A method and system for reducing nitrogen oxide generation during ammonia coal combustion

Abstract

The present application belongs to the field of pollutant control, and specifically discloses a method and system for reducing the generation of nitrogen oxides during the combustion of ammonia coal. The method is specifically as follows: liquid ammonia is gasified and then subjected to a thermal catalytic reaction to generate hydrogen and nitrogen to obtain an ammonia-blended mixed gas, and whether the ratio of hydrogen to ammonia concentration in the ammonia-blended mixed gas is greater than or equal to a threshold is determined. If so, the ammonia-blended mixed gas is discharged for co-combustion, and if not, the ammonia-blended mixed gas is subjected to a thermal catalytic reaction again. The present application uses the ratio of hydrogen to ammonia concentration in the ammonia-blended mixed gas as a criterion for determining whether it can be co-combusted, and balances the effects of H2 and NH3 on NO during the combustion process. x The influence of the generation is studied, and a calculation formula for the threshold value is proposed, which can flexibly adjust the raw material side according to the actual blending situation, effectively reducing the generation of nitrogen oxides during the combustion of ammonia coal, and there is no need to adjust the combustion side, which will not affect the combustion stability and boiler thermal efficiency, and has the advantages of simple operation and low cost.

Description

Technical Field

[0001] The present application belongs to the field of pollutant control, and more specifically, relates to a method and system for reducing nitrogen oxide generation during ammonia coal combustion. Background Art

[0002] The International Energy Agency has identified the use of hydrogen and ammonia as a key technological pathway to achieving carbon neutrality in sectors such as electricity. Coal is primarily used in my country for power generation. Using hydrogen and ammonia as a partial replacement for coal in existing large-scale coal-fired power plant boilers is a particularly suitable option for my country's coal-based energy system.

[0003] The higher nitrogen content in ammonia fuel leads to NO x Emissions increase sharply. Experimental studies have shown that when the ammonia ratio is greater than 10%, NO x The amount of ammonia generated increases dramatically. Currently, the existing control methods are mainly based on combustion side regulation. CN118794020A discloses a low-nitrogen ammonia coal stable combustion swirl burner, CN115949936A discloses an ultra-low-nitrogen ammonia coal mixed combustion gas-solid two-phase burner with water spraying and hydrogenation, and CN117160203A discloses a dynamic control system and method for flexible ammonia injection in an ammonia-blended coal-fired power plant. The above patents all adjust the burner structure and boiler structure, change the air distribution method and fuel injection method during the combustion process, so as to control NO in the process of ammonia-coal blending combustion. x The generation of NO can be suppressed, but the adjustment of the combustion mode can easily lead to unstable combustion and reduced boiler combustion efficiency. In addition, for coal-fired ammonia-blended boilers, CN112879942A discloses a mixed ammonia fuel thermal power generation system and method, CN114576647A discloses a coal-fired boiler ammonia-blended combustion and nitrogen reduction control system and operation method, and CN117906165A discloses a method for coal-fired boilers to add ammonia to reduce NO. x The above patents set up a multi-stage ammonia injection system and control method in the furnace to use SNCR technology or SCR technology to generate NO x However, this technology is prone to a large amount of ammonia slip during implementation. Furthermore, the SCR catalyst is expensive and has a short service life, resulting in excessively high implementation costs.

[0004] Fuel-side regulation includes adding other substances to the fuel, changing the fuel composition, and regulating NOx during the ammonia-coal co-combustion process. CN115949936A discloses a water-sprayed hydrogenated ultra-low nitrogen ammonia-coal mixed combustion gas-solid two-phase burner, which reduces the concentration of nitrogen oxides produced by combustion by designing the burner structure to spray water during the ammonia co-combustion process. However, adding water during the combustion process may reduce the combustion efficiency of the fuel, and a large amount of water vapor will cause the boiler carbon monoxide emission concentration to be high. CN219414771U discloses a plasma-assisted coal-fired boiler ammonia combustion and NO x Ultra-low emission system, CN115930220A discloses a plasma-assisted coal-fired boiler with ammonia combustion and NO x Ultra-low emission system and method, the above patent uses plasma-assisted thermal catalysis to decompose a small amount of ammonia to form a hydrogen-ammonia mixture, which is injected into the reburning zone to reduce the nitrogen oxides generated when ammonia-coal is mixed in the main combustion zone. When implementing this technology, it is necessary to reasonably control the reburning zone to reduce NO x The content of hydrogen-ammonia mixture and the amount of ammonia added in the main combustion zone can effectively control NO x emissions without affecting the combustion efficiency of the fuel in the main combustion zone. Summary of the Invention

[0005] In response to the defects of the existing technology, the present application provides a method and system for reducing the generation of nitrogen oxides in the ammonia coal combustion process, aiming to solve the problem that the existing combustion-side regulation easily leads to unstable combustion and reduced boiler combustion efficiency.

