A system and method for co-firing ammonia in a counter-firing boiler

Abstract

This invention relates to the field of ammonia co-firing technology, specifically to a system and method for ammonia co-firing in a counter-firing boiler. The system includes a boiler body, a coal supply system, an ammonia preheating system, and an ammonia pre-decomposition system. The coal supply system includes an ammonia pre-decomposition device, a premixing device, and a secondary air fan. The inlet of the air preheating unit in the tail flue of the boiler body is connected to the secondary air fan; the outlet of the air preheating unit is connected to the premixing device; the outlet of the ammonia preheating system is connected to the ammonia pre-decomposition device, and the first outlet of the ammonia pre-decomposition device is connected to the premixing device; the premixing device is connected to the secondary air nozzle of the combustion unit; the coal supply system is connected to the second inlet of the ammonia pre-decomposition device, and the ammonia pre-decomposition device is connected to the primary air nozzle of the combustion unit. The method of this invention solves the problems of increased cost or system complexity in existing ammonia-coal co-firing technologies, as well as the problems of high cost and difficulty in ensuring combustion stability during coal-fired boiler retrofitting.

Description

Technical Field

[0001] This invention relates to the field of coal-fired ammonia blending technology, specifically to a system and method for ammonia blending in a counter-firing boiler. Background Technology

[0002] In the current energy structure, coal-fired power generation plays a crucial role, contributing approximately 29% of primary energy consumption. However, this power generation method also presents significant environmental challenges, particularly the persistently high CO2 emissions from coal-fired boilers. Given the urgency of reducing greenhouse gas emissions in addressing climate change, optimizing coal-fired power generation processes, especially reducing CO2 emissions from coal-fired boilers in thermal power plants, has become a critical issue that urgently needs to be addressed in the energy sector.

[0003] Ammonia, as an emerging zero-carbon hydrogen-rich fuel, boasts advantages such as easy liquefaction, easy storage, and mature production and transportation methods. It also has the potential to serve as a hydrogen carrier, making it a suitable boiler fuel for large-scale CO2 emission reduction. However, directly using ammonia as fuel in coal-fired boilers also presents several challenges. For example, ammonia fuel has a high auto-ignition temperature, high ignition energy, low net calorific value, and potential NOx emission risks. Furthermore, ammonia has a very low combustion rate. Therefore, achieving stable combustion after ammonia-coal co-firing is a pressing issue that needs to be addressed.

[0004] Currently, despite the significant advantages of ammonia as a fuel, the lack of systematic data to support key parameters such as combustion rate, flame structure, ignition temperature, and NOx emissions under various conditions, coupled with the incomplete understanding of the ammonia combustion reaction mechanism, directly limits the direct use of pure ammonia in current coal-fired power units. Therefore, ammonia cannot directly replace coal as a mainstream fuel in the short term.

[0005] Against this backdrop, ammonia-coal co-combustion technology has emerged as an important direction for the thermal power industry to explore ways to reduce CO2 emissions. However, existing ammonia-coal co-combustion technologies mostly rely on the pretreatment of ammonia, such as high-temperature preheating, or the mixing of other flammable gases such as H2 / CH4 and oxygen-enriched combustion. While these technologies can improve the combustion characteristics of ammonia to some extent, they are often accompanied by increased costs or system complexity, such as the need for additional oxygen or fuel gas supply systems.

[0006] Furthermore, retrofitting coal-fired boilers to accommodate ammonia-coal co-firing also faces challenges such as high retrofitting costs and difficulty in ensuring combustion stability. Traditional methods, such as adding a separate ammonia burner or modifying existing combustion units, can achieve ammonia co-firing, but often involve significant changes to the boiler structure, increasing operational risks and maintenance difficulties, and are prone to combustion instability. Summary of the Invention

[0007] To address the issues of increased costs or system complexity associated with existing ammonia-coal co-firing technologies, as well as the high costs and difficulty in ensuring combustion stability during coal-fired boiler retrofitting, this invention aims to provide a system and method for co-firing ammonia in offset combustion boilers. This invention aims to achieve the effective application of ammonia-coal co-firing technology without significantly increasing costs or affecting the stable operation of the boiler.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows.

