A flue gas reheating system for full-load operation of coal-fired units for denitrification

Abstract

The present invention relates to a flue gas reheating system for full-load operation of coal-fired units for denitrification, comprising a flue gas reheating gas burner, a gas pipeline system, and an air distribution pipeline system. The flue gas reheating gas burner adopts an axial double-nozzle premixed two-stage ignition design, the ignition device uses an electric spark to ignite the ignition air gun, and the ignition air gun ignites the main air gun to ensure the safe ignition of the gas and the sufficient combustion and heat release of the gas under a negative pressure environment. Based on the feedback signal of the temperature measurement point of the denitrification system, the SCR inlet flue gas temperature rise requirement and the required consumption of natural gas are calculated in real time. By controlling the automatic control regulating valve on the corresponding pipeline, the flow of natural gas and combustion-supporting air is adjusted to ensure that the SCR inlet flue gas temperature meets the denitrification requirements. The present invention can significantly increase the denitrification system inlet flue gas temperature during the startup and low-load operation of the coal-fired unit, and can achieve the normal operation of the denitrification equipment from the startup of the unit to the 100% BMCR full-load condition.

Description

Technical Field

[0001] The present invention relates to a flue gas reheating system for full-load operation of a coal-fired unit for denitrification, which is used to increase the flue gas temperature at the SCR inlet of the coal-fired unit to meet the unit's operation requirements from unit startup to 100% BMCR full-load operation, and belongs to the field of boiler environmental protection technology. Background Art

[0002] In recent years, with the rapid growth of installed capacity of clean energy sources such as wind and solar power, my country's power generation and consumption structures have been continuously changing. This has necessitated the long-term operation of coal-fired power units at low loads to address the increasingly prominent peak-shaving problem of the power grid. However, as the average load factor of thermal power plants decreases and the duration of low-load operation increases, when the peak-shaving load drops below 40%, the flue gas temperature entering the SCR denitrification system becomes too low, preventing the SCR system from operating properly and causing excessive NOx emissions. Furthermore, with increasingly stringent environmental protection requirements, some provinces and cities have begun assessing NOx emissions during the startup phase of coal-fired units. However, during the startup phase, the flue gas temperature of coal-fired power plant boilers is relatively low, failing to reach the normal operating temperature window for SCR catalysts, which can also lead to excessive NOx emissions.

[0003] Based on current practical applications, traditional wide-load denitrification (DNO) systems are primarily categorized into low-temperature catalysts and boiler-side modifications. Low-temperature catalysts primarily broaden the denitrification catalyst temperature window, enabling it to maintain denitrification efficiency under low-load flue gas temperature conditions. Boiler-side modifications primarily involve modifying the boiler's flue gas, air, and steam-water systems to increase the SCR inlet flue gas temperature at low loads, enabling normal denitrification. Key technologies include flue gas bypass, feedwater bypass, economizer staging, economizer feedwater replacement, and 0# high-pressure heating. These technologies primarily increase the economizer inlet water temperature at low loads, or directly raise the economizer outlet flue gas temperature (SCR inlet flue gas temperature) at low loads, ensuring efficient operation of the SCR denitrification system at low loads. Each of these technologies has its advantages and disadvantages. Flue gas bypass may experience issues such as baffle sticking during commissioning; economizer staging is primarily suitable for new units, while retrofitting existing units is subject to significant spatial limitations; economizer feedwater replacement and 0# high-pressure heating technologies, which regulate temperature from the water side, are relatively complex and require high investment, and can also reduce boiler efficiency. Summary of the Invention

[0004] The purpose of the present invention is to increase the flue gas temperature at the inlet of the denitrification equipment, ensure the normal operation of the denitrification equipment, meet the environmental protection requirements of NOx emissions, and thus realize the full operation of the denitrification equipment from the start-up to the full load condition of 100% BMCR of the coal-fired power station boiler.

