High-efficiency direct-current burner and cyclone burner synergistic combustion device and synergistic combustion method

Abstract

This invention relates to a high-efficiency co-combustion device and method for a direct-flow burner and a swirl burner, within the field of tangential boiler combustion technology. To address the problem of tangential boilers failing to operate stably at 15% or lower rated loads, and the issues of nozzle overheating and burnout due to low primary air velocity in the direct-flow burner, as well as pulverized coal blockage in the pipes, this application utilizes a co-combustion method combining a direct-flow burner and a swirl burner. By introducing a system to increase the air velocity and temperature of the direct-flow burner and a supplementary air system for the swirl burner, the direct-flow primary air velocity is increased, thereby enhancing the direct-flow primary air ejection capacity. This allows for adjustment of the shape and size of the central recirculation zone and prevents nozzle overheating and burnout due to low air velocity in the duct. Simultaneously, increasing the temperature of the direct-flow primary air and the self-regulating combustion burner's primary air increases the pulverized coal temperature at the boiler inlet, strengthening initial ignition and burnout of the pulverized coal. This application is primarily intended to improve the stable combustion effect of boilers operating below 15% of rated power.

Description

Technical Field

[0001] This invention relates to the field of tangential boiler combustion technology, specifically to a high-efficiency direct-flow burner and swirl burner co-combustion device and co-combustion method. Background Technology

[0002] The proportion of fossil fuels in the energy mix is ​​declining year by year, while the proportion of new energy power generation is increasing, which is undoubtedly a positive measure to promote environmental protection and sustainable development. However, new energy power generation also has some shortcomings, the most significant being its intermittent generation and instability due to environmental influences. These shortcomings limit its ability to meet the power supply demand during peak grid load periods. Therefore, flexible retrofitting of thermal power units is necessary to enable them to absorb more clean energy. When new energy power generation is unstable, the output of thermal power units can be fully utilized, while power generation can be reduced during off-peak periods or when new energy generation is stable, thereby achieving deep peak shaving. The most critical issue in the flexible retrofitting of units to improve peak shaving capacity is to achieve stable operation of boilers under low loads of 20%-30% or even lower.

[0003] Coal-fired boiler power generation is currently the mainstay of my country's energy structure. The combustion method of coal-fired boilers primarily employs direct-flow burners arranged at the four or eight corners of the boiler furnace. Pulverized coal gas flow and secondary air are injected into the furnace through the direct-flow burner jets, converging in a tangential circular pattern. The pulverized coal gas flow towards the fire is ignited by the direct impact of the high-temperature flames in the upstream adjacent corners. The four (or eight) corner jets support each other, forming a rotating combustion flame. The four-corner (or eight) tangential pulverized coal combustion boiler is the most widely used and mature boiler type in my country's power plants, accounting for approximately 70% or more of the total installed capacity. Currently, domestic coal-fired power units using four-corner (or eight) tangential pulverized coal boilers can achieve a stable combustion load of 30%-40% without oil injection, but relying solely on pulverized coal combustion is insufficient to achieve a stable combustion effect of 20%-30% of the rated load, resulting in the four-corner (or eight) tangential pulverized coal boiler failing to meet deep peak-shaving requirements.

[0004] Currently, tangential (or octagonal) tangential boilers require micro-oil or plasma technology to achieve stable combustion at 20%-30% of rated load. Micro-oil combustion technology uses a small amount of oil (oil gun output 0.4t / h-0.6t / h) to ignite pulverized coal, enhancing ignition and stable combustion through its own combustion heat release. It has the advantage of strong coal adaptability, suitable for boilers from lignite to anthracite. However, long-term operation has a negative impact on electrostatic precipitator electrodes and desulfurization slurry. Furthermore, using oil guns for stable combustion can consume tens of thousands of tons of oil annually, resulting in poor economic efficiency and extremely high costs. Plasma combustion technology mainly uses a high-power plasma gun to generate a high-temperature arc, enhancing pulverized coal ignition and stable combustion. It is economical and environmentally friendly, but suffers from a short cathode lifespan and poor coal adaptability, and is often used in boilers burning bituminous coal with high volatile matter content.

[0005] Existing technology has developed a co-combustion device for a direct-flow burner and a swirl burner, which sets up a self-sustaining combustion burner between the direct-flow primary air and direct-flow secondary air. The original direct-flow burner and the self-sustaining combustion burner perform co-combustion, enabling tangential (or octagonal) boilers to operate stably at 20%-30% of rated load relying solely on pulverized coal combustion, while improving burnout efficiency at high loads. However, practical application shows that after applying this device, tangential boilers cannot operate stably at lower rated loads (below 15%), and problems such as nozzle overheating and burnout due to excessively low primary air velocity and pulverized coal blockage in the pipes occur. Therefore, to solve the above problems, this invention proposes a high-efficiency co-combustion device and method for a direct-flow burner and a swirl burner. Summary of the Invention

[0006] In order to solve the problem that the four-corner tangential boiler cannot operate stably under a lower rated load of 15%, and that the direct current burner will overheat and burn out the nozzle due to the low primary air velocity and the pipe will be blocked, the present invention provides a high-efficiency direct current burner and swirl burner co-combustion device and co-combustion method.

[0007] A high-efficiency direct-current burner and swirl burner co-combustion device is disclosed. The co-combustion device includes a tangentially circular pulverized coal combustion boiler, a secondary air box, and four direct-current pulverized coal burners. The four direct-current pulverized coal burners are respectively arranged at the four corners of the tangentially circular pulverized coal combustion boiler. Each direct-current pulverized coal burner corresponds to at least one coal mill. The direct-current primary air nozzle of the direct-current pulverized coal burner is connected to the coal outlet of the coal mill via a coal supply pipeline. The direct-current secondary air nozzle of the direct-current pulverized coal burner is connected to the air outlet of the secondary air box via an air supply pipeline. Each direct-current pulverized coal burner includes at least one self-sustaining combustion burner, and each self-sustaining combustion burner is arranged in a... Between the DC primary air nozzle and the DC secondary air nozzle located on the same layer in the corresponding DC pulverized coal burner, the self-stable combustion burner is connected to the coal supply pipeline of the adjacent DC primary air nozzle and the air supply pipeline of the adjacent DC secondary air nozzle through the air-coal system. The co-combustion device also includes an air supply system and an air-temperature make-up air system. The first air outlet of the air supply system is connected to the air inlet of each coal mill, the second air outlet of the air supply system is connected to the air inlet of the secondary air box, the air inlet of the air-temperature make-up air system is connected to the air supply system, the DC make-up air end of the air-temperature make-up air system is connected to the coal supply pipeline, and the swirl make-up air end of the air-temperature make-up air system is connected to the air-coal system.

[0008] Furthermore, each coal mill is equipped with a corresponding coal feeder, and the coal outlet end of each coal feeder is connected to the coal inlet end of the corresponding coal mill through a coal drop pipe.

[0009] Furthermore, the coal supply pipeline includes a DC primary air channel, a primary air duct, and a No. 1 regulating valve. One end of the DC primary air channel is connected to the corresponding DC primary air nozzle, one end of the primary air duct is connected to the coal outlet of the corresponding coal mill, and the other end of the DC primary air channel is connected to the other end of the primary air duct. A No. 1 regulating valve is installed at the connection between the DC primary air channel and the primary air duct.

[0010] The coal supply pipeline also includes No. 2 regulating valve, No. 3 regulating valve, No. 1 pulverized coal pipeline and pulverized coal separation device. The coal inlet end of the pulverized coal separation device is connected to the primary air duct, and No. 2 regulating valve is connected in series on the primary air duct. The No. 1 coal outlet end of the pulverized coal separation device is connected to the DC primary air channel through No. 1 pulverized coal pipeline, and No. 3 regulating valve is connected in series on No. 1 pulverized coal pipeline.

[0011] Furthermore, the air supply pipeline includes a DC secondary air duct, a secondary air duct, and a No. 4 regulating valve. One end of the DC secondary air duct is connected to the corresponding DC secondary air nozzle, one end of the secondary air duct is connected to the air outlet of the corresponding secondary air box, and the other end of the DC secondary air duct is connected to the other end of the secondary air duct. A No. 4 regulating valve is installed at the connection between the DC secondary air duct and the secondary air duct.

[0012] Furthermore, the self-sustaining combustion burner includes a combustion stabilizing chamber, a swirling internal secondary air channel, and a self-sustaining combustion burner direct primary air channel. The swirling internal secondary air channel is coaxially sleeved outside the self-sustaining combustion burner direct primary air channel, and one end of the self-sustaining combustion burner direct primary air channel and one end of the swirling internal secondary air channel are both connected to the combustion stabilizing chamber. The other end of the self-sustaining combustion burner direct primary air channel is connected to the coal supply pipeline through the air-coal system, and the other end of the swirling internal secondary air channel is connected to the air supply pipeline through the air-coal system. An axial blade group is provided between the self-sustaining combustion burner direct primary air channel and the swirling internal secondary air channel, and the axial blade group is located close to the combustion stabilizing chamber. The axial blade group includes multiple axial blades, which are equidistantly arranged circumferentially between the self-sustaining combustion burner direct primary air channel and the swirling internal secondary air channel. One end of each axial blade is connected to the outer wall of the self-sustaining combustion burner direct primary air channel, and the other end of each axial blade is connected to the inner wall of the swirling internal secondary air channel.

[0013] Furthermore, the air-coal system includes a direct coal supply pipeline and a swirl air supply pipeline. The coal supply pipeline is connected to the direct primary air channel of the self-stable combustion burner through the direct coal supply pipeline, and the air supply pipeline is connected to the secondary air channel inside the swirl through the swirl air supply pipeline.

