System and method for mixed combustion of ammonia gas in opposed firing boiler

Abstract

The invention relates to the technical field of coal blending combustion of ammonia gas, in particular to a system and a method for blending combustion of ammonia gas in an opposed firing boiler. The system comprises a boiler body, a coal supply system, an ammonia gas preheating system and an ammonia gas pre-decomposition system, wherein the coal supply system comprises an ammonia gas pre-decomposition device, a premixing device and a secondary fan; an air preheating unit inlet of a tail flue of the boiler body is connected with a secondary fan; an outlet of the air preheating unit is connected with the premixing device; an outlet of the ammonia preheating system is connected with the ammonia pre-decomposition device, and a first outlet of the ammonia pre-decomposition device is connected with the premixing device; the premixing device is connected with a secondary air nozzle of the combustion unit; the coal supply system is connected with a second inlet of the ammonia gas pre-decomposition device, and the ammonia gas pre-decomposition device is connected with the primary air nozzle of the combustion unit. According to the method, the problems that the cost is increased or the system complexity is improved in the existing ammonia-coal mixed combustion technology, and the cost is high and the combustion stability is difficult to guarantee in the coal-fired boiler transformation process are solved.

Description

Technical Field

[0001] The invention relates to the technical field of coal-combined combustion with ammonia, and in particular to a system and method for a counter-combustion boiler mixed combustion with ammonia. Background Art

[0002] In the current energy structure, coal-fired power generation occupies a pivotal position, contributing about 29% of primary energy. However, this power generation method is also accompanied by significant environmental challenges, especially the high CO2 emissions from coal-fired boilers. Given the urgency of reducing greenhouse gas emissions in response to climate change, optimizing the coal-fired power generation process, especially reducing CO2 emissions from coal-fired boilers in thermal power plants, has become a key issue that needs to be urgently addressed in the energy field.

[0003] Ammonia, as an emerging zero-carbon, hydrogen-rich fuel, has the advantages of easy liquefaction, easy storage, mature production and transportation methods, and has the potential to be a hydrogen carrier, so it can be used as a boiler fuel to reduce CO2 emissions on a large scale. However, there are also some problems with the direct use of ammonia as a fuel in coal-fired boilers. For example, ammonia fuel has a high auto-ignition temperature, high ignition energy, low low-quality calorific value, and potential NOx emission risks. In addition, the combustion rate of ammonia is very low. Therefore, achieving stable combustion after ammonia-coal co-combustion has become an urgent problem to be solved.

[0004] At present, although ammonia has significant advantages as a fuel, the key parameters of ammonia fuel combustion under various conditions, such as combustion speed, flame structure, ignition temperature, and NOx emissions, still lack systematic data support, and the reaction mechanism of ammonia combustion is not yet fully understood, which directly limits the direct use of pure ammonia in coal-fired units at this stage. Therefore, in the short term, ammonia energy cannot directly replace coal and become a mainstream fuel.

[0005] In this context, ammonia-coal co-firing technology came into being and became an important direction for the thermal power industry to explore ways to reduce CO2 emissions. However, existing ammonia-coal co-firing technologies mostly rely on pretreatment of ammonia, such as high-temperature preheating, or mixing with other flammable gases such as H2 / CH4 and oxygen-enriched combustion. Although these technologies can improve the combustion characteristics of ammonia to a certain extent, they are often accompanied by increased costs or increased system complexity, such as the need to add additional oxygen supply systems or gas supply systems.

