Low-nitrogen combustion system

Abstract

This invention relates to the field of combustion equipment, specifically to a low-NOx combustion system, including a boiler. A burner is connected to the front wall of the boiler, and the boiler receives and exchanges heat with the high-temperature flue gas after combustion. The boiler's flue gas outlet is connected to the flue gas inlet of an economizer heat exchanger, which recovers waste heat from the high-temperature flue gas. The economizer heat exchanger's flue gas outlet is connected to the hot flue gas inlet of a waste heat recovery device, which recovers waste heat from the low-temperature flue gas to preheat the combustion air of the burner. Condensate is collected from the flue gas and transported through a condensate outlet and pipeline to an atomizing water gun located at the center of the burner, spraying water mist onto the front end of the burner to reduce the temperature of the combustion zone and the concentration of the combustion gas mixture. This invention achieves low-NOx combustion while ensuring a wide range of hydrogen regulation, and simultaneously recovers the latent heat of vaporization from the flue gas. The atomizing water comes from the condensate in the flue gas, achieving self-circulation and high overall efficiency.

Description

Technical Field

[0001] This invention relates to the field of combustion equipment technology, and more specifically to a low-NOx combustion system. Background Technology

[0002] With the dwindling availability of non-renewable energy sources like fossil fuels and increasing pressure on environmental protection, renewable clean energy sources such as hydrogen are becoming a key research focus. While hydrogen is the ideal fuel for industrial combustion furnaces, its physical properties limit its effectiveness. Technologies like flue gas recirculation and staged combustion, used to reduce NOx, can decrease the thermal efficiency of hydrogen combustion. Achieving a balance between NOx emissions <50mg / m³ (the industrial low-NOx requirement) and thermal efficiency >90% is a core challenge in combustion equipment development. Furthermore, low-load regulation in combustion equipment relies on precise fuel-air ratios. However, hydrogen, due to its rapid combustion reaction rate, is prone to flame detachment, pulsation, or even extinction at low loads, making it difficult to meet the wide-range load regulation requirements of industrial combustion furnaces (e.g., boilers requiring flexible switching between 30%-100% load). If strong flame stabilization and rapid mixing are used to achieve stable combustion at wide loads to improve thermal efficiency, this may increase NOx levels.

[0003] Based on the above technical problems, this invention proposes a low-NOx energy-saving combustion system that can reduce NOx emissions, ensure thermal efficiency, and meet the needs of wide-range combustion load adjustment. Summary of the Invention

[0004] To address the issues that existing technologies, such as flue gas recirculation used to reduce NOx, reduce the thermal efficiency of hydrogen combustion and fail to meet the requirements of the combustion furnace for a wide range of combustion load adjustments, a low-NOx combustion system is proposed that can reduce NOx while ensuring hydrogen combustion within a relatively wide adjustment range.

[0005] To achieve the above objectives, a low-NOx combustion system is proposed, including a boiler, with a burner connected to the front wall of the boiler, and the boiler receiving the high-temperature flue gas after combustion by the burner and exchanging heat. The boiler's flue gas outlet is connected to the flue gas inlet of the economizer heat exchanger, which is used to recover waste heat from the high-temperature flue gas. The flue gas outlet of the economizer heat exchanger is connected to the hot flue gas inlet of the flue gas waste heat recovery device. The flue gas waste heat recovery device recovers the waste heat from low-temperature flue gas to preheat the combustion air of the burner, and collects condensate in the flue gas. The condensate is then transported through the condensate outlet and pipeline to the atomizing water gun located at the center of the burner, where water mist is sprayed onto the front end of the burner to reduce the temperature of the combustion zone and the concentration of the combustion gas mixture.

[0006] Preferably, the waste heat from the flue gas recovered by the economizer heat exchanger is used to preheat the water entering the boiler, and the preheated water then enters the boiler for further heating.

