A high-temperature ammonia spraying denitrification system and method in the main combustion zone based on urea dry spraying

Abstract

The present invention discloses a high-temperature ammonia spraying denitrification system and method for the main combustion zone based on urea dry spraying, comprising a coal-fired boiler, a urea dry spraying device and a flue gas recirculation device; a low-nitrogen burner and a SOFA air nozzle are arranged on the side wall of the coal-fired boiler; the urea dry spraying device comprises a urea powder supply device, a urea nozzle and a NO X Concentration detection probe; urea powder supply device is connected to urea nozzle; urea nozzle is located between low nitrogen burner and SOFA air nozzle; NO X The detection end of the concentration detection probe extends into the coal-fired boiler above the SOFA air nozzle, and the signal output end is connected to the urea powder supply device; the flue gas recirculation device includes a recirculating flue gas extraction pipe and an oxygen concentration detection probe; the recirculating flue gas extraction pipe is provided with a first control valve and an extraction pump in sequence along the airflow direction, the extraction end extends into the economizer inlet, and the output end is connected to the urea nozzle; the detection end of the oxygen concentration detection probe extends into the coal-fired boiler below the urea nozzle, and the signal output end is connected to the first control valve.

Description

Technical Field

[0001] The present invention relates to a flue gas denitration technology for thermal power plants, and in particular to a high-temperature ammonia spraying denitration system and method in a main combustion zone based on urea dry spraying. Background Art

[0002] Nitrogen oxides are one of the main sources of atmospheric pollution in coal-fired power plants. Currently, commonly used NOx reduction technologies in coal-fired power plants include low-NOx combustion, non-selective catalytic reduction (SNCR), and selective catalytic reduction (SCR). Conventional SNCR technology involves injecting an ammonia-based reducing agent in the temperature range of 850°C-1150°C in the presence of oxygen to reduce NO to N2 and H2O. Research has shown that SNCR technology can also be extended to high-temperature applications, namely, ammonia injection denitrification in the high-temperature reduction zone. This high-temperature reduction zone ammonia injection denitrification technology combines multiple denitrification technologies based on air staging. Ammonia-based reducing agents are injected into the high-temperature (1400-1600°C) and oxygen-deficient (O2% = 0-1%) environment of the main combustion zone within the furnace to reduce NOx in the flue gas. Compared to SNCR technology, ammonia injection denitrification in the high-temperature reduction zone is more efficient and does not produce ammonia slip.

[0003] The main factors affecting the denitration efficiency of ammonia injection in the high-temperature reduction zone are the injection location, oxygen concentration, and temperature. Research has shown that within the 1400-1600°C temperature range, higher temperatures increase denitration efficiency, while lower oxygen concentrations increase denitration efficiency. To ensure high denitration efficiency, the oxygen concentration should generally be less than 0.5%. Due to the uneven oxygen concentration within the furnace, even with the existing air-staged combustion technology, areas in the main combustion zone with oxygen concentrations exceeding 0.5% still exist, which in turn reduces the denitration efficiency of high-temperature ammonia injection. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention provides a main combustion zone ammonia spraying denitrification system and method based on urea dry spraying, which has a reasonable design, is simple and efficient, stable and feasible, and effectively solves the problem of low efficiency of main combustion zone ammonia spraying denitrification technology.

[0005] The present invention is achieved through the following technical solutions:

[0006] A high-temperature ammonia injection denitrification system in a main combustion zone based on urea dry injection comprises a coal-fired boiler, a urea dry injection device and a flue gas recirculation device connected to the coal-fired boiler;

[0007] The side wall of the coal-fired boiler is provided with a low nitrogen burner and a SOFA air nozzle in sequence from bottom to top along the height direction;

[0008] The urea dry spray device includes a urea powder supply device, a urea nozzle and a NO XConcentration detection probe; the urea powder supply device is connected to the urea nozzle; the urea nozzle is arranged on the side wall of the coal-fired boiler between the low nitrogen burner and the SOFA air nozzle; the NO X The detection end of the concentration detection probe is inserted into the coal-fired boiler above the SOFA air nozzle, and the signal output end is connected to the urea powder supply device;

[0009] The flue gas recirculation device includes a recirculating flue gas extraction pipe and an oxygen concentration detection probe; a first control valve and an extraction pump are sequentially arranged on the recirculating flue gas extraction pipe along the airflow direction, the extraction end extends into the inlet of the economizer at the tail flue of the coal-fired boiler, and the output end is connected to the urea nozzle; the detection end of the oxygen concentration detection probe extends into the coal-fired boiler below the urea nozzle, and the signal output end is connected to the first control valve.

