Low nitrogen oxide combustion system and method for pure ammonia gas boiler

Abstract

The invention discloses a low-nitrogen-oxide combustion system and method for a pure ammonia gas boiler, and relates to the technical field of boiler combustion. The problems that in the existing ammonia combustion process, ammonia gas is poor in combustion characteristic and not prone to combustion, combustible gas needs to be doped, consequently, system operation regulation and control are complex, and meanwhile the NOX emission concentration is high are solved. The system comprises a water cooling wall, a hearth, an ammonia gas burner, a boiler heating surface, an air preheater, a combustion fan, an over-fire air burner I, an over-fire air burner II and an SCR (Selective Catalytic Reduction) device, wherein the ammonia gas burner is arranged at the lower part of the water cooling wall of the front wall of the hearth; over-fire air combustors I and over-fire air combustors II are sequentially arranged on water cooling walls of the front wall and the rear wall above the ammonia gas combustor from bottom to top, and cold air sucked in by a combustion fan is heated through heat absorption of an air preheater and then provides combustion-supporting air for the ammonia gas combustor, the over-fire air combustors I and the over-fire air combustors II. The method is used for low-nitrogen combustion of the boiler.

Description

Technical Field

[0001] This invention relates to the field of boiler combustion technology, specifically to a low-NOx combustion system and method for a pure ammonia gas-fired boiler. Background Technology

[0002] Ammonia, due to its zero-carbon, hydrogen-rich characteristics, is considered an ideal renewable alternative fuel, effectively overcoming the bottlenecks in hydrogen energy development. Using ammonia as a fuel offers several advantages: Ammonia is easily liquefied; it liquefies at room temperature by pressurizing to 1.03 MPa, providing milder liquefaction conditions compared to hydrogen. Ammonia has relatively good safety; its flammable volume concentration in air ranges from 15% to 28%, making it safer during storage and transportation and less prone to ignition and explosion. Ammonia has a high energy density, giving it a significant advantage in storage and transportation costs.

[0003] The use of ammonia as a fuel also has some obvious drawbacks, and the comprehensive application of ammonia in combustion equipment still faces huge challenges, requiring in-depth research to overcome these problems.

[0004] Question 1: Ammonia is a non-flammable fuel. Its high ignition temperature, large ignition energy, slow flame propagation speed, and narrow flammability limit make it difficult to ignite and burn, resulting in poor combustion stability and burnout. Compared to hydrogen and methane, ammonia fuel has significantly lower reactivity, with a maximum laminar flame propagation speed of approximately 7 cm / s, only 1 / 5 that of methane. It also has a narrower flame limit and a higher ignition temperature.

[0005] Question 2: Ammonia combustion under lean fuel conditions produces high nitrogen oxide emissions, while combustion under rich fuel conditions produces high ammonia slip. Ammonia contains a high proportion (82.3%) of nitrogen, and the fuel-type nitrogen oxides (NOx) generated during combustion... X The potential emission concentration is high, and the fuel-type NO X It is difficult to reduce the concentration of NO by lowering the combustion temperature; low NO X Pollutant emissions have become the main evaluation indicator for ammonia combustion technology.

[0006] These characteristics limit the application of direct ammonia combustion, and currently, ammonia burners on the market have not fully solved the above technical problems.

[0007] To address the issue of ammonia's poor flammability, a common technical approach is to incorporate a more reactive combustible gas, such as natural gas or hydrogen, to enhance the combustion reactivity of the mixture. This method not only requires an additional combustible gas supply system but also increases the system's complexity and the difficulty of operation and control.

