SNCR (selective non-catalytic reduction) system and method for cooperatively removing dioxin in furnace

Abstract

The invention belongs to the technical field of waste incineration flue gas purification, and particularly relates to an SNCR (selective non-catalytic reduction) system and method for cooperatively removing dioxin in a furnace. The SNCR system comprises a urea solution supply branch, a dilution water supply branch, a sodium hydroxide dissolving and adding branch, an SNCR spray gun and a grate furnace; an inlet of the SNCR spray gun is connected with the urea solution supply branch and the dilution water supply branch and used for spraying a mixed solution of urea, dilution water and a sodium hydroxide solution into a temperature area of the grate furnace. The NaOH solution is introduced as an alkaline synergist, so that the temperature window of the SNCR reaction in the grate furnace can be reduced, decomposition and removal of dioxin can be synergistically promoted, and the technical contradictions that the temperature window of the traditional SNCR technology is limited, so that the low-load denitration efficiency is poor, an additional device is needed for removal of dioxin, and the removal of dioxin cannot be coordinated with the denitration process are solved; the deep synergistic removal of the two pollutants is realized.

Description

Technical Field

[0001] This invention belongs to the field of waste incineration flue gas purification technology, specifically relating to an in-furnace SNCR system and method for synergistic removal of dioxins. Background Technology

[0002] Waste incineration is one of the core methods for reducing and harmlessly treating urban solid waste. However, the waste incineration process produces nitrogen oxides (NOx). x And highly toxic pollutants such as dioxins. Among them, NO... x These pollutants can cause environmental problems such as acid rain and photochemical smog. Dioxins, due to their strong carcinogenicity and high bioaccumulation, are listed as a priority persistent organic pollutant under the Stockholm Convention. Therefore, nitrogen oxides (NOx)... x The efficient synergistic removal of dioxins and other pollutants is a core technological challenge facing the waste incineration industry.

[0003] Selective non-catalytic reduction (SNCR) technology is the mainstream NO reduction technology in waste incinerators. x The control technology works by spraying urea or ammonia solution into a high-temperature zone of 850℃~1100℃ inside the furnace, where it reacts with NO through reducing groups. x A gas-phase reaction occurs, producing N2. However, existing SNCR technology has a narrow reaction temperature window, typically stabilizing only between 900℃ and 1050℃. When the boiler is operating at low load, the furnace temperature easily drops below 850℃, causing a sharp decline in SNCR denitrification efficiency. Furthermore, traditional SNCR systems only target NO. x The design makes almost no contribution to the removal of dioxins, and additional equipment such as activated carbon injection and quench towers are required to achieve dioxin control. This not only increases the complexity of the system, but also significantly increases the investment and operating costs of equipment. Summary of the Invention

[0004] In view of the technical defects in the existing technology, such as the limited temperature window of SNCR denitrification, which leads to low denitrification efficiency when the boiler is running at low load, and the fact that dioxin removal and SNCR denitrification processes are independent of each other and require additional equipment to assist, resulting in a complex system and the inability to remove dioxins simultaneously and efficiently, this invention provides an SNCR system and method for in-furnace co-removal of dioxins.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows.

[0006] The first aspect of this invention provides an in-furnace synergistic dioxin removal SNCR system, comprising: A urea solution supply branch is used to provide urea solution; a dilution water supply branch is used to provide dilution water; a sodium hydroxide dissolution and addition branch includes a NaOH storage tank, the inlet end of which is connected to the dilution water supply branch via an inlet pipe, and the outlet end of which is connected to the dilution water supply branch via an outlet pipe, for providing sodium hydroxide solution as an alkaline synergist, the mass concentration of which is 5wt% to 10wt%; a grate furnace, wherein an SNCR spray gun is installed on the temperature zone of the grate furnace, the inlet of which is connected to both the urea solution supply branch and the dilution water supply branch, for spraying a mixture of urea, dilution water, and sodium hydroxide solution into the temperature zone of the grate furnace.

[0007] This invention introduces a 5wt%–10wt% NaOH solution as an alkaline synergist. By controlling the concentration of the sodium hydroxide solution, it not only lowers the lower limit of the SNCR reaction temperature window in the grate furnace by 50°C–100°C, significantly widening the effective temperature window of the SNCR reaction and achieving efficient denitrification under low-load conditions, but also synergistically promotes the decomposition and removal of dioxins. This eliminates the need for additional dioxin removal equipment, simplifying the process and reducing costs. Simultaneously, the appropriate concentration of NaOH solution ensures long-term stable system operation, avoiding corrosion and scaling problems. This invention's SNCR system solves the technical contradictions of traditional SNCR technology, such as the limited temperature window leading to poor low-load denitrification efficiency, and the need for additional equipment for dioxin removal, which cannot be coordinated with the denitrification process. It provides optimized conditions for both denitrification and dioxin removal within a single SNCR system, achieving deep synergistic removal of both pollutants.

