A staged combustion system and process for a coal gas boiler

Abstract

This invention belongs to the field of iron and steel metallurgy technology, specifically relating to a staged combustion system and process for a gas boiler. The system includes a burner connected to the gas boiler, a combustion-supporting gas structure, and a combustion-supporting air structure. The burner includes a combustion stabilizing plate, located at the front end of the burner and connected to the gas boiler. The combustion stabilizing plate has three layers of staged ignition units evenly arranged around its center: an inner layer, a middle layer, and an outer layer. The middle layer ignition unit includes multiple externally mixed combustion nozzles, where combustion-supporting air and gas mix outside the combustion stabilizing plate. The outer layer ignition unit includes multiple internally mixed combustion nozzles, where combustion-supporting air and gas mix inside the combustion stabilizing plate. The combustion-supporting gas structure provides fuel to the burner, and the combustion-supporting air structure provides combustion-supporting air to the burner. This invention effectively achieves complete combustion of the gas, reduces nitrogen oxide production, and provides a stable flame, demonstrating good performance in terms of safety, environmental protection, and efficiency.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically, it relates to a staged combustion system and process for a gas boiler. Background Technology

[0002] In metallurgical enterprises, boilers are energy-saving and environmentally friendly thermal equipment. To ensure the normal combustion of the flame within the furnace, a complete combustion system is required. Existing combustion systems, such as... Figure 1 , 2 As shown: The system includes a burner 1 and a fuel oil ignition gun 12 mounted on the burner. The fuel oil ignition gun uses diesel fuel for ignition, and blast furnace gas is supplied to the burner as fuel. The combustion air is delivered directly to the combustion stabilizer 11. However, the existing combustion system has the following problems:

[0003] 1. With the need for clean, environmentally friendly, safe and efficient production, the previous combustion equipment used diesel to ignite the combustion first and then introduced gas to assist combustion, which often resulted in difficulty in ignition, incomplete combustion and black smoke during the ignition process.

[0004] 2. Improper ratio of combustion air and gas during combustion can lead to unstable combustion and sudden flameout.

[0005] 3. The existing burner structure makes it difficult to control the central combustion air and gas supply, resulting in the generation of more nitrogen oxides and flue gas emissions that are prone to failing to meet standards, posing certain problems in terms of safety, environmental protection, and efficiency.

[0006] 4. When the boiler is operating at high load, the high furnace temperature may lead to an increase in the generation of thermal nitrogen oxides.

[0007] In view of this, the present invention is proposed. Summary of the Invention

[0008] To solve the above-mentioned technical problems, the basic concept of the technical solution adopted by the present invention is as follows:

[0009] The present invention first discloses a staged combustion system for a gas boiler, the system comprising a burner connected to the gas boiler, a combustion gas structure, a combustion air structure, and a flue gas recovery structure;

[0010] The burner includes a combustion stabilizing plate; the combustion stabilizing plate is located at the front end of the entire burner and connected to the gas boiler; the combustion stabilizing plate is uniformly surrounded by three layers of staged ignition units: inner, middle, and outer; the middle layer ignition unit includes multiple nozzles for external mixing combustion, where combustion air and gas are mixed outside the combustion stabilizing plate; the outer layer ignition unit includes multiple nozzles for internal mixing combustion, where combustion air and gas are mixed inside the combustion stabilizing plate.

[0011] The combustion-supporting gas structure is used to provide fuel to the burner;

[0012] The combustion-supporting air structure is used to provide combustion-supporting air to the burner.

[0013] As a preferred technical solution, the burner further includes a gas distribution chamber, a combustion air chamber, an oil ignition gun, and a direct-fired gas ignition gun; the gas distribution chamber, connected to blast furnace gas, is arranged at the rear end of the burner, and the rear end of the gas distribution chamber gathers the gas and transports it to the combustion stabilization plate through various gas passages; the combustion air chamber is located between the combustion stabilization plate and the gas distribution chamber; a combustion air passage connecting the combustion air chamber is sleeved on the outside of each gas passage, and each gas passage and the combustion air passage sleeved on its outside form an independent flame nozzle on the combustion stabilization plate; the ignition end of the oil ignition gun passes through the gas distribution chamber and the combustion air chamber and is installed at the center of the combustion stabilization plate, and multiple ignition ventilation holes are arranged around the outside of the oil ignition gun; the direct-fired gas ignition gun is located in the middle layer ignition unit.

