A denitration dilution air system based on flue gas reuse

Abstract

The present invention discloses a denitration dilution air system based on flue gas reuse, which includes a dilution air system and a monitoring and control system. The dilution air system includes a flue gas reuse pipeline, an air bypass, a dilution air booster fan, a dilution air heater, a dilution air heater control device, a hot primary air bypass, an ammonia supply pipeline, an ammonia-gas flue gas mixer, an ammonia-gas flue gas mixing pipeline, etc.; the monitoring and control system includes a flow rate monitoring module, a temperature monitoring module, and a pressure monitoring module. The heating amount of the dilution air is adjusted by the dilution air heater control device, and the dilution air volume is adjusted by the regulating valve of the flue gas reuse pipeline. Under normal operating conditions, the original flue gas with a certain temperature, pressure, low dust, and low oxygen is used as the source of dilution air. Before the unit starts, air can be used as the source of dilution air. When there is a problem with the flue gas reuse pipeline, hot primary air can be used as the source of dilution air. The application of the present invention reduces the energy consumption of the denitration dilution air system and improves the safety and reliability of the denitration dilution air system.

Description

Technical Field

[0001] The present invention belongs to the field of coal-fired power generation, and particularly relates to a denitration dilution air system based on flue gas reuse. Background Technique

[0002] As one of the important technical paths for ammonia production from urea hydrolysis, the urea hydrolysis process for ammonia production has been widely applied in engineering. However, the urea hydrolysis process for ammonia production has certain parameter requirements for denitration dilution air: (1) Flow rate, ensuring that the ammonia-air ratio is less than 5% to avoid ammonia reaching the explosion limit in the air; (2) Pressure, generally greater than 6 kPa to avoid blockage of the ammonia injection grid; (3) Temperature, generally greater than 180 °C to avoid cooling and crystallization of ammonia vapor; (4) Dust content, generally less than 10 mg / m 3 , to avoid blockage inside the ammonia injection pipeline.

[0003] Currently, there are mainly three sources of denitration dilution air: (1) Air, which requires a dilution fan to boost the pressure and then be heated to a certain temperature by a heater; (2) Cold primary air, that is, air is boosted by a cold primary air fan, saving the dilution fan, but also needs to be heated to a certain temperature by a heater; (3) Hot primary air, that is, air is boosted by a cold primary air fan and then heated by an air preheater. Although the temperature and pressure can both meet the requirements of denitration dilution air, the hot primary air carries dust and needs to be dust-removed again. It can be seen that the essence of the first two types of denitration dilution air is to heat and boost normal-temperature and normal-pressure air to certain parameters, and the basic energy consumption is relatively high. The last type of denitration dilution air requires a high-temperature dust-removal device (when the system resistance of the high-temperature dust-removal device is large, a dilution air booster fan needs to be set up again), occupying a large space and the system is relatively complex. Summary of the Invention

[0004] Based on the above requirements and problems, the purpose of the present invention is to provide a denitration dilution air system based on flue gas reuse, which makes full use of the raw flue gas with certain temperature, pressure, low dust and low oxygen after the induced draft fan and before the desulfurization system, so as to reduce the energy consumption of the denitration dilution air system and improve the safety and reliability of the denitration dilution air system.

[0005] The present invention is implemented by adopting the following technical solutions:

[0006] A denitration dilution air system based on flue gas reuse, comprising a dilution air system and a monitoring and control system;

[0007] The dilution air system includes a flue gas reuse pipeline, a regulating valve for the flue gas reuse pipeline, an air bypass, an air bypass valve, a dilution air booster fan, a dilution air booster fan isolation valve, a dilution air heater, a dilution air heater control device, a flue gas reuse pipeline valve, a hot primary air bypass, a hot primary air bypass valve, an ammonia supply pipeline, an ammonia-gas mixer, and an ammonia-gas mixing pipeline; the monitoring and control system includes a flow rate monitoring module, a temperature monitoring module, and a pressure monitoring module;