[0007] Preferably, the flue gas waste heat recovery device is connected to a combustion fan, which sends combustion air into the flue gas waste heat recovery device for heating through the combustion air cold air inlet; and delivers the heated combustion air to the burner through a pipeline through the combustion air hot air outlet. The cold flue gas outlet of the flue gas waste heat recovery device is connected to an induced draft fan, and the cooled flue gas is discharged through the induced draft fan.

[0008] Preferably, the burner is provided with a hot air inlet for supplying combustion air at the top and a hydrogen inlet at the bottom; The combustion air hot air inlet is connected to the combustion air passage inside the burner, and a hydrogen nozzle is installed along its axial direction inside the combustion air passage, which is connected to the hydrogen inlet. An atomizing water gun is installed inside the combustion air duct along its central axis, with its front end located at the front end of the burner; its rear end is connected to a condensate inlet for conveying condensate water and an atomizing compressed air inlet for conveying atomized air.

[0009] Preferably, the combustion air hot air inlet includes a central air inlet, a secondary air inlet, and an outer ring air inlet arranged sequentially adjacent to each other; The combustion air duct includes a central air duct, a secondary air duct, and an outer ring air duct arranged sequentially from the inside to the outside of the burner housing. The central air duct is a cavity divided by a partial shell and a central air duct body; The secondary air duct is a cavity formed by a partial shell, a central air duct, and a secondary air duct. The outer ring air duct is a cavity formed by a partial shell, a secondary air duct, and an outer ring air duct. The central air inlet is connected to the central air channel located at the center of the housing. The secondary air inlet is connected to the secondary air channel located around the central air duct. The outer ring air inlet is connected to the outer ring air channel located around the periphery of the secondary air cylinder; The central air duct and the secondary air duct are respectively equipped with central air cyclone blades and secondary air cyclone blades at their front ends.

[0010] Preferably, the central air inlet, secondary air inlet, and outer ring air inlet are respectively equipped with a central air regulating mechanism, a secondary air regulating mechanism, and an outer ring air regulating mechanism for adjusting the amount of combustion-supporting air.

[0011] Preferably, the hydrogen inlet includes a first hydrogen inlet located below the tail of the burner and a second hydrogen inlet located below its middle section; The first hydrogen inlet is connected to the first hydrogen collection box at the tail of the burner, and the second hydrogen inlet is connected to the second hydrogen collection box located on the periphery of the outer ring wind tunnel body. The hydrogen nozzle includes a central hydrogen nozzle, a second-ring hydrogen nozzle, and an outer-ring hydrogen nozzle; The hydrogen central nozzle is located inside the central air duct and is positioned around the atomizing water gun. The hydrogen second ring nozzle passes through the central air channel and the secondary air channel; The tail ends of the hydrogen central nozzle and the hydrogen second ring nozzle are connected to the first hydrogen collection box, and their front ends extend out of the front ends of the central wind cyclone blade and the secondary wind cyclone blade, respectively. The hydrogen outer ring nozzle is located inside the outer ring air channel, and its tail end is connected to the second hydrogen gas collection box. Its front end is provided with an outer ring air direct injection stabilizing body.

[0012] Preferably, the central air duct has a circular cross-sectional shape, and two rings of hydrogen central nozzles are arranged inside the central air channel; The secondary air duct body has a square cross-sectional shape, and the second ring of hydrogen nozzles is fixed to the secondary air duct body by the second ring of hydrogen nozzle support plates; the second ring of hydrogen nozzles at the four corners of the secondary air channel are fixed to the second ring of hydrogen nozzles in the inner ring by the second ring of hydrogen nozzle support plates. The outer ring air duct has a square cross-section, and the hydrogen outer ring nozzle is fixed between the secondary air duct and the outer ring air duct through the hydrogen outer ring nozzle support plate. An outer ring wind support plate is installed at the front between the secondary air duct and the outer ring air duct to provide stability.

