A w-flame boiler controlling the flame center by combined tertiary air

Abstract

The application discloses a W flame boiler capable of controlling a flame center through combined tertiary air, which comprises a furnace, a flue gas circulating fan, a flue gas interface, two groups of pulverized coal burner assemblies installed on a lower furnace arch, two groups of cold ash hopper tertiary air nozzle assembly installed on the bottom of the lower furnace, two groups of arch tertiary air nozzle assembly installed on the junction of the lower furnace arch and front and back walls, two groups of upper tertiary air nozzles installed on the front and back walls above the throat of the upper furnace, and one group of soot blowing tertiary air nozzle assembly installed on the inclined flue above the elbow, wherein the flue gas volume of different tertiary air nozzles is adjusted by adding corresponding tertiary air nozzles at different positions of the furnace, so as to change the momentum of the furnace bottom fire support, the momentum of the arch up and down, the momentum of the throat downward and the momentum of the elbow soot blowing disturbance, and the regulation and control ability of the combustion air distribution system on the main pulverized coal airflow downward injection capacity, the cold ash hopper area temperature, the upper and lower furnace throat area temperature and the horizontal flue ash deposition condition is strengthened, and the reasonable flame center position is maintained.

Description

Technical Field

[0001] This invention relates to the field of energy-saving and environmental protection retrofitting technology for pulverized coal boilers, specifically a W-flame boiler that controls the flame center through a combined tertiary air system. Background Technology

[0002] W-flame boilers are the main type of boiler in my country that burns low-volatile coal. To ensure complete combustion of pulverized coal, W-flame boilers need to maintain a high furnace temperature. This is achieved by extending the effective residence time of the pulverized coal in the high-temperature zone through the process of ignition, combustion, and subsequent tumbling of the pulverized coal in the furnace arch. The concept of the flame center is actually used to vividly evaluate the temperature distribution in the main combustion zone of the lower furnace. The higher the temperature in the lower furnace outlet area, the more advanced the combustion, indicating a rising flame center. In recent years, to achieve ultra-low emissions, W-flame boilers have generally undergone low-NOx combustion retrofitting, employing air staging to reduce NOx emissions. x As some secondary air moves upwards into the burnout zone, the downward thrust of the main pulverized coal airflow is insufficient, and the excess air coefficient in the lower furnace is low. This causes the flame center to generally shift upwards, leading to overheating of the convective heating surfaces and excessive desuperheating water volume. Simultaneously, due to the general increase in power generation costs, the fluctuation in the type of coal fed into W-flame boilers is becoming increasingly large. When burning coals with different volatile compositions, the flame center frequently changes, causing steam temperature fluctuations and significantly impacting the safe and stable operation of the unit.

[0003] Given that the inherent structure and characteristics of W-flame boilers cannot well adapt to the requirements of ultra-low emissions and variable coal type operation, and the flame center adjustment is not flexible enough, problems have arisen that affect the safe and stable operation of the unit. Therefore, it is necessary to develop a W-flame boiler that controls the flame center through a combined tertiary air system to solve the above problems. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a W-flame boiler that controls the flame center through a combined tertiary air system. The boiler equipment used has a simple structure, safe and controllable operation, and utilizes the newly added combined tertiary air system to participate in combustion and flow field organization, thus achieving combustion without affecting NO at the furnace outlet. x While controlling and ensuring the complete combustion of pulverized coal, the combustion air distribution system should be strengthened to regulate the downward injection capacity of the main pulverized coal airflow, the temperature of the cold ash hopper area, the temperature of the upper and lower furnace throat areas, and the ash accumulation in the horizontal flue. This will maintain a reasonable flame center position and improve the W-flame boiler's ability to flexibly adjust to ultra-low emission operating conditions with large fluctuations in the quality of the incoming coal.

[0005] This invention is achieved through the following technical solution:

[0006] A W-flame boiler with flame center control via a combined tertiary air system includes an upper furnace, a lower furnace, a flue gas circulation fan, and a flue gas interface. Two sets of pulverized coal burner assemblies are installed on the arch of the lower furnace; two sets of cold ash hopper tertiary air nozzle assemblies are installed at the bottom of the lower furnace; two sets of arch-mounted tertiary air nozzle assemblies are installed at the junction of the lower furnace arch and the front and rear walls; and a set of soot-blowing tertiary air nozzle assemblies is installed at the inclined flue above the flame deflector of the boiler.

[0007] The inlet of the flue gas recirculation fan is connected to the flue gas interface through a flue gas duct, and the outlet of the flue gas recirculation fan is connected to two sets of cold ash hopper tertiary air nozzle assemblies, two sets of arch tertiary air nozzle assemblies, two sets of upper tertiary air nozzle assemblies and one set of soot blowing tertiary air nozzle assemblies through a flue gas duct; the flue gas recirculation fan is installed on the flue gas duct.

[0008] Preferably, the two sets of pulverized coal burner assemblies are symmetrically installed on the front and rear arches of the lower furnace, and each set of pulverized coal burner assemblies includes 12 or 18 independent pulverized coal burners.

