Ammonia injection optimization method and device based on scr reaction kinetics model and medium

Abstract

This invention discloses an optimization method, apparatus, and medium for ammonia injection based on an SCR reaction kinetic model. The method includes: acquiring flue gas data; validating the CFD model of the SCR denitrification system based on the acquired flue gas data, visually analyzing the trajectory and influence area of ​​the ammonia injection fluid, defining the ammonia injection flow influence coefficient, and determining the correspondence between different zones / nozzles of the ammonia injection grid and the upstream cross-sectional area of ​​the catalyst; solving the SCR reaction kinetic model to obtain the mathematical relationship between the NH3 concentration at the upstream cross-section of the catalyst and the NOx concentration at the SCR outlet; coupling the optimization matrix equations of the ammonia injection flow influence coefficients of different zones / nozzles, and quantitatively solving for the optimized ammonia injection rate corresponding to the ammonia injection grid with the goal of achieving the most uniform NOx concentration distribution at the SCR outlet. This invention can quantitatively solve for the optimized ammonia injection rate corresponding to the ammonia injection grid based on the characteristics of the outlet NOx concentration distribution. This invention can be widely applied in the field of flue gas SCR denitrification technology.

Description

Technical Field

[0001] This invention relates to the field of flue gas SCR denitrification technology, and in particular to an optimized ammonia injection method, apparatus and medium based on an SCR reaction kinetic model. Background Technology

[0002] Nitrogen oxides (NOx) are one of the major air pollutants. To implement stricter environmental standards, it is required that NOx emission concentrations not exceed 50 mg / Nm³ under a baseline oxygen content of 6%. 3 Selective Catalytic Reduction (SCR) is currently the main flue gas denitrification technology used in domestic power plants. Under ultra-low emission requirements, increasing the ammonia injection rate can improve NOx removal efficiency, but it can also cause excessive ammonia slip in some areas, increasing the risk of air preheater blockage and SCR catalyst poisoning. Adjusting the ammonia injection rate in different areas of the ammonia injection grid is an important measure to improve the mixing and matching degree of ammonia-nitrogen concentration in the flue. A reasonable ammonia-nitrogen mixing equivalent ratio can ensure complete SCR denitrification reaction and improve the uniformity of NOx concentration distribution at the outlet. Therefore, it is necessary to perform zoned ammonia injection fine-tuning of the SCR denitrification system.

[0003] Currently, most ammonia injection regulation processes in engineering rely on manual experience, which is highly unpredictable and lacks theoretical guidance. However, CFD numerical simulation technology can visualize the flue gas flow trajectory and its affected area, providing a theoretical reference for optimizing ammonia injection in on-site ammonia grids. In existing studies, researchers have used CFD numerical simulation technology to optimize ammonia injection, and the proposed optimization strategies often focus on solving the problem of uniformity of ammonia-nitrogen mixture concentration distribution upstream of the first catalyst layer. The ammonia injection amount is adjusted based on minimizing the relative deviation of the ammonia-nitrogen ratio at the upstream cross-section of the catalyst to achieve an equal ammonia-nitrogen ratio. The results show that the NOx concentration at the SCR outlet cannot achieve the optimal distribution requirements, and problems such as large deviation of outlet NOx concentration and large local ammonia escape still exist after optimization. At the same time, most simulation optimization studies require multiple trial calculations to obtain the corresponding ammonia injection amount for the ammonia grid zone under the optimal ammonia injection strategy, and the adjustment work has a certain degree of unpredictability and takes a long time. In the current technology, no researchers have analyzed the corresponding influence of the ammonia injection amount in different zones of the ammonia injection grid on the NOx concentration distribution at the SCR outlet. Therefore, it is impossible to give a clear mathematical relationship based on the characteristics of the NOx concentration distribution at the outlet to quantitatively calculate the ammonia injection amount required for different zones of the ammonia injection grid. This results in poor accuracy and specificity of the existing adjustment strategies and a large degree of blindness in ammonia injection adjustment. Summary of the Invention

[0004] In order to at least partially solve one of the technical problems existing in the prior art, the present invention aims to provide an optimized method, device and medium for ammonia injection based on an SCR reaction kinetic model.

[0005] The technical solution adopted in this invention is:

[0006] An optimization method for ammonia injection based on an SCR reaction kinetic model includes the following steps:

[0007] Acquire flue gas data;

[0008] Based on the obtained flue gas data, the CFD model of the SCR denitrification system was validated, the trajectory and influence area of ​​the ammonia injection fluid were visualized and analyzed, the ammonia injection flow influence coefficient was defined, and the correspondence between different zones / nozzles of the ammonia injection grid and the upstream cross-sectional area of ​​the catalyst was determined.

[0009] Solving the SCR reaction kinetic model yields the mathematical relationship between the NH3 concentration at the upstream cross section of the catalyst and the NOx concentration at the SCR outlet.

[0010] The optimization matrix equations of the ammonia injection flow influence coefficients of different zones / nozzles are coupled, and the optimized ammonia injection rate corresponding to the ammonia injection grid with the goal of the most uniform NOx concentration distribution at the SCR outlet is quantitatively solved.

[0011] Furthermore, the overall structure of the SCR system includes inlet and outlet flues, ammonia injection grilles, guide vanes, static mixers, rectifier grilles, and catalyst layers.