[0013] Preferably, the hydrogen outer ring nozzle includes a hydrogen outer ring straight nozzle and a hydrogen outer ring oblique nozzle, and the inclination angle of the hydrogen outer ring oblique nozzle is 5°-10°. Hydrogen outer ring direct injection pipes and hydrogen outer ring oblique injection pipes are alternately and evenly distributed in the outer ring air passage; The outer ends of the hydrogen outer ring direct injection pipe and the hydrogen outer ring oblique injection pipe are respectively equipped with an outer ring air direct injection stabilizing body and an outer ring air oblique air stabilizing body; The tilt angle of the outer ring wind-sloping combustion stabilizer is matched with the setting of the outer ring oblique nozzle for hydrogen; The outer ring direct injection combustion stabilizer and the outer ring oblique wind combustion stabilizer are fixed on the outer ring combustion stabilizer mounting plate, and the outer ring combustion stabilizer mounting plate is connected to the outside of the secondary air duct.

[0014] Preferably, the atomizing water gun is fitted with a water gun sleeve in the middle, and the front of the water gun sleeve is provided with a water gun adjustment device to keep the atomizing water gun in the center of the burner. The two ends of the water gun adjustment device are respectively connected to the outside of the water gun sleeve and the inside of the central air duct. The front end of the atomizing water gun is equipped with a bubble-forming plate and an atomizing plate, as well as a spray nozzle with an atomization angle of 100°-130°.

[0015] The beneficial effects of this invention are: 1. In this invention, the flue gas from the burner heats the boiler. The heated, high-temperature flue gas, carrying residual heat, enters the economizer heat exchanger. The heat from the high-temperature flue gas preheats the water before it enters the boiler. The preheated water then enters the boiler for heating, thus lowering the flue gas temperature. The flue gas waste heat recovery device further recovers the waste heat from the low-temperature flue gas discharged from the economizer heat exchanger. The recovered waste heat is used to heat the combustion air, improving thermal efficiency. Simultaneously, the water condensed from the flue gas is recovered and recycled back to the burner. Finally, the cooled flue gas is discharged.

[0016] 2. This invention no longer uses flue gas recirculation technology to achieve low NOx emissions. Instead, it uses an atomized water gun to spray heated condensed water (approximately 70°C) into the front combustion zone of the burner for cooling. Combined with staged combustion technology, this achieves NOx emissions of ≤40mg / Nm³ for the hydrogen burner. The water vapor generated in the combustion zone of the burner by the atomized water gun also has a dilution effect, reducing the concentration of hydrogen-air mixture, slowing flame propagation, and mitigating the risk of backfire in the hydrogen burner to some extent.

[0017] 3. The first and second hydrogen inlets of this invention can broaden the lower limit of hydrogen quantity adjustment, precisely control the hydrogen supply, and optimize the structure of multi-hole multi-stage nozzles and swirling mixing to form a synergy, ensuring safe and stable combustion of hydrogen within a wide adjustment range (achieving a wide adjustment ratio of 20-110%).

[0018] 4. This invention achieves low-NOx combustion while ensuring a wide range of hydrogen regulation, guaranteeing thermal efficiency and safe and stable combustion. It can also recover the latent heat of vaporization in the flue gas, preheat the combustion air, and improve thermal efficiency. The atomization water comes from the condensate in the flue gas, without introducing other water sources, achieving self-circulation and high overall efficiency. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall process flow of the present invention; Figure 2 This is a schematic diagram of the internal structure of the burner of the present invention; Figure 3 for Figure 2 Enlarged schematic diagram of the internal structure of the front end of the burner; Figure 4 for Figure 2 AA cross-sectional view of the interior of the combustion head; Figure 5 for Figure 2 Enlarged cross-sectional view of section B of the atomizing water gun; Figure 6This is a schematic diagram of the outer ring wind-stabilized combustion body mounting plate structure in this invention.