[0010] Furthermore, the urea powder supply device includes a urea granule storage hopper, a metering device and a grinder connected in sequence; the inlet of the grinder is connected to the urea granule storage hopper and the metering device in sequence, and the outlet is connected to the urea nozzle.

[0011] Furthermore, the metering device includes a second control valve and a weighing device connected in sequence; the second control valve is connected to NO X Signal output end of the concentration detection probe.

[0012] Furthermore, the outlet of the grinder is also provided with a check valve.

[0013] Furthermore, a pressurizing fan is provided on the recirculating flue gas extraction pipe; the pressurizing fan is provided between the extraction pump and the urea nozzle.

[0014] Furthermore, the low-nitrogen burner and urea nozzle are arranged in the main combustion zone of the coal-fired boiler.

[0015] Furthermore, the SOFA air nozzle is arranged in the burnout zone of the coal-fired boiler.

[0016] A method for high-temperature ammonia spraying denitrification in a main combustion zone based on urea dry spraying, comprising:

[0017] The burnout air is sent into the burnout zone of the coal-fired boiler through the SOFA air nozzle, and the flue gas at the economizer inlet and the dry urea powder in the urea powder supply device are sent into the main combustion zone of the coal-fired boiler through the recirculating flue gas extraction pipe and the urea nozzle. X The data detected by the concentration detection probe is used to control the amount of recycled flue gas drawn in and the amount of dry urea powder injected into the main combustion zone, ultimately completing the catalytic reduction of nitrogen oxides in the flue gas.

[0018] Furthermore, the air volume of the SOFA air nozzle is 30%-40% of the total air volume of the boiler;

[0019] According to the oxygen concentration detected by the oxygen concentration detection probe, the intake amount of recirculated flue gas is controlled by controlling the opening of the first control valve; when the detected oxygen concentration in the main combustion zone is greater than 1%, the opening of the first control valve is increased to control the oxygen concentration range of the main combustion zone to 0-1%; when the detected oxygen concentration signal of the main combustion zone is less than 1%, the opening of the first control valve is kept unchanged, and the amount of recirculated flue gas is 5-20% of the total flue gas volume

[0020] NO in the burnout zone X Concentration detection probe detects NO X The concentration is fed back to the urea dry spray device, and the required urea amount is converted according to the set threshold of the ammonia-nitrogen ratio; the injection amount of dry urea powder in the main combustion zone is controlled by the second control valve to control the ammonia-nitrogen ratio NSR between 1-2.

[0021] Furthermore, the injection amount of the dry urea powder is measured and displayed in real time by a weighing device.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] The system of the present invention utilizes the low-nitrogen burner and SOFA wind nozzle to reduce the excess air coefficient of the main combustion zone, increase the SOFA wind, and make the main combustion zone of the coal-fired boiler present a reducing atmosphere; moreover, the dry urea powder provided by the urea powder supply device is used as a denitrification reducing agent. Compared with ammonia water and liquid ammonia, there is no safety risk in the transportation and storage process, and the flue gas at the economizer inlet is extracted as recycled flue gas, so that the urea particles are ground and sent into the main combustion zone together with the recycled flue gas. The use of recycled flue gas to transport urea can reduce the local oxygen concentration in the main combustion zone, form a local reducing atmosphere, reduce the generation of nitrogen oxides and improve the denitrification efficiency of the urea injected into the urea nozzle and the nitrogen oxides in the furnace; at the same time, the urea particles are ground into powder and then sent into the main combustion zone in the furnace, which can increase the contact area between urea and flue gas, increase the reaction rate of urea to be pyrolyzed into ammonia at high temperature in the furnace, and thus improve the denitrification efficiency of high-temperature ammonia injection; in addition, NO in the burnout zone X The concentration detection probe detects NO X The concentration is fed back to the urea injection device in real time, and the required ammonia amount is converted according to the set threshold of the ammonia-nitrogen ratio, which can realize real-time monitoring of the reaction inside the boiler and real-time supply of urea.