[0014] The DC coal supply pipeline includes a DC connection duct for the self-stable combustion burner, a No. 5 regulating valve, a No. 2 pulverized coal channel, and a No. 6 regulating valve. The primary air duct is connected to the DC primary air channel of the self-stable combustion burner through the DC connection duct, and the No. 5 regulating valve is connected in series on the DC connection duct. The No. 2 coal outlet of the pulverized coal separator is connected to the DC primary air channel of the self-stable combustion burner through the No. 2 pulverized coal channel, and the No. 6 regulating valve is connected in series on the No. 2 pulverized coal channel.

[0015] The swirl air supply pipeline includes the swirl connecting air duct of the self-stable burner and the No. 7 regulating valve. The secondary air duct is connected to the secondary air channel inside the swirl through the swirl connecting air duct of the self-stable burner. The No. 7 regulating valve is connected in series at the connection between the secondary air channel inside the swirl and the connecting air duct of the self-stable burner.

[0016] Furthermore, the air supply system includes a blower, a primary air fan, a secondary air duct, an air preheater, a cold primary air header, a hot primary air header, and a hot secondary air duct. The air preheater is installed at the end of the furnace flue. The outlet of the blower is connected to the first air inlet of the air preheater via a pipe. The outlet of the primary air fan is connected to the second air inlet of the air preheater via a pipe. The inlet of the cold primary air header is connected to the connecting pipe between the primary air fan and the air preheater. The outlet of the cold primary air header... It is equipped with multiple primary air sub-pipes. The air inlet of each primary air sub-pipe is connected to the air outlet of the cold primary air main pipe. The air outlet of each cold primary air sub-pipe is connected to the air inlet of a coal mill. The air inlet of the hot primary air main pipe is connected to the first air outlet of the air preheater. The air outlet of the hot primary air main pipe is connected to the air outlet of the cold primary air main pipe. The air inlet of the hot secondary air pipe is connected to the second air outlet of the air preheater. The air outlet of the hot secondary air pipe is connected to the air inlet of the secondary air box.

[0017] A coal mill cold air regulating valve is connected in series on the primary cold air main pipe;

[0018] A coal mill hot air regulating valve is connected in series on the primary hot air main pipe;

[0019] A shut-off valve is connected in series on the primary air duct;

[0020] Furthermore, the primary air supply system includes a hot primary air supply main pipe, a cold primary air supply main pipe, a No. 1 cold primary air supply pipe, a No. 2 cold primary air supply pipe, a No. 1 hot primary air supply pipe, and a No. 2 hot primary air supply pipe. The air inlet of the hot primary air supply main pipe is connected to the hot primary air supply main pipe. The No. 1 air outlet of the hot primary air supply main pipe is connected to the DC primary air channel through the No. 1 hot primary air supply pipe. The No. 2 air outlet of the hot primary air supply main pipe is connected to the DC primary air channel of the self-stable combustion burner through the No. 2 hot primary air supply pipe. The air inlet of the cold primary air supply main pipe is connected to the cold primary air supply main pipe. The No. 1 air outlet of the cold primary air supply main pipe is connected to the No. 1 hot primary air supply pipe through the No. 1 cold primary air supply pipe. The No. 2 air outlet of the cold primary air supply main pipe is connected to the No. 2 hot primary air supply pipe through the No. 2 cold primary air supply pipe.

[0021] A hot primary air regulating valve is connected in series on the hot primary air makeup air main pipe;

[0022] A primary air regulating valve is connected in series on the primary air makeup air main pipe;

[0023] A primary air supply damper for cooling is connected in series on the primary air supply duct for cooling.

[0024] The No. 2 primary air supply air duct is connected in series with the No. 2 primary air supply air regulating damper.

[0025] The No. 1 hot primary air supply duct is connected in series with the No. 2 shut-off valve, the No. 1 supply air regulating valve, the No. 1 wind speed measuring device, and the No. 1 temperature measuring device along the gas direction. The No. 2 shut-off valve, the No. 1 supply air regulating valve, the No. 1 wind speed measuring device, and the No. 1 temperature measuring device are all located between the No. 1 cold primary air supply duct and the DC primary air channel.

[0026] The No. 3 shut-off valve, the No. 2 make-up air valve, the No. 2 temperature measuring device, and the purge valve are connected in series along the gas direction. The No. 3 shut-off valve, the No. 2 make-up air regulating valve, the No. 2 temperature measuring device, and the purge valve are all located between the No. 2 cold primary air make-up air pipe and the DC primary air channel of the self-stable combustion burner.

[0027] The air temperature make-up air system also includes a heat exchanger, which is connected in series in the DC primary air channel of the self-stable combustion burner. The heat exchanger's heat exchange air inlet is connected to the No. 2 hot primary air make-up air pipeline through the induced draft pipe, and the induced draft pipe is located between the No. 2 temperature measuring device and the purge valve. A heat exchange valve is connected in series on the induced draft pipe. The heat exchanger's heat exchange air return end is connected to the hot primary air main pipe through the heat exchanger return pipe.

[0028] Furthermore, a heater is connected in series on the primary air supply air main pipe;

[0029] An efficient co - combustion method for direct - current burners and swirl burners, the specific operation is as follows when the boiler is operating under the condition of less than 15% of the rated load:

[0030] Shut off the first regulating valve and the fifth regulating valve, open the second regulating valve. The pulverized coal air flow controls the primary air velocity entering the direct - current primary air passage to u2 = 16 - 18 m / s by changing the opening of the third regulating valve. On the premise of basically not changing the original operation mode of the coal mill, high - temperature and high - pressure hot primary air is provided to the air temperature compensation system by adjusting the hot primary air regulating valve and the cold primary air regulating valve. Open the second shut - off valve, and control the hot primary air volume and air temperature supplemented into the direct - current primary air passage by adjusting the opening of the first air supplement regulating valve and the first cold primary air supplement regulating valve. Among them, the air supplement velocity u1 is 30 - 32 m / s, the air supplement temperature T1 is 280 - 300 °C. After supplementing, it merges into the direct - current primary air passage. At this time, the direct - current primary air velocity u2 is increased to 24 - 27 m / s, and the temperature of the air - powder flow is increased from T3 = 50 - 90 °C to T3 = 180 - 210 °C. Through the above operations, by increasing the direct - current primary air velocity, a large - range central recirculation zone is formed in the stable combustion chamber and the furnace. The diameter D of the recirculation zone is 2De < D < 2.5De, and the length L is 4De < L < 4.5De;

[0031] On the premise of not changing the original operation mode of the coal mill, high - temperature and high - pressure hot primary air is provided to the air temperature compensation system by adjusting the hot primary air regulating valve and the cold primary air regulating valve. Open the third shut - off valve, and control the air temperature entering the second hot primary air supplement pipeline by adjusting the opening of the second air supplement regulating valve and the second cold primary air supplement regulating valve. The air supplement temperature T2 is 280 - 300 °C. Close the purging valve and open the heat - exchange valve to increase the air - powder mixture air temperature in the direct - current primary air passage of the self - stabilizing combustion burner. The supplemented air after heat - exchange flows back to the hot primary air header through the heat - exchanger return pipe. The air - powder flow temperature is increased from T3 = 50 - 90 °C to T3 = 180 - 210 °C. Through the above operations, the air - powder flow temperature in the direct - current primary air passage and the direct - current primary air passage of the self - stabilizing combustion burner is increased to 180 - 210 °C, so as to achieve the purpose of increasing the primary air - powder temperature at the inlets of the direct - current burner and the self - stabilizing combustion burner when operating at less than 15% of the rated load.

[0032] The beneficial effects of this application compared with the prior art:

[0033] 1. The co - combustion device and co - combustion method for an efficient direct - current burner and swirl burner provided by the present invention achieve stable combustion of four - corner or eight - corner tangentially fired boilers at an ultra - low load of 15%, and improve the deep peak - shaving ability of the boiler;

[0034] At present, the power station boiler adopts a coordinated combustion system of direct current burners and swirl burners, and the lowest stable combustion load can reach 20%. When the boiler operates at 20% of the rated load, a central recirculation zone with a certain shape and size is generated. The diameter of the recirculation zone is 1.5De < D < 2De, the length is 3.5De < L < 4De, and the maximum flue gas recirculation volume is 7-8 times the primary air volume. It cannot meet the lower load peak shaving requirements. Practice shows that when the boiler operates at an ultra-low load, the flue gas temperature in the main combustion zone decreases, and a large-sized recirculation zone is required to entrain more high-temperature flue gas to stabilize the pulverized coal combustion. At the same time, increasing the primary air temperature can reduce the heat required for pulverized coal ignition, thereby improving the low-load stable combustion ability of the boiler.

[0035] In this invention, a system for increasing the wind speed and temperature of the direct current burner and a wind temperature supplement system for the swirl burner are added to the coordinated combustion system of the direct current burner and the swirl burner, so as to increase the direct current primary air speed, and then improve the entrainment ability of the direct current primary air, promote more high-temperature flue gas to flow back to the recirculation zone of the self-stable combustion burner, significantly enhance the recirculation effect, and expand the range of the recirculation zone. At 15% of the rated load, a large-scale central recirculation zone is formed in the stable combustion chamber and the furnace by increasing the direct current primary air speed. The diameter of the recirculation zone is 2De < D < 2.5De, the length is 4De < L < 4.5De, and the maximum flue gas recirculation volume is 9-10 times the primary air volume. The large-scale recirculation zone can provide a more stable high-temperature environment for combustion, which helps to maintain the stability of the flame. At the same time, by adding a system for increasing the wind speed and temperature of the direct current burner and a wind temperature supplement system for the swirl burner, the primary air-pulverized coal mixture can be increased from the original 50-90°C to 180-210°C significantly, significantly increasing the primary air-pulverized coal temperature at the inlets of the direct current burner and the self-stable combustion burner, reducing the heat required for pulverized coal ignition, and strengthening the initial ignition of pulverized coal. Under the action of the large-scale recirculation zone as a high-temperature heat source and the significant increase in the primary air-pulverized coal temperature at the boiler inlet, the boiler can be ensured to have stable combustion at 15% of the rated load, improving the deep peak shaving ability.

