A coal-fired unit full-time efficient denitration system and denitration method

Abstract

The present application relates to the technical field of coal-fired flue gas pollutant control, and particularly relates to a coal-fired unit full-time efficient denitration system and a denitration method, wherein an ozone injection device is arranged in a flue between a coal economizer and a denitration reactor, so that the device is adapted to the reaction requirements of two working conditions of NO full oxidation in a start-up stage and NO partial oxidation in a deep peak regulation stage for rapid selective catalytic reduction reaction (FASTSCR) denitration, the system further comprises an ozone generation unit, a flue gas parameter monitoring unit and a central control unit, the central control unit automatically switches the operation mode according to the flue gas parameters and controls the ozone generation unit output and the ammonia injection amount, full-time NOx ultra-low emission of the coal-fired unit is realized, the ozone is only put into operation in the start-up and low load stages, the operation cost is greatly reduced, and the transformation cost is low and the compatibility is strong.

Description

Technical Field

[0001] This invention relates to the technical field of flue gas pollutant control in coal-fired power plants, and particularly to a high-efficiency denitrification system and method for coal-fired power units throughout the day. Background Technology

[0002] The mainstream denitrification technology for current coal-fired power units is Selective Catalytic Reduction (SCR). A typical system configuration involves placing an SCR denitrification reactor between the economizer and air preheater of the coal-fired boiler. Using a vanadium-titanium catalyst, within a temperature window of 320-420℃, ammonia (NH3) is injected to reduce NOx in the flue gas, producing nitrogen and water, thus removing NOx. To address the issue of SCR catalysts not being operational at low temperatures, some existing technologies supplement this with ozone oxidation denitrification technology. This involves injecting ozone (O3) into the flue gas to oxidize nitric oxide (NO) in the flue gas into water-soluble nitrogen dioxide (NO2), which is then absorbed and removed by a downstream wet desulfurization tower. This technology is not limited by flue gas temperature and can achieve denitrification at low temperatures.

[0003] Existing all-time high-efficiency denitrification systems for coal-fired power units cannot effectively operate during the boiler start-up and deep peak-shaving low-load phases due to flue gas temperatures falling below the catalyst's minimum operating temperature, resulting in prolonged periods of excessive emissions. Conventional ozone oxidation denitrification technology requires the complete oxidation of NO in the entire flue gas volume, leading to extremely high ozone consumption and energy costs. The economic cost of relying solely on this technology to achieve ultra-low emissions throughout the entire time is 5-10 times that of conventional SCR technology, making large-scale engineering promotion impractical. Summary of the Invention

[0004] The purpose of this invention is to provide a high-efficiency denitrification system and method for coal-fired power units throughout all time periods, solving the technical problems of conventional SCR technology being unable to operate due to insufficient flue gas temperature and having a window period of exceeding standards during start-up and low-load stages, and conventional ozone denitrification requiring full oxidation of NO and having high operating costs, making it difficult to simultaneously meet the requirements of NOx emission standards and economic operation of coal-fired power units under all operating conditions.

[0005] In a first aspect, the present invention provides a high-efficiency denitrification system for coal-fired power units, comprising a coal-fired boiler, an economizer, a denitrification reactor, an air preheater, a dust removal device, a wet desulfurization tower, and a chimney. The flue gas outlet of the coal-fired boiler is sequentially connected to the economizer, the denitrification reactor, the air preheater, the dust removal device, the wet desulfurization tower, and the chimney. The system also includes an ozone generation unit, an ozone injection device, a flue gas parameter monitoring unit, and a central control unit. The ozone injection device is arranged in the flue between the flue gas outlet of the economizer and the flue gas inlet of the denitrification reactor. The ozone injection device is configured to simultaneously adapt to the reaction residence time required for the full oxidation of NO in the start-up stage and the reaction residence time required for the partial oxidation of NO and rapid selective catalytic reduction in the deep peak shaving low load and rapid load change stages. The ozone outlet of the ozone generating unit is connected to the ozone injection device and is used to provide ozone to the ozone injection device. The flue gas parameter monitoring unit is used to collect flue gas parameters at different locations of the coal-fired unit in real time; The central control unit is connected to the ozone generating unit, the ammonia injection system of the denitrification reactor, and the flue gas parameter monitoring unit. The central control unit is configured to automatically switch and control the output of the ozone generating unit and the operation of the ammonia injection system of the denitrification reactor based on the signals collected by the flue gas parameter monitoring unit, so as to achieve the removal of nitrogen oxides under multiple operating conditions.