[0020] In the diagram: First hydrogen inlet 1, First hydrogen collection box 1-1, Central hydrogen nozzle 1-2, Second ring hydrogen nozzle 1-3, Second ring hydrogen nozzle support plate 1-4, Second hydrogen inlet 2, Second hydrogen collection box 2-1, Outer ring hydrogen oblique nozzle 2-2, Outer ring hydrogen direct nozzle 2-3, Outer ring hydrogen nozzle support plate 2-4, Central air inlet 3, Central air regulating mechanism 3-1, Central air cylinder 3-2, Central air cyclone blade 3-3, Central air passage 3-4, Secondary air inlet 4, Secondary air regulating mechanism 4-1, Secondary air cylinder 4-2, Secondary air cyclone blade 4-3, Secondary air passage 4-4, Outer ring air inlet 5, Outer ring air regulating mechanism 5-1, Outer ring air cylinder 5-2, Outer ring air... 5-3 Inclined air stabilizing body, 5-4 Outer ring air direct injection stabilizing body, 5-5 Outer ring air support plate, 5-6 Outer ring air stabilizing body mounting plate, 5-7 Outer ring air duct, 6 Housing, 7 Mounting flange, 8 Atomizing water gun, 8-1 Water gun sleeve, 8-2 Condensate inlet, 8-3 Atomizing compressed air inlet, 8-4 Foaming plate, 8-5 Atomizing plate, 8-6 Spray gun head, 8-7 Water gun adjustment device, 9 Boiler, 10 Economizer heat exchange equipment, 11 Flue gas waste heat recovery device, 11-1 Combustion air cold air inlet, 11-2 Condensate outlet, 11-3 Combustion air hot air outlet, 11-4 Hot flue gas inlet, 11-5 Cold flue gas outlet, 12 Exhaust fan, 13 Combustion fan, 14 High-pressure water pump, 15 Burner. Detailed Implementation

[0021] The following will be combined with the appendix Figures 1-6 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] like Figures 1-6 As shown, the present invention provides a low-NOx combustion system, including a boiler 9, with a burner 15 connected to the front wall of the boiler 9. The boiler 9 receives high-temperature flue gas generated by the combustion of the burner 15 and performs heat exchange. The flue gas outlet of the boiler 9 is connected to the flue gas inlet of an economizer heat exchanger 10, which is used to recover the waste heat of the high-temperature flue gas. The flue gas outlet of the economizer heat exchanger 10 is connected to the hot flue gas inlet 11-4 of a flue gas waste heat recovery device 11, which recovers the waste heat of the low-temperature flue gas to preheat the combustion air of the burner 15 and collects condensate in the flue gas. The condensate is then transported through a condensate outlet 11-2 and a pipeline to an atomizing water gun 8 located at the center of the burner 15, where water mist is sprayed onto the front end of the burner 15 to reduce the temperature of the combustion zone and the concentration of the combustion gas mixture.

[0023] The waste heat recovered from the flue gas by the economizer heat exchanger 10 is used to preheat the water entering the boiler 9, and the preheated water then enters the boiler 9 for further heating. The flue gas waste heat recovery device 11 is connected to the combustion air blower 13, which sends combustion air into the flue gas waste heat recovery device 11 for heating through the combustion air cold air inlet 11-1; and delivers the heated combustion air to the burner 15 through a pipeline through the combustion air hot air outlet 11-3; the cold flue gas outlet 11-5 of the flue gas waste heat recovery device 11 is connected to the induced draft fan 12, and the cooled flue gas is discharged through the induced draft fan 12.

[0024] The burner 15 has a combustion air hot air inlet at the top for supplying combustion air and a hydrogen inlet at the bottom. The combustion air hot air inlet is connected to the combustion air channel inside the burner 15. A hydrogen nozzle is installed along the axial direction of the combustion air channel and is connected to the hydrogen inlet. An atomizing water gun 8 is installed along the central axis of the combustion air channel, penetrating the combustion air channel. Its front end is located at the front end of the burner 15. Its rear end is connected to a condensate inlet 8-2 for supplying condensate and an atomizing compressed air inlet 8-3 for supplying atomized air.