[0009] Preferably, the two sets of cold ash hopper tertiary air nozzle assemblies are symmetrically installed in a horizontal row on the front and rear walls of the lower furnace. Each set of cold ash hopper tertiary air nozzle assemblies includes 12 or 18 independent cold ash hopper tertiary air nozzles, and the positions of the cold ash hopper tertiary air nozzles correspond one-to-one with the positions of the pulverized coal burners.

[0010] Preferably, the two sets of tertiary air nozzle assemblies on the arch are symmetrically installed on the lower furnace arch near the junction of the front and rear walls, and are arranged in an alternating manner. Each set of tertiary air nozzle assemblies on the arch includes 12 or 18 independent tertiary air nozzles on the arch, and the positions of the tertiary air nozzles on the arch correspond one-to-one with the positions of the pulverized coal burners.

[0011] Preferably, the two sets of upper tertiary air nozzle assemblies are symmetrically and evenly installed in a horizontal row on the front and rear walls above the throat of the upper furnace. Each set of upper tertiary air nozzle assemblies includes 12 or 18 independent upper tertiary air nozzles, and the positions of the upper tertiary air nozzles correspond one-to-one with the positions of the pulverized coal burners.

[0012] Preferably, the set of soot blowing tertiary air nozzle assemblies is uniformly installed in an array on the inclined flue above the flame deflector, and each set of soot blowing tertiary air nozzle assemblies includes multiple independent soot blowing tertiary air nozzles.

[0013] Preferably, the tertiary air nozzle of the cold ash hopper is installed perpendicular to the plane of the cold ash hopper, and the center line of the tertiary air nozzle of the cold ash hopper makes an angle of 50-55° with the vertical direction; the tertiary air nozzle on the arch is installed perpendicular to the ground, and the center line of the tertiary air nozzle on the arch makes an angle of 0° with the vertical direction; the upper tertiary air nozzle is installed obliquely downward, and the center line of the upper tertiary air nozzle makes an angle of 30-45° with the vertical direction; the soot blowing tertiary air nozzle is installed perpendicular to the plane of the oblique flue above the flame deflector, and the center line of its soot blowing tertiary air nozzle makes an angle of 35-40° with the vertical direction.

[0014] Preferably, a first flue gas regulating valve is provided on the flue gas duct at the inlet of the tertiary air nozzle of the cold ash hopper; a second flue gas regulating valve is provided on the flue gas duct at the inlet of the tertiary air nozzle of the arch; a third flue gas regulating valve is provided on the flue gas duct at the inlet of the upper tertiary air nozzle; and a fourth flue gas regulating valve is provided on the flue gas duct at the inlet of the tertiary air nozzle of the soot blowing.

[0015] Preferably, the flue gas velocity passing through the tertiary air nozzle of the cold ash hopper is 8-12 m / s, the flue gas velocity passing through the tertiary air nozzle on the arch is 20-30 m / s, the flue gas velocity passing through the upper tertiary air nozzle is 20-30 m / s, and the flue gas velocity passing through the tertiary air nozzle for soot blowing is 20-30 m / s; the oxygen content of the flue gas in the flue gas circulation fan is 2.5-5%, the temperature is 400-500℃, and its flue gas circulation volume is 5-10% of the total flue gas volume generated by boiler combustion.

[0016] Preferably, a screen-type superheater is provided at the top of the upper furnace near the flame deflector.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects:

[0018] This invention provides a W-flame boiler with flame center control via a combined tertiary air system. The boiler equipment has a simple structure and is safe and controllable in operation. It includes two sets of cold ash hopper tertiary air nozzle assemblies, two sets of arch-mounted tertiary air nozzle assemblies, two sets of upper tertiary air nozzles, and one set of soot-blowing tertiary air nozzle assembly. By adding a combined tertiary air system and corresponding tertiary air nozzles, this invention introduces different forms and functions of tertiary air at different stages of pulverized coal ignition and combustion, and in different areas of the furnace. Utilizing the characteristics of tertiary air—low oxygen content, strong inertia, and minimal participation in combustion chemical reactions—by adjusting its jet velocity and the distribution of tertiary air volume at different locations, it achieves flame center control without affecting NO₂ levels. x Optimizing the airflow organization and temperature field distribution within the furnace under controlled conditions achieves the goal of controlling the flame center. Utilizing newly added combined tertiary air to participate in combustion and flow field organization can improve NO₂ levels at the furnace outlet without affecting combustion. xWhile controlling and ensuring complete combustion of pulverized coal, this invention enhances the combustion air distribution system's ability to regulate the downward injection capacity of the main pulverized coal airflow, the temperature of the cold ash hopper area, the temperature of the upper and lower furnace throat areas, and the ash accumulation in the horizontal flue. This maintains a reasonable flame center position and improves the W-flame boiler's flexibility in handling ultra-low emission operation conditions with large fluctuations in the quality of the incoming coal. Traditional W-flame boilers, once the equipment configuration is determined, cannot flexibly adjust their flame center. This invention, by adding a combined tertiary air system, improves the flexibility of flame center control during the operation of the W-flame boiler.