[0006] According to one aspect of the present application, a method for reducing nitrogen oxide generation during ammonia-coal combustion is provided, specifically comprising: gasifying liquid ammonia and subjecting it to a thermal catalytic reaction to generate hydrogen and nitrogen to obtain an ammonia-blended mixed gas; determining whether the ratio of hydrogen to ammonia concentration in the ammonia-blended mixed gas is greater than or equal to a threshold value; if so, discharging the ammonia-blended mixed gas for co-combustion; if not, subjecting the ammonia-blended mixed gas to a thermal catalytic reaction again until the ratio of hydrogen to ammonia concentration in the ammonia-blended mixed gas is greater than or equal to a threshold value; the threshold value is determined according to the following formula:

[0007] A=

[0008] Where A is the threshold value, X is the ammonia blending ratio of ammonia coal combustion, and the unit is %.

[0009] Through the above technical solution conceived by the present application, compared with the existing technology, the present application limits the concentration ratio of hydrogen to ammonia in the ammonia-blended mixed gas, which can effectively reduce NO in the process of ammonia coal combustion. x Generation.

[0010] As a further preference, when the ammonia blending ratio is less than 20%, flue gas is used to provide heat for liquid ammonia gasification and ammonia thermal catalysis; when the ammonia blending ratio is greater than or equal to 20%, flue gas and steam are used to provide heat for liquid ammonia gasification and ammonia thermal catalysis.

[0011] As a further preference, the outlet flue gas of the air preheater is used to provide heat for the gasification of liquid ammonia, and the outlet flue gas of the economizer is used to provide heat for the thermal catalysis of ammonia.

[0012] According to another aspect of the present application, an ammonia-doping system for reducing nitrogen oxide generation during ammonia-coal combustion is provided. The ammonia-doping system includes a liquid ammonia gasification unit, an ammonia catalytic unit, and a temperature control unit. The liquid ammonia gasification unit is used to gasify liquid ammonia to obtain ammonia and feed it into the ammonia catalytic unit; the ammonia catalytic unit is used to thermally catalyze the ammonia to generate hydrogen and nitrogen, thereby obtaining an ammonia-doped mixed gas. The ammonia catalytic unit is further used to determine whether the ratio of hydrogen to ammonia concentration in the ammonia-doped mixed gas is greater than or equal to a threshold value. If so, the ammonia-doped mixed gas is discharged for co-combustion. If not, the ammonia-doped mixed gas is subjected to a thermal catalytic reaction again. The threshold value is determined using the following formula:

[0013] A=

[0014] Where A is the threshold value, X is the ammonia ratio of ammonia coal combustion, and the unit is %;

[0015] The temperature control unit is connected to the liquid ammonia gasification unit and the ammonia catalysis unit, and is used to provide heat for the liquid ammonia gasification and ammonia thermal catalysis.

[0016] As further preferred, the temperature control unit controls the temperature of ammonia discharged from the liquid ammonia gasification unit to be 20°C to 40°C, and controls the temperature of ammonia before catalysis in the ammonia catalytic unit to be greater than 250°C and the temperature of ammonia during catalysis to be 250°C to 300°C.

[0017] As a further preference, the liquid ammonia gasification unit includes a preset number of liquid ammonia tanks and a gasifier, and each of the liquid ammonia tanks is connected to the gasifier through a liquid ammonia transport pipeline to provide liquid ammonia to the gasifier; a gasification heat exchange pipe is provided inside the gasifier to gasify the liquid ammonia into ammonia through heat exchange, the outlet of the gasification heat exchange pipe is connected to the ammonia catalytic unit, and a thermometer and pressure gauge is provided at its outlet for detecting the temperature and pressure of the ammonia discharged from the liquid ammonia gasification unit.