[0008] Another type of patented solution in the field of ammonia combustion addresses the problem of ammonia being decomposed into hydrogen and nitrogen through a catalytic decomposition reaction. The hydrogen produced by the catalytic decomposition has excellent combustion characteristics and is used to increase the combustion reaction rate of the resulting gas mixture. However, the additional ammonia catalytic decomposer complicates the burner's structure, increases its space requirements, and limits its ease of use and reliability. Summary of the Invention

[0009] This invention addresses the problems in existing ammonia combustion processes, such as poor ammonia combustion characteristics, difficulty in combustion, and the need to incorporate combustible gases, which complicates system operation and control. Simultaneously, NO... X To address the issue of high emission concentrations, a low-NOx combustion system and method for pure ammonia gas-fired boilers are proposed. This system utilizes ammonia directly as fuel in the power plant boiler, creating a gas-fired boiler combustion system that uses only ammonia as fuel. It features stable combustion, high ammonia burnout rate, and effective control of NOx emissions during combustion. X Emission concentration.

[0010] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0011] The low-NOx combustion system of the pure ammonia gas boiler includes water-cooled walls, a furnace, ammonia gas burners, boiler heating surfaces, an air preheater, a combustion air fan, burnout air burner I, burnout air burner II, and an SCR device. The furnace is surrounded by water-cooled walls. The ammonia gas burner is located at the lower part of the water-cooled wall on the front wall of the furnace. Burnout air burner I and burnout air burner II are installed sequentially from bottom to top on the water-cooled walls above the ammonia gas burner on both the front and rear walls. The boiler heating surfaces, SCR device, and air preheater are installed sequentially from front to back on the rear side of the upper part of the furnace. The cold air drawn in by the combustion air fan is heated by the air preheater and then provides combustion air to the ammonia gas burner, burnout air burner I, and burnout air burner II.

[0012] Furthermore, the air inlet of the ammonia gas burner is connected to the main ammonia gas pipeline.

[0013] Furthermore, the ammonia gas burner is installed inside the combustion air box, which is connected to the air outlet of the air preheater through a hot combustion air duct; burnout air burner I is installed inside burnout air box I, and burnout air burner II is installed inside burnout air box II. Burnout air boxes I and II are connected to the hot combustion air duct through a burnout air branch duct.

[0014] Furthermore, the combustion air box is equipped with a combustion air regulating damper, which is located on both sides of the ammonia gas burner. The burnout air I box is equipped with a burnout air I regulating damper, which is located on both sides of the burnout air burner I. The burnout air II box is equipped with a burnout air II regulating damper, which is located on both sides of the burnout air burner II.

[0015] Furthermore, the ammonia gas burner includes multiple layers of ammonia gas burners arranged sequentially from bottom to top, with each layer of ammonia gas burner housed in a combustion air box.

[0016] Furthermore, each layer of ammonia gas burner is connected to the main ammonia gas pipeline via an ammonia gas branch pipe.

[0017] Furthermore, a flow regulating valve is installed on the ammonia branch pipeline.

[0018] Furthermore, the outlet of the combustion blower is connected to the inlet of the air preheater through a cold combustion air duct.

[0019] The low-NOx combustion method for pure ammonia gas-fired boilers includes the following combustion process:

[0020] The ammonia gas burner injects ammonia fuel into the main combustion zone of the furnace for combustion. The combustion air box provides combustion air for the ammonia fuel, and the amount of combustion air provided is less than the theoretical combustion air volume of the ammonia fuel. The burnout air burner I and burnout air burner II respectively supplement the remaining combustion air. The ammonia fuel is burned in the primary burnout zone and the secondary burnout zone in the furnace, respectively. During the combustion process, the ammonia fuel exchanges heat with the water-cooled wall through radiation. The high-temperature flue gas generated after combustion flows upward in the furnace and exchanges heat through the boiler heating surface, SCR device and air preheater in sequence before being discharged from the flue gas outlet. The cold air is pressurized by the combustion air fan and heated by the air preheater before providing combustion air for the ammonia gas burner, burnout air burner I and burnout air burner II.

[0021] Furthermore, the furnace space below the elevation of burnout air burner I is the main combustion zone, the furnace space between the elevations of burnout air burner I and burnout air burner II is the primary combustion zone, and the furnace space above the elevation of burnout air burner II is the secondary combustion zone.