[0009] The first aspect of this invention provides a system for co-firing ammonia in a counter-firing boiler, comprising a boiler body; further comprising a coal supply system, an ammonia preheating system, and an ammonia pre-decomposition system; the ammonia pre-decomposition system comprising an ammonia pre-decomposition device, a premixing device, and a secondary air fan; an air preheating unit is arranged in the tail flue of the boiler body, the inlet of the air preheating unit being connected to the outlet of the secondary air fan; the outlet of the air preheating unit being connected to the first inlet of the premixing device; the outlet of the ammonia preheating system being connected to the first inlet of the ammonia pre-decomposition device, and the first outlet of the ammonia pre-decomposition device being connected to the second inlet of the premixing device; a combustion unit is configured on the boiler body, the combustion unit having a central air nozzle, a primary air nozzle, and a secondary air nozzle respectively arranged from the inside to the outside; the outlet of the premixing device being connected to the secondary air nozzle of the combustion unit; the air preheating unit being connected to the secondary air nozzle and the central air nozzle of the combustion unit via pipelines; the outlet of the coal supply system being connected to the second inlet of the ammonia pre-decomposition device, and the second outlet of the ammonia pre-decomposition device being connected to the primary air nozzle of the combustion unit.

[0010] This invention, through the co-firing of pulverized coal and ammonia, effectively reduces the amount of pulverized coal required, thereby lowering CO2 emissions from coal-fired boilers. Simultaneously, this invention utilizes the heat from the high-temperature flue gas generated during pulverized coal combustion to pre-decompose ammonia, which improves ammonia combustion efficiency, ensures stable ignition and combustion, and addresses the issues of increased cost or system complexity associated with existing ammonia-coal co-firing technologies, as well as the high costs and difficulty in guaranteeing combustion stability during coal-fired boiler retrofitting.

[0011] Preferably, the ammonia preheating system includes a liquid ammonia storage device, a heat exchange unit, a buffer device, and a power unit; the outlet of the liquid ammonia storage device is connected to the inlet of the heat exchange unit, so that the liquid ammonia released from the liquid ammonia storage device exchanges heat with the heat exchange medium in the heat exchange unit and is heated, and the heated liquid ammonia is converted into ammonia gas; the outlet of the heat exchange unit is connected to the inlet of the power unit, and the outlet of the power unit is connected to the first inlet of the ammonia pre-decomposition system.

[0012] Preferably, the power unit is an induced draft fan, which provides the power to drive ammonia gas to flow into the ammonia pre-decomposition device; an ammonia flow control valve is configured on the connecting pipeline between the buffer device and the induced draft fan to control the flow rate of ammonia gas entering the ammonia pre-decomposition device.

[0013] Preferably, the tail flue of the boiler body is equipped with an economizing unit, the medium outlet of the economizing unit is connected to the inlet of the water pump, the outlet of the water pump is connected to the medium inlet of the heat exchange unit, and the medium outlet of the heat exchange unit is connected to the medium inlet of the economizing unit.

[0014] Preferably, the ammonia pre-decomposition device includes an ammonia pre-decomposition chamber and a pulverized coal reaction channel, wherein the pulverized coal reaction channel is fixedly disposed in the ammonia pre-decomposition chamber; the inlet of the pulverized coal reaction channel is connected to the outlet of the coal supply system, and the outlet of the pulverized coal reaction channel is connected to the primary air nozzle of the combustion unit; the inlet of the ammonia pre-decomposition chamber is connected to the outlet of the ammonia preheating system, and the outlet of the ammonia pre-decomposition chamber is connected to the second inlet of the premixing device.

[0015] Preferably, a backflow prevention valve is provided on the connecting pipeline between the ammonia pre-decomposition device and the premixing device to prevent secondary air from flowing back into the premixing device; a secondary air control valve is provided on the connecting pipeline between the premixing device and the air preheating unit to control the flow rate of secondary air entering the premixing device.

[0016] Preferably, the coal supply system includes a coal supply device and a primary air fan. The outlet of the coal supply device is connected to the second inlet of the ammonia pre-decomposition device, and the connecting pipeline between the coal supply device and the ammonia pre-decomposition device is connected to the outlet of the primary air fan through a branch pipeline.

[0017] Preferably, the ammonia pre-decomposition device is filled with an ammonia decomposition catalyst to achieve rapid decomposition of ammonia. Specifically, the ammonia decomposition catalyst can be purchased directly from the market. For example, the ammonia decomposition catalyst is specifically composed of high-temperature calcined MgO as a support, loaded with the active component Ni and other growth promoters, the other growth promoters being Al2O3. For example, the ammonia decomposition catalyst provided by CN1086151C.

[0018] Preferably, the combustion unit is configured from the inside out with a central air nozzle, a primary air nozzle, an inner secondary air nozzle, and an outer secondary air nozzle; the outlet of the premixing device is connected to the inner secondary air nozzle, the outer secondary air nozzle, and the central air nozzle; the air preheating unit is connected to the inner secondary air nozzle, the outer secondary air nozzle, and the central air nozzle via pipelines; the outlet of the pulverized coal reaction channel of the ammonia pre-decomposition device is connected to the primary air nozzle; and the central air nozzle of the combustion unit is used to supply air to the boiler body.