[0008] The flue gas reuse pipeline is arranged after the induced draft fan, and a regulating valve for the flue gas reuse pipeline, a dilution air booster fan isolation valve, a dilution air booster fan, a dilution air booster fan isolation valve, a dilution air heater, and a flue gas reuse pipeline valve are arranged in sequence along the flue gas flow direction; the ammonia-gas mixer is arranged at the confluence of the flue gas reuse pipeline and the ammonia supply pipeline, and the mixed gas is transported to the ammonia injection grid through the ammonia-gas mixing pipeline; the air bypass is arranged between the regulating valve for the flue gas reuse pipeline and the dilution air booster fan isolation valve, and the air bypass valve is arranged on the air bypass; the hot primary air bypass is arranged between the flue gas reuse pipeline valve and the ammonia-gas mixer, and the hot primary air bypass valve is arranged on the hot primary air bypass; the dilution air heater control device is arranged on the dilution air heater to control the heating amount of the dilution air heater; the flow rate monitoring module, the temperature monitoring module, and the pressure monitoring module are arranged after the confluence of the flue gas reuse pipeline and the hot primary air bypass and before the ammonia-gas mixer;

[0009] The flue gas at the boiler tail flows through the ammonia injection grid, the SCR reactor, the air preheater, the dust collector, the induced draft fan, and the desulfurization system.

[0010] A further improvement of the present invention is that the dilution air heater is an electric heater, a steam heater, or a flue gas heater, and the dilution air heater control device is an electric power controller, a steam regulating valve, or a flue gas regulating valve; the heating amount of the dilution air heater is adjusted through the dilution air heater control device.

[0011] A further improvement of the present invention is that the dilution air temperature at the temperature monitoring module should be greater than 180 °C. The dilution air temperature target control value is input into the monitoring and control system. According to the comparison between the real-time value of the dilution air temperature and the dilution air temperature target control value, a control instruction for the dilution air heater control device is formed, thereby realizing the closed-loop control of the dilution air temperature.

[0012] A further improvement of the present invention is that two parallel dilution air booster fans are arranged, and dilution air booster fan isolation valves are arranged before and after the dilution air booster fans to facilitate switching and isolation for maintenance in case of a failure of the dilution air booster fans.

[0013] A further improvement of the present invention is that the dilution air pressure at the pressure monitoring module is greater than 6 kPa.

[0014] A further improvement of the present invention lies in that the dilution air volume is regulated by the flue gas reuse pipeline regulating valve to ensure that the ammonia-air ratio is lower than 5%.

[0015] A further improvement of the present invention lies in that the calculation formula of the ammonia-air ratio is:

[0016] Ammonia-air ratio = ammonia gas volume flow rate ÷ (ammonia vapor volume flow rate + dilution air volume flow rate);

[0017] Ammonia gas volume flow rate = ammonia vapor mass flow rate × mass ratio of ammonia generated corresponding to urea solution concentration × 22.4 ÷ 17;

[0018] Ammonia vapor volume flow rate = ammonia vapor mass flow rate × 22.4 ÷ 22.487.

[0019] A further improvement of the present invention lies in that before the unit starts, the flue gas reuse pipeline regulating valve is closed, the air bypass valve is opened, and air is used as the source of dilution air. After the unit operates stably, the flue gas reuse pipeline regulating valve is opened, and the air bypass valve is closed, and the original flue gas is used as the source of dilution air.

[0020] A further improvement of the present invention lies in that the hot primary air bypass is connected to the hot primary air pipeline. When two dilution air booster fans in the flue gas reuse pipeline fail simultaneously and the dilution air heater fails, the hot primary air bypass valve is opened, and the flue gas reuse pipeline valve is closed, and the hot primary air is used as the source of dilution air.

[0021] A further improvement of the present invention lies in that the flow monitoring module, the temperature monitoring module, and the pressure monitoring module are all set with low-level alarm values.

[0022] The present invention has at least the following beneficial technical effects:

[0023] (1) The temperature of the original flue gas is generally about 100°C to 150°C. Compared with normal-temperature air, the energy consumption required to heat it to 180°C can be reduced by about 50% to 80%.

[0024] (2) The pressure of the original flue gas is generally about 2 kPa to 3 kPa. Compared with atmospheric-pressure air, the energy consumption required to pressurize it to 6 kPa can be reduced by about 33% to 50%.

[0025] (3) The original flue gas has been dust-removed, and the dust content can reach 10 mg / m 3 Below, which meets the low-dust requirement of the denitrification dilution air and avoids blockage inside the ammonia injection pipeline.

[0026] (4) The explosion limit of ammonia in air is 16 - 25%, that is, when ammonia and oxygen in the air reach the explosion limit, an explosion will occur when encountering an open flame or static electricity; while the oxygen content of the original flue gas is generally about 6%, which is much lower than that of air with an oxygen content of 21%, reducing the possibility of explosion.

