Ammonia-hydrogen mixed pulverized coal MILD combustion system

Abstract

The utility model discloses an ammonia and hydrogen mixed pulverized coal MILD combustion system which comprises a boiler, an ammonia fuel inlet and a hydrogen fuel inlet are formed in the lower middle portion of the boiler, and the hydrogen fuel inlet is located below the ammonia fuel inlet. The ammonia fuel inlet is connected with an ammonia supply system, and the hydrogen fuel inlet is connected with a hydrogen supply system; and an SCR denitration device is arranged at the tail part of the boiler. According to the utility model, flameless combustion and ammonia combustion are combined, so that low-nitrogen combustion of NH3 is expected to be realized; hydrogen is mixed, water vapor is generated through combustion, the volume fraction of NOx can be reduced to 10 <-5 >-10 <-4 >, and the combustion stability is ensured by reducing the ignition delay time of ammonia flames, improving the flame speed of ammonia laminar flow and improving the heat release rate; the system disclosed by the utility model can be applied to various occasions such as fire coal, fuel gas and biomass power generation, and has the characteristics of high combustion efficiency, less pollutant emission and the like.

Description

Technical Field

[0001] This utility model belongs to the field of combustion technology, specifically relating to an ammonia-hydrogen blended pulverized coal MILD combustion system. Background Technology

[0002] By increasing the initial momentum of the reactants under low-temperature preheating conditions and enhancing the entrainment rate within the furnace, MILD (Moderate and Intense Low-Oxygen Dilution) combustion, also known as flameless combustion, can be achieved. This combustion is a volumetric combustion under low-oxygen and low-temperature conditions, characterized by flameless transparency, uniform heat flow distribution, low combustion noise, and minimal temperature fluctuations. Compared to traditional localized high-temperature flaming combustion, low-temperature combustion requires a smaller furnace space, significantly improving thermal efficiency. Due to the absence of a flame front and uniform temperature distribution, NOx formation is low, making it a novel, low-pollution combustion method that ensures complete combustion. Currently, pulverized coal MILD combustion technology is still immature and has not been widely applied. Combustion stability needs improvement, and its beneficial effects on low nitrogen and carbon emissions from pulverized coal combustion have not been fully realized. Utility Model Content

[0003] The technical problem to be solved by this utility model is to provide an ammonia-hydrogen blended coal pulverized coal MILD combustion system, which solves the problems of the current difficulty in ensuring the combustion stability and low nitrogen and low carbon emission effects of coal pulverized coal MILD, and consumes clean energy such as ammonia and hydrogen produced from renewable energy sources, and blends them with traditional fossil energy coal pulverized coal for combustion to achieve low nitrogen and low carbon emissions.

[0004] According to the technical solution of this utility model, this utility model provides an ammonia-hydrogen blended pulverized coal MILD combustion system, including a boiler, an ammonia fuel inlet and a hydrogen fuel inlet are provided in the lower part of the boiler, and the hydrogen fuel inlet is located below the ammonia fuel inlet; the ammonia fuel inlet is connected to an ammonia supply system, and the hydrogen fuel inlet is connected to a hydrogen supply system; an SCR denitrification device is provided at the tail end of the boiler.

[0005] Furthermore, a primary air inlet is provided directly below the boiler, and a lower secondary air inlet and an upper secondary air inlet are staggered on both sides of the boiler furnace.

[0006] Furthermore, a secondary economizer and a primary economizer are sequentially installed at the tail end of the boiler, with the SCR denitrification device located between the secondary economizer and the primary economizer.

[0007] Furthermore, a cyclone separator is also installed upstream of the secondary economizer.

[0008] Furthermore, temperature detectors, oxygen concentration detectors, and ammonia concentration detectors are installed in both the boiler and the SCR denitrification unit, and these detectors are connected to the monitoring system.

[0009] Furthermore, the boiler is equipped with a coal feed port, which is located below the hydrogen fuel inlet.

[0010] Compared with the prior art, the beneficial technical effects of this utility model are as follows:

[0011] 1. This invention employs an ammonia-hydrogen blended pulverized coal method. MILD combustion has wide applications in low-calorific-value fuels, and NH3 happens to be a medium-calorific-value gaseous fuel, with a calorific value only 40% of that of CH4. Combining flameless combustion with ammonia combustion is expected to achieve low-NOx combustion of NH3. The addition of hydrogen, which produces water vapor upon combustion, can reduce the NOx volume fraction to 10%. -5 ~10 -4 Combustion stability is ensured by reducing the ignition delay time of ammonia flames, increasing the laminar flow velocity of ammonia flames, and increasing the heat release rate.

[0012] 2. This invention injects ammonia into the downstream of the boiler bed via an ammonia supply system to avoid increasing the NO concentration of combustion products; injects hydrogen into the area below the ammonia fuel inlet via a hydrogen supply system to enhance the promoting effect of hydrogen on ammonia combustion; preferably, an SCR denitrification device is installed between the secondary economizer and the primary economizer at the tail of the boiler to reduce NOx emissions and solve ammonia escape; low-NOx combustion is achieved by stratified air supply and optimized air volume; and the reaction zone generated by the separation of primary and secondary air jets is not destroyed, avoiding local high temperatures, which is conducive to stable MILD combustion, while extending the residence time of pulverized coal and improving the overall burnout rate.

