A coal-fired boiler ammonia-doping combustion system and method based on high-temperature and strong reduction

Abstract

The present invention discloses an ammonia-doped combustion system and method for a coal-fired boiler based on high-temperature strong reduction, belonging to the technical field of boiler combustion. In the ammonia-coal co-firing boiler body, a main combustion zone and an original burnout air zone are sequentially arranged from bottom to top. A primary air nozzle and a secondary air nozzle are installed in the main combustion zone. The primary air nozzle is connected to a pulverized coal pipeline, an ammonia pipeline, and a primary air pipeline through a four-way joint. The secondary air nozzle is connected to a combustion-supporting oxygen pipeline and a secondary air pipeline through a three-way joint. An original burnout air nozzle and a high burnout air nozzle are installed in the original burnout air zone. Both the original burnout air nozzle and the high burnout air nozzle are connected to a burnout air pipeline. The ammonia-doped combustion system and method for a coal-fired boiler based on high-temperature strong reduction of the present invention couple oxygen-enriched combustion with deep air staging technology, solving the internal contradiction problem of the low theoretical combustion temperature of ammonia and the high risk of excessive NO x emission exceeding the standard.

Description

Technical Field

[0001] The present invention relates to an ammonia - blended combustion system and method for a coal - fired boiler based on high - temperature and strong reduction, belonging to the technical field of boiler combustion. Background Art

[0002] There are significant differences between coal and ammonia in terms of combustion characteristics, combustion product components, radiation properties, and pollutant emissions. Compared with the volatile matter in coal, ammonia is more difficult to ignite, and the theoretical combustion temperature of ammonia is lower than that of coal. Therefore, large - scale ammonia - blended combustion may cause problems such as difficult fuel ignition and reduced main combustion zone temperature. At the same time, compared with pulverized coal combustion, after ammonia blending, the content of particulate matter with strong radiation ability such as carbon black and fly ash in the furnace significantly decreases, and the flue gas radiation ability weakens, which will affect the heat transfer process in the furnace. In addition, the mass fraction of N element in ammonia molecules is very high. After large - scale ammonia - blended combustion, there is a risk of NO x emission exceeding the standard.

[0003] Currently, there have been studies on ammonia - coal co - combustion technology. For example, Chinese Patent Application No.: 202221843821.8 discloses an ammonia - only burner layout structure for a pulverized coal boiler and a boiler furnace, which uses a newly added ammonia - only burner to send ammonia and pulverized coal into the furnace for combustion respectively; Chinese Patent Application No.: 202121801588.2 discloses a pulverized coal boiler system with ammonia co - combustion, which sets up three - stage ammonia pipelines to ensure the rapid ignition of ammonia; Chinese Patent Application No.: 202210327223.3 discloses an ammonia - blended combustion and nitrogen reduction control system and operation method for a coal - fired boiler, which couples ammonia - blended combustion with SNCR and SCR denitration systems to reduce the NO x emission concentration. However, the above - mentioned technical solutions all require the installation of new ammonia burners and do not fundamentally solve the problems of low ammonia combustion temperature and easy NO x emission exceeding the standard. And using conventional methods (such as oxygen - enriched combustion) to increase the combustion temperature in the main combustion zone will lead to a further increase in NO x emission. Therefore, in order to solve the internal contradiction problem of low theoretical combustion temperature of ammonia and high risk of NOx emission exceeding the standard, it is urgent to develop a new combustion organization method, and it is necessary to propose an ammonia - blended combustion system and method for a coal - fired boiler based on high - temperature and strong reduction. Summary of the Invention

[0004] To solve the above problems, the present invention proposes an ammonia - blended combustion system and method for a coal - fired boiler based on high - temperature and strong reduction, which couples oxygen - enriched combustion with deep air staging technology. On the one hand, the relatively high oxygen concentration of the secondary air promotes the ignition of ammonia fuel and creates high - temperature conditions. On the other hand, the lower excess air coefficient in the main combustion zone maintains a reducing atmosphere. At the same time, the position of the burnout air entering the furnace is raised to create an ideal high - temperature and strong - reduction atmosphere in the ammonia - coal co - combustion boiler.

[0005] The coal-fired boiler ammonia combustion system based on high temperature strong reduction of the present invention comprises an ammonia coal-fired boiler body; the ammonia coal-fired boiler body is sequentially provided with a main combustion zone and an original burnout air zone from bottom to top;

[0006] The primary air nozzle and the secondary air nozzle are installed in the main combustion zone, and the secondary air nozzle is located above the primary air nozzle; the primary air nozzle is connected to the pulverized coal pipeline, the ammonia pipeline and the primary air pipeline respectively through a four-way joint; the secondary air nozzle is connected to the combustion-supporting oxygen pipeline and the secondary air pipeline respectively through a three-way joint; the combustion-supporting oxygen pipeline is installed with an oxygen valve;

[0007] The original burnout wind zone is provided with an original burnout wind nozzle and a high burnout wind nozzle, and the high burnout wind nozzle is located above the original burnout wind nozzle; the original burnout wind nozzle and the high burnout wind nozzle are both connected to the burnout wind air duct.