[0027] In summary, after the application of the present invention, the energy consumption of the denitration dilution air system can be reduced by more than 50%, and the safety and reliability of the denitration dilution air system are improved. Brief Description of the Drawings

[0028] Figure 1 It is a process flow diagram of an embodiment of the present invention.

[0029] Description of the Reference Numerals:

[0030] 1. Flue gas reuse pipeline; 2. Flue gas reuse pipeline regulating valve; 3. Air bypass; 4. Air bypass valve; 5. Dilution air booster fan; 6. Dilution air booster fan isolation valve; 7. Dilution air heater; 8. Dilution air heater control device; 9. Flue gas reuse pipeline valve; 10. Hot primary air pipeline; 11. Hot primary air bypass; 12. Hot primary air bypass valve; 13. Flow monitoring module; 14. Temperature monitoring module; 15. Pressure monitoring module; 16. Ammonia supply pipeline; 17. Ammonia-gas mixer; 18. Ammonia-gas mixing pipeline; 19. Ammonia injection grid; 20. SCR reactor; 21. Air preheater; 22. Dust collector; 23. Induced draft fan. Detailed Description of the Embodiment

[0031] The present invention will be described in detail below with reference to the drawings.

[0032] The present invention first proposes to use the original flue gas with certain temperature, pressure, low dust and low oxygen as the source of denitration dilution air. Compared with conventional air, cold primary air and hot primary air, the energy consumption of the denitration dilution air system is reduced and the safety and reliability are improved. Moreover, the higher the temperature and pressure of the original flue gas, the better the energy-saving effect; the lower the dust content and oxygen content of the original flue gas, the higher the safety and reliability.

[0033] As Figure 1 shown, a denitration dilution air system based on flue gas reuse provided by the present invention includes a dilution air system and a monitoring and control system; wherein, the dilution air system includes a flue gas reuse pipeline 1, a flue gas reuse pipeline regulating valve 2, an air bypass 3, an air bypass valve 4, a dilution air booster fan 5, a dilution air booster fan isolation valve 6, a dilution air heater 7, a dilution air heater control device 8, a flue gas reuse pipeline valve 9, a hot primary air bypass 11, a hot primary air bypass valve 12, an ammonia supply pipeline 16, an ammonia-gas mixer 17 and an ammonia-gas mixing pipeline 18; the monitoring and control system includes a flow monitoring module 13, a temperature monitoring module 14 and a pressure monitoring module 15.

[0034] The flue gas reuse pipeline 1 is arranged behind the induced draft fan 23, and a flue gas reuse pipeline regulating valve 2, a dilution air booster fan isolation valve 6, a dilution air booster fan 5, a dilution air booster fan isolation valve 6, a dilution air heater 7, and a flue gas reuse pipeline valve 9 are arranged in sequence according to the flue gas flow direction; an ammonia-gas flue gas mixer 17 is arranged at the confluence of the flue gas reuse pipeline 1 and the ammonia supply pipeline 16, and the mixed gas is transported through an ammonia-gas flue gas mixing pipeline 18 to an ammonia injection grid 19; an air bypass 3 is arranged between the flue gas reuse pipeline regulating valve 2 and the dilution air booster fan isolation valve 6, and an air bypass valve 4 is arranged on the air bypass 3; a primary hot air bypass 11 is arranged between the flue gas reuse pipeline valve 9 and the ammonia-gas flue gas mixer 17, and a primary hot air bypass valve 12 is arranged on the primary hot air bypass 11; a dilution air heater control device 8 is arranged on the dilution air heater 7 for controlling the heating amount of the dilution air heater 7; a flow monitoring module 13, a temperature monitoring module 14, and a pressure monitoring module 15 are arranged after the confluence of the flue gas reuse pipeline 1 and the primary hot air bypass 11 and before the ammonia-gas flue gas mixer 17.

[0035] The flue gas at the boiler tail flows through the ammonia injection grid 19, the SCR reactor 20, the air preheater 21, the dust collector 22, the induced draft fan 23, and the desulfurization system.