[0018] As a further preferred embodiment, the ammonia catalytic unit includes a catalyst and a preset number of buffer tanks, the catalyst is connected to the liquid ammonia gasification unit through an ammonia pipeline to provide ammonia to the catalyst; a catalytic tube filled with catalyst is provided inside the catalyst for thermally catalyzing ammonia to generate an ammonia-blended mixed gas, the outlet of the catalytic tube is provided with a gas detection module, and its outlet is respectively connected to the buffer tank and the ammonia recycling module, the gas detection module is used to detect whether the ratio of hydrogen to ammonia concentration in the ammonia-blended mixed gas is greater than or equal to a threshold value, if so, the ammonia-blended mixed gas is sent to the buffer tank, if not, the ammonia-blended mixed gas is sent to the inlet of the catalytic tube through the ammonia recycling module, and the catalytic tube is also provided with a plurality of temperature sensors for detecting the temperature of the ammonia before catalysis and the temperature of the ammonia during catalysis.

[0019] As a further preferred embodiment, the temperature control unit includes a control module and a temperature collection module, a flue gas heating module and a steam heating module connected to the control module. The temperature collection module is connected to the thermometer and the temperature detector to collect measurement values ​​and feed them back to the control module; the flue gas heating module and the steam heating module are respectively connected to the gasifier and the catalyst to pass flue gas and steam into the gasifier and the catalyst for heating under the regulation of the control module, wherein the flue gas heating module is in a normally open state, and the steam heating module is only in an open state when the ammonia blending ratio exceeds 20%.

[0020] As further preferred, the flue gas heating module includes a first flue gas duct, a first switch, a second flue gas duct and a second switch, the first flue gas duct is connected to the catalyst, and the first flue gas duct is connected to the economizer outlet through the first switch; the second flue gas duct is connected to the gasifier, and the second flue gas duct is connected to the air preheater outlet through the second switch.

[0021] As further preferred, the steam heating module includes a steam branch pipeline and a steam switch, the steam branch pipeline is connected to the catalyst and the gasifier in sequence, and the steam branch pipeline is connected to the reheater through the steam switch.

[0022] In general, the above technical solutions conceived by this application have the following technical advantages compared with the existing technologies:

[0023] 1. This application uses the ratio of hydrogen to ammonia concentration in the ammonia-blended gas as the criterion for determining whether it can be blended and burned. By balancing the effects of H2 and NH3 on NO x The influence of the generation of nitrogen oxides was studied and a calculation formula for the threshold value was proposed. Then, the fuel side can be flexibly regulated according to the actual blending situation, effectively reducing the generation of nitrogen oxides during the combustion of ammonia coal. There is no need to regulate the combustion side, which will not affect the combustion stability and boiler thermal efficiency. It has the advantages of simple operation and low cost.

[0024] 2. At the same time, this application stipulates that when the ammonia blending ratio is greater than 20%, steam is introduced to provide heat for liquid ammonia vaporization and ammonia thermal catalysis. This can ensure normal liquid ammonia vaporization and that the temperature of the ammonia before and during catalysis is within the appropriate catalytic temperature, thereby meeting the ammonia blending requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of an ammonia blending system and a boiler system for reducing nitrogen oxide generation during ammonia-coal combustion, as provided in an embodiment of the present application;

[0026] Figure 2 2. This is a schematic structural diagram of a liquid ammonia gasification unit in an ammonia blending system for reducing nitrogen oxide generation during ammonia-coal combustion, provided in an embodiment of the present application;

[0027] Figure 3 2 is a schematic structural diagram of an ammonia catalytic unit in an ammonia-doping system for reducing nitrogen oxide generation during ammonia-coal combustion, provided in an embodiment of the present application;

[0028] Figure 4 This is a schematic diagram of the connection between the temperature control unit and the liquid ammonia gasification unit, the ammonia catalytic unit and the boiler system in the ammonia blending system for reducing the generation of nitrogen oxides in the ammonia coal combustion process provided in an embodiment of the present application.