[0008] Preferably, the urea concentration in the mixture is 20wt%–30wt%; the NaOH concentration in the flue gas is controlled at 30ppm–50ppm. By controlling the NaOH concentration in the flue gas, this invention not only lowers the lower limit of the SNCR reaction temperature window in the grate furnace by 50°C–100°C, significantly widening the effective temperature window of the SNCR reaction and achieving efficient denitrification under low-load conditions, but also synergistically promotes the decomposition and removal of dioxins. Furthermore, the appropriate concentration of sodium hydroxide in the flue gas ensures long-term stable operation of the system, avoiding problems such as corrosion and scaling.

[0009] Preferably, the SNCR reaction temperature window of the grate furnace is 850℃~1100℃.

[0010] Preferably, the dilution water supply branch includes a dilution water branch and a mixing branch. The inlet end of the mixing branch is connected to the dilution water branch and the outlet pipe, respectively, for pre-mixing the dilution water with the sodium hydroxide solution. The inlet end of the SNCR spray gun is connected to a mixing pipe, which is connected to the mixing branch and the urea solution supply branch, respectively.

[0011] Preferably, a first control valve is provided on the urea solution supply branch to control the flow rate of the urea solution; a second control valve is provided on the dilution water supply branch to control the total flow rate of the dilution water; a third control valve is provided on the mixing branch to control the flow rate of the alkaline synergist entering the mixing pipeline; a fourth control valve is provided on the liquid inlet pipeline to control the flow rate of the dilution water entering the NaOH storage tank; and a fifth control valve is provided on the liquid outlet pipeline to control the flow rate of the alkaline synergist entering the mixing branch.

[0012] Preferably, the first control valve, the second control valve, the third control valve, the fourth control valve, and the fifth control valve are all electric control valves with flow metering function.

[0013] In this invention, each branch uses an electric control valve with flow metering function. Combined with the precise control of the electric mixer, the flow rate and mixing ratio of urea solution, dilution water and NaOH solution can be dynamically adjusted according to the real-time operating conditions of the grate furnace (such as load and flue gas composition), ensuring that the system maintains efficient and stable purification performance under different operating conditions.

[0014] Preferably, the SNCR system includes a flue gas waste heat utilization branch, which includes a flue gas outlet pipe and a heat exchanger. The heat exchanger is coiled around the outer wall of the NaOH storage tank, and the cold side of the heat exchanger is connected to the NaOH storage tank in a loop to draw out the liquid to be dissolved or the circulating liquid in the NaOH storage tank. One end of the flue gas outlet pipe is connected to the flue gas outlet of the waste heat boiler of the grate furnace, and the other end of the flue gas outlet pipe is connected to the hot side inlet of the heat exchanger to draw out the flue gas discharged from the flue gas outlet of the waste heat boiler of the grate furnace, and to exchange heat with the liquid to be dissolved or the circulating liquid on the cold side of the heat exchanger using the waste heat of the flue gas.

[0015] Preferably, the SNCR system includes a waste liquid treatment unit, which is connected to the hot-side outlet of the heat exchanger and is used to collect the mixture of urea and sodium hydroxide precipitated in the flue gas after being cooled by the heat exchanger; the cold-side medium of the heat exchanger is the liquid to be dissolved or the circulating liquid in the NaOH storage tank; and the hot-side medium of the heat exchanger is the flue gas transported by the flue gas outlet pipeline.

[0016] A second aspect of the present invention provides an in-furnace synergistic dioxin removal SNCR method, which employs the in-furnace synergistic dioxin removal SNCR system described in the first aspect. The SNCR method includes the following steps: Open the dilution water supply branch and adjust the total flow rate of the dilution water; add solid sodium hydroxide or sodium hydroxide solution to be diluted to the NaOH storage tank, and at the same time open the inlet pipe to adjust the mass concentration of sodium hydroxide solution in the NaOH storage tank to 5wt%~10wt%; open the outlet pipe and adjust the flow rate of sodium hydroxide solution; open the urea solution supply branch and adjust the flow rate of urea solution; the mixture of urea, dilution water and sodium hydroxide solution is sprayed into the temperature zone of the grate furnace through the SNCR spray gun, using sodium hydroxide to increase the concentration of free radicals in the flue gas, thereby reducing the SNCR reaction temperature window in the temperature zone of the grate furnace, and simultaneously removing nitrogen oxides and dioxins from the flue gas.

