Green ammonia collaborative coal combustion and staged denitration-based system and staged denitration method thereof

Abstract

The invention relates to the field of comprehensive utilization of clean energy and pollution control, in particular to a system based on green ammonia collaborative coal combustion and staged denitration and a staged denitration method thereof. The system comprises a photo-thermal hydrogen production and ammonia synthesis subsystem which drives a solid oxide electrolytic cell to electrolyze water at high temperature to produce hydrogen through a tower-type condensation system, and green ammonia is synthesized under the action of an iron-based catalyst in combination with air separation nitrogen; the ammonia-coal synergistic combustion subsystem is used for mixing generated green ammonia and pulverized coal according to the mass ratio of 0-30% and then spraying the mixture into a main combustion zone for low-nitrogen combustion, redundant H2 is sprayed into a hearth in a re-combustion zone to form a reducing atmosphere so as to realize NOX in-situ reduction, and preheated over-fire air at the temperature of 300-400 DEG C is sprayed into a burnout zone so as to improve the burnout rate; the graded denitration adopts the combination of first-stage reduction in a reburning area and second-stage denitration of SCR (selective catalytic reduction). Hydrogen production energy consumption is reduced through photo-thermal-electrolysis synergism, carbon emission is reduced in combination with ammonia coal blending combustion, and a multi-stage denitration technology is adopted, so that the method is suitable for low-carbon transformation of a coal-fired power plant, and efficient denitration is achieved.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of clean energy and pollution control, specifically to a system and method based on green ammonia co-combustion and staged denitrification. Background Technology

[0002] The combustion of fossil fuels is a major source of greenhouse gases carbon dioxide (CO2) and nitrogen oxide pollutants (NOx).

[0003] Ammonia, as a renewable energy source, boasts advantages such as easy liquefaction, convenient storage and transportation, high energy density, and good energy storage performance. By developing key technologies for ammonia blending in coal-fired power units, the clean, efficient, and large-scale utilization of ammonia energy can be achieved. Compared to traditional fossil fuels, ammonia-coal co-combustion results in lower carbon emissions. Simultaneously, the mature development of solar thermal and photovoltaic technologies has made it possible to use solar energy to drive the preparation of green ammonia and optimize the combustion process, providing a scalable decarbonization pathway for high-carbon emission industries (such as power, shipping, and chemicals). However, ammonia co-combustion with coal faces multiple challenges: firstly, the fuel characteristics of ammonia and coal differ significantly, leading to competition for oxygen during combustion, resulting in delayed ignition, unstable combustion, and reduced efficiency; secondly, the high nitrogen content of ammonia significantly increases the risk of NOx emissions from the furnace outlet. Existing coal-fired power units face technical bottlenecks in ammonia-coal blending control, such as difficulties in ratio adjustment and fluctuations in combustion conditions, which easily lead to incomplete combustion. Under current stringent air pollutant emission standards, there is a dual dilemma of exceeding nitrogen oxide emission standards and increasing environmental compliance pressure.

[0004] Traditional coal-fired boilers rely on pure coal combustion, producing large amounts of CO2 and NOx. When a single SCR / SNCR denitrification system operates at low loads, insufficient furnace temperature leads to decreased catalyst activity and a significant reduction in denitrification efficiency (typically below 70%), with ammonia slip concentrations often exceeding 5 ppm, posing a risk of secondary pollution. Traditional ammonia synthesis processes (such as the Haber-Bosch process) require high temperatures (400-500℃) and high pressures (15-25 MPa), relying on fossil fuels for hydrogen production. Energy consumption per ton of ammonia is as high as 28-35 GJ, with a carbon emission intensity of approximately 1.8 tons of CO2 per ton of ammonia, resulting in poor economic and environmental performance. Liquid ammonia storage and transportation require high pressure or low temperatures, posing leakage and explosion risks and incurring high safety costs. Existing technologies do not fully utilize clean energy sources such as solar thermal and wind power for hydrogen and ammonia production, leaving coal-fired systems still reliant on high-carbon energy sources. Waste heat from traditional boiler flue gas (200-300℃) is only used for preheating air or feedwater, resulting in an overall thermal efficiency typically below 70%, leading to significant energy waste.

[0005] In summary, existing technologies still have many problems in achieving low-carbon coal-fired power units, clean and efficient utilization of ammonia energy, and comprehensive energy utilization. There is an urgent need to propose a new technical solution to solve these problems. Summary of the Invention

[0006] To address or alleviate at least one of the problems in the prior art, this invention proposes a system and method based on green ammonia co-combustion and staged denitrification. This is a technology that combines a photothermal system to produce synthetic ammonia feedstock and applies it to a combustion boiler for ammonia co-combustion, while also incorporating advanced denitrification technology to achieve a highly efficient and clean combustion process.