[0014] As a preferred technical solution, the combustion chamber is divided into two independent parts: a direct current chamber and a swirl chamber. The outer gas pipeline has a direct current air channel connected to the direct current chamber to provide combustion air to the outer ignition unit. The middle gas pipeline has a swirl chamber connected to the swirl chamber to provide combustion air to the middle ignition unit. A swirl plate is provided near the swirl chamber in the swirl chamber, and the combustion air from the swirl chamber enters the swirl chamber through the swirl plate.

[0015] As a preferred technical solution, each ignition unit is equipped with a mixing blade; the outer gas passage and its direct current air passage are flush and located at a certain position inside the outer mixing blade; the middle gas passage and its swirl air passage are flush with the middle mixing blade.

[0016] As a preferred technical solution, the combustion air structure includes a combustion air supply pipeline and a combustion air opening regulating valve, a mixing box, and a blower installed on the pipeline. The combustion air supply pipeline includes two branch pipelines: one branch pipeline is connected to the combustion air chamber to provide combustion air for flame combustion, and the other branch pipeline is connected to the direct-fired gas torch to provide combustion air for flame generation. The combustion air opening regulating valve, the mixing box, and the blower are installed on the main pipeline of the combustion air supply pipeline. The combustion air opening regulating valve is used to regulate the flow rate of the combustion air supply pipeline; the mixing box is used to mix the combustion air and the recovered flue gas; and the blower is used to regulate the wind speed of the combustion air.

[0017] As a preferred technical solution, one end of the flue gas recovery structure is connected to the flue gas outlet of the boiler, and the other end is connected to the mixing box.

[0018] This invention also discloses a process for a staged combustion system for a gas boiler, wherein the ratio of combustion air to gas is controlled by the following formula: F=M+P S; where F is the set value of the combustion air regulating valve; M is the gas regulating valve opening feedback; P is the gas pressure feedback; S is the gas pressure coefficient, S is 0~4.5.

[0019] As a preferred technical solution, the oxygen content in boiler combustion is 2-4%.

[0020] As a preferred technical solution, the boiler furnace is maintained at a pressure of -350~50pa.

[0021] As a preferred technical solution, the intensity of the flame core is set to reach more than 60%, and the intensity of the main fire is set to reach more than 40%.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. The burner of the present invention has multiple independent gas passages in the middle and outer ignition units of the combustion stabilization plate. A combustion air passage connecting to the combustion air chamber is provided on the outside of each gas passage. Each gas passage and the combustion air passage on its outside form an independent flame nozzle on the combustion stabilization plate, thereby realizing complete combustion of gas and flame stability.

[0024] 2. The combustion chamber is divided into two independent parts: a direct-flow chamber and a swirl chamber. The outer gas pipeline has a direct-flow air channel connected to the direct-flow chamber to provide combustion air to the outer ignition unit. The middle gas pipeline has a swirl chamber connected to the swirl chamber to provide combustion air to the middle ignition unit. In other words, this invention adopts a direct-flow-swirl-direct-flow staged combustion arrangement from the inside out, dividing the entire combustion equipment into a central external mixing rotary combustion and a peripheral multi-head internal mixing combustion, effectively achieving low-NOx performance and stabilizing the root flame.

[0025] 3. This burner primarily uses blast furnace gas as ignition fuel, which can be directly ignited, making ignition convenient, simple, and ensuring complete combustion of the fuel. The fuel oil ignition gun uses fuel oil as a backup ignition method to prevent ignition failure in case of abnormal gas conditions. The air blown out by the ventilation holes around the fuel oil ignition gun can prevent the gas and combustion air in the boiler from flowing back along the burner, thus achieving a certain sealing effect.

[0026] 4. Both the direct current air chamber and the swirl air chamber are equipped with air adjustment handles, which can be used to adjust the air intake of the direct current air and the swirl air to change the flame shape, so as to ensure a stable flame shape and complete combustion.

[0027] 5. When the boiler is operating at high load and the furnace temperature is high, which may lead to an increase in the generation of thermal nitrogen oxides, this flue gas recovery structure can introduce circulating flue gas into the furnace to reduce the flame temperature and stably achieve low nitrogen emissions.

[0028] 6. By rationally configuring the combustion air and fuel, the outer ignition unit is kept in a state of oxygen-deficient combustion, the flame is directed straight, the flame diameter is lengthened, the flame combustion speed is reduced, and the temperature distribution of the flame is uniform along the entire length of the furnace, avoiding the generation of thermal nitrogen oxides caused by the flame being in a high-temperature, over-oxygenated state.