[0017] The beneficial effects of this invention are: 1. This invention introduces a 5wt%–10wt% NaOH solution as an alkaline synergist. By controlling the concentration of the sodium hydroxide solution, the lower limit of the SNCR reaction temperature window in the grate furnace can be reduced by 50°C–100°C, significantly widening the effective temperature window of the SNCR reaction and achieving efficient denitrification under low-load conditions. It also synergistically promotes the decomposition and removal of dioxins, eliminating the need for additional dioxin removal equipment, simplifying the process, and reducing costs. Simultaneously, the appropriate concentration of NaOH solution ensures long-term stable system operation, avoiding corrosion and scaling problems. This invention's SNCR system solves the technical contradictions of traditional SNCR technology, such as the limited temperature window leading to poor low-load denitrification efficiency, and the need for additional equipment for dioxin removal, which cannot be coordinated with the denitrification process. It provides optimized conditions for both denitrification and dioxin removal within a single SNCR system, achieving deep synergistic removal of both pollutants.

[0018] 2. This invention utilizes the effect of NaOH solution to increase the concentration of free radicals in flue gas, which significantly reduces the temperature window of the SNCR reaction and significantly improves the denitrification efficiency under low load conditions. At the same time, the alkaline properties of NaOH can synergistically destroy the dioxin molecular structure and promote its decomposition, eliminating the need for additional dioxin removal devices.

[0019] 3. This invention eliminates the need for traditional additional dioxin removal systems, such as activated carbon injection systems, simplifying the process flow, avoiding secondary pollution problems, and significantly reducing equipment investment and operation and maintenance costs at the system level. Attached Figure Description

[0020] Figure 1 A schematic diagram of the structure of the in-furnace synergistic dioxin removal SNCR system provided for an embodiment of the present invention.

[0021] In the diagram: 1. First control valve; 2. Second control valve; 3. Third control valve; 4. Fourth control valve; 5. Fifth control valve; 6. NaOH storage tank; 7. Stirring equipment; 8. SNCR spray gun; 9. Grate furnace; 10. Flue gas outlet pipeline; 11. Heat exchanger; 12. Waste liquid tank. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Existing SNCR technology suffers from a narrow reaction temperature window, typically stabilizing only between 900℃ and 1050℃. When the boiler is operating at low load, the furnace temperature easily drops below 850℃, leading to a sharp decline in SNCR denitrification efficiency. Furthermore, traditional SNCR systems only target NO. x The design makes almost no contribution to the removal of dioxins, and additional equipment such as activated carbon injection and quench towers are required to achieve dioxin control. This not only increases the complexity of the system, but also significantly increases the investment and operating costs of equipment.

[0025] For dioxin removal, existing technologies mainly rely on a combined strategy of "inhibition of formation and end-of-pipe purification." In the furnace, "3T+E" (temperature, residence time, turbulence intensity, and excess air coefficient) is used to optimize and inhibit dioxin synthesis. However, in actual engineering, due to fluctuations in incineration conditions, it is difficult to consistently control dioxin formation at extremely low levels. At the end, activated carbon adsorption and baghouse dust collectors are used to remove dioxins already formed in the flue gas. However, activated carbon consumption is high, requiring 0.5 kg to 1.5 kg of activated carbon per ton of waste. Furthermore, saturated activated carbon is classified as hazardous waste, posing significant secondary disposal costs and environmental risks. In addition, some studies have attempted to disrupt the chlorination environment for dioxin synthesis by injecting alkaline substances such as CaO and NaOH into the furnace. However, these technologies are mostly in the laboratory pilot stage and lack integration with existing SNCR systems, making direct application in engineering modifications difficult.

[0026] In summary, existing waste incineration flue gas purification technologies suffer from significant drawbacks, including poor low-load denitrification efficiency of SNCR, the need for additional equipment for dioxin removal, low system integration, and high costs. If, based on existing SNCR systems, technological improvements can simultaneously address NOx emissions... x (Especially NO under low load) xThe synergistic removal of dioxins and SNCRs will significantly simplify flue gas purification processes and reduce environmental costs, demonstrating significant engineering application value and environmental benefits. Therefore, developing an integrated system and method that can synergistically optimize the SNCR reaction window and efficiently remove dioxins has become a pressing technical challenge in this field.