[0006] Furthermore, the flue gas parameter monitoring unit includes a first flue gas monitoring module, a second flue gas monitoring module, and a third flue gas monitoring module; the first flue gas monitoring module is arranged in the flue gas outlet duct of the economizer and is used to collect the flue gas temperature, flue gas flow rate, nitrogen oxide concentration, O2 concentration, and unit load change rate at the economizer outlet; the second flue gas monitoring module is arranged in the flue gas outlet duct of the denitrification reactor and is used to collect the nitrogen oxide concentration and ammonia slip concentration at the denitrification reactor; the third flue gas monitoring module is arranged in the flue gas outlet duct of the wet desulfurization tower and is used to collect the nitrogen oxide concentration at the desulfurization tower outlet.

[0007] Furthermore, the ozone injection device includes multiple sets of injection grids evenly arranged along the cross-section of the flue. Each set of injection grids is equipped with multiple dual-fluid atomizing nozzles. The injection direction of the dual-fluid atomizing nozzles is set in the same direction or opposite to the flue gas flow direction. The dual-fluid atomizing nozzles cover the entire cross-section of the flue to ensure that the mixing uniformity of ozone and flue gas is ≥95%.

[0008] Furthermore, the ozone generating unit adopts an oxygen source ozone generator, with an ozone output concentration of not less than 80 mg / L, an ozone output adjustment range of 0-100% of rated output, and a response time ≤10s.

[0009] Secondly, the present invention also provides a method for efficient denitrification of coal-fired power units throughout all time periods, based on the aforementioned efficient denitrification system for coal-fired power units throughout all time periods, comprising the following steps: Step 1: When the economizer outlet flue gas temperature is detected to rise from ambient temperature and the flue gas volume begins to increase, the boiler ignition to grid-connected start-up operation mode is executed: the ammonia injection system of the denitrification reactor is shut down; the central control unit controls the ozone generation unit to start and adjust the ozone output based on the flue gas volume and nitrogen oxide concentration of the economizer collected by the flue gas parameter monitoring unit, and injects ozone into the flue gas duct through the ozone injection device, where it reacts with NO in the flue gas to generate NO2; the NO2-containing flue gas flows sequentially through the denitrification reactor, the air preheater, and the dust removal device before entering the wet desulfurization tower, where NO2 is simultaneously absorbed and removed by the desulfurization slurry in the wet desulfurization tower, and the clean flue gas is discharged through the chimney in compliance with standards; Step 2: When the outlet flue gas temperature of the economizer is detected to be within the low-efficiency reaction flue gas temperature range of the denitrification reactor, the unit's deep peak shaving low-load and rapid load change operation mode is executed: the ammonia injection system of the denitrification reactor is started; the central control unit controls the ozone generation unit to start and adjust the ozone output according to the flue gas parameters collected by the flue gas parameter monitoring unit, oxidizing part of the NO in the flue gas to NO2 and adjusting the molar ratio of NO to NO2 in the flue gas to the optimal range; the flue gas containing NO and NO2 enters the denitrification reactor and undergoes a rapid selective catalytic reduction reaction with the injected ammonia to achieve efficient removal of nitrogen oxides; during the deep peak shaving and rapid load change stage of the unit, based on the characteristic that the rapid selective catalytic reduction reaction rate is faster than that of the conventional catalytic reduction reaction, it quickly responds to the instantaneous fluctuations in the concentration of nitrogen oxides in the flue gas; the denitrified flue gas flows sequentially through the air preheater, the dust removal device, and the wet desulfurization tower before being discharged through the chimney in compliance with standards; Step 3: When the outlet flue gas temperature of the economizer is found to be compatible with the reaction flue gas temperature range of the denitrification reactor, the unit's normal load operation mode is executed: the ozone generation unit is shut down, and nitrogen oxides are removed only through the conventional catalytic reduction reaction of the denitrification reactor.

