Nozzle optimization method of urea direct injection system for waste heat boiler denitration

Abstract

The invention relates to the field of numerical simulation, and discloses a nozzle optimization method of a urea direct injection system for waste heat boiler denitration, which is used for improving the denitration efficiency and the operation stability of the urea direct injection system and reducing the ammonia escape rate and the operation cost. Comprising the following steps: establishing a three-dimensional parameterized CFD nozzle model based on parameters such as a waste heat boiler flue structure, generating a plurality of distribution diagrams, screening out a candidate scheme set of which the mixing uniformity reaches the standard, processing and manufacturing a replaceable nozzle physical sample unit according to parameters of the candidate scheme set, and measuring a denitration efficiency value and an ammonia escape rate value of each model machine under an actual operation condition. And performing correlation analysis on various distribution diagrams, denitration efficiency values and ammonia escape rate values, delimiting an effective mixing zone boundary based on a flue gas flow velocity field and the like, and outputting optimal nozzle geometric dimension parameters meeting engineering application. According to the method, through multi-dimensional modeling, calculation, experiment and correlation analysis, the optimal nozzle geometric dimension parameters meeting engineering application are accurately output, the denitration efficiency is effectively improved, and the ammonia escape rate is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of numerical simulation, and in particular to a nozzle optimization method for a urea direct injection system for denitration of a waste heat boiler. BACKGROUND

[0002] In the industrial field, waste heat boilers, as important energy-saving equipment, are widely used in steel, chemical, building material and other industries to recover waste heat in high-temperature flue gas to produce steam or hot water, thereby improving energy utilization efficiency. With the increasing strictness of environmental protection requirements, the control of nitrogen oxide emissions in the flue gas of waste heat boilers has become a key problem. Selective catalytic reduction and selective non-catalytic reduction are two commonly used denitration technologies, among which the urea direct injection system, as an application form of SNCR technology, has a broad application prospect in the denitration of small and medium-sized waste heat boilers due to its low investment cost and simple operation and maintenance.

[0003] The core component of the urea direct injection system is the nozzle, and its performance directly affects the mixing uniformity of urea solution and flue gas, denitration efficiency and ammonia slip rate. Ammonia slip not only causes waste of urea and increases operating costs, but also forms ammonium salt deposits in subsequent equipment, causing equipment corrosion and blockage, and poses a threat to the safe operation of the boiler. Therefore, optimizing the design of the nozzle, improving the mixing effect of urea solution and flue gas, and achieving efficient denitration while controlling ammonia slip are the keys to the development of waste heat boiler denitration technology.

[0004] Disadvantages in the prior art: Traditional nozzle design is mostly based on experience or simple theoretical calculations, lacking in-depth analysis of the complex flow field characteristics of the flue of the waste heat boiler. The flue structure, operating parameters and urea physical property parameters of different boilers differ, making it difficult for universal nozzles to adapt to diverse engineering needs, resulting in poor mixing uniformity and low denitration efficiency; Although computational fluid dynamics technology has been applied to nozzle design to some extent, existing models are mostly static or semi-static, and cannot be adjusted in real time according to the dynamic changes in nozzle geometry, making it difficult to fully simulate the flow field characteristics of nozzles of different sizes. In addition, the correlation between CFD calculation results and actual operating conditions is insufficient, and there is a lack of effective verification methods, resulting in a lack of reliability in optimized design; Existing nozzle performance experiments mostly use single or limited operating conditions for testing, which cannot fully cover the load variation range in actual boiler operation, and the test section and measurement point arrangement are not reasonable, resulting in insufficient representativeness of the data and making it difficult to accurately evaluate the denitration efficiency and ammonia slip rate of the nozzle under different operating conditions. In addition, there is a lack of effective compensation for interference factors such as temperature drift during the experiment, further reducing the accuracy of the measurement results.

[0005] Therefore, we propose a nozzle optimization method for a urea direct injection system for denitration of a waste heat boiler to solve the above problems. SUMMARY

[0006] The application provides a nozzle optimization method of a urea direct injection system for waste heat boiler denitration, which is used for improving the denitration efficiency and operation stability of the urea direct injection system, reducing the ammonia escape rate and operation cost.

