A composite reducing agent synergistic denitration system and method for coal-fired boilers
By using air-level combustion, low nitrogen burner and SOFA air combined with amino reducing agent and methane injection system in coal-fired boiler, the problem of low denitrification efficiency of low volatile coal powder in the existing technology is solved, and high efficiency reduction of nitrogen is achieved Oxide emissions and reducing SCR pressure ensure system stability and environmental benefits.
Patent Information
- Application Number
- CN202010387484.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2020-05-09
- Publication Date
- 2024-12-17
- Estimated Expiration
- 2040-05-09
AI Technical Summary
When existing coal-fired power plants use ammonia injection denitrification technology in the main combustion zone, the coal species has poor adaptability, especially the denitrification efficiency of low-volatilization coal powder, which makes it difficult to effectively reduce nitrogen oxide emissions, and the SCR denitrification system is easy. Problems such as blockage of air preheater due to excessive ammonia spraying.
A coal-fired boiler composite reducing agent collaborative denitrification system is designed, using air-level combustion, low-nitrogen burner and SOFA air nozzle, combining amino reducing agent and methane injection system, and injecting amino reducing agent and methane into the main combustion zone. Reactive free radicals are generated to improve denitrification efficiency, and the nitrogen oxide concentration is further reduced through the SCR flue gas denitrification system to ensure no ammonia escape and reduce SCR pressure.
It has achieved high-efficiency nitrogen oxide reduction for different volatile coal types, reduced the nitrogen oxide concentration at the furnace outlet to below 50mg/m3, reduced the SCR denitrification pressure, avoided the blockage of air preheater, and had good economic and environmental benefits. .
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Figure CN111457409B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a flue gas denitration technology for a thermal power plant, and in particular to a composite reducing agent coordinated denitration system and method for a coal-fired boiler. Background Art
[0002] Nitrogen oxides are one of the main sources of air pollution in coal-fired power plants. At present, the commonly used nitrogen oxide reduction technologies in coal-fired power plants include low-nitrogen combustion technology, non-selective catalytic reduction technology (SNCR) and selective catalytic reduction technology (SCR). The combination or joint use of different denitrification processes will be an important development direction of denitrification technology. Innovative denitrification mechanisms and the development of multi-stage composite denitrification processes are becoming the development direction.
[0003] Conventional SNCR technology is to inject an amino reducing agent to reduce NO to N in the temperature range of 850℃-1150℃ under aerobic conditions. 2 and H 2 O. Studies have shown that SNCR technology can also be extended to the high-temperature section, that is, high-temperature ammonia injection denitrification technology. High-temperature ammonia injection denitrification technology is a method of combining multiple denitrification technologies based on air classification. Ammonia reducing agents are injected into the high-temperature, oxygen-deficient environment formed in the main combustion zone of the furnace to reduce NOx in the flue gas.
[0004] At present, power plant boilers generally adopt air-staged low-nitrogen combustion technology, and the main combustion zone is in a reducing atmosphere, which provides conditions for the application of ammonia spraying denitrification technology in the main combustion zone. Domestic researchers have proposed different methods for the implementation and control of ammonia spraying denitrification technology in the main combustion zone. For example, Chinese patent CN201810917125.9 discloses a denitrification system and method for low-nitrogen burners in power plant boilers in coordination with high-temperature ammonia spraying. The invention adopts a low-nitrogen burner, arranges SOFA wind in the burnout zone, and introduces recirculated flue gas into the main combustion zone, so that the main combustion zone is a high-temperature reducing atmosphere. At this time, the reducing agent sprayed into the main combustion zone can react with nitrogen oxides in the flue gas to reduce the concentration of nitrogen oxides. For example, Chinese patent CN201821111988.9 discloses a supercritical carbon dioxide cyclone furnace structure based on spraying ammonia in a high-temperature reducing zone to reduce nitrogen oxides. Ammonia agent nozzles are arranged below the burnout air nozzles in the main furnace of the cyclone furnace, and the ammonia agent nozzles are arranged in multiple layers and tilted, which enhances the mixing effect of ammonia agent and flue gas, thereby improving the denitrification efficiency of ammonia spraying. However, the above method has poor adaptability to coal types. When the coal type is low-volatile pulverized coal, the denitrification efficiency of ammonia injection in the main combustion zone is low. Summary of the invention
[0005] In view of the problems existing in the prior art, the present invention provides a composite reducing agent coordinated denitrification system and method for a coal-fired boiler, which has a reasonable design, is simple and efficient, stable and feasible, and can be applied to coals with different volatile contents.