[0010] Furthermore, in step one, the ozone molar ratio is 0.9-1.2, and the oxidation rate of NO in the flue gas is not less than 90%.

[0011] Furthermore, in step two, the inefficient reaction flue gas temperature range of the denitrification reactor is 270-320℃; the molar ratio of NO to NO2 in the flue gas is controlled at 0.8-1.2:1, and the ozone addition molar ratio is 0.4-0.6; when the unit rapidly changes load, the central control unit dynamically adjusts the ozone output based on the real-time nitrogen oxide concentration to maintain the NO to NO2 molar ratio stable within the optimal range.

[0012] Furthermore, in step three, the reaction flue gas temperature range of the denitrification reactor is 320-420℃.

[0013] Furthermore, the desulfurization slurry in the wet desulfurization tower is any one of limestone-gypsum slurry, ammonia desulfurization slurry, or magnesium desulfurization slurry.

[0014] Furthermore, the central control unit automatically and seamlessly switches between steps one, two, and three based on a preset flue gas temperature threshold, and adjusts ozone output and ammonia injection in a closed loop according to the real-time flue gas nitrogen oxide concentration and the rate of change of unit load, thereby achieving optimal control of operating energy consumption while ensuring compliance with emission standards.

[0015] Compared with existing technologies, the all-time high-efficiency denitrification system for coal-fired power units provided by this invention arranges the ozone injection device in the flue between the economizer and the denitrification reactor, making it adaptable to the reaction residence time requirements of both the full oxidation of NO during the start-up phase and the rapid selective catalytic reduction reaction of partial oxidation of NO during the deep peak shaving phase. With the automatic switching control of the flue gas parameter monitoring unit and the central control unit, ultra-low NO emissions of coal-fired power units are achieved throughout the entire time from ignition, start-up, low load to normal load. Moreover, ozone is only activated during the start-up and low load phases, which reduces ozone consumption and significantly lowers operating costs. It has low retrofit costs, strong compatibility, and broad engineering promotion value. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure provided in an embodiment of the present invention.

[0018] Figure label: 101. Economizer; 102. Economizer; 103. Denitrification reactor; 104. Air preheater; 105. Dust removal device; 106. Wet desulfurization tower; 107. Chimney; 200. Ozone generating unit; 300. Ozone injection device; 410. First flue gas monitoring module; 420. Second flue gas monitoring module; 430. Third flue gas monitoring module; 500. Central control unit. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. These terms are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0023] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0024] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0026] Example 1 This invention provides a high-efficiency denitrification system for coal-fired power units operating around the clock. See also... Figure 1 This embodiment uses a 300MW coal-fired power unit in China as the implementation object. The existing flue gas treatment system of this unit consists of a pulverized coal boiler + economizer + vanadium-titanium SCR denitrification reactor + air preheater + electrostatic precipitator + limestone-gypsum wet desulfurization tower + chimney. The optimal reaction temperature of the SCR catalyst is 320-420℃. The minimum load for deep peak shaving of the unit is 30% of the rated load, and the maximum load change rate is 2.5% of the rated load / min. The requirement is that the NOx emission concentration throughout the entire period should be ≤35mg / m³ (standard dry, 6% O2). The following is combined with... Figure 1 The system structure of the present invention will be described in detail below.

[0027] This embodiment provides a high-efficiency denitrification system for coal-fired power units, including a coal-fired boiler 101, an economizer 102, a denitrification reactor 103, an air preheater 104, a dust removal device 105, a wet desulfurization tower 106, and a chimney 107. The flue gas outlet of the coal-fired boiler 101 is sequentially connected to the economizer 102, the denitrification reactor 103, the air preheater 104, the dust removal device 105, the wet desulfurization tower 106, and the chimney 107, forming the main flue gas flow path.

[0028] The core improvement of this system is that it also includes an ozone generation unit 200, an ozone injection device 300, a flue gas parameter monitoring unit, and a central control unit 500.