[0007] The first aspect of the application provides a nozzle optimization method of a urea direct injection system for waste heat boiler denitration, which comprises: establishing a three-dimensional parameterized CFD nozzle model based on the waste heat boiler flue structure, design working condition parameters and urea physical property parameters; performing iterative calculation on the three-dimensional parameterized CFD nozzle model by a CFD solver to generate a flue gas flow velocity field distribution map, a urea droplet trajectory cloud picture and a concentration field distribution map under different nozzle geometric sizes, and screening out a candidate scheme set; processing and manufacturing a replaceable nozzle physical prototype set according to the nozzle geometric size parameters of the candidate scheme set; installing the replaceable nozzle physical prototype set on a waste heat boiler denitration experimental platform, and respectively measuring the denitration efficiency value and the ammonia escape rate value of each nozzle prototype under actual operation conditions; correlating and analyzing the flue gas flow velocity field distribution map, the urea droplet trajectory cloud picture and the concentration field distribution map with the denitration efficiency value and the ammonia escape rate value, and outputting the optimal nozzle geometric size parameters.

[0008] Optionally, in the first implementation manner of the first aspect of the application, the method comprises: generating a basic nozzle three-dimensional geometric model based on the waste heat boiler flue structure, the design working condition parameters and the urea physical property parameters; selecting the nozzle throat diameter, the outlet diffusion angle and the length-diameter ratio as adjustable geometric parameters to establish a geometric parameter library; and binding the geometric parameter library and the topological structure of the basic nozzle three-dimensional geometric model by geometric correlation rules in a CFD pre-processing software to form the three-dimensional parameterized CFD nozzle model.

[0009] Optionally, in the second implementation manner of the first aspect of the application, the method comprises: generating a characteristic size combination matrix by an orthogonal test design method based on the nozzle throat diameter, the outlet diffusion angle and the length-diameter ratio in the geometric parameter library; inputting the characteristic size combination matrix into a CFD solver to drive the three-dimensional parameterized CFD nozzle model to automatically deform and iteratively solve, and outputting the flue gas flow velocity field distribution map, the urea droplet trajectory cloud picture and the concentration field distribution map corresponding to each group of parameters; extracting the urea concentration standard deviation in all concentration field distribution maps, and defining the area ratio of the region with a standard deviation ≤5% as a mixing uniformity quantitative value; and taking the mixing uniformity quantitative value ≥90% as a constraint condition to extract the qualified parameter group from the characteristic size combination matrix to form the candidate scheme set.

[0010] Optionally, in the third implementation form of the first aspect of the present application, the method further comprises: extracting three groups of parameters of throat diameter, outlet diffusion angle and length-diameter ratio based on the geometric size parameter table of the candidate scheme set, re-grouping according to a gradient rule of a parameter value difference amplitude ≥ 15%, and generating a gradient nozzle three-dimensional model group.

[0011] Optionally, in the fourth implementation form of the first aspect of the present application, a unified specification buckle type quick mounting interface is integrated at the flange end of the gradient nozzle three-dimensional model group, to ensure the physical interchangeability of all prototype and experimental platform lance seats; a five-axis numerical control machine tool is used for cutting processing according to the gradient nozzle three-dimensional model group, and a hole diameter processing precision compensation of +0.1mm~+0.15mm is applied to the prototype with a throat diameter <10mm, and an output replaceable nozzle physical prototype group is output.

[0012] Optionally, in the fifth implementation form of the first aspect of the present application, the method further comprises: setting a first detection section and a second detection section downstream of the nozzle in the experimental platform flue; sequentially installing the replaceable nozzle physical prototype group to the experimental platform lance seat, controlling the boiler load to change in a gradient of 10% in the range of 80%~110% of the design value, and after stable operation for 30 minutes at each load point, synchronously triggering the ammonia concentration and NO x concentration data acquisition of the two sections; monitoring the flue temperature fluctuation in real time, when the temperature change exceeds ±5℃, injecting standard concentration ammonia gas to the ammonia concentration analyzer for online calibration, correcting the original measurement value of the ammonia escape rate at the load point based on the calibration result; calculating the denitration efficiency value of the current prototype at the current load point according to the first section NO x concentration C1 and the second section NO x concentration C2, denitration efficiency=(C1-C2) / C1×100%, taking the average value of the ammonia concentration of the second section 4 measuring points as the ammonia escape rate value of the working condition; collecting the denitration efficiency value and the ammonia escape rate value of all prototypes under the full load gradient to form a stable working condition performance data set.

