A method for injecting dry denitrification agent and its application and dry denitrification process of boiler flue gas

Abstract

The application discloses a kind of dry denitrification agent injection method and its application and dry denitrification process of boiler flue gas.The injection method of the dry denitrification agent is according to the load value of boiler operation, determines that dry denitrification agent is injected from first layer injection device, second layer injection device, third layer injection device, fourth layer injection device or fifth layer injection device, guarantees that flue gas and furnace, horizontal flue or tail flue are injected with dry denitrification agent and mixed to occur sufficient HSR denitrification reaction, and SCR denitrification is coupled, realizes overall efficient denitrification, significantly reduces ammonia escape and prevents air preheater blockage.The application is according to the load value of unit boiler operation, determines that dry denitrification agent is injected from different positions, to meet the flexible peak regulation, deep denitrification and long-term stable operation of unit in multiple scenes in high load, medium load and low load of coal-fired power plant.

Description

Technical Field

[0001] This invention relates to the field of flue gas denitrification technology, specifically to a dry denitrification agent injection method and its application, and a dry denitrification process for boiler flue gas. Background Technology

[0002] In the SCR (Sequencing and Reduction) process for flue gas denitrification in coal-fired power plants, liquid ammonia, ammonia water, or urea-based ammonia are mainly used as the denitrification reducing agent. Liquid ammonia (ammonia water) is a hazardous chemical, highly corrosive, flammable, and explosive, posing a significant hazard. Urea-based ammonia production has high energy consumption and poses a risk of crystallization and pipe blockage. Furthermore, existing SCR denitrification processes suffer from uneven ammonia injection through the grid and uneven flue gas flow, resulting in uneven mixing of ammonia and flue gas at the SCR reactor inlet. This leads to high ammonia escape at the SCR reactor outlet. The escaped ammonia reacts with sulfur trioxide in the flue gas to form ammonium bisulfate (ABS), which deposits in the air preheater and on the electrostatic precipitator electrode plates. This increases the pressure differential in the air preheater, causes blockage, reduces heat exchange efficiency, and affects the efficiency of the electrostatic precipitator. This severely restricts the long-term safe and stable operation of thermal power units. Especially when thermal power plants face further requirements for nitrogen oxide emission reduction and emission standard upgrades, and given that the current fluctuations in wind and solar power necessitate flexible deep peak shaving for thermal power units (note: deep peak shaving leads to SCR reactor inlet flue gas temperatures falling below design values ​​and reduced SCR denitrification efficiency), which has become the norm in the industry, excessive ammonia injection is necessary to achieve nitrogen oxide emission standards. This further accelerates the formation of ammonia superoxide dismutase (ABS) and increases the pressure differential and blockage of the air preheater, resulting in high air preheater exhaust temperatures, increased coal consumption, increased induced draft fan energy consumption, and even significant losses such as abnormal shutdowns. These problems have long been thorny issues plaguing thermal power plants both domestically and internationally and have become a focus of industry attention.

[0003] To address issues such as high ammonia slip, increased air preheater pressure differential, and blockage during SCR denitrification, various methods have been employed, including precise ammonia injection via grilles, hot air purging of the air preheater, increasing SCR flue gas temperature by adding flue bypasses, and installing SCR catalysts. While these methods have alleviated the problems to some extent, they have not fundamentally solved them. Furthermore, these modifications not only involve significant investment but also increase coal consumption, hindering energy conservation and carbon reduction. For example, uneven flue gas flow prevents precise ammonia injection from achieving 100% accuracy; hot air purging of the air preheater is ineffective, resulting in large hot air volumes and high energy consumption; while adding SCR catalysts improves the denitrification rate, it increases wind resistance and energy consumption, and ammonia slip remains high under deep emission reduction requirements; increasing flue gas temperature by adding bypasses leads to increased coal consumption. Therefore, effectively resolving ammonia slip and air preheater blockage remains a crucial and unresolved issue for the thermal power industry for decades.

[0004] Patent document CN 211316226 U discloses a novel and highly efficient combined synergistic denitrification device. This scheme employs a dry powder reaction system, achieving good overall denitrification performance. It uses spray guns to inject dry powder denitrification agent, which mixes thoroughly with the flue gas generated at the bottom of the furnace, causing a denitrification reaction and selectively reducing nitrogen oxides in the flue gas to harmless gases. However, this scheme only involves installing spray guns at a specific location in the furnace and is only suitable for denitrification of flue gas from furnaces with stable loads. With the advancement of the "dual carbon" goal and profound changes in the energy structure, the proportion of intermittent and fluctuating green power generation methods such as wind power and photovoltaics in the power grid is rapidly increasing. To ensure the stability and security of the power grid, coal-fired power plants, as the traditional main power source, are shifting their role from providing stable basic power to becoming flexible regulating power sources undertaking peak-shaving tasks. This means that thermal power units need to adjust loads to adapt to the fluctuations in renewable energy generation; long-term full-load operation has become the exception, while variable load, low load, and high load operation have become the new normal. The current development of wind and solar power, flexible peak shaving of generating units, emission reduction and upgrading, and energy conservation and carbon reduction have brought unprecedented contradictions and problems to the long-term stable operation of thermal power plants. However, despite high investment and operating costs, various upgrading and transformation methods developed by the thermal power industry over the past decades have not yielded satisfactory results in practical engineering applications. Energy structure adjustment has become a long-term national development strategy in my country. Improving denitrification efficiency, reducing ammonia slip, and preventing air preheater blockage in power plant flue gas denitrification are crucial safeguards for promoting national energy structure adjustment and stable development. Therefore, innovative ideas and technologies are urgently needed to solve these long-standing and intractable problems. Summary of the Invention

[0005] This invention addresses the problems of existing technologies by providing a dry denitrification agent injection method and its application, as well as a dry denitrification process for boiler flue gas. By installing injection devices at different locations such as the inner wall of the furnace, the inner wall of the horizontal flue, or the tail flue, the dry denitrification agent is injected from different locations according to different boiler operating load values. This ensures that the flue gas in different temperature zones reacts with the denitrification agent, allowing the agent to fully mix and react with the flue gas, reducing material waste and ammonia slip, thus meeting the needs of flexible peak shaving and deep, efficient denitrification in one or more scenarios of high, medium, and low loads in coal-fired power plants.