[0005] In order to achieve the above-mentioned purpose, the technical solution of the present invention is to provide a flue gas reheating system for full-load operation of denitrification coal-fired units, which is characterized in that it includes a gas pipeline system, an air distribution pipeline system and N flue gas reheating gas burners, N≥1, and the number of flue gas reheating gas burners is mainly determined based on the design parameters of the unit and the simulation calculation results. The flue gas reheating gas burner is embedded and fixedly installed in the slope area of ​​the economizer ash hopper through an embedded hole provided on the slope area of ​​the economizer ash hopper of the coal-fired unit. The gas pipeline system and the air distribution pipeline system are connected to the flue gas reheating gas burner through a bellows flange. The combustible gas and combustion-supporting air enter the flue gas reheating gas burner through the gas pipeline system and the air distribution pipeline system respectively. The combustible gas and combustion-supporting air are fully mixed in the flue gas reheating gas burner and then ignited and enter the flue outlet of the economizer of the coal-fired unit to burn and release heat. The high-temperature flue gas generated is fully mixed with the flue gas in the flue after diversion, so that the average temperature of the flue gas at the inlet of the SCR catalyst reaches above 310°C.

[0006] Preferably, the number of the flue gas reheat gas burners is 4 to 8, and the design gas flow rate of a single flue gas reheat gas burner is 200 to 500 Nm 3 / h; all the flue gas reheating gas burners are arranged in two layers, upper and lower, to ensure that the reheated flue gas directly enters the horizontal flue in the economizer area of ​​the coal-fired unit, the gas flame is consistent with the flue gas flow direction, to ensure the uniformity of the temperature field and flow field and the safety of the tail flue, and to ensure that the flue gas temperature of the desulfurization system on both sides can meet the requirements at the same time.

[0007] Preferably, the flue gas reheating gas burner includes an ignition gas gun, a main gas gun, a fire detection cooling and purge air duct, a gas combustion-supporting air distribution duct, a high-energy igniter, an ultraviolet fire detection device and a premixing cavity. One end of the ignition gas gun, the high-energy igniter and the ultraviolet fire detection device is inserted into the fire detection cooling and purge air duct and then extends into the premixing cavity, and is communicated with the gas combustion-supporting air distribution duct in the premixing cavity; the other end of the ignition gas gun is connected to the gas pipeline system through the ignition gas gun nozzle by a gold soft bellows; the other end of the high-energy igniter and the ultraviolet fire detection device is located in the economizer of the coal-fired unit; one end of the main gas gun is connected to the premixing cavity and is communicated with the gas combustion-supporting air duct, and the other end is connected to the gas pipeline system through the main gas gun nozzle by a gold soft bellows; the fire detection cooling and purge air duct and the gas combustion-supporting air duct are connected to the air distribution duct system through the fire detection cooling and purge air duct nozzle and the gas combustion-supporting air duct nozzle by a gold soft bellows respectively.

[0008] Preferably, the gas pipeline enters the flue gas reheating gas burner via two routes, one of which has a flow rate of 50 Nm 3 / h of low flow combustible gas, and the other one has a flow rate of 150~450Nm 3 / h of large-flow combustible gas, and small-flow combustible gas is mixed in the premixing cavity by the ignition gas gun and the combustion-supporting air of the gas combustion-supporting air duct, and then ignited by the high-energy igniter, and then further ignites the large-flow combustible gas of the gas main air gun.

[0009] Preferably, a manual shut-off valve 1 and a pneumatic quick-break valve are provided on the connecting pipe between the gas pipeline and the nozzle of the ignition gas gun, which are used to start and stop the ignition gas gun; the flow of the main gas gun is adjustable, and a manual shut-off valve 2, a gas flow control valve and a gas pressure transmitter are provided on the connecting pipe between the gas pipeline and the nozzle of the main gas gun, which are used to adjust and control the output of the main gas gun.

[0010] Preferably, the air distribution duct is provided with a manual shut-off valve 3, an air distribution flow control valve and an air distribution pressure transmitter for adjusting the air distribution and cooling air volume.

[0011] Preferably, the SCR inlet flue gas temperature rise requirement and the required natural gas consumption are calculated in real time based on the feedback signal of the existing temperature and flue gas flow rate of the coal-fired unit denitrification system, and the flow and pressure of natural gas and combustion-supporting air are adjusted by controlling the gas flow control valve, the gas pressure transmitter, the air distribution flow control valve, and the air distribution pressure transmitter to ensure that the SCR inlet flue gas temperature meets the denitrification requirements.

