. The test conditions included a flue gas flow rate of 10 m / s and a continuous monitoring time of 60 minutes. The test results are shown in the following table:

[0084] Example 1 Example 2 Example 3 Example 4 Example 5 Denitrification efficiency (%) 70.9 74.1 78.8 76.5 72.4 <![CDATA[NH3 Slip (ppm)]]> 2.7 2.2 1.7 1.9 2.6

[0085] Reducing agent environmental friendliness test (COD and toxicity)

[0086] Take 20 mL of the reducing agent solution prepared in step S1 of Example 1-5, dilute it 10 times, and use Hach DRB200 COD digester and Hach DR6000 spectrophotometer to test the reducing agent environmental friendliness (COD and toxicity).

[0087] The following table shows the test results:

[0088] Example 1 Example 2 Example 3 Example 4 Example 5 COD (mg / L) 1710 1570 1510 1550 1655

[0089] Carbon dioxide recovery purity test

[0090] A gas sample was collected from the carbon dioxide separation outlet in step S6 of Example 1-5, and the carbon dioxide recovery purity was tested using an Agilent 7890B gas chromatograph with a TCD detector. The components were analyzed using a preset separation column (Porapak Q). The carbon dioxide peak area was read and the concentration was calculated by comparing with the standard curve.

[0091] The following table shows the test results:

[0092]

Claims

1. A SNCR steam denitrification process for boiler flue gas treatment, characterized in that: The steps include: S1. Preparation of modified reducing agent: Add 50% of the total amount of deionized water solvent to the reaction vessel, turn on the stirring system, the speed is 300-500 rpm, heat to 40-50 ° C, slowly add 25-35% of the total amount of industrial-grade granular urea, stir and dissolve for 10-18 minutes to disperse evenly, slowly add 2-5% of the total amount of hydroxylamine hydrochloride, stir and dissolve for 8-12 minutes to disperse evenly, slowly add 5-10% of the total amount of bio-based organic amine triethanolamine, stir and dissolve for 12-20 minutes to disperse evenly, slowly add 0.5-1.5% of the total amount of complexing agent sodium citrate, stir and dissolve for 6-10 minutes to disperse evenly, replenish deionized water to 100%, continue stirring for 12-20 minutes, use a precision pH meter to monitor the pH, the target control is 7.5-9.0, if the pH is too low, add a small amount of triethanolamine, if the pH is too high, add a small amount of 5% citric acid aqueous solution, and finally filter with a 0.45um filter membrane to obtain a modified reducing agent; S2. The reducing agent and superheated steam of step S1 are mixed in a volume ratio of 2-4:1 to form a premixed gas, which is heated to 200-240° C. in a pyrolysis chamber for 1-3 seconds. S3, spraying the mixed pyrolysis gas described in step S2 into the denitration temperature zone of the boiler furnace after being atomized by a nozzle, wherein the spraying parameters are as follows: the nozzle type is a swirl atomizing nozzle made of 316L stainless steel, the nozzle aperture is 0.8-1.5mm, the spraying pressure is 0.3-0.6MPa, the spraying temperature range is 600-1160°C, the spraying time is 0.6-2 seconds, the spraying layer is set to 3-5 layers, each layer contains 2-4 nozzles, and the nozzles are distributed in the vertical direction of the furnace; S4. Adding a reaction-promoting additive to expand the temperature window into the spraying area, wherein the additive is hydrogen peroxide, and the amount added is 1-3% of the total volume of the reducing agent; S5. The flue tail gas is passed through a cooling adsorption system to absorb unreacted ammonia and residual reducing agent liquid, and the residual liquid is recycled to the reducing agent preparation unit after liquid phase purification; S6. The by-product carbon dioxide is collected and compressed and stored through the carbon dioxide separation module installed at the tail gas outlet for subsequent carbon resource utilization; S7. Set up a flue gas online analysis feedback control system to monitor the flue gas temperature, NOx concentration, oxygen concentration, and ammonia escape concentration in real time, and adjust the nozzle switch state, nozzle injection flow rate and additive ratio according to the feedback signal to achieve intelligent closed-loop operation of the system.

2. The SNCR steam denitrification process for boiler flue gas treatment according to claim 1, characterized in that: The modified reducing agent in step S1 is a biodegradable material with a COD lower than 2000 mg / L and a toxicity level of non-hazardous goods.

3. The SNCR steam denitrification process for boiler flue gas treatment according to claim 1, characterized in that: The superheated steam in step S2 is superheated steam with a temperature of 200-240° C. and a pressure of 0.2-0.5 MPa.

4. The SNCR steam denitrification process for boiler flue gas treatment according to claim 1, characterized in that: In step S3, the spray droplet particle size of the atomizing nozzle is controlled to be 20-50 μm.

5. The SNCR steam denitrification process for boiler flue gas treatment according to claim 1, characterized in that: In step S4, the temperature window of the reaction zone is widened to 600-1160°C, and the denitrification efficiency is optimal in the temperature range of 750-1050°C.

6. The SNCR steam denitrification process for boiler flue gas treatment according to claim 1, characterized in that: The boiler is a 35-75 t / h coal-fired, waste incineration or biomass boiler.

7. The SNCR steam denitrification process for boiler flue gas treatment according to claim 1, characterized in that: The ammonia escape concentration is controlled to be less than 3 ppm, and the denitrification efficiency is greater than 70%.

8. The SNCR steam denitrification process for boiler flue gas treatment according to claim 1, characterized in that: The tail gas treatment system includes an integrated condensation absorption tower, the absorption liquid of which is a dilute sulfuric acid solution, and the pH value is controlled at 3-5.

9. The SNCR steam denitrification process for boiler flue gas treatment according to claim 1, characterized in that: The carbon dioxide recovered in step S6 can reach a purity of more than 95% after compression, and can be used in application scenarios such as mineral carbon solidification, cement clinker reaction, greenhouse crop fertilization or microalgae cultivation.

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