[0008] Furthermore, a high burnout wind zone is provided in the original burnout wind zone; the high burnout wind zone includes a spraying area of a high burnout wind nozzle.

[0009] Furthermore, the combustion-supporting oxygen pipeline is connected to the oxygen output end of the water electrolysis equipment in the green ammonia process at one end away from the ammonia-coal blended combustion boiler body.

[0010] As a preferred embodiment, the excess air coefficient of the main combustion zone is controlled below 0.7.

[0011] Furthermore, the pulverized coal pipeline, ammonia pipeline, primary air pipeline, secondary air pipeline and the connection points between the original overburnt air nozzle and high overburnt air nozzle and the overburnt air pipeline are respectively installed with switch valves.

[0012] The ammonia-blended combustion method for a coal-fired boiler based on high-temperature strong reduction of the present invention comprises the following steps:

[0013] When pure coal is burning, pulverized coal and primary air enter the main combustion zone from the primary air nozzle; open the switch valve at the burnout air duct connected to the original burnout air nozzle, and close the switch valve at the burnout air duct connected to the high burnout air nozzle, so that the original burnout air nozzle is opened and the high burnout air nozzle is closed; at the same time, keep the oxygen valve closed, and the furnace is in a conventional air staged combustion state;

[0014] When ammonia is co-fired, first, ammonia and pulverized coal are mixed and enter the main combustion zone from the primary air nozzle. The volatile matter in the pulverized coal promotes the ignition and combustion of ammonia. Second, an oxygen-enriched combustion strategy is adopted. The oxygen valve is opened. In addition to hot air, oxygen is additionally supplied through the combustion-supporting oxygen pipeline at the secondary air nozzle, increasing the oxygen concentration of the secondary air in the main combustion zone and raising the temperature of the main combustion zone. Third, the air volume in the secondary air pipeline is reduced, strengthening the reducing atmosphere in the main combustion zone and further increasing the temperature of the main combustion zone. Fourth, the original burnout air nozzle is closed, and the high burnout air nozzle is opened, delaying the time when the burnout air enters the furnace and maintaining a high-temperature and strong reducing atmosphere in a large space inside the furnace to inhibit the generation of NO x while promoting the reduction of NO by NH3, CO, and coke. x

[0015] As a preferred embodiment, when ammonia is co-fired, since the original burnout air nozzle is closed and the high burnout air nozzle is opened, the actual area of the main combustion zone expands upward, including the area below the high burnout air nozzle in the original burnout air zone.

[0016] Compared with the prior art, the ammonia co-firing combustion system and method for a coal-fired boiler based on high-temperature and strong reduction of the present invention integrate the effect of increasing the combustion temperature by oxygen-enriched combustion and the effect of maintaining a strong reducing atmosphere in the main combustion zone by deep air staging; creating a high-temperature and strong reducing atmosphere in an ammonia-coal co-fired boiler, improving the ignition conditions of ammonia while increasing the combustion temperature in the main combustion zone, and at the same time inhibiting the conversion of N elements in ammonia fuel to NO x to ensure that the NO x emissions meet environmental protection requirements; and there is no need to specially set up a pure ammonia burner, and the transformation cost is relatively low; and the oxygen used for oxygen-enriched combustion comes from the electrolyzed water link in the green ammonia production process, and the overall economy is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic structural diagram of the whole of the present invention.

[0018] The markings of each component in the drawings are as follows: 1 - ammonia-coal co-fired boiler body, 2 - main combustion zone, 3 - original burnout air zone, 4 - high burnout air zone, 5 - primary air nozzle, 6 - secondary air nozzle, 7 - original burnout air nozzle, 8 - high burnout air nozzle, 9 - combustion-supporting oxygen pipeline, 10 - oxygen valve, 11 - secondary air pipeline, 12 - burnout air pipeline, 13 - pulverized coal pipeline, 14 - ammonia pipeline, 15 - primary air pipeline, 16 - on-off valve. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] As Figure 1 shown, the ammonia co-firing combustion system for a coal-fired boiler based on high-temperature and strong reduction includes an ammonia-coal co-fired boiler body 1; inside the ammonia-coal co-fired boiler body 1, a main combustion zone 2 and an original burnout air zone 3 are sequentially arranged from bottom to top; ​

[0020] In the main combustion zone 2, a primary air nozzle 5 and a secondary air nozzle 6 are installed, and the secondary air nozzle 6 is located above the primary air nozzle 5. The primary air nozzle 5 is respectively connected to a pulverized coal pipeline 13, an ammonia pipeline 14, and a primary air pipeline 15 through a four-way joint. The secondary air nozzle 6 is respectively connected to a combustion-supporting oxygen pipeline 9 and a secondary air pipeline 11 through a three-way joint. An oxygen valve 10 is installed on the combustion-supporting oxygen pipeline 9.