[0012] Furthermore, the acquisition of flue gas data includes:

[0013] The flow field characteristics at the inlet measurement section of the SCR system are measured to obtain flue gas data; wherein, the flue gas data includes the velocity field, concentration field, and temperature field of the inlet measurement section, as well as the inlet parameters from CFD numerical simulation.

[0014] Furthermore, the steps for establishing the CFD model of the SCR denitrification system include:

[0015] The standard k-ε model is used as the turbulence model;

[0016] A component transport model was used to simulate the mixing and transport of multiple gas components in flue gas; these multiple gas components included NO, NH3, H2O, CO2, O2, and N2.

[0017] A standard SCR reaction was selected to represent the entire reaction process. After the CFD model was validated using the flue gas data, it was used to reflect the flue gas flow of the SCR system.

[0018] Furthermore, the definition of the ammonia injection flow influence coefficient includes:

[0019] The effect of inlet ammonia injection rate on the inlet ammonia concentration of the first catalyst layer was quantitatively analyzed using Fluent flow field simulation. Ammonia flow diagrams of ammonia injection at different ammonia injection grids were given to analyze the flow law of ammonia gas traces.

[0020] To determine the correspondence between different zones / nozzles of the ammonia injection grid and the upstream cross-sectional area of ​​the catalyst, the following definition of the ammonia injection flow influence coefficient is given:

[0021]

[0022] In the formula, a i The influence coefficient of different ammonia injection zones / nozzles, m i The effect of ammonia injection in a single zone / nozzle on the ammonia concentration in a certain area upstream of the catalyst is represented by m, where m is the total ammonia concentration injected in a single zone / nozzle.

[0023] Furthermore, the solution to the SCR reaction kinetic model yields the mathematical relationship between the NH3 concentration upstream of the catalyst and the NOx concentration at the SCR outlet, including:

[0024] By solving the SCR reaction kinetic model, the mathematical relationship between the NH3 concentration at the upstream section of the catalyst and the NOx concentration at the outlet was obtained. With the goal of minimizing the relative deviation of the uniformity of the NOx concentration distribution at the SCR outlet, the ammonia concentration distribution in different zones of the catalyst inlet section was calculated.

[0025] Furthermore, the optimization matrix equation is as follows:

[0026]

[0027] In the formula, a i,j Y represents the influence coefficient of ammonia injection in the i-th section of the ammonia injection grid on a certain j-th region upstream of the catalyst; i Both represent the ammonia concentration requirement in the i-th region upstream of the catalyst; X i This indicates the amount of ammonia injected at the corresponding zone / nozzle of the ammonia injection grid to be determined.

[0028] Furthermore, the quantitative solution yields the optimized ammonia injection rate corresponding to the ammonia injection grid with the objective of achieving the most uniform NOx concentration distribution at the SCR outlet, including:

[0029] With the goal of achieving the most uniform NOx concentration distribution at the SCR outlet, the NH3 concentration distribution at the inlet of the first-layer catalyst was determined using the mathematical relationship between the NH3 concentration at the upstream cross section of the catalyst and the NOx concentration at the outlet.

[0030] Based on the obtained optimization matrix equations of ammonia flow influence coefficients in different zones / nozzles, a quantitative calculation correlation between the ammonia injection rate and the outlet NOx concentration distribution characteristics of different zones of the ammonia injection grid is established, and the optimized ammonia injection rate is calculated using the correlation.

[0031] Furthermore, the optimized ammonia injection rate obtained through correlation calculation includes:

[0032] By analyzing the corresponding influence of ammonia injection rate in different zones of the ammonia injection grid on the outlet NOx concentration distribution, the optimization matrix equation was solved using the gradient descent method in MATLAB to obtain the optimal ammonia injection rate corresponding to different zones / nozzles of the ammonia injection grid with the most uniform outlet NOx concentration distribution.

[0033] Another technical solution adopted in this invention is:

[0034] An optimized ammonia injection device based on an SCR reaction kinetic model includes:

[0035] At least one processor;

[0036] At least one memory for storing at least one program;

[0037] When the at least one program is executed by the at least one processor, the at least one processor implements the method described above.

[0038] Another technical solution adopted in this invention is:

[0039] A computer-readable storage medium storing a processor-executable program, which, when executed by a processor, performs the method described above.

[0040] The beneficial effects of this invention are as follows: This invention aims to achieve optimal uniformity of NOx concentration distribution at the outlet. It derives a mathematical relationship between the NH3 concentration upstream of the catalyst and the NOx concentration at the outlet, based on a standard SCR reaction kinetic model. This allows for the quantitative calculation of the optimal ammonia injection rate for the ammonia injection grid based on the outlet NOx concentration distribution characteristics. Furthermore, the SCR reaction kinetic model is simple, making it easy to model and derive a quantitative mathematical relationship between the ammonia injection rate and the outlet NOx concentration, thus improving computational efficiency. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following description is provided with accompanying drawings of the relevant technical solutions in the embodiments of the present invention or the prior art. It should be understood that the accompanying drawings described below are only for the purpose of clearly illustrating some embodiments of the technical solutions of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a flowchart of an ammonia injection simulation optimization method for an SCR denitrification system according to an embodiment of the present invention;

[0043] Figure 2 This is a three-dimensional overall schematic diagram of the SCR denitrification system in an embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of the ammonia flow trajectory when ammonia is sprayed individually in the five zones in this embodiment of the invention;

[0045] Figure 4 This is a cloud map of NOx concentration distribution at the outlet measurement section of the SCR system in this embodiment of the invention;

[0046] Figure 5 This is a statistical chart of NOx concentrations in 18 zones at the outlet of the SCR system in this embodiment of the invention;

[0047] Figure 6 This is a flowchart illustrating the steps of an ammonia injection optimization method based on an SCR reaction kinetic model in an embodiment of the present invention.