[0006] In addition, the transformation of coal-fired boilers to adapt to ammonia-coal co-firing also faces the problems of high transformation 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 require major changes to the boiler structure, increasing operational risks and maintenance difficulties, and are prone to combustion instability. Summary of the invention

[0007] In order to solve the problems of increased cost or increased system complexity in the existing ammonia-coal co-firing technology, as well as the high cost and difficulty in ensuring combustion stability in the process of coal-fired boiler transformation, the purpose of the present invention is to provide a system and method for mixing ammonia in a hedge combustion boiler. The present 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 the present invention provides a system for mixing ammonia in a counter-combustion boiler, comprising a boiler body; a coal supply system, an ammonia preheating system and an ammonia predecomposition system; the ammonia predecomposition system comprises an ammonia predecomposition device, a premixing device and a secondary fan; an air preheating unit is arranged in the tail flue of the boiler body, the inlet of the air preheating unit is connected to the outlet of the secondary fan; the outlet of the air preheating unit is connected to the first inlet of the premixing device; the outlet of the ammonia preheating system is connected to the first inlet of the ammonia predecomposition device, and the first outlet of the ammonia predecomposition device is connected to the second inlet of the premixing device; a combustion unit is arranged on the boiler body, and the combustion unit is respectively provided 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 is connected to the secondary air nozzle of the combustion unit; the air preheating unit is connected to the secondary air nozzle and the central air nozzle of the combustion unit through a pipeline; the outlet of the coal supply system is connected to the second inlet of the ammonia predecomposition device, and the second outlet of the ammonia predecomposition device is connected to the primary air nozzle of the combustion unit.

[0010] The present invention can effectively reduce the amount of pulverized coal added by mixing pulverized coal with ammonia, thereby reducing the CO2 emissions generated by coal-fired boilers. At the same time, the present invention uses the heat of high-temperature flue gas mixed with pulverized coal to pre-decompose ammonia, which is conducive to improving the combustion efficiency of ammonia, achieving stable ignition and combustion of ammonia, and solving the problems of increased cost or increased system complexity in the existing ammonia-coal mixed combustion technology, as well as the high cost and difficulty in ensuring combustion stability in the process of coal-fired boiler transformation.

[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 by the liquid ammonia storage device can be heat-exchanged and heated with the heat exchange medium in the heat exchange unit, and the liquid ammonia after heat exchange and heating is converted into ammonia; 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 predecomposition system.

[0012] Preferably, the power unit is an induced draft fan, which is used to provide power to drive ammonia to flow toward the ammonia pre-decomposition device; an ammonia flow control valve is arranged on the connecting pipeline between the buffer device and the induced draft fan; and is used to control the flow of ammonia entering the ammonia pre-decomposition device.

[0013] Preferably, the tail flue of the boiler body is provided with a coal-saving unit, the medium outlet of the coal-saving unit is connected to the inlet of a 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 coal-saving unit.

[0014] Preferably, the ammonia predecomposition device comprises an ammonia predecomposition chamber and a pulverized coal reaction channel, wherein the pulverized coal reaction channel is fixedly arranged in the ammonia predecomposition 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 predecomposition chamber is connected to the outlet of the ammonia preheating system, and the outlet of the ammonia predecomposition chamber is connected to the second inlet of the premixing device.

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

[0016] Preferably, the coal supply system includes a coal supply device and a primary 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 fan through a branch pipeline.

[0017] Preferably, the ammonia pre-decomposition device is filled with an ammonia decomposition catalyst for realizing rapid decomposition of ammonia. Specifically, the ammonia decomposition catalyst can be directly purchased on the market. For example, the ammonia decomposition catalyst is specifically composed of high-temperature calcined MgO as a carrier, loaded with active components Ni and other promoters, and the other promoters are Al2O3. For example, the ammonia decomposition catalyst provided by CN1086151C.

[0018] Preferably, the combustion unit is respectively configured with a central air nozzle, a primary air nozzle, an inner secondary air nozzle and an outer secondary air nozzle from the inside to the outside; the outlet of the premixing device is respectively connected to the inner secondary air nozzle, the outer secondary air nozzle and the central air nozzle; the air preheating unit is respectively connected to the inner secondary air nozzle, the outer secondary air nozzle and the central air nozzle through pipelines; the outlet of the pulverized coal reaction channel of the ammonia predecomposition device is connected to the primary air nozzle; the central air nozzle of the combustion unit is used to provide air to the boiler body.