[0029] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0030] 1: Liquid ammonia vaporization unit, 1-1: Liquid ammonia tank, 1-2: Liquid ammonia transport pipeline, 1-3: Vaporizer, 1-4: Vaporization heat exchange tube, 1-5: Thermobarometer, 2: Ammonia catalytic unit, 2-1: Ammonia pipeline, 2-2: Catalyst, 2-3: Gas detection module, 2-4: Ammonia recirculation module, 2-5: Second control valve, 2-6: Catalytic tube, 2-7: Buffer tank, 2-8: First control valve, 2-9: Thermostat, 3: Temperature control unit, 3-1: Temperature collection module, 3-2: Flue gas heating module, 3-21: First flue gas pipeline, 3-22: Second flue gas pipeline, 3-23: First switch, 3-24: Second switch, 3-3: Steam heating module, 3-31: Steam switch, 3-32: Steam branch pipeline, 4: Flue, 5: Air preheater, 6: SCR, 7: Economizer. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0032] The present application provides a method for reducing nitrogen oxide generation during ammonia coal combustion, specifically comprising: gasifying liquid ammonia and subjecting it to a thermal catalytic reaction to generate hydrogen and nitrogen, thereby obtaining an ammonia-blended mixed gas comprising a mixture of ammonia, hydrogen, and nitrogen; determining whether the ratio of hydrogen to ammonia concentration in the ammonia-blended mixed gas is greater than or equal to a threshold; if so, discharging the ammonia-blended mixed gas for co-combustion; if not, subjecting the ammonia-blended mixed gas to a thermal catalytic reaction again until the ratio of hydrogen to ammonia concentration in the ammonia-blended mixed gas is greater than or equal to the threshold; the threshold is determined according to the following formula:

[0033] A=

[0034] Where A is the threshold value, X is the ammonia ratio of ammonia coal combustion, and the unit is %. For example, when X is 15%, A is 3.53.

[0035] This application uses the ratio of hydrogen to ammonia concentration in the ammonia-blended mixed gas as a criterion for determining whether it can be blended and associates it with the ammonia blending ratio. After ammonia is blended with pulverized coal, the nitrogen in the coal will form HCN during the volatile matter pyrolysis stage and convert into HNO and further generate NO, while the nitrogen in the ammonia will mainly react through two pathways: NH3→H2NO→HNO→NO and NH3→NH2→NNH→N2. When the blending ratio is greater than 10% (calorific value ratio), the HNO content will increase, so after blending ammonia with pulverized coal, NO x The content will increase significantly.

[0036] After ammonia is pre-decomposed, what actually enters the furnace to be mixed with coal powder is H2 and NH3. The relative content of the two is related to the decomposition rate. However, the addition of H2 will lead to an increase in the flame temperature, which will promote the increase in the conversion rate of thermal nitrogen oxides and fuel nitrogen oxides. At the same time, the combustion of H2 will lead to an increase in H free radicals during the combustion process, causing NH3 in the mixing process to be more inclined to the reaction path NH3→H2NO→HNO→NO, and by promoting the reactions N2O + H<=>NH + NO and HNO + H<=>NO+ H2, the nitrogen in NH3 is promoted to NO x As the fuel nitrogen content decreases, fuel nitrogen is converted to NO x The conversion rate of NO will also increase to a certain extent. Therefore, it is necessary to reasonably control the pre-decomposition rate of ammonia so that the reduction of fuel nitrogen content will have a positive effect on NO x In the embodiment, we control the concentration ratio of hydrogen / ammonia after ammonia decomposition to be greater than a certain value to ensure that the reduction of fuel nitrogen caused by ammonia decomposition has a significant impact on NO xWhen the hydrogen / ammonia concentration ratio is greater than or equal to the threshold we set, the ammonia decomposition rate is guaranteed to be above 50%. At the same time, the calorific value ratio of ammonia to pulverized coal during actual combustion is no higher than 5%, which can effectively reduce the formation of nitrogen oxides during combustion. There is no need to regulate the combustion side, which will not affect combustion stability and boiler thermal efficiency. It has the advantages of simple operation and low cost.

[0037] Furthermore, when the ammonia blending ratio is less than 20%, the flue gas is used to provide heat for liquid ammonia gasification and ammonia thermal catalysis. When the ammonia blending ratio is greater than or equal to 20%, the flue gas and steam are used to provide heat for liquid ammonia gasification and ammonia thermal catalysis. Preferably, the flue gas at the outlet of the air preheater 5 is used to provide heat for liquid ammonia gasification, and the flue gas at the outlet of the economizer 7 is used to provide heat for ammonia thermal catalysis.