[0024] Furthermore, the system of the present invention adopts a urea granule storage hopper to store dry urea granules, and adopts dry urea as a reducing agent, which can avoid the water in the urea solution absorbing heat and lowering the local temperature in the furnace, resulting in a decrease in the efficiency of high-temperature ammonia injection denitrification and a decrease in boiler combustion efficiency; and the grinder is used to grind the urea granules into powder, which is feasible, safe and reliable, and can effectively grind the urea granules into powder to improve the reaction efficiency; at the same time, the second control valve and the weighing device are arranged with NO XThe connection of concentration detection probe can ensure the urea feeding amount, thereby improving the denitrification efficiency.

[0025] Furthermore, the system of the present invention effectively prevents the recirculated flue gas from flowing back into the grinder by providing a check valve, thereby ensuring safe operation and the transportation of dry urea powder.

[0026] Furthermore, the system of the present invention uses a pressurized fan to pressurize the recirculated flue gas, thereby increasing its kinetic energy, allowing the sprayed dry urea powder to have a longer range, increasing the coverage area of ​​urea in the furnace, improving the utilization rate of the reducing agent urea, and further reducing nitrogen oxides at the furnace outlet.

[0027] Furthermore, the system of the present invention can oxidize the unreacted escaped ammonia in the main combustion zone by arranging SOFA air nozzles in the burnout zone, thereby preventing ammonia escape.

[0028] The method of the present invention adopts an air-staged combustion mode, through the reasonable arrangement of SOFA air nozzles, urea nozzles and low-nitrogen burners, using dry urea powder as a denitrification reducing agent, and feeding the dry urea powder and recycled flue gas together, while the oxygen concentration detection probe and NO X Concentration detection probe realizes air supply volume and furnace outlet NO X The control of the concentration can effectively reduce the emission of nitrogen oxides at the furnace outlet without causing ammonia escape, which has good economic and environmental benefits. It can also increase the reaction rate of urea in the furnace during high-temperature pyrolysis to produce ammonia, further improving the denitrification efficiency of high-temperature ammonia injection. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the system according to an embodiment of the present invention.

[0030] In the figure: 1-urea granule storage hopper; 2-second control valve; 3-weighing device; 4-metering device; 5-grinder; 6-check valve; 7-pressurized fan; 8-air pump; 9-low nitrogen burner; 10-oxygen concentration detection probe; 11-urea nozzle; 12-SOFA air nozzle; 13-NO X Concentration detection probe; 14-recirculating flue gas extraction pipe; 15-economizer, 16-first control valve. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0032] The present invention provides a main combustion zone high temperature ammonia spraying denitrification system based on urea dry spraying, such as Figure 1 As shown, it includes a boiler, a flue gas recirculation system and a urea dry injection system; a low nitrogen burner 9 and a SOFA air nozzle 12 are sequentially arranged on the side wall of the boiler from bottom to top along the height direction;

[0033] The urea dry spray system includes a urea powder supply device consisting of a urea granule storage hopper 1, a metering device 4 and a grinder 5, a check valve 6, a urea nozzle 11 and a NO X Concentration detection probe 13; the metering device 4 includes a second control valve 2 and a weighing device 3; the urea granule storage hopper 1, the second control valve 2, the weighing device 3 and the grinder 5 are sequentially connected to the exhaust pipe 14 of the recirculating flue gas after the air outlet of the exhaust pump 8; the NO X The concentration detection probe 13 is arranged on the side wall of the coal-fired boiler above the SOFA air nozzle 12, with its detection end extending into the coal-fired boiler above the SOFA air nozzle 12, and its signal output end is connected to the second control valve 2; the urea nozzle 11 is arranged between the low-nitrogen burner 9 and the SOFA air nozzle 12;

[0034] The flue gas recirculation system includes a recirculating flue gas extraction pipe 14, an extraction pump 8 and a pressurized fan 7, which are connected in sequence, and an oxygen concentration detection probe 10; the oxygen concentration detection probe 10 is arranged on the side wall of the coal-fired boiler between the low-nitrogen burner 9 and the urea nozzle 11, and its detection end extends into the coal-fired boiler below the urea nozzle 11, and the signal output is connected to the first control valve 16; one end of the recirculating flue gas extraction pipe 14 is arranged at the inlet of the tail flue economizer 15, and the other end is connected to the urea nozzle 11; preferably, the pressurized fan 7 provided on the recirculating flue gas extraction pipe is used to increase the kinetic energy of the circulating flue gas, so that the urea injected into the furnace is better mixed with the flue gas and the coverage area of ​​urea in the furnace is increased.