[0013] Optionally, in the sixth implementation form of the first aspect of the present application, the first detection section is set at 1.5m downstream of the nozzle and the second detection section is set at 3m downstream of the nozzle in the experimental platform flue, and 4 laser ammonia concentration analyzers and flue gas sampling probes are uniformly distributed in the circumferential direction of each section.

[0014] Optionally, in the seventh implementation manner of the first aspect of the present application, the method further comprises: based on the flue gas velocity field distribution map, marking the region with a flow velocity of 0.5-3 m / s as a low-speed mixing zone; based on the urea droplet trajectory cloud map, marking the region with a droplet residence time of greater than or equal to 0.8 s as an effective reaction zone; taking the spatial intersection of the low-speed mixing zone and the effective reaction zone as the boundary of an effective mixing zone; within the boundary of the effective mixing zone, extracting the urea concentration standard deviation σ of the concentration field distribution map, and recording the area ratio of the region with σ less than or equal to 2.5% as an effective uniformity index; in the stable state working condition performance data set, marking the working condition with a denitration efficiency greater than 95% and an ammonia escape rate less than 3 ppm as a qualified working condition, correlating the nozzle geometric size, the effective uniformity index and the measured ammonia escape rate value corresponding to each qualified working condition, and generating a three-dimensional performance matrix; in the three-dimensional performance matrix, screening the working condition point with an effective uniformity index greater than or equal to 92% and the lowest ammonia escape rate, and outputting the nozzle throat diameter, the outlet diffusion angle and the length-diameter ratio corresponding to the working condition point as the optimal nozzle geometric size parameters.

[0015] The mechanism of the present application is as follows: the principles of fluid mechanics and thermodynamics are converted into quantifiable engineering thresholds to form a mechanism-driven closed-loop optimization chain, which improves efficiency compared to the traditional trial-and-error method. Beneficial effects: The three-dimensional parameterized CFD model of the nozzle with dynamically adjustable geometric size constructed by the present application fully integrates the flue structure, working condition parameters and urea physical property parameters into the design process, realizes the precision and individualization of nozzle design, breaks through the limitations of traditional design, and can better adapt to the actual needs of different boilers. The orthogonal experimental design method is used to construct a parameter combination matrix, which can cover the full spatial combination of the nozzle throat diameter, the outlet diffusion angle and the length-diameter ratio with fewer test times, more systematically and comprehensively explore the parameter space compared to the traditional one-by-one test method, avoid missing potential optimal solutions, and provide a solid foundation for screening high-performance nozzle designs. The urea concentration standard deviation in the concentration field distribution map is extracted, and the area ratio of the region with a standard deviation less than or equal to 5% is defined as a mixing uniformity quantitative value, which provides an objective and accurate quantitative index for evaluating the mixing performance of the nozzle, avoids the uncertainty of subjective evaluation, and makes the comparison of mixing effects between different design schemes more scientific and reliable. Based on the candidate scheme set, a gradientized three-dimensional model group is generated, and the group is re-grouped according to the gradient rule with a parameter value difference amplitude greater than or equal to 15%, so that a replaceable nozzle physical prototype group with size gradient differences is manufactured, which can cover a wider parameter range, meet the comprehensive testing needs of nozzle performance under different working conditions, and help to find more potential optimal designs. Based on the flue gas flow velocity field distribution map and the urea droplet trajectory cloud map, the low-speed mixing zone and the effective reaction zone are demarcated, and the spatial intersection of the two is defined as the effective mixing zone boundary, which comprehensively considers the influence of the flow field velocity and the droplet residence time on the mixing reaction, can more accurately determine the key area of the nozzle performance, and provides an accurate spatial range for subsequent analysis. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 An embodiment of the nozzle optimization method of the urea direct injection system for the waste heat boiler denitration in the embodiment of the present application is shown. Figure 2 An embodiment of the nozzle optimization device of the urea direct injection system for the waste heat boiler denitration in the embodiment of the present application is shown. DETAILED DESCRIPTION