[0048] Figure 2 The attached diagrams are labeled as follows: 1. SCR denitrification system inlet; 2. Baffle plate; 3. Inlet measurement section; 4. Ammonia injection grid; 5. Static mixer; 6. Guide rectifier grid; 7. Catalyst layer; 8. Outlet measurement section; 9. SCR system outlet. Detailed Implementation

[0049] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. The step numbers in the following embodiments are set only for ease of explanation, and there is no limitation on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0050] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and 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 limiting this invention.

[0051] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0052] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0053] Existing technologies have the following drawbacks:

[0054] (1) When the boiler load changes, the NOx concentration field changes. In actual engineering, the ammonia injection adjustment process mostly relies on manual experience, which is highly blind and lacks theoretical guidance, and the commissioning work takes a long time.

[0055] (2) At present, the simulation work of adjusting the ammonia injection in the SCR denitrification system is based on minimizing the relative deviation of the ammonia-nitrogen ratio at the upstream section of the catalyst to optimize the ammonia injection amount with equal ammonia-nitrogen ratio. The results show that the NOx concentration at the SCR outlet cannot meet the requirements of the optimal distribution. Even after optimization, there are still problems such as large deviation of the outlet NOx concentration and large local ammonia escape.

[0056] (3) When using CFD numerical simulation technology to conduct research on SCR ammonia injection optimization, most scholars often need to perform multiple trials to determine the corresponding ammonia injection grid zone ammonia injection amount under the optimal ammonia injection strategy. The adjustment work is somewhat blind, the calculation efficiency is low, and the simulation time is long.

[0057] (4) Existing studies have failed to analyze the corresponding influence of ammonia injection amount in different zones of the ammonia injection grid on the NOx concentration distribution at the SCR outlet. It is impossible to give a clear mathematical relationship based on the NOx concentration distribution characteristics at the outlet to quantitatively calculate the ammonia injection amount required in different zones of the ammonia injection grid. This results in poor accuracy and specificity of the existing adjustment strategies and a large degree of blindness in ammonia injection adjustment.

[0058] (5) An existing technical solution, the ammonia injection optimization method based on the influence factor, aims to optimize ammonia injection with the goal of the most uniform distribution of ammonia nitrogen ratio at the inlet of the first catalyst layer. It only guides the adjustment of the ammonia injection valve by establishing the influence factor of different partition ammonia injection amounts on the ammonia nitrogen ratio at the inlet of the first catalyst layer. It does not take the minimum relative deviation of the NOx concentration distribution at the SCR outlet as the optimization goal. Therefore, the NOx concentration at the SCR outlet cannot meet the requirements of the optimal distribution. After optimization, there will still be problems such as large deviation of NOx concentration at the outlet and large local ammonia escape.

[0059] (6) Another existing technical solution is to obtain a mathematical model of SCR reaction based on 6 sets of highly nonlinear coupled differential equations, which is used to output the mathematical relationship between the outlet NOx concentration and the inlet influencing factors. This model is too complex, difficult to model, and the calculation steps are cumbersome. It fails to directly give the mathematical relationship between the NH3 concentration upstream of the catalyst and the NOx concentration at the SCR outlet in one step. Therefore, it is difficult to directly establish a quantitative calculation correlation between the ammonia injection amount of different zones / nozzles of the ammonia injection grid and the distribution characteristics of the outlet NOx concentration.

[0060] Based on one of the above issues, see Figure 1 and Figure 6 This embodiment provides an ammonia injection optimization method based on an SCR reaction kinetic model, including the following steps:

[0061] S1. Obtain flue gas data.

[0062] As an optional implementation, flue gas data is obtained through on-site performance testing. The performance test uses measuring equipment to measure the flow field characteristics at the inlet measurement section of the SCR system, obtaining the velocity field, concentration field, and temperature field of the inlet measurement section, providing inlet parameters for CFD numerical simulation.

[0063] S2. Based on the obtained flue gas data, the CFD model of the SCR denitrification system is validated, the trajectory and influence area of ​​the ammonia injection fluid are visualized and analyzed, the ammonia injection flow influence coefficient is defined, and the correspondence between different zones / nozzles of the ammonia injection grid and the upstream cross-sectional area of ​​the catalyst is determined.

[0064] As an optional implementation, see Figure 2 The overall structural model of the SCR denitrification system was established, including the inlet and outlet flues, ammonia injection grid 4, guide plate 2, static mixer 5, guide and rectifier grid 6, and catalyst layer 7.

[0065] As an optional implementation, the CFD model establishment process mainly includes the following steps: The standard k-ε model is selected as the turbulence model; a component transport model is used to simulate the mixing and transport of six gaseous components—NO, NH3, H2O, CO2, O2, and N2—in the flue gas, without considering the influence of fly ash; a standard SCR reaction is selected to represent the entire reaction process, ignoring the adsorption, desorption, and oxidation processes of ammonia. After verifying the CFD model with the field measurement data from step S1, it can accurately reflect the actual flue gas flow of the SCR system.