[0029] 7. Adjust the intensity of the flame core and main flame appropriately to ensure stable combustion.

[0030] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0031] In the attached diagram:

[0032] Figure 1 This is a front view of a fuel-stabilizing disc in the prior art;

[0033] Figure 2 for Figure 1 Side view;

[0034] Figure 3 This is a schematic diagram of a combustion system in the prior art;

[0035] Figure 4 This is a schematic diagram of the combustion system in this invention;

[0036] Figure 5 This is a front view of the combustion stabilization disc in this invention;

[0037] Figure 6 for Figure 5 Side view.

[0038] In the diagram: 1. Burner; 11. Flame stabilizer; 12. Fuel oil ignition gun; 13. Direct-fired gas ignition gun; 14. Gas distribution chamber; 15. Combustion air chamber; 16. Gas passage; 17. Direct current air chamber; 171. Direct current air passage; 18. Swirl air chamber; 181. Swirl air passage; 19. Swirl plate; 110. Ventilation hole; 111. Mixing blade; 112. Air adjustment handle; 113. High-energy igniter;

[0039] 2. Combustion gas structure; 21. Blast furnace gas transmission pipeline; 22. Ignition gas pipeline; 23. Main gas pipeline;

[0040] 3. Combustion air structure; 31. Combustion air delivery pipeline; 32. Combustion air opening regulating valve; 33. Mixing box; 34. Blower;

[0041] 4. Flue gas recovery structure; 5. Boiler; 6. Oil tank. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention.

[0043] like Figures 3 to 4 As shown, the present invention discloses a staged combustion system for a gas boiler 5, the system including a burner 1 connected to the gas boiler 5, a combustion gas structure 2, a combustion air structure 3, and a flue gas recovery structure 4.

[0044] The burner 1 includes a combustion stabilizing plate 11, an oil ignition gun 12, a direct-fired gas ignition gun 13, a gas distribution chamber 14, and a combustion-supporting air chamber 15. The combustion stabilizing plate 11 is located at the front end of the burner 1 and connected to the gas boiler 5. The gas distribution chamber 14, which is connected to blast furnace gas, is arranged at the rear end of the burner 1. The combustion-supporting air chamber 15 is located between the combustion stabilizing plate 11 and the gas distribution chamber 14. The ignition end of the oil ignition gun 12 passes through the gas distribution chamber 14 and the combustion-supporting air chamber 15 and is installed at the center of the combustion stabilizing plate 11. The direct-fired gas ignition gun 13 is located on one side of the oil ignition gun 12. This burner 1 mainly uses blast furnace gas as ignition fuel, which can be directly ignited, making ignition convenient and simple, and achieving complete combustion of the fuel. The oil ignition gun 12 uses oil as a backup ignition method to prevent ignition failure in case of abnormal gas conditions.

[0045] The combustion gas structure 2 includes a blast furnace gas conveying pipeline 21. The gas is divided into two parts and enters the burner 1, namely the ignition gas pipeline 22 and the main gas pipeline 23. The ignition gas pipeline 22 is used to connect to the direct-fired gas ignition gun 13 to provide it with ignition fuel, and the main gas pipeline 23 is used to connect to the gas diversion chamber 14.

[0046] The combustion air structure 3 includes a combustion air conveying pipe 31 and a combustion air opening regulating valve 32, a mixing box 33, and a blower 34 installed in the pipe; the combustion air conveying pipe 31 includes two branch pipes, one branch pipe is connected to the combustion air chamber 15 to provide combustion air for flame combustion, and the other branch pipe is connected to the direct-fired gas torch to provide combustion air for generating flame.

[0047] The combustion air opening regulating valve 32, the mixing box 33, and the blower 34 are located on the main pipeline of the combustion air conveying pipeline 31. The combustion air opening regulating valve 32 is used to regulate the flow rate of the combustion air conveying pipeline 31; the mixing box 33 is used to mix the combustion air and the recovered flue gas; and the blower 34 is used to regulate the wind speed of the combustion air.

[0048] One end of the flue gas recovery structure 4 is connected to the flue gas outlet of the boiler 5, and the other end is connected to the mixing box 33. When the boiler 5 is operating at high load and the furnace temperature is high, which may cause an increase in the generation of thermal nitrogen oxides, the flue gas recovery structure 4 can introduce circulating flue gas into the furnace to reduce the flame temperature and stably achieve low nitrogen emissions.