[0038] like Figure 1 As shown, according to another aspect of the present application, an ammonia-doping system for reducing the generation of nitrogen oxides during the combustion process of ammonia coal is provided. The ammonia-doping system includes a liquid ammonia gasification unit 1, an ammonia catalytic unit 2, and a temperature control unit 3. The liquid ammonia gasification unit 1 is used to gasify liquid ammonia to obtain ammonia and feed it into the ammonia catalytic unit 2; the ammonia catalytic unit 2 is used to thermally catalyze the ammonia to generate hydrogen and nitrogen, thereby obtaining an ammonia-doped mixed gas. The ammonia catalytic unit 2 is also used to determine whether the ratio of the hydrogen to ammonia concentration in the ammonia-doped mixed gas is greater than or equal to a threshold value. If so, the ammonia-doped mixed gas is discharged for co-combustion. If not, the ammonia-doped mixed gas is re-submitted to a thermal catalytic reaction. The threshold value is determined according to the following formula:

[0039] A=

[0040] Where A is the threshold value, X is the ammonia ratio of ammonia coal combustion, and the unit is %;

[0041] The temperature control unit 3 is connected to the liquid ammonia gasification unit 1 and the ammonia catalysis unit 2 and is used to provide heat for the liquid ammonia gasification and ammonia thermal catalysis.

[0042] Furthermore, the temperature control unit 3 controls the temperature of the ammonia discharged from the liquid ammonia gasification unit 1 to be 20°C to 40°C, and controls the temperature of the ammonia before catalysis in the ammonia catalysis unit 2 to be greater than 250°C and the temperature of the ammonia during catalysis to be 250°C to 300°C.

[0043] Furthermore, the liquid ammonia vaporization unit 1 includes a preset number of liquid ammonia tanks 1-1 and a vaporizer 1-3. Each liquid ammonia tank 1-1 is connected to the vaporizer 1-3 via a liquid ammonia delivery pipeline 1-2 to supply liquid ammonia to the vaporizer 1-3. The specific number of liquid ammonia tanks 1-1 can be determined based on the boiler scale, the ammonia blending ratio range, and the liquid ammonia tank capacity, and is preferably 2 to 4. The number of liquid ammonia delivery pipelines 1-2 is consistent with the number of liquid ammonia tanks 1-1. The vaporizer 1-3 is internally provided with a serpentine multi-row arrangement of vaporization heat exchange tubes 1-4 to vaporize the liquid ammonia into ammonia gas through heat exchange. The outlet of the vaporization heat exchange tubes 1-4 is connected to the ammonia catalytic unit 2, and a thermometer and pressure gauge 1-5 is provided at the outlet for detecting the temperature and pressure of the ammonia gas discharged from the liquid ammonia vaporization unit 1. Preferably, the diameter of the vaporization heat exchange tubes 1-4 gradually increases from the inlet to the outlet, and the inlet to outlet diameter ratio is preferably 1:4 to 1:5.

[0044] In a preferred embodiment of the present application, the ammonia temperature setting is 30°C and the pressure setting is 0.2 MPa. Ammonia vaporization is considered complete when the ammonia temperature deviates from the set temperature by no more than 10K and the pressure exceeds the set pressure. The temperature and pressure are set with reference to the saturation temperature and pressure of ammonia. The temperature and pressure setting values ​​of the ammonia gas should be adjusted as needed to meet the ammonia vaporization conditions.

[0045] Furthermore, the ammonia catalytic unit 2 includes a catalyst 2-2 and a preset number of buffer tanks 2-7. The catalyst 2-2 is connected to the liquid ammonia gasification unit 1 through an ammonia pipeline 2-1 to provide ammonia to the catalyst 2-2; a catalyst tube 2-6 filled with catalyst is provided inside the catalyst 2-2 for thermally catalyzing the ammonia to generate an ammonia-doped mixed gas. The outlet of the catalyst tube 2-6 is provided with a gas detection module 2-3, and its outlet is connected to the buffer tank 2-7 through a first control valve 2-8, and is also connected to the ammonia recycling module 2-4 through a second control valve 2-5. The ammonia recycling module The other end of 2-4 is connected to the inlet of the catalytic tube 2-6. During operation, the gas detection module 2-3 is used to detect whether the ratio of the hydrogen and ammonia concentrations in the ammonia-blended mixed gas is greater than or equal to the threshold value. If so, the first control valve 2-8 is opened to send the ammonia-blended mixed gas into the buffer tank 2-7. If not, the second control valve 2-5 is opened to send the ammonia-blended mixed gas into the catalytic tube 2-6 through the ammonia recycling module 2-4. At the same time, a plurality of temperature detectors 2-9 are also provided on the catalytic tube 2-6 for detecting the temperature at multiple points along the catalytic tube 2-6 to obtain the temperature of the ammonia before catalysis and the temperature of the ammonia during catalysis.