[0006] The first objective of this invention is to provide a flue gas denitrification treatment system, comprising a furnace, a horizontal flue, a tail flue, and an SCR reactor. The flue gas generated in the furnace flows to the SCR reactor through the horizontal flue and the tail flue. Injection devices are provided at different positions on the inner wall of the furnace and / or on the inner wall of the horizontal flue and / or on the inner wall of the tail flue. The injection devices are used to inject dry denitrification agents.

[0007] Preferably, the furnace includes a flame deflector; the arrangement of the injection devices at different positions on the inner wall of the furnace includes: a first layer of injection devices arranged on the inner wall of the furnace within a range of three meters above and below the elevation of the flame deflector; a second layer of injection devices arranged above the first layer of injection devices; a third layer of injection devices arranged above the second layer of injection devices; a fourth layer of injection devices arranged on the inner wall of the horizontal flue; and a fifth layer of injection devices arranged on the inner wall of the tail flue.

[0008] Preferably, the distance between the first layer of injection devices and the top of the furnace is d, the distance between the second layer of injection devices and the first layer of injection devices is 1 / 4 to 1 / 3 d, and the distance between the third layer of injection devices and the first layer of injection devices is 2 / 3 to 3 / 4 d. For example, if the distance between the first layer of injection devices and the top of the furnace is 15 m, the distance between the second layer of injection devices and the first layer of injection devices is 4 to 6 m, and the distance between the third layer of injection devices and the first layer of injection devices is 8 to 12 m.

[0009] Preferably, the first, second, third, fourth, and fifth spraying devices are all spray guns arranged in a row.

[0010] Further preferred, the first, second, third, fourth, and fifth spraying devices are selectively activated as needed; and the spray guns in different positions of each spraying device are selectively activated as needed.

[0011] The second objective of this invention is to provide a method for injecting a dry denitrification agent, implemented through the aforementioned flue gas denitrification treatment system. Based on the boiler operating load, the dry denitrification agent is injected from a first-layer injection device, a second-layer injection device, a third-layer injection device, a fourth-layer injection device, or a fifth-layer injection device, ensuring that the flue gas mixes fully with the dry denitrification agent injected into the furnace, horizontal flue, or tail flue to achieve a complete denitrification reaction.

[0012] Preferably, when the boiler operating load is 20%-40% of the rated load, the first layer of injection devices injects dry denitrification agent; when the boiler operating load is 40%-60% of the rated load, the second layer of injection devices injects dry denitrification agent; when the boiler operating load is 60%-80% of the rated load, the third layer of injection devices injects dry denitrification agent; when the boiler operating load is 80%-100% of the rated load, the fourth layer of injection devices injects dry denitrification agent; and when the boiler is overloaded, the fifth layer of injection devices injects dry denitrification agent.

[0013] A third objective of this invention is to provide the application of the aforementioned spraying method in dry denitrification processes.

[0014] The fourth objective of this invention is to provide a dry denitrification process for boiler flue gas, comprising the following steps:

[0015] S1. The dry denitrification agent is injected into the furnace, horizontal flue or tail flue through the first layer injection device, the second layer injection device, the third layer injection device, the fourth layer injection device or the fifth layer injection device, and mixes with the flue gas generated by the combustion in the furnace of the boiler body to carry out a full denitrification reaction, so that the nitrogen oxides in the flue gas are selectively reduced to harmless gases. The remaining unreacted denitrification agent is mixed evenly with the flue gas and then enters the SCR reactor.

[0016] S2. Under the action of the catalyst in the SCR reactor, the concentration of nitrogen oxides in the flue gas reaches the emission standard. The mixture of harmless gas and flue gas is removed by the dust collector and finally discharged through the flue gas outlet chimney.

[0017] Preferably, the temperature inside the furnace is 500℃-1200℃.

[0018] The first, second, third, fourth, and fifth layer injection devices proposed in this invention each include several parallel injection ports and temperature measuring points for monitoring the temperature of each injection port. Each injection port is equipped with a control valve to control the amount of dry denitrification agent delivered.

[0019] In step S2, the harmless gas includes nitrogen, water, and carbon dioxide.

[0020] The SCR reactor proposed in this invention is equipped with a first gas flow meter for detecting nitrogen oxide concentration at the inlet and a second gas flow meter for detecting nitrogen oxide concentration and ammonia slip concentration at the outlet. The SCR reactor contains several layers of catalyst, which includes a support and SCR denitrification active material supported on the support. The support is a hollow honeycomb structure, and the SCR denitrification active material includes one or more of V₂O₅, WO₃, and MoO₃.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The dry denitrification process proposed in this invention not only achieves safe, energy-saving and efficient denitrification, but also significantly reduces ammonia escape, prevents or slows down air preheater blockage, reduces wind resistance and improves heat exchange efficiency.