[0006] The present invention is achieved through the following technical solutions:
[0007] A composite reducing agent synergistic denitration system for a coal-fired boiler, comprising a boiler, an amino reducing agent injection system and a methane injection system;
[0008] The amino reducing agent injection system comprises an amino reducing agent supply unit and an amino reducing agent spray gun connected in sequence;
[0009] The methane injection system comprises a methane supply unit and a methane injection gun connected in sequence;
[0010] The boiler adopts air staged combustion, a low-nitrogen burner is provided in the main combustion zone of the boiler, and a SOFA air nozzle is provided in the burnout zone; an SCR flue gas denitrification system is provided in the tail flue of the boiler, and the outlet flue of the SCR flue gas denitrification system is connected to an air preheater;
[0011] The methane spray gun and the amino reducing agent spray gun are arranged in sequence between the low nitrogen burner and the SOFA air nozzle.
[0012] Preferably, the amino reducing agent supply unit comprises an amino reducing agent storage tank, a feeding pump, an amino reducing agent metering device and an amino reducing agent control valve which are connected in sequence, and the output end of the amino reducing agent control valve is connected to the input end of the amino reducing agent spray gun.
[0013] Furthermore, the amino reductant supply unit also includes a first processor and a NO concentration detection probe arranged at the boiler furnace outlet; the input end of the first processor is connected to the NO concentration detection probe, and the output end is connected to the control end of the amino reductant control valve, and the first processor is used to control the opening of the amino reductant control valve according to the detected NO concentration and the set threshold value of the ammonia nitrogen ratio.
[0014] Preferably, the methane supply unit comprises a methane storage tank, an output valve, a methane metering device and a methane control valve which are connected in sequence, and the output end of the methane control valve is connected to the input end of the methane spray gun.
[0015] Furthermore, the methane supply unit also includes a second processor, the output end of the second processor is connected to the control end of the amino reductant control valve, and the second processor is used to control the opening of the methane control valve according to the threshold value of the heat released by methane to the total fuel heat.
[0016] Preferably, the methane spray gun and the amino reducing agent spray gun are arranged in sequence close to the low nitrogen burner.
[0017] A composite reductant synergistic denitration method for a coal-fired boiler, based on any of the above-mentioned systems, in the main combustion zone of the boiler furnace, a methane spray gun is arranged below the amino reductant spray gun in the main combustion zone, and the injected methane is pyrolyzed to produce CHi + and H+ Active free radical, CHi + and H + The active free radicals react with the amino reducing agent sprayed from the amino reducing agent spray gun to generate NH 2 - , improve the denitrification efficiency of ammonia injection in the main combustion zone.
[0018] Preferably, the method specifically comprises the following steps:
[0019] Step 1: The NO concentration detected by the NO concentration detection probe arranged at the furnace outlet is converted into the required ammonia amount according to the set threshold of the ammonia-nitrogen ratio, and then the amount of amino reducing agent injected into the main combustion zone is controlled by the amino reducing agent control valve; the amino reducing agent metering device measures and displays the injection amount of the amino reducing agent in real time;
[0020] Step 2, the methane supply is converted according to the threshold value of the heat released by methane to the total fuel heat, and then the methane injection amount in the main combustion zone is controlled by the methane control valve; the methane metering device measures and displays the injection amount of methane gas in real time.
[0021] Furthermore, in step 2, the threshold value for burning high-volatile coal powder is lower than the threshold value for burning low-volatile coal powder.
[0022] Preferably, the amino reducing agent includes at least one of liquid ammonia, urea, and aqueous ammonia.