[0066] As an optional implementation, the ammonia injection flow influence coefficient is quantitatively analyzed using Fluent flow field simulation to determine the impact of the inlet ammonia injection rate on the ammonia concentration at the inlet of the first-layer catalyst. Ammonia flow diagrams for different ammonia injection grids are provided to analyze the ammonia gas trajectory flow pattern. To determine the correspondence between different sections / nozzles of the ammonia injection grid and the upstream cross-sectional area of ​​the catalyst, the following definition of the ammonia injection flow influence coefficient is given:

[0067]

[0068] In the formula: a i The influence coefficient of different ammonia injection zones / nozzles, m i The effect of ammonia injection in a single zone / nozzle on the ammonia concentration in a certain area upstream of the catalyst is represented by m, where m is the total ammonia concentration injected in a single zone / nozzle.

[0069] S3. Solve the SCR reaction kinetic model to obtain the mathematical relationship between the NH3 concentration at the upstream section of the catalyst and the NOx concentration at the SCR outlet.

[0070] Specifically, based on the SCR reaction kinetic model given by the global kinetic mechanism of standard SCR chemical reaction, the mathematical relationship between the NH3 concentration at the upstream section of the catalyst and the NOx concentration at the outlet is obtained by solving the model. With the goal of minimizing the relative deviation of the uniformity of the NOx concentration distribution at the SCR outlet, the ammonia concentration distribution in different zones of the catalyst inlet section is calculated.

[0071] As an optional implementation, the catalyst is a V2O5-WO3 / TiO2 monolithic honeycomb catalyst.

[0072] As a further optional implementation, the kinetic model involved in this V2O5-WO3 / TiO2 monolithic honeycomb catalyst is as follows:

[0073]

[0074] The mathematical relationship between the NH3 concentration at the upstream cross section of the catalyst and the NOx concentration at the outlet, obtained by solving the model integral, is expressed as follows:

[0075]

[0076] Where: C NH3 C NO These represent the concentrations of NH3 and NO in the flue gas, respectively; k NO is the rate constant for the denitrification reaction. and The concentrations of NH3 and NO in different sections of the outlet measurement section are respectively. and These represent the concentrations of NH3 and NO in the upstream cross-sectional area of ​​the corresponding catalyst.

[0077] S4. The optimization matrix equation of the ammonia injection flow influence coefficient of different zones / nozzles is used to quantitatively solve the optimal ammonia injection rate corresponding to the ammonia injection grid with the goal of the most uniform NOx concentration distribution at the SCR outlet.

[0078] The optimization matrix equation is defined as follows:

[0079]

[0080] In the formula: a i,j Y represents the influence coefficient of ammonia injection in the i-th section of the ammonia injection grid on a certain j-th region upstream of the catalyst; i Both represent the ammonia concentration requirement in the i-th region upstream of the catalyst; X i This indicates the amount of ammonia injected at the corresponding zone / nozzle of the ammonia injection grid to be determined.

[0081] With the goal of achieving the most uniform NOx concentration distribution at the SCR outlet, the mathematical relationship between the NH3 concentration at the upstream cross section of the catalyst and the NOx concentration at the outlet, obtained in step S3 based on the standard SCR reaction kinetic model, is used to determine the NH3 concentration distribution at the inlet of the first-layer catalyst. Simultaneously, combined with the optimization matrix equation based on the ammonia injection flow influence coefficient of different zones / nozzles obtained in step S4, a quantitative calculation correlation between the ammonia injection rate and the NOx concentration distribution characteristics at the outlet of different zones of the ammonia injection grid can be established. The standard SCR reaction kinetic model is simple and easy to model, and the optimized ammonia injection rate can be directly calculated using the correlation.

[0082] Furthermore, by analyzing the corresponding influence of ammonia injection rate in different zones of the ammonia injection grid on the outlet NOx concentration distribution, the optimization matrix equation described in step S4 is solved using the gradient descent method in MATLAB, thus obtaining the optimal ammonia injection rate corresponding to different zones / nozzles of the ammonia injection grid with the most uniform outlet NOx concentration distribution.

[0083] The optimized ammonia injection rate can be considered as a relative value and converted proportionally. Combined with on-site ammonia injection valve commissioning experience, this provides guidance for the scale adjustment of the ammonia injection butterfly valve.

[0084] The above method will be explained in detail below with reference to the accompanying drawings and specific embodiments.

[0085] An optimization method for ammonia injection based on an SCR reaction kinetic model includes the following steps:

[0086] S101. The flue gas flow characteristics at 12×3 grid points at the inlet measurement section of the SCR system under 100% load were measured using measuring equipment to obtain the velocity field, concentration field, and temperature field of the inlet measurement section, providing inlet parameters for CFD numerical simulation. The average inlet velocity of the SCR system was 2.9 m / s, and the calculated ammonia injection flow rate per nozzle was 0.046 kg / s, with an ammonia volume fraction of 2.35%.

[0087] S102, such as Figure 2 As shown, taking reactor A as an example, the overall structure of the SCR system is geometrically modeled, and the ammonia injection grid is specifically divided into zones. Then, mesh generation is performed, with unstructured meshes used for the ammonia injection grid, guide vanes, and mixer, and the nozzle positions are fined; other regular areas use structured meshes.