[0021] In the original burnout air zone 3, an original burnout air nozzle 7 and a high burnout air nozzle 8 are installed, and the high burnout air nozzle 8 is located above the original burnout air nozzle 7. Both the original burnout air nozzle 7 and the high burnout air nozzle 8 are connected to a burnout air pipeline 12.

[0022] Among them, a high burnout air zone 4 is arranged in the original burnout air zone 3. The high burnout air zone 4 includes the jet area of the high burnout air nozzle 8. One end of the combustion-supporting oxygen pipeline 9 away from the ammonia-coal co-firing boiler body 1 is connected to the oxygen output end (not shown) of the electrolytic water equipment in the green ammonia process. The excess air coefficient of the main combustion zone 2 is controlled below 0.7 to ensure a strong reducing atmosphere in the main combustion zone 2. Switch valves 16 are respectively installed at the connections of the pulverized coal pipeline 13, the ammonia pipeline 14, the primary air pipeline 15, the secondary air pipeline 11, and the original burnout air nozzle 7 and the high burnout air nozzle 8 with the burnout air pipeline 12.

[0023] The ammonia-coal co-firing method for a coal-fired boiler based on high-temperature strong reduction of the present invention includes the following steps:

[0024] During pure coal combustion, pulverized coal and primary air enter the main combustion zone 2 from the primary air nozzle 5. The switch valve 16 at the connection of the burnout air pipeline 12 connected to the original burnout air nozzle 7 is opened, and the switch valve 16 at the connection of the burnout air pipeline 12 connected to the high burnout air nozzle 8 is closed, so that the original burnout air nozzle 7 is opened and the high burnout air nozzle 8 is closed. At the same time, the oxygen valve 10 is kept closed, and the furnace is in a conventional air staging combustion state.

[0025] When ammonia is co-fired, first, ammonia and pulverized coal are mixed and enter the main combustion zone 2 from the primary air nozzle 5, and the volatile matter in the pulverized coal promotes the ignition and combustion of ammonia. Secondly, an oxygen-enriched combustion strategy is adopted. The oxygen valve 10 is opened, and in addition to hot air being introduced at the secondary air nozzle 6, oxygen is additionally supplied through the combustion-supporting oxygen pipeline 9 to increase the oxygen concentration of the secondary air in the main combustion zone 2 and raise the temperature of the main combustion zone 2. Thirdly, the air volume in the secondary air pipeline 11 is reduced to strengthen the reducing atmosphere in the main combustion zone 2 and further raise the temperature of the main combustion zone 2. Thirdly, the original burnout air nozzle 7 is closed and the high burnout air nozzle 8 is opened to delay the time of burnout air entering the furnace, maintaining a high-temperature strong reduction atmosphere in a large space in the furnace, inhibiting the generation of NO x while promoting the reduction of NO by NH3, CO, coke, etc.x Restoration. Among them, when ammonia is co-fired, since the original over-fire air nozzle 7 is closed and the high over-fire air nozzle 8 is opened, the actual area of the main combustion zone 2 expands upward, including the area below the high over-fire air nozzle 4 in the original over-fire air zone 3.

[0026] Example 1:

[0027] Taking a 600 MW front and rear wall opposed fired boiler as an example for research; the numerical simulation calculation results show that when the ammonia co-firing ratio is 50%, if no oxygen-enriched combustion or deep air staging retrofit is carried out, the furnace flue gas temperature drops by more than 100 K; increasing the oxygen concentration of the secondary air to 30% can achieve a furnace temperature level equivalent to the original coal combustion condition, but the NO x emission will increase by 47.2%; on the basis of oxygen-enriched combustion, reducing the excess air coefficient in the main combustion zone to 0.65 and increasing the SOFA air inlet position can create high-temperature and strong reduction conditions in a large space inside the furnace, reducing the NO x emission by 49.6%, while increasing the furnace combustion temperature and meeting the environmental protection requirements.