[0007] The present invention is achieved using the following technical solution: A green ammonia-coal combustion and staged denitrification system includes a solar thermal collector unit, an air nitrogen generator unit, a water electrolysis device, an ammonia synthesis device, an ammonia storage tank, an oxygen storage tank, a molten salt energy storage tank, a gas mixer, a coal mill, an air preheater, and a boiler body. The boiler body contains a furnace, a denitrification reaction unit, a main economizer, and a staged economizer. The multi-stage combustion zones in the furnace, from bottom to top, are: a main combustion zone, a recombustion zone, and a burnout zone. The main combustion zone is equipped with dual-fluid nozzles, the recombustion zone is equipped with H2 injectors, and the burnout zone is equipped with burnout air nozzles. The solar thermal collector focuses heat and carries it into the molten salt storage tank through molten salt circulation. The molten salt storage tank is connected to the water electrolysis unit. One H2 outlet of the water electrolysis unit is connected to the inlet of the ammonia synthesis unit, and the other H2 outlet is connected to the H2 injector in the reburning zone. The N2 outlet of the air nitrogen generation unit is connected to the inlet of the ammonia synthesis unit. The outlet of the ammonia synthesis unit is connected to the ammonia storage tank. The ammonia outlet of the ammonia storage tank is connected to the dual-fluid nozzle in the main combustion zone. The O2 outlets of the air nitrogen generation unit and the water electrolysis unit are both connected to the inlet of the oxygen storage tank. The outlet of the oxygen storage tank is connected to the inlet of the gas mixer. The outlet of the gas mixer is connected to the air preheater. The outlet of the air preheater is connected to the inlet of the coal mill and the burnout air nozzle, respectively. The outlet of the coal mill is connected to the dual-fluid nozzle. The main economizer and the staged economizer are arranged in series. The main economizer is located above the furnace. The furnace outlet, the main economizer, the inlet of the denitrification reaction unit, and the flue of the staged economizer are connected in sequence.

[0008] In the above technical solution, O2 in the gas mixer is introduced into air and mixed to form burnout air. The burnout air and primary air enter the air preheater to be preheated to the required temperature and then introduced into the furnace for combustion. The burnout air can also be used for oxygen-enriched combustion or industrial oxygen supply.

[0009] In the above technical solution, the denitrification reaction unit is an SCR reactor, and the catalyst used is a vanadium-tungsten-titanium catalyst.

[0010] In the above technical solution, further, the support of the vanadium-tungsten-titanium catalyst is anatase titanium dioxide, the active component is vanadium pentoxide, and the co-catalyst is tungsten trioxide; by mass percentage, titanium dioxide is 80-90 wt%, vanadium pentoxide is 1-5 wt%, and the co-catalyst is 5-10 wt%; wherein, Support: Anatase titanium dioxide (TiO2, 80-90 wt%), providing a high specific surface area (50-150 m²). 2 / g) and porous structure; Active component: Vanadium pentoxide (V₂O₅, 1-5wt%), via V 5+ ↔V 4+ Redox cycle catalytic reduction of NO by NH3 X ; Co-catalyst: Tungsten trioxide (WO3, 5-10wt%) enhances thermal stability, resistance to sulfur poisoning, and regulates the distribution of acidic sites.

[0011] This configuration ensures that the catalyst can efficiently remove nitrification at flue gas temperatures of 300-400℃.

[0012] In the above technical solution, the re-ignition zone adopts a vortex-stabilized combustion structure, which extends the reduction reaction time to ≥1.2s. The present invention also provides a staged denitrification method, the method employing the aforementioned system and comprising the following steps: (1) Photothermal hydrogen production and green ammonia synthesis: The solar thermal collector focuses solar energy to heat molten salt, which drives the water electrolysis device to electrolyze water to produce hydrogen. Hydrogen produced by water electrolysis and nitrogen produced by air separation are fed into the ammonia synthesis unit at a molar ratio of 2.8:1 to 3.5:1. Under the action of an iron-based catalyst, green ammonia is synthesized and stored in an ammonia storage tank. The oxygen produced as a byproduct of hydrogen production through water electrolysis is stored in an oxygen storage tank. (2) Fuel co-combustion and primary denitrification: After being ground by a coal mill, the coal powder is injected into the ammonia-coal mixture from the coal mill and the ammonia storage tank through the dual-fluid nozzles in the main combustion zone. The proportion of ammonia added to the ammonia-coal mixture is 0-30%. The gas-solid two-phase flow is uniformly mixed through the dual-fluid nozzles. In the reburning zone, excess hydrogen from the water electrolysis unit is injected into the reburning zone via an H2 injector as a reducing agent, providing a reducing atmosphere for the reduction reaction. In the reburning zone, H2 and NH3 synergistically reduce NOx to achieve in-situ denitrification, with a reduction reaction time ≥1.2s; the temperature of the reburning zone is 1450K-1610K. The design of the vortex-stabilized combustion structure is based on fluid dynamics principles, with the core being the synergistic effect of a V-shaped blunt body and a concave cavity to construct a stable low-speed recirculating vortex region. Specifically: Flow field construction mechanism: When flue gas flows through the vortex structure at 1450K-1610K, the sudden expansion of the cross section generates a reverse pressure gradient, which causes the flue gas in the mainstream area to flow back into the concave cavity, forming a low-speed vortex core area. At the same time, the periodic shedding of the Karman vortex street at the trailing edge of the V-shaped blunt body (the shedding frequency matches the flow velocity) further increases the turbulence intensity to ≥15%, enhancing the turbulent mixing characteristics of the vortex region. Functional coupling effect: The reflux zone formed by the concave cavity provides the H2 reducing agent with a unique mixing environment characterized by "low velocity (flow velocity reduced by 40%-60%) and high turbulence (turbulent kinetic energy increased by 2-3 times compared to the mainstream zone)". This flow field characteristic allows the reducing agent to mix with NO. X The contact area is increased and the reaction path is prolonged. Performance advantages: Compared to the conventional stable combustion structure's reaction time of 0.3-0.8s, this structure significantly extends the effective reaction time to ≥1.2s through flow field optimization, providing more sufficient kinetic conditions for the denitrification reaction and fundamentally improving the utilization efficiency of the reducing agent and NO. X The removal rate.