[0023] Compared with the prior art, the present invention has the following beneficial technical effects:
[0024] The present invention adopts an air-staged combustion method, and utilizes the low-nitrogen burner and SOFA wind nozzle to reduce the excess air coefficient of the main combustion zone. Increase the SOFA wind to make the main combustion zone present a reducing atmosphere. Spray an amino reducing agent (liquid ammonia, urea, ammonia water, etc.) into the reduction zone of the main combustion zone. The amino reducing agent (liquid ammonia, urea, ammonia water, etc.) can react with nitrogen oxides in the flue gas under a high-temperature reducing atmosphere to reduce the nitrogen oxide concentration at the furnace outlet. By spraying methane gas above the low-nitrogen burner, the oxygen concentration in the main combustion zone is reduced, and active free radicals such as CHi and H are generated at the same time. Active free radicals such as CHi and H can react with the amino reducing agent to generate NH 2 , improve the denitration efficiency of the ammonia spray reaction in the main combustion zone, and further reduce the nitrogen oxide concentration at the furnace outlet. The unreacted amino reducing agent sprayed into the main combustion zone is oxidized through the SOFA air nozzle, so there is no ammonia escape. Through the above arrangement, the denitration pressure of the tail SCR is reduced, and the air preheater blockage caused by excessive ammonia spraying of the SCR is prevented. The main combustion zone after air classification sprays methane and ammonia step by step, and combined with the SCR flue gas denitration technology, the nitrogen oxide emission concentration can eventually be reduced to 50mg / m 3 the following. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 This is a diagram of the composite reducing agent coordinated denitrification system for coal-fired boilers according to the present invention.
[0026] In the figure: 1-amino reducing agent storage tank; 2-feeding pump; 3-amino reducing agent metering device; 4-amino reducing agent control valve; 5-methane storage tank; 6-methane metering device; 7-methane control valve; 8-low nitrogen burner; 9-methane spray gun; 10-NO concentration detection probe; 11-amino reducing agent spray gun; 12-SOFA air nozzle; 13-boiler; 14-SCR flue gas denitrification system; 15-air preheater. DETAILED DESCRIPTION
[0027] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.
[0028] The present invention provides a composite reducing agent synergistic denitration system for a coal-fired boiler, such as Figure 1 As shown, it includes a boiler 13, an amino reducing agent storage tank 1, a methane storage tank 5, a NO concentration detection probe 10 and an SCR flue gas denitration system 14; the boiler 13 adopts air staged combustion technology, and the boiler 13 is provided with a low nitrogen burner 8 in the main combustion zone and a SOFA air nozzle 12 in the burnout zone. A methane spray gun 9 and an amino reducing agent spray gun 11 are sequentially arranged above the low nitrogen burner 8, a NO concentration detection probe 10 is arranged at the boiler furnace outlet, and an SCR flue gas denitration system 14 is arranged at the tail flue of the boiler 13. The amino reducing agent includes at least one of liquid ammonia, urea, and ammonia water.
[0029] The methane storage tank 5 is connected to the input end of the methane injection gun 9 via the output valve, the methane metering device 6 and the methane control valve 7 in sequence; the methane control valve 7 is controlled by the coal feeding amount and the type of coal, and the methane metering device 6 can measure and display the injection amount of methane in real time. When burning bituminous coal, the methane injection amount is converted according to the threshold value of the heat released by methane to the total fuel heat; and when burning anthracite, the methane injection amount is converted according to the threshold value of the heat released by methane to the total fuel heat; the threshold value when using bituminous coal is lower than the threshold value when using anthracite, and 2% and 4% are used respectively in this preferred embodiment.
[0030] The amino reducing agent storage tank 1 is connected to the input end of the amino reducing agent spray gun 11 through the feed pump 2, the amino reducing agent metering device 3 and the amino reducing agent control valve 4 in sequence. The amino reducing agent control valve 4 is controlled by the NO concentration at the furnace outlet, and the amino reducing agent metering device 3 can measure and display the injection amount of the amino reducing agent in real time. According to the NO concentration signal detected by the NO concentration detection probe 10 before the main combustion zone is sprayed with ammonia, the injection amount of the amino reducing agent is converted according to the set threshold value of the ammonia nitrogen ratio. In this preferred embodiment, it is converted according to the ammonia nitrogen ratio of 2.