[0025] The combustion air inlet includes a central air inlet 3, a secondary air inlet 4, and an outer ring air inlet 5 arranged sequentially adjacent to each other; the combustion air duct includes a central air duct 3-4, a secondary air duct 4-4, and an outer ring air duct 5-7 arranged sequentially from the inside to the outside of the burner housing 6; the central air duct 3-4 is a cavity formed by a portion of the housing 6 and the central air duct 3-2; the secondary air duct 4-4 is a cavity formed by a portion of the housing 6, the central air duct 3-2, and the secondary air duct 4-2; the outer ring air duct 5-7... It is a cavity divided by a portion of the casing 6, a secondary air duct 4-2, and an outer ring air duct 5-2; the central air inlet 3 is connected to the central air channel 3-4 located at the center of the casing 6; the secondary air inlet 4 is connected to the secondary air channel 4-4 located around the central air duct 3-2; the outer ring air inlet 5 is connected to the outer ring air channel 5-7 located around the secondary air duct 4-2; a central air cyclone vane 3-3 and a secondary air cyclone vane 4-3 are respectively installed at the front end of the central air channel 3-4 and the secondary air channel 4-4. The central air inlet 3, the secondary air inlet 4, and the outer ring air inlet 5 are respectively equipped with a central air regulating mechanism 3-1, a secondary air regulating mechanism 4-1, and an outer ring air regulating mechanism 5-1 for adjusting the combustion air volume.

[0026] The hydrogen inlet includes a first hydrogen inlet located below the tail of the burner 15 and a second hydrogen inlet 2 located below its middle section; the first hydrogen inlet is connected to a first hydrogen collection box 1-1 at the tail of the burner 15, and the second hydrogen inlet 2 is connected to a second hydrogen collection box 2-1 located around the outer ring air duct 5-2; the hydrogen nozzle includes a central hydrogen nozzle 1-2, a second ring hydrogen nozzle 1-3, and an outer ring hydrogen nozzle; the central hydrogen nozzle 1-2 is located within the central air duct 3-4, and its... The atomizing water gun 8 is positioned around the atomizing nozzle 8; the second ring of hydrogen nozzles 1-3 passes through the central air channel 3-4 and the secondary air channel 4-4; the tail ends of the central hydrogen nozzle 1-2 and the second ring of hydrogen nozzles 1-3 are connected to the first hydrogen collection box 1-1, and their front ends extend out of the front ends of the central wind cyclone blade 3-3 and the secondary wind cyclone blade 4-3, respectively; the outer ring of hydrogen nozzles is located in the outer ring air channel 5-7, and its tail end is connected to the second hydrogen collection box 2-1, and its front end is provided with the outer ring direct injection stabilizing body 5-4.

[0027] The central air duct 3-2 has a circular cross-section, and two rings of hydrogen central nozzles 1-2 are installed inside the central air channel 3-4. The secondary air duct 4-2 has a square cross-section, and the second ring of hydrogen nozzles 1-3 are fixed to the secondary air duct 4-2 by hydrogen second ring nozzle support plates 1-4. The hydrogen second ring nozzles 1-3 at the four corners of the secondary air channel 4-4 are fixed to the inner ring of hydrogen second ring nozzles 1-3 by hydrogen second ring nozzle support plates 1-4. The outer ring air duct 5-2 has a square cross-section, and the outer ring of hydrogen nozzles is fixed between the secondary air duct 4-2 and the outer ring air duct 5-2 by hydrogen outer ring nozzle support plates 2-4. An outer ring air support plate 5-5 is installed at the front between the secondary air duct 4-2 and the outer ring air duct 5-2 to provide stability.