[0013] The burnout air nozzles in the burnout zone inject burnout air preheated to 300-400℃ by the air preheater, with the excess air coefficient controlled at 1.05-1.15; this promotes the complete oxidation of unburned carbon and CO. (3) Secondary denitrification: The flue gas from the reburning zone is sequentially catalytically reduced by the SCR reactor in the denitrification reaction unit.

[0014] In the above technical solution, the first-stage denitrification in the above step is further achieved through an amino radical chain reaction to achieve in-situ denitrification: .

[0015] In the above technical solution, the water electrolysis device further adopts a solid oxide electrolysis cell.

[0016] The molten salt energy storage heat exchanger in the system of this invention is used to store heat and regulate the production of synthetic ammonia at night.

[0017] The nitrogen produced by air separation (N2) and the by-product oxygen from water electrolysis are stored in stages for precise control of oxygen concentration in the combustion zone. The primary air inlet duct and the burnout air inlet duct are respectively connected to the air preheater. The primary air is heated by the air preheater and then directly supplied to the furnace. The burnout air is deheated by the air preheater and then sent to the gas mixer to mix with the oxygen byproduct of water electrolysis and then introduced into the burnout zone for oxygen-enriched combustion.

[0018] The system and staged denitrification method of this invention are as follows: Main combustion zone (oxygen-deficient combustion): Coal powder is ground by a coal mill and mixed with green ammonia at a mass ratio of 0-30%, and uniform co-combustion is achieved through a dual-fluid nozzle to suppress the formation of fuel-type NOx; Re-combustion zone (deep oxygen-deficient): Excess hydrogen from the water electrolysis device is injected through an H2 injector to form a strong reducing atmosphere, further reducing the NOx remaining in the main combustion zone; Burnout zone (oxygen-enriched combustion): Preheated burnout air (oxygen and air byproducts of water electrolysis) is introduced to promote the complete oxidation of unburned carbon and CO.

[0019] This invention is based on a green ammonia-coal combustion and staged denitrification system. When there is excess power generation from new energy sources, it provides energy for the water electrolysis unit. The hydrogen produced and the nitrogen produced by the air nitrogen generation unit are synthesized into ammonia by the ammonia synthesis unit under the action of a catalyst. The synthesized ammonia is then stored in an ammonia storage tank. After the coal is crushed in the coal mill, the primary air preheated by the air preheater is mixed with ammonia through a dual-fluid nozzle and introduced into the main combustion zone. The heat from the coal combustion assists in the combustion of ammonia, thereby achieving ammonia-coal co-combustion in the boiler. The excess hydrogen from the water electrolysis unit is injected into the re-combustion zone as a reducing agent through an H2 injector to form a strong reducing atmosphere, further reducing the NOx remaining in the main combustion zone. The byproduct oxygen from the water electrolysis unit is stored in an oxygen storage tank and mixed with air in a gas mixer to generate oxygen-enriched gas. After air preheating, it is used for oxygen-enriched combustion in the burnout zone, thereby improving the burnout rate of coal powder and increasing combustion efficiency.

[0020] In this invention, hydrogen is produced and then directly transported to the electrocatalytic ammonia production unit and boiler for on-site use. After use, the hydrogen production unit is immediately shut down. The entire process does not produce hydrogen, thus avoiding the safety risks associated with hydrogen storage.