[0019] Furthermore, a first flue gas regulating valve is installed on the flue gas duct at the inlet of the tertiary air nozzle in the cold ash hopper; a second flue gas regulating valve is installed on the flue gas duct at the inlet of the tertiary air nozzle on the arch; a third flue gas regulating valve is installed on the flue gas duct at the inlet of the upper tertiary air nozzle; and a fourth flue gas regulating valve is installed on the flue gas duct at the inlet of the tertiary air nozzle for soot blowing. With this invention, operators can adjust the flue gas volume at different tertiary air nozzles using the flue gas regulating valves to change the momentum of the furnace bottom support fire, the momentum of the arch's upward and downward thrust, and the downward momentum at the throat. This adapts to problems such as imbalances in the heat absorption ratio of the radiative and convective heating surfaces, excessive screen overheating, and large desuperheating water volumes caused by changes in coal quality or operating conditions.

[0020] Furthermore, in W-flame boilers with a π-shaped flame arrangement, the upper slope angle of the flame deflector is generally less than 40°, which easily leads to excessive fly ash accumulation, causing ash collapse and boiler flameout. This invention addresses this by adding multiple tertiary sootblowing air nozzles in a group located in the ash-accumulating area of ​​the flame deflector, serving as a means to control ash accumulation during operation. Using this technology, operators can periodically adjust the amount of flue gas entering the tertiary sootblowing air nozzles to create disturbance in the ash layer, promoting orderly ash collapse and reducing the ash height at the upper part of the flame deflector.

[0021] Furthermore, when the high-temperature flue gas from the W-flame boiler passes through the throat into the upper furnace region from the lower furnace, it is extremely prone to coking at the throat location. This invention addresses this by adding an upper tertiary air nozzle above the throat, creating localized airflow disturbances and temperature fluctuations in this area, promoting dynamic coke shedding, and preventing large coke formation in this region.

[0022] Furthermore, according to the combustion method adopted by the W-flame boiler, the extended residence time of fly ash in the combustion zone facilitates complete combustion, while the slag immediately enters the slag pool after passing through the lower furnace, resulting in an unsatisfactory combustion rate. This is especially true when burning low-quality coal that is difficult to ignite, as the ignition of the pulverized coal itself is delayed, increasing the carbon content in the large slag. This invention addresses this by adding a cold ash hopper and tertiary air nozzle to the lower furnace. The tertiary air, with its relatively larger momentum compared to the downward-flowing flue gas, forms a fire-supporting layer at the furnace bottom, allowing some slag to extend its effective residence time through suspension combustion, thereby reducing the unburned carbon content in the large slag. Attached Figure Description

[0023] Figure 1 This is a side view of the system structure described in the example of the present invention.

[0024] Figure 2 A top view showing the plan layout of the tertiary air nozzles in the cold ash hopper.

[0025] Figure 3 A top view showing the plan layout of the tertiary air nozzles for soot blowing.

[0026] In the diagram: 1. Furnace; 2. Flue gas circulation fan; 3. Flue gas interface; 4. Screen-type superheater; 5. Pulverized coal burner; 6. Cold ash hopper tertiary air nozzle; 7. First flue gas regulating valve; 8. Arch-mounted tertiary air nozzle; 9. Second flue gas regulating valve; 10. Upper tertiary air nozzle; 11. Third flue gas regulating valve; 12. Soot blowing tertiary air nozzle; 13. Fourth flue gas regulating valve. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0028] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0029] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] A W-flame boiler with flame center controlled by a combined tertiary air system includes a furnace 1, a flue gas circulating fan 2, a flue gas inlet 3, a screen-type superheater 4 installed at the top of the upper furnace near the flame deflector, two sets of pulverized coal burner assemblies installed on the lower furnace arch, two sets of cold ash hopper tertiary air nozzle assemblies installed at the bottom of the lower furnace, two sets of arch-mounted tertiary air nozzle assemblies installed at the junction of the lower furnace arch and the front and rear walls, two sets of upper tertiary air nozzle assemblies installed on the front and rear walls above the throat of the upper furnace, and a set of soot blowing tertiary air nozzle assemblies installed on the inclined flue above the flame deflector. Its features include: a flue gas recirculation fan 2 installed on a flue gas duct; the inlet of the flue gas recirculation fan 2 connected to a flue gas interface 3 via the flue gas duct; and the outlet of the flue gas recirculation fan 2 connected via the flue gas duct to two sets of cold ash hopper tertiary air nozzle assemblies, two sets of arch-mounted tertiary air nozzle assemblies, two sets of upper tertiary air nozzle assemblies, and one set of soot blowing tertiary air nozzle assemblies installed on the front and rear walls, respectively; two sets of pulverized coal burner assemblies symmetrically installed on the front and rear arches of the lower furnace, arranged in a staggered manner; each set of pulverized coal burner assemblies includes 12 or 18 independent pulverized coal burners 5; such as Figure 2 As shown, two sets of cold ash hopper tertiary air nozzle assemblies are symmetrically and evenly installed in a horizontal line on the front and rear walls of the lower furnace. Each set of cold ash hopper tertiary air nozzle assemblies includes 12 or 18 independent cold ash hopper tertiary air nozzles 6, and the positions of the cold ash hopper tertiary air nozzles 6 correspond one-to-one with the positions of the pulverized coal burners 5. Two sets of arch-mounted tertiary air nozzle assemblies are symmetrically installed on the furnace arch of the lower furnace near the junction of the front and rear walls, arranged in an alternating pattern. Each set of arch-mounted tertiary air nozzle assemblies includes 12 or 18 independent arch-mounted tertiary air nozzles 6. The secondary air nozzles 8 and the tertiary air nozzles 8 on the arch correspond one-to-one with the positions of the pulverized coal burners 5; two sets of upper tertiary air nozzle assemblies are symmetrically and evenly installed in a horizontal line on the front and rear walls above the upper furnace throat, each set of upper tertiary air nozzle assemblies includes 12 or 18 independent upper tertiary air nozzles 10, and the upper tertiary air nozzles 10 correspond one-to-one with the positions of the pulverized coal burners 5; a set of soot blowing tertiary air nozzle assemblies is evenly installed in an array on the inclined flue above the flame deflector, avoiding the heating surface tubes on the furnace wall, such as... Figure 3 As shown, each set of soot blowing tertiary air nozzle assembly includes multiple independent soot blowing tertiary air nozzles 12.