[0028] The hydrogen outer ring nozzle includes a hydrogen outer ring direct injection nozzle 2-3 and a hydrogen outer ring oblique injection nozzle 2-2, with the oblique injection nozzle 2-2 having an inclination angle of 5°-10°. The hydrogen outer ring direct injection nozzle 2-3 and the hydrogen outer ring oblique injection nozzle 2-2 are alternately and evenly distributed in the outer ring air passage 5-7. The outer ends of the hydrogen outer ring direct injection nozzle 2-3 and the hydrogen outer ring oblique injection nozzle 2-2 are respectively provided with an outer ring air direct injection stabilizing body 5-4 and an outer ring air oblique injection stabilizing body 5-3. The inclination angle of the outer ring air oblique injection stabilizing body 5-3 is matched with that of the hydrogen outer ring oblique injection nozzle 2-2. The outer ring air direct injection stabilizing body 5-4 and the outer ring air oblique injection stabilizing body 5-3 are fixed on the outer ring air stabilizing body mounting plate 5-6, which is connected to the outside of the secondary air duct 4-2.

[0029] The atomizing water gun 8 is fitted with a water gun sleeve 8-1 in the middle. The front of the water gun sleeve 8-1 is provided with a water gun adjustment device 8-7 to keep the atomizing water gun 8 in the center of the burner 15. The two ends of the water gun adjustment device 8-7 are connected to the outside of the water gun sleeve 8-1 and the inside of the central air duct 3-2, respectively. The front end of the atomizing water gun 8 is provided with a bubble plate 8-4 and an atomizing plate 8-5, and a spray head 8-6 is also provided. The atomization angle of the spray head 8-6 is 100°-130°.

[0030] In this invention, as a preferred embodiment, the flue gas waste heat recovery device 11 is a phase change air preheater; the optimal atomization angle of the spray gun head 8-6 is 120°, which can ensure that the water mist covers the entire combustion interface; the burner 15 is connected to the front wall of the boiler 9 through the mounting flange 7.

[0031] Unlike conventional low-NOx hydrogen burners 15, this invention does not require flue gas recirculation technology. Instead, it efficiently recovers and utilizes the heat from the flue gas. Furthermore, through the atomizing water gun 8, a core component located at the center of the burner 15, NOx generation is reduced at the source, while ensuring hydrogen production remains within a wide adjustable range. Specifically: The flue gas from the burner 15 first heats the boiler 9. The high-temperature flue gas from the boiler 9 then enters the economizer heat exchanger 10. The economizer heat exchanger 10 uses the heat from the high-temperature flue gas to preheat the water before it enters the boiler 9. The preheated water then enters the boiler 9 for further heating, significantly improving the thermal efficiency of the boiler 9. The low-temperature flue gas after passing through the economizer heat exchanger 10 then passes through the flue gas waste heat recovery device 11 to recover the waste heat from the low-temperature flue gas, which is then used to preheat the combustion air and improve thermal efficiency. Meanwhile, the flue gas waste heat recovery device 11 collects condensate from the flue gas after hydrogen combustion at its bottom, and delivers it to the atomizing water gun 8 via the high-pressure water pump 14. After being atomized by compressed air, the water mist is sprayed onto the main combustion zone. The strong endothermic effect of water decomposition can quickly reduce the local temperature of the combustion zone (generally reducing the flame temperature by 200-500℃), reducing NOx generation from the source and achieving the emission target of NOx ≤ 40mg / Nm³ for the hydrogen burner 15. At the same time, the water sprayed into the high-temperature zone quickly forms water vapor. The dilution effect of the water vapor can reduce the mixing concentration of hydrogen and air, slow down the flame propagation speed, and reduce the risk of backfire of the hydrogen burner 15 to a certain extent. The first hydrogen inlet 1 and the second hydrogen inlet 2 can broaden the lower limit of hydrogen quantity adjustment. Flow meters are installed on the hydrogen flow pipeline to accurately control the amount of hydrogen supplied. Hydrogen is mixed through multi-hole, multi-stage nozzles and swirling flow. Through the flow meter installed on the combustion air pipeline and the high-pressure water pump 14, which is controlled by a frequency converter, the hydrogen quantity, air volume, and water volume are coordinated in terms of flow control and structural optimization, ensuring safe and stable combustion of hydrogen within a wide adjustment range (achieving a wide adjustment ratio of 20-110%).