[0017] The embodiment of the present application provides a nozzle optimization method of a urea direct injection system for a waste heat boiler denitration, which is used for improving the denitration efficiency and operation stability of the urea direct injection system, and reducing the ammonia escape rate and operation cost. The terms "first", "second", "third", "fourth" and the like (if any) in the specification and claims of the present application and the above drawings are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "include" or "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0018] For the sake of understanding, the specific flow of the embodiment of the present application is described below, please refer to Figure 1 The nozzle optimization method of the urea direct injection system for the waste heat boiler denitration in the embodiment of the present application includes: 101. Construct a three-dimensional parameterized CFD nozzle model: based on the waste heat boiler flue structure, design working condition parameters and urea physical property parameters, a three-dimensional parameterized CFD nozzle model with dynamically adjustable nozzle geometric size is established; It can be understood that the execution subject of the present application can be a nozzle optimization device of a urea direct injection system for a waste heat boiler denitration, and can also be a terminal or a server, which is not limited here. The embodiment of the present application takes the server as the execution subject for example.

[0019] It should be noted that the basic nozzle three-dimensional geometry is constructed: based on the flue gas structure of the waste heat boiler, the design working condition parameters and the urea physical property parameters, a basic nozzle three-dimensional geometric model containing an atomization cone angle area, a jet flow channel and a mounting interface is generated; The key size parameter library is defined: the nozzle throat diameter, the outlet diffusion angle and the length-diameter ratio are selected as adjustable geometric parameters, and a geometric parameter library independently controlling each parameter is established; The parameterized driving logic is established: in the CFD pre-processing software, the geometric parameter library is bound to the topological structure of the basic nozzle three-dimensional geometric model through geometric association rules, forming a three-dimensional parameterized CFD nozzle model which can be driven by modifying the parameter library values in real time to deform the model.

[0020] 102, Perform multi-parameter flow field pre-screening: through the CFD solver, the three-dimensional parameterized CFD nozzle model is iteratively calculated to generate flue gas velocity field distribution maps, urea droplet trajectory cloud maps and concentration field distribution maps under different nozzle geometric sizes, and a candidate scheme set that meets the mixing uniformity standard is screened out; It should be noted that the orthogonal test parameter combination matrix is constructed: based on the nozzle throat diameter, the outlet diffusion angle and the length-diameter ratio in the geometric parameter library, an orthogonal test design method is used to generate a feature size combination matrix covering the entire parameter space; Perform parameterized CFD batch calculation: input the feature size combination matrix into the CFD solver to drive the three-dimensional parameterized CFD nozzle model to automatically deform and iteratively solve, and output the flue gas velocity field distribution map, urea droplet trajectory cloud map and concentration field distribution map corresponding to each group of parameters; Quantify the mixing uniformity index: extract the standard deviation of urea concentration in all concentration field distribution maps, and define the area ratio of the region with a standard deviation ≤5% as the quantified value of mixing uniformity; Screen the candidate scheme set: with the constraint condition that the quantified value of mixing uniformity is ≥90%, extract the standard parameter set from the feature size combination matrix to form a candidate scheme set and output a geometric size parameter table.

[0021] 103, Manufacture replaceable physical prototypes: according to the nozzle geometric size parameters of the candidate scheme set, process and manufacture a group of replaceable nozzle physical prototypes with size gradient differences; It should be noted that a group of gradientized prototype three-dimensional models is generated: based on the geometric size parameter table of the candidate scheme set, three groups of parameters of throat diameter, outlet diffusion angle and length-diameter ratio are extracted, and are regrouped according to the gradient rule with a parameter value difference amplitude ≥15% to generate a group of gradientized nozzle three-dimensional models covering the parameter space; Design a replaceable mounting structure: integrate a unified specification buckle type quick mounting interface on the flange end of the group of gradientized nozzle three-dimensional models to ensure the physical interchangeability of all prototypes with the experimental platform lance seat; Gradient compensation machining is performed: a five-axis CNC machine tool is used to perform cutting machining based on the gradient nozzle three-dimensional model group, and a hole diameter machining accuracy compensation of +0.1mm~+0.15mm is applied to the prototype with throat diameter <10mm, and a replaceable nozzle physical prototype group with size gradient difference is output.