[0036] 2. The coordinated combustion device and coordinated combustion method of the high-efficiency direct current burner and swirl burner provided by this invention increase the primary air-pulverized coal temperature at the boiler inlet, effectively reduce the flue gas exhaust temperature, are beneficial to the complete combustion of pulverized coal, and thus improve the boiler efficiency;

[0037] Primary air carries and dries pulverized coal, while also providing oxidant for the initial combustion phase. However, the complex internal structure of the coal mill and the tendency for pulverized coal to accumulate, coupled with limitations imposed by inlet air temperature and explosion-proof requirements, pulverizers must operate at low temperatures, with outlet air temperature generally not exceeding 100°C. When the actual coal used has a higher total moisture content than the design coal, the outlet air-coal mixing temperature is even lower, affecting the unit's adaptability to different coal types. Increased cold air intake leads to higher flue gas temperature. Verification has shown that when the pulverizer outlet air-coal mixing temperature increases from 76°C to 90°C, the flue gas temperature can decrease by 9.8°C, reducing coal consumption for power generation by approximately 1.5 g / kW·h. Furthermore, a lower pulverized coal mixing temperature reduces the combustion rate, prolongs the ignition distance, affects pulverized coal burnout, and is detrimental to stable combustion. Meanwhile, during low-load operation, as the coal feed rate decreases, the heat released by pulverized coal combustion decreases, while the furnace volume and the heating surface area inside the furnace remain unchanged. This leads to a drop in the temperature of the furnace burner area, which is below 900℃ at 15% of the rated load. The lower furnace temperature is not conducive to the complete combustion of pulverized coal.

[0038] This invention adds a supplementary air system to the co-combustion system of a DC burner and a swirl burner, increasing the air velocity and temperature of the DC burner and the air temperature of the swirl burner. While ensuring the safe operation of the pulverizing system, the primary air-coal mixture temperature can be significantly increased from the original 50-90℃ to 180-210℃. This significantly increases the inlet primary air-coal temperature of both the DC burner and the self-stabilizing burner. The higher temperature accelerates the combustion process of pulverized coal, allowing for more complete combustion of the combustible components and thus improving combustion efficiency. Simultaneously, the flue gas temperature in the large central recirculation zone can reach over 1300℃, increasing the burner zone temperature and helping to reduce incomplete combustion losses in the boiler, thereby improving the boiler's thermal efficiency. It also reduces the amount of cold air introduced into the coal mill, further lowering the exhaust gas temperature and improving boiler efficiency.

[0039] 3. The present invention provides a high-efficiency DC burner and swirl burner co-combustion device and co-combustion method that effectively solves the problems of pulverized coal pipeline backfire, nozzle burn-out, coking, and water-cooled wall metal temperature overheating caused by low DC primary air velocity.

[0040] As the boiler load decreases, the coal pulverization rate is gradually reduced and the pulverizer is shut down. This significantly reduces the amount of pulverized coal fed into the furnace, resulting in a substantial decrease in pulverizer output and consequently, a reduction in primary air velocity. Simultaneously, the power plant boiler employs a combined combustion system of once-through burners and swirl burners. This system primarily uses a pulverized coal distributor to extract a portion of the primary air-coal mixture from the once-through burner's primary air duct and supply it to the self-contained combustion stabilizer burner. The self-contained combustion stabilizer burner needs to be operational at both high and low loads. To prevent excessive differences in pipe resistance, pipes of the same diameter are typically used. This leads to excessively low velocity (16-18 m / s) in the original once-through burner's primary air duct due to the extraction of the primary air-coal mixture. This weakens the rigidity of the pulverized coal airflow, making it prone to bending and deformation, skewed against the wall, poorly circularized, and with weak turbulence, resulting in slow combustion. This, in turn, causes burn-out of the primary air nozzles, coking around the once-through burner, and overheating of the water-cooled wall metal. Furthermore, the reduced velocity of the original once-through primary air-coal mixture within the pulverized coal duct may cause the mixture to accumulate within the duct and reach combustible conditions. When the mixture is ignited, the flame can propagate upstream in the pipeline, causing a backfire and damaging the pulverized coal pipeline.

[0041] This invention adds a supplementary air system to the co-combustion system of a DC burner and a swirl burner, increasing the air velocity and temperature of the DC burner and the air temperature of the swirl burner. When the boiler operates at 15% of its rated load, this system supplements the primary air duct of the DC burner by increasing the air velocity and temperature of the DC burner and the air temperature of the swirl burner. This eliminates the problem of excessively low air velocity in the primary air duct of the original DC burner, which was caused by the self-sustaining combustion burner providing part of the primary air-coal mixture. Simultaneously, the high DC primary air velocity (24-27 m / s, a 50% increase) significantly enhances the rigidity of the pulverized coal airflow, preventing pulverized coal combustion near the nozzle. This effectively solves the problems of nozzle burnout, coking around the burner, and overheating of the water-cooled wall metal, ensuring the safe and stable operation of the system. Meanwhile, the air velocity and temperature of the DC burner and the air temperature and temperature of the swirl burner are increased. When the DC burner and the swirl burner are put into operation and shut down, the air supply system performs high-speed purging of the DC primary air channel and the DC primary air channel of the swirl burner. This avoids the deposition of pulverized coal in the pipeline, thereby reducing the phenomenon of pipe blockage and preventing backfire caused by the accumulation of air-coal mixture in the pipeline, which could burn the pulverized coal pipeline.

[0042] 4. The efficient DC burner and swirl burner co-combustion device and co-combustion method provided by the present invention effectively improves the primary air-coal temperature at the boiler inlet without significantly changing the original operation mode of the coal mill, preventing spontaneous combustion in the pipeline and ensuring safety.

[0043] Coal mills typically have complex internal structures and coal dust tends to accumulate. Furthermore, due to limitations imposed by inlet air temperature and explosion-proof requirements, coal mills can only operate at low temperatures, with outlet air temperature generally not exceeding 100℃. When the total moisture content of the coal actually used is higher than the design coal type, the outlet air-coal mixing temperature is even lower, resulting in a lower air-coal mixing temperature entering the burner. If the coal mill outlet temperature is increased, due to the greater distance from the burner outlet, the slow oxidation reaction under high-temperature conditions takes a sufficiently long time to reach combustible conditions, easily leading to spontaneous combustion within the pipeline and damaging the coal dust pipeline.

[0044] This invention regulates the air intake of the coal mill by switching on and off the dampers and adjusting the hot and cold air dampers. By adjusting the hot and cold primary air dampers, it ensures that high-temperature, high-pressure primary air is supplied to the DC burner and swirl burner primary air supply systems without significantly altering the original operation of the coal mill. The DC burner primary air supply system is installed in the DC burner primary air duct, and the swirl burner primary air supply system is installed in the self-stabilizing combustion burner DC primary air duct. This method essentially does not affect the inlet and outlet temperatures and velocities of the coal mill. The high-temperature, high-pressure primary air increases the primary pulverized coal temperature in the primary air-coal mixture, maintaining a coal mill outlet temperature of 50-90℃ while achieving a primary air-coal mixture temperature of 180-210℃ entering the burner. This effectively increases the boiler inlet primary air-coal temperature without causing spontaneous combustion within the pipeline.

[0045] 5. The present invention provides a high-efficiency direct-flow burner and swirl burner co-combustion device and co-combustion method that can precisely control the heating temperature according to different coal types;

[0046] Different types of coal exhibit significant differences in characteristics within the pulverizing system. The ignition temperature of coal is related to its volatile matter content; generally, the ignition temperature decreases as the volatile matter content increases. Lignite typically ignites at 400-600℃, lean coal at around 700℃, and anthracite at over 800℃. Therefore, the required heating temperatures vary accordingly.

[0047] When burning bituminous coal with a Vdaf > 25%, the temperature of the primary air-coal mixture can reach 90-180℃; when burning lean coal with a Vdaf of 10%-25%, the temperature can reach 180-210℃; and when burning anthracite with a Vdaf < 10%, the temperature can reach 210-350℃. Where higher temperatures cannot be achieved solely through hot primary air, a heater can be installed on the hot primary air make-up air header to increase the temperature of the air entering the system that improves the velocity and temperature of the direct-flow burner and the temperature of the swirl burner, thus achieving a primary air-coal mixture temperature of 210-350℃. The heating device consists of a steam heater and a flue gas heater: the steam heater is a surface heater, with the heat source taken from the outlet steam of the screen-type superheater, high-temperature superheater, or high-temperature reheater. The flue gas heater is a surface heater or a mixing heater, with the heat source taken from the outlet flue gas of the high-temperature superheater or high-temperature reheater. Electric heating can also be used. The three heating methods described above offer high heating efficiency, large temperature rise, flexibility, reliability, and wide applicability. Through precise control, the pulverizing system can quickly adjust operating parameters according to changes in coal type, providing optimal pulverizing and combustion conditions for different coal types and enhancing the system's adaptability to various coal types.

[0048] 6. The present invention provides a high-efficiency direct-current burner and swirl burner co-combustion device and co-combustion method that can improve the wind speed and temperature of the direct-current burner and the wind temperature of the swirl burner. The air supply system can be switched to meet different boiler requirements.