[0028] The ammonia co-firing combustion system and method for coal-fired boilers based on high-temperature and strong reduction of the present invention couples oxygen-enriched combustion with deep air staging technology, improves the existing ammonia-coal co-firing boiler, creates a high-temperature and strong reduction atmosphere in the ammonia-coal co-firing boiler, and meets the concentration requirement of NO x emission while maintaining high-temperature combustion conditions inside the furnace; by adopting oxygen-enriched combustion, the oxygen concentration in the secondary air is increased, making the combustion reaction more intense and improving the ignition condition of ammonia; in addition, oxygen-enriched combustion means a decrease in the nitrogen flow rate, and the combustion temperature in the main combustion zone is increased; at the same time, adopting a deep air staging strategy to maintain a strong reducing atmosphere in the main combustion zone, inhibiting the transformation of N element into NO x and using the reducibility of ammonia to reduce some of the already generated NO x to N2; the system does not need to add a pure ammonia burner, and the oxygen used in oxygen-enriched combustion comes from the electrolyzed water link in the green ammonia production process, with good overall economy.

[0029] The above embodiments are only preferred embodiments of the present invention. Therefore, all equivalent changes or modifications made according to the structures, features and principles described in the scope of the present invention patent application are included in the scope of the present invention patent application.

Claims

1. A method for ammonia-doped combustion in a coal-fired boiler based on high-temperature strong reduction. The method for ammonia-doped combustion in a coal-fired boiler uses a system for ammonia-doped combustion in a coal-fired boiler based on high-temperature strong reduction. The system for ammonia-doped combustion in a coal-fired boiler includes an ammonia-coal co-firing boiler body. It is characterized in that: The main combustion zone and the original burnout air zone are sequentially arranged in the ammonia-coal mixed combustion boiler body from bottom to top; The primary air nozzle and the secondary air nozzle are installed in the main combustion zone, and the secondary air nozzle is located above the primary air nozzle; the primary air nozzle is connected to the pulverized coal pipeline, the ammonia pipeline and the primary air pipeline respectively through a four-way joint; the secondary air nozzle is connected to the combustion-supporting oxygen pipeline and the secondary air pipeline respectively through a three-way joint; the combustion-supporting oxygen pipeline is installed with an oxygen valve; The original burnout air nozzle and the high burnout air nozzle are installed in the original burnout air zone, and the high burnout air nozzle is located above the original burnout air nozzle; the original burnout air nozzle and the high burnout air nozzle are both connected to the burnout air duct; The pulverized coal pipeline, ammonia pipeline, primary air pipeline, secondary air pipeline and the connection between the original overburnt air nozzle and high overburnt air nozzle and the overburnt air pipeline are respectively installed with switch valves; The coal-fired boiler ammonia-blended combustion method comprises the following steps: When pure coal is burning, pulverized coal and primary air enter the main combustion zone from the primary air nozzle; open the switch valve at the burnout air duct connected to the original burnout air nozzle, and close the switch valve at the burnout air duct connected to the high burnout air nozzle, so that the original burnout air nozzle is opened and the high burnout air nozzle is closed; at the same time, keep the oxygen valve closed, and the furnace is in a conventional air staged combustion state; When ammonia is co-fired, first, ammonia and pulverized coal are mixed and enter the main combustion zone from the primary air nozzle. The volatile matter in the pulverized coal promotes the ignition and combustion of ammonia. Second, an oxygen-enriched combustion strategy is adopted. The oxygen valve is opened. In addition to the hot air introduced at the secondary air nozzle, oxygen is additionally supplied through the combustion-supporting oxygen pipeline, increasing the oxygen concentration of the secondary air in the main combustion zone and raising the temperature of the main combustion zone. Third, the air volume in the secondary air pipeline is reduced, strengthening the reducing atmosphere in the main combustion zone and further raising the temperature of the main combustion zone. Fourth, the original overfire air nozzle is closed and the high overfire air nozzle is opened, delaying the time for overfire air to enter the furnace and maintaining a high-temperature and strong reducing atmosphere in a large space in the furnace to inhibit the generation of NO x while promoting the reduction of NO x by NH3, CO and coke.

2. The ammonia-doped combustion method for a coal-fired boiler based on high-temperature and strong reduction according to claim 1, wherein: A high burnout wind zone is arranged in the original burnout wind zone; the high burnout wind zone includes the injection area of the high burnout wind nozzle.

3. The method for ammonia-doped combustion of a coal-fired boiler based on high-temperature and strong reduction according to claim 1, characterized in that: The combustion-supporting oxygen pipeline is connected to the oxygen output end of the water electrolysis equipment in the green ammonia process at one end away from the ammonia-coal blended combustion boiler body.

4. The method for ammonia-doped combustion of a coal-fired boiler based on high-temperature strong reduction according to claim 1, wherein: The excess air coefficient of the main combustion zone is controlled below 0.

7.

5. The method for ammonia-doped combustion of a coal-fired boiler based on high-temperature strong reduction according to claim 1, wherein: When ammonia is mixed, since the original burnout air nozzles are closed and the high burnout air nozzles are opened, the actual area of the main combustion zone expands upward to include the area below the high burnout air nozzles in the original burnout air zone.

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