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

[0020] The ammonia preheating system is used to provide preheated ammonia; the preheated ammonia is sent to the ammonia predecomposition device for predecomposition, so that part of the ammonia is decomposed into hydrogen and nitrogen; the predecomposed ammonia, hydrogen and nitrogen enter the premixing device; the secondary fan is used to provide secondary air, which enters the premixing device after being preheated by the air preheating unit, and is fully mixed with the predecomposed ammonia, hydrogen and nitrogen, and then is sent to the boiler body through the combustion unit for combustion; the coal supply system is used to provide pulverized coal, which is sent to the ammonia predecomposition device for preliminary combustion, so that part of the pulverized coal forms incompletely burned flue gas; the pulverized coal and its incompletely burned flue gas enter the boiler body through the primary air nozzle of the combustion unit for combustion.

[0021] Preferably, the preheating method of 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, and the liquid ammonia is pumped from the liquid ammonia storage device to the heat exchange unit for preheating and conversion into ammonia; the water pump sends part of the circulating hot water in the economizer unit at the rear of the boiler body into the heat exchange unit, and re-enters the economizer unit after heat exchange.

[0023] Beneficial effects of the present invention:

[0024] 1. The present invention can effectively reduce the amount of pulverized coal added by mixing pulverized coal with ammonia, thereby reducing the CO2 emissions generated by coal-fired boilers. At the same time, the present invention uses the heat of high-temperature flue gas mixed with pulverized coal to pre-decompose ammonia, which is beneficial to improving the combustion efficiency of ammonia, achieving stable ignition and combustion of ammonia, and solving the problems of increased cost or increased system complexity in the existing ammonia-coal mixed combustion technology, as well as the high cost and difficulty in ensuring combustion stability in the process of coal-fired boiler transformation.

[0025] 2. The present invention can improve the ignition performance of coal powder mixed with ammonia combustion, and improve the stability of coal powder mixed with ammonia combustion. The present invention utilizes the heat of high-temperature flue gas generated by the initial combustion of coal powder to thermally decompose part of the ammonia to produce H2 and N2. The decomposed NH3 / H2 mixed gas can reduce the ignition delay time and increase the laminar combustion speed by more than 100%, so thermally decomposing part of the ammonia into H2 is beneficial to improving the poor combustion characteristics of NH3 itself. After the ammonia pre-decomposed gas containing H2 is fully mixed with the secondary air through the premixing device, it enters the furnace of the boiler body through the secondary air nozzle of the burner. Compared with pure ammonia, the decomposed NH3 / H2 mixed gas has a lean combustion limit reduction and a rich combustion limit increase of more than 50%. The wider range of flammable limits and the full mixing of gases provide favorable conditions for the stability of the combustion of the mixed fuel.

[0026] 3. The present invention can effectively inhibit the generation of nitrogen oxides. In the present invention, no external heat is needed to thermally decompose ammonia, but the heat of the high-temperature flue gas of the coal powder itself is fully utilized to heat and decompose ammonia. The flue gas cooled after heat exchange and the remaining coal powder are sprayed into the combustion chamber, effectively alleviating the generation of thermal nitrogen oxides.

[0027] 4. The present invention can reduce the cost of transformation. The present invention does not need to transform the original swirl burner of the boiler. It only needs to transform the original secondary air duct and connect it to the premixing device to achieve the mixed combustion of ammonia. The mixed combustion scheme is easy to implement, and after the transformation, it can realize the combustion of single pulverized coal or the mixed combustion of pulverized coal and ammonia, which can meet the needs of different actual conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A system layout diagram of a counter-firing boiler with ammonia combustion provided in one embodiment of the present invention.