[0029] An ozone injection device 300 is located in the flue gas duct between the flue gas outlet of the economizer 102 and the flue gas inlet of the denitrification reactor 103. This ozone injection device 300 is configured to simultaneously meet the reaction requirements for full-volume NO oxidation denitrification during the start-up phase, as well as the reaction requirements for partial NO oxidation in FASTSCR denitrification during the deep peak shaving low-load and rapid load change phases. Specifically, the location of the ozone injection device 300 ensures sufficient oxidation reaction time between ozone and NO during the start-up phase, allowing for thorough mixing and oxidation to produce NO2. It also ensures that during the deep peak shaving low-load and rapid load change phases, the oxidized flue gas can directly enter the denitrification reactor 103, preventing NO2 decomposition in the excessively long high-temperature flue gas duct. This effectively meets the process requirements of the FASTSCR reaction, enabling the reuse of a single injection device across all operating conditions.

[0030] In this embodiment, the ozone injection device 300 includes three sets of injection grids evenly arranged along the cross-section of the flue, with twenty dual-fluid atomizing nozzles on each set of injection grids. The injection direction of the dual-fluid atomizing nozzles is set in the same direction as the flue gas flow direction, and the nozzles cover the entire cross-section of the flue to ensure that the mixing uniformity of ozone and flue gas is ≥95%, thereby improving the oxidation reaction efficiency and ozone utilization rate. It is understood that the number of injection grid sets and the number of nozzles can be appropriately adjusted according to the different dimensions and shapes of the flue cross-section; the injection direction of the nozzles can also be set to a combination of reverse or partially unidirectional and partially reverse directions according to the actual flow field conditions.

[0031] The ozone outlet of the ozone generating unit 200 is connected to the ozone injection device 300 to supply ozone to the ozone injection device 300. In this embodiment, the ozone generating unit 200 uses two oxygen-source ozone generators, each with a rated output of 50 kg / h and an ozone production concentration of 100 mg / L. The ozone output adjustment range is 0-100% of the rated output, and the response time is ≤10s, which can quickly adapt to the dynamic adjustment requirements of ozone dosage under variable load conditions of the unit. The outlet of the ozone generating unit 200 is connected to each group of injection grids of the ozone injection device 300 through a 316L stainless steel pipe to ensure corrosion resistance and safety during the ozone delivery process.

[0032] The flue gas parameter monitoring unit is used to collect flue gas parameters at different locations of the coal-fired unit in real time. In this embodiment, the flue gas parameter monitoring unit includes a first flue gas monitoring module 410, a second flue gas monitoring module 420, and a third flue gas monitoring module 430. The first flue gas monitoring module 410 is located in the flue gas outlet duct of the economizer 102, specifically in the duct between the economizer 102 outlet and the ozone injection device 300, and is used to collect parameters such as flue gas temperature, flue gas flow rate, NOx concentration, O2 concentration, and unit load change rate at the economizer outlet. The second flue gas monitoring module 420 is located in the flue gas outlet duct of the denitrification reactor 103, and is used to collect the NOx concentration and ammonia slip concentration at the denitrification reactor outlet to monitor the SCR denitrification efficiency and excessive ammonia injection in real time. The third flue gas monitoring module 430 is located in the flue gas outlet duct of the wet desulfurization tower 106. It is used to collect the NOx concentration at the outlet of the desulfurization tower as a monitoring and feedback signal for the final emission concentration, so as to ensure that the chimney emission concentration meets the ultra-low emission limit requirements.

[0033] The central control unit 500 is connected to the ozone generating unit 200, the ammonia injection system of the denitrification reactor 103, and the flue gas parameter monitoring units (i.e., the first flue gas monitoring module 410, the second flue gas monitoring module 420, and the third flue gas monitoring module 430). Simultaneously, the central control unit 500 is also linked to the unit's DCS system to acquire real-time unit operating status information. The central control unit 500 is configured to automatically switch and control the output of the ozone generating unit 200 and the operation of the ammonia injection system of the denitrification reactor 103 based on signals collected by the flue gas parameter monitoring units, thereby achieving NOx removal under multiple operating conditions. Its built-in multi-condition adaptive switching control logic enables seamless automatic switching between three operating modes based on key parameters such as the economizer outlet flue gas temperature, without manual intervention.

[0034] Example 2 This invention provides a method for efficient denitrification of coal-fired power units throughout all time periods, based on the system implementation of Embodiment 1. This embodiment takes a 300MW coal-fired power unit from Embodiment 1 as an example, and details its specific operating steps and control logic under different operating modes.