[0031] The present invention provides a method for coal-fired boiler composite reducing agent coordinated denitration, based on the denitration system of the present invention, comprising the following steps:
[0032] Step 1: The NO concentration detected by the NO concentration detection probe arranged at the furnace outlet is converted into the required ammonia amount according to the ammonia-nitrogen ratio of 2, and then the amino reducing agent metering device and the amino reducing agent control valve are used to control the injection amount of the main combustion zone.
[0033] Step 2: by arranging a methane spray gun below the amino reducing agent spray gun in the main combustion zone, the injected methane is pyrolyzed to produce CHi + , H + Active free radicals such as CHi and H can react with amino reducing agents to generate NH 2 - , improve the denitrification efficiency of ammonia injection in the main combustion zone. When burning high-volatile coal powder such as bituminous coal, the coal powder will volatilize and analyze faster during combustion, and the CH generated in the main combustion zone + , H + When there are more active free radicals, the amount of methane injected is calculated based on the heat of injected methane accounting for 2% of the total fuel heat. When burning low-volatile coal powder such as anthracite, the coal pyrolysis rate is slow, the oxygen concentration in the main combustion zone is high, and Chi + , H + There are fewer free radicals, so more methane needs to be injected. The amount of methane injected is calculated based on the heat of injected methane accounting for 4% of the total fuel heat.
[0034] The method can effectively reduce the nitrogen oxide concentration at the furnace outlet of pulverized coal with different volatile contents, reduce the denitration pressure of the tail SCR, and prevent the blockage of the air preheater caused by excessive ammonia injection of the SCR. It has good economic and environmental benefits.
[0035] The present invention adopts an air-staged combustion method, and is provided with a low-nitrogen burner 8 and a SOFA wind nozzle 12. By reducing the excess air coefficient of the main combustion zone and increasing the SOFA wind, the main combustion zone is made to present a reducing atmosphere. An amino reducing agent spray gun 11 with water cooling is provided above the low-nitrogen burner 8. The amino reducing agent is sprayed into the furnace reduction zone through the amino reducing agent spray gun 11. Under the high temperature environment of the main combustion zone, the sprayed amino reducing agent can react with nitrogen oxides in the flue gas. A methane spray gun 9 is provided below the amino reducing agent spray gun 11. The injected methane is pyrolyzed at high temperature to produce active free radicals such as CHi and H. These active free radicals can react with the amino reducing agent to generate NH 2 , further improving the denitrification efficiency of high-temperature ammonia injection in the main combustion zone.
[0036] For coals with high volatile content such as bituminous coal, the pulverized coal is volatilized and analyzed quickly during combustion, and the Chi generated in the main combustion zone + , H + When there are more active free radicals, the amount of methane injected is calculated based on the heat of injected methane accounting for 2% of the total fuel heat. When burning low-volatile coal powder such as anthracite, the coal pyrolysis rate is slow, the oxygen concentration in the main combustion zone is high, and Chi + , H + There are fewer free radicals, so more methane needs to be injected. The amount of methane injected is calculated based on the heat of injected methane accounting for 4% of the total fuel heat.
[0037] In addition, the burnout zone is provided with a SOFA air nozzle 12, which can oxidize the unreacted ammonia injected into the main combustion zone, so there is no ammonia escape.
[0038] Through the above arrangement, the concentration of nitrogen oxides at the furnace outlet can be effectively reduced, and there is no ammonia escape, which reduces the pressure of SCR denitration at the tail end and prevents the blockage of the air preheater caused by excessive ammonia injection in the SCR. Through air classification, high-temperature ammonia injection and methane injection in the main combustion zone and the final SCR flue gas denitration system, the synergistic denitration of the composite reductant can be achieved, and the nitrogen oxide emission concentration can be reduced to 50mg / m 3 the following.