[0012] The present invention provides a flue gas reheating system capable of increasing the flue gas temperature at the inlet of the denitrification equipment of the coal-fired unit boiler. The flue gas temperature at the inlet of the denitrification system can be significantly increased during the startup and low-load operation of the coal-fired unit, with the maximum temperature rise reaching 160°C. This realizes the full operation of the denitrification equipment from the startup of the unit to the full-load operation of 100% BMCR, meeting the ultra-low emission environmental protection requirements.

[0013] The present invention has the following characteristics:

[0014] The present invention primarily incorporates a partial flue gas reheat burner at the exit flue of the original SCR inlet economizer. Natural gas, such as natural gas, is primarily introduced into the burner. Through the burner's dual nozzles, natural gas enters the premixing chamber where it is thoroughly mixed with air. After ignition by a high-energy igniter, it enters the economizer exit flue to burn and release heat. The resulting high-temperature flue gas is then diverted and thoroughly mixed with the original flue gas, raising the average flue gas temperature at the SCR catalyst inlet to above 310°C.

[0015] Taking into account the uniformity of the flue gas temperature field and flow field after reheating and the safety of the tail flue, the installation-related parameters of the flue gas reheating burner described in the present invention are simulated through calculation. The flue gas reheating gas burner adopts an embedded installation method. By opening an embedded hole in the slope area of ​​the economizer ash hopper of the original coal-fired unit, the flue gas reheating gas burner is embedded and fixedly installed in the slope area of ​​the economizer ash hopper, and arranged in two layers.

[0016] Considering the negative pressure environment of the tail flue, the flue gas reheating gas burner described in the present invention adopts a double nozzle two-stage ignition premixing design, and some small flow (50Nm 3 / h) Natural gas is mixed with the air in the gas combustion air duct in the premixing chamber through the ignition gas gun and ignited by the high-energy igniter; and then further ignites the high flow rate (150~450Nm 3 / h) natural gas, ensuring that the flow rate at the natural gas nozzle outlet is greater than the tempering speed of the natural gas and a wide output adjustment range.

[0017] Taking into account load fluctuations and the wide adjustment range of the flue gas reheating system, the control logic described in the present invention calculates the flue gas temperature rise requirement at the SCR inlet and the required natural gas consumption in real time based on feedback signals from measurement points such as the denitrification system temperature and flue gas flow rate. By controlling the automatic control regulating valves and pressure transmitters on the natural gas and combustion air inlet pipelines, the flow rates of natural gas and combustion air are adjusted to ensure the flue gas temperature at the SCR inlet.

[0018] Based on the above characteristics, compared with other existing technical routes for increasing the flue gas temperature at the SCR inlet, the system of the present invention is simple, safe and reliable. It heats the flue gas by releasing heat through natural gas combustion. The maximum temperature rise of the flue gas at the SCR inlet can reach 160°C. The temperature rise effect is significant and has no impact on the boiler itself. In addition, the gas consumption can be controlled and adjusted based on real-time feedback of the flue gas temperature at the SCR inlet, thereby reducing operating costs and realizing the full commissioning of the denitrification equipment of the coal-fired power station boiler from startup to 100% BMCR full load condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Shown is a schematic diagram of the system structure of the present invention.

[0020] Figure 2 Shown is a schematic structural diagram of the flue gas reheating gas burner in the present invention.

[0021] Figure 3 Shown is a schematic diagram of the automatic temperature regulation control logic of the flue gas reheating gas burner in the present invention.

[0022] In the figure, 1 represents the slope area of ​​the economizer ash hopper of the coal-fired unit, 2 represents the flue gas reheat gas burner, 3 represents the gas pipeline system, 4 represents the air distribution pipeline system, and 5 represents the horizontal flue area of ​​the economizer of the coal-fired unit.

[0023] Reference numeral 21 indicates the gas ignition gun for the flue gas reheat gas burner; 22 indicates the main gas gun for the flue gas reheat gas burner; 23 indicates the flame detection, cooling, and purge air duct for the flue gas reheat gas burner; 24 indicates the combustion-supporting air duct for the flue gas reheat gas burner; 25 indicates the high-energy igniter on the flue gas reheat gas burner; 26 indicates the ultraviolet flame detection device on the flue gas reheat gas burner; and 27 indicates the premixing chamber on the flue gas reheat gas burner. Reference numeral 211 indicates the nozzle of the gas ignition gun; 221 indicates the nozzle of the main gas gun; 231 indicates the nozzle of the flame detection, cooling, and purge air duct; and 241 indicates the nozzle of the combustion-supporting air duct.