[0035] The all-time high-efficiency denitrification method for coal-fired power units in this embodiment includes the following three adaptive switching operating modes: Step 1: Boiler ignition to grid connection and start-up operation mode When the first flue gas monitoring module 410 detects that the outlet flue gas temperature of the economizer 102 starts to rise from room temperature and the flue gas volume begins to increase, it determines that the unit is in the boiler ignition to grid connection start-up stage. During this stage, the central control unit 500 controls and executes the boiler ignition to grid connection start-up operation mode. The specific operation procedure is as follows: First, the central control unit 500 issues an instruction to shut down the ammonia injection system of the denitrification reactor 103, completely stopping ammonia injection. This is because the flue gas temperature is too low at this time, and the SCR catalyst does not have catalytic activity. The injected ammonia not only cannot participate in the denitrification reaction, but will also react with SO3 in the flue gas to produce ammonium bisulfate, causing blockage of the catalyst micropores and blockage and corrosion of the downstream air preheater 104.

[0036] Subsequently, the central control unit 500 calculates the required ozone dosage based on the real-time flue gas volume and NOx concentration data collected by the first flue gas monitoring module 410 at the economizer 102 outlet, and controls the ozone generating unit 200 to start and adjust the ozone output. The ozone molar ratio O3 / NO is controlled at 1.05 to ensure that the oxidation rate of NO in the flue gas is not less than 90%. The ozone is transported through pipeline to the ozone injection device 300, and is evenly injected into the flue through the atomizing nozzles of three sets of injection grids, where it undergoes a rapid oxidation reaction with NO in the flue gas: NO + O3 → NO2 + O2, converting NO into NO2.

[0037] In actual operation, during the initial startup phase, the economizer outlet flue gas volume is approximately 5 × 10⁻⁶. 4 With a flow rate of m³ / h and an initial NOx concentration of 220 mg / m³, the central control unit 500 controls the output of the ozone generating unit 200 to 8 kg / h, achieving a NO oxidation rate of 93%. Flue gas containing high NO2 concentrations flows sequentially through the denitrification reactor 103 (at which point no catalytic reaction occurs, serving only as a flue gas passage), air preheater 104, and dust removal device 105 before entering the wet desulfurization tower 106. Inside the wet desulfurization tower 106, NO2 reacts with limestone-gypsum slurry and is simultaneously absorbed and removed. The core reaction is: 2NO2 + CaSO3 + H2O → CaSO4 + 2HNO2. The wet desulfurization tower 106 achieves a NO2 removal efficiency of 91%, and the final NOx concentration at the chimney 107 outlet is 13.8 mg / m³.

[0038] As the unit heats up, the economizer outlet flue gas volume increases to 3×10⁻⁶ per cubic meter one hour before grid connection. 5 With a flow rate of m³ / h, the initial NOx concentration rises to 350 mg / m³. The central control unit 500 automatically adjusts the output of the ozone generating unit 200 to 42 kg / h based on real-time data, adjusts the O3 / NO molar ratio to 1.1, achieves a NO oxidation rate of 95%, maintains a NO2 removal efficiency of 92% in the wet desulfurization tower 106, and finally achieves a NOx concentration of 26.6 mg / m³ at the outlet of the chimney 107.

[0039] Throughout the entire start-up phase (approximately 6 hours from boiler ignition to grid connection), the denitrification system operated stably, with the NOx concentration at the 107 outlet of the chimney consistently meeting standards. Since the unit's flue gas volume during this phase is only 10%-30% of the rated load, the ozone demand is extremely low, and operating costs are controllable. This completely avoids the high energy consumption issue of conventional ozone denitrification systems operating at full load and effectively solves the problem of prolonged emission windows during the start-up phase.

[0040] Step 2: Deep Peak Shaving and Rapid Load Change Operation Modes of the Unit When the first flue gas monitoring module 410 detects that the outlet flue gas temperature of the economizer 102 is within the low-efficiency reaction flue gas temperature range of the denitrification reactor 103, it determines that the unit is in the deep peak-shaving low-load operation stage. In this embodiment, the low-efficiency reaction flue gas temperature range of the denitrification reactor 103 is 270-320℃. During this stage, the central control unit 500 controls the deep peak-shaving low-load and rapid load change operation modes of the unit. The specific operation process is as follows: First, the central control unit 500 issues a command to start the ammonia injection system of the denitrification reactor 103, enabling the SCR denitrification reactor to have basic denitrification capabilities.