[0019] A second aspect of the present invention provides a method for co-firing ammonia in a counter-firing boiler, based on the system for co-firing ammonia in a counter-firing boiler described in the first aspect, and the specific method includes the following steps:

[0020] The ammonia preheating system provides preheated ammonia. The preheated ammonia is fed into the ammonia pre-decomposition device for pre-decomposition, where some ammonia is decomposed into hydrogen and nitrogen. The pre-decomposed ammonia, hydrogen, and nitrogen then enter the premixing device. A secondary air fan provides secondary air, which is preheated by an air preheating unit before entering the premixing device and fully mixed with the pre-decomposed ammonia, hydrogen, and nitrogen. This mixture is then fed into the boiler body via a combustion unit for combustion. The coal supply system provides pulverized coal, which is fed into the ammonia pre-decomposition device for preliminary combustion, resulting in some pulverized coal forming incompletely combusted flue gas. The pulverized coal and its incompletely combusted flue gas enter the boiler body via the primary air nozzle of the combustion unit for combustion.

[0021] The preferred method for preheating ammonia is as follows:

[0022] The ammonia preheating system includes a liquid ammonia storage device and a heat exchange unit. The liquid ammonia storage device is used to provide liquid ammonia, which is pumped from the liquid ammonia storage device to the heat exchange unit for preheating and conversion into ammonia gas. A water pump sends part of the circulating hot water from the economizing unit at the tail of the boiler body into the heat exchange unit, and after heat exchange, it re-enters the economizing unit.

[0023] The beneficial effects of this invention are:

[0024] 1. This invention, through the co-firing of pulverized coal and ammonia, effectively reduces the amount of pulverized coal added, thereby lowering CO2 emissions from coal-fired boilers. Simultaneously, this invention utilizes the heat from the high-temperature flue gas generated during pulverized coal combustion to pre-decompose ammonia, which improves ammonia combustion efficiency, ensures stable ignition and combustion, and solves the problems of increased cost or system complexity associated with existing ammonia-coal co-firing technologies, as well as the high costs and difficulty in guaranteeing combustion stability during coal-fired boiler retrofitting.

[0025] 2. This invention improves the ignition performance and stability of pulverized coal mixed with ammonia combustion. This invention utilizes the heat from the high-temperature flue gas generated during the initial combustion of pulverized coal to thermally decompose some ammonia into H2 and N2. The decomposed NH3 / H2 mixture reduces ignition delay time and increases laminar combustion speed by over 100%, thus improving the poor combustion characteristics of NH3 itself. The pre-decomposed ammonia gas containing H2 is thoroughly mixed with secondary air via a premixing device and then enters the boiler furnace through the secondary air nozzle. Compared to pure ammonia, the decomposed NH3 / H2 mixture exhibits a reduction of over 50% in lean-burn limit and an increase of over 50% in rich-burn limit. This wider range of flammability limits and thorough gas mixing provides favorable conditions for the stability of mixed fuel combustion.

[0026] 3. This invention can effectively suppress the formation of nitrogen oxides. This invention does not require external heat to thermally decompose ammonia; instead, it fully utilizes the heat from the high-temperature flue gas of the pulverized coal itself to heat and decompose ammonia. The cooled flue gas after heat exchange, along with the remaining pulverized coal, is injected into the combustion chamber, effectively mitigating the formation of thermal nitrogen oxides.

[0027] 4. This invention can reduce modification costs. This invention does not require modification of the boiler's original swirl burner; it only requires modifying the existing secondary air duct to connect to the premixing device to achieve ammonia co-firing. The co-firing scheme is easy to implement, and after modification, it can achieve single-burning of pulverized coal or co-firing of pulverized coal and ammonia, meeting the needs of different practical situations. Attached Figure Description

[0028] Figure 1 This is a system layout diagram of an offset combustion boiler co-firing ammonia gas according to one embodiment of the present invention.

[0029] Figure 2 This is a schematic diagram of the cross-section of each nozzle of the combustion unit provided in one embodiment of the present invention.

[0030] The attached figures are labeled as follows:

[0031] 1. Liquid ammonia storage device; 2. Heat exchange unit; 3. Buffer device; 4. Premixing device; 5. Coal supply device; 6. Ammonia pre-decomposition device; 7. Boiler body; 8. Economizer unit; 9. Air preheating unit; 10. Secondary air fan; 11. Primary air fan; 12. Combustion unit; 13. Water pump; 14. Exhaust fan; 15. Ammonia flow control valve; 16. Anti-backflow valve; 17. Secondary air control valve; A. Central air nozzle; B. Primary air nozzle; C. Internal secondary air nozzle; D. External secondary air nozzle. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The technical solution of the present invention will be further described below through specific embodiments.

[0035] In the following embodiments, unless otherwise specified, the methods are conventional methods; and the equipment, unless otherwise specified, can be purchased on the market.