[0035] Preferably, a check valve 6 is provided below the grinder 5 to prevent the recycled flue gas from flowing back into the grinder 5 .

[0036] In practical application, the system of the present invention is used to carry out high-temperature ammonia spraying denitrification in the main combustion zone of a combustion boiler, including the following steps:

[0037] Step 1: The coal-fired boiler adopts an air staged combustion mode, the excess air coefficient of the main combustion zone is maintained at 0.8-0.9, SOFA air nozzles 12 are set, and the air volume is increased to 25%-35% of the total air volume;

[0038] Step 2: Flue gas at the inlet of the economizer 15 is extracted through the recirculating flue gas extraction pipe 14 as recirculating flue gas. An oxygen concentration detection probe 10 is installed in the main combustion zone. The first control valve 16 is controlled according to the detected oxygen concentration signal to control the recirculating flue gas volume, so that the oxygen concentration in the main combustion zone is maintained at 0-1%, and the recirculating flue gas volume is controlled at 5-20%. The recirculating flue gas can reduce the local oxygen concentration in the main combustion zone, forming a local reducing atmosphere and reducing the formation of nitrogen oxides.

[0039] In step 3, dry urea is used as an amino reducing agent. After being ground by a grinder 5, the dry urea powder is sent into the main combustion zone together with the recycled flue gas. The recycled flue gas reduces the oxygen concentration at the urea injection position and improves the denitrification efficiency of the reaction between the injected urea and nitrogen oxides.

[0040] Among them, in step 2, the NO X NO detected by concentration detection probe 13 X The required urea concentration is converted according to the set threshold of the ammonia-nitrogen ratio, and the urea injection amount in the main combustion zone is controlled by the second control valve 2 and the weighing device 3 to control the ammonia-nitrogen ratio NSR between 1-2.

[0041] Among them, in step 1, SOFA air nozzles 12 are arranged in the burnout zone to oxidize the unreacted escaped ammonia in the main combustion zone, and no ammonia escape is generated.

[0042] Based on the above system, the present invention also provides a method for high-temperature ammonia spraying denitrification in the main combustion zone based on urea dry spraying, comprising:

[0043] The burnout air is sent into the burnout zone of the coal-fired boiler through the SOFA air nozzle 12, and the flue gas at the inlet of the economizer 15 and the dry urea powder in the urea powder supply device are sent into the main combustion zone of the coal-fired boiler through the recirculating flue gas extraction pipe 14 and the urea nozzle 11. X The data detected by the concentration detection probe 13 controls the amount of recirculated flue gas drawn in and the amount of urea injected into the main combustion zone, thereby ultimately completing the catalytic reduction of nitrogen oxides in the flue gas.

[0044] The air volume of the SOFA air nozzle 12 is 30%-40% of the total air volume of the boiler; the total air volume of the boiler includes primary air, secondary air and burnout air;

[0045] The opening of the first control valve 16 is controlled according to the oxygen concentration detected by the oxygen concentration detection probe 10, thereby controlling the amount of recirculated flue gas drawn in. When the detected oxygen concentration in the main combustion zone is greater than 1%, the opening of the first control valve 16 is increased to control the oxygen concentration in the main combustion zone within the range of 0-1%. When the monitored oxygen concentration signal in the main combustion zone is less than 1%, the opening of the first control valve 16 can be kept unchanged. Generally, the amount of recirculated flue gas is controlled at 5-20%.

[0046] NO in the burnout zone X Concentration detection probe 13 detects NO X The concentration is fed back to the urea dry spray device, and the required urea amount is converted according to the set threshold of the ammonia-nitrogen ratio; the injection amount of urea powder in the main combustion zone is controlled by the second control valve 2 to control the ammonia-nitrogen ratio, and the NSR is between 1-2.