[0027] The system and method of the present invention, by introducing NaOH alkaline synergist, can not only reduce the SNCR reaction temperature window to adapt to low-load conditions, but also synergistically promote dioxin removal, achieving efficient synergistic purification of two pollutants in a single SNCR system, simplifying the process and reducing costs.

[0028] The technical solution of the present invention will be further described below through specific embodiments.

[0029] In the following embodiments, unless otherwise specified, the methods described are conventional methods; and unless otherwise specified, the reagents and materials described are commercially available.

[0030] like Figure 1 An in-furnace synergistic dioxin removal SNCR system includes a urea solution supply branch, a dilution water supply branch, a sodium hydroxide dissolution and addition branch, an SNCR spray gun 8, and a grate furnace 9.

[0031] The urea solution supply branch is used to provide urea solution; the dilution water supply branch is used to provide dilution water; the sodium hydroxide dissolution and addition branch includes a NaOH storage tank 6, the inlet end of which is connected to the dilution water supply branch via an inlet pipe, and the outlet end of which is connected to the dilution water supply branch via an outlet pipe, for providing sodium hydroxide solution as an alkaline synergist, the mass concentration of which is 5wt% to 10wt%; an SNCR spray gun 8 is installed in the temperature zone of the grate furnace 9, the inlet of which is connected to both the urea solution supply branch and the dilution water supply branch, for spraying a mixture of urea, dilution water and sodium hydroxide solution into the temperature zone of the grate furnace 9.

[0032] In this embodiment of the invention, the urea solution supply branch, the dilution water supply branch, and the outlet pipe of the NaOH storage tank are respectively connected to the inlet end of the mixing pipe to mix the urea solution, dilution water, and sodium hydroxide solution to form a mixture. The outlet end of the mixing pipe is connected to the SNCR spray gun 8, which is positioned in the corresponding temperature reaction zone of the grate furnace 9 to spray the mixture into the corresponding temperature reaction zone of the grate furnace 9. The urea solution supply branch is used to provide urea solution; the dilution water supply branch is used to provide dilution water; and the outlet pipe of the NaOH storage tank is used to provide sodium hydroxide solution. The mass concentration of the sodium hydroxide solution is 5% to 10%.

[0033] Specifically, the mass concentration of urea in the mixture is 20wt%–30wt%; the concentration of NaOH in the flue gas is controlled at 30ppm–50ppm. The SNCR reaction temperature window in the temperature zone of grate furnace 9 is 850℃–1100℃.

[0034] In this embodiment of the invention, the injection position of the SNCR spray gun 8 corresponds to the corresponding temperature reaction zone inside the grate furnace 9, and the NaOH solution provided by the NaOH storage tank acts as an alkaline synergist, which can reduce the lower limit of the temperature window of the SNCR reaction inside the grate furnace 9 by 50°C to 100°C.

[0035] Based on the above embodiments, the dilution water supply branch includes a dilution water branch and a mixing branch. The inlet end of the mixing branch is connected to the dilution water branch and the outlet pipe, respectively, for pre-mixing the dilution water with the sodium hydroxide solution. The inlet end of the SNCR spray gun 8 is connected to a mixing pipe, which is connected to the mixing branch and the urea solution supply branch, respectively.

[0036] Based on the above implementation method, a first control valve 1 is provided on the urea solution supply branch to control the flow rate of the urea solution; a second control valve 2 is provided on the dilution water supply branch to control the total flow rate of the dilution water; a third control valve 3 is provided on the mixing branch to control the flow rate of the alkaline synergist entering the mixing pipeline; a fourth control valve 4 is provided on the liquid inlet pipeline to control the flow rate of the dilution water entering the NaOH storage tank; and a fifth control valve 5 is provided on the liquid outlet pipeline to control the flow rate of the alkaline synergist entering the mixing branch.

[0037] Based on the above implementation method, the first control valve 1, the second control valve 2, the third control valve 3, the fourth control valve 4 and the fifth control valve 5 are all electric control valves with flow metering function.