[0036] The dilution air heater 7 can be an electric heater, a steam heater, or a flue gas heater. Correspondingly, the dilution air heater control device 8 can be an electric power controller, a steam regulating valve, or a flue gas regulating valve; the heating amount of the dilution air heater 7 is adjusted through the dilution air heater control device 8. The dilution air temperature at the temperature monitoring module 14 should be greater than 180 °C. The dilution air temperature target control value is input into the monitoring and control system. According to the comparison between the real-time value of the dilution air temperature and the dilution air temperature target control value, a control instruction for the dilution air heater control device 8 is formed, thereby realizing the closed-loop control of the dilution air temperature.

[0037] Two parallelly arranged dilution air booster fans 5 are provided, and dilution air booster fan isolation valves 6 are arranged before and after the dilution air booster fan 5 to facilitate switching and isolation maintenance in case of a failure of the dilution air booster fan 5. The dilution air pressure at the pressure monitoring module 15 is greater than 6 kPa.

[0038] The dilution air volume is adjusted through the flue gas reuse pipeline regulating valve 2 to ensure that the ammonia-air ratio is lower than 5%. The formula for calculating the ammonia-air ratio is:

[0039] Ammonia-air ratio = ammonia gas volume flow rate ÷ (ammonia vapor volume flow rate + dilution air volume flow rate);

[0040] Ammonia gas volume flow rate = ammonia vapor mass flow rate × ammonia mass ratio corresponding to urea solution concentration × 22.4 ÷ 17;

[0041] Ammonia vapor volume flow rate = Ammonia vapor mass flow rate × 22.4 ÷ 22.487.

[0042] Note: The mass ratio of ammonia generated corresponding to the urea solution concentration: The concentration of 40% urea solution is 21.63%, the concentration of 45% urea solution is 24.97%, and the concentration of 50% urea solution is 28.46%.

[0043] Before the unit starts, close the regulating valve 2 of the flue gas reuse pipeline, open the air bypass valve 4, and use air as the source of dilution air. After the unit operates stably, open the regulating valve 2 of the flue gas reuse pipeline and close the air bypass valve 4, and use the original flue gas as the source of dilution air.

[0044] The hot primary air bypass 11 is connected to the hot primary air pipeline 10. When problems such as simultaneous failures of two dilution air booster fans 5 and failure of the dilution air heater 7 occur in the flue gas reuse pipeline 1, the hot primary air bypass valve 12 can be opened and the flue gas reuse pipeline valve 9 can be closed to use the hot primary air as the source of dilution air, but it is not suitable for long-term operation.

[0045] The flow monitoring module 13, the temperature monitoring module 14, and the pressure monitoring module 15 are all set with low alarm values.

[0046] The present invention has the following advantages:

[0047] (1) The temperature of the original flue gas is generally about 100°C to 150°C. Compared with normal-temperature air, the energy consumption required to heat it to 180°C can be reduced by about 50% to 80%.

[0048] (2) The pressure of the original flue gas is generally about 2 kPa to 3 kPa. Compared with atmospheric-pressure air, the energy consumption required to pressurize it to 6 kPa can be reduced by about 33% to 50%.

[0049] (3) The original flue gas has been dust-removed, and the dust content can reach 10 mg / m 3 Below, meeting the low-dust requirement of the denitrification dilution air and avoiding blockage inside the ammonia injection pipeline.

[0050] (4) The explosion limit of ammonia in air is 16 - 25%, that is, when ammonia and oxygen in the air reach the explosion limit, explosion will occur when encountering open fire or static electricity; while the oxygen content of the original flue gas is generally about 6%, far lower than that of air with an oxygen content of 21%, reducing the possibility of explosion.

[0051] After the application of the present invention, the energy consumption of the denitrification dilution air system can be reduced by more than 50%, and the safety and reliability of the denitrification dilution air system are improved.

[0052] Those skilled in the art can also make various modifications to the above content without departing from the spirit and scope of the present invention defined by the claims. Therefore, the scope of the present invention is not limited to the above description, but is determined by the scope of the claims.