[0088] S103. The numerical simulation of the entire SCR denitrification system model includes turbulent flow models, component transport models, and chemical reaction models. Selecting appropriate mathematical models and parameter values ​​in Fluent ensures reliable simulation results. The standard k-ε model is used for the turbulence model. A component transport model is employed to simulate the mixing and transport of six gaseous components in the flue gas: NO, NH3, H2O, CO2, O2, and N2, without considering the influence of fly ash. The standard SCR reaction is used to represent the entire reaction process, ignoring the adsorption and desorption processes of ammonia and the oxidation reaction, thus realistically reflecting the actual flue gas flow in the SCR system. The three catalyst layers are set as porous media regions, and the drag coefficient is calculated based on the actual pressure drop.

[0089] S104. Based on the NOx concentration and temperature distribution at the inlet measurement section of the performance test, inversely calculate the NOx concentration and temperature distribution at the simulated inlet section. Perform numerical calculations in Fluent. After the calculations are confirmed to be converged, compare the calculation results with the experimental data to verify the reliability of the CFD model.

[0090] S105 describes a simulation optimization method for ammonia injection in an SCR denitrification system under 100% load, but this method is also applicable to other operating conditions. Based on previous simulation reports, the flow field of the entire SCR system is relatively uniform, and the internal flow guiding device is reasonably configured, meeting the flow field design requirements. When a uniform ammonia injection method is used for denitrification reaction simulation, the uniformity of the outlet NOx concentration distribution is as follows: Figure 4 As shown in (a), when uniform ammonia injection is used, the ammonia-nitrogen concentration equivalence ratio in the catalytic reactor is mismatched. Excessive ammonia injection occurs in the right-side region of the reactor, leading to a lower NOx concentration at the outlet in that region and a risk of ammonia escape. Simultaneously, the NOx concentration at the outlet in the left-side region is higher, exceeding 50 mg / Nm³. 3The project requirements are met. The NOx concentration distribution uniformity at the outlet measurement section is poor, with a relative standard deviation as high as 40.14%. This indicates that an unreasonable ammonia-nitrogen mixing equivalent ratio in different zones within the reactor will lead to severely uneven NOx concentration distribution at the outlet. Therefore, it is necessary to optimize the ammonia injection grid by zoned ammonia injection to improve the uniformity of the outlet NOx concentration. Among these, Figure 4 (a) is a contour map of the NOx concentration distribution at the outlet under the uniform ammonia injection method. Figure 4 (b) is a contour map of the NOx concentration distribution at the outlet under the five zoning optimization methods. Figure 4 (c) is a cloud map of the NOx concentration distribution at the outlet under 42 nozzle optimization methods.

[0091] S106. Using Fluent flow field simulation, the impact of inlet ammonia injection rate on the ammonia concentration distribution at the inlet of the first-layer catalyst was quantitatively analyzed. Taking an actual power plant as an example, the inlet cross-section of the first-layer catalyst was divided into 6×3=18 zones, named C11, C12…C62, C63, corresponding to the 18 zones for gridded NOx sampling at the outlet. Flow field visualization analysis was performed on the ammonia gas flowing out of five different zones of the ammonia injection grid. Figure 3 This is a schematic diagram of the ammonia trajectory flow in the ammonia injection grid. Due to the flow guiding structure within the flue restricting the mixing and diffusion of NH3 injected from the branch pipes within the flue, and the limited mixing distance, the ammonia injection in each zone / nozzle affects the ammonia concentration distribution in the 18 zones at the catalyst inlet within a certain area. Therefore, in order to determine the correspondence between different zones / nozzles of the ammonia injection grid and the upstream cross-sectional area of ​​the catalyst, the following definition of the ammonia injection flow influence coefficient is given:

[0092]

[0093] In the formula: a i The influence coefficient of different ammonia injection zones / nozzles, m i The effect of ammonia injection in a single zone / nozzle on the ammonia concentration in a certain area upstream of the catalyst is represented by m, where m is the total ammonia concentration injected in a single zone / nozzle.

[0094] S107. Based on the definition of the ammonia injection flow influence coefficient in formula (1) above, the influence coefficients of the five zones of the ammonia injection grid on the 18 zones of the catalyst inlet are obtained as shown in Table 1. The influence coefficient of each zone on the 18 zones of the catalyst inlet is different. Taking zone 1 as an example, the ammonia injection in this zone mainly affects the inlet C11-C13 and C23 regions, with an influence coefficient exceeding 0.1, and has a smaller impact on other regions. Due to space limitations, the ammonia injection flow influence coefficients of the 42 nozzles are omitted, and their solution method is consistent with the optimization method of the five zones.

[0095] Table 1. Ammonia Injection Flow Influence Coefficients in Different Zones

[0096]

[0097] S108. To achieve the optimization goal of the most uniform NOx concentration distribution at the outlet measurement section, it is necessary to further determine the correspondence between the NOx concentration in different zones of the outlet section and the ammonia concentration distribution in the 18 zones upstream of the catalyst. The standard SCR chemical reaction global kinetic mechanism is represented by reaction equation (2):

[0098] 4NO + 4NH3 + O2 → 4N2 + 6H2O (2)

[0099] The kinetic model involved in the V2O5-WO3 / TiO2 monolithic honeycomb catalyst is represented by the following equation (3):

[0100]

[0101] In the process of solving the model, it is assumed that the consumption rates of NO and NH3 in the reaction are the same, that is, it conforms to (4); according to formula (3) and by substituting the initial data into the integral, the mathematical relationship between the NH3 concentration at the upstream section of the catalyst and the NOx at the outlet is obtained (6).