[0013] 3. In this invention, the lower and upper secondary air are preferably staggered in the MILD combustion device for pulverized coal. Compared with double symmetrical nozzles, asymmetrical nozzles can further increase the air jet flow, enhance internal recirculation, thereby expanding the reaction zone, reducing the reaction rate, making the temperature distribution more uniform, reducing the peak temperature, and reducing NOx emissions by about 33%. In addition, by increasing the distance between the primary and secondary flows or the coal jet injection angle, more flue gas is entrained in the pulverized coal jet, the reactant concentration is significantly reduced, and the establishment of MILD combustion is promoted. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the system structure provided by this utility model.

[0015] Explanation of reference numerals in the attached figures:

[0016] 1. Boiler; 2. Ammonia supply system; 3. Hydrogen supply system; 4. SCR denitrification device; 5. Monitoring system; 6. Secondary economizer; 7. Primary economizer; 8. Cyclone separator; 9. Primary air outlet; 10. Lower secondary air outlet; 11. Upper secondary air outlet; 12. Coal feed inlet. Detailed Implementation

[0017] This invention provides an ammonia-hydrogen blended pulverized coal MILD combustion system, belonging to the field of combustion technology. It solves the problems of unstable combustion and difficulty in guaranteeing low-NOx and low-carbon emissions in current pulverized coal MILD combustion systems. It utilizes clean energy from renewable energy sources, namely ammonia and hydrogen, blended with traditional fossil fuel pulverized coal for combustion, allowing for flexible and wide-range load adjustment. A typical ammonia-hydrogen blended pulverized coal MILD combustion system includes: a boiler, an ammonia supply system, a hydrogen supply system, an SCR denitrification device, and a monitoring system. The ammonia and hydrogen supply systems are located downstream of the boiler, with the hydrogen supply system below the ammonia supply system. An SCR denitrification device is installed at the tail end of the boiler. The monitoring system monitors the temperature, oxygen concentration, and ammonia concentration of the boiler and the SCR denitrification device throughout the entire combustion process. This ammonia-hydrogen blended pulverized coal MILD combustion system can be applied to various applications, including coal-fired, gas-fired, and biomass power generation, and features high combustion efficiency and low pollutant emissions.

[0018] Please see Figure 1 This utility model discloses an ammonia-hydrogen blended pulverized coal MILD combustion system, comprising a boiler 1. An ammonia fuel inlet and a hydrogen fuel inlet are located in the lower part of the boiler 1 (more specifically, the main combustion zone), with the hydrogen fuel inlet located below the ammonia fuel inlet. The ammonia fuel inlet is connected to an ammonia supply system 2, and the hydrogen fuel inlet is connected to a hydrogen supply system 3. This allows ammonia to be injected into the lower part of the boiler bed via the ammonia supply system 2, preventing an increase in the concentration of the combustion product NO, while hydrogen is injected below the ammonia fuel inlet via the hydrogen supply system 3, enhancing the promoting effect of hydrogen on ammonia combustion. An SCR denitrification device 4 is installed at the tail end of the boiler 1.

[0019] Preferably, a primary air inlet 9 is located directly below the boiler 1, and a lower secondary air inlet 10 and an upper secondary air inlet 11 are staggered on both sides of the furnace of the boiler 1 to promote uniform mixing of fuel and air. Existing combustion systems generally also have primary and secondary air inlets; the improvement of this design lies in their number and location. The lower secondary air inlet 10 and the upper secondary air inlet 11 are located on opposite sides of the furnace and are asymmetrical with different heights. By layering air supply and optimizing airflow, low-NOx combustion is achieved. Further preferably, the primary air flow rate is less than 100 m / s, which does not disrupt the reaction zone generated by the separation of primary and secondary air jets, avoids localized high temperatures, and is conducive to stable MILD combustion, while also extending the residence time of pulverized coal and improving the overall burnout rate.

[0020] Furthermore, a secondary economizer 6 and a primary economizer 7 are sequentially installed at the tail end of boiler 1. An SCR denitrification device 4 is located between the secondary economizer 6 and the primary economizer 7 to reduce NOx emissions and address ammonia escape. Boiler 1 is equipped with a coal feed inlet 12, located below the hydrogen fuel inlet, for the input of pulverized coal. A cyclone separator 8 is also installed upstream of the secondary economizer 6 to separate unreacted particles from the high-temperature flue gas discharged from the boiler 1 furnace outlet, which are then returned to boiler 1 via a return pipeline (e.g., including a return feeder) to continue circulating and combustion.