Claims

1. A denitration dilution air system based on flue gas reuse, characterized in that, It includes a dilution air system and a monitoring and control system; The dilution air system includes a flue gas reuse pipeline (1), a regulating valve for the flue gas reuse pipeline (2), an air bypass (3), an air bypass valve (4), a dilution air booster fan (5), a dilution air booster fan isolation valve (6), a dilution air heater (7), a control device for the dilution air heater (8), a valve for the flue gas reuse pipeline (9), a hot primary air bypass (11), a hot primary air bypass valve (12), an ammonia supply pipeline (16), an ammonia-gas flue gas mixer (17), and an ammonia-gas flue gas mixing pipeline (18); the monitoring and control system includes a flow rate monitoring module (13), a temperature monitoring module (14), and a pressure monitoring module (15); The flue gas reuse pipeline (1) is arranged after the induced draft fan (23), and successively arranged with the regulating valve for the flue gas reuse pipeline (2), the dilution air booster fan isolation valve (6), the dilution air booster fan (5), the dilution air booster fan isolation valve (6), the dilution air heater (7), and the valve for the flue gas reuse pipeline (9) in the flue gas flow direction; the ammonia-gas flue gas mixer (17) is arranged at the confluence of the flue gas reuse pipeline (1) and the ammonia supply pipeline (16), and conveys the mixed gas through the ammonia-gas flue gas mixing pipeline (18) to the ammonia injection grid (19); the air bypass (3) is arranged between the regulating valve for the flue gas reuse pipeline (2) and the dilution air booster fan isolation valve (6), and the air bypass valve (4) is arranged on the air bypass (3); the hot primary air bypass (11) is arranged between the valve for the flue gas reuse pipeline (9) and the ammonia-gas flue gas mixer (17), and the hot primary air bypass valve (12) is arranged on the hot primary air bypass (11); the control device for the dilution air heater (8) is arranged on the dilution air heater (7) to control the heating amount of the dilution air heater (7); the flow rate monitoring module (13), the temperature monitoring module (14), and the pressure monitoring module (15) are arranged after the confluence of the flue gas reuse pipeline (1) and the hot primary air bypass (11) and before the ammonia-gas flue gas mixer (17); The flue gas at the boiler tail flows through the ammonia injection grid (19), the SCR reactor (20), the air preheater (21), the dust collector (22), the induced draft fan (23), and the desulfurization system; The dilution air heater (7) is an electric heater, a steam heater, or a flue gas heater, and the control device for the dilution air heater (8) is an electric power controller, a steam regulating valve, or a flue gas regulating valve; the heating amount of the dilution air heater (7) is adjusted through the control device for the dilution air heater (8); the dilution air temperature at the temperature monitoring module (14) should be greater than 180 °C, the dilution air temperature target control value is input on the monitoring and control system, and according to the comparison between the real-time value of the dilution air temperature and the dilution air temperature target control value, a control instruction for the control device for the dilution air heater (8) is formed, thereby realizing the closed-loop control of the dilution air temperature; Before the unit starts up, close the regulating valve (2) of the flue gas recycling pipeline, open the air bypass valve (4), and use air as the source of dilution air. After the unit operates stably, open the regulating valve (2) of the flue gas recycling pipeline and close the air bypass valve (4), and use the original flue gas as the source of dilution air; The dilution air pressure at the pressure monitoring module (15) is greater than 6 kPa; adjust the dilution air volume through the regulating valve (2) of the flue gas recycling pipeline to ensure that the ammonia-air ratio is lower than 5%.

2. The denitration dilution air system based on flue gas reuse according to claim 1, wherein Two parallel dilution air booster fans (5) are provided. Isolation valves (6) for the dilution air booster fans are provided before and after the dilution air booster fans (5) to facilitate switching and isolation maintenance in case of failure of the dilution air booster fans (5).

3. The denitration dilution air system based on flue gas reuse according to claim 1, characterized in that The calculation formula for the ammonia-air ratio is: Ammonia-air ratio = ammonia gas volume flow rate ÷ (ammonia vapor volume flow rate + dilution air volume flow rate); Ammonia gas volume flow rate = ammonia vapor mass flow rate × ammonia mass ratio corresponding to urea solution concentration × 22.4 ÷ 17; Ammonia vapor volume flow rate = ammonia vapor mass flow rate × 22.4 ÷ 22.487 4. A denitration dilution air system based on flue gas reuse according to claim 1, characterized in that, The hot primary air bypass (11) is connected to the hot primary air pipeline (10). When two dilution air booster fans (5) and the dilution air heater (7) fail simultaneously in the flue gas recycling pipeline (1), open the hot primary air bypass valve (12) and close the flue gas recycling pipeline valve (9), and use the hot primary air as the source of dilution air.

5. The denitration dilution air system based on flue gas reuse according to claim 1, characterized in that, Low alarm values are set for the flow monitoring module (13), the temperature monitoring module (14), and the pressure monitoring module (15).

Images