[0102]

[0103]

[0104]

[0105] Where: C NH3 C NO These represent the concentrations of NH3 and NO in the flue gas, respectively; k NO Here, k is the pre-exponential coefficient; Ea is the apparent activation energy characterizing the reaction rate; T is the temperature of the denitrification reactor; R represents the gas constant; and t is the residence time. and The concentrations of NH3 and NO were measured in 18 sections of the outlet measurement section, respectively. and These represent the concentrations of NH3 and NO in the 18 sections of the upstream cross-section of the corresponding catalyst.

[0106] S109. The matrix equation defined based on the ammonia injection influence coefficient is as follows:

[0107]

[0108] This invention performs two optimizations: partitioning and nozzle optimization. Therefore, in Equation 7: 1) If 5 partitions are optimized, then a i,j (i = 1:5, j = 1:18) represents the influence coefficient of ammonia injection in the i-th section of the ammonia injection grid on a certain j-th region among the 18 regions upstream of the catalyst; 2) If optimization is performed with 42 nozzles, then a i,j(i = 1:42, j = 1:18) represents the influence coefficient of the i-th nozzle of the ammonia injection grid on a certain j-th region among the 18 regions upstream of the catalyst; in both cases, Y i Both represent the ammonia concentration requirement in the i-th region among the 18 regions upstream of the catalyst; X i This indicates the amount of ammonia injected at the corresponding zone / nozzle of the ammonia injection grid to be determined.

[0109] S110. With the goal of achieving the most uniform NOx concentration distribution at the outlet, the NH3 concentration distribution at the inlet of the first-layer catalyst is determined based on the mathematical relationship between the NH3 concentration at the upstream section of the catalyst and the NOx concentration at the outlet, according to the standard SCR reaction kinetic model. Simultaneously, by combining the optimization matrix equation based on the influence coefficient of ammonia injection flow in different zones / nozzles, a quantitative calculation correlation between the ammonia injection rate and the NOx concentration distribution characteristics at the outlet of different zones of the ammonia injection grid can be established. This standard SCR reaction kinetic model is simple and easy to model, allowing for the quantitative solution of the ammonia injection rate mathematical relationship. This improves the accuracy and targeting of ammonia injection adjustments, reduces the blindness of adjustment work, and increases computational efficiency.

[0110] S111. By analyzing the corresponding influence of ammonia injection rate in different zones of the ammonia injection grid on the outlet NOx concentration distribution, based on the simulation results of uniform ammonia injection, the average NOx concentration at the outlet section is kept constant (below 50 mg / Nm³). 3 (Engineering standards), assuming the target NOx concentration at the outlet of each zone is a cross-sectional average of 41.7 mg / Nm³. 3 (0.0004458mol / m 3 To minimize the relative deviation of the NOx concentration at the outlet, the NH3 concentration distribution at the inlet of the first-layer catalyst is calculated by back-calculating the mathematical relationship between the NH3 concentration at the upstream section of the catalyst and the NOx concentration at the outlet using formula (6). The required amount Y of the NH3 concentration distribution at the inlet of different zones is then calculated. i Substituting into the optimization matrix equation (7), the optimal ammonia injection rate X corresponding to different zones of the ammonia injection grid with the most uniform NOx concentration distribution at the outlet is obtained by using the gradient descent method in MATLAB. i The optimized ammonia injection rates for different zones were substituted into Fluent for simulation calculations. Specific simulation results are as follows: Figure 4 NOx concentration distribution cloud map at the outlet measurement section of the SCR system and Figure 5 The NOx concentration statistics for the 18 zones at the outlet of the SCR system are shown in the figure.

[0111] S112. After optimization with ammonia injection in 5 zones, the uniformity of NOx concentration distribution at the outlet improved. The areas of the low NOx concentration region on the right and the high NOx concentration region in the upper left decreased, and the relative standard deviation dropped to 33.0%. Compared with the uniform ammonia injection method, the optimization effect on the uniformity of NOx concentration distribution at the outlet improved by 17.7%. To further optimize the uniformity of NOx concentration distribution at the outlet, a more refined ammonia injection optimization adjustment method is needed. After optimization with 42 nozzles, the NOx concentration in the 18 outlet zones tended to approach a cross-sectional average of 40 mg / Nm³. 3 There is no risk of NOx concentration being too low, excessive ammonia injection, or ammonia escape exceeding the emission standard, nor is there any exceedance of the emission standard of 50 mg / Nm³. 3 The region can achieve NOx emission at the designated level to meet environmental protection requirements, while avoiding areas with excessively high or low denitrification efficiency, thus achieving the goal of improving the uniformity of NOx concentration distribution at the outlet.

[0112] S113. Assuming the initial valve opening is 70° under uniform ammonia injection conditions, and the valve opening range is 0-100°, the optimized ammonia injection rate of 42 nozzles under 100% load conditions is compared with that under uniform ammonia injection conditions. The relative values ​​for adjusting the opening of the 42 optimized ammonia injection valves are shown in Table 2. Compared to the opening size of the 42 valves under the uniform ammonia injection strategy, valve A4-3 needs to be reduced by 17.5°, i.e., this valve has a minimum opening of 52.5°. Valve A14-1 needs to be increased by 13.8°, i.e., this valve has a maximum opening of 83.8°. After obtaining the optimized opening of the 42 ammonia injection valves, and combining on-site ammonia injection valve commissioning experience and the gridded measurement results of the outlet NOx concentration, the ammonia injection valves are adjusted to achieve the goal of optimizing ammonia injection in the SCR denitrification system and improving the uniformity of the outlet NOx concentration distribution.