Claims
1. A method for synergistic denitration of coal-fired boilers using composite reductants. It is characterized in that A composite reducing agent synergistic denitration system for a coal-fired boiler, the system comprising a boiler (13), an amino reducing agent injection system and a methane injection system; The amino reducing agent injection system comprises an amino reducing agent supply unit and an amino reducing agent spray gun (11) connected in sequence; The methane injection system comprises a methane supply unit and a methane injection gun (9) connected in sequence; The boiler (13) adopts air staged combustion, a low nitrogen burner (8) is provided in the main combustion zone of the boiler (13), and a SOFA air nozzle (12) is provided in the burnout zone; an SCR flue gas denitration system (14) is provided in the tail flue of the boiler (13), and the outlet flue of the SCR flue gas denitration system (14) is connected to an air preheater (15); A methane spray gun (9) and an amino reducing agent spray gun (11) are sequentially arranged between the low nitrogen burner (8) and the SOFA air nozzle (12); In the main combustion zone of the boiler furnace, a methane spray gun is arranged below the ammonia reducing agent spray gun in the main combustion zone. The injected methane is pyrolyzed to produce CHi + and H + Active free radical, CHi + and H + The active free radicals react with the amino reducing agent sprayed from the amino reducing agent spray gun to generate NH 2 - , improve the denitrification efficiency of ammonia injection in the main combustion zone; The specific steps include: Step 1, the NO concentration detected by the NO concentration detection probe arranged at the furnace outlet is converted into the required ammonia amount according to the set threshold of the ammonia-nitrogen ratio, and then the amount of amino reducing agent injected into the main combustion zone is controlled by the amino reducing agent control valve (4); the amino reducing agent metering device (3) measures and displays the injection amount of the amino reducing agent in real time; Step 2, the methane supply is converted according to the threshold value of the heat released by methane to the total fuel heat, and then the methane injection amount of the main combustion zone is controlled by the methane control valve (7); the methane metering device (6) measures and displays the injection amount of methane gas in real time.
2. A method for synergistic denitration of a coal-fired boiler using a composite reducing agent according to claim 1, It is characterized in that In step 2, the threshold value for burning high-volatile coal powder is lower than the threshold value for burning low-volatile coal powder.
3. A method for synergistic denitration of a coal-fired boiler using a composite reducing agent according to claim 1, It is characterized in that The amino reducing agent includes at least one of liquid ammonia, urea, and aqueous ammonia.
4. A method for synergistic denitration of a coal-fired boiler using a composite reducing agent according to claim 1, It is characterized in that The amino reducing agent supply unit comprises an amino reducing agent storage tank (1), a feed pump (2), an amino reducing agent metering device (3) and an amino reducing agent control valve (4) which are connected in sequence, and the output end of the amino reducing agent control valve (4) is connected to the input end of the amino reducing agent spray gun (11).
5. A method for synergistic denitration of a coal-fired boiler using a composite reducing agent according to claim 4, It is characterized in that The amino reducing agent supply unit further comprises a first processor and a NO concentration detection probe (10) arranged at the furnace outlet of the boiler (13); the input end of the first processor is connected to the NO concentration detection probe (10), and the output end is connected to the control end of the amino reducing agent control valve (4); the first processor is used to control the opening of the amino reducing agent control valve (4) according to the detected NO concentration and the set threshold value of the ammonia nitrogen ratio.
6. A method for synergistic denitration of a coal-fired boiler using a composite reducing agent according to claim 1, It is characterized in that The methane supply unit comprises a methane storage tank (5), an output valve, a methane metering device (6) and a methane control valve (7) which are connected in sequence, and the output end of the methane control valve (7) is connected to the input end of the methane spray gun (9).
7. A method for synergistic denitration of a coal-fired boiler using a composite reducing agent according to claim 6, It is characterized in that The methane supply unit further comprises a second processor, the output end of the second processor being connected to the control end of the amino reductant control valve (4), and the second processor being used to control the opening of the methane control valve (7) according to a threshold value of the heat released by methane to the total heat of the fuel.
8. A method for synergistic denitration of a coal-fired boiler using a composite reducing agent according to claim 1, It is characterized in that The methane spray gun (9) and the amino reducing agent spray gun (11) are arranged in sequence near the low nitrogen burner (8).