[0049] When the co-combustion system of a DC burner and a swirl burner operates above 50% of its rated load, there is no need to increase the air velocity and temperature of the DC burner or the air temperature of the swirl burner. When operating between 20% and 50% of the rated load, the primary air-coal temperature of the swirl burner needs to be increased to reduce the ignition heat of the pulverized coal, thus facilitating ignition of the DC burner's primary air-coal flame in the central recirculation zone. However, when operating below 15% of the rated load, the primary air velocity and temperature of the DC burner and the primary air-coal temperature of the swirl burner need to be increased. Furthermore, when the self-stabilizing burner and the DC pulverized coal burner are taken out of service or put into operation, the air velocity and temperature of the DC burner and the air temperature of the swirl burner need to be increased to purge the pipelines.

[0050] This invention enables flexible switching of the primary air supply system for increasing the wind speed and temperature of the DC burner and the wind temperature of the swirl burner under different boiler requirements by changing the opening of the regulating valve. Based on the pulverized coal tube temperature requirements of the DC burner, the hot primary air regulating valve, the cold primary air regulating valve, the No. 1 supplementary air regulating valve, and the No. 1 cold primary air supplementary air regulating valve are opened or closed to jointly regulate the temperature and volume of the hot primary air entering the DC primary air channel. The No. 2 shut-off valve cuts off and connects the primary air supply system for increasing the wind speed and temperature of the DC burner and the wind temperature of the swirl burner entering the DC primary air channel. Based on the pulverized coal tube temperature requirements of the self-stable combustion burner, the No. 2 supplementary air regulating valve and the No. 2 cold primary air supplementary air regulating valve are opened or closed to jointly regulate the heat exchange capacity of the hot primary air entering the DC primary air channel of the self-stable combustion burner. Furthermore, by closing the purge valve and opening the heat exchange valve, heat exchange is performed on the primary air in the DC primary air channel of the self-stable combustion burner. The heat-exchanged hot primary air then returns to the hot primary air main pipe through the heat exchanger return pipe. The No. 3 shut-off valve controls the connection and disconnection of the DC primary air supply system (including the booster air velocity and temperature for the DC burner and the swirl burner) entering the self-sustaining combustion burner. The purging process of the DC primary air supply system and the DC primary air supply channel can be performed by opening the purge door and the No. 2 shut-off valve to prevent blockage or burnout of the pulverized coal pipeline. Each component of the booster air velocity and temperature for the DC burner and the swirl burner can be independently adjusted and controlled to meet the needs of different locations and stages for hot primary air supply and heat exchange. When system connection is required, the regulating door restores the booster air velocity and temperature for the DC burner and the swirl burner to a unified whole, ensuring the rational distribution and effective utilization of hot primary air throughout the system.

[0051] 7. The present invention provides a high-efficiency DC burner and swirl burner co-combustion device and co-combustion method that uses a temperature sensor and a wind speed measuring device to monitor temperature and air volume in real time to achieve precise control.

[0052] Simply adjusting the opening of the regulating valves in each pipe is insufficient to accurately monitor the actual situation of the makeup air volume and heat exchange. This invention installs temperature and wind speed measuring points in the hot primary air makeup air duct, as well as temperature measuring points in the hot primary air makeup air duct itself. Temperature data measured by temperature sensors can be read through a DSC interface, enabling real-time monitoring of the heat exchange temperature. Wind speed data measured by a wind speed measuring device can also be read through the DSC interface, enabling real-time monitoring of the makeup air volume. Combined with the adjusting valve openings in each pipe, this allows for precise control of the temperature and volume of the hot primary air requiring makeup and heat exchange. Temperature and wind speed measuring points are also installed in the DC primary air channel, as well as in the DC primary air channel of the self-regulating burner. Temperature data measured by temperature sensors can be read through a DSC interface, enabling real-time monitoring of the heat exchange temperature. Wind speed data measured by a wind speed measuring device can also be read through the DSC interface, enabling real-time monitoring of the makeup air volume. Combined with the adjusting valve openings in each pipe, this allows for precise control of the temperature and volume of the DC primary air after makeup and the temperature of the primary air in the self-regulating burner after heat exchange. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the tangential ignition principle of the synergistic combustion device described in this application.

[0054] Figure 2 This is a side view showing the arrangement of the self-stable combustion burner in the co-combustion device described in this application;

[0055] Figure 3 This is a front view of the arrangement of the self-stable combustion burner in the co-combustion device described in this application;

[0056] Figure 4 This is a schematic diagram of the arrangement of the air temperature supply system in the co-combustion device described in this application;

[0057] Figure 5 This is a schematic diagram of the morphology of the combustion stabilization chamber and the recirculation zone in the furnace of the self-stable combustion burner after the make-up air in the co-combustion device described in this application;

[0058] Figure 6 This is a schematic diagram of the wind speed measuring device in the co-combustion device described in this application;

[0059] Figure 7 This is a schematic diagram of the temperature sensor in the co-combustion device described in this application;

[0060] Figure 8 This is a schematic diagram of the arrangement of the air temperature makeup air system containing a heater in the co-combustion device described in this application;

[0061] Figure 9 This is a schematic diagram of the layout of the co-combustion device described in this application, which includes a wind temperature and air supply system.

[0062] Figure 10 This is a schematic diagram of the arrangement of two air temperature and air supply systems in the co-combustion device described in this application;

[0063] Figure 11 This is a schematic diagram of the arrangement of three air temperature and air supply systems in the co-combustion device described in this application. Detailed Implementation

[0064] Specific implementation method one: Combining Figures 1 to 11 This embodiment describes a high-efficiency DC burner and swirl burner co-combustion device. The co-combustion device includes a tangentially circular pulverized coal combustion boiler 11, a secondary air box 31, and four DC pulverized coal burners 10. The four DC pulverized coal burners 10 are respectively arranged at the four corners of the tangentially circular pulverized coal combustion boiler 11. Each DC pulverized coal burner 10 corresponds to at least one coal mill 21. The DC primary air nozzle 1 in the DC pulverized coal burner 10 is connected to the coal outlet of the coal mill 21 via a coal supply pipeline. The DC secondary air nozzle 3 in the DC pulverized coal burner 10 is connected to the air outlet of the secondary air box 31 via an air supply pipeline. Each DC pulverized coal burner 10 has at least one self-sustaining combustion burner 2. Each self-stable combustion burner 2 is arranged between the DC primary air nozzle 1 and the DC secondary air nozzle 3 on the same layer in the corresponding DC pulverized coal burner 10. The self-stable combustion burner 2 is connected to the coal supply pipeline of the adjacent DC primary air nozzle 1 and the air supply pipeline of the adjacent DC secondary air nozzle 3 through the air-coal system. The co-combustion device also includes an air supply system and an air-temperature make-up air system 63. The first air outlet of the air supply system is connected to the air inlet of each coal mill 21, the second air outlet of the air supply system is connected to the air inlet of the secondary air box 31, the air inlet of the air-temperature make-up air system 63 is connected to the air supply system, the DC make-up air end of the air-temperature make-up air system 63 is connected to the coal supply pipeline, and the swirl make-up air end of the air-temperature make-up air system 63 is connected to the air-coal system.

[0065] Each coal mill 21 is equipped with a corresponding coal feeder 19. The coal outlet end of each coal feeder 19 is connected to the coal inlet end of the corresponding coal mill 21 through the coal drop pipe 20.

[0066] The coal supply pipeline includes a DC primary air channel 5, a primary air duct 22, and a No. 1 regulating valve 23. One end of the DC primary air channel 5 is connected to the corresponding DC primary air nozzle 1, one end of the primary air duct 22 is connected to the coal outlet end of the corresponding coal mill 21, and the other end of the DC primary air channel 5 is connected to the other end of the primary air duct 22. A No. 1 regulating valve 23 is installed at the connection between the DC primary air channel 5 and the primary air duct 22. A No. 3 temperature measuring device 54 and a No. 3 air volume measuring device 55 are sequentially installed on the DC primary air channel 5 along the air flow direction.

[0067] The coal supply pipeline also includes a No. 2 regulating valve 25, a No. 3 regulating valve 26, a No. 1 pulverized coal pipeline 27, and a pulverized coal separator 28. The coal inlet end of the pulverized coal separator 28 is connected to the primary air duct 22, and the No. 2 regulating valve 25 is connected in series on the primary air duct 22. The No. 1 coal outlet end of the pulverized coal separator 28 is connected to the DC primary air channel 5 through the No. 1 pulverized coal pipeline 27, and the No. 3 regulating valve 26 is connected in series on the No. 1 pulverized coal pipeline 27.

[0068] The air supply pipeline includes a DC secondary air channel 7, a secondary air duct 32, and a No. 4 regulating valve 34. One end of the DC secondary air channel 7 is connected to the corresponding DC secondary air nozzle 3. One end of the secondary air duct 32 is connected to the air outlet of the corresponding secondary air box 31. The other end of the DC secondary air channel 7 is connected to the other end of the secondary air duct 32. A No. 4 regulating valve 34 is installed at the connection between the DC secondary air channel 7 and the secondary air duct 32.