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

[0030] The accompanying drawings are marked as follows:

[0031] 1. Liquid ammonia storage device; 2. Heat exchange unit; 3. Buffer device; 4. Premixing device; 5. Coal supply device; 6. Ammonia predecomposition device; 7. Boiler body; 8. Coal saving unit; 9. Air preheating unit; 10. Secondary fan; 11. Primary fan; 12. Combustion unit; 13. Water pump; 14. Draft fan; 15. Ammonia flow control valve; 16. Anti-backflow valve; 17. Secondary air control valve; A. Central air nozzle; B. Primary air nozzle; C. Inner secondary air nozzle; D. Outer secondary air nozzle. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0033] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

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

[0035] In the following embodiments, the methods are conventional methods unless otherwise specified; the equipment are commercially available unless otherwise specified.

[0036] See also Figure 1 A system for mixing ammonia with a counter-combustion boiler comprises a boiler body 7, a coal supply system, an ammonia preheating system, and an ammonia predecomposition system.

[0037] The ammonia predecomposition system includes an ammonia predecomposition device 6, a premixing device 4 and a secondary fan 10; an air preheating unit 9 is arranged at the tail flue of the boiler body 7, and the inlet of the air preheating unit 9 is connected to the outlet of the secondary 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 predecomposition device 6, and the first outlet of the ammonia predecomposition device 6 is connected to the second inlet of the premixing device 4; the boiler body 7 is provided with a combustion unit 12, and the combustion unit 12 is respectively provided with a central air nozzle A, a primary air nozzle B 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 of the combustion unit 12 and the central air nozzle A through a pipeline.

[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 is used to recover the flue gas heat in the tail flue of the boiler body 7, and to exchange heat with the secondary air provided by the secondary air fan 10, and the secondary air after heat exchange enters the premixing device 4. The ammonia preheating system is used to provide gasified ammonia; the ammonia predecomposition device 6 is used to partially decompose the gasified ammonia, and partially decompose to form hydrogen and nitrogen. The mixture of partially decomposed ammonia, hydrogen and nitrogen enters the premixing device 4, and is fully mixed with the secondary air after heat exchange in the premixing device 4. The mixed gas is directly sent to the secondary air nozzle of the combustion unit 12. Ammonia is sent into the secondary air nozzle with high swirl intensity and large air volume. On the one hand, it can reduce the impact on the original secondary air speed of the boiler. On the other hand, ammonia can have a higher swirl intensity, which is conducive to the full mixing of ammonia and high-temperature flue gas, and realizes stable ignition and combustion of ammonia.

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

[0042] The embodiment of the present invention can effectively reduce the amount of pulverized coal added by mixing pulverized coal with ammonia, thereby reducing the CO2 emissions generated by coal-fired boilers. At the same time, the heat of the high-temperature flue gas mixed with pulverized coal is used to pre-decompose ammonia, which is conducive to improving the combustion efficiency of ammonia, achieving stable ignition and combustion of ammonia, and solving the problems of increased cost or increased system complexity in the existing ammonia-coal mixed combustion technology, as well as the high cost and difficulty in ensuring combustion stability in the process of coal-fired boiler transformation.

[0043] On the basis of the above-mentioned embodiment, 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 by the liquid ammonia storage device 1 can be heat-exchanged and heated with the heat exchange medium in the heat exchange unit 2, and the liquid ammonia after heat exchange and heating is converted into ammonia; 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 predecomposition system, so that the ammonia can enter the ammonia predecomposition 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 exchange and heat up the liquid ammonia, and convert the liquid ammonia into gasified ammonia. The buffer device 3 is used to store the gasified ammonia. In the embodiment of the present invention, the liquid ammonia is converted into gasified ammonia after the heat exchange and temperature increase of the heat exchange unit 2, and the gasified ammonia is stored in the buffer device 3. The gasified ammonia enters the ammonia pre-decomposition device 6 under the driving action of the power unit, and is partially decomposed in the ammonia pre-decomposition device 6, and the partially decomposed ammonia is converted into hydrogen and nitrogen. In the embodiment of the present invention, the liquid ammonia is converted into gasified ammonia through the heat exchange and temperature increase of the heat exchange unit 2, and the heat of the heat exchange medium of the heat exchange unit 2 comes from part of the circulating hot water in the coal-saving unit 8 at the rear of the boiler body 7. In this way, the waste heat of the flue gas at the rear of the boiler body 7 can be fully utilized, while improving the waste heat utilization rate and reducing costs.