[0046] Preferably, the catalyst is installed in the middle and rear sections of catalytic tubes 2-6, while the front section of catalytic tubes 2-6 is not installed. This is primarily to preheat the ammonia gas to maintain a high temperature during the catalytic reaction and to vaporize and heat any condensed ammonia gas from the previous stage. The number of buffer tanks 2-7 is determined by the actual design scale, preferably 2 to 4.

[0047] In a preferred embodiment of the present application, the ammonia blending ratio is 15%, the hydrogen / ammonia concentration ratio threshold is 2, and the concentration ratio is a volume concentration ratio. When the hydrogen / ammonia concentration ratio is greater than 2, the ammonia decomposition rate is considered to have met the standard, and the ammonia-blended mixed gas is sent to the buffer tank.

[0048] Furthermore, the temperature control unit 3 includes a control module 3-4 and a temperature collection module 3-1, a flue gas heating module 3-2 and a steam heating module 3-3 connected to the control module 3-4. The temperature collection module 3-1 is connected to the thermometer 1-5 and the temperature detector 2-9 to collect measurement values ​​and feed them back to the control module 3-4. The temperature detector 2-9 preferably adopts a corrosion-resistant thermocouple; the flue gas heating module 3-2 and the steam heating module 3-3 are respectively connected to the gasifier 1-3 and the catalyst 2-2 to pass flue gas and steam into the gasifier 1-3 and the catalyst 2-2 for heating under the regulation of the control module 3-4, wherein the flue gas heating module 3-2 is in a normally open state, and the steam heating module 3-3 is in an open state only when the ammonia mixing ratio exceeds 20%, and is used to supplement the heat required by the flue gas heating module 3-2 and the steam heating module 3-3 to avoid excessive extraction of flue gas due to an increase in the ammonia mixing ratio, which affects the safe operation of the boiler;

[0049] The flue gas heating module 3-2 includes a first flue gas duct 3-21, a first switch 3-23, a second flue gas duct 3-22 and a second switch 3-24. The first flue gas duct 3-21 is connected to the catalyst 2-2, and the first flue gas duct 3-21 is connected to the outlet of the economizer 7 through the first switch 3-23, so that the catalyst 2-2 is heated by the flue gas from the outlet of the economizer 7 to ensure that the temperature of the catalyst 2-2 reaches above 300°C. The direction of the flue gas in the catalyst 2-2 is opposite to that of the ammonia gas. The flue gas exhausted from the catalyst 2-2 is returned to the flue 4; the second flue gas duct 3-22 is connected to the gasifier 1-3, and the second flue gas duct 3-22 is connected to the outlet of the air preheater 5 via the second switch 3-24, so that the gasifier 1-3 is heated by the flue gas at the outlet of the air preheater 5, and the flue gas exhausted from the gasifier 1-3 is returned to the flue 4. The flow rate of the flue gas in the economizer 7 and the gasifier 1-3 is controlled by adjusting the opening of the first switch 3-23 and the second switch 3-24;

[0050] The steam heating module 3-3 includes a steam branch pipe 3-32 and a steam switch 3-31. The steam branch pipe 3-32 is connected to the catalyst 2-2 and the gasifier 1-3 in sequence, and the steam branch pipe 3-32 is connected to the reheater through the steam switch 3-31, so that the steam in the reheater is sent to the catalyst 2-2 and the gasifier 1-3 in sequence for heat exchange. The reaction temperature in the catalyst 2-2 is relatively high, so the steam after use still has a certain temperature and can continue to enter the gasifier 1-3 to work.

[0051] In a preferred embodiment of the present application, when the ammonia blending ratio is increased to 25% or 30%, the steam bypass pipe 3-32 is opened to ensure normal gasification of liquid ammonia, the outlet temperature is between 20°C and 40°C, the temperature of ammonia before catalysis is close to 250°C, and the temperature of the catalytic tube 2-6 equipped with the catalyst is maintained at 250°C to 300°C.