[0069] The self-sustaining combustion stabilizer 2 includes a combustion stabilizing chamber 4, a swirl-flow internal secondary air channel 6, and a self-sustaining combustion stabilizer direct primary air channel 8. The swirl-flow internal secondary air channel 6 is coaxially sleeved outside the self-sustaining combustion stabilizer direct primary air channel 8, and one end of the self-sustaining combustion stabilizer direct primary air channel 8 and one end of the swirl-flow internal secondary air channel 6 are both connected to the combustion stabilizing chamber 4. The other end of the self-sustaining combustion stabilizer direct primary air channel 8 is connected to the coal supply pipeline through an air-coal system, and the other end of the swirl-flow internal secondary air channel 6 is connected to the air supply pipeline through an air-coal system. The pipeline connection is configured such that an axial blade group 9 is provided between the DC primary air channel 8 of the self-stable combustion burner and the swirl inner secondary air channel 6. The axial blade group 9 is located close to the combustion stabilization chamber 4. The axial blade group 9 includes multiple axial blades, which are equidistantly arranged circumferentially between the DC primary air channel 8 of the self-stable combustion burner and the swirl inner secondary air channel 6. One end of each axial blade is connected to the outer wall of the DC primary air channel 8 of the self-stable combustion burner, and the other end of each axial blade is connected to the inner wall of the swirl inner secondary air channel 6.

[0070] The air-coal system includes a DC coal supply pipeline and a swirl air supply pipeline. The coal supply pipeline is connected to the DC primary air channel 8 of the self-stable combustion burner through the DC coal supply pipeline, and the air supply pipeline is connected to the secondary air channel 6 inside the swirl through the swirl air supply pipeline.

[0071] The DC coal supply pipeline includes a DC connection duct for the self-stable combustion burner, a No. 5 regulating valve 24, a No. 2 pulverized coal channel 29, and a No. 6 regulating valve 30. The primary air duct 22 is connected to the DC primary air channel 8 of the self-stable combustion burner through the DC connection duct, and the No. 5 regulating valve 24 is connected in series on the DC connection duct. The No. 2 coal outlet end of the pulverized coal separation device 28 is connected to the DC primary air channel 8 of the self-stable combustion burner through the No. 2 pulverized coal channel 29, and the No. 6 regulating valve 30 is connected in series on the No. 2 pulverized coal channel 29.

[0072] The swirl air supply pipeline includes a swirl connecting air duct for the self-stable burner and a No. 7 regulating valve 33. The secondary air duct 32 is connected to the secondary air channel 6 inside the swirl through the swirl connecting air duct for the self-stable burner. The No. 7 regulating valve 33 is connected in series at the connection point between the secondary air channel 6 inside the swirl and the connecting air duct for the self-stable burner.

[0073] The air supply system includes a blower 14, a primary air fan 15, a secondary air duct 16, an air preheater 17, a cold primary air header 35, a hot primary air header 36, and a hot secondary air duct 37. The air preheater 17 is installed at the end of the furnace flue 18. The outlet of the blower 14 is connected to the first air inlet of the air preheater 17 via a pipe. The outlet of the primary air fan 15 is connected to the second air inlet of the air preheater 17 via a pipe. The inlet of the cold primary air header 35 is connected to the connecting pipe between the primary air fan 15 and the air preheater 17. The outlet end is equipped with multiple primary air sub-pipes. The air inlet end of each primary air sub-pipe is connected to the air outlet end of the cold primary air main pipe 35. The air outlet end of each cold primary air sub-pipe is connected to the air inlet end of a coal mill 21. The air inlet end of the hot primary air main pipe 36 is connected to the first air outlet end of the air preheater 17. The air outlet end of the hot primary air main pipe 36 is connected to the air outlet end of the cold primary air main pipe 35. The air inlet end of the hot secondary air pipe 37 is connected to the second air outlet end of the air preheater 17. The air outlet end of the hot secondary air pipe 37 is connected to the air inlet end of the secondary air box 31.

[0074] A coal mill cold air regulating valve 56 is connected in series on the primary cold air main pipe 35;

[0075] A coal mill hot air regulating valve 57 is connected in series on the primary hot air main pipe 36;

[0076] A shut-off valve 58 is connected in series on the primary air duct;

[0077] The primary air supply system 63 includes a hot primary air supply main pipe 38, a cold primary air supply main pipe 39, a first cold primary air supply pipe 40, a second cold primary air supply pipe 41, a first hot primary air supply pipe 42, and a second hot primary air supply pipe 43. The air inlet of the hot primary air supply main pipe 38 is connected to the hot primary air supply main pipe 36, and the first air outlet of the hot primary air supply main pipe 38 is connected to the direct current primary air channel 5 through the first hot primary air supply pipe 42. The No. 2 air outlet of 8 is connected to the DC primary air channel 8 of the self-stable combustion burner through the No. 2 hot primary air make-up air pipe 43. The air inlet of the cold primary air make-up air main pipe 39 is connected to the cold primary air main pipe 35. The No. 1 air outlet of the cold primary air make-up air main pipe 39 is connected to the No. 1 hot primary air make-up air pipe 42 through the No. 1 cold primary air make-up air pipe 40. The No. 2 air outlet of the cold primary air make-up air main pipe 39 is connected to the No. 2 hot primary air make-up air pipe 43 through the No. 2 cold primary air make-up air pipe 41.

[0078] A hot primary air regulating valve 44 is connected in series on the hot primary air makeup air header 38;

[0079] A primary air regulating valve 45 is connected in series on the primary air makeup air main pipe 39;

[0080] A primary air supply damper 46 is connected in series on the primary air supply duct 40.

[0081] The No. 2 primary air supply air duct 41 is connected in series with the No. 2 primary air supply air regulating damper 47.

[0082] The No. 1 hot primary air supply duct 42 is connected in series with the No. 2 shut-off valve 59, the No. 1 supply air regulating valve 61, the No. 1 wind speed measuring device 49 and the No. 1 temperature measuring device 48 along the gas direction. The No. 2 shut-off valve 59, the No. 1 supply air regulating valve 61, the No. 1 wind speed measuring device 49 and the No. 1 temperature measuring device 48 are all located between the No. 1 cold primary air supply duct 40 and the DC primary air channel 5.

[0083] The No. 2 hot primary air supply duct 43 is connected in series along the gas direction with the No. 3 shut-off valve 60, the No. 2 supply air regulating valve 62, the No. 2 temperature measuring device 50 and the purge valve 51. The No. 3 shut-off valve 60, the No. 2 supply air regulating valve 62, the No. 2 temperature measuring device 50 and the purge valve 51 are all located between the No. 2 cold primary air supply duct 41 and the DC primary air channel 8 of the self-sustaining burner.

[0084] The air temperature make-up air system 63 also includes a heat exchanger 53, which is connected in series on the direct primary air channel 8 of the self-stable combustion burner. The heat exchange air inlet of the heat exchanger 53 is connected to the No. 2 hot primary air make-up air pipeline 43 through the induced draft pipe, and the induced draft pipe is located between the No. 2 temperature measuring device 50 and the purge valve 51. A heat exchange valve 66 is connected in series on the induced draft pipe. The heat exchange air return end of the heat exchanger 53 is connected to the hot primary air main pipe 36 through the heat exchanger return pipe 65.

[0085] A heater 64 is also connected in series on the primary air makeup air main pipe 38.

[0086] This embodiment provides a high-efficiency direct-flow burner and swirl burner co-combustion device, wherein the direct-flow pulverized coal burners 10 in the corner-circular pulverized coal combustion boiler 11 are arranged at the four corners of the furnace, and the outlet of the direct-flow pulverized coal burner 10 consists of a set of rectangular nozzles. The primary air pulverized coal airflow and the secondary air required for combustion are injected into the furnace in the form of direct-flow jets through different nozzles. The direct-flow primary air nozzles 1 and direct-flow secondary air nozzles 3 are arranged alternately. The flame at the upstream adjacent corner is ignited at the root of the downstream direct-flow pulverized coal burner 10 to form an actual flame zone 12, and an imaginary tangential circle 13 is formed at the center of the corner-circular pulverized coal combustion boiler. Four self-sustaining combustion burners 2 are arranged at the four corners between the direct-flow primary air nozzles 1 and the direct-flow secondary air nozzles 3 of the direct-flow pulverized coal burner 10. The self-regulating combustion burner 2 consists of, from the inside out, a direct-flow primary air channel 8, a swirling internal secondary air channel 6, and a combustion stabilization chamber 4. The direct-flow primary air channel 8 and the swirling internal secondary air channel 6 are coaxially arranged and positioned at the front end of the combustion stabilization chamber 4, flush with its inner wall. The outlet end of the combustion stabilization chamber 4 is flush with the outlet ends of the direct-flow primary air nozzle 1 and the direct-flow secondary air nozzle 3. Sixteen axially curved blades 9 at 60° are installed within the swirling internal secondary air channel 6. The specific working process of this application is as follows:

[0087] After being pressurized by the primary air fan, the primary air is supplied to the coal mill 21 in one path, sequentially through the air preheater 17, the hot primary air header 36, and the coal mill hot air regulating baffle 57, for coal powder drying and transportation. The other path supplies cold air to the coal mill sequentially through the cold primary air header 35 and the coal mill cold air regulating valve 56, regulating the temperature of the hot primary air entering the coal mill. The airflow into the coal mill is regulated by adjusting the coal mill hot air regulating valve 57 and the coal mill cold air regulating valve 56. This path is switched off and connected via the first shut-off valve 58. In the primary air supply system 63, a portion of the hot primary air is drawn from the primary air main pipe 36 and passes through the primary air regulating valve 44 and the primary air supply main pipe 38, then splits into two paths. One path passes through the second shut-off valve 59, the first primary air supply pipe 42, and the first supply air regulating valve 61 before converging into the direct primary air channel 5 to heat the direct primary air. This process is for improving the wind speed and temperature of the direct burner subsystem. The other path passes through the third shut-off valve 60, the second primary air supply pipe 43, and the second supply air regulating valve 62, then splits into two paths: one path passes through the heat exchange valve 66, the heat exchanger 53, and the heat exchanger return pipe 65 before returning to the primary air main pipe 36 to heat the direct primary air of the self-stable combustion burner; the other path passes through the purge valve 51 and converges into the direct primary air channel 8 of the self-stable combustion burner to purge the direct primary air channel 8. This process is for improving the wind temperature and supply system of the swirl burner. One portion of the cold primary air is drawn from the cold primary air main pipe 35, passing through the cold primary air regulating valve 45 and the cold primary air makeup air main pipe 39, and then splits into two paths. One path passes through the No. 1 cold primary air makeup air regulating valve 46 and merges into the No. 1 hot primary air makeup air pipe 42 to regulate the air temperature inside the No. 1 hot primary air makeup air pipe 42. The other path passes through the No. 2 cold primary air makeup air regulating valve 47 and merges into the No. 2 hot primary air makeup air pipe 43 to regulate the air temperature inside the No. 2 hot primary air makeup air pipe 43.