[0032] Its flue gas duct system is equipped with multiple flow regulating valves, including flue gas regulating valve 7 that regulates the flow of flue gas from the blower outlet flue gas main pipe into the two sets of cold ash hopper tertiary air nozzle assemblies, flue gas regulating valve 9 that regulates the flow of flue gas from the blower outlet flue gas main pipe into the two sets of arch tertiary air nozzle assemblies, flue gas regulating valve 11 that regulates the flow of flue gas from the blower outlet flue gas main pipe into the two sets of upper tertiary air nozzle assemblies, and flue gas regulating valve 13 that regulates the flow of flue gas from the blower outlet flue gas main pipe into a set of soot blowing tertiary air nozzle assemblies.

[0033] Two sets of tertiary air nozzle assemblies for cold ash hoppers are installed perpendicular to the plane of the cold ash hoppers, with their center lines forming an angle of 50-55° with the vertical direction; two sets of tertiary air nozzle assemblies for the arch are installed vertically downwards, with their center lines forming an angle of 0° with the vertical direction; two sets of upper tertiary air nozzle assemblies are installed obliquely downwards, with their center lines forming an angle of 30-45° with the vertical direction; and one set of tertiary air nozzle assemblies for soot blowing is installed perpendicular to the plane of the oblique flue above the flame deflector, with its center line forming an angle of 35-40° with the vertical direction.

[0034] Each cold ash hopper tertiary air nozzle 6 is a narrow rectangular nozzle with a length-to-width ratio of 5:1. The interior is divided into 8 sections by a grid. The nozzles are placed between the tube screens on the heating surface of the cold ash hopper, and the different cold ash hopper tertiary air nozzles 6 are parallel to each other. Each arch-shaped tertiary air nozzle 8 is a square nozzle with a side length of 300mm to 400mm. Each upper tertiary air nozzle 10 is a circular nozzle with a diameter of 400mm to 500mm. Each soot blowing tertiary air nozzle 12 is a cylindrical nozzle with a diameter of 50mm to 80mm and a height of 300mm to 500mm. The top is a hemispherical surface with the same diameter as the cylinder. Along the circumference, a soot blowing hole is opened every 120° at a position with an angle of 45° to the axis on the sphere. The hole diameter is 10mm to 15mm. Each soot blowing tertiary air nozzle 12 has three soot blowing holes. A set of soot blowing tertiary air nozzles consists of 3 to 5 rows of soot blowing tertiary air nozzles 12 arranged in parallel.

[0035] The flue gas velocity passing through the two sets of cold ash hopper tertiary air nozzle assemblies is 8–12 m / s, the flue gas velocity passing through the two sets of arch-mounted tertiary air nozzle assemblies is 20–30 m / s, the flue gas velocity passing through the two sets of upper tertiary air nozzle assemblies is 20–30 m / s, and the flue gas velocity passing through the one set of soot blowing tertiary air nozzle assemblies is 20–30 m / s.

[0036] The flue gas entering the flue gas circulation fan 2 comes from the turning chamber of the vertical flue at the tail of the boiler. It has an oxygen content of 2.5-5% and a temperature of 400-500℃. Its flue gas circulation volume is 5-10% of the total flue gas generated by the boiler combustion.

[0037] Furthermore, in traditional W-flame boiler low-NOx combustion systems, the main combustion zone accounts for approximately 75% of the total secondary air volume, with the remaining 25% shifting upwards to the burnout zone. The excess air coefficient in the lower furnace is below 0.8, leading to incomplete combustion due to oxygen deficiency and a rising flame center. This can easily cause overheating of the screen and an increase in desuperheating water volume. During deep peak-shaving operation, the proportion of heat absorbed by the radiant heating surface increases, causing the flame center to shift downwards, which can easily result in lower reheat steam temperatures. For W-flame boilers burning low-volatile coal, when the volatile content of the coal increases, ignition occurs earlier, and the flame center moves upwards, easily causing overheating of the screen and an increase in desuperheating water volume. For W-flame boiler systems with a defined equipment configuration, the secondary air distribution strategy should prioritize NOx. xThe control requirements and the need for complete combustion of pulverized coal cannot be resolved by adjusting the existing equipment.