[0045] On the basis of the above embodiment, as a more preferred embodiment, the power unit is an induced draft fan 14 , which is used to provide power to drive the ammonia to flow toward the ammonia pre-decomposition device 6 .

[0046] Specifically, the induced draft fan 14 is used to drive the ammonia provided by the buffer device 3 to flow toward the ammonia pre-decomposition device 6 .

[0047] Based on the above embodiment, as a more preferred embodiment, an ammonia flow control valve 15 is arranged 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 of ammonia entering the ammonia pre-decomposition device 6.

[0048] Specifically, when the combustion is not mixed with 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. At the same time, the center of the ammonia pre-decomposition device 6 does not need to be ignited to partially burn the coal powder. At this time, the coal powder and the primary air will be directly sent to the primary air nozzle B of the combustion unit 12. x The embodiment of the present invention can adjust the ammonia flow rate sent into the furnace of the boiler body 7 through 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, and there is no need to make a lot of modifications to the original burner and secondary air duct, which is low in cost.

[0049] On the basis of the above-mentioned embodiment, as a more preferred embodiment, the ammonia predecomposition device 6 includes an ammonia predecomposition chamber and a pulverized coal reaction channel. A pulverized coal reaction channel is arranged inside the ammonia predecomposition device 6; both ends of the pulverized coal reaction channel pass through the ammonia predecomposition 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 predecomposition device 6 includes an ammonia predecomposition chamber, and the pulverized coal reaction channel is fixedly arranged in the ammonia predecomposition chamber. The inlet of the ammonia predecomposition chamber is connected to the outlet of the ammonia preheating system, and the outlet of the ammonia predecomposition chamber is connected to the second inlet of the premixing device 4.

[0050] Specifically, the ammonia pre-decomposition chamber is used to provide a reaction space for partially decomposing ammonia to form hydrogen and nitrogen. The pulverized coal reaction channel is used to provide a reaction space for initially burning pulverized coal to form incomplete combustion flue gas. At the same time, since the pre-decomposition of ammonia is also within the ammonia pre-decomposition device 6, the heat of the pre-decomposition of ammonia can be effectively utilized to achieve the initial combustion of pulverized coal, thereby improving the combustion efficiency of pulverized coal. In the embodiment of the present invention, ammonia is introduced from the side of the ammonia pre-decomposition chamber; pulverized coal is partially burned in the pulverized coal reaction channel, and the generated flue gas does not contact the ammonia, and heat is provided for the decomposition of ammonia through wall heat exchange.

[0051] On the basis of the above-mentioned embodiment, as a more preferred embodiment, the ammonia pre-decomposition system includes an ammonia pre-decomposition device 6, a pre-mixing device 4, a secondary air blower 10, an air pre-heating unit 9, a backflow prevention valve 16 and a secondary air control valve 17. The connecting pipeline between the ammonia pre-decomposition device 6 and the pre-mixing device 4 is provided with a backflow prevention valve 16 to prevent the secondary air from flowing back into the pre-mixing device 4; the connecting pipeline between the pre-mixing device 4 and the air pre-heating unit 9 is provided with a secondary air control valve 17 to control the flow rate of the secondary air entering the pre-mixing device 4; the air pre-heating unit 9 is connected to the secondary air nozzle and the central air nozzle of the combustion unit 12 through a pipeline to further increase the flow rate of the secondary air nozzle and the central air nozzle of the combustion unit 12, so as to provide secondary air with high swirl intensity and large air volume at the secondary air nozzle and the central air nozzle of the combustion unit 12.