[0021] The denitrification method of this invention comprises the following steps: In the main combustion zone (oxygen-deficient combustion) of the boiler, pulverized coal is ground by a coal mill and mixed with green ammonia at a mass ratio of 0-30%, achieving uniform co-combustion through a dual-fluid nozzle to suppress the formation of fuel-type NOx; in the recombustion zone (deep oxygen-deficient combustion), excess hydrogen from the water electrolysis unit is injected through an H2 injector to create a strongly reducing atmosphere, achieving in-situ denitrification through an amino radical chain reaction; in the burnout zone (oxygen-enriched combustion), preheated burnout air (oxygen and air from water electrolysis byproducts) is introduced to promote the complete oxidation of unburned carbon and CO. The flue gas undergoes further denitrification treatment in an SCR reactor (vanadium-tungsten-titanium catalyst).

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: This study proposes a photothermal molten salt-driven green ammonia synthesis and pulverized coal co-firing synergistic system. High-temperature, low-carbon hydrogen production is achieved through tower-type concentrated solar energy storage (~700℃) coupled with solid oxide electrolysis. Zero-carbon green ammonia (replacing 0–30% of pulverized coal) is then synthesized via catalytic synthesis, constructing a complete carbon footprint reduction pathway. Innovative gas-solid two-phase flow mixing technology and a staged air distribution strategy (excess air coefficient of 1.1 in the main combustion zone, 1.15–1.2 in the upper burnout zone, and 0.7–0.9 in the reburning zone) are employed. This maintains a stable temperature field in the combustion core zone (with a highly consistent gradient distribution of ammonia co-firing ratios from 0–30%) and combustion efficiency >95%, while achieving deep synergistic control of carbon and nitrogen pollutants. At the denitrification level, the residence time of the reducing agent is extended (≥1.2 s) through a vortex structure, triggering the NH2+NO→N2+H2O free radical chain reaction. This is coupled with a vanadium-tungsten-titanium SCR catalyst to form a multi-stage redundant denitrification mechanism, achieving an overall efficiency >90%. This invention integrates electrolytic byproduct oxygen directly into oxygen-enriched combustion to achieve a closed-loop oxygen cycle, dynamically absorbs hydrogen energy to establish an inherently safe paradigm, and further enhances energy efficiency by leveraging the waste heat from the economizer's cascade process. This invention significantly reduces carbon emission intensity through carbon atom replacement (monotonically increasing with ammonia blending ratio), and combines green ammonia cost optimization and catalyst consumption reduction to build a competitive advantage throughout the entire life cycle, ultimately achieving a triple synergistic optimization of carbon reduction, stable combustion, and ultra-low emissions, providing a scalable path for the low-carbon transformation of coal-fired power plants. This invention reduces hydrogen production energy consumption through a combination of solar thermal and electrolysis, reduces carbon emissions through ammonia-coal blending, and achieves efficient denitrification through multi-stage denitrification technology, making it suitable for low-carbon retrofitting of coal-fired power plants, combining the advantages of low-carbon emission reduction and high-efficiency environmental protection. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a green ammonia-co-coal combustion and staged denitrification system according to an embodiment of the present invention.

[0024] 1. Solar thermal collector unit; 2. Air nitrogen generator unit; 3. Water electrolysis device; 4. Ammonia synthesis device; 5. Ammonia storage tank; 6. Oxygen storage tank; 7. Molten salt energy storage tank; 8. Gas mixer; 9. Coal mill; 10. Air preheater; 11. Denitrification reaction unit; 12. Main economizer; 13. Staged economizer; 14. Dual-fluid nozzle; 15. H2 injector; 16. Combustion air nozzle; 17. Boiler body.

[0025] Figure 2 Temperature field contour maps for different ammonia doping ratios of 0%, 10%, 20%, and 30%.

[0026] Figure 3 CO2 mass fraction cloud plots at different ammonia blending ratios of 0%, 10%, 20%, and 30%.

[0027] Figure 4 Contour plots of NO mass fraction at different ammonia blending ratios of 0%, 10%, 20%, and 30%. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0029] This invention is based on a green ammonia-coal co-combustion and staged denitrification system. It utilizes clean energy to electrolyze water to produce hydrogen and synthesize green ammonia as a zero-carbon fuel for ammonia-coal co-combustion, thereby achieving a highly efficient and clean combustion process. See attached Figure 1 The system provided by this invention is as follows: Heat is focused by a solar collector to drive the outlet of the solid oxide electrolyzer for water electrolysis to produce hydrogen and the air separation unit for nitrogen production, which is then connected to the inlet of the ammonia synthesis unit. The synthesized ammonia is transported to an ammonia storage tank. The ammonia in the storage tank is preheated in a molten salt storage tank and then injected into the main combustion zone of the boiler through a dual-fluid nozzle. Oxygen, a byproduct of water electrolysis, is fed into an oxygen storage tank, mixed with air, and used as oxygen-enriched burnout air. This air is preheated by an air preheater and then introduced into the burnout zone of the furnace through burnout air nozzles.