[0032] In the above process, the outer ring of hydrogen nozzles is divided into a direct hydrogen outer ring nozzle 2-3 and an oblique hydrogen outer ring nozzle 2-2. The angle of the oblique hydrogen outer ring nozzle 2-2 is between 5-10°, which is adjusted according to the furnace size of boiler 9. This design can optimize the combustion direction and path of hydrogen. In addition, a central hydrogen nozzle 1-2 and a second ring of hydrogen nozzles 1-3 are set. The hydrogen nozzles at different positions work together with multiple adjustable combustion air channels to achieve staged and phased combustion. The flue gas waste heat recovery device 11, namely the phase change air preheater, cools the flue gas at about 150°C at the outlet of the economizer heat exchanger 10 to 60°C. It absorbs the latent heat of phase change of water vapor in the flue gas into the combustion air, improving thermal efficiency. At the same time, it collects condensate at about 70°C in the flue gas and delivers it to the atomizing water gun 8 through the high-pressure water pump 14.

[0033] This invention achieves low-NOx combustion while ensuring a wide range of hydrogen regulation, guaranteeing thermal efficiency and safe and stable combustion. It can also recover the latent heat of vaporization in the flue gas, preheat the combustion air, and improve thermal efficiency. The atomization water comes from the condensate in the flue gas, without introducing other water sources, achieving self-circulation and high overall efficiency.

Claims

1. A low-NOx combustion system, characterized in that, This includes a boiler, with a burner connected to the front wall of the boiler. The boiler receives the high-temperature flue gas after combustion in the burner and performs heat exchange. The boiler's flue gas outlet is connected to the flue gas inlet of the economizer heat exchanger, which is used to recover waste heat from the high-temperature flue gas. The flue gas outlet of the economizer heat exchanger is connected to the hot flue gas inlet of the flue gas waste heat recovery device. The flue gas waste heat recovery device recovers the waste heat of low-temperature flue gas to preheat the combustion air of the burner; and collects condensate in the flue gas, which is then transported through the condensate outlet and pipeline to the atomizing water gun located at the center of the burner to spray water mist onto the front end of the burner, thereby reducing the temperature of the combustion zone and the concentration of the combustion gas mixture. The burner is provided with a combustion air hot air inlet at the top for supplying combustion air and a hydrogen inlet at the bottom; The combustion air hot air inlet is connected to the combustion air passage inside the burner, and a hydrogen nozzle is installed along its axial direction inside the combustion air passage, which is connected to the hydrogen inlet. An atomizing water gun is installed in the combustion air duct along its central axis, with its front end located at the front end of the burner; its rear end is connected to a condensate inlet for conveying condensate water and an atomizing compressed air inlet for conveying atomized air. The combustion air hot air inlet includes a central air inlet, a secondary air inlet, and an outer ring air inlet arranged sequentially and adjacently. The combustion air duct includes a central air duct, a secondary air duct, and an outer ring air duct arranged sequentially from the inside to the outside of the burner housing. The hydrogen inlet includes a first hydrogen inlet located below the tail of the burner and a second hydrogen inlet located below the middle of the burner; The first hydrogen inlet is connected to the first hydrogen collection box at the tail of the burner, and the second hydrogen inlet is connected to the second hydrogen collection box located on the periphery of the outer ring wind tunnel body. The hydrogen nozzle includes a central hydrogen nozzle, a second-ring hydrogen nozzle, and an outer-ring hydrogen nozzle; The hydrogen central nozzle is located inside the central air duct and is positioned around the atomizing water gun. The hydrogen second ring nozzle passes through the central air channel and the secondary air channel; The tail ends of the hydrogen central nozzle and the hydrogen second ring nozzle are connected to the first hydrogen collection box, and their front ends extend out of the front ends of the central wind cyclone blade and the secondary wind cyclone blade, respectively. The hydrogen outer ring nozzle is located inside the outer ring air channel, and its tail end is connected to the second hydrogen gas collection box. Its front end is provided with an outer ring air direct injection stabilizing body.