[0023] 2. This invention provides several injection devices along the path of the flue gas flowing into the SCR reactor, thereby adapting to flue gas under different unit loads and temperature zones. This ensures that the dry denitrification agent injected by the injection devices is fully mixed with the flue gas, and the dry denitrification agent immediately decomposes into ammonia and ammonia free radicals, which react with nitrogen oxides in the flue gas to achieve a denitrification reaction, thereby efficiently and selectively reducing and removing NOx.

[0024] 3. This invention, by incorporating several injection devices along the path of flue gas towards the SCR reactor, activates different numbers and locations of these devices under varying loads. This allows for flexible peak shaving and deep denitrification in one or more scenarios at high, medium, and low loads in coal-fired power plants, achieving ultra-low emissions and even ultra-ultra-low emission requirements. Furthermore, dry denitrification offers significant advantages such as safe operation, no corrosion, non-flammability and non-explosiveness, no wastewater generation, significant energy saving and carbon reduction, significantly reduced ammonia escape, prevention of air preheater blockage, and improved boiler energy efficiency.

[0025] 4. By employing the process technology of this invention for flue gas denitrification, the ammonia injection at the grid in the original SCR denitrification system can be eliminated or reduced. Since liquid ammonia is a major hazard source, its elimination can significantly reduce safety risks for enterprises and reduce the initial investment and operating costs of the SCR denitrification system. Furthermore, using the invented process technology for flue gas denitrification can also reduce the number of catalysts in the original SCR denitrification system. The number of catalyst layers can be reduced by more than one layer compared to the original design, thereby reducing fixed asset investment and system air resistance, achieving energy saving, consumption reduction, and efficiency improvement. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the components of an existing conventional SCR denitrification system;

[0027] Figure 2 This is a schematic diagram of the composition of the flue gas denitrification treatment system provided in the embodiments of this application;

[0028] Figure 3 This is a schematic diagram of the left wall view of the flue gas denitrification treatment provided in the embodiments of this application;

[0029] In the diagram: 1. Furnace; 11. Right wall; 12. Front wall; 110. Flame deflector; 2. Fifth layer injection device; 3. First layer injection device; 4. Second layer injection device; 5. Third layer injection device; 6. Horizontal flue; 61. Horizontal flue roof; 62. Right wall of horizontal flue; 63. Bottom of horizontal flue; 7. Fourth layer injection device; 8. Tail flue; 81. Rear wall of tail flue. Detailed Implementation

[0030] The following embodiments are further illustrations of the present invention, but not limitations thereof.

[0031] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention. Unless otherwise specified, the experimental materials and reagents used herein are commercially available products conventionally available in this technical field.

[0032] like Figure 1 The diagram shown is a schematic of the composition of an existing flue gas denitrification system. It has only one layer of spray guns on the front wall of the furnace and is only suitable for flue gas denitrification in boilers with stable loads.

[0033] The high-efficiency selective reduction (HSR) dry denitrification technology proposed in this invention involves directly injecting the HSR dry denitrification reducing agent into the corresponding high-temperature furnace or high-temperature flue through a dry injection device, completely or partially replacing the ammonia injection at the inlet of the SCR denitrification reactor (hereinafter referred to as the SCR reactor). It has the following advantages:

[0034] Firstly, this technology involves injecting HSR dry denitrification agent into a high-temperature furnace or flue. The dry denitrification agent and its decomposition products can be well mixed with the flue gas, ensuring a complete denitrification reaction. This can thoroughly solve the problems of uneven ammonia injection through the grid and uneven flue gas flow field in the original SCR denitrification system, thereby greatly reducing ammonia escape, preventing the formation of ammonium bisulfate (ABS) from the source, preventing scaling and clogging of the air preheater, improving the heat exchange efficiency of the air preheater, and achieving the goal of energy saving and carbon reduction.

[0035] Secondly, this technology allows for highly efficient selective reduction (HSR) denitrification directly within the high-temperature furnace and flue gas when the denitrification agent is injected. This removes 30%-80% of nitrogen oxides from the flue gas (the denitrification rate can be adjusted as needed, and even higher rates can be achieved). The remaining nitrogen oxides and unreacted denitrification agent are thoroughly mixed and then removed in the subsequent SCR denitrification reactor, thus forming a highly efficient "HSR+SCR" combined denitrification process. Compared to single SCR denitrification, the HSR+SCR combined denitrification efficiency is significantly improved. This not only increases denitrification efficiency but also further reduces ammonia slip and extends the SCR catalyst lifespan by more than 50%. The HSR+SCR combined denitrification process provides a strong guarantee for deep reduction and upgrading of nitrogen oxide emissions in thermal power plants, reducing ammonia slip, and preventing air preheater blockage.

[0036] Finally, the injection devices of this HSR dry denitrification technology are arranged in zones or sections and layers. Each layer of injection devices can intelligently start and stop or intelligently track and adjust according to changes in unit load, thus achieving an adaptive state with the flexible peak shaving of the unit. That is, no matter how the unit load is adjusted, it can achieve efficient denitrification and meet emission standards, completely solving the problem of the original single SCR denitrification process being unable to adapt to the flexible peak shaving of the unit. For example, in the original single SCR denitrification process, when the unit is in flexible peak shaving and the load is low, the flue gas temperature in the SCR reactor drops, the denitrification efficiency decreases, and under the normal ammonia injection state of the grid, nitrogen oxides cannot meet the emission standards. At this time, it is necessary to increase the amount of ammonia injected into the grid (i.e., excessive ammonia injection) to meet the emission standards. However, during this period, due to excessive ammonia injection, ammonia escape is very high, ABS generation is large, and the air preheater pressure difference rises rapidly, which seriously restricts the long-term stable operation of the unit and may even lead to serious problems such as abnormal shutdown.