[0038] This invention introduces a combined tertiary air system and corresponding tertiary air nozzles, allowing different forms and functions of tertiary air to be introduced at different stages of pulverized coal ignition and combustion, and in different areas of the furnace. Utilizing the characteristics of tertiary air—low oxygen content, high inertness, and minimal participation in combustion chemical reactions—the invention adjusts its jet velocity and the distribution of tertiary air volume at different locations without affecting NO₂ levels. x Under controlled conditions, the airflow organization and temperature field distribution within the furnace are optimized to achieve the goal of controlling the flame center. By adopting the technology of this invention, operators can adjust the flue gas volume of different tertiary air nozzles to change the momentum of the furnace bottom support, the upward and downward momentum of the arch, and the downward momentum at the throat. This allows them to adapt to problems such as imbalances in the heat absorption ratio of the radiative and convective heating surfaces, excessive overheating of the screen, and large amounts of desuperheating water caused by changes in coal quality or operating conditions.

[0039] 1. Traditional W-flame boilers, once the equipment type is determined, cannot flexibly adjust the flame center. This invention improves the flexibility of flame center control during the operation of W-flame boilers by adding a combined tertiary air system.

[0040] In traditional W-flame boiler low-NOx combustion systems, the primary combustion zone accounts for approximately 75% of the total secondary air volume, with the remaining 25% shifting upwards to the burnout zone. The excess air coefficient in the lower furnace is below 0.8, leading to incomplete combustion due to oxygen deficiency and a rising flame center. This can easily cause overheating in the heat exchanger and increase the amount of desuperheating water required. During deep peak-shaving operation, the increased heat absorption of the radiant heating surface and the downward shift of the flame center can easily result in lower reheat steam temperatures. For W-flame boilers burning low-volatile coal, when the volatile content of the coal increases, ignition occurs earlier, and the flame center moves upwards, easily causing overheating in the heat exchanger and increasing the amount of desuperheating water required. For W-flame boiler systems with a fixed equipment configuration, the secondary air distribution strategy should prioritize NOx. x The control requirements and the need for complete combustion of pulverized coal cannot be resolved by adjusting the existing equipment.

[0041] This invention introduces a combined tertiary air system and corresponding tertiary air nozzles, allowing different forms and functions of tertiary air to be introduced at different stages of pulverized coal ignition and combustion, and in different areas of the furnace. Utilizing the characteristics of tertiary air—low oxygen content, high inertness, and minimal participation in combustion chemical reactions—the invention adjusts its jet velocity and the distribution of tertiary air volume at different locations without affecting NO₂ levels. xUnder controlled conditions, the airflow organization and temperature field distribution within the furnace are optimized to achieve the goal of controlling the flame center. By adopting the technology of this invention, operators can adjust the flue gas volume of different tertiary air nozzles to change the momentum of the furnace bottom support, the upward and downward momentum of the arch, and the downward momentum at the throat. This allows them to adapt to problems such as imbalances in the heat absorption ratio of the radiative and convective heating surfaces, excessive overheating of the screen, and large amounts of desuperheating water caused by changes in coal quality or operating conditions.

[0042] 2. By adding a third-stage air nozzle for soot blowing, the amount of ash accumulating in the upper part of the flame deflector is reduced.

[0043] In W-flame boilers with a π-type flame arrangement, the upper slope angle of the flame deflector is generally less than 40°, which easily leads to excessive fly ash accumulation, causing ash collapse and boiler flameout. This invention addresses this by adding multiple tertiary sootblowing air nozzles in a group located in the ash-accumulating area of ​​the flame deflector, serving as a means of controlling ash accumulation during operation. Using this technology, operators can periodically adjust the amount of flue gas entering the tertiary sootblowing air nozzles to create disturbance in the ash layer, promoting orderly ash collapse and reducing the ash height at the upper part of the flame deflector.

[0044] 3. Add a third air nozzle at the upper part of the throat to alleviate the coking problem in the vicinity of the throat.

[0045] When high-temperature flue gas from a W-flame boiler passes through the throat from the lower furnace to the upper furnace region, it is highly prone to coking at the throat. This invention addresses this by adding an upper tertiary air nozzle above the throat, creating localized airflow disturbances and temperature fluctuations in that area, promoting dynamic coke shedding, and preventing large coke deposits from forming in that region.

[0046] 4. By adding a cold ash hopper and a tertiary air nozzle to the lower furnace, the unburned carbon content in the slag is reduced.

[0047] According to the combustion method used in W-flame boilers, fly ash has a longer residence time in the combustion zone, making it easier to burn completely. However, slag enters the slag pool immediately after passing through the lower furnace, resulting in an unsatisfactory burnout rate. This is especially true when burning low-quality coal that is difficult to ignite, as the ignition of the pulverized coal itself is delayed, increasing the carbon content in the large slag. This invention adds a cold ash hopper and tertiary air nozzle to the lower furnace. By utilizing the relatively larger momentum of the tertiary air compared to the downward flue gas, a fire-supporting layer is formed at the bottom of the furnace. This allows some slag to extend its effective residence time through suspension combustion, thereby reducing the unburned carbon content in the large slag.