[0024] Reference numeral 31 indicates the manual gas shut-off valve on the gas pipeline in front of the gas igniter nozzle; reference numeral 32 indicates the pneumatic quick-break valve on the gas pipeline in front of the gas igniter nozzle; reference numeral 33 indicates the manual gas shut-off valve on the gas pipeline in front of the main gas gun nozzle; reference numeral 34 indicates the gas flow control valve on the gas pipeline in front of the main gas gun nozzle; reference numeral 35 indicates the gas pressure transmitter on the gas pipeline in front of the main gas gun nozzle. Reference numeral 41 indicates the manual air supply shut-off valve on the air supply duct; reference numeral 42 indicates the air supply flow control valve on the air supply duct; and reference numeral 43 indicates the air supply pressure transmitter on the air supply duct. DETAILED DESCRIPTION

[0025] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0026] like Figure 1 As shown, the present invention provides a flue gas reheating system for full-load operation of coal-fired units for denitrification, which is mainly composed of a gas pipeline system 3, an air distribution pipeline system 4, and a flue gas reheating gas burner 2. In addition, the nitrogen purge system, the venting system, the protection alarm system and other auxiliary systems belong to the conventional design of the gas system and are not described in detail in the present invention. The flue gas reheating gas burner 2 is installed in an embedded manner. By opening an embedded hole in the slope area 1 of the economizer ash hopper of the original coal-fired unit, the flue gas reheating gas burner 2 is embedded and fixedly installed in the slope area 1 of the economizer ash hopper. The gas pipeline system 3 and the air distribution pipeline system 4 are connected to the flue gas reheating gas burner 2 through a bellows flange.

[0027] The flue gas reheating system of the present invention includes 4 to 8 flue gas reheating gas burners 2, and the design gas flow rate of a single flue gas reheating gas burner 2 is 200 to 500 Nm 3 / h. The number of flue gas reheat burners 2 is determined primarily based on the unit's design parameters and simulation results. All flue gas reheat burners 2 are arranged in a two-tiered, embedded configuration to ensure that reheated flue gas enters the economizer area's horizontal flue directly. The gas flame aligns with the flue gas flow, ensuring uniformity in the temperature and flow fields, as well as the safety of the tail flue. This ensures that the flue gas temperature on both sides of the degassing system meets requirements.

[0028] like Figure 2 As shown, the flue gas reheat gas burner 2 is mainly composed of an ignition gas gun 21, a main gas gun 22, a fire detection cooling and purge air duct 23, a gas combustion-supporting air distribution duct 24, a high-energy igniter 25, an ultraviolet fire detection device 26 and a premixing chamber 27.

[0029] One end of the ignition gas gun 21, high-energy igniter 25, and ultraviolet flame detection device 26 is inserted into the flame detection cooling and purge air duct 23 and communicates with the gas combustion-supporting air duct 24 within the premixing chamber 27. The other end is connected to the gas pipeline system 3 via the ignition gas gun nozzle 211 using a soft gold bellows. The main gas gun 22 is connected to the premixing chamber 27 and communicates with the gas combustion-supporting air duct 24. The other end is connected to the gas pipeline system 3 via the main gas gun nozzle 221 using a soft gold bellows. The flame detection cooling and purge air duct 23 and the gas combustion-supporting air duct 24 are connected to the air distribution duct system 4 via the flame detection cooling and purge air duct nozzle 231 and the gas combustion-supporting air duct nozzle 241 using soft gold bellows, respectively.

[0030] In order to meet the wide output adjustment range and the requirements of negative pressure combustion in the tail flue area, the flue gas reheating gas burner 2 adopts a double nozzle two-stage ignition design, and some small flow (50Nm 3 / h) Natural gas is mixed with the air in the gas combustion air pipe 24 in the premixing chamber 27 through the ignition gas gun 21 and ignited by the high-energy igniter 25; and then ignites the high flow rate (150~450Nm 3 / h) natural gas, ensuring that the natural gas nozzle outlet velocity exceeds the natural gas tempering velocity. The designed gas flow rate for a single burner is 200-500 Nm³ / h. After ignition and combustion in the burner, the gas enters the economizer ash hopper horizontal flue 5, thereby heating the flue gas and increasing the flue gas temperature.