[0030] The main body of the boiler includes the furnace, the main economizer located above the furnace, the denitrification device, the staged economizer, and the air preheater; the furnace is divided into the main combustion zone, the recombustion zone, and the burnout zone from bottom to top; the furnace, the main economizer, the inlet of the denitrification reaction unit, and the flue of the staged economizer are connected in sequence; the primary air and the burnout air are preheated by the air preheater.

[0031] This invention is based on a green ammonia-coal combustion and staged denitrification system. When there is excess power generation from new energy sources, it provides energy for the water electrolysis unit. The hydrogen produced and the nitrogen produced by the air nitrogen generation unit are synthesized into ammonia by the ammonia synthesis unit under the action of a catalyst. The synthesized ammonia is then stored in an ammonia storage tank. After the coal is crushed in the coal mill, the primary air preheated by the air preheater is mixed with ammonia through a dual-fluid nozzle and introduced into the main combustion zone. The heat from the coal combustion assists in the combustion of ammonia, thereby achieving ammonia-coal co-combustion in the boiler. The excess hydrogen from the water electrolysis unit is injected into the re-combustion zone as a reducing agent through an H2 injector to form a strong reducing atmosphere, further reducing the NOx remaining in the main combustion zone. The byproduct oxygen from the water electrolysis unit is stored in an oxygen storage tank and mixed with air in a gas mixer to generate oxygen-enriched gas. After air preheating, it is used for oxygen-enriched combustion in the burnout zone, thereby improving the burnout rate of coal powder and increasing combustion efficiency.

[0032] In this invention, hydrogen is produced and then directly transported to the electrocatalytic ammonia production unit and the re-combustion zone in the boiler for on-site utilization. After use, the hydrogen production unit is immediately shut down. The entire process does not involve storing hydrogen, thus avoiding the safety risks associated with hydrogen storage.

[0033] The denitrification method of this invention comprises the following steps: Boiler main combustion zone (oxygen-deficient combustion): Pulverized coal is ground by a coal mill and mixed with green ammonia at a mass ratio of 0-30%, and uniform co-firing is achieved through a dual-fluid nozzle to suppress the formation of fuel-type NOx; Re-combustion zone (deep oxygen-deficient): Excess hydrogen from the water electrolysis device is injected through an H2 injector to form a strong reducing atmosphere, and in-situ denitrification is achieved through an amino free radical chain reaction; Combustion zone (oxygen-enriched combustion): Preheated combustion air (oxygen and air from water electrolysis byproducts) is introduced to promote the complete oxidation of unburned carbon and CO.

[0034] The oxygen-deficient conditions in the reburning zone inhibit the oxidation pathway and promote the reduction reaction of NOx→N2: The reactions involved in the chain reaction of H· and NH2· free radicals are as follows: .

[0035] The above reactions can further improve the denitrification efficiency of ammonia injection in the main combustion zone under the minimum stable combustion load and reduce the nitrogen oxide emissions at the furnace outlet.

[0036] The flue gas undergoes another denitrification treatment in an SCR reactor (vanadium-tungsten-titanium catalyst).

[0037] Example 1 A green ammonia-co-coal combustion and staged denitrification system includes a solar thermal collector unit 1, an air nitrogen generator unit 2, a water electrolysis device 3, an ammonia synthesis device 4, an ammonia storage tank 5, an oxygen storage tank 6, a molten salt energy storage tank 7, a gas mixer 8, a coal mill 9, an air preheater 10, and a boiler body 17. The boiler body contains a furnace, a denitrification reaction unit 11, a main economizer 12, and a staged economizer 13. The multi-stage combustion zones in the furnace, from bottom to top, are: a main combustion zone, a re-combustion zone, and a burnout zone. The main combustion zone is equipped with a dual-fluid nozzle 14, the re-combustion zone is equipped with an H2 injector 15, and the burnout zone is equipped with a burnout air nozzle 16. The solar thermal collector 1 focuses heat and carries it into the molten salt storage tank 7 via molten salt circulation. The molten salt storage tank 7 is connected to the water electrolysis device 3. One H2 outlet of the water electrolysis device 3 is connected to the inlet of the ammonia synthesis device 4, and the other H2 outlet is connected to the H2 injector 15 in the re-combustion zone. The N2 outlet of the air nitrogen generator 2 is connected to the inlet of the ammonia synthesis device 4. The outlet of the ammonia synthesis device 4 is connected to the ammonia storage tank 5. The ammonia outlet of the ammonia storage tank 5 is connected to the dual-fluid nozzle 14 in the main combustion zone. The O2 outlet of the air nitrogen generator 2... The O2 outlets of both the inlet and the water electrolysis unit 3 are connected to the inlet of the oxygen storage tank 6. The outlet of the oxygen storage tank 6 is connected to the inlet of the gas mixer 8. The outlet of the gas mixer 8 is connected to the air preheater 10. The outlet of the air preheater 10 is connected to the inlet of the coal mill 9 and the burnout air nozzle 16. The outlet of the coal mill 9 is connected to the dual-fluid nozzle 14. The main economizer 12 and the staged economizer 13 are arranged in series. The furnace outlet, the main economizer 12, the inlet of the denitrification reaction unit 11, and the flue of the staged economizer 13 are connected in sequence. The O2 in the gas mixer 8 is introduced into the air and mixed to form burnout air. The burnout air and the primary air enter the air preheater 10 for preheating to the required temperature and are then introduced into the furnace for combustion. The denitrification reaction unit 11 is an SCR reactor, and the catalyst used is a vanadium-tungsten-titanium catalyst. The support of the vanadium-tungsten-titanium catalyst is anatase titanium dioxide, the active component is vanadium pentoxide, and the co-catalyst is tungsten trioxide. By mass percentage, titanium dioxide is 80-90 wt%, vanadium pentoxide is 1-5 wt%, and co-catalyst is 5-10 wt%. The reburning zone adopts a vortex-stabilized combustion structure (when the fluid flows through a concave cavity, one or more vortices are generated in the cavity, and the fuel burns in the vortex with good combustion characteristics and can obtain high combustion efficiency). The vortex-stabilized combustion structure is used to extend the reduction reaction time to ≥1.2s.