[0037] like Figure 2 and Figure 3 As shown, the flue gas denitrification treatment system provided by the present invention mainly includes a furnace 1, a horizontal flue 6, a tail flue 8, and an SCR reactor. The flue gas generated in the furnace 1 flows sequentially to the SCR reactor through the horizontal flue 6 and the tail flue 8. Injection devices are provided at different positions on the inner wall of the furnace 1 and / or on the inner wall of the horizontal flue and / or on the inner wall of the tail flue. The injection devices are used to inject dry denitrification agents.

[0038] In the preferred embodiments described below, injection devices are installed on the inner walls of one or more locations in the furnace 1, horizontal flue 6, and tail flue 8 to meet the requirements of different scenarios. This invention, by installing several injection devices along the path of flue gas flow to the SCR reactor, activates different numbers and locations of injection devices under different loads, thereby meeting the requirements of flexible peak shaving and deep denitrification in one or more scenarios of high, medium, and low loads in coal-fired power plants. This ensures that the denitrification agent and flue gas contact and mixing reaction process is always maintained within the optimal reaction temperature range (700℃-950℃). The dry denitrification agent and nitrogen oxides in the flue gas undergo a complete denitrification reaction, and the dry denitrification agent immediately decomposes into ammonia and ammonia free radicals, etc., removing NO... x Highly efficient selective reduction removal:

[0039] NO x +O2+R(NH2) n →N2+H2O+CO2

[0040] The remaining unreacted denitrification agent is mixed evenly with the flue gas and then enters the SCR reactor. Under the action of the catalyst in the SCR reactor, (NH3 + NO) x +O2→N2+H2O), ultimately NO xThe removal rate reaches over 95% to meet ultra-low or ultra-ultra-low emission standards, ensuring that the nitrogen oxide concentration in the flue gas meets the emission requirements of national and local environmental protection authorities. The denitrified flue gas then undergoes heat exchange, dust removal, and wet desulfurization before being discharged through the flue gas outlet, achieving ultra-low emission requirements.

[0041] In the preferred embodiment described below, the furnace 1 is generally rectangular, including a right wall 11, a front wall 12, a rear wall, and a left wall; the area in the furnace 1 where the flue gas bends is the flame deflector 110; as shown below. Figure 2-3 As shown, injection devices are installed at different positions on the inner wall of the furnace 1, including: a first layer of injection devices 3 are installed on the inner walls of the furnace 1 within a three-meter range above and below the flame deflector 110 elevation, namely the inner walls of the front wall 12, rear wall, left wall, and right wall 12, to ensure that the dry denitrification agent injected by the first layer of injection devices 3 and the nitrogen oxides in the flue gas undergo a sufficient denitrification reaction; similarly, a second layer of injection devices 4 and a third layer of injection devices 5 are sequentially installed on the inner wall of the furnace 1 above the first layer of injection devices 3, so that the dry denitrification agent injected by the second layer of injection devices 4 and the third layer of injection devices 5 can undergo a sufficient denitrification reaction with the nitrogen oxides in the flue gas.

[0042] Specifically, the distance between the first layer of injection devices and the top of the furnace is d, the distance between the second layer of injection devices and the first layer of injection devices is 1 / 4 to 1 / 3 d, and the distance between the third layer of injection devices and the first layer of injection devices is 2 / 3 to 3 / 4 d. If the distance between the first layer of injection devices and the top of the furnace is 9 m, the distance between the second layer of injection devices and the first layer of injection devices is 2.25 to 3 m, and the distance between the third layer of injection devices and the first layer of injection devices is 6 to 6.75 m.

[0043] The horizontal flue 6 is preferably rectangular in shape, including a horizontal flue ceiling 61, a horizontal flue bottom 63, a horizontal flue right wall 62, and a horizontal flue left wall (this left wall is on the left side of the horizontal flue, in...). Figure 2 (Obstructed from view and cannot be displayed); a fourth layer of injection devices 7 is provided on the inner walls of the horizontal flue ceiling 61, the bottom 63, the right wall 62, and the left wall of the horizontal flue. The tail flue 8 is preferably rectangular in shape, including the tail flue rear wall 81, and a fifth layer of injection devices 2 is provided on the inner wall of the tail flue rear wall 81.

[0044] The first layer of spraying devices 3, the second layer of spraying devices 4, the third layer of spraying devices 5, the fourth layer of spraying devices 7, and the fifth layer of spraying devices 2 are all spray guns arranged in rows. This row arrangement of spray guns further ensures that the dry denitrification agent sprayed from the spray guns can fully react with the nitrogen oxides in the flue gas to achieve a complete denitrification reaction. The spray guns in different positions within each layer of spraying devices (such as the front wall, rear wall, left wall, right wall, or upper, lower, left, and right, etc.) can be selectively started or stopped as needed, ensuring that the dry denitrification agent sprayed from the spray guns can fully react with the nitrogen oxides in the flue gas to achieve a complete denitrification reaction while preventing waste of the dry denitrification agent.

[0045] In the preferred embodiment described below, a first gas detector for detecting nitrogen oxide concentration and other indicators is installed at the inlet of the SCR reactor, and a second gas detector for detecting nitrogen oxide concentration and other indicators is installed at the outlet, enabling real-time monitoring of nitrogen oxide concentration and other indicators. The SCR reactor contains several layers of catalyst, which includes a support and SCR denitrification active material supported on the support. The support is a honeycomb structure, and the SCR denitrification active material includes one or more of V₂O₅, WO₃, and MoO₃. The catalyst used in the SCR reactor proposed in this invention is not limited to the specifically listed supports and active materials; any catalyst capable of achieving the same technical objective is acceptable.