[0048] The preferred specific implementation method is as follows:

[0049] This implementation method takes a 660MW unit with a W-flame boiler using Foster Wheeler technology as an example. The boiler burns a mixture of lean coal, bituminous coal and anthracite, and operates at a load between 20% and 100%.

[0050] Combination Figure 1As shown, the W-flame boiler with flame center controlled by combined tertiary air according to this embodiment includes a furnace 1, a flue gas circulating fan 2, a flue gas interface 3, a screen-type superheater 4 installed at the top of the upper furnace near the flame deflector, two sets of pulverized coal burner assemblies installed on the lower furnace arch, two sets of cold ash hopper tertiary air nozzle assemblies installed at the bottom of the lower furnace, two sets of arch-mounted tertiary air nozzle assemblies installed at the junction of the lower furnace arch and the front and rear walls, two sets of upper tertiary air nozzle assemblies installed on the front and rear walls above the throat of the upper furnace, and a set of soot blowing tertiary air nozzle assemblies installed on the inclined flue above the flame deflector. A flue gas recirculation fan 2 is installed on a flue gas duct. The inlet of the flue gas recirculation fan 2 is connected to a flue gas interface 3 via a flue gas duct. The outlet of the flue gas recirculation fan 2 is connected to two sets of cold ash hopper tertiary air nozzle assemblies, two sets of arch-mounted tertiary air nozzle assemblies, two sets of upper tertiary air nozzle assemblies, and one set of soot blowing tertiary air nozzle assemblies installed on the front and rear walls of the furnace, respectively, via a flue gas duct. Two sets of pulverized coal burner assemblies are symmetrically installed on the front and rear arches of the lower furnace, arranged in an alternating pattern. Each set of pulverized coal burner assemblies includes 18 independent pulverized coal burners 5. Two sets of cold ash hopper tertiary air nozzle assemblies are symmetrically and evenly installed in a horizontal line on the front and rear walls of the lower furnace. Each set of cold ash hopper tertiary air nozzle assemblies includes 18 independent cold ash hopper tertiary air nozzles 6. The cold ash hopper tertiary air nozzles 6 are connected to the pulverized coal burners 5. The positions of the two sets of tertiary air nozzles are one-to-one; the two sets of tertiary air nozzle assemblies are symmetrically installed on the lower furnace arch near the junction of the front and rear walls, and are staggered. Each set of tertiary air nozzle assemblies includes 18 independent tertiary air nozzles 8, and the positions of the tertiary air nozzles 8 and the pulverized coal burners 5 are one-to-one; the two sets of upper tertiary air nozzle assemblies are symmetrically and evenly installed in a horizontal row on the front and rear walls above the throat of the upper furnace. Each set of upper tertiary air nozzle assemblies includes 18 independent upper tertiary air nozzles 10, and the positions of the upper tertiary air nozzles 10 and the pulverized coal burners 5 are one-to-one; a set of soot blowing tertiary air nozzle assemblies is evenly installed in an array on the inclined flue above the flame deflector, avoiding the heating surface tubes on the furnace wall. Each set of soot blowing tertiary air nozzle assemblies includes multiple independent soot blowing tertiary air nozzles 12.

[0051] Furthermore, the flue gas duct system in this embodiment is equipped with multiple flow regulating valves, including a flue gas regulating valve 7 that regulates the flow of flue gas from the blower outlet flue gas main pipe into two sets of cold ash hopper tertiary air nozzle assemblies, a flue gas regulating valve 9 that regulates the flow of flue gas from the blower outlet flue gas main pipe into two sets of arch tertiary air nozzle assemblies, a flue gas regulating valve 11 that regulates the flow of flue gas from the blower outlet flue gas main pipe into two sets of upper tertiary air nozzle assemblies, and a flue gas regulating valve 13 that regulates the flow of flue gas from the blower outlet flue gas main pipe into a set of soot blowing tertiary air nozzle assemblies.

[0052] Furthermore, in this embodiment, the two sets of cold ash hopper tertiary air nozzle assemblies are installed perpendicular to the plane of the cold ash hopper, with their center lines forming an angle of 50° with the vertical direction; the two sets of arch-mounted tertiary air nozzle assemblies are installed vertically downwards, with their center lines forming an angle of 0° with the vertical direction; the two sets of upper tertiary air nozzle assemblies are installed obliquely downwards, with their center lines forming an angle of 30° with the vertical direction; and the set of soot blowing tertiary air nozzle assemblies is installed perpendicular to the plane of the oblique flue above the flame deflector, with its center line forming an angle of 30° with the vertical direction.