[0038] The staged denitrification method using the above system specifically includes the following steps: (1) Photothermal hydrogen production and green ammonia synthesis: Solar thermal collector 1 focuses solar energy to heat molten salt, which drives water electrolysis device 3, namely solid oxide electrolyzer, to electrolyze water to produce hydrogen. Hydrogen produced by water electrolysis and nitrogen produced by air separation nitrogen production unit 2 are fed into ammonia synthesis unit 4 at a molar ratio of 3:1. Under the action of iron-based catalyst, green ammonia is synthesized and stored in ammonia storage tank 5. The byproduct oxygen from water electrolysis for hydrogen production is stored in oxygen storage tank 6. (2) Fuel co-combustion and primary denitrification: The dual-fluid nozzle 14 in the main combustion zone injects ammonia-coal mixed fuel from the coal mill 9 and the ammonia storage tank 5 respectively. The proportion of ammonia added to the ammonia-coal mixed fuel is 0-30%. The gas-solid two-phase flow is uniformly mixed through the dual-fluid nozzle 14. In the reburning zone, excess hydrogen gas from the electrolysis water device 4 is injected into the H2 injector as a reducing agent to provide a reducing atmosphere for the reduction reaction. In the reburning zone, H2 and NH3 synergistically reduce NOx to achieve in-situ denitrification, and the reduction reaction time is ≥1.2s. The temperature of the reburning zone is 1450K-1610K. Primary denitrification achieves in-situ denitrification through an amino radical chain reaction: .

[0039] The burnout air nozzle 15 in the burnout zone injects burnout air preheated to 300-400℃ by the air preheater 10, and the excess air coefficient is controlled at 1.05-1.15; to promote the complete oxidation of unburned carbon and CO. (3) Secondary denitrification: The flue gas in the reburning zone is catalytically reduced by passing it through the SCR reactor in the denitrification reaction unit 11.

[0040] Example 2 The staged denitrification system and method described in Example 1 were applied. Numerical simulations of in-furnace ammonia-coal co-combustion were performed using Ansys Fluent software. The NOx was then denitrified using a post-processing method. The results are shown in [the original text]. Figures 2-4 .