[0036] See Figure 1 A system for co-firing ammonia in a counter-fired boiler includes a boiler body 7, a coal supply system, an ammonia preheating system, and an ammonia pre-decomposition system.

[0037] The ammonia pre-decomposition system includes an ammonia pre-decomposition device 6, a premixing device 4, and a secondary air fan 10; an air preheating unit 9 is arranged in the tail flue of the boiler body 7, the inlet of the air preheating unit 9 is connected to the outlet of the secondary air fan 10; the outlet of the air preheating unit 9 is connected to the first inlet of the premixing device 4.

[0038] The outlet of the ammonia preheating system is connected to the first inlet of the ammonia pre-decomposition device 6, and the first outlet of the ammonia pre-decomposition device 6 is connected to the second inlet of the premixing device 4. A combustion unit 12 is mounted on the boiler body 7, and the combustion unit 12 is equipped with a central air nozzle A, a primary air nozzle B, and a secondary air nozzle from the inside out. The outlet of the premixing device 4 is connected to the secondary air nozzle of the combustion unit 12. The air preheating unit 9 is connected to the secondary air nozzle and the central air nozzle A of the combustion unit 12 via pipelines.

[0039] The outlet of the coal supply system is connected to the second inlet of the ammonia pre-decomposition device 6, and the second outlet of the ammonia pre-decomposition device 6 is connected to the primary air nozzle B of the combustion unit 12.

[0040] Specifically, the air preheating unit 9 recovers heat from the flue gas in the tail flue of the boiler body 7 and exchanges heat with the secondary air provided by the secondary air fan 10. The heat-exchanged secondary air then enters the premixing device 4. The ammonia preheating system provides gasified ammonia. The ammonia pre-decomposition device 6 partially decomposes the gasified ammonia, forming hydrogen and nitrogen. The mixture of the partially decomposed ammonia with hydrogen and nitrogen enters the premixing device 4 and is thoroughly mixed with the heat-exchanged secondary air. The mixed gas is then directly fed into the secondary air nozzle of the combustion unit 12. The ammonia is fed into the secondary air nozzle with high swirl intensity and large air volume. This reduces the impact on the original secondary air velocity of the boiler and allows the ammonia to have a high swirl intensity, which is beneficial for the thorough mixing of ammonia with the high-temperature flue gas, achieving stable ignition and combustion of the ammonia.

[0041] In addition, the coal supply system is used to supply pulverized coal, which undergoes preliminary combustion in the ammonia pre-decomposition device 6. Then, the pulverized coal and its incompletely combusted flue gas are directly sent to the primary air nozzle of the combustion unit 12 for further combustion in the boiler body 7, thereby improving the combustion efficiency of pulverized coal while reducing combustion costs.

[0042] This invention, through the co-firing of pulverized coal and ammonia, effectively reduces the amount of pulverized coal required, thereby lowering CO2 emissions from coal-fired boilers. Simultaneously, utilizing the heat from the high-temperature flue gas generated during pulverized coal combustion to pre-decompose ammonia improves combustion efficiency, ensuring stable ignition and combustion. This addresses the issues of increased cost or system complexity associated with existing ammonia-coal co-firing technologies, as well as the high costs and difficulty in guaranteeing combustion stability during coal-fired boiler retrofitting.

[0043] Based on the above embodiments, as a more preferred embodiment, the ammonia preheating system includes a liquid ammonia storage device 1, a heat exchange unit 2, a buffer device 3, and a power unit. The outlet of the liquid ammonia storage device 1 is connected to the inlet of the heat exchange unit 2, so that the liquid ammonia released from the liquid ammonia storage device 1 exchanges heat with the heat exchange medium in the heat exchange unit 2 and is heated, and the heated liquid ammonia is converted into ammonia gas. The outlet of the heat exchange unit 2 is connected to the inlet of the power unit, and the outlet of the power unit is connected to the first inlet of the ammonia pre-decomposition system, so that the ammonia gas enters the ammonia pre-decomposition system under the driving action of the power unit.

[0044] Specifically, the liquid ammonia storage device 1 is used to provide liquid ammonia; the heat exchange unit 2 is used to heat and raise the temperature of the liquid ammonia, converting it into vaporized ammonia gas. The buffer device 3 is used to store the vaporized ammonia gas. In this embodiment of the invention, after the liquid ammonia is heated by the heat exchange unit 2, it is converted into vaporized ammonia gas, which is stored in the buffer device 3. The vaporized ammonia gas enters the ammonia pre-decomposition device 6 under the drive of the power unit, where it undergoes partial decomposition, and the partially decomposed ammonia gas is converted into hydrogen and nitrogen. In this embodiment of the invention, the heat exchange unit 2 is used to convert liquid ammonia into vaporized ammonia gas, and the heat of the heat exchange medium in the heat exchange unit 2 comes from part of the circulating hot water in the economizing unit 8 at the tail of the boiler body 7. This fully utilizes the waste heat of the flue gas at the tail of the boiler body 7, improving the waste heat utilization rate while reducing costs.