[0038] In this embodiment of the invention, the inlet end of the NaOH storage tank is connected to an inlet pipe, which is connected to a dilution water supply branch. A fourth control valve 4 is installed on the inlet pipe to draw a portion of dilution water from the dilution water supply branch into the NaOH storage tank 6 to dissolve solid NaOH or a concentrated NaOH solution with a concentration >10%, and the resulting NaOH solution serves as an alkaline synergist. The concentration of the concentrated NaOH solution can be selected according to actual needs; for example, the concentration of the concentrated NaOH solution is 15%–30%. A fifth control valve 5 is installed on the outlet pipe of the NaOH storage tank 6 to control the outflow of the dissolved NaOH solution. The inlet end of the mixing pipe is connected to a mixing branch, which is connected to both the dilution water supply branch and the outlet pipe of the NaOH storage tank 6. A third control valve 3 is installed on the mixing branch to control the flow rate of the alkaline synergist entering the mixing pipe.

[0039] Based on the above embodiments, the SNCR system includes a flue gas waste heat utilization branch, which includes a flue gas outlet pipe 10 and a heat exchanger 11. The heat exchanger 11 is coiled around the outer wall of the NaOH storage tank 6, and the cold side of the heat exchanger 11 is connected to the NaOH storage tank 6 in a loop to draw out the liquid to be dissolved or the circulating liquid in the NaOH storage tank 6. One end of the flue gas outlet pipe 10 is connected to the flue gas outlet of the waste heat boiler of the grate furnace 9, and the other end of the flue gas outlet pipe 10 is connected to the hot side inlet of the heat exchanger 11 to draw out the flue gas discharged from the flue gas outlet of the waste heat boiler of the grate furnace 9, and to exchange heat with the liquid to be dissolved or the circulating liquid on the cold side of the heat exchanger 11 using the waste heat of the flue gas.

[0040] In this embodiment of the invention, the SNCR spray gun 8 is connected to both the urea solution supply branch and the mixing branch. The mixing branch is connected to both the dilution water supply branch and the outlet pipe of the NaOH storage tank 6, and is used to spray the mixed solution into the grate furnace 9. Specifically, the NaOH storage tank 6 is equipped with a stirring device 7, for example, an electric stirrer.

[0041] Based on the above implementation, the SNCR system includes a waste liquid treatment unit, which is connected to the hot side outlet of the heat exchanger and is used to collect the mixture of urea and sodium hydroxide precipitated in the flue gas after being cooled by the heat exchanger; the cold side medium of the heat exchanger 11 is the liquid to be dissolved or the circulating liquid in the NaOH storage tank 6; the hot side medium of the heat exchanger 11 is the flue gas transported by the flue gas outlet pipeline 10.

[0042] In this embodiment of the invention, the other end of the flue gas outlet pipe 10 is connected to the hot-side inlet of the heat exchanger 11 to draw out the flue gas containing residual heat and unreacted urea and NaOH; the cold side of the heat exchanger is connected to the NaOH storage tank in a loop to heat the solution in the NaOH storage tank 6 using the residual heat of the flue gas, thereby promoting the dissolution of NaOH. Specifically, the waste liquid treatment unit includes a waste liquid tank 12, which is connected to the hot-side outlet of the heat exchanger 11 to collect the mixture containing unreacted urea and NaOH precipitated from the flue gas cooled by the heat exchanger 11 for subsequent processing. Specifically, the heat exchanger 11 is a corrosion-resistant heat exchanger, such as a plate heat exchanger or a finned tube heat exchanger.

[0043] An in-furnace synergistic dioxin removal SNCR method, employing the aforementioned in-furnace synergistic dioxin removal SNCR system, includes the following steps: Open the dilution water supply branch and adjust the total flow rate of the dilution water; add solid sodium hydroxide or sodium hydroxide solution to be diluted to the NaOH storage tank 6, and at the same time open the liquid inlet pipe to adjust the mass concentration of sodium hydroxide solution in the NaOH storage tank 6 to 5wt%~10wt%; open the liquid outlet pipe and adjust the flow rate of sodium hydroxide solution; open the urea solution supply branch and adjust the flow rate of urea solution; the mixture of urea, dilution water and sodium hydroxide solution is sprayed into the temperature zone of the grate furnace 9 through the SNCR spray gun 8, using sodium hydroxide to increase the concentration of free radicals in the flue gas, thereby reducing the SNCR reaction temperature window in the temperature zone of the grate furnace 9, and simultaneously removing nitrogen oxides and dioxins from the flue gas.