[0049] The structure of burner 1 is described in detail below: The stabilizing plate 11 is located at the front end of the entire burner 1; the gas distribution chamber 14, connected to blast furnace gas, is arranged at the rear end of the burner 1; the combustion-supporting air chamber 15 is located between the stabilizing plate 11 and the gas distribution chamber 14; the ignition end of the fuel oil ignition gun 12 passes through the gas distribution chamber 14 and the combustion-supporting air chamber 15 and is installed at the center of the stabilizing plate 11; the direct-fired gas ignition gun 13 is located on one side of the fuel oil ignition gun 12. This equipment mainly uses blast furnace gas as ignition fuel, which can be directly ignited, making ignition convenient and simple, and achieving complete combustion of fuel; the fuel oil ignition gun 12 uses fuel oil as a backup ignition method to prevent ignition failure in case of abnormal gas conditions; the fuel oil ignition gun 12 is equipped with an oil inlet connected to the fuel oil tank 6 and an air inlet connected to the fuel oil ignition atomizing air.

[0050] The combustion stabilizing plate 11 is uniformly arranged with three layers of graded ignition units (inner, middle, and outer) around the fuel ignition gun 12. The middle and outer ignition units each include multiple independent gas channels 16. The gas distribution chamber 14 gathers the gas at the rear end and then transports it to the combustion stabilizing plate 11 through each gas channel 16. A combustion air channel connecting to the combustion air chamber 15 is sleeved on the outside of each gas channel 16. The gas outlet of each gas channel 16 and the gas outlet of the combustion air channel sleeved on its outside form an independent flame nozzle on the combustion stabilizing plate 11, realizing complete combustion of gas and flame stabilization.

[0051] Specifically, the combustion chamber 15 is divided into two independent parts: a direct-flow chamber 17 and a swirl chamber 18. The outer gas pipeline has a direct-flow channel 171 connected to the direct-flow chamber 17 to provide combustion air to the outer ignition unit. The middle gas pipeline has a swirl channel 181 connected to the swirl chamber 18 to provide combustion air to the middle ignition unit. Preferably, a swirl plate 19 is provided near the swirl chamber 18 in the swirl channel, and the combustion air from the swirl chamber 18 must pass through the swirl plate 19 to enter the swirl channel. Since the direct-fired gas ignition gun 13 is located in the middle ignition unit, therefore... Combustion requires the assistance of swirling air. Furthermore, the direct-fired gas ignition gun 13 is equipped with a gas inlet and a combustion air inlet connected to the combustion air delivery pipe 31. Part of the blast furnace gas enters the direct-fired gas ignition gun 13 through the ignition pipe and gas inlet, while another part enters the gas distribution chamber 14 through the main gas pipe 23. Excess gas is released. The fuel oil ignition gun 12 is located in the inner ignition unit. Multiple ignition ventilation holes 110 are arranged around the outer side of the fuel oil ignition gun 12. During ignition, direct-flow combustion air is ejected through these ventilation holes 110 and mixes with the fuel oil at the outlet of the fuel oil ignition gun 12, thus aiding combustion. Simultaneously, the air blown out from the ventilation holes 110 around the fuel oil ignition gun 12 prevents the gas and combustion air inside the boiler 5 from flowing back along the burner 1, providing a certain degree of sealing.

[0052] Preferably, each ignition unit of the inner, middle, and outer layers of the combustion stabilizing plate 11 is equipped with a mixing blade 111; the outlet of the outer layer gas channel 16 is flush with the outlet of its direct current air channel and located 8-10 cm inside the outer layer mixing blade 111, so that the gas and direct current combustion air in the outer layer gas channel 16 are mixed in the space inside the outer layer mixing blade 111 before being sprayed out; the outlet of the middle layer gas channel 16 and the outlet of its swirl air channel are flush with the middle layer mixing blade 111, so that the gas and combustion air in the middle layer gas channel 16 are mixed outside the middle layer mixing blade 111; the present invention adopts a staged combustion technology of direct current-swirl-direct current from the inside out, which effectively achieves a low nitrogen effect and stabilizes the root flame. During combustion, the flame root is located 4-5 cm away from the combustion stabilizing plate.