[0041] Meanwhile, the central control unit 500, based on comprehensive parameters such as flue gas temperature, NOx concentration, and unit load change rate collected by the first flue gas monitoring module 410, controls the ozone generating unit 200 to operate at partial output. The ozone dosing molar ratio O3 / NO is controlled at 0.5, oxidizing only about 50% of the NO in the flue gas to NO2, precisely regulating the molar ratio of NO to NO2 in the flue gas to about 1:1, which is the optimal ratio range for the FASTSCR reaction.

[0042] A mixed flue gas containing equimolar amounts of NO and NO2 enters the denitrification reactor 103, where it undergoes a FASTSCR reaction with injected ammonia on the surface of a vanadium-titanium catalyst: 2NO + 2NO2 + 4NH3 → 4N2 + 6H2O. Because the activation energy of the FASTSCR reaction is much lower than that of the conventional SCR reaction (4NH3 + 4NO + O2 → 4N2 + 6H2O), and the reaction rate is an order of magnitude faster than conventional SCR, a denitrification efficiency of over 95% can be achieved within the low-efficiency reaction temperature range of 270-320℃ for conventional SCR catalysts.

[0043] In the actual operation of this embodiment, the unit operates at 30% rated load (90MW) in steady-state deep peak-shaving mode, with an economizer outlet flue gas temperature of 290℃. When the conventional SCR operates alone, the denitrification efficiency is only 72%, the outlet NOx concentration is 98mg / m³, and ammonia slip is as high as 3.8ppm, failing to meet emission requirements. After activating the FASTSCR mode of this invention, the central control unit 500 controls the output of the ozone generation unit 200 to 22kg / h, with an O3 / NO molar ratio of 0.5, oxidizing 50% of the NO to NO2, and adjusting the NO / NO2 molar ratio in the flue gas to approximately 1:1. The mixed flue gas enters the denitrification reactor 103 for the FASTSCR reaction, achieving a denitrification efficiency of 93.2%. The NOx concentration at the denitrification reactor outlet is 25.3mg / m³, ammonia slip drops to 0.7ppm, and finally, the NOx concentration at the chimney outlet 107 stabilizes below 30mg / m³, meeting ultra-low emission requirements.

[0044] In this embodiment, under rapid load change conditions, the central control unit 500 dynamically adjusts the output of the ozone generating unit 200 based on the real-time NOx concentration and load change rate collected by the first flue gas monitoring module 410. Through the rapid response (response time ≤ 10s) of the ozone injection device 300, the NO / NO2 molar ratio is consistently maintained at approximately 1:1. Utilizing the rapid reaction rate characteristic of FASTSCR, the inherent lag problem of conventional ammonia injection regulation is effectively eliminated. In this embodiment, the unit rapidly increases and decreases the load at a rate of 2.5% of rated load / min between 30% and 50% of rated load. The flue gas NOx concentration fluctuates drastically between 180 and 420 mg / m³. After adopting the FASTSCR mode of this invention, the denitrification efficiency stabilizes above 94%, the NOx concentration at the chimney 107 outlet is consistently less than 25 mg / m³ with no instantaneous exceedances, and ammonia slip is consistently less than 1.5 ppm, significantly improving the denitrification stability under variable load conditions.

[0045] This stage only requires the oxidation of a portion of the NO, and the ozone consumption is only 40%-60% of that of conventional full-volume ozone denitrification. The operating cost is controllable, achieving an effective balance between low-load, high-efficiency denitrification and economical operation.

[0046] Step 3: Unit's Normal Load Operation Mode When the first flue gas monitoring module 410 detects that the outlet flue gas temperature of the economizer 102 matches the reaction flue gas temperature range of the denitrification reactor 103, it determines that the unit is in the normal load operation stage. In this embodiment, the reaction flue gas temperature range of the denitrification reactor 103 is 320-420℃. During this stage, the central control unit 500 controls and executes the normal load operation mode of the unit, and the specific operation procedure is as follows: The central control unit 500 issues a command to shut down the ozone generator 200, stopping ozone supply and injection. At this point, NOx removal is achieved entirely through the conventional SCR reaction in the denitrification reactor 103. The conventional SCR reaction exhibits ideal catalytic activity within a temperature window of 320-420℃, with a stable denitrification efficiency above 88%. The NOx concentration at the outlet of chimney 107 is consistently less than 40 mg / m³, meeting emission requirements.