[0046] The first, second, third, fourth, and fifth injection devices each include several parallel injection ports and temperature measuring points to monitor the temperature of each injection port. Each injection port is equipped with a control valve to control the delivery amount of the dry denitrification agent. Temperature sensors monitor the temperature of the corresponding area of ​​the injection device to ensure that the dry denitrification agent injected by each injection device and the nitrogen oxides in the flue gas undergo a full denitrification reaction while preventing the waste of the dry denitrification agent.

[0047] The dry denitrification agent injection method proposed in this invention is implemented through the above-mentioned flue gas denitrification treatment system. Based on the boiler operating load value, the dry denitrification agent is injected from the first layer injection device 3, the second layer injection device 4, the third layer injection device 5, the fourth layer injection device 7, or the fifth layer injection device 2 to ensure that the flue gas mixes with the dry denitrification agent injected into the furnace, horizontal flue, or tail flue to achieve a sufficient denitrification reaction.

[0048] In the preferred embodiment described below, when the boiler 1 is operating at 20%-40% of its rated load, a dry denitrification agent is injected through a first layer of injection devices 3 installed around the inner wall of the furnace 1 within a three-meter range above and below the flame deflector 110 elevation. Other injection devices are not in operation. At this time, the first layer of injection devices 3 injects the dry denitrification agent, allowing the mixture of the dry denitrification agent and nitrogen oxides in the flue gas to undergo a complete denitrification reaction.

[0049] When the operating load of boiler 1 is 40%-60% of the rated load, the second-layer injection device 4 injects dry denitrification agent, so that the dry denitrification agent and the nitrogen oxides in the flue gas can undergo a full denitrification reaction. Other injection devices do not work.

[0050] When the operating load of boiler 1 is 60%-80% of the rated load, the third-layer injection device 5 injects dry denitrification agent, so that the dry denitrification agent and the nitrogen oxides in the flue gas undergo a full denitrification reaction, and other injection devices do not work.

[0051] When the operating load of boiler 1 is 80%-100% of the rated load, the fourth injection device 7 injects dry denitrification agent, so that the dry denitrification agent and the nitrogen oxides in the flue gas undergo a full denitrification reaction, and other injection devices do not work.

[0052] When boiler 1 is overloaded, the fifth injection device injects dry denitrification agent, so that the dry denitrification agent and the nitrogen oxides in the flue gas can undergo a full denitrification reaction, and the other injection devices do not work.

[0053] Example 1

[0054] A dry denitrification process for flue gas from coal-fired boilers, used to treat flue gas from 300 MW coal-fired boilers in thermal power plants or combined heat and power plants with an average NOx concentration of 500 mg / m³ at the inlet of the original SCR denitrification reactor, includes the following steps:

[0055] S1. The boiler operating load is 30% of the rated load. The first layer of injection devices (multiple spray guns arranged in rows, with a horizontal spacing of 1-3 meters, evenly distributed, 10 sets on the front wall, 5 sets on the left wall, and 5 sets on the right wall) is installed within a 3-meter range above and below the 110mm elevation of the flame deflector on the inner wall of the furnace. When the unit load increases, one of the second to fifth layers of spray guns should be activated as needed. The unit's average daily load is approximately 75%, with a minimum load of 30% and a maximum load of 98%, varying according to grid dispatch requirements. HSR dry denitrification agent is injected using pneumatic conveying (simultaneously, the original ammonia injection through the grid is gradually stopped). The denitrification agent mixes thoroughly with the flue gas generated from combustion at the bottom of the boiler furnace, resulting in a selective reduction reaction (HSR). The dry denitrification agent decomposes into active ammonia and amino groups, reducing some NOx to nitrogen, water, and carbon dioxide, achieving a removal rate of 75%. The remaining unreacted denitrification agent and unremoved nitrogen oxides are mixed evenly in the flue gas and then enter the SCR reactor along with the flue gas.

[0056] The first gas detector at the inlet of the S2 and SCR reactors detected a 75% decrease in NOx concentration in the flue gas. Two layers of honeycomb catalyst (loaded with active materials such as V2O5 and WO3) are installed inside the SCR reactor. Under the action of the catalyst, a denitrification reaction occurs: NH3 + NOx + O2 → N2 + H2O, further removing NOx from the flue gas. The second gas detector at the outlet of the SCR reactor detected a further 20% decrease in NOx concentration. The residual NOx concentration in the flue gas is 13 mg / Nm³ (in existing technologies using urea-based ammonia production, grid ammonia injection, and single SCR denitrification, the residual NOx concentration is less than 42 mg / Nm³). The method in this embodiment not only meets the requirements for ultra-low emissions (less than 50 mg / m³) but also ultra-ultra-low emissions (less than 20 mg / m³). Furthermore, compared to existing technologies using grid ammonia injection and single SCR denitrification, in this embodiment, after injecting dry denitrification agent into the furnace, the ammonia escape concentration at the SCR reactor outlet also decreases from 3.5 mg / Nm³ to 0.3 mg / Nm³. The ammonia slip concentration decreased significantly, resulting in a reduction of ammonium bisulfate (ABS) formation by over 90%. This prevented rapid deposition and clogging of ABS on the air preheater surface, reducing the air preheater downtime flushing cycle from 3-4 times per year to a simple flushing during a major overhaul once a year. The air preheater exhaust temperature decreased by an average of 15°C (corresponding to a coal saving of approximately 1.5% for the unit). Therefore, by replacing urea-based ammonia production and grid-based ammonia injection with in-furnace dry denitrification agent, and forming a coupled process of in-furnace HSR dry denitrification and SCR denitrification, significant improvements in denitrification efficiency were achieved. This also provided a strong guarantee for improving air preheater heat exchange efficiency, reducing induced draft fan power consumption, and ensuring long-term stable operation of the unit.