[0088] After being pressurized by the blower 14, the secondary air passes through the secondary air duct 16, the air preheater 17, the hot secondary air duct 37, and the secondary air box 31 in sequence, and enters the secondary air duct 32. The outlet of the secondary air duct 32 is divided into two paths: one path flows through the regulating valve 33 into the vortex inner secondary air channel 6, and then flows through the axially curved blades 9 in the channel before entering the combustion chamber 4 in a rotating manner; the other path flows through the regulating valve 34 into the direct flow secondary air channel 7 and enters the furnace in a direct flow manner.

[0089] After passing through the coal mill 21, the primary air and pulverized coal enter the primary air main pipe 22 and split into three paths: one path passes through the No. 1 regulating valve 23 and enters the direct primary air channel 5, where it mixes with the hot primary air from the No. 1 hot primary air make-up air pipe 42 and is then injected into the furnace in a direct flow; another path passes through the No. 2 regulating valve 25 and enters the pulverized coal distributor 28; and the third path passes through the No. 5 regulating valve 24 and enters the direct primary air channel 8 of the self-sustaining combustion burner, where it exchanges heat with the hot primary air from the heat exchanger 53 and is then injected into the combustion stabilization chamber 4 in a direct flow. The air-pulverized coal mixture passes through the pulverized coal distributor 28 and splits into two paths: one path passes through the No. 3 regulating valve 26 and enters the No. 1 pulverized coal pipe 27, then flows through the direct primary air channel 5 and mixes with the hot primary air from the No. 1 hot primary air make-up air pipe 42 and is then injected into the furnace in a direct flow; the other path passes through the No. 6 regulating valve 30 and enters the No. 2 pulverized coal channel 29, then flows through the direct primary air channel 8 of the self-sustaining combustion burner, where it exchanges heat with the hot primary air from the heat exchanger 53 and is then injected into the combustion stabilization chamber 4 in a direct flow. Under the action of secondary air in the swirling flow and combustion stabilization chamber 4, the primary air and pulverized coal form a stable reflux zone in the center of the combustion stabilization chamber and enter the furnace in the form of a reflux zone.

[0090] The cold air regulating valves 56 and 57 of the coal mill jointly regulate the temperature and airflow entering the coal mill. The No. 1 shut-off valve 58 cuts off and connects the airflow entering the coal mill 21. The hot primary air regulating valve 44 on the hot primary air supply main pipe 38 and the cold primary air regulating valve 45 on the cold primary air supply main pipe 39 jointly regulate the airflow and temperature entering the inlet of the air supply system 63 for increasing the velocity and temperature of the DC burner and the swirl burner. The No. 1 supply air regulating valve 61 on the No. 1 hot primary air supply pipe 42 and the No. 1 cold primary air supply air regulating valve 46 on the No. 1 cold primary air supply pipe 40 jointly regulate the temperature and airflow of the hot primary air entering the DC primary air channel 5. The No. 2 shut-off valve 59 cuts off and connects the airflow system for increasing the velocity and temperature of the DC burner and the swirl burner entering the DC primary air channel 5. The No. 2 make-up air regulating valve 62, installed on the No. 2 hot primary air make-up air duct 43, and the No. 2 cold primary air make-up air regulating valve 47, installed on the No. 2 cold primary air make-up air duct 41, jointly regulate the air volume and temperature of the make-up air system for the self-sustaining burner's DC primary air channel 8, which increases the DC burner's wind speed and temperature. The purge valve 51 regulates the purge steps of the self-sustaining burner's DC primary air channel 8; the heat exchange valve 66 regulates the heat exchange capacity of the self-sustaining burner's DC primary air channel 8. The No. 3 shut-off valve 60 controls the disconnection and connection of the make-up air system for the self-sustaining burner's DC primary air channel 8, which increases the DC burner's wind speed and temperature and the swirl burner's temperature. The No. 1 make-up air regulating valve 61 and the No. 1 regulating valve 23 located on the DC primary air channel 5, together with the regulating valve 26 located on the No. 1 pulverized coal channel 27, regulate the DC primary air velocity. The No. 2 make-up air regulating valve 62 and the No. 6 regulating valve 30 located on the No. 2 pulverized coal channel 29, together with the No. 5 regulating valve 24 located on the DC primary air channel 8 of the self-sustaining combustion burner, regulate the DC primary air velocity of the self-sustaining combustion burner. The No. 7 regulating valve 33 located on the swirl inner secondary air channel 6 regulates the inner secondary air velocity of the swirl, and the No. 4 regulating valve 34 located on the DC secondary air channel 7 regulates the DC secondary air velocity.

[0091] Wind speed measurement: An anemometer is inserted perpendicularly into the pipe wall. When primary airflow occurs, the total pressure is measured on the windward side and the static pressure on the leeward side. The total and static pressures of the airflow are collected and transmitted to the anemometer sensor. The pressure is then detected by connecting to the positive and negative terminals of a differential pressure transmitter. This allows for connection to a DCS (Distributed Control System) to display the wind speed and airflow, thereby controlling the wind speed to achieve the desired effect. Temperature sensors are fixed to the pipe wall by a support tube. Part of the temperature sensing element and protective sleeve extend into the inner wall of the pipe to measure the temperature. The temperature sensing element transmits the temperature signal to the DSC (Distributed Control System) in real time, allowing the DSC to monitor the temperature information within the pipe.

[0092] Specific Implementation Method Two: Combining Figures 1 to 11This embodiment provides a collaborative combustion method for a high-efficiency direct current burner and a swirl burner when the boiler operates under a condition of less than 15% of the rated load. The specific operation method is as follows:

[0093] Shut off the first regulating valve 23 and the fifth regulating valve 24, open the second regulating valve 25. The pulverized coal air flow controls the primary air velocity entering the direct current primary air passage 5 to u2 = 16 - 18 m / s by changing the opening degree of the third regulating valve 26. Without basically changing the original operation mode of the coal mill, high-temperature and high-pressure hot primary air is provided to the air temperature compensation system 63 by adjusting the hot primary air regulating valve 44 and the cold primary air regulating valve 45. Open the second shut-off valve 59, and control the hot primary air volume and air temperature supplemented into the direct current primary air passage by adjusting the opening degrees of the first air supplement regulating valve 61 and the first cold primary air supplement regulating valve 46. Among them, the air supplement velocity u1 is 30 - 32 m / s, and the air supplement temperature T1 is 280 - 300 °C. After air supplement, it converges into the direct current primary air passage 5. At this time, the direct current primary air velocity u2 increases to 24 - 27 m / s, and the temperature of the air-powder flow increases from T3 = 50 - 90 °C to T3 = 180 - 210 °C. Through the above operations, by increasing the direct current primary air velocity, a large-scale central recirculation zone is formed in the stable combustion chamber 4 and the furnace. The diameter D of the recirculation zone is 2De < D < 2.5De, and the length L is 4De < L < 4.5De;

[0094] Without changing the original operation mode of the coal mill, high-temperature and high-pressure hot primary air is provided to the air temperature compensation system 63 by adjusting the hot primary air regulating valve 44 and the cold primary air regulating valve 45. Open the third shut-off valve 60, and control the air temperature entering the second hot primary air supplement pipeline 43 by adjusting the opening degrees of the second air supplement regulating valve 62 and the second cold primary air supplement regulating valve 47. The air supplement temperature T2 is 280 - 300 °C. Close the purge valve 51, open the heat exchange valve 66, and increase the air temperature of the primary air-powder mixture in the direct current primary air passage 8 of the self-stabilizing combustion burner. The air supplement after heat exchange flows back to the hot primary air header 36 through the heat exchanger return pipe 65. The air temperature of the air-powder flow increases from T3 = 50 - 90 °C to T3 = 180 - 210 °C. Through the above operations, the air temperature of the air-powder flow in the direct current primary air passage 5 and the direct current primary air passage 8 of the self-stabilizing combustion burner increases to 180 - 210 °C, so as to achieve the purpose of increasing the primary air-powder temperature at the inlets of the direct current burner and the self-stabilizing combustion burner when operating at less than 15% of the rated load.

[0095] The collaborative combustion method provided in this embodiment is used when the boiler operates under a condition of less than 15% of the rated load. The attached drawing Figure 4This invention provides a schematic diagram of the combustion stabilization chamber and recirculation zone within the furnace of the self-sustaining combustion stabilizer after air replenishment. In the diagram, T1 represents the air temperature measured by temperature measuring device 48 on the first hot primary air replenishment duct 42; T2 represents the air temperature measured by temperature sensor 50 on the second hot primary air replenishment duct 43; T3 represents the air temperature measured by temperature sensor 54 on the DC primary air channel 5; T4 represents the air temperature measured by temperature sensor 52 on the DC primary air channel 8 of the self-sustaining combustion stabilizer; u1 represents the air velocity measured by wind speed measuring device 49 on the first hot primary air replenishment duct 42; u2 represents the air velocity measured by wind speed measuring device 55 on the DC primary air channel 5; De represents the inner secondary air diameter; L represents the recirculation zone length; and D represents the recirculation zone diameter. Specifically, under 15% rated load, the DC primary air velocity u2 in DC primary air channel 5 after makeup air supply ranges from 24 to 27 m / s, the swirl secondary air velocity in swirl secondary air channel 6 ranges from 35 to 40 m / s, and the DC secondary air velocity in DC secondary air channel 32 ranges from 30 to 35 m / s. The DC primary air temperature T3 in DC primary air channel 5 after makeup air supply ranges from 180 to 210℃, and the DC primary air temperature T4 in DC primary air channel 8 of the self-regulating burner after makeup air supply ranges from 180 to 210℃.