[0047] The amount of dry urea powder injected is measured and displayed in real time by the weighing device 3 .

Claims

1. A high-temperature ammonia spraying denitrification system in the main combustion zone based on urea dry spraying, characterized in that: It includes a coal-fired boiler, and a urea dry spray device and a flue gas recirculation device connected to the coal-fired boiler; The side wall of the coal-fired boiler is provided with a low nitrogen burner (9) and a SOFA air nozzle (12) in sequence from bottom to top along the height direction; The urea dry spray device comprises a urea powder supply device, a urea nozzle (11) and a NO X Concentration detection probe (13); the urea powder supply device is connected to the urea nozzle (11); the urea nozzle (11) is arranged on the side wall of the coal-fired boiler between the low nitrogen burner (9) and the SOFA air nozzle (12); the NO X The detection end of the concentration detection probe (13) extends into the coal-fired boiler above the SOFA air nozzle (12), and the signal output end is connected to the urea powder supply device; The flue gas recirculation device comprises a recirculating flue gas extraction pipe (14) and an oxygen concentration detection probe (10); a first control valve (16) and an extraction pump (8) are sequentially arranged on the recirculating flue gas extraction pipe (14) along the airflow direction, the extraction end of which extends into the inlet of the economizer (15) at the tail flue of the coal-fired boiler, and the output end of which is connected to the urea nozzle (11); the detection end of the oxygen concentration detection probe (10) extends into the coal-fired boiler below the urea nozzle (11), and the signal output end of the probe is connected to the first control valve (16); The urea powder supply device comprises a urea granule storage hopper (1), a metering device (4), and a grinder (5) connected in sequence; the inlet of the grinder (5) is connected in sequence to the urea granule storage hopper (1) and the metering device (4), and the outlet is connected to the urea nozzle (11); The metering device (4) comprises a second control valve (2) and a weighing device (3) connected in sequence; the second control valve (2) is connected to the signal output end of the NOx concentration detection probe (13); The low nitrogen burner (9) and the urea nozzle (11) are arranged in the main combustion zone of the coal-fired boiler; The SOFA air nozzle (12) is arranged in the burnout zone of the coal-fired boiler; The outlet of the grinder (5) is also provided with a check valve (6); A pressurizing fan (7) is also provided on the recirculating flue gas extraction pipe (14); the pressurizing fan (7) is provided between the extraction pump (8) and the urea nozzle (11).

2. A method for high-temperature ammonia spraying denitrification in the main combustion zone based on urea dry spraying, characterized in that: The system according to claim 1, comprising: The burnout air is sent into the burnout zone of the coal-fired boiler through the SOFA air nozzle (12), and the flue gas at the inlet of the economizer (15) and the dry urea powder in the urea powder supply device are sent into the main combustion zone of the coal-fired boiler through the recirculation flue gas extraction pipe (14) and the urea nozzle (11). X The data detected by the concentration detection probe (13) are used to control the amount of recirculated flue gas drawn in and the amount of dry urea powder injected into the main combustion zone, thereby ultimately completing the catalytic reduction of nitrogen oxides in the flue gas; The air volume of the SOFA air nozzle (12) is 30%-40% of the total air volume of the boiler; According to the oxygen concentration detected by the oxygen concentration detection probe (10), the intake amount of the recirculated flue gas is controlled by controlling the opening of the first control valve (16); when the detected oxygen concentration in the main combustion zone is greater than 1%, the opening of the first control valve (16) is increased so that the oxygen concentration in the main combustion zone is controlled within a range of 0-1%; when the detected oxygen concentration signal in the main combustion zone is less than 1%, the opening of the first control valve (16) is kept unchanged, and the amount of recirculated flue gas is 5-20% of the total flue gas amount; NO in the burnout zone X Concentration detection probe (13) detects NO X The concentration is fed back to the urea dry spray device, and the required urea amount is converted according to the set threshold value of the ammonia nitrogen ratio; the injection amount of the dry urea powder in the main combustion zone is controlled by the second control valve (2), and the ammonia nitrogen ratio NSR is controlled between 1 and 2; The amount of dry urea powder injected is measured and displayed in real time by a weighing device (3).

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