[0045] Based on the above embodiments, as a more preferred embodiment, the power unit is an induced draft fan 14, which is used to provide power to drive ammonia gas to flow into the ammonia pre-decomposition device 6.

[0046] Specifically, the ammonia gas supplied by the buffer device 3 is driven by the induced draft fan 14 to flow to the ammonia pre-decomposition device 6.

[0047] Based on the above embodiments, as a more preferred embodiment, an ammonia flow control valve 15 is installed on the connecting pipeline between the buffer device 3 and the induced draft fan 14. The ammonia flow control valve 15 is used to control the flow rate of ammonia entering the ammonia pre-decomposition device 6.

[0048] Specifically, when combustion is performed without ammonia, the ammonia flow control valve 15 after the buffer device 3 can be closed to prevent ammonia from entering the subsequent ammonia pre-decomposition device 6. Simultaneously, the ammonia pre-decomposition device 6 does not require ignition to partially burn the pulverized coal. In this case, the pulverized coal and primary air are directly fed into the primary air nozzle B of the combustion unit 12. Based on the NO content in the exhaust gas... x The ammonia flow rate in the furnace of the boiler body 7 can be adjusted by using the ammonia flow control valve 15 and the induced draft fan. Ammonia and its preheated decomposition gas are mixed with secondary air in the premixing device 4, eliminating the need for extensive modifications to the existing burners and secondary air ducts, thus reducing costs.

[0049] Based on the above embodiments, as a more preferred embodiment, the ammonia pre-decomposition device 6 includes an ammonia pre-decomposition chamber and a pulverized coal reaction channel. The pulverized coal reaction channel is disposed within the ammonia pre-decomposition device 6; both ends of the pulverized coal reaction channel extend out of the ammonia pre-decomposition device 6; the inlet of the pulverized coal reaction channel is connected to the outlet of the coal supply system, and the outlet of the pulverized coal reaction channel is connected to the primary air nozzle of the combustion unit 12. The ammonia pre-decomposition device 6 includes an ammonia pre-decomposition chamber, and the pulverized coal reaction channel is fixedly disposed within the ammonia pre-decomposition chamber. The inlet of the ammonia pre-decomposition chamber is connected to the outlet of the ammonia preheating system, and the outlet of the ammonia pre-decomposition chamber is connected to the second inlet of the premixing device 4.

[0050] Specifically, the ammonia pre-decomposition chamber provides a reaction space for the partial decomposition of ammonia into hydrogen and nitrogen. The pulverized coal reaction channel provides a reaction space for the initial combustion of pulverized coal to form incomplete combustion flue gas. Simultaneously, since the pre-decomposition of ammonia also occurs within the ammonia pre-decomposition device 6, the heat from the pre-decomposition of ammonia can be effectively utilized to achieve the initial combustion of pulverized coal, thereby improving the combustion efficiency of the pulverized coal. In this embodiment of the invention, ammonia is introduced from the side of the ammonia pre-decomposition chamber; the pulverized coal undergoes partial combustion within the pulverized coal reaction channel, and the resulting flue gas does not come into contact with the ammonia, providing heat for the decomposition of ammonia through wall heat exchange.

[0051] Based on the above embodiments, as a more preferred embodiment, the ammonia pre-decomposition system includes an ammonia pre-decomposition device 6, a premixing device 4, a secondary air fan 10, an air preheating unit 9, an anti-backflow valve 16, and a secondary air control valve 17. An anti-backflow valve 16 is installed on the connecting pipeline between the ammonia pre-decomposition device 6 and the premixing device 4 to prevent secondary air from flowing back into the premixing device 4; a secondary air control valve 17 is installed on the connecting pipeline between the premixing device 4 and the air preheating unit 9 to control the flow rate of secondary air entering the premixing device 4; the air preheating unit 9 is connected to the secondary air nozzle and the central air nozzle of the combustion unit 12 via a pipeline to further increase the flow rate of secondary air at the secondary air nozzle and the central air nozzle of the combustion unit 12, so as to provide secondary air with higher swirl intensity and larger air volume at the secondary air nozzle and the central air nozzle of the combustion unit 12.

[0052] Specifically, the vaporized ammonia is buffered in the buffer device 3, and then the ammonia is sent to the ammonia pre-decomposition device 6 by the induced draft fan 14 to be partially decomposed into hydrogen and nitrogen. After that, the gas enters the premixing device 4 and is fully mixed with the secondary air before being sent to the secondary air nozzle of the combustion unit 12.