[0044] Specifically, an in-furnace synergistic dioxin removal SNCR method, based on the aforementioned SNCR system, includes the following steps: S1. Add solid NaOH or a concentrated NaOH solution with a concentration >10% to the NaOH storage tank 6. Start the stirring device 7. Simultaneously, draw some dilution water from the dilution water supply branch into the NaOH storage tank 6 through the fourth control valve 4. Start the sixth electric control valve of the flue gas outlet pipe 10 and the circulation pump of the heat exchanger 11, so that the flue gas from the waste heat boiler enters the hot side inlet of the heat exchanger through the flue gas outlet pipe 10. The waste heat of the flue gas is transferred to the solution in the NaOH storage tank 6 through the heat exchanger 11 to heat and dissolve sodium hydroxide, forming a NaOH solution with a mass concentration of 5% to 10%. The NaOH solution acts as an alkaline synergist. After the flue gas is cooled by heat exchanger 11, unreacted urea and NaOH precipitate out and are collected in the waste liquid tank 12 through the pipeline.

[0045] S2. The total flow rate of dilution water is adjusted by the second control valve 2. Part of the dilution water drawn by the fourth control valve 4 is used to dissolve sodium hydroxide in step S1. The remaining dilution water and sodium hydroxide solution are mixed in the mixing branch and then mixed with the urea solution flowing out of the urea solution supply branch through the first control valve 1. The flow rate of the remaining dilution water makes the mass concentration of urea after mixing 20% ​​to 30%.

[0046] The dissolved NaOH solution in the S3 and NaOH storage tank 6 flows out through the fifth electric control valve 5 and the third electric control valve 3. After mixing with the remaining dilution water in the mixing branch, it is then mixed with the urea solution flowing out through the first control valve 1 in the urea solution supply branch to form a mixed solution. Then, it is sprayed into the corresponding temperature reaction zone in the grate furnace 9 through the SNCR spray gun 8. Among them, the NaOH solution, as an alkaline synergist, can increase the concentration of free radicals in the flue gas, promote the SNCR chain reaction, reduce the lower limit of the SNCR reaction temperature window by 50℃~100℃, improve the reaction rate of SNCR at low temperature and the denitrification efficiency at low load, and simultaneously remove dioxins.

[0047] Specifically, the flow rate of the remaining dilution water is such that the mass concentration of urea in the mixed solution is 30% to 50%.

[0048] Specifically, the stirring speed of the stirring device 7 is 200 r / min to 300 r / min, and the stirring time is 5 min to 15 min. The flue gas flow rate of the flue gas outlet pipe 10 is adjusted according to the heating requirements of the solution in the NaOH storage tank 6 to maintain the solution temperature at 40℃ to 60℃, so as to promote the dissolution of sodium hydroxide.

[0049] The following provides a specific example illustrating the in-furnace synergistic dioxin removal SNCR system and method of the present invention.

[0050] Example 1 The flue gas from a certain waste incinerator, after pretreatment by a waste heat boiler, reaches a temperature of approximately 350℃, and its NO... x The initial concentration was approximately 300 mg / Nm 3 Of which NO accounted for approximately 95% by volume, NO2 approximately 5%, and dioxin concentration approximately 5.0 ng TEQ / Nm³. 3 .

[0051] The in-furnace synergistic dioxin removal SNCR method employs... Figure 1 The SNCR system shown is used, and the specific SNCR method includes the following steps: Step 1: Open the first control valve 1 on the urea solution supply branch and adjust the urea solution flow rate so that the mass concentration of urea after mixing with the remaining dilution water is 30%; at the same time, open the second control valve 2 on the dilution water supply branch and adjust the total dilution water flow rate to allocate water volume for subsequent NaOH dissolution and urea dilution.

[0052] Step 2: Add solid NaOH to NaOH storage tank 6, turn on stirring device 7, set stirring speed to 250 r / min, and stirring time to 10 min; draw some dilution water from dilution water supply branch through fourth control valve 4 into NaOH storage tank 6 to dissolve solid NaOH and form NaOH solution with a mass concentration of 8%, which will be used as alkaline synergist for later use.

[0053] Step 3: The NaOH solution dissolved in NaOH storage tank 6 enters the mixing pipeline after the flow rate is adjusted by the third control valve 3 and the fifth control valve 5, and is fully mixed with the urea solution passing through the first control valve 1 and the remaining dilution water passing through the second control valve 2.

[0054] Step 4: The mixed solution is sprayed into the grate furnace 9 through the SNCR spray gun 8 into a temperature zone of approximately 850°C.