[0052] Specifically, the gasified ammonia is buffered in the buffer device 3, and then the ammonia is sent to the ammonia pre-decomposition device 6 through the induced draft fan 14 to be partially decomposed into hydrogen and nitrogen. After that, this part of 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. When ammonia is mixed and burned, the secondary air control valve 17 is closed, and the secondary air will not enter the premixing device 4; at the same time, the anti-backflow valve 16 behind the premixing device 4 can prevent the secondary air from flowing back into the premixing device 4. The embodiment of the present invention can control whether the boiler is mixed and burned with ammonia through the ammonia flow control valve 15, the anti-backflow valve 16 and the secondary air control valve 17. After closing the ammonia flow control valve 15, the anti-backflow valve 16 and the secondary air control valve 17, the secondary air will be directly sent from the secondary air nozzle of the combustion unit and the central air nozzle into the boiler body 7.

[0054] On the basis of the above-mentioned embodiment, as a more preferred embodiment, Figure 2 The combustion unit 12 is respectively 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 to the outside. The outlet of the premixing device 4 is respectively connected to the inner secondary air nozzle C, the outer secondary air nozzle D and the central air nozzle A; the air preheating unit 9 is respectively connected to the inner secondary air nozzle C, the outer secondary air nozzle D and the central air nozzle A through pipelines; the outlet of the pulverized coal reaction channel of the ammonia predecomposition device 6 is connected to the primary air nozzle B; the central air nozzle A of the combustion unit 12 is used to provide air to the boiler body 7.

[0055] Specifically, the outlet of the premixing device 4 is respectively connected to the inner secondary air nozzle C, the outer secondary air nozzle D and the central air nozzle A, wherein the inner secondary air nozzle C and the outer secondary air nozzle D provide secondary air to the boiler body 7; the central air nozzle A provides central air to the boiler body 7, and the central air is air. The central air is provided by the secondary air fan 10, so that the temperature of the central air is the same as the temperature of the secondary air. The function of the central air is to provide a certain amount of oxygen for the initial combustion of coal powder and ammonia, control the position of the ignition point, help stabilize the flame, ensure a good mixing of combustibles and air, and thus improve the combustion efficiency of ammonia and coal powder in the boiler. After the ammonia is fully mixed with the inner secondary air in the combustion unit 12, it is sent into the boiler body 7 at the secondary air nozzle.

[0056] On the basis of the above embodiment, as a more preferred embodiment, the coal supply system includes a coal supply device 5 and a primary 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 fan 11 through a branch pipeline.

[0057] Specifically, the coal supply device 5 is used to provide pulverized coal; the primary fan 11 is used to provide power for the pulverized coal to be transported into the ammonia pre-decomposition device 6. The primary air is provided by the primary fan 11, and the pulverized coal enters the ammonia pre-decomposition device 6 under the power of the primary air, and uses the waste heat of the partial decomposition of ammonia to perform preliminary combustion in the ammonia pre-decomposition device 6 to cause partial decomposition, and the partially decomposed ammonia is converted into incomplete combustion flue gas. The pulverized coal and its incomplete combustion flue gas sent from the center of the ammonia pre-decomposition device 6 are directly sent to the primary air nozzle B of the combustion unit 12, and further burned in the boiler body 7. In this way, the cost is reduced on the basis of improving the efficiency of waste heat utilization.

[0058] On the basis of the above-mentioned embodiment, as a more preferred embodiment, the tail flue of the boiler body 7 is provided with a coal-saving unit 8, the medium outlet of the coal-saving 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 coal-saving unit 8.