[0052] This application utilizes boiler preheating to gasify and decompose ammonia fuel before the furnace, thereby reducing the nitrogen content of the fuel and thus reducing NOx generation while improving boiler efficiency. Based on research on the thermal catalytic decomposition of ammonia into hydrogen, liquid ammonia is transported via a pipeline to the boiler flue gas side. The ammonia is heated in multiple stages using the boiler's waste heat. After vaporization, the liquid ammonia is partially decomposed into hydrogen and nitrogen using a thermal catalytic method, which is then blended with pulverized coal for combustion. The liquid ammonia is pumped into the liquid ammonia transport pipeline 1-2 via a liquid pump and then enters the vaporizer 1-3. The vaporizer 1-3 is installed at the end of the air preheater 5 and uses the low-grade flue gas after the air preheater 5 to heat the liquid ammonia for vaporization. The vaporized ammonia enters the next-stage catalyst 2-2, which is installed between the economizer 7 and the SCR 6. The flue gas is extracted and fed into the catalyst 2-2 to operate. The flue gas extraction rate is adjusted according to the temperature inside the catalyst 2-2 to ensure that the temperature of the catalyst 2-2 remains stable. Inside the catalyst 2-2, there is a serpentine-shaped catalytic tube 2-6, and at the rear of the catalytic tube 2-6, there is a catalyst for catalytically decomposing the incoming hot ammonia. The catalytic ammonia-blended mixed gas, i.e., the hydrogen, ammonia, and nitrogen mixed gas, is transported through a pipeline to the corresponding fuel pipeline of the ammonia-coal blended combustion burner or the pure ammonia burner. This method reduces the total nitrogen content of the boiler fuel and reduces the generation of NO from the source during the ammonia-coal blended combustion process. Without changing the combustion method, NO is reduced. x The generation of carbon monoxide will not affect the normal combustion of the boiler.

[0053] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0054] Additionally, references throughout this specification to "one embodiment," "one embodiment," "an example," or similar language indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present application. Thus, appearances of the phrase "in one embodiment," "in one embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0055] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for reducing nitrogen oxides generation during ammonia coal combustion, characterized in that: Specifically, liquid ammonia is vaporized and then subjected to a thermal catalytic reaction to generate hydrogen and nitrogen to obtain an ammonia-blended mixed gas. It is determined whether the ratio of the concentration of hydrogen to ammonia in the ammonia-blended mixed gas is greater than or equal to a threshold value. If so, the ammonia-blended mixed gas is discharged for co-firing. If not, the ammonia-blended mixed gas is subjected to a thermal catalytic reaction again until the ratio of the concentration of hydrogen to ammonia in the ammonia-blended mixed gas is greater than or equal to the threshold value. The threshold value is determined according to the following formula: A= Where A is the threshold value, X is the ammonia ratio of ammonia coal combustion, and the unit is %.

2. The method according to claim 1, wherein When the ammonia blending ratio is less than 20%, the flue gas is used to provide heat for the gasification of liquid ammonia and the thermal catalysis of ammonia; when the ammonia blending ratio is greater than or equal to 20%, the flue gas and steam are used to provide heat for the gasification of liquid ammonia and the thermal catalysis of ammonia.

3. The method according to claim 1, wherein The outlet flue gas of the air preheater (5) is used to provide heat for the gasification of liquid ammonia, and the outlet flue gas of the economizer (7) is used to provide heat for the thermal catalysis of ammonia.

4. An ammonia blending system for reducing nitrogen oxides generation during ammonia coal combustion, characterized in that: The ammonia blending system comprises a liquid ammonia gasification unit (1), an ammonia catalytic unit (2) and a temperature control unit (3). The liquid ammonia gasification unit (1) is used to gasify liquid ammonia to obtain ammonia and send it to the ammonia catalytic unit (2); the ammonia catalytic unit (2) is used to perform thermal catalysis on ammonia to generate hydrogen and nitrogen, thereby obtaining an ammonia-blended mixed gas. The ammonia catalytic unit (2) is also used to determine whether the ratio of the concentration of hydrogen to ammonia in the ammonia-blended mixed gas is greater than or equal to a threshold value. If so, the ammonia-blended mixed gas is discharged for blending and combustion. If not, the ammonia-blended mixed gas is subjected to thermal catalytic reaction again. The threshold value is determined by the following formula: A= Where A is the threshold value, X is the ammonia ratio of ammonia coal combustion, and the unit is %; The temperature control unit (3) is connected to the liquid ammonia gasification unit (1) and the ammonia catalysis unit (2) and is used to provide heat for liquid ammonia gasification and ammonia thermal catalysis.