[0057] In this embodiment, the HSR dry denitrification agent has no energy loss during use. Compared with urea-based ammonia production and grid-injected ammonia SCR denitrification, the HSR dry denitrification agent dosage is basically equivalent to that of urea, with a daily dosage of 6.4-6.6 tons / day for both. The comprehensive energy consumption for urea-based ammonia production is 1000 yuan / ton of denitrification agent, resulting in a total daily energy cost of approximately 6500 yuan / day, which is 6500 yuan / day more than that of dry powder denitrification agent injection. Furthermore, due to the significant reduction in ABS production, the air preheater no longer gets clogged, and the flue gas temperature decreases, resulting in a 1.5% coal saving, an average daily coal saving of 38 tons, and an average daily coal saving of 38 tons * 700 yuan / ton = 26730 yuan / day. It is evident that, compared with the original urea-based ammonia production and single SCR denitrification, the process technology of this invention not only significantly improves denitrification efficiency and achieves deep reduction and ultra-low emissions of nitrogen oxide pollutants, but also significantly reduces operating costs, saving an average of 6,500 yuan + 26,730 yuan = 33,230 yuan per day.

[0058] Example 2

[0059] Similar to Example 1, except that: the boiler is a 300 MW coal-fired boiler, and the operating load is 50% of the rated load. HSR dry denitrification agent is sprayed through the second layer of injection devices (arranged 5 m above the first layer of injection devices on the inner wall of the furnace, with multiple spray guns arranged in a row, with a horizontal spacing of 1-3 meters, evenly distributed, 10 sets on the front wall, 5 sets on the left wall, and 5 sets on the right wall; when the unit load increases or decreases, one of the other four layers of spray guns should be activated as appropriate) while the grid ammonia injection is stopped. The daily dry denitrification agent injection rate is 6.1-6.3 tons / day (equivalent to the urea injection rate for single SCR denitrification). The average NOx concentration at the inlet of the original SCR reactor was 475 mg / Nm³. After the dry denitrification agent injection, the HSR reaction removal rate in the furnace reached 74%, and the NOx concentration at the outlet of the SCR reactor dropped to 11 mg / Nm³. The combined denitrification rate of in-furnace HSR denitrification + SCR denitrification reached 97.7%. The ammonia slip data and daily operating costs are basically the same as in Example 1. Compared with traditional urea ammonia production and grid ammonia injection for single SCR denitrification, the dry denitrification agent injection has significant advantages in pollution reduction, energy consumption, and operating costs.

[0060] Example 3

[0061] Similar to Example 1, except that: the boiler is a 300 MW coal-fired boiler, with an operating load of 70% of the rated load. HSR dry denitrification agent is sprayed through a third layer of injection devices (arranged 5 m above the second layer of injection devices, with multiple spray guns arranged in a row, with a horizontal spacing of 1-3 meters, evenly distributed, 10 sets on the front wall, 5 sets on the left wall, and 5 sets on the right wall; when the unit load increases or decreases, one of the other four layers of spray guns should be activated as needed) (at the same time, ammonia injection through the grid is stopped). The average daily injection volume is 6.3-6.5 tons / day. When the original urea ammonia production is combined with grid ammonia injection and single SCR denitrification, the average nitrogen oxide concentration at the SCR reactor inlet is 490 mg / Nm³, the denitrification rate of the HSR dry denitrification reaction in the furnace reaches 75%, and the NOx concentration at the SCR reactor outlet drops to 9.5 mg / Nm³.

[0062] Example 4

[0063] A dry denitrification process for boiler flue gas is used to treat 600 MW pulverized coal boilers. When using ammonia injection via a grid for urea-to-ammonia production and single SCR denitrification, the average NOx concentration at the SCR reactor inlet is 450 mg / m³. The process includes the following steps:

[0064] S1. The boiler operates at 90% of its rated load. A fourth layer of injection devices (rows of spray guns, 10 sets on the ceiling and 4 sets on each wall, evenly distributed) is installed on the horizontal flue roof and left and right walls. When the unit load increases or decreases, one of the other four layers of spray guns should be activated as needed. The unit's average daily load is approximately 60%, with a minimum of 30% and a maximum of 95%, varying according to grid dispatch requirements. HSR dry denitrification agent is injected via pneumatic conveying (simultaneously, ammonia injection through the grille is stopped). The average daily injection volume is 10.8-11.2 tons / day. The in-furnace HSR denitrification reaction achieves a removal rate of 73.8%, meaning 73.8% of nitrogen oxides (NOx) are selectively reduced and removed. The remaining unreacted denitrification agent and unremoved NOx are mixed evenly with the flue gas and then enter the SCR reactor.