[0031] The gas pipeline 3 enters the burner through two routes, and the flow rate of the ignition gas gun 21 is fixed at 50Nm 3 / h. A manual shut-off valve 31 and a pneumatic quick-break valve 32 are installed on the connecting pipe between the gas pipeline 3 and the ignition gas gun nozzle 211 to start and stop the ignition gas gun 21. The flow rate of the main gas gun 22 is adjustable. A manual shut-off valve 33, a gas flow control valve 34, and a gas pressure transmitter 35 are installed on the connecting pipe between the gas pipeline 3 and the main gas gun nozzle 221 to adjust and control the output of the main gas gun 22. The air distribution pipe 4 is equipped with a manual shut-off valve 41, an air distribution flow control valve 42, and an air distribution pressure transmitter 43 to adjust the air distribution and cooling air volume.

[0032] like Figure 3 As shown, based on the feedback signals of the existing temperature and flue gas flow of the coal-fired unit denitrification system, the flue gas temperature rise requirement at the SCR inlet and the required natural gas consumption are calculated in real time. By controlling the gas flow control valve 34, the gas pressure transmitter 35, the air distribution flow control valve 42, and the air distribution pressure transmitter 43, the flow and pressure of the natural gas and combustion-supporting air are adjusted to ensure that the flue gas temperature at the SCR inlet meets the denitrification requirements.

[0033] Taking a 300MW subcritical boiler produced by Shanghai Boiler Plant as an example, this implementation case provides a flue gas reheating system for increasing the flue gas temperature at the inlet of the boiler denitrification equipment.

[0034] In this embodiment, when the SCR inlet flue gas temperature collection point detects that the flue gas temperature at the economizer outlet is too low to reach the normal operating temperature window of the catalyst, the operator issues a command to activate the flue gas reheating system described in the present invention to increase the flue gas temperature. The specific operation is as follows:

[0035] (1) During unit startup and low-load operation, the operator inputs instructions through the DCS control system to start the flue gas reheat burners one by one. At this time, the flue gas reheat burners are started according to the set logic program. First, the air flow control valve 42 on the air distribution duct is adjusted so that the air pressure transmitter on the air distribution duct reaches the set value. Then the high-energy igniter 25 ignites, and the gas pneumatic quick-off valve 32 on the gas pipeline in front of the gas ignition gun nozzle is opened. When the flame detection device 26 detects fire, the high-energy igniter 25 stops igniting, and the gas flow control valve 34 on the gas pipeline is adjusted so that the gas pressure transmitter reaches the set value 35. Then, the single flue gas reheat burner is successfully put into operation.

[0036] (2) Using the same startup method, the operator inputs instructions through the DCS control system to start the flue gas reheating gas burners at different locations to ensure that the flue gas temperatures on both sides of the denitrification system meet the requirements. At this time, the flue gas reheating system is successfully started.

[0037] (3) As the flue gas temperature rises, the temperature rise requirement gradually decreases, and the natural gas consumption also gradually decreases. At this time, the control system calculates the gas flow rate based on the flue gas temperature, and controls the natural gas consumption by controlling the opening of the regulating valves on each branch pipe. If necessary, the pneumatic ball valves at the inlet gas pipelines of some flue gas reheating gas burners are closed to reduce the number of burners in operation. When the boiler load rises to 40% or above, the SCR inlet flue gas temperature can meet the operation requirements, the natural gas consumption is 0, and the flue gas reheating system is decommissioned.