[0022] The beneficial effects of this invention compared to the prior art are:

[0023] (1) The combustion system is designed with a staged air distribution technology, with an excess air coefficient of 0.80–0.95 in the main combustion zone. Ammonia burns under oxygen-deficient conditions in the main combustion zone, which can suppress the formation of fuel-type nitrogen oxides (NOx) from ammonia combustion. X The concentration of the product.

[0024] (2) The burnout air is supplied to the furnace in two stages to control the unburned ammonia in the main combustion zone to burn under low oxygen conditions, which can suppress the fuel-type nitrogen oxides (NOx) generated by ammonia combustion. X The NO generation concentration. The design value of the excess air coefficient after the lower-level burnout air supply is 1.0 to 1.03. The application of a two-stage burnout air design scheme reduces NO. XThe effect is better than a design scheme that only sets a single burnout air level.

[0025] (3) The upper burnout air is positioned at a relatively high elevation. The design value of the excess air coefficient after the upper burnout air is supplied is 1.10–1.15. The flue gas temperature after mixing with the flue gas in the furnace is approximately 1200℃. By adjusting the combined upper and lower burnout air volumes, a small amount of unburned ammonia is maintained at the upper burnout air elevation position to enter the secondary burnout zone. The flue gas temperature in the secondary burnout zone gradually decreases due to heat exchange, especially in the temperature range of 950℃–1150℃, where ammonia reacts with NO. X The reduction reaction.

[0026] Ammonia, as a reducing agent, can remove NO pollutants generated in the main combustion zone and burnout zone. X The NOx is reduced to harmless nitrogen. Due to the thorough mixing of the upper burnout air and the high-temperature flue gas, the reduction reaction is relatively complete. Within the secondary burnout zone, the NOx reduction efficiency can reach ≥60%. After the reduction reaction, the NOx pollutant in the flue gas... X Concentration reduced to ≤100mg / Nm 3 The temperature and oxygen concentration conditions in the secondary burnout zone can ensure the ammonia burnout rate at the furnace outlet, with an ammonia concentration at the furnace outlet ≤3ppm, preventing ammonia escape from the boiler.

[0027] (4) The combustion system features graded air distribution, a two-stage burnout air arrangement, and unburned ammonia in the secondary burnout zone for NO. X The combination of reduction reaction and SCR device technology can reduce NO pollutants in boiler tail gas. X Concentration reduced to ≤30mg / Nm 3 It meets the highest domestic emission standards for gas-fired boilers.

[0028] (5) Pure ammonia gas-fired boilers with low NO X The combustion system design is simple and easy to implement, and can be used for the renovation of gas boilers and the design of new units. Attached Figure Description

[0029] Figure 1 This is a front view schematic diagram of the overall structure of the present invention;

[0030] Figure 2 yes Figure 1 A schematic diagram of the left-side view structure.

[0031] In the diagram, 1-water-cooled wall, 2-furnace, 3-ammonia gas burner, 4-combustion air box, 5-main ammonia pipeline, 6-ammonia branch pipeline, 7-flow regulating valve, 8-boiler heating surface, 9-air preheater, 10-combustion air fan, 11-cold combustion air duct, 12-hot combustion air duct, 13-burnout air branch duct, 14-burnout air burner I, 15-burnout air burner II, 16-combustion air regulating damper, 17-burnout air I box, 18-burnout air II box, 19-burnout air I regulating damper, 20-burnout air II regulating damper, 21-SCR device. Detailed Implementation