[0113] Table 2. Relative values ​​of opening adjustment for 42 ammonia injection valves

[0114]

[0115]

[0116] S113. When the boiler load changes, the corresponding relationship between the NOx concentration distribution characteristics of different zones / nozzles of the ammonia injection grid and the outlet section can be determined by establishing flue gas flow and reaction models under different operating conditions and repeating the above calculation steps. This can significantly help and improve the debugging efficiency of the ammonia injection control valve under different operating conditions, and provide theoretical reference for actual ammonia injection optimization adjustment tests and operation.

[0117] In summary, the method of this embodiment has the following advantages and beneficial effects compared with the prior art:

[0118] (1) The present invention adopts simulated inlet boundary conditions based on experimental measured values, which can more realistically reflect the overall flue gas flow of the SCR system. It can visualize and analyze the flue gas flow, ammonia-nitrogen mixing and denitrification reaction characteristics, obtain the flow law of ammonia trace, find the regional range of downstream SCR inlet ammonia concentration distribution affected by upstream ammonia injection and the regional range of SCR outlet NOx concentration distribution after reaction, provide theoretical reference for actual ammonia injection optimization and adjustment test and operation, and reduce the blindness of adjustment work.

[0119] (2) This invention aims to optimize the uniformity of NOx concentration distribution at the outlet. It obtains a mathematical relationship between the NH3 concentration at the upstream section of the catalyst and the NOx concentration at the outlet based on the standard SCR reaction kinetic model, determines the NH3 concentration distribution at the inlet of the first catalyst layer, and combines the optimization matrix equation based on the influence coefficient of ammonia injection flow in different zones / nozzles to establish a quantitative calculation correlation between the ammonia injection amount and the NOx concentration distribution characteristics at the outlet of different zones of the ammonia injection grid. It can quantitatively solve the optimized ammonia injection amount corresponding to the ammonia injection grid based on the NOx concentration distribution characteristics at the outlet. The standard SCR reaction kinetic model is simple and easy to model to obtain a quantitative calculation mathematical relationship between the ammonia injection amount and the NOx concentration at the outlet of the ammonia injection grid, thus improving the calculation efficiency.

[0120] (3) The optimized ammonia injection method obtained by simulation can not only control the ammonia injection amount in the ammonia injection grid, but also be applied to the control valve of each nozzle in the ammonia injection grid in a more refined manner. Combined with the on-site debugging experience, the valve opening of the optimized ammonia injection amount obtained by simulation is proportionally converted to guide the adjustment of the ammonia injection control valve.

[0121] (4) The optimization method of the present invention can be applied to different working conditions. By establishing flow and reaction models under different working conditions, repeating the above calculation steps can also determine the correspondence between the NOx concentration distribution characteristics of different zones / nozzles of the ammonia injection grid and the outlet section, which can significantly help and improve the debugging efficiency of the ammonia injection control valve under different working conditions.

[0122] This embodiment also provides an ammonia injection optimization device based on an SCR reaction kinetic model, including:

[0123] At least one processor;

[0124] At least one memory for storing at least one program;

[0125] When the at least one program is executed by the at least one processor, the at least one processor implements Figure 6 The method shown.

[0126] This embodiment of the ammonia injection optimization device based on the SCR reaction kinetic model can execute the ammonia injection optimization method based on the SCR reaction kinetic model provided in the method embodiment of the present invention. It can execute any combination of the implementation steps of the method embodiment and has the corresponding functions and beneficial effects of the method.

[0127] This application also discloses a computer program product or computer program, which includes computer instructions stored in a computer-readable storage medium. A processor of a computer device can read the computer instructions from the computer-readable storage medium, and the processor executes the computer instructions, causing the computer device to perform... Figure 6 The method shown.

[0128] This embodiment also provides a storage medium storing instructions or programs that can execute the ammonia injection optimization method based on the SCR reaction kinetic model provided in the method embodiment of the present invention. When the instructions or programs are run, any combination of implementation steps of the method embodiment can be executed, and the method has the corresponding functions and beneficial effects.

[0129] In some alternative embodiments, the functions / operations mentioned in the block diagrams may not occur in the order shown in the operation diagrams. For example, depending on the functions / operations involved, two consecutively shown blocks may actually be executed substantially simultaneously, or the blocks may sometimes be executed in reverse order. Furthermore, the embodiments presented and described in the flowcharts of this invention are provided by way of example to provide a more comprehensive understanding of the technology. The disclosed methods are not limited to the operations and logic flows presented herein. Alternative embodiments are contemplated in which the order of various operations is altered and sub-operations described as part of a larger operation are executed independently.

[0130] Furthermore, although the invention has been described in the context of functional modules, it should be understood that, unless otherwise stated, one or more of the described functions and / or features may be integrated into a single physical device and / or software module, or one or more functions and / or features may be implemented in a separate physical device or software module. It is also understood that a detailed discussion of the actual implementation of each module is unnecessary for understanding the invention. Rather, given the properties, functions, and internal relationships of the various functional modules in the apparatus disclosed herein, the actual implementation of the module will be understood within the scope of conventional skill of an engineer. Therefore, those skilled in the art can implement the invention as set forth in the claims using ordinary techniques without excessive experimentation. It is also understood that the specific concepts disclosed are merely illustrative and not intended to limit the scope of the invention, which is determined by the full scope of the appended claims and their equivalents.