[0053] Specifically, the anti-backflow valve 16 is a one-way valve. During ammonia-blended combustion, the secondary air control valve 17 is closed, preventing secondary air from entering the premixing device 4; simultaneously, the anti-backflow valve 16 downstream of the premixing device 4 prevents secondary air from flowing back into the premixing device 4. This embodiment of the invention allows control of whether the boiler blends ammonia using the ammonia flow control valve 15, the anti-backflow valve 16, and the secondary air control valve 17. After closing these valves, secondary air is directly supplied to the boiler body 7 from the secondary air nozzle and the central air nozzle of the combustion unit.

[0054] Based on the above implementation methods, as a more preferred implementation method, such as... Figure 2 The combustion unit 12 is equipped with a central air nozzle A, a primary air nozzle B, an inner secondary air nozzle C, and an outer secondary air nozzle D from the inside out. The outlet of the premixing device 4 is connected to the inner secondary air nozzle C, the outer secondary air nozzle D, and the central air nozzle A, respectively. The air preheating unit 9 is connected to the inner secondary air nozzle C, the outer secondary air nozzle D, and the central air nozzle A via pipelines. The outlet of the pulverized coal reaction channel of the ammonia pre-decomposition device 6 is connected to the primary air nozzle B. The central air nozzle A of the combustion unit 12 is used to supply air to the boiler body 7.

[0055] Specifically, the outlet of the premixing device 4 is connected to the inner secondary air nozzle C, the outer secondary air nozzle D, and the central air nozzle A. The inner and outer secondary air nozzles C and D supply secondary air to the boiler body 7; the central air nozzle A supplies central air (air) to the boiler body 7. The central air is provided by the secondary air fan 10, ensuring that its temperature is the same as the secondary air temperature. The function of the central air is to provide a certain amount of oxygen for the initial combustion of pulverized coal and ammonia, control the ignition point, help stabilize the flame, and ensure good mixing of combustibles and air, thereby improving the combustion efficiency of ammonia and pulverized coal in the boiler. After thorough mixing with the inner secondary air in the combustion unit 12, the ammonia is fed into the boiler body 7 through the secondary air nozzle.

[0056] Based on the above embodiments, as a more preferred embodiment, the coal supply system includes a coal supply device 5 and a primary air fan 11. The outlet of the coal supply device 5 is connected to the second inlet of the ammonia pre-decomposition device 6, and the connecting pipeline between the coal supply device 5 and the ammonia pre-decomposition device 6 is connected to the outlet of the primary air fan 11 through a branch pipeline.

[0057] Specifically, the coal supply device 5 provides pulverized coal; the primary air fan 11 provides the power to transport the pulverized coal into the ammonia pre-decomposition device 6. Through the primary air fan 11, the pulverized coal enters the ammonia pre-decomposition device 6 under the power of the primary air, and utilizes the waste heat from the partial decomposition of ammonia to undergo preliminary combustion within the ammonia pre-decomposition device 6, resulting in partial decomposition. The partially decomposed ammonia is converted into incompletely combusted flue gas. The pulverized coal and its incompletely combusted flue gas from the center of the ammonia pre-decomposition device 6 are directly fed into the primary air nozzle B of the combustion unit 12 for further combustion within the boiler body 7. This improves waste heat utilization efficiency while reducing costs.

[0058] Based on the above embodiments, as a more preferred embodiment, the tail flue of the boiler body 7 is equipped with an economizing unit 8. The medium outlet of the economizing unit 8 is connected to the inlet of the water pump 13, the outlet of the water pump 13 is connected to the medium inlet of the heat exchange unit 2, and the medium outlet of the heat exchange unit 2 is connected to the medium inlet of the economizing unit 8.

[0059] Specifically, heat exchange unit 2 is a water bath heat exchanger. Liquid ammonia is pumped from the liquid ammonia storage device 1 to the heat exchange unit 2 for preheating and conversion into ammonia gas, which then enters the buffer device 3. The water in the heat exchange unit 2 is supplied by a water pump 13, which delivers a portion of the circulating hot water from the economizer unit 8 in the tail flue of the boiler body 7. The water pump 13 then provides pressure to allow the heat-exchanged water to re-enter the economizer unit 8, thus achieving water circulation and recycling of waste heat from the flue gas.

[0060] This invention enables partial decomposition of ammonia into H2 and N2 in the ammonia pre-decomposition chamber before it enters the furnace. Simultaneously, the ammonia is fed into the furnace along with secondary air, minimizing its impact on the flow field and enhancing stable combustion. Furthermore, the water-bath heat exchange unit effectively utilizes the heat exchange medium in the boiler's economizer, achieving low-temperature waste heat recovery. Moreover, it eliminates the need to modify the boiler's existing swirl burner; simply connecting the existing secondary air duct to the premixing device allows for ammonia co-firing. This co-firing scheme is easy to implement and can accommodate either single-fuel coal combustion or ammonia-coated coal combustion, meeting the needs of various practical situations.