[0065] The nitrogen oxide concentration at the inlet of the S2 and SCR reactors was 117.8 mg / m³. After SCR denitrification, the outlet nitrogen oxide concentration dropped to a daily average of 16 mg / m³ (compared to 38 mg / m³ under the original urea-to-ammonia production and single SCR denitrification methods, which met the conventional ultra-low emission requirement of less than 50 mg / Nm³), achieving deep reduction or ultra-low emission of nitrogen oxides. The flue gas was discharged after dust removal and desulfurization. Simultaneously, compared to the original method of ammonia injection via grid and single SCR denitrification, the ammonia slip concentration at the SCR reactor outlet decreased from 3.6 mg / Nm³ to 0.3 mg / Nm³ after dry denitrification agent injection, a significant reduction in ammonia slip concentration. This resulted in a 90% reduction in the formation of ammonium bisulfate (ABS), preventing rapid deposition and blockage of ABS on the air preheater surface, and an average decrease in air preheater flue gas temperature of 13°C (corresponding to a coal saving of approximately 1.3% for the unit). Therefore, by replacing urea-based ammonia production and grid-based ammonia injection with in-furnace dry denitrification agent, and forming a coupled process of in-furnace HSR dry denitrification and SCR denitrification, the heat exchange efficiency of the air preheater was improved and the power consumption of the induced draft fan was reduced.

[0066] In this embodiment, the HSR dry denitrification agent has no energy loss during use. Compared with urea-based ammonia production and single SCR denitrification, the amount of HSR dry denitrification agent used is comparable to that of solid urea. Compared with urea-based ammonia production, the daily energy cost savings for ammonia production are approximately 11,000 yuan / day. Furthermore, due to the significant reduction in ABS production, the air preheater is no longer clogged, and the flue gas temperature decreases, resulting in a 1.3% coal saving, with an average daily coal saving of 54.6 tons / day. The average daily coal cost saving is: 54.6 tons * 700 yuan / ton = 38,220 yuan / day. Therefore, compared with the original urea-based ammonia production and single SCR denitrification, the process method of this invention not only significantly improves denitrification efficiency and achieves deep reduction of nitrogen oxide pollutants, but also significantly reduces operating costs, saving an average of 11,000 yuan + 38,220 yuan = 49,220 yuan / day. In addition, because the nitrogen oxide concentration at the inlet of the SCR reactor is reduced by more than 70%, the service life of the SCR catalyst can be extended by at least 50%, which will further reduce the operating cost of the denitrification system.

[0067] Example 5

[0068] Similar to Example 4, the difference lies in the following: The operating load of the 600 MW unit is 60% of the rated load. The second layer of injection devices is activated (when the unit load changes, the corresponding layer of the other four injection devices is activated. The unit's average daily load is approximately 60%, the minimum load is 30%, and the maximum load is 99%, which varies according to the requirements of the power grid dispatch). HSR dry denitrification agent is injected at an average daily injection rate of 11.05 t / d. The HSR reaction removal rate in the furnace reaches 72%, and the NOx concentration at the SCR reactor outlet drops to 18.5 mg / Nm³, improving denitrification efficiency and achieving nitrogen oxide emission reduction. Furthermore, ammonia slip concentration and BAS generation are significantly reduced, preventing air preheater blockage, improving air preheater heat exchange efficiency and saving coal. The unit operates safely, and dry denitrification does not corrode the equipment. The SCR reactor is designed with 3+1 layers of catalyst, but the actual filling volume is 3 layers. Because the nitrogen oxide concentration at the SCR reactor inlet is reduced by about 70%, the service life of the SCR reactor catalyst can be significantly extended, further reducing the operating cost of the denitrification system.

[0069] Example 6

[0070] The denitrification process is the same as in the other embodiments described above, except that: the operating load of the 200 MW unit's thermal power boiler is 105% of the rated load. The fifth layer of injection devices is activated (when the unit load changes, the corresponding layer of the other four injection devices is activated. The unit's average daily load is approximately 70%, the minimum load is 30%, and the maximum load is 105%, which varies with the power and heat supply requirements). HSR dry denitrification agent is injected at an average daily injection rate of 4.6 t / d. The HSR denitrification reaction in the furnace achieves a removal rate of 76%, and the NOx concentration at the SCR reactor outlet drops to 16 mg / Nm³. The overall denitrification efficiency is high, and deep reduction of nitrogen oxide pollutants is achieved. Furthermore, the ammonia slip concentration decreases from 5.8 mg / Nm³ to 0.4 mg / Nm³, and the BAS generation is significantly reduced. The air preheater heat exchange efficiency is improved, the unit operates safely, and the dry denitrification process does not corrode the equipment. The SCR reactor is designed with 2+1 catalyst layers, but the actual filling volume is 2 layers. Because the nitrogen oxide concentration at the inlet of the SCR reactor is reduced by about 76%, the service life of the SCR reactor catalyst is significantly extended, further reducing the operating cost of the denitrification system.

[0071] Comparative Example 1

[0072] Similar to Example 1, the difference is that the unit is a 300 MW pulverized coal boiler. Regardless of whether the operating load is 30%, 50%, 70%, 90% or 100% of the rated load, HSR dry powder denitrification agent is sprayed through the first layer of injection device. The injection position is not adjusted according to the load, so stable denitrification at full load cannot be achieved. Therefore, in Comparative Example 1, nitrogen oxides cannot be stably discharged in compliance with standards, and the ammonia escape concentration also fluctuates greatly.