Claims

1. A flue gas reheating system for full-load operation of coal-fired units for denitrification, characterized in that: The invention comprises a gas pipeline system (3), an air distribution pipeline system (4) and N flue gas reheating gas burners (2), N≥1, the flue gas reheating gas burners (2) are embedded and fixedly installed in the economizer ash hopper slope area (1) through an embedded hole provided on the economizer ash hopper slope area (1) of the coal-fired unit, the gas pipeline system (3) and the air distribution pipeline system (4) are connected to the flue gas reheating gas burners (2) through a bellows flange, the combustible gas and the combustion-supporting air enter the flue gas reheating gas burners (2) through the gas pipeline system (3) and the air distribution pipeline system (4), the combustible gas and the combustion-supporting air are fully mixed in the flue gas reheating gas burners (2), ignited, and then enter the flue gas outlet of the coal-fired unit to burn and release heat, the generated high-temperature flue gas is fully mixed with the flue gas in the flue gas after diversion, so that the average temperature of the flue gas at the inlet of the SCR catalyst reaches above 310°C; The flue gas reheating gas burner (2) is embedded and fixedly installed in the slope area of ​​the economizer ash hopper and arranged in two layers; The flue gas reheating gas burner (2) comprises an ignition gas gun (21), a main gas gun (22), a fire detection cooling and purge air duct (23), a gas combustion-supporting air distribution duct (24), a high-energy igniter (25), an ultraviolet fire detection device (26) and a premixing cavity (27). One end of the ignition gas gun (21), the high-energy igniter (25) and the ultraviolet fire detection device (26) is inserted into the fire detection cooling and purge air duct (23) and then extends into the premixing cavity (27), and communicates with the gas combustion-supporting air distribution duct (24) in the premixing cavity (27); the other end of the ignition gas gun (21) adopts a gold soft bellows to pass through the ignition gas gun nozzle (2 11) is connected to the gas pipeline system (3); the other end of the high-energy igniter (25) and the ultraviolet flame detection device (26) are located in the economizer of the coal-fired unit; one end of the main gas gun (22) is connected to the premixing cavity (27) and communicates with the gas combustion-supporting air duct (24), and the other end is connected to the gas pipeline system (3) through the main gas gun nozzle (221) using a gold soft bellows; the flame detection cooling and purge air duct (23) and the gas combustion-supporting air duct (24) are connected to the air distribution pipe system (4) through the flame detection cooling and purge air duct nozzle (231) and the gas combustion-supporting air duct nozzle (241) using a gold soft bellows respectively; The gas pipeline (3) enters the flue gas reheating gas burner (2) through two routes, one of which has a flow rate of 50Nm 3 / h of low flow combustible gas, and the other one has a flow rate of 150~450Nm 3 / h of high-flow combustible gas, the low-flow combustible gas is mixed in the premixing cavity (27) with the combustion-supporting air of the gas combustion-supporting air pipe (24) through the ignition gas gun (21), and then ignited by the high-energy igniter (25), and then further ignited the high-flow combustible gas of the gas main air gun (22).

2. A flue gas reheating system for full-load operation of a coal-fired unit for denitrification according to claim 1, characterized in that: The number of the flue gas reheating gas burners (2) is 4 to 8, and the design gas flow rate of a single flue gas reheating gas burner (2) is 200 to 500 Nm 3 / h; all the flue gas reheating gas burners (2) are arranged in two layers, upper and lower, to ensure that the flue gas after reheating directly enters the horizontal flue in the economizer area of ​​the coal-fired unit, the gas flame is consistent with the flue gas flow direction, the uniformity of the temperature field and flow field and the safety of the tail flue are ensured, and the flue gas temperature of the degassing system on both sides can meet the requirements at the same time.

3. A flue gas reheating system for full-load operation of a coal-fired unit for denitrification according to claim 1, characterized in that: A manual stop valve (31) and a pneumatic quick-break valve (32) are provided on the connecting pipe between the gas pipeline (3) and the nozzle of the ignition gas gun (211) for starting and stopping the ignition gas gun (21); the flow of the main gas gun (22) is adjustable, and a manual stop valve (33), a gas flow control valve (34) and a gas pressure transmitter (35) are provided on the connecting pipe between the gas pipeline (3) and the nozzle of the main gas gun (221) for adjusting and controlling the output of the main gas gun (22).

4. A flue gas reheating system for full-load operation of a coal-fired unit for denitrification according to claim 3, characterized in that: The air distribution duct (4) is provided with a manual stop valve (41), an air distribution flow control valve (42) and an air distribution pressure transmitter (43) for adjusting the air distribution and cooling air volumes.

5. A flue gas reheating system for full-load operation of a coal-fired unit for denitrification according to claim 4, characterized in that: Based on the feedback signals of the existing temperature and flue gas flow rate of the coal-fired unit denitrification system, the SCR inlet flue gas temperature rise requirement and the required natural gas consumption are calculated in real time, and the flow and pressure of natural gas and combustion-supporting air are adjusted by controlling the gas flow control valve (34), the gas pressure transmitter (35), the air distribution flow control valve (42), and the air distribution pressure transmitter (43), so as to ensure that the SCR inlet flue gas temperature meets the denitrification requirement.

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