[0053] Preferably, the density of the middle and inner layer mixing blades 111 is greater than that of the outer layer mixing blades 111. This is to ensure that during external mixing combustion, the fuel gas and its combustion-supporting air are fully mixed at the mixing blades 111. Since the fuel gas and its combustion-supporting air are mixed inside the combustion stabilization plate 11, the mixing effect is better due to the limited internal space, and the number of outer layer mixing blades 111 can be appropriately reduced. More preferably, the number of outer layer mixing blades 111 is 12, and the number of outer layer flame nozzles is also 12, with each flame nozzle located below the corresponding mixing blade 111; the number of middle and inner layer mixing blades 111 is 20 each, and the number of middle layer flame nozzles is 4.

[0054] An air regulating handle 112 is provided on the outer wall of both the direct current air chamber 17 and the swirl air chamber 18. The handle end of the air regulating handle 112 is located on the outside of its respective air chamber, and the end of the handle end is connected to an air regulating valve plate located at the air chamber inlet. By rotating the handle end within the range of 0 to 90 degrees, the air regulating valve plate can be rotated, thereby adjusting the air intake of the direct current air and the swirl air to change the flame shape, so as to ensure a stable flame shape and complete combustion. Specifically, when the air regulating handle 112 is rotated to the 90° position, the air regulating valve plate is fully open, and when the air regulating handle 112 is rotated to the 0° position, the air regulating valve plate is fully closed. Within this range, the air volume of the direct current air can affect the flame length; the air volume of the swirl air can affect the flame thickness, which needs to be adjusted according to the flame shape observed in the furnace of boiler 5 by the flame camera.

[0055] Coal-fired boiler 5 produces flue gas containing CO2, SO2, etc. during combustion. Incomplete combustion also produces small amounts of CO and CH4. Therefore, maintaining an appropriate excess air supply to ensure complete combustion of pulverized coal in the furnace is essential. However, if the air distribution in boiler 5 is improper, an increase in the amount of air supplied for combustion will result in some oxygen not being utilized and being emitted as hot flue gas from the chimney. This not only increases heat loss in the flue gas but also directly affects the economic efficiency of boiler 5 operation. Therefore, controlling the oxygen content and combustion air distribution in boiler 5 is particularly important and is one of the bases for evaluating boiler 5 performance. Preferably, the oxygen content in boiler 5 combustion is 2-4%.

[0056] In this application, the ratio of combustion air to coal gas is controlled by the following formula: F=M+P S; where F is the set value of the combustion air regulating valve; M is the gas regulating valve opening feedback; P is the gas pressure feedback; S is the gas pressure coefficient, S is 0~4.5. By pre-setting the gas regulating valve opening feedback M, the system can automatically calculate and adjust the opening F of the combustion air regulating valve according to the above formula to adapt to the operation under changes in gas calorific value or fluctuations in operating conditions, ensuring the safety and reliability of boiler 5.

[0057] Tables 1 and 2 show the air-fuel ratio settings for the two burners 1:

[0058] Table 1 Air-fuel ratio settings for burner #1

[0059]

[0060] Table 2 Air-fuel ratio settings for burner #2

[0061]

[0062] The above configuration ensures that the outer ignition unit is in a state of oxygen-deficient combustion, with the flame shooting straight out, lengthening the flame diameter, reducing the flame's combustion speed, and making the temperature distribution uniform along the entire length of the furnace. This avoids the generation of thermal nitrogen oxides caused by the flame being in a high-temperature, over-oxygenated state.

[0063] Preferably, the pressure in the furnace of boiler 5 is maintained at -350~50pa, preferably -80pa, by adjusting the combustion air and induced draft volume, so as to keep the pressure in the steam drum above boiler 5 constant;

[0064] Preferably, both the direct-fired gas ignition gun 13 and the fuel oil ignition gun 12 are ignited by the high-energy igniter 113. When igniting, the ignition position is adjusted to 2-3 cm inward from the combustion plate, which can directly ignite the blast furnace gas from the ignition pipeline. After the ignition flame is established, the valve of the blast furnace main gas pipeline 23 is opened, and the main gas combustion is put into operation.

[0065] Preferably, in order to observe the stability of combustion, a flame detector is installed in the furnace, mainly to detect the intensity of the flame core and the main flame. The flame core refers to the ignition flame of the stabilizing plate 11, and the main flame is the flame column around the flame core on the stabilizing plate 11. Since the main flame is easily affected by the swirling air and the surrounding pressure, it is prone to fluctuation and oscillation. However, the flame of the flame core is relatively stable. Therefore, the higher the intensity of the flame core, the more stable the combustion. Thus, during combustion, the intensity of the flame core should be higher than that of the main flame. Preferably, this application sets the flame core intensity to be above 60% and the main flame intensity to be above 40% for stable combustion. In order to maintain a better combustion state, the flame core intensity of burner 1 is 98.5%, and the flame core intensity of burner 2 is 81.5%; the flame core intensity of burner 2 is 98.3%, and the flame core intensity of burner 2 is 80.3%.