[0053] Furthermore, in this embodiment, the single cold ash hopper tertiary air nozzle 6 adopts a narrow rectangular nozzle with a length-to-width ratio of 5:1. The interior is divided into 8 sections by a grid. The nozzle is placed between the tube screens on the heating surface of the cold ash hopper, and the different cold ash hopper tertiary air nozzles 6 are parallel to each other. The single arch-top tertiary air nozzle 8 adopts a square nozzle with a side length of 350mm. The single upper tertiary air nozzle 10 adopts a circular nozzle with a diameter of 450mm. The single soot blowing tertiary air nozzle 12 adopts a cylindrical nozzle with a diameter of 60mm and a height of 400mm. The top is a hemispherical surface with the same diameter as the cylinder. Along the circumference, a soot blowing hole with a diameter of 12mm is opened every 120° at a position with an angle of 45° to the axial direction on the sphere. The single soot blowing tertiary air nozzle 12 has three soot blowing holes. A set of soot blowing tertiary air nozzle assemblies consists of 4 rows of soot blowing tertiary air nozzles 12 arranged in parallel.

[0054] Furthermore, in this embodiment, the flue gas velocity through the two sets of cold ash hopper tertiary air nozzle assemblies is 8-12 m / s, the flue gas velocity through the two sets of arch tertiary air nozzle assemblies is 20-30 m / s, the flue gas velocity through the two sets of upper tertiary air nozzle assemblies is 20-30 m / s, and the flue gas velocity through the one set of soot blowing tertiary air nozzle assembly is 20-30 m / s.

[0055] Furthermore, in this embodiment, the flue gas entering the flue gas circulation fan 2 comes from the turning chamber of the vertical flue at the tail of the boiler, with an oxygen content of 2.5-5% and a temperature of 400-500°C. Its flue gas circulation volume is 5-10% of the total flue gas generated by the boiler combustion.

[0056] The working principle of the W-flame boiler flame center controlled by the combined tertiary air in this embodiment is as follows: Figure 1As shown, the main combustion process occurs in furnace 1. Fuel enters furnace 1 from pulverized coal burner 5. Secondary air required for combustion is gradually introduced into the furnace through secondary air inlets at different locations to mix with primary air and is used to organize the combustion process and the flow field inside the furnace. According to the design concept of W-flame boiler, after leaving pulverized coal burner 5, the pulverized coal gas flow is heated and ignited by the high-temperature flue gas in furnace 1. Then, utilizing the initial momentum of the gas flow, it descends to the lowest point and then turns upward, passing through the throat and entering the upper furnace for complete combustion. Finally, it leaves the furnace and exchanges heat with the screen and various stages of heating surfaces. Some of the fly ash in the flue gas settles on the inclined surface above the flame deflector when passing through the furnace outlet. After the addition of the combined tertiary air system, the pulverized coal gas flow is heated and ignited by the high-temperature flue gas in the furnace 1 after leaving the pulverized coal burner 5. The tertiary air from the rear of the pulverized coal burner 5 is injected downwards and guides the main pulverized coal gas flow downwards to the area above the cold ash hopper. At this time, the tertiary air from the cold ash hopper is ejected obliquely upwards, which lifts the downward-injected gas flow. The main pulverized coal gas flow turns upwards and, after passing through the throat, the tertiary air is added to the mainstream flue gas. In this area, the air flow is disturbed and the temperature in this area is reduced to prevent slag from forming on the wall. After some fly ash in the flue gas settles to the upper part of the flame deflector, the tertiary air blowing is periodically opened to disturb the settled ash layer and cause it to collapse dynamically.

[0057] In this embodiment, corresponding tertiary air nozzles are added at different positions in the furnace. The flue gas volume of different tertiary air nozzles is adjusted to change the momentum of the bottom fire support, the momentum of the arch thrust, the downward momentum at the throat, and the momentum of the flame deflector ash blowing disturbance. This enhances the ability of the combustion air distribution system to control the downward jetting capacity of the main pulverized coal, the temperature of the cold ash hopper area, the temperature of the upper and lower furnace throat areas, and the ash accumulation in the horizontal flue. It maintains a reasonable flame center position, alleviates steam-water system problems and flame deflector ash collapse problems caused by changes in coal quality and load, and improves the flexible adjustment capability of the flame center of the W-flame boiler in ultra-low emission operation conditions with large fluctuations in the quality of the incoming coal. This invention is an important supplement to the existing W-flame boiler combustion technology. Moreover, implementing the solution described in this invention can improve the boiler's adaptability to multiple coal types and variable load conditions. Most of the original combustion system components of the boiler can be reused. Only the addition of tertiary air nozzles for the cold ash hopper, tertiary air nozzles for the arch, upper tertiary air nozzles, soot blowing tertiary air nozzles, water-cooled jackets, flue gas dampers, and auxiliary equipment is required. The investment and risk of the modification are small.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A W-flame boiler with flame center controlled by a combined tertiary air system, characterized in that, The boiler includes an upper furnace, a lower furnace, a flue gas circulating fan (2), and a flue gas interface (3). Two sets of pulverized coal burner assemblies are installed on the arch of the lower furnace. Two sets of cold ash hopper tertiary air nozzle assemblies are installed at the bottom of the lower furnace. Two sets of upper tertiary air nozzle assemblies are installed on the front and rear walls above the throat of the upper furnace. Two sets of arch upper tertiary air nozzle assemblies are installed at the junction of the arch of the lower furnace and the front and rear walls. A set of soot blowing tertiary air nozzle assemblies is installed at the inclined flue above the flame deflector of the boiler. The inlet of the flue gas circulation fan (2) is connected to the flue gas interface (3) through the flue gas pipe, and the outlet of the flue gas circulation fan (2) is connected to two sets of cold ash hopper tertiary air nozzle assemblies, two sets of arch tertiary air nozzle assemblies, two sets of upper tertiary air nozzle assemblies and one set of soot blowing tertiary air nozzle assemblies through the flue gas pipe; the flue gas circulation fan (2) is installed on the flue gas pipe; The tertiary air nozzle (6) of the cold ash hopper is installed perpendicular to the plane of the cold ash hopper, and the center line of the tertiary air nozzle (6) of the cold ash hopper is at an angle of 50~55° with the vertical direction; the tertiary air nozzle (8) of the arch is installed perpendicular to the ground, and the center line of the tertiary air nozzle (8) of the arch is at an angle of 0° with the vertical direction; the upper tertiary air nozzle (10) is installed obliquely downward, and the center line of the upper tertiary air nozzle (10) is at an angle of 30~45° with the vertical direction; the tertiary air nozzle (12) of the soot blowing is installed perpendicular to the plane of the oblique flue above the flame deflector, and the center line of the soot blowing tertiary air nozzle (12) is at an angle of 35~40° with the vertical direction.