[0032] To make the technical problems solved, the technical solutions, and the beneficial effects of the present invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0033] Specific implementation method one: Combining Figures 1 to 2 This embodiment describes a pure ammonia gas-fired boiler low-NOx combustion system comprising a water-cooled wall 1, a furnace 2, an ammonia gas burner 3, a boiler heating surface 8, an air preheater 9, a combustion air fan 10, a burnout air burner I14, a burnout air burner II15, and an SCR device 21. The furnace 2 is surrounded by water-cooled walls 1. An ammonia gas burner 3 is located at the lower part of the water-cooled wall 1 on the front wall of the furnace 2. Burnout air burners I14 and II15 are sequentially arranged from bottom to top on the water-cooled walls 1 on the front and rear walls above the ammonia gas burner 3. The boiler heating surface 8, the SCR device 21, and the air preheater 9 are sequentially arranged from front to back on the rear side of the upper part of the furnace 2. The cold air drawn in by the combustion air fan 10 is heated by the air preheater 9 and then provides combustion air to the ammonia gas burner 3, burnout air burner I14, and burnout air burner II15.

[0034] The boiler combustion system is designed with staged combustion technology. All ammonia gas (fuel) is supplied to the main combustion zone of the furnace 2 by ammonia gas burner 3. The combustion air supply to the ammonia combustion chamber 4 is less than the theoretical combustion air volume of ammonia gas. The remaining combustion air (burnout air) is supplied by burner I 14 and burnout air burner II 15 respectively.

[0035] The burner I14 injects burnout air into the furnace 2, forming a full coverage within the furnace cross-section at the nozzle elevation, ensuring thorough mixing of burnout air and high-temperature flue gas.

[0036] The burner Ⅱ15 injects burnout air into the furnace chamber 2, forming a full coverage within the furnace chamber cross-section at the nozzle elevation, ensuring thorough mixing of burnout air and high-temperature flue gas.

[0037] The upper burnout air is positioned at a relatively high elevation, with an excess air coefficient designed to be 1.10–1.15 after its supply. The flue gas temperature after mixing with the furnace gas is approximately 1200℃. By adjusting the combined upper and lower burnout air volumes, a small amount of unburned ammonia is maintained at the upper burnout air elevation, allowing it to enter the secondary burnout zone. The flue gas temperature in the secondary burnout zone gradually decreases due to heat exchange, particularly within the 950℃–1150℃ temperature range, where ammonia reacts with NO. X The reduction reaction. Its chemical reaction formula is as follows:

[0038] 4NH3 + 4NO + O2 → 4N2 + 6H2O

[0039] 4NH3 + 2NO + 2O2 → 3N2 + 6H2O

[0040] Ammonia, as a reducing agent, can remove NO pollutants generated in the main combustion zone and burnout zone. X It is reduced to harmless nitrogen. Due to the thorough mixing of the upper burnout air and the high-temperature flue gas, the reduction reaction is relatively complete, and NO is reduced in the secondary burnout zone. X The reduction efficiency can reach ≥60%, and after the reduction reaction, the NO pollutant in the flue gas is reduced. X Concentration reduced to ≤100mg / Nm 3 The temperature and oxygen concentration conditions in the secondary burnout zone can ensure the ammonia burnout rate at the furnace outlet, with an ammonia concentration at the furnace outlet ≤3ppm, preventing ammonia escape from the boiler.

[0041] Ammonia combustion generates high-temperature flue gas. Inside furnace 2, the ammonia flame exchanges heat with the water-cooled wall 1 via radiation. The high-temperature flue gas flows upward within the furnace and passes through boiler heating surfaces 8, which are arranged in multiple stages. The boiler working fluid exchanges heat with the high-temperature flue gas through these surfaces, and the flue gas temperature gradually decreases after heat exchange. Along the flue gas flow path, it sequentially passes through boiler heating surfaces 8, SCR device 21, and air preheater 9.

[0042] The furnace 2 serves as the main reaction space for fuel combustion and heat release. Inside the furnace 2, the fuel is organized to burn and release heat by the combustion system. The four sides of the furnace 2 are enclosed by water-cooled walls 1, which absorb the heat released by the combustion flame inside the furnace through radiative heat exchange.