[0061] Based on the above embodiments, as a more preferred embodiment, the ammonia pre-decomposition device 6 is filled with an ammonia decomposition catalyst to achieve rapid decomposition of ammonia.

[0062] Specifically, ammonia decomposition catalysts are commercially available. For example, an ammonia decomposition catalyst may consist of high-temperature calcined MgO as a support, loaded with the active component Ni and other growth promoters, such as Al2O3. For instance, CN1086151C provides an ammonia decomposition catalyst. The ammonia decomposition catalyst provided in this invention exhibits good catalytic activity, heat resistance, and anti-coking properties, meeting the requirements for catalytic ammonia decomposition under high-temperature conditions.

[0063] The following is a detailed explanation of the application method of the system for co-firing ammonia in a counter-firing boiler.

[0064] A method for co-firing ammonia in a counter-firing boiler includes the following steps:

[0065] Step 1: Liquid ammonia is pumped from the liquid ammonia storage device 1 to the heat exchange unit 2 for preheating and conversion into vaporized ammonia gas; water in the heat exchange unit 2 is pumped by water pump 13 to send part of the circulating hot water in the coal-saving unit 8 at the tail of the boiler, and after heat exchange, it re-enters the coal-saving unit 8.

[0066] Step 2: The vaporized ammonia is buffered in buffer device 3, and then the ammonia is sent to ammonia pre-decomposition device 6 by induced draft fan 14 for pre-decomposition, so that part of the ammonia is decomposed into hydrogen and nitrogen. Then, this part of the mixed gas is sent to premixing device 4 and fully mixed with secondary air.

[0067] Step 3: The air preheating unit 9 is arranged in the flue at the tail of the boiler. The secondary air provided by the secondary air fan 10 is preheated by the air preheating unit 9 and then fully mixed with the preheated ammonia in the premixing device 4. When no ammonia is added, the secondary air is directly sent into the combustion unit 12 through the secondary air duct.

[0068] Step 4: The pulverized coal generated by the coal supply device 5 is carried by the primary air fan 11 into the ammonia pre-decomposition device 6 for preliminary combustion. The pulverized coal and its incompletely combusted flue gas sent from the center of the ammonia pre-decomposition device 6 are directly sent to the primary air nozzle of the combustion unit 12 for further combustion in the boiler body 7.

[0069] In this embodiment of the invention, ammonia gas is introduced through the inner secondary air nozzle C, which has a high swirl intensity and a large air volume. This reduces the impact on the original secondary air velocity in the boiler and allows the ammonia gas to have a high swirl intensity, facilitating thorough mixing with the high-temperature flue gas and achieving stable ignition and combustion. This invention utilizes the heat from the pulverized coal and the high-temperature flue gas generated during combustion to pre-decompose the ammonia gas, thereby improving its combustion efficiency.

[0070] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for co-firing ammonia in a counter-firing boiler, comprising a boiler body (7); characterized in that, It also includes a coal supply system, an ammonia preheating system, and an ammonia pre-decomposition system; The ammonia pre-decomposition system includes an ammonia pre-decomposition device (6), a premixing device (4), and a secondary air fan (10); an air preheating unit (9) is arranged in the tail flue of the boiler body (7), the inlet of the air preheating unit (9) is connected to the outlet of the secondary air fan (10); the outlet of the air preheating unit (9) is connected to the first inlet of the premixing device (4). The outlet of the ammonia preheating system is connected to the first inlet of the ammonia pre-decomposition device (6), and the first outlet of the ammonia pre-decomposition device (6) is connected to the second inlet of the premixing device (4); a combustion unit (12) is configured on the boiler body (7), and the combustion unit (12) is configured with a central air nozzle, a primary air nozzle and a secondary air nozzle from the inside to the outside; the outlet of the premixing device (4) is connected to the secondary air nozzle of the combustion unit (12); the air preheating unit (9) is connected to the secondary air nozzle and the central air nozzle of the combustion unit (12) through a pipeline; The outlet of the coal supply system is connected to the second inlet of the ammonia pre-decomposition device (6), and the second outlet of the ammonia pre-decomposition device (6) is connected to the primary air nozzle of the combustion unit (12).