[0055] Step 5, monitoring results show: NO at grate furnace outlet xWhen the concentration is consistently below 50 mg / Nm³, the denitrification efficiency is approximately 83%; when the dioxin concentration is below 0.5 ng TEQ / Nm³, the removal efficiency is approximately 90%.

[0056] Comparative Example 1 Traditional SNCR methods do not have the synergistic effect of NaOH alkaline agents.

[0057] The flue gas treated in Comparative Example 1 is from the same source as that in Example 1. Specifically, the flue gas from a waste incinerator, after pretreatment by a waste heat boiler, reaches a temperature of approximately 350°C, and its NO content... x The initial concentration was approximately 300 mg / Nm 3 Of which NO accounted for approximately 95% by volume, NO2 approximately 5%, and dioxin concentration approximately 5.0 ng TEQ / Nm³. 3 .

[0058] The traditional SNCR system differs from Example 1 in that the NaOH storage tank, inlet and outlet pipelines are removed, and only the urea solution supply branch, dilution water supply branch, SNCR spray gun 8 and grate furnace 9 are retained.

[0059] Traditional SNCR methods include the following steps: Step 1: Open the first control valve 1 on the urea solution supply branch to adjust the urea solution flow rate. Simultaneously, open the second control valve 2 on the dilution water supply branch to adjust the total dilution water flow rate, distributing water volume for subsequent urea dilution, so that the mass concentration of urea after mixing with the dilution water is 25%. After mixing the urea solution with the dilution water, spray it into the 850°C area inside the grate furnace through an SNCR spray gun.

[0060] Step 2, monitoring results show that: due to the temperature window of the traditional SNCR reaction being 950℃~1050℃, the NO at the grate furnace outlet... x Concentration approximately 150 mg / Nm 3 Furthermore, without the synergistic effect of NaOH, dioxins were not significantly removed, and the dioxin concentration at the grate furnace outlet remained at approximately 3.0 ng TEQ / Nm³. 3 .

[0061] Comparative Example 2 Comparative Example 2 uses flue gas from the same source as Example 1. Specifically, the flue gas from a waste incinerator, after pretreatment by a waste heat boiler, reaches a temperature of approximately 350°C, and its NO... x The initial concentration was approximately 300 mg / Nm 3 Of which NO accounted for approximately 95% by volume, NO2 approximately 5%, and dioxin concentration approximately 5.0 ng TEQ / Nm³. 3 .

[0062] The in-furnace synergistic dioxin removal SNCR method employs... Figure 1The SNCR system shown differs from Example 1 in that the NaOH solution concentration exceeds the suitable range (suitable range is 5% to 10%), specifically, the NaOH solution prepared in NaOH storage tank 6 has a mass concentration of 15%. The specific SNCR method includes the following steps:

[0063] Step 1: Flue gas treatment was performed according to the operating steps of Example 1. Due to the excessively high concentration of NaOH solution, the corrosiveness of the solution increased, resulting in slight scaling on the SNCR spray gun 8 and related pipelines. Furthermore, after being injected into the grate furnace 9, the local alkalinity of the furnace was excessively high, leading to some NO... x It reacts with sodium to form salts such as NaNO3, which affects the selectivity of gaseous products in the denitrification reaction.

[0064] Step 2, Monitoring Results: NO at grate furnace outlet x Concentration approximately 65 mg / Nm 3 The denitrification efficiency is approximately 78%, slightly lower than that of Example 1; the dioxin removal efficiency is approximately 85%, slightly lower than that of Example 1; at the same time, the maintenance cycle of the SNCR spray gun is shorter than that of Example 1, and the operating cost is increased.

[0065] Compared with the monitoring results of Comparative Examples 1 and 2, Example 1 of the present invention, through the system design and precise concentration control of introducing NaOH alkaline synergist, can not only reduce the lower limit of the SNCR reaction temperature window in the grate furnace 9 by 50°C to 100°C, significantly widening the SNCR reaction temperature window and achieving efficient denitrification under low load conditions, but also synergistically promote the decomposition and removal of dioxins, eliminating the need for additional dioxin removal devices, simplifying the process, and reducing costs; at the same time, the appropriate concentration of NaOH solution can also ensure the long-term stable operation of the system and avoid problems such as corrosion and scaling.