5. The ammonia blending system according to claim 4, characterized in that: The temperature control unit (3) controls the temperature of ammonia discharged from the liquid ammonia gasification unit (1) to be 20°C to 40°C, and controls the temperature of ammonia before catalysis in the ammonia catalysis unit (2) to be greater than 250°C and the temperature of ammonia during catalysis to be 250°C to 300°C.

6. The ammonia blending system according to claim 4, characterized in that: The liquid ammonia gasification unit (1) comprises a preset number of liquid ammonia tanks (1-1) and a gasifier (1-3). Each of the liquid ammonia tanks (1-1) is connected to the gasifier (1-3) via a liquid ammonia transport pipeline (1-2) to provide liquid ammonia to the gasifier (1-3). A gasification heat exchange pipe (1-4) is provided inside the gasifier (1-3) to gasify the liquid ammonia into ammonia gas through heat exchange. The outlet of the gasification heat exchange pipe (1-4) is connected to the ammonia catalytic unit (2), and a thermometer (1-5) is provided at the outlet thereof for detecting the temperature and pressure of the ammonia gas discharged from the liquid ammonia gasification unit (1).

7. The ammonia blending system according to claim 6, characterized in that: The ammonia catalytic unit (2) comprises a catalyst (2-2) and a preset number of buffer tanks (2-7). The catalyst (2-2) is connected to the liquid ammonia gasification unit (1) via an ammonia pipeline (2-1) to provide ammonia to the catalyst (2-2). A catalyst tube (2-6) filled with a catalyst is provided inside the catalyst (2-2) for thermally catalyzing the ammonia to generate an ammonia-doped mixed gas. The outlet of the catalyst tube (2-6) is provided with a gas detection module (2-3), and its outlet is respectively connected to the buffer tank (2-7). The tank (2-7) is connected to the ammonia recirculation module (2-4), and the gas detection module (2-3) is used to detect whether the ratio of hydrogen to ammonia concentration in the ammonia-blended mixed gas is greater than or equal to a threshold value. If so, the ammonia-blended mixed gas is sent to the buffer tank (2-7); if not, the ammonia-blended mixed gas is sent to the inlet of the catalytic tube (2-6) through the ammonia recirculation module (2-4). At the same time, a plurality of temperature detectors (2-9) are also provided on the catalytic tube (2-6) for detecting the temperature of the ammonia before catalysis and the temperature of the ammonia during catalysis.

8. The ammonia blending system according to claim 7, characterized in that: The temperature control unit (3) comprises a control module (3-4) and a temperature collection module (3-1), a flue gas heating module (3-2) and a steam heating module (3-3) connected to the control module (3-4). The temperature collection module (3-1) is connected to a thermometer (1-5) and a temperature detector (2-9) for collecting measurement values ​​and feeding them back to the control module (3-4). The flue gas heating module (3-2) and the steam heating module (3-3) are respectively connected to the gasifier (1-3) and the catalyst (2-2) so as to pass flue gas and steam into the gasifier (1-3) and the catalyst (2-2) for heating under the regulation of the control module (3-4). The flue gas heating module (3-2) is in a normally open state, and the steam heating module (3-3) is in an open state only when the ammonia blending ratio exceeds 20%.

9. The ammonia blending system according to claim 8, characterized in that: The flue gas heating module (3-2) comprises a first flue gas duct (3-21), a first switch (3-23), a second flue gas duct (3-22) and a second switch (3-24); the first flue gas duct (3-21) is connected to the catalyst (2-2), and the first flue gas duct (3-21) is connected to the outlet of the economizer (7) via the first switch (3-23); the second flue gas duct (3-22) is connected to the gasifier (1-3), and the second flue gas duct (3-22) is connected to the outlet of the air preheater (5) via the second switch (3-24).

10. The ammonia blending system according to claim 8, characterized in that: The steam heating module (3-3) comprises a steam branch line (3-32) and a steam switch (3-31); the steam branch line (3-32) is connected to the catalyst (2-2) and the gasifier (1-3) in sequence, and the steam branch line (3-32) is connected to the reheater via the steam switch (3-31).

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