[0047] During this phase, there is no ozone consumption and no additional operating energy consumption, ensuring the economical operation of the unit under normal load.

[0048] During the switching process of the three operating modes mentioned above, the central control unit 500 automatically and seamlessly switches between steps one, two, and three based on preset flue gas temperature and flue gas volume thresholds (economizer outlet flue gas temperature starts to rise from ambient temperature and flue gas volume begins to increase; inefficient reaction flue gas temperature range: 270-320℃; reaction flue gas temperature range: 320-420℃). When the flue gas temperature gradually rises from the low-temperature zone and crosses the threshold boundary, the central control unit 500 adopts a hysteresis control strategy to avoid frequent mode switching near the threshold, ensuring the stability of system operation. At the same time, the central control unit 500 adjusts the ozone output and ammonia injection in a closed loop according to parameters such as real-time flue gas NOx concentration and unit load change rate, achieving optimal control of operating energy consumption while ensuring compliance with emission standards.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-efficiency denitrification system for a coal-fired power unit, comprising a coal-fired boiler, an economizer, a denitrification reactor, an air preheater, a dust removal device, a wet desulfurization tower, and a chimney, wherein the flue gas outlet of the coal-fired boiler is sequentially connected to the economizer, the denitrification reactor, the air preheater, the dust removal device, the wet desulfurization tower, and the chimney, characterized in that, It also includes an ozone generation unit, an ozone injection device, a flue gas parameter monitoring unit, and a central control unit; The ozone injection device is arranged in the flue between the flue gas outlet of the economizer and the flue gas inlet of the denitrification reactor. The ozone injection device is configured to simultaneously adapt to the reaction time required for the full oxidation of NO in the start-up stage and the reaction time required for the partial oxidation of NO and rapid selective catalytic reduction in the deep peak shaving low load and rapid load change stages. The ozone outlet of the ozone generating unit is connected to the ozone injection device and is used to provide ozone to the ozone injection device. The flue gas parameter monitoring unit is used to collect flue gas parameters at different locations of the coal-fired unit in real time; The central control unit is connected to the ozone generating unit, the ammonia injection system of the denitrification reactor, and the flue gas parameter monitoring unit. The central control unit is configured to automatically switch and control the output of the ozone generating unit and the operation of the ammonia injection system of the denitrification reactor based on the signals collected by the flue gas parameter monitoring unit, so as to achieve the removal of nitrogen oxides under multiple operating conditions.

2. The all-time high-efficiency denitrification system for coal-fired power units according to claim 1, characterized in that, The flue gas parameter monitoring unit includes a first flue gas monitoring module, a second flue gas monitoring module, and a third flue gas monitoring module. The first flue gas monitoring module is located in the flue gas outlet duct of the economizer and is used to collect the flue gas temperature, flue gas flow rate, nitrogen oxide concentration, O2 concentration, and unit load change rate at the economizer outlet. The second flue gas monitoring module is located in the flue gas outlet duct of the denitrification reactor and is used to collect the nitrogen oxide concentration and ammonia slip concentration at the denitrification reactor. The third flue gas monitoring module is located in the flue gas outlet duct of the wet desulfurization tower and is used to collect the nitrogen oxide concentration at the desulfurization tower outlet.

3. The all-time high-efficiency denitrification system for coal-fired power units according to claim 1, characterized in that, The ozone injection device includes multiple sets of injection grids evenly arranged along the cross-section of the flue. Each set of injection grids is equipped with multiple dual-fluid atomizing nozzles. The injection direction of the dual-fluid atomizing nozzles is set in the same direction or opposite to the flue gas flow direction. The dual-fluid atomizing nozzles cover the entire cross-section of the flue to ensure that the mixing uniformity of ozone and flue gas is ≥95%.