[0022] 104. Actual measured denitrification performance indicators: Install the replaceable nozzle physical prototype group on the waste heat boiler denitrification experimental platform, and measure the denitrification efficiency and ammonia slip rate of each nozzle prototype under actual operating conditions. It should be noted that a dual-section synchronous measurement system was constructed: in the flue of the experimental platform, the first detection section was set 1.5m downstream of the nozzle and the second detection section was set 3m downstream. Four laser ammonia concentration analyzers and flue gas sampling probes were evenly distributed circumferentially in each section. Perform steady-state gradient testing: The replaceable nozzle physical prototype assembly was installed sequentially onto the spray gun mount of the experimental platform. The boiler load is controlled to vary in 10% increments within the range of 80% to 110% of the design value. After 30 minutes of stable operation at each load point, the ammonia concentration and NOx concentration data of the two cross sections are collected simultaneously. Dynamic compensation for temperature drift error: Real-time monitoring of flue temperature fluctuations; when the temperature change exceeds ±5℃, inject standard concentration ammonia gas into the ammonia concentration analyzer for online calibration. The original measured value of ammonia slip at this load point was corrected based on the calibration results; Calculate the denitrification performance indicators: According to the first section NO x Concentration C1 and NO in the second cross section x For concentration C2, calculate the denitrification efficiency of the current prototype at the current load point using the formula: Denitrification efficiency = (C1-C2) / C1×100%. The average ammonia concentration at the four measuring points of the second section is taken as the ammonia escape rate value under this working condition; Output steady-state performance dataset: Summarize the denitrification efficiency and ammonia slip rate of all prototypes under full load gradient to form a steady-state operating condition performance dataset.

[0023] 105. Generate optimized decision scheme: Correlate the flue gas velocity field distribution map, urea droplet trajectory cloud map and concentration field distribution map with the denitrification efficiency value and ammonia slip rate value, and output the optimal nozzle geometric dimension parameters that meet the engineering application with the constraints of denitrification efficiency > 95% and ammonia slip rate < 3ppm.

[0024] It should be noted that the effective mixing region boundary is defined as follows: Based on the flue gas velocity field distribution map, the area with a flow velocity of 0.5-3 m / s is marked as a low-speed mixing area; Based on the urea droplet trajectory cloud map, the area with a droplet residence time of greater than or equal to 0.8 s is marked as an effective reaction area; The spatial intersection of the low-speed mixing area and the effective reaction area is defined as the effective mixing area boundary; Extract the concentration field correlation index: Within the effective mixing area boundary, the urea concentration standard deviation σ of the concentration field distribution map is extracted; The area ratio of the area with σ less than or equal to 2.5% is recorded as the effective uniformity index; Construct a double-threshold performance matrix: In the stable state working condition performance data set, the working condition with a denitration efficiency greater than 95% and an ammonia escape rate less than 3 ppm is marked as a standard working condition; Correlate the nozzle geometry size, effective uniformity index and measured ammonia escape rate value corresponding to each standard working condition to generate a three-dimensional performance matrix; Output the optimal geometric parameters: In the three-dimensional performance matrix, filter the working condition points with an effective uniformity index greater than or equal to 92% and the lowest ammonia escape rate; Output the nozzle throat diameter, outlet diffusion angle and length-diameter ratio corresponding to the working condition point as the optimal nozzle geometric size parameters.