[0041] Figure 2 Temperature field cloud maps (ammonia blending ratios of 0%, 10%, 20%, and 30%) show that during the ammonia-coal co-combustion process, the temperature gradient distribution in the combustion core region remains consistent (2100 K → 473 K), and the morphology of the high-temperature zone does not undergo significant distortion. This confirms the synergistic effectiveness of gas-solid two-phase flow mixing technology and staged air distribution strategy. Combustion stability: When the ammonia blending ratio is increased to 30%, the distribution range of the high-temperature core zone (>1600 K) basically overlaps with that of pure coal combustion (0%), indicating that the introduction of ammonia fuel does not destroy the flame structure, successfully overcomes the combustion oscillation problem caused by the difference in ammonia / coal combustion rate, and maintains a combustion efficiency of >95%. Denitrification environment protection: The temperature of the reburning zone is stabilized at 1450K-1610K (corresponding to the working temperature of the vortex structure), which provides the necessary thermodynamic conditions for the amino radical chain reaction (NH2+NO→N2+H2O), supporting the in-furnace primary denitrification efficiency >60%. Breakthrough in thermodynamic boundaries: The temperature gradient in the burnout zone decreases smoothly (1600 K→473 K), confirming the enhanced burnout effect of preheated oxygen-enriched air (300–400℃); The uniform distribution of the low-temperature zone (<600 K) in the economizer area verifies the effect of cascaded waste heat recovery on improving system energy efficiency. Proof of the cross-condition stability of the temperature field: Stability of ammonia-blended combustion: Within the ammonia blending ratio range of 0–30%, the system achieves invariance of the combustion temperature field morphology through fuel homogenization and graded oxygen concentration control; Pollution control compatibility: Stability in the high-temperature zone ensures the denitrification reaction temperature window, while evolution in the medium and low-temperature zone supports deep waste heat recovery, forming a synergistic optimization of "emission reduction and energy efficiency"; Technical universality: The uniformity of temperature distribution provides an engineering feasibility basis for the large-scale ammonia substitution in coal-fired power units. Figure 3 The CO2 mass fraction cloud map (ammonia blending ratio 0%, 10%, 20%, 30%) shows: Distribution stability: The CO2 mass fraction gradient distribution is consistent under all operating conditions (2.47 × 10⁻⁶). -1 → 0) In the case of high concentration (>1.98×10) -1 The concentration of these gases in the core combustion zone confirms the sufficiency of fuel combustion and the uniformity of the flow field. Dynamic characteristics of carbon emission reduction: As the ammonia blending ratio increases to 30%, the high CO2 concentration zone (>1.73×10⁻⁶) shows a significant increase. -1 The distribution range shows a systematic contraction, which intuitively characterizes the carbon atom replacement effect of green ammonia—directly reducing carbon emission intensity by replacing carbon elements in coal with hydrogen-based fuels; Combustion compatibility evidence: The CO2 distribution pattern was not distorted due to ammonia doping, which, together with the temperature field stability (see the previous analysis), verifies the effectiveness of the gas-solid two-phase flow mixing technology, ensuring that no local carbon enrichment or decrease in burnout rate occurred during the combustion process within the range of 0–30% ammonia doping. CO2 cloud map reveals: Essential carbon reduction: The shrinkage of the high-concentration zone proves the carbon atom replacement effect of green ammonia on pulverized coal, providing visual evidence for the reduction of the system's carbon footprint; Combustion robustness: The uniformity of the distribution pattern reflects that the addition of ammonia has not disrupted the integrity of combustion, maintaining high thermal efficiency (>95%) and burnout rate; Technology universality: The stability of CO2 gradient distribution across operating conditions indicates that this technology is suitable for large-scale ammonia replacement retrofitting of existing coal-fired power units.

[0042] Figure 4 The mass fraction cloud plots of nitrogen oxides (NO) (ammonia doping ratios of 0%, 10%, 20%, and 30%) reveal: Source suppression effect: With the increase of ammonia blending ratio, the high NO concentration zone in the main combustion zone (>8.96×10) -4 The significant contraction confirms that the graded air distribution strategy (O2 < 15% in the main combustion zone) effectively suppresses the formation of fuel-type NOx. Enhanced reburning reduction: When the ammonia doping ratio is increased to 30%, the NO mass fraction gradient in the reburning zone decays more rapidly, directly demonstrating the effectiveness of the vortex structure in extending the reduction time (≥1.2 s)—the low-speed, high-turbulence environment promotes the H2-triggered amino radical chain reaction (NH2·+NO→N2+H2O), achieving a furnace-level primary denitrification efficiency >60%; Synergistic effect of multi-stage denitrification: Low NO concentration zone in the outlet area (<2.24×10⁻⁶) -4 The continued expansion of this mechanism demonstrates that the combined denitrification efficiency of the "vortex reduction + SCR catalysis" dual mechanism is >90%, meeting the ultra-low emission standard (<50 mg / Nm³). 3 ). NO cloud map empirical evidence: Pollution control compatibility: The high nitrogen characteristics of ammonia fuel are transformed and utilized by innovative combustion structure to achieve synergy between "ammonia blending for emission reduction" and "nitrogen oxide suppression"; Advantages of the technology's universality: The NO distribution gradient evolution pattern is consistent within the range of 0–30% ammonia doping, verifying the system's adaptability to large-scale ammonia substitution; Engineering reliability: The shrinkage in the high-concentration zone and the stability of the low-temperature zone distribution (see temperature field analysis) together confirm the robustness of the entire combustion-denitrification process.