[0059] Specifically, the 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, and then enters the buffer device 3. The water in the heat exchange unit 2 is pumped by the water pump 13 from part of the circulating hot water in the economizer unit 8 of the tail flue of the boiler body 7, and then the water pump 13 provides pressure to allow the water after heat exchange to re-enter the economizer unit 8, thereby realizing the recycling of flue gas waste heat while realizing water circulation.

[0060] The embodiment of the present invention can realize that ammonia is partially decomposed into H2 and N2 in the ammonia pre-decomposition chamber before entering the furnace. At the same time, ammonia is sent into the furnace together with the secondary air, which has little effect on the flow field in the furnace and strengthens the stable combustion of ammonia. Moreover, the water bath heat exchange unit can effectively utilize the heat exchange medium in the boiler's coal-saving unit to achieve low-temperature waste heat recovery for the boiler. At the same time, there is no need to modify the original swirl burner of the boiler. It is only necessary to modify the original secondary air pipeline and connect it to the premixing device to achieve the mixed combustion of ammonia. The mixed combustion scheme is easy to implement, and after the modification, it can realize single coal combustion or ammonia coal mixed combustion, which can meet the needs of different actual situations.

[0061] On the basis of the above-mentioned embodiment, as a more preferred embodiment, the ammonia pre-decomposition device 6 is filled with an ammonia decomposition catalyst for realizing rapid decomposition of ammonia.

[0062] Specifically, the ammonia decomposition catalyst can be directly purchased on the market. For example, the ammonia decomposition catalyst is specifically composed of high-temperature calcined MgO as a carrier, loaded with active components Ni and other promoters, and the other promoters are Al2O3. For example, the ammonia decomposition catalyst provided by CN1086151C. The ammonia decomposition catalyst provided by the embodiment of the present invention has good catalytic activity, heat resistance and coking resistance, and can meet the requirements of catalytic ammonia decomposition under high temperature conditions.

[0063] The following is a detailed description of the application method of the system for blending ammonia into a counter-firing boiler.

[0064] A method for mixing ammonia in a counter-combustion boiler comprises the following steps:

[0065] In 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; the water in the heat exchange unit 2 is pumped by the water pump 13 with part of the circulating hot water in the coal-saving unit 8 at the tail end of the boiler, and re-enters the coal-saving unit 8 after heat exchange.

[0066] In step 2, the gasified ammonia is buffered in the buffer device 3, and then the ammonia is sent to the ammonia pre-decomposition device 6 through the induced draft fan 14 for pre-decomposition, so that part of the ammonia is decomposed into hydrogen and nitrogen, and then the part of the mixed gas is sent to the premixing device 4 and fully mixed with the secondary air.

[0067] In step 3, the air preheating unit 9 is arranged in the flue at the rear of the boiler. The secondary air provided by the secondary 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] In step 4, the pulverized coal produced by the coal supply device 5 is carried by the primary fan 11 into the ammonia predecomposition device 6 for preliminary combustion. The pulverized coal and its incompletely burned flue gas sent from the center of the ammonia predecomposition 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 the embodiment of the present invention, ammonia is introduced into the internal secondary air nozzle C with high swirl intensity and large air volume, which can reduce the impact on the original secondary air velocity of the boiler on the one hand, and on the other hand, ammonia can have a high swirl intensity, which is conducive to the full mixing of ammonia and high-temperature flue gas, and realizes stable ignition and combustion of ammonia. The present invention uses the heat of coal powder and high-temperature flue gas generated by combustion to pre-decompose ammonia, which is conducive to improving the combustion efficiency of ammonia.

[0070] The above are only 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 in the protection scope of the present invention.