[0043] The ammonia gas burner 3 is located at the lower part of the water-cooled wall at the front of the furnace 2. The function of the ammonia gas burner 3 is to inject ammonia gas (fuel) and combustion air into the furnace 2 and organize the flow field and combustion process. The number of ammonia gas burners 3 is determined by the boiler capacity, and several ammonia gas burners 3 are installed. Under suitable combustion conditions, ammonia gas and combustion air undergo a combustion reaction to form a flame.

[0044] SCR unit 21 employs selective catalytic reduction technology to remove NO pollutant from flue gas. X It is reduced to harmless nitrogen gas.

[0045] The air preheater facilitates heat transfer between the flue gas and the combustion gas in the furnace. The combustion air blower 10 draws in air from the ambient atmosphere, pressurizes it, and then sends it to the combustion air inlet of the air preheater 9 through the cold combustion air duct 11. The combustion air absorbs heat and rises in temperature within the air preheater 9. The hot combustion air duct 12 sends the heated combustion air to the periphery of the furnace 2, where the combustion system organizes and distributes the combustion air and supplies it into the furnace 2 for combustion.

[0046] Above the uppermost ammonia burner 3, burnout air burners I14 and II15 are installed along the flame path inside the furnace, with one layer each on the front and rear walls of furnace 2. Based on the ammonia combustion process, furnace 2 is divided into three zones: the main combustion zone, the primary burnout zone, and the secondary burnout zone. The space in furnace 2 below the elevation of burnout air burner I14 is the main combustion zone; the space between the elevations of burnout air burners I14 and II15 is the primary burnout zone; and the space in furnace 2 above the elevation of burnout air burner II15 is the secondary burnout zone.

[0047] Specific Implementation Method Two: Combining Figures 1 to 2 This embodiment describes a method where the inlet end of the ammonia gas burner 3 is connected to the main ammonia gas pipeline 5.

[0048] The undisclosed technical features in this embodiment are the same as those in Specific Embodiment 1.

[0049] Specific implementation method three: Combining Figures 1 to 2 In this embodiment, the ammonia gas burner 3 is installed inside the combustion air box 4, which is connected to the air outlet of the air preheater 9 via the hot combustion air duct 12. The burnout air burner I14 is installed inside the burnout air box I 17, and the burnout air burner II15 is installed inside the burnout air box II 18. The burnout air box I 17 and the burnout air box II 18 are connected to the hot combustion air duct 12 via the burnout air branch duct 13.

[0050] The undisclosed technical features in this embodiment are the same as those in Specific Embodiment Two.

[0051] The ammonia burner 3 is installed inside the combustion air box 4, and the combustion air required for ammonia combustion is supplied by the combustion air box 4.

[0052] The burnout air branch duct 13 introduces burnout air into burnout air box 17 (I) and burnout air box 18 (II), respectively. The burnout air originates from the heat-supporting combustion air duct 12. Burnout air box 17 (I) provides burnout air to burnout air burner 14 (I), and burnout air box 18 (II) provides burnout air to burnout air burner 15 (II).

[0053] Specific implementation method four: Combination Figures 1 to 2 This embodiment describes a combustion air box 4 equipped with a combustion air regulating damper 16, which is located on both sides of the ammonia burner 3. A burnout air I box 17 equipped with a burnout air I regulating damper 19, which is located on both sides of the burnout air burner I 14. A burnout air II box 18 equipped with a burnout air II regulating damper 20, which is located on both sides of the burnout air burner II 15.

[0054] The undisclosed technical features in this embodiment are the same as those in Specific Embodiment Three.

[0055] The burnout air I air box 17 is equipped with burnout air I regulating dampers 19 on both sides, and the burnout air II air box 18 is equipped with burnout air II regulating dampers 20 on both sides. The burnout air flow rate is adjusted according to the boiler load and combustion adjustment needs.

[0056] Specific Implementation Method Five: Combining Figures 1 to 2 This embodiment describes an ammonia gas burner 3 comprising multiple layers of ammonia gas burners 3 arranged sequentially from bottom to top, with each layer of ammonia gas burner 3 housed within a combustion air box 4.