[0073] When the operating load is 30% of the rated load, the denitrification effect is consistent with that in Example 1. When the operating load increases to 60%-80%, the denitrification rate of the in-furnace denitrification reaction drops below 50%, and the NOx concentration at the SCR reactor inlet rises to above 200 mg / m³. It is necessary to increase the grid ammonia injection to provide a reducing agent for SCR denitrification in order to meet the standard, resulting in an ammonia slip of more than 5 ppm. When the operating load increases to 80%-100%, due to the high flue gas temperature at the injection point, most of the dry powder denitrification agent injected into the furnace is ineffectively decomposed, and the utilization rate and denitrification rate of the denitrification agent are greatly reduced. Even if more dry powder denitrification agent is injected, the denitrification rate in the furnace cannot be higher than 10%. At this time, it is necessary to inject ammonia through the grid to provide a reducing agent for the SCR reactor in order to make the NOx concentration at the SCR outlet less than 50 mg / m³. It is impossible to reduce ammonia slip and prevent air preheater blockage, and it cannot meet the unit's flexible peak-shaving requirements.

[0074] Comparative Example 2

[0075] Similar to Example 2, the difference is that the unit is a 300 MW pulverized coal boiler. Regardless of whether the operating load is 50%, 70%, 90% or 100% of the rated load, HSR dry powder denitrification agent is sprayed through the second layer of injection device. The injection position is not adjusted according to the load, so stable denitrification at full load cannot be achieved. Therefore, in Comparative Example 2, nitrogen oxides cannot be stably discharged in compliance with standards, and the ammonia escape concentration also fluctuates greatly.

[0076] Comparative Example 3

[0077] Similar to Example 3, the difference is that the unit is a 300 MW pulverized coal boiler. Regardless of whether the operating load is 70%, 90% or 100% of the rated load, the HSR dry powder denitrification agent is sprayed through the third-layer injection device. The injection position is not adjusted according to the load, so it is impossible to achieve stable denitrification at full load. Therefore, in Comparative Example 3, nitrogen oxides cannot be stably discharged in compliance with standards, and the ammonia escape concentration also fluctuates greatly.

[0078] The above description of the embodiments is only for the purpose of helping to understand the technical solution and core idea of ​​the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A flue gas denitrification treatment system, characterized in that, The system includes a furnace, a horizontal flue, a tail flue, and an SCR reactor. The flue gas generated in the furnace flows to the SCR reactor through the horizontal flue and the tail flue. Injection devices are installed at different positions on the inner wall of the furnace and / or on the inner wall of the horizontal flue and / or on the inner wall of the tail flue. The injection devices are used to inject dry denitrification agents.

2. The flue gas denitrification treatment system according to claim 1, characterized in that, The furnace includes a flame deflector; the spraying devices installed at different positions on the inner wall of the furnace include: a first layer of spraying devices installed on the inner wall of the furnace within a three-meter range above and below the elevation of the flame deflector; a second layer of spraying devices installed above the first layer of spraying devices; a third layer of spraying devices installed above the second layer of spraying devices; a fourth layer of spraying devices installed on the inner wall of the horizontal flue; and a fifth layer of spraying devices installed on the inner wall of the tail flue.

3. The flue gas denitrification treatment system according to claim 2, characterized in that, The distance between the first layer of injection devices and the top of the furnace is d, the distance between the second layer of injection devices and the first layer of injection devices is 1 / 4 to 1 / 3 d, and the distance between the third layer of injection devices and the first layer of injection devices is 2 / 3 to 3 / 4 d.

4. The flue gas denitrification treatment system according to claim 2, characterized in that, The first, second, third, fourth, and fifth spraying devices are all spray guns arranged in rows.

5. The flue gas denitrification treatment system according to claim 4, characterized in that, The first, second, third, fourth, and fifth spray devices can be selectively activated as needed. The spray guns in different positions of each spraying device are selectively activated as needed.

6. A method for injecting a dry denitrification agent, characterized in that, This is achieved through the flue gas denitrification treatment system described in claim 2. Based on the boiler operating load value, the dry denitrification agent is injected from the first layer injection device, the second layer injection device, the third layer injection device, the fourth layer injection device, or the fifth layer injection device, ensuring that the flue gas mixes with the dry denitrification agent injected into the furnace, horizontal flue, or tail flue to achieve a sufficient denitrification reaction.

7. The spraying method according to claim 6, characterized in that, When the boiler operating load is 20%-40% of the rated load, the first layer of injection devices injects dry denitrification agent; when the boiler operating load is 40%-60% of the rated load, the second layer of injection devices injects dry denitrification agent; when the boiler operating load is 60%-80% of the rated load, the third layer of injection devices injects dry denitrification agent; when the boiler operating load is 80%-100% of the rated load, the fourth layer of injection devices injects dry denitrification agent; and when the boiler is overloaded, the fifth layer of injection devices injects dry denitrification agent.

8. The application of the spraying method according to claim 6 or 7 in a dry denitrification process.

9. A dry denitrification process for boiler flue gas, characterized in that, Includes the following steps: S1. The dry denitrification agent is injected into the furnace, horizontal flue or tail flue through the first layer injection device, the second layer injection device, the third layer injection device, the fourth layer injection device or the fifth layer injection device, and mixes with the flue gas generated by the combustion in the furnace of the boiler body to carry out a full denitrification reaction, so that the nitrogen oxides in the flue gas are selectively reduced to harmless gases. The remaining unreacted denitrification agent is mixed evenly with the flue gas and then enters the SCR reactor. S2. Under the action of the catalyst in the SCR reactor, nitrogen oxides in the flue gas are selectively catalytically reduced and removed, thereby enabling the concentration of nitrogen oxides in the flue gas to meet the emission standards.

10. The dry denitrification process according to claim 9, characterized in that, The first, second, third, fourth, and fifth layer injection devices each include several parallel injection ports and temperature measuring points for monitoring the temperature of each injection port. Each injection port is equipped with a control valve to control the amount of dry denitrification agent delivered.

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