[0021] Preferably, it also includes a monitoring system 5. Temperature detectors, oxygen concentration detectors, and ammonia concentration detectors are installed in both the boiler 1 and the SCR denitrification device 4. The temperature detectors, oxygen concentration detectors, and ammonia concentration detectors are connected to the monitoring system 5. The monitoring system 5 can monitor the temperature, oxygen concentration, and ammonia concentration of the boiler and the SCR denitrification device 4 throughout the entire combustion process, thereby providing assistance in the adjustment of the combustion conditions.

[0022] The concept, principle and beneficial technical effects of this utility model are further explained below based on more specific preferred embodiments.

[0023] Fuel and air are preheated before being fed into the furnace. The pulverized coal combustion zone is located at the bottom of the combustion zone and is in a lean-burn state to provide O2 and heat for the combustion of ammonia in the upper layer. Oxygen-enriched combustion reduces the content of non-reactive nitrogen in the flue gas, thereby increasing the flame temperature and the concentration of free radicals, enhancing the ammonia combustion process. After ammonia-blended combustion, the furnace temperature level decreases and radiative heat transfer weakens. When the ammonia blending ratio is 20%, the radiative heat flux density in the furnace decreases by about 10%; when the ammonia blending ratio is higher than 40%, the high-temperature zone in the furnace shrinks significantly. To ensure stable combustion of the MILD, the furnace temperature should be maintained above 980℃.

[0024] Ammonia, as a gaseous fuel, burns more completely than pulverized coal. Pulverized coal primarily undergoes volatile matter release and combustion in the primary air zone, while coke combustion occurs more extensively in the secondary air and burnout air zones. Replacing pulverized coal with ammonia results in faster ammonia burnout, necessitating a more efficient primary air ratio. The faster combustion of ammonia in a strongly reducing atmosphere is beneficial for NOx control and also promotes the ignition and stability of pulverized coal. The main combustion zone, comprised of the primary and secondary air zones, should maintain a weakly reducing atmosphere. This effectively suppresses NOx formation while ensuring near-complete ammonia combustion.

[0025] Under low load conditions, adding a small amount of hydrogen (5%) can significantly enhance the stability of NH3 combustion, reduce the autoignition temperature, and eliminate flame rise.

[0026] In the MILD combustion device for pulverized coal, compared with dual-symmetric nozzles, asymmetric nozzles can further increase the air jet flow rate, enhance internal recirculation, thereby expanding the reaction zone, reducing the reaction rate, making the temperature distribution more uniform, reducing the peak temperature, and reducing NOx emissions by about 33%. In addition, by increasing the distance between the primary and secondary flows or the coal jet injection angle, more flue gas is entrained in the pulverized coal jet, the reactant concentration is significantly reduced, and the establishment of MILD combustion is promoted.

[0027] MILD combustion has wide applications in low-calorific-value fuels, and NH3 happens to be a medium-calorific-value gaseous fuel, with a calorific value only 40% of that of CH4. Combining flameless combustion with ammonia combustion holds promise for achieving low-NOx combustion of NH3; mixing in hydrogen and burning it to produce water vapor can reduce the NOx volume fraction to 10%. -5 ~10 -4 Combustion stability is ensured by reducing the ignition delay time of ammonia flames, increasing the laminar flow velocity of ammonia flames, and increasing the heat release rate.

Claims

1. An ammonia-hydrogen hybrid pulverized coal MILD combustion system, characterized by, The boiler (1) is provided with an ammonia fuel inlet and a hydrogen fuel inlet at the lower part, and the hydrogen fuel inlet is below the ammonia fuel inlet; the ammonia fuel inlet is connected with an ammonia supply system (2), and the hydrogen fuel inlet is connected with a hydrogen supply system (3); and the boiler (1) is provided with an SCR denitration device (4) at the tail.

2. The ammonia-hydrogen hybrid coal MILD combustion system according to claim 1, wherein A primary air inlet (9) is arranged directly below the boiler (1), and a lower secondary air inlet (10) and an upper secondary air inlet (11) are arranged in a staggered manner at both sides of the furnace chamber of the boiler (1).

3. The ammonia-hydrogen hybrid coal MILD combustion system of claim 1, wherein, A two-stage economizer (6) and a one-stage economizer (7) are sequentially arranged at the tail of the boiler (1), and the SCR denitration device (4) is located between the two-stage economizer (6) and the one-stage economizer (7).

4. The ammonia-hydrogen hybrid coal MILD combustion system according to claim 3, wherein A cyclone separator (8) is further arranged on the upstream side of the two-stage economizer (6).

5. The ammonia-hydrogen hybrid coal MILD combustion system according to any one of claims 1-4, wherein, Temperature detectors, oxygen concentration detectors and ammonia gas concentration detectors are arranged in the boiler (1) and the SCR denitration device (4), and the temperature detectors, the oxygen concentration detectors and the ammonia gas concentration detectors are connected with a monitoring system (5).

6. The ammonia-hydrogen hybrid coal MILD combustion system according to any one of claims 1-4, wherein, The boiler (1) is provided with a coal feeding port (12), and the coal feeding port (12) is below the hydrogen fuel inlet.

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