Claims

1. A system for mixing ammonia in a counter-combustion boiler, comprising a boiler body (7); characterized in that: It also includes a coal supply system, an ammonia preheating system and an ammonia predecomposition system; The ammonia pre-decomposition system comprises an ammonia pre-decomposition device (6), a pre-mixing device (4) and a secondary fan (10); an air pre-heating unit (9) is arranged at the tail flue of the boiler body (7), the inlet of the air pre-heating unit (9) is connected to the outlet of the secondary fan (10); the outlet of the air pre-heating unit (9) is connected to the first inlet of the pre-mixing device (4); The outlet of the ammonia preheating system is connected to the first inlet of the ammonia predecomposition device (6), and the first outlet of the ammonia predecomposition device (6) is connected to the second inlet of the premixing device (4); the boiler body (7) is provided with a combustion unit (12), and the combustion unit (12) is respectively provided 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 mixing ammonia with a counter-firing boiler according to claim 1 is characterized in that: The ammonia preheating system comprises 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) is heat-exchanged with the heat exchange medium in the heat exchange unit (2) to increase the temperature, and the liquid ammonia after heat exchange and temperature increase 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 mixing ammonia with a counter-firing boiler according to claim 2 is characterized in that: The power unit is an induced draft fan (14) for providing power to drive ammonia to flow toward the ammonia pre-decomposition device (6); an ammonia flow control valve (15) is arranged on the connecting pipeline between the buffer device (3) and the induced draft fan (14) for controlling the flow of ammonia entering the ammonia pre-decomposition device (6).

4. The system for mixing ammonia with a counter-firing boiler according to claim 2 is characterized in that: The tail flue of the boiler body (7) is provided with a coal-saving unit (8), the medium outlet of the coal-saving unit (8) is connected to the inlet of a 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 coal-saving unit (8).

5. The system for mixing ammonia with a counter-firing boiler according to claim 1, characterized in that: The ammonia pre-decomposition device (6) comprises an ammonia pre-decomposition chamber and a pulverized coal reaction channel, wherein 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 mixing ammonia with a counter-firing boiler according to claim 1, characterized in that: A backflow prevention valve (16) is arranged on the connecting pipeline between the ammonia pre-decomposition device (6) and the pre-mixing device (4) to prevent the secondary air from flowing back into the pre-mixing device (4); and a secondary air control valve (17) is arranged on the connecting pipeline between the pre-mixing device (4) and the air preheating unit (9) to control the flow rate of the secondary air entering the pre-mixing device (4).

7. The system for mixing ammonia with a counter-firing boiler according to claim 1, characterized in that: The coal supply system comprises a coal supply device (5) and a primary 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 fan (11) via a branch pipeline.

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

9. A method for mixing ammonia in a counter-combustion boiler, characterized in that: Based on the system for mixing ammonia with the counter-firing boiler according to claim 1, the specific method comprises the following steps: The ammonia preheating system is used to provide preheated ammonia; The preheated ammonia is sent to the ammonia pre-decomposition device (6) for pre-decomposition, so that part of the ammonia is decomposed into hydrogen and nitrogen; the pre-decomposed ammonia, hydrogen and nitrogen enter the premixing device (4); The secondary air fan (10) is used to provide secondary air. The secondary air is preheated by the air preheating unit (9) and then enters the premixing device (4). The secondary air is fully mixed with the pre-decomposed ammonia, hydrogen and nitrogen, and then sent to the boiler body (7) through the combustion unit (12) for combustion. The coal supply system is used to provide pulverized coal, which is fed into the ammonia pre-decomposition device (6) for preliminary combustion, so that part of the pulverized coal forms incompletely burned flue gas; the pulverized coal and its incompletely burned flue gas enter the boiler body (7) through the primary air nozzle of the combustion unit (12) for combustion.

10. The method for mixing ammonia in a counter-firing boiler according to claim 9, characterized in that: The preheating method of ammonia is as follows: The ammonia preheating system comprises a liquid ammonia storage device (1) and a heat exchange unit (2); the liquid ammonia storage device (1) is used to provide liquid ammonia, and the liquid ammonia 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) delivers part of the circulating hot water in the economizer unit (8) at the rear of the boiler body (7) into the heat exchange unit (2), and re-enters the economizer unit (8) after heat exchange.

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