2. The system for co-firing ammonia in a counter-firing boiler according to claim 1, characterized in that, The ammonia preheating system includes a liquid ammonia storage device (1), a heat exchange unit (2), a buffer device (3), and a power unit; the outlet of the liquid ammonia storage device (1) is connected to the inlet of the heat exchange unit (2) so that the liquid ammonia released by the liquid ammonia storage device (1) can exchange heat with the heat exchange medium in the heat exchange unit (2) and be heated, and the liquid ammonia after heat exchange and heating is converted into ammonia gas; The outlet of the heat exchange unit (2) is connected to the inlet of the power unit, and the outlet of the power unit is connected to the first inlet of the ammonia pre-decomposition system.

3. The system for co-firing ammonia in a counter-firing boiler according to claim 2, characterized in that, The power unit is an induced draft fan (14), which provides the power to drive ammonia to flow into the ammonia pre-decomposition device (6); an ammonia flow control valve (15) is configured on the connecting pipe between the buffer device (3) and the induced draft fan (14) to control the flow rate of ammonia entering the ammonia pre-decomposition device (6).

4. The system for co-firing ammonia in a counter-firing boiler according to claim 2, characterized in that, The tail flue of the boiler body (7) is equipped with an economizing unit (8). The medium outlet of the economizing unit (8) is connected to the inlet of the water pump (13), the outlet of the water pump (13) is connected to the medium inlet of the heat exchange unit (2), and the medium outlet of the heat exchange unit (2) is connected to the medium inlet of the economizing unit (8).

5. The system for co-firing ammonia in a counter-firing boiler according to claim 1, characterized in that, The ammonia pre-decomposition device (6) includes an ammonia pre-decomposition chamber and a pulverized coal reaction channel. The pulverized coal reaction channel is fixedly arranged in the ammonia pre-decomposition chamber. The inlet of the pulverized coal reaction channel is connected to the outlet of the coal supply system, and the outlet of the pulverized coal reaction channel is connected to the primary air nozzle of the combustion unit (12). The inlet of the ammonia pre-decomposition chamber is connected to the outlet of the ammonia preheating system, and the outlet of the ammonia pre-decomposition chamber is connected to the second inlet of the premixing device (4).

6. The system for co-firing ammonia in a counter-firing boiler according to claim 1, characterized in that, A backflow prevention valve (16) is provided on the connecting pipeline between the ammonia pre-decomposition device (6) and the premixing device (4) to prevent secondary air from flowing back into the premixing device (4); a secondary air control valve (17) is provided on the connecting pipeline between the premixing device (4) and the air preheating unit (9) to control the flow rate of secondary air entering the premixing device (4).

7. The system for co-firing ammonia in a counter-firing boiler according to claim 1, characterized in that, The coal supply system includes a coal supply device (5) and a primary air fan (11). The outlet of the coal supply device (5) is connected to the second inlet of the ammonia pre-decomposition device (6). The connecting pipeline between the coal supply device (5) and the ammonia pre-decomposition device (6) is connected to the outlet of the primary air fan (11) through a branch pipeline.

8. The system for co-firing ammonia in a counter-firing boiler according to claim 1, characterized in that, The ammonia pre-decomposition device (6) is filled with an ammonia decomposition catalyst to achieve rapid decomposition of ammonia.

9. A method for co-firing ammonia in a counter-firing boiler, characterized in that, Based on the system for co-firing ammonia in a counter-firing boiler as described in claim 1, the specific method includes the following steps: The ammonia preheating system is used to provide preheated ammonia. The preheated ammonia gas is fed into the ammonia pre-decomposition device (6) for pre-decomposition, so that part of the ammonia gas is decomposed into hydrogen and nitrogen. The pre-decomposed ammonia gas, as well as hydrogen and nitrogen, enter the premixing device (4). The secondary air fan (10) is used to provide secondary air. After being preheated by the air preheating unit (9), the secondary air enters the premixing device (4) and is fully mixed with the pre-decomposed ammonia, hydrogen and nitrogen. Then, it is sent to the boiler body (7) through the combustion unit (12) for combustion. The coal supply system is used to provide pulverized coal. After the pulverized coal is fed into the ammonia pre-decomposition device (6), it undergoes preliminary combustion, causing some of the pulverized coal to form incompletely combusted flue gas. The pulverized coal and its incompletely combusted flue gas enter the boiler body (7) through the primary air nozzle of the combustion unit (12) for combustion.

10. The method for co-firing ammonia in a counter-firing boiler according to claim 9, characterized in that, The preheating method for ammonia is as follows: The ammonia preheating system includes a liquid ammonia storage device (1) and a heat exchange unit (2); the liquid ammonia storage device (1) is used to provide liquid ammonia, which is pumped from the liquid ammonia storage device (1) to the heat exchange unit (2) for preheating and conversion into ammonia. The water pump (13) sends part of the circulating hot water in the coal-saving unit (8) at the tail of the boiler body (7) into the heat exchange unit (2), and after heat exchange, it re-enters the coal-saving unit (8).

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