[0057] The undisclosed technical features in this embodiment are the same as those in Specific Embodiment Three.

[0058] Several ammonia gas burners 3 are arranged in multiple layers. Each layer of ammonia gas burners 3 is equipped with a combustion air box 4. Each layer of combustion air box 4 is equipped with a combustion air regulating damper 16 on both sides. The combustion air flow rate supplied to each layer of ammonia gas burners 3 is adjusted according to the boiler load and combustion adjustment needs.

[0059] Specific Implementation Method Six: Combination Figures 1 to 2 In this embodiment, each layer of ammonia gas burner 3 is connected to the main ammonia gas pipeline 5 via an ammonia gas branch pipeline 6.

[0060] The undisclosed technical features in this embodiment are the same as those in Specific Embodiment Five.

[0061] The main ammonia pipeline 5 introduces ammonia into the boiler side, and the ammonia branch pipeline 6 supplies ammonia to each ammonia burner 3.

[0062] Specific implementation method seven: Combination Figure 1 This embodiment describes a flow regulating valve 7 installed on the ammonia branch pipe 6.

[0063] The undisclosed technical features in this embodiment are the same as those in Specific Embodiment Six.

[0064] A flow regulating valve 7 is installed in each ammonia branch pipe 6 to adjust the ammonia flow rate supplied to each ammonia gas burner 3 according to the boiler load and combustion adjustment needs.

[0065] Specific implementation method eight: Combination Figure 1 In this embodiment, the air outlet of the combustion fan 10 is connected to the air inlet of the air preheater 9 through the cold combustion air duct 11.

[0066] The undisclosed technical features in this embodiment are the same as those in Specific Embodiment 1.

[0067] Specific Implementation Method Nine: Combining Figure 1 This embodiment describes a low-NOx combustion method for a pure ammonia gas-fired boiler, which includes the following combustion process:

[0068] Ammonia gas burner 3 injects ammonia fuel into the main combustion zone of furnace 2 for combustion. Combustion air box 4 provides combustion air for ammonia fuel, and the amount of combustion air provided is less than the theoretical combustion air volume of ammonia fuel. Burnout air burner I 14 and burnout air burner II 15 respectively supplement the remaining combustion air. Ammonia fuel is burned in the primary burnout zone and the secondary burnout zone in furnace 2 respectively. During the combustion process, ammonia fuel exchanges heat with water-cooled wall 1 through radiation. The high-temperature flue gas generated after combustion flows upward in furnace 2 and exchanges heat with boiler heating surface 8, SCR device 21 and air preheater 9 in sequence before being discharged from the flue gas outlet. Cold air is pressurized by combustion air fan 10 and heated by air preheater 9 to provide combustion air for ammonia gas burner 3, burnout air burner I 14 and burnout air burner II 15 respectively.

[0069] Specific Implementation Method Ten: Combining Figure 1 In this embodiment, the furnace space below the elevation of burnout air burner I14 is the main combustion zone, the furnace space between the elevations of burnout air burner I14 and burnout air burner II15 is the primary combustion zone, and the furnace space above the elevation of burnout air burner II15 is the secondary combustion zone.

[0070] The undisclosed technical features in this embodiment are the same as those in specific embodiment nine.

[0071] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A low-NOx combustion system for a pure ammonia gas-fired boiler, characterized in that: The furnace includes a water-cooled wall (1), a furnace (2), an ammonia gas burner (3), a boiler heating surface (8), an air preheater (9), a combustion air fan (10), a burnout air burner I (14), a burnout air burner II (15), and an SCR device (21). The furnace (2) is surrounded by water-cooled walls (1). The ammonia gas burner (3) is located at the lower part of the water-cooled wall (1) on the front wall of the furnace (2). The water-cooled walls (1) on the front and rear walls above the ammonia gas burner (3) are also located at the lower part of the water-cooled wall (1). The furnace (2) is equipped with burnout air burner I (14) and burnout air burner II (15) from bottom to top. The boiler heating surface (8), SCR device (21) and air preheater (9) are arranged in sequence from front to back on the upper rear side of the furnace (2). The cold air drawn in by the combustion fan (10) is heated by the air preheater (9) and then provides combustion air to the ammonia gas burner (3), burnout air burner I (14) and burnout air burner II (15).