2. A W-flame boiler with flame center controlled by a combined tertiary air system according to claim 1, characterized in that, The two sets of pulverized coal burner assemblies are symmetrically installed on the front and rear arches of the lower furnace, and each set of pulverized coal burner assemblies includes 12 or 18 independent pulverized coal burners (5).

3. A W-flame boiler with flame center controlled by a combined tertiary air system according to claim 2, characterized in that, The two sets of cold ash hopper tertiary air nozzle assemblies are symmetrically installed in a horizontal row on the front and rear walls of the lower furnace. Each set of cold ash hopper tertiary air nozzle assemblies includes 12 or 18 independent cold ash hopper tertiary air nozzles (6), and the positions of the cold ash hopper tertiary air nozzles (6) and the pulverized coal burners (5) correspond one-to-one.

4. A W-flame boiler with flame center controlled by a combined tertiary air system according to claim 3, characterized in that, The two sets of arch-mounted tertiary air nozzle assemblies are symmetrically installed on the lower furnace arch near the junction of the front and rear walls, and are arranged in an alternating manner. Each set of arch-mounted tertiary air nozzle assemblies includes 12 or 18 independent arch-mounted tertiary air nozzles (8), and the positions of the arch-mounted tertiary air nozzles (8) correspond one-to-one with the positions of the pulverized coal burners (5).

5. A W-flame boiler with flame center controlled by a combined tertiary air system according to claim 4, characterized in that, The two sets of upper tertiary air nozzle assemblies are symmetrically and evenly installed in a horizontal row on the front and rear walls above the throat of the upper furnace. Each set of upper tertiary air nozzle assemblies includes 12 or 18 independent upper tertiary air nozzles (10), and the positions of the upper tertiary air nozzles (10) and the pulverized coal burners (5) correspond one-to-one.

6. A W-flame boiler with flame center controlled by a combined tertiary air system according to claim 5, characterized in that, The set of soot blowing tertiary air nozzle assemblies are uniformly installed in an array on the inclined flue above the flame deflector, and each set of soot blowing tertiary air nozzle assemblies includes multiple independent soot blowing tertiary air nozzles (12).

7. A W-flame boiler with flame center controlled by a combined tertiary air system according to claim 6, characterized in that, A first flue gas regulating valve (7) is provided on the flue gas duct at the inlet of the tertiary air nozzle (6) of the cold ash hopper; a second flue gas regulating valve (9) is provided on the flue gas duct at the inlet of the tertiary air nozzle (8) of the arch; a third flue gas regulating valve (11) is provided on the flue gas duct at the inlet of the upper tertiary air nozzle (10); and a fourth flue gas regulating valve (13) is provided on the flue gas duct at the inlet of the tertiary air nozzle (12) of the soot blowing.

8. A W-flame boiler with flame center controlled by a combined tertiary air system according to claim 6, characterized in that, The flue gas velocity passing through the tertiary air nozzle (6) of the cold ash hopper is 8~12m / s, the flue gas velocity passing through the tertiary air nozzle (8) of the arch is 20~30m / s, the flue gas velocity passing through the upper tertiary air nozzle (10) is 20~30m / s, and the flue gas velocity passing through the tertiary air nozzle (12) of the soot blowing is 20~30m / s; the oxygen content of the flue gas in the flue gas circulation fan (2) is 2.5~5%, the temperature is 400~500℃, and its flue gas circulation volume is 5~10% of the total flue gas volume generated by boiler combustion.

9. A W-flame boiler with flame center controlled by a combined tertiary air system according to claim 1, characterized in that, A screen-type superheater (4) is installed at the top of the upper furnace near the flame deflector.

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