[0066] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A staged combustion system for a coal-fired boiler, comprising: The system includes a burner connected to a gas boiler, a combustion gas structure, a combustion air structure, and a flue gas recovery structure; The burner includes a combustion stabilizing plate; the combustion stabilizing plate is located at the front end of the entire burner and connected to the gas boiler; the combustion stabilizing plate is uniformly surrounded by three layers of staged ignition units: inner, middle, and outer; the middle layer ignition unit includes multiple nozzles for external mixing combustion, where combustion air and gas are mixed outside the combustion stabilizing plate; the outer layer ignition unit includes multiple nozzles for internal mixing combustion, where combustion air and gas are mixed inside the combustion stabilizing plate. The combustion-supporting gas structure is used to provide fuel to the burner; The combustion air structure is used to provide combustion air to the burner; The burner also includes a gas distribution chamber, a combustion air chamber, an oil ignition gun, and a direct-fired gas ignition gun. The gas distribution chamber, connected to blast furnace gas, is located at the rear end of the burner. After the gas is collected at the rear end of the gas distribution chamber, it is transported to the combustion stabilization plate through various gas passages. The combustion air chamber is located between the combustion stabilization plate and the gas distribution chamber. A combustion air passage connecting the combustion air chamber is sleeved on the outside of each gas passage. Each gas passage and the combustion air passage sleeved on its outside form an independent flame nozzle on the combustion stabilization plate. The ignition end of the oil ignition gun passes through the gas distribution chamber and the combustion air chamber and is installed at the center of the combustion stabilization plate. Multiple ignition ventilation holes are arranged around the outside of the oil ignition gun. The direct-fired gas ignition gun is located in the middle ignition unit.

2. The staged combustion system for a coal-fired boiler of claim 1, wherein: The combustion chamber is divided into two independent parts: a direct current chamber and a swirl chamber. The outer gas pipeline has a direct current air channel connected to the direct current chamber to provide combustion air to the outer ignition unit. The middle gas pipeline has a swirl chamber connected to the swirl chamber to provide combustion air to the middle ignition unit. A swirl plate is provided near the swirl chamber in the swirl chamber, and the combustion air from the swirl chamber enters the swirl chamber through the swirl plate.

3. The staged combustion system for a coal-fired boiler of claim 2, wherein: Each ignition unit is equipped with a mixing blade; the outer gas passage and its direct current air passage are flush with each other and located at a certain position inside the outer mixing blade; the middle gas passage and its swirl air passage are flush with the middle mixing blade.

4. The staged combustion system for a gas boiler as described in claim 1, characterized in that: The combustion air structure includes a combustion air delivery pipeline and a combustion air opening regulating valve, a mixing box, and a blower installed on the pipeline. The combustion air delivery pipeline includes two branch pipelines: one branch pipeline is connected to the combustion air chamber to provide combustion air for flame combustion, and the other branch pipeline is connected to the direct-fired gas torch to provide combustion air for flame generation. The combustion air opening regulating valve, the mixing box, and the blower are located on the main pipeline of the combustion air delivery pipeline. The combustion air opening regulating valve is used to regulate the flow rate of the combustion air delivery pipeline; the mixing box is used to mix the combustion air and the recovered flue gas; and the blower is used to regulate the wind speed of the combustion air.

5. The staged combustion system for a gas boiler as described in claim 4, characterized in that: One end of the flue gas recovery structure is connected to the flue gas outlet of the boiler, and the other end is connected to the mixing box.

6. The process for a staged combustion system for a gas boiler as described in claim 1, characterized in that: The ratio of combustion air to coal gas is controlled by the following formula: F=M+P S; where F is the set value of the combustion air regulating valve; M is the gas regulating valve opening feedback; P is the gas pressure feedback; S is the gas pressure coefficient, S is 0~4.

5.

7. The process for a staged combustion system for a gas boiler as described in claim 6, characterized in that: The oxygen content during boiler combustion is 2-4%.

8. The process for a staged combustion system for a gas boiler as described in claim 6, characterized in that: The boiler furnace is maintained at a pressure of -350~50pa.

9. The process for a staged combustion system for a gas boiler as described in claim 6, characterized in that: Set the flame core intensity to over 60% and the main flame intensity to over 40%.

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