[0096] This application, by introducing a hot air supply system 63, can also perform high-temperature and high-pressure purging of the DC primary air channels 8 and 5 of the self-stable combustion burner to prevent blockage or burnout of the pulverized coal pipeline. The specific operation is as follows: when the self-stable combustion burner 2 and the DC burner 10 are out of service or put into operation, the purging steps of the DC primary air channels 8 and 5 of the self-stable combustion burner can be performed by opening the No. 3 shut-off valve 60, opening the purging valve 51, closing the heat exchange valve 66, and opening the No. 2 shut-off valve 59, respectively. The monitoring personnel should pay attention to the wind speed of each pulverized coal pipe (>18m / s). If the wind speed continues to drop below 18m / s, the burner system is cut off, and the hot air supply system for increasing the wind speed and temperature of the DC burner and the swirl burner is turned on for purging (the purging wind speed is generally above 20m / s). After purging for 10 minutes, the hot air supply system for increasing the wind speed and temperature of the DC burner and the swirl burner is turned off. When the self-regulating burner 2 and the DC burner 10 are deactivated or put into operation, activate the air supply system to increase the air velocity and temperature of the DC burner and the air temperature of the swirl burner for purging. Purge the pulverized coal pipes one by one, paying attention to the air velocity during purging and maintaining it above 25 m / s. Increase the purging time to 20 minutes. This is to prevent blockage or burnout of the pulverized coal pipes and to prevent backfire caused by the accumulation of air-coal mixture in the pipes, which could damage the pulverized coal pipes.

[0097] The present invention has been disclosed above with preferred embodiments, but it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed structure and technical content to create equivalent embodiments without departing from the scope of the present invention. However, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention. Specific implementation examples:

[0099] This technology has been applied to a 600MW subcritical pressure drum boiler, which employs a tangential combustion method. Four self-sustaining combustion burners are positioned at the four corners between the DC primary air nozzle and the DC secondary air nozzle of the second-layer DC pulverized coal burner. Pulverized coal is drawn from branch pipes of the third-layer pulverizing system, and air is drawn from the secondary air box. Before the burner modification, the boiler's minimum non-oil-injected stable combustion load was 20%. The pulverized coal outlet air temperature was 65℃, the burner inlet temperature was 63℃, and the pulverized coal inlet air temperature was approximately 240℃. There was a problem of pulverized coal blockage in the DC primary air pipe, affecting boiler combustion stability, reducing unit output, and even causing flameout. In severe cases, it caused spontaneous combustion of pulverized coal, burning out the air pipes, resulting in costs exceeding one million yuan due to pipe damage. After one year of stable operation, during a shutdown maintenance, it was found that there were partial burn-out and slagging problems at the nozzles of the DC burners and self-sustaining combustion burners.

[0100] By employing the apparatus and method described in this invention, and adding a supplementary air system 63 to the co-combustion system of the DC burner and swirl burner to increase the wind speed and temperature of the DC burner and the wind temperature of the swirl burner, the minimum non-oil-injection stable combustion load of the boiler can reach 15%. Operating at 15% rated load, the supplementary air heat exchange technology using hot and cold primary air increases the primary air velocity of the DC burner, thereby improving the DC air ejection capacity. After supplementary air, the DC primary air velocity in the DC primary air channel 5 can reach 24-27 m / s, and the DC primary air temperature range in the DC primary air channel 5 is 180-210℃. After heat exchange, the DC primary air temperature in the self-sustaining combustion burner DC primary air channel 8 is 180-210℃. The carbon content of the boiler fly ash is reduced from 6% before the modification to 4.4%, and the boiler efficiency is increased from 92.9% to 94.1%. The problem of pipe clogging is completely solved, reducing losses. The total cost savings are 2 million yuan.

[0101] Under the requirement of "fully utilizing the emergency peak-shaving capacity of existing coal-fired power units," the load for deep-load regulation of thermal power units will be further reduced, and the duration of deep-load regulation will increase significantly. To encourage thermal power units to reduce their load to below 30% of rated load, various regions have adopted tiered pricing policies, setting higher upper limits for bids for load rates below 30%. Taking Heilongjiang Province as an example, when the load rate reaches below 25%, a bid price of 0.7-1 yuan / kWh can be submitted. Using the present invention, "A method and apparatus for improving the synergistic combustion capability of direct-flow burners and swirl burners," stable combustion at 15% rated load can be achieved. Overall, the increased revenue from deep-load regulation after burner modification is estimated at 80-85 million yuan compared to before modification.

Claims

1. A high-efficiency direct-flow burner and swirl burner co-combustion device, the co-combustion device comprising a tangentially circular pulverized coal combustion boiler (11), a secondary air box (31) and four direct-flow pulverized coal burners (10), the four direct-flow pulverized coal burners (10) being respectively arranged at the four corners of the tangentially circular pulverized coal combustion boiler (11), each direct-flow pulverized coal burner (10) corresponding to at least one coal mill (21), the direct-flow primary air nozzle (1) in the direct-flow pulverized coal burner (10) supplying coal through... The pipeline is connected to the coal outlet of the coal mill (21), and the DC secondary air nozzle (3) in the DC pulverized coal burner (10) is connected to the air outlet of the secondary air box (31) through the air supply pipeline. Each DC pulverized coal burner (10) has at least one self-sustaining combustion burner (2), and each self-sustaining combustion burner (2) is arranged between the DC primary air nozzle (1) and the DC secondary air nozzle (3) located on the same layer in the corresponding DC pulverized coal burner (10). The feature is that: The self-stable combustion burner (2) is connected to the coal supply pipeline of the adjacent DC primary air nozzle (1) and the air supply pipeline of the adjacent DC secondary air nozzle (3) through the air-coal system. The co-combustion device also includes an air supply system and an air temperature make-up air system (63). The first air outlet of the air supply system is connected to the air inlet of each coal mill (21). The second air outlet of the air supply system is connected to the air inlet of the secondary air box (31). The air inlet of the air temperature make-up air system (63) is connected to the air supply system. The DC make-up air end of the air temperature make-up air system (63) is connected to the coal supply pipeline. The swirl make-up air end of the air temperature make-up air system (63) is connected to the air-coal system. The air supply system includes a primary air fan (15), an air preheater (17), a cold primary air main pipe (35) and a hot primary air main pipe (36). The air inlet of the cold primary air main pipe (35) is connected to the connecting pipe of the primary air fan (15) and the air preheater (17), and the air inlet of the primary air main pipe (36) is connected to the first air outlet of the air preheater (17). The primary air supply system (63) includes a hot primary air supply main pipe (38), a cold primary air supply main pipe (39), a first cold primary air supply pipe (40), a second cold primary air supply pipe (41), a first hot primary air supply pipe (42), and a second hot primary air supply pipe (43). The air inlet of the hot primary air supply main pipe (38) is connected to the hot primary air supply main pipe (36), and the first air outlet of the hot primary air supply main pipe (38) is connected to the direct current primary air channel (5) through the first hot primary air supply pipe (42). The No. 2 air outlet of (38) is connected to the DC primary air channel (8) of the self-stable combustion burner through the No. 2 hot primary air make-up air pipe (43). The air inlet of the cold primary air make-up air main pipe (39) is connected to the cold primary air main pipe (35). The No. 1 air outlet of the cold primary air make-up air main pipe (39) is connected to the No. 1 hot primary air make-up air pipe (42) through the No. 1 cold primary air make-up air pipe (40). The No. 2 air outlet of the cold primary air make-up air main pipe (39) is connected to the No. 2 hot primary air make-up air pipe (43) through the No. 2 cold primary air make-up air pipe (41).

2. The high-efficiency direct-flow burner and swirl burner co-combustion device according to claim 1, characterized in that: Each coal mill (21) is equipped with a corresponding coal feeder (19), and the coal outlet end of each coal feeder (19) is connected to the coal inlet end of the corresponding coal mill (21) through the coal drop pipe (20).

3. The high-efficiency direct-flow burner and swirl burner co-combustion device according to claim 2, characterized in that: The coal supply pipeline includes a DC primary air channel (5), a primary air pipe (22), and a No. 1 regulating valve (23). One end of the DC primary air channel (5) is connected to the corresponding DC primary air nozzle (1), one end of the primary air pipe (22) is connected to the coal outlet of the corresponding coal mill (21), and the other end of the DC primary air channel (5) is connected to the other end of the primary air pipe (22). A No. 1 regulating valve (23) is installed at the connection between the DC primary air channel (5) and the primary air pipe (22). The coal supply pipeline also includes a No. 2 regulating valve (25), a No. 3 regulating valve (26), a No. 1 pulverized coal pipeline (27), and a pulverized coal separator (28). The coal inlet end of the pulverized coal separator (28) is connected to the primary air duct (22), and the No. 2 regulating valve (25) is connected in series on the primary air duct (22). The No. 1 coal outlet end of the pulverized coal separator (28) is connected to the DC primary air channel (5) through the No. 1 pulverized coal pipeline (27), and the No. 3 regulating valve (26) is connected in series on the No. 1 pulverized coal pipeline (27).