[0066] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An in-furnace synergistic dioxin removal SNCR system, characterized in that, include: The urea solution supply branch is used to provide urea solution; The dilution water supply branch is used to provide dilution water; The sodium hydroxide dissolution and addition branch includes a NaOH storage tank. The inlet of the NaOH storage tank is connected to the dilution water supply branch via an inlet pipe, and the outlet of the NaOH storage tank is connected to the dilution water supply branch via an outlet pipe. This branch is used to provide a sodium hydroxide solution as an alkaline synergist, wherein the mass concentration of the sodium hydroxide solution is 5wt%–10wt%. A grate furnace is provided with an SNCR spray gun in the temperature zone of the grate furnace. The inlet of the SNCR spray gun is connected to the urea solution supply branch and the dilution water supply branch, respectively, for spraying a mixture of urea, dilution water and sodium hydroxide solution into the temperature zone of the grate furnace.

2. The SNCR system for in-furnace synergistic dioxin removal according to claim 1, characterized in that, In the mixture, the mass concentration of urea is 20wt% to 30wt%; the concentration of NaOH in the flue gas is controlled at 30ppm to 50ppm.

3. The SNCR system for in-furnace synergistic dioxin removal according to claim 1, characterized in that, The SNCR reaction temperature window of the grate furnace is 850℃~1100℃.

4. The SNCR system for in-furnace synergistic dioxin removal according to claim 1, characterized in that, The dilution water supply branch includes a dilution water branch and a mixing branch. The inlet end of the mixing branch is connected to the dilution water branch and the outlet pipe, respectively, for pre-mixing the dilution water with the sodium hydroxide solution. The inlet end of the SNCR spray gun is connected to a mixing pipeline, which is connected to the mixing branch and the urea solution supply branch respectively.

5. The in-furnace synergistic dioxin removal SNCR system according to claim 4, characterized in that, A first control valve is installed on the urea solution supply branch to control the flow rate of the urea solution; a second control valve is installed on the dilution water supply branch to control the total flow rate of the dilution water; a third control valve is installed on the mixing branch to control the flow rate of the alkaline synergist entering the mixing pipeline; a fourth control valve is installed on the liquid inlet pipeline to control the flow rate of the dilution water entering the NaOH storage tank; and a fifth control valve is installed on the liquid outlet pipeline to control the flow rate of the alkaline synergist entering the mixing branch.

6. The SNCR system for in-furnace synergistic dioxin removal according to claim 1, characterized in that, The SNCR system includes a flue gas waste heat utilization branch, which includes a flue gas outlet pipe and a heat exchanger. The heat exchanger is coiled around the outer wall of the NaOH storage tank, and the cold side of the heat exchanger is connected to the NaOH storage tank in a loop to draw out the liquid to be dissolved or the circulating liquid in the NaOH storage tank. One end of the flue gas outlet pipe is connected to the flue gas outlet of the waste heat boiler of the grate furnace, and the other end of the flue gas outlet pipe is connected to the hot side inlet of the heat exchanger. It is used to draw out the flue gas discharged from the waste heat boiler outlet of the grate furnace and to exchange heat with the liquid to be dissolved or the circulating liquid on the cold side of the heat exchanger using the waste heat of the flue gas.

7. The SNCR system for in-furnace synergistic dioxin removal according to claim 6, characterized in that, The SNCR system includes a waste liquid treatment unit, which is connected to the hot side outlet of the heat exchanger and is used to collect the mixture of urea and sodium hydroxide precipitated in the flue gas after being cooled by the heat exchanger. The cold-side medium of the heat exchanger is the solution to be dissolved or the circulating liquid in the NaOH storage tank; the hot-side medium of the heat exchanger is the flue gas transported by the flue gas outlet pipeline.

8. A furnace-based synergistic SNCR method for removing dioxins, characterized in that, The SNCR system for in-furnace synergistic dioxin removal, as described in any one of claims 1 to 7, is used, and the SNCR method includes the following steps: Turn on the dilution water supply branch and adjust the total flow rate of the dilution water; Add solid sodium hydroxide or sodium hydroxide solution to be diluted to the NaOH storage tank, and simultaneously open the inlet pipe to adjust the mass concentration of the sodium hydroxide solution in the NaOH storage tank to 5wt%~10wt%; Turn on the outlet pipe and adjust the flow rate of the sodium hydroxide solution; Turn on the urea solution supply branch and adjust the flow rate of the urea solution; A mixture of urea, dilution water, and sodium hydroxide solution is injected into the temperature zone of the grate furnace through an SNCR spray gun. The sodium hydroxide increases the concentration of free radicals in the flue gas, thereby lowering the SNCR reaction temperature window in the temperature zone of the grate furnace and simultaneously removing nitrogen oxides and dioxins from the flue gas.

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