[0131] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, essentially, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0132] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0133] More specific examples of computer-readable media (a non-exhaustive list) include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0134] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0135] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," or "some embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0136] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

[0137] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A method for optimizing ammonia injection based on an SCR reaction kinetic model, characterized in that, Includes the following steps: Acquire flue gas data; Based on the obtained flue gas data, the CFD model of the SCR denitrification system was validated, the trajectory and influence area of ​​the ammonia injection fluid were visualized and analyzed, the ammonia injection flow influence coefficient was defined, and the correspondence between different zones / nozzles of the ammonia injection grid and the upstream cross-sectional area of ​​the catalyst was determined. By solving the SCR reaction kinetic model, the mathematical relationship between the NH3 concentration at the upstream section of the catalyst and the NOx concentration at the outlet was obtained. With the goal of minimizing the relative deviation of the uniformity of the NOx concentration distribution at the SCR outlet, the ammonia concentration distribution in different zones of the catalyst inlet section was calculated. The optimization matrix equations of the ammonia injection flow influence coefficients of different zones / nozzles are used to quantitatively solve the optimal ammonia injection rate corresponding to the ammonia injection grid with the goal of achieving the most uniform NOx concentration distribution at the SCR outlet. The definition of the ammonia injection flow influence coefficient includes: The effect of inlet ammonia injection rate on the inlet ammonia concentration of the first catalyst layer was quantitatively analyzed using Fluent flow field simulation. Ammonia flow diagrams of ammonia injection at different ammonia injection grids were given to analyze the flow law of ammonia gas traces. To determine the correspondence between different zones / nozzles of the ammonia injection grid and the upstream cross-sectional area of ​​the catalyst, the following definition of the ammonia injection flow influence coefficient is given: In the formula, The influence coefficient of different ammonia injection zones / nozzles, The ammonia injection from a single zone / nozzle affects the ammonia concentration in a specific region upstream of the catalyst. The total concentration of ammonia injected in a single zone / nozzle.

2. The ammonia injection optimization method based on the SCR reaction kinetics model according to claim 1, characterized in that, The acquisition of flue gas data includes: The flow field characteristics at the inlet measurement section of the SCR system are measured to obtain flue gas data; wherein, the flue gas data includes the velocity field, concentration field, and temperature field of the inlet measurement section, as well as the inlet parameters from CFD numerical simulation.

3. The ammonia injection optimization method based on the SCR reaction kinetics model according to claim 1, characterized in that, The steps for establishing the CFD model of the SCR denitrification system include: The standard k-ε model is used as the turbulence model; A component transport model was used to simulate the mixing and transport of multiple gas components in flue gas; these multiple gas components included NO, NH3, H2O, CO2, O2, and N2. A standard SCR reaction was selected to represent the entire reaction process. After the CFD model was validated using the flue gas data, it was used to reflect the flue gas flow of the SCR system.

4. The ammonia injection optimization method based on the SCR reaction kinetics model according to claim 1, characterized in that, The optimization matrix equation is: In the formula, It represents the influence coefficient of ammonia injection in the i-th section of the ammonia injection grid on a certain j-th region upstream of the catalyst; Both represent the ammonia concentration requirement in the i-th region upstream of the catalyst; This indicates the amount of ammonia injected at the corresponding zone / nozzle of the ammonia injection grid to be determined.

5. The ammonia injection optimization method based on the SCR reaction kinetics model according to claim 1, characterized in that, The quantitative solution yields the optimized ammonia injection rate corresponding to the ammonia injection grid, with the goal of achieving the most uniform NOx concentration distribution at the SCR outlet. This includes: With the goal of achieving the most uniform NOx concentration distribution at the SCR outlet, the NH3 concentration distribution at the inlet of the first-layer catalyst was determined using the mathematical relationship between the NH3 concentration at the upstream cross section of the catalyst and the NOx concentration at the outlet. Based on the obtained optimization matrix equations of ammonia flow influence coefficients in different zones / nozzles, a quantitative calculation correlation between the ammonia injection rate and the outlet NOx concentration distribution characteristics of different zones of the ammonia injection grid is established, and the optimized ammonia injection rate is calculated using the correlation.

6. The ammonia injection optimization method based on the SCR reaction kinetics model according to claim 5, characterized in that, The optimized ammonia injection rate obtained through correlation calculation includes: By analyzing the corresponding influence of ammonia injection rate in different zones of the ammonia injection grid on the outlet NOx concentration distribution, the optimization matrix equation was solved using the gradient descent method in MATLAB to obtain the optimal ammonia injection rate corresponding to different zones / nozzles of the ammonia injection grid with the most uniform outlet NOx concentration distribution.

7. An optimized ammonia injection device based on an SCR reaction kinetic model, characterized in that, include: At least one processor; At least one memory for storing at least one program; When the at least one program is executed by the at least one processor, the at least one processor implements the method according to any one of claims 1-6.

8. A computer-readable storage medium storing a processor-executable program, characterized in that, The processor-executable program, when executed by the processor, is used to perform the method as described in any one of claims 1-6.

Images