2. The low-NOx combustion system for a pure ammonia gas-fired boiler according to claim 1, characterized in that: The inlet end of the ammonia gas burner (3) is connected to the main ammonia gas pipeline (5).

3. The low-NOx combustion system for a pure ammonia gas-fired boiler according to claim 2, characterized in that: The ammonia gas burner (3) is installed in the combustion air box (4), which is connected to the air outlet of the air preheater (9) through the hot combustion air duct (12); the burnout air burner I (14) is installed in the burnout air box I (17), and the burnout air burner II (15) is installed in the burnout air box II (18). The burnout air box I (17) and the burnout air box II (18) are connected to the hot combustion air duct (12) through the burnout air branch duct (13).

4. The low-NOx combustion system for a pure ammonia gas-fired boiler according to claim 3, characterized in that: The combustion air box (4) is equipped with a combustion air regulating damper (16), which is located on both sides of the ammonia gas burner (3). The burnout air I box (17) is equipped with a burnout air I regulating damper (19), which is located on both sides of the burnout air burner I (14). The burnout air II box (18) is equipped with a burnout air II regulating damper (20), which is located on both sides of the burnout air burner II (15).

5. The low-NOx combustion system for a pure ammonia gas-fired boiler according to claim 3, characterized in that: The ammonia gas burner (3) includes multiple layers of ammonia gas burners (3) arranged sequentially from bottom to top, with each layer of ammonia gas burner (3) housed in a combustion air box (4).

6. The low-NOx combustion system for a pure ammonia gas-fired boiler according to claim 5, characterized in that: Each ammonia burner (3) is connected to the main ammonia pipeline (5) via an ammonia branch pipeline (6).

7. The low-NOx combustion system for a pure ammonia gas-fired boiler according to claim 6, characterized in that: A flow regulating valve (7) is installed on the ammonia branch pipe (6).

8. The low-NOx combustion system for a pure ammonia gas-fired boiler according to claim 1, characterized in that: The air outlet of the combustion blower (10) is connected to the air inlet of the air preheater (9) through the cold combustion air duct (11).

9. The combustion method of the low-NOx combustion system of a pure ammonia gas boiler according to any one of claims 1 to 8, characterized in that: The combustion process includes the following: The ammonia gas burner (3) injects ammonia fuel into the main combustion zone of the furnace (2) for combustion. The combustion air box (4) provides combustion air for the ammonia fuel, and the amount of combustion air provided is less than the theoretical combustion air volume of the ammonia fuel. The burnout air burner I (14) and burnout air burner II (15) respectively supplement the remaining combustion air. The ammonia fuel is burned in the primary burnout zone and the secondary burnout zone in the furnace (2). The ammonia fuel combustion process exchanges heat with the water-cooled wall (1) through radiation. The high-temperature flue gas generated after combustion flows upward in the furnace (2) and exchanges heat with the boiler heating surface (8), SCR device (21) and air preheater (9) in sequence before being discharged from the flue gas outlet. The cold air is pressurized by the combustion air fan (10) and heated by the air preheater (9) to provide combustion air for the ammonia gas burner (3), burnout air burner I (14) and burnout air burner II (15).

10. The method for low-NOx combustion in a pure ammonia gas-fired boiler according to claim 9, characterized in that: The furnace (2) space below the elevation of burnout air burner I (14) is the main combustion zone, the furnace (2) space between the elevations of burnout air burner I (14) and burnout air burner II (15) is the primary combustion zone, and the furnace (2) space above the elevation of burnout air burner II (15) is the secondary combustion zone.

Images