4. The all-time high-efficiency denitrification system for coal-fired power units according to claim 1, characterized in that, The ozone generating unit uses an oxygen source ozone generator with an ozone output concentration of not less than 80 mg / L, an ozone output adjustment range of 0-100% of the rated output, and a response time of ≤10s.

5. A method for efficient denitrification of coal-fired power units throughout all time periods, characterized in that, The all-time high-efficiency denitrification system for coal-fired power units, based on any one of claims 1 to 4, includes the following steps: Step 1: When the economizer outlet flue gas temperature is detected to rise from ambient temperature and the flue gas volume begins to increase, the boiler ignition to grid-connected start-up operation mode is executed: the ammonia injection system of the denitrification reactor is shut down; the central control unit controls the ozone generation unit to start and adjust the ozone output based on the flue gas volume and nitrogen oxide concentration of the economizer collected by the flue gas parameter monitoring unit, and injects ozone into the flue gas duct through the ozone injection device, where it reacts with NO in the flue gas to generate NO2; the NO2-containing flue gas flows sequentially through the denitrification reactor, the air preheater, and the dust removal device before entering the wet desulfurization tower, where NO2 is simultaneously absorbed and removed by the desulfurization slurry in the wet desulfurization tower, and the clean flue gas is discharged through the chimney in compliance with standards; Step 2: When the outlet flue gas temperature of the economizer is detected to be within the low-efficiency reaction temperature range of the denitrification reactor, the unit's deep peak shaving low-load and rapid load change operation mode is executed: the ammonia injection system of the denitrification reactor is started; the central control unit controls the ozone generation unit to start and adjust the ozone output according to the flue gas parameters collected by the flue gas parameter monitoring unit, oxidizing some of the NO in the flue gas to NO2, and adjusting the molar ratio of NO to NO2 in the flue gas to the optimal range; the flue gas containing NO and NO2 enters the denitrification reactor and undergoes a rapid selective catalytic reduction reaction with the injected ammonia to achieve efficient removal of nitrogen oxides; during the deep peak shaving and rapid load change stage of the unit, based on the characteristic that the rapid selective catalytic reduction reaction rate is faster than that of the conventional catalytic reduction reaction, it quickly responds to the instantaneous fluctuations in the concentration of nitrogen oxides in the flue gas; the denitrified flue gas flows sequentially through the air preheater, the dust removal device, and the wet desulfurization tower before being discharged through the chimney in compliance with standards; Step 3: When the outlet flue gas temperature of the economizer is found to be compatible with the reaction flue gas temperature range of the denitrification reactor, the unit's normal load operation mode is executed: the ozone generation unit is shut down, and nitrogen oxides are removed only through the conventional catalytic reduction reaction of the denitrification reactor.

6. The all-time high-efficiency denitrification method for coal-fired power units according to claim 5, characterized in that, In step one, the ozone molar ratio is 0.9-1.2, and the oxidation rate of NO in the flue gas is not less than 90%.

7. The all-time high-efficiency denitrification method for coal-fired power units according to claim 5, characterized in that, In step two, the inefficient reaction flue gas temperature range of the denitrification reactor is 270-320℃; the molar ratio of NO to NO2 in the flue gas is controlled at 0.8-1.2:1, and the ozone addition molar ratio is 0.4-0.6; when the unit rapidly changes load, the central control unit dynamically adjusts the ozone output based on the real-time nitrogen oxide concentration to maintain the NO to NO2 molar ratio stable within the optimal range.

8. The all-time high-efficiency denitrification method for coal-fired power units according to claim 5, characterized in that, In step three, the reaction flue gas temperature range of the denitrification reactor is 320-420℃.

9. The method for efficient denitrification of coal-fired power units throughout all time periods according to claim 5, characterized in that, The desulfurization slurry in the wet desulfurization tower is any one of limestone-gypsum slurry, ammonia desulfurization slurry, or magnesium desulfurization slurry.

10. The method for efficient denitrification of coal-fired power units throughout all time periods according to claim 5, characterized in that, The central control unit automatically and seamlessly switches between steps one, two, and three based on a preset flue gas temperature threshold. It also adjusts ozone output and ammonia injection in a closed loop according to the real-time flue gas nitrogen oxide concentration and the rate of change of unit load, thereby achieving optimal control of operating energy consumption while ensuring compliance with emission standards.

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