[0043] Although embodiments of the present disclosure have been shown and described, it will be understood by those skilled in the art that variations and combinations of elements may be made to these embodiments without departing from the principles and spirit of the present disclosure, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A system based on green ammonia synergistic coal combustion and staged denitrification, characterized in that, The system includes a solar thermal collector (1), an air nitrogen generator (2), an electrolysis water device (3), an ammonia synthesis device (4), an ammonia storage tank (5), an oxygen storage tank (6), a molten salt energy storage tank (7), a gas mixer (8), a coal mill (9), an air preheater (10), and a boiler body (17). The boiler body contains a furnace, a denitrification reaction unit (11), a main economizer (12), and a staged economizer (13). The multi-stage combustion zones in the furnace, from bottom to top, are: the main combustion zone, the re-combustion zone, and the burnout zone. The main combustion zone is equipped with a dual-fluid nozzle (14), the re-combustion zone is equipped with an H2 injector (15), and the burnout zone is equipped with a burnout air nozzle (16). The solar thermal collector (1) focuses heat and carries it into the molten salt storage tank (7) through a molten salt circulation system. The molten salt storage tank (7) is connected to the water electrolysis device (3). One H2 outlet of the water electrolysis device (3) is connected to the inlet of the ammonia synthesis device (4), and the other H2 outlet is connected to the H2 injector (15) in the reburning zone. The N2 outlet of the air nitrogen generator (2) is connected to the inlet of the ammonia synthesis device (4), and the outlet of the ammonia synthesis device (4) is connected to the ammonia storage tank (5). The ammonia outlet of the ammonia storage tank (5) is connected to the dual-fluid nozzle (14) in the main combustion zone. The O2 outlet of the air nitrogen generator (2) and The O2 outlet of the water electrolysis device (3) is connected to the inlet of the oxygen storage tank (6), the outlet of the oxygen storage tank (6) is connected to the inlet of the gas mixer (8), the outlet of the gas mixer (8) is connected to the air preheater (10), the outlet of the air preheater (10) is connected to the inlet of the coal mill (9) and the burnout air nozzle (16), and the outlet of the coal mill (9) is connected to the dual-fluid nozzle (14); the main economizer (12) and the stage economizer (13) are arranged in series; the furnace outlet, the main economizer (12), the inlet of the denitrification reaction unit (11), and the flue of the stage economizer (13) are connected in sequence.

2. The system according to claim 1, characterized in that, O2 in the gas mixer (8) is introduced into the air and mixed to form burnout air. The burnout air and primary air enter the air preheater (10) to be preheated to the required temperature and then introduced into the furnace for combustion.

3. The system according to claim 1, characterized in that, The denitrification reaction unit (11) is an SCR reactor, and the catalyst used is a vanadium-tungsten-titanium catalyst.

4. The system according to claim 3, characterized in that, The vanadium-tungsten-titanium catalyst is supported by anatase titanium dioxide, the active component is vanadium pentoxide, and the co-catalyst is tungsten trioxide; by mass percentage, titanium dioxide is 80-90 wt%, vanadium pentoxide is 1-5 wt%, and co-catalyst is 5-10 wt%.

5. The system according to claim 1, characterized in that, The reburning zone adopts a vortex-stabilized combustion structure.

6. A staged denitrification method, characterized in that, The method employs the system described in any one of claims 1 to 4, and includes the following steps: (1) Photothermal hydrogen production and green ammonia synthesis: The solar thermal collector (1) focuses solar energy to heat molten salt, driving the water electrolysis device (3) to electrolyze water to produce hydrogen; Hydrogen produced by water electrolysis and nitrogen produced by air separation nitrogen production unit (2) are fed into ammonia synthesis unit (4) at a molar ratio of 2.8:1 ~ 3.5:

1. Under the action of iron-based catalyst, green ammonia is synthesized and stored in ammonia storage tank (5). The byproduct oxygen from water electrolysis for hydrogen production is stored in an oxygen storage tank (6); (2) Fuel co-combustion and primary denitrification: The dual-fluid nozzle (14) in the main combustion zone injects ammonia-coal mixed fuel from the coal mill (9) and the ammonia storage tank (5) respectively. The proportion of ammonia added to the ammonia-coal mixed fuel is 0-30% of the ammonia-coal mixed fuel. The gas-solid two-phase flow is uniformly mixed through the dual-fluid nozzle (14). The excess hydrogen gas in the reburning zone is injected into the water electrolysis device (3) via the H2 injector as a reducing agent to provide a reducing atmosphere for reduction reaction. In the reburning zone, H2 and NH3 synergistically reduce NOx to achieve in-situ denitrification. The reduction reaction time is ≥1.2s. The temperature of the reburning zone is 1450K-1610K. The burnout air nozzle (15) in the burnout zone injects burnout air preheated to 300-400°C by the air preheater (10), and the excess air coefficient is controlled to be 1.15-1.2; to promote the complete oxidation of unburned carbon and CO; (3) Secondary denitrification: The flue gas in the reburning zone is catalytically reduced by passing through the SCR reactor in the denitrification reaction unit (11).

7. The staged denitrification method according to claim 6, characterized in that, The primary denitrification in step (2) is achieved through an amino radical chain reaction to achieve in-situ denitrification: 。 8. The staged denitrification method according to claim 6, characterized in that, The water electrolysis device (3) adopts a solid oxide electrolysis cell.

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