4. The high-efficiency direct-flow burner and swirl burner co-combustion device according to claim 3, characterized in that: The air supply pipeline includes a DC secondary air channel (7), a secondary air duct (32), and a No. 4 regulating valve (34). One end of the DC secondary air channel (7) is connected to the corresponding DC secondary air nozzle (3), one end of the secondary air duct (32) is connected to the air outlet of the corresponding secondary air box (31), and the other end of the DC secondary air channel (7) is connected to the other end of the secondary air duct (32). A No. 4 regulating valve (34) is installed at the connection between the DC secondary air channel (7) and the secondary air duct (32).

5. The high-efficiency direct-flow burner and swirl burner co-combustion device according to claim 4, characterized in that: The self-sustaining combustion burner (2) includes a combustion stabilizing chamber (4), a swirling internal secondary air channel (6), and a self-sustaining combustion burner direct primary air channel (8). The swirling internal secondary air channel (6) is coaxially sleeved outside the self-sustaining combustion burner direct primary air channel (8), and one end of the self-sustaining combustion burner direct primary air channel (8) and one end of the swirling internal secondary air channel (6) are both connected to the combustion stabilizing chamber (4). The other end of the self-sustaining combustion burner direct primary air channel (8) is connected to the coal supply pipeline through the air-coal system, and the other end of the swirling internal secondary air channel (6) is connected to the coal supply pipeline through the air-coal system. The air duct is connected and an axial blade group (9) is provided between the DC primary air channel (8) of the self-stable combustion burner and the swirl inner secondary air channel (6). The axial blade group (9) is located close to the combustion chamber (4). The axial blade group (9) includes multiple axial blades. The multiple axial blades are equidistantly arranged in the circumferential direction between the DC primary air channel (8) of the self-stable combustion burner and the swirl inner secondary air channel (6). One end of each axial blade is connected to the outer wall of the DC primary air channel (8) of the self-stable combustion burner, and the other end of each axial blade is connected to the inner wall of the swirl inner secondary air channel (6).

6. The high-efficiency direct-flow burner and swirl burner co-combustion device according to claim 5, characterized in that: The air-coal system includes a DC coal supply pipeline and a swirl air supply pipeline. The coal supply pipeline is connected to the DC primary air channel (8) of the self-stable combustion burner through the DC coal supply pipeline, and the air supply pipeline is connected to the secondary air channel (6) inside the swirl through the swirl air supply pipeline. The DC coal supply pipeline includes a DC connection duct for the self-stable combustion burner, a No. 5 regulating valve (24), a No. 2 pulverized coal channel (29), and a No. 6 regulating valve (30). The primary air duct (22) is connected to the DC primary air channel (8) of the self-stable combustion burner through the DC connection duct for the self-stable combustion burner, and the No. 5 regulating valve (24) is connected in series on the DC connection duct for the self-stable combustion burner. The No. 2 coal outlet end of the pulverized coal separation device (28) is connected to the DC primary air channel (8) of the self-stable combustion burner through the No. 2 pulverized coal channel (29), and the No. 6 regulating valve (30) is connected in series on the No. 2 pulverized coal channel (29). The swirl air supply pipeline includes the self-stable burner swirl connection air duct and the No. 7 regulating valve (33). The secondary air duct (32) is connected to the secondary air channel (6) inside the swirl through the self-stable burner swirl connection air duct. The No. 7 regulating valve (33) is connected in series at the connection between the secondary air channel (6) inside the swirl and the self-stable burner connection air duct.

7. The high-efficiency direct-flow burner and swirl burner co-combustion device according to claim 6, characterized in that: The air supply system also includes a blower (14), a secondary air duct (16), and a hot secondary air duct (37). The air preheater (17) is installed at the end of the furnace (18). The outlet of the blower (14) is connected to the first air inlet of the air preheater (17) through a pipe. The outlet of the primary air blower (15) is connected to the second air inlet of the air preheater (17) through a pipe. The outlet of the cold primary air main duct (35) is equipped with multiple primary air sub-ducts, each of which... The air inlet of the air duct is connected to the air outlet of the cold primary air main duct (35), the air outlet of each cold primary air duct is connected to the air inlet of a coal mill (21), the air outlet of the hot primary air main duct (36) is connected to the air outlet of the cold primary air main duct (35), the air inlet of the hot secondary air duct (37) is connected to the second air outlet of the air preheater (17), and the air outlet of the hot secondary air duct (37) is connected to the air inlet of the secondary air box (31). A coal mill cold air regulating valve (56) is connected in series on the primary cold air main pipe (35); A coal mill hot air regulating valve (57) is connected in series on the primary hot air main pipe (36); A shut-off valve (58) is connected in series on the primary air duct.

8. The high-efficiency direct-flow burner and swirl burner co-combustion device according to claim 7, characterized in that: A hot primary air regulating valve (44) is connected in series on the hot primary air makeup air main pipe (38); A primary air regulating valve (45) is connected in series on the primary air makeup air main pipe (39); A primary air supply damper (46) is connected in series on the primary air supply duct (40). The No. 2 primary air supply air duct (41) is connected in series with the No. 2 primary air supply air regulating valve (47). The No. 1 hot primary air supply pipe (42) is connected in series with the No. 2 shut-off valve (59), the No. 1 supply air regulating valve (61), the No. 1 wind speed measuring device (49), and the No. 1 temperature measuring device (48) along the gas direction. The No. 2 shut-off valve (59), the No. 1 supply air regulating valve (61), the No. 1 wind speed measuring device (49), and the No. 1 temperature measuring device (48) are all located between the No. 1 cold primary air supply pipe (40) and the DC primary air channel (5). The No. 2 hot primary air make-up duct (43) is successively connected in series with a No. 3 shut-off valve (60), a No. 2 make-up air regulating valve (62), a No. 2 temperature measuring device (50) and a purging valve (51) along the gas direction, and the No. 3 shut-off valve (60), the No. 2 make-up air regulating valve (62), the No. 2 temperature measuring device (50) and the purging valve (51) are all located between the No. 2 cold primary air make-up duct (41) and the direct current primary air passage (8) of the self-stabilizing combustion burner; The air temperature make-up system (63) further includes a heat exchanger (53). The heat exchanger (53) is connected in series on the direct current primary air passage (8) of the self-stabilizing combustion burner. The heat exchange air inlet end of the heat exchanger (53) is communicated with the No. 2 hot primary air make-up duct (43) through an induced air duct. The induced air duct is located between the No. 2 temperature measuring device (50) and the purging valve (51), and a heat exchange valve (66) is connected in series on the induced air duct. The heat exchange air return end of the heat exchanger (53) is communicated with the hot primary air header (36) through a heat exchanger return pipe (65).

9. The high-efficiency direct-flow burner and swirl burner co-combustion device according to claim 8, characterized in that, A heater (64) is also connected in series on the hot primary air make-up header (38).

10. A method for synergistic combustion of a boiler operating at less than 15% rated load, using a high-efficiency direct-flow burner and a swirl burner synergistic combustion device as described in claim 8 or claim 9, characterized in that: The specific operation of the co-combustion method is as follows: Shut off the No. 1 regulating valve (23) and the No. 5 regulating valve (24), open the No. 2 regulating valve (25). The pulverized coal air flow controls the primary air velocity entering the direct current primary air passage (5) to u2 = 16 - 18 m / s by changing the opening of the No. 3 regulating valve (26). By adjusting the hot primary air regulating valve (44) and the cold primary air regulating valve (45), high-temperature and high-pressure hot primary air is provided to the air temperature make-up system (63) on the premise of basically not changing the original operation mode of the coal mill. Open the No. 2 shut-off valve (59). By adjusting the opening of the No. 1 make-up air regulating valve (61) and the No. 1 cold primary air make-up valve (46), the hot primary air volume and temperature supplied to the direct current primary air passage are controlled. Among them, the make-up air velocity u1 is 30 - 32 m / s, the make-up air temperature T1 is 280 - 300 °C, and after make-up, it merges into the direct current primary air passage (5). At this time, the direct current primary air velocity u2 is increased to 24 - 27 m / s, and the air-powder flow temperature is increased from T3 = 50 - 90 °C to T3 = 180 - 210 °C. Through the above operations, by increasing the direct current primary air velocity, a large-scale central recirculation zone is formed in the stable combustion chamber (4) and the furnace. The diameter D of the recirculation zone is 2De < D < 2.5De, and the length L is 4De < L < 4.5De; By adjusting the hot primary air regulating valve (44) and the cold primary air regulating valve (45), high-temperature and high-pressure hot primary air is supplied to the air temperature make-up air system (63) without changing the original operation mode of the coal mill. The No. 3 shut-off valve (60) is opened, and the air temperature entering the No. 2 hot primary air make-up air pipeline (43) is controlled by adjusting the opening of the No. 2 make-up air regulating valve (62) and the No. 2 cold primary air make-up air regulating valve (47). The make-up air temperature T2 is 280-300℃. The purge valve (51) is closed, and the heat exchange valve (66) is opened to achieve self-stable combustion. The temperature of the primary air-coal mixture in the DC primary air channel (8) of the burner is increased. The makeup air after heat exchange flows back to the hot primary air main pipe (36) through the heat exchanger return pipe (65). The temperature of the air-coal gas flow increases from T3=50-90℃ to T3=180-210℃. After the above operation, the temperature of the air-coal gas flow in the DC primary air channel (5) and the DC primary air channel (8) of the self-stable combustion burner is increased to 180-210℃, thereby achieving the purpose of increasing the inlet primary air-coal temperature of the DC burner and the self-stable combustion burner when operating at less than 15% of the rated load.

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