2. The low-NOx combustion system according to claim 1, characterized in that, The waste heat from the flue gas recovered by the economizer heat exchanger is used to preheat the water entering the boiler, and the preheated water then enters the boiler for further heating.

3. The low-NOx combustion system according to claim 1, characterized in that, The flue gas waste heat recovery device is connected to the combustion air blower. The combustion air blower sends the combustion air into the flue gas waste heat recovery device for heating through the combustion air cold air inlet; and delivers the heated combustion air to the burner through the pipeline through the combustion air hot air outlet. The cold flue gas outlet of the flue gas waste heat recovery device is connected to an induced draft fan, and the cooled flue gas is discharged through the induced draft fan.

4. The low-NOx combustion system according to claim 1, characterized in that, The central air duct is a cavity divided by a partial shell and a central air duct body; The secondary air duct is a cavity formed by a partial shell, a central air duct, and a secondary air duct. The outer ring air duct is a cavity formed by a partial shell, a secondary air duct, and an outer ring air duct. The central air inlet is connected to the central air channel located at the center of the housing. The secondary air inlet is connected to the secondary air channel located around the central air duct. The outer ring air inlet is connected to the outer ring air channel located around the periphery of the secondary air cylinder; The central air duct and the secondary air duct are respectively equipped with central air cyclone blades and secondary air cyclone blades at their front ends.

5. The low-NOx combustion system according to claim 4, characterized in that, The central air inlet, secondary air inlet, and outer ring air inlet are respectively equipped with a central air regulating mechanism, a secondary air regulating mechanism, and an outer ring air regulating mechanism for adjusting the amount of combustion-supporting air.

6. The low-NOx combustion system according to claim 4, characterized in that, The central air duct has a circular cross-sectional shape, and two rings of hydrogen central nozzles are installed inside the central air channel. The secondary air duct body has a square cross-sectional shape, and the second ring of hydrogen nozzles is fixed to the secondary air duct body by the second ring of hydrogen nozzle support plates; the second ring of hydrogen nozzles at the four corners of the secondary air channel are fixed to the second ring of hydrogen nozzles in the inner ring by the second ring of hydrogen nozzle support plates. The outer ring air duct has a square cross-section, and the hydrogen outer ring nozzle is fixed between the secondary air duct and the outer ring air duct by a hydrogen outer ring nozzle support plate. An outer ring wind support plate is installed at the front between the secondary air duct and the outer ring air duct to provide stability.

7. The low-NOx combustion system according to claim 4, characterized in that, The hydrogen outer ring nozzle includes a hydrogen outer ring straight nozzle and a hydrogen outer ring oblique nozzle, and the inclination angle of the hydrogen outer ring oblique nozzle is 5°-10°. Hydrogen outer ring direct injection pipes and hydrogen outer ring oblique injection pipes are alternately and evenly distributed in the outer ring air passage; The outer ends of the hydrogen outer ring direct injection pipe and the hydrogen outer ring oblique injection pipe are respectively equipped with an outer ring air direct injection stabilizing body and an outer ring air oblique air stabilizing body; The tilt angle of the outer ring wind-sloping combustion stabilizer is matched with the setting of the outer ring oblique nozzle for hydrogen; The outer ring direct injection combustion stabilizer and the outer ring oblique wind combustion stabilizer are fixed on the outer ring combustion stabilizer mounting plate, and the outer ring combustion stabilizer mounting plate is connected to the outside of the secondary air duct.

8. The low-NOx combustion system according to claim 4, characterized in that, The atomizing water gun is fitted with a water gun sleeve in the middle. The front of the water gun sleeve is equipped with a water gun adjustment device to keep the atomizing water gun in the center of the burner. The two ends of the water gun adjustment device are connected to the outside of the water gun sleeve and the inside of the central air duct body, respectively. The front end of the atomizing water gun is equipped with a bubble-forming plate and an atomizing plate, as well as a spray nozzle with an atomization angle of 100°-130°.

Images