[0025] In the embodiment of the application, a three-dimensional parameterized CFD nozzle model is constructed, the geometric size can be dynamically adjusted, the model under different parameters can be quickly generated, the orthogonal test design method and CFD batch calculation are combined, the candidate scheme with standard mixing uniformity is efficiently screened out, the research and development cycle is greatly shortened, the research and development efficiency is improved, a large number of repeated tests are reduced compared with the traditional trial-and-error method, and the research and development cost is saved; a replaceable nozzle physical prototype group with size gradient difference is manufactured, a unified specification buckle type quick mounting interface is designed, the prototype is conveniently replaced for testing on an experimental platform, the parameter space can be fully covered, more abundant experimental data can be obtained, a more comprehensive basis is provided for subsequent optimization, and the reliability and accuracy of the experiment are improved; a double-section synchronous measurement system is constructed, detection sections are arranged at different positions, ammonia concentration and NO xThe concentration data, considering temperature drift error and dynamic compensation, can more accurately measure denitration efficiency value and ammonia escape rate value, comprehensively evaluate nozzle performance, and avoid inaccurate measurement caused by single measurement position and uncompensated error; the correlation analysis simulates data and measured data, defines the boundary of the effective mixing zone, extracts the concentration field correlation index, constructs a double-threshold performance matrix, comprehensively considers denitration efficiency, ammonia escape rate, effective uniformity index and other factors, outputs the optimal nozzle geometric size parameter meeting the engineering application, realizes comprehensive optimization of nozzle performance, improves the overall performance and stability of the waste heat boiler denitration system, and reduces the operation cost and environmental pollution risk.

[0026] Figure 2 The structure diagram of the nozzle optimization equipment of the urea direct injection system for waste heat boiler denitration provided by the embodiment of the present application, the nozzle optimization equipment 200 of the urea direct injection system for waste heat boiler denitration can have relatively large differences due to different configurations or performances, and can include one or more processors (central processing units, CPU) 210 (for example, one or more processors) and a memory 220, one or more storage media 230 (for example, one or more mass storage devices) storing application programs 233 or data 232. Wherein, the memory 220 and the storage medium 230 can be temporary storage or persistent storage. The program stored in the storage medium 230 can include one or more modules (not shown in the figure), each module can include a series of instruction operations in the nozzle optimization equipment 200 of the urea direct injection system for waste heat boiler denitration. Further, the processor 210 can be configured to communicate with the storage medium 230, and execute a series of instruction operations in the storage medium 230 on the nozzle optimization equipment 200 of the urea direct injection system for waste heat boiler denitration.

[0027] The nozzle optimization equipment 200 of the urea direct injection system for waste heat boiler denitration can also include one or more power supplies 240, one or more wired or wireless network interfaces 250, one or more input / output interfaces 260, and / or one or more operating systems 231, such as Windows Serve, Mac OS X, Unix, Linux, FreeBSD, etc. Those skilled in the art can understand that, Figure 2 The structure of the nozzle optimization equipment of the urea direct injection system for waste heat boiler denitration shown does not constitute a limitation on the nozzle optimization equipment of the urea direct injection system for waste heat boiler denitration, and can include more or fewer components than shown, or combine certain components, or different component arrangements.

[0028] The application further provides a nozzle optimization device of a urea direct injection system for waste heat boiler denitration, the nozzle optimization device of the urea direct injection system for waste heat boiler denitration comprising a memory and a processor, the memory storing computer readable instructions, and the computer readable instructions being executed by the processor to make the processor execute the steps of the nozzle optimization method of the urea direct injection system for waste heat boiler denitration in each of the above embodiments.

[0029] The application further provides a computer readable storage medium, which can be a non-volatile computer readable storage medium or a volatile computer readable storage medium, the computer readable storage medium storing instructions, and the instructions making a computer execute the steps of the nozzle optimization method of the urea direct injection system for waste heat boiler denitration when the instructions are run on the computer.

[0030] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described system, device and unit can refer to the corresponding processes in the foregoing method embodiments, which will not be described here.

[0031] The integrated unit, if realized in the form of a software function unit and sold or used as an independent product, can be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the application or the whole or part of the technical solutions that make essential contributions to the prior art can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a plurality of instructions to make a computer device (which can be a personal computer, a server, or a network device, etc.) execute all or part of the steps of the method described in each embodiment of the application. The foregoing storage medium includes a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and various media that can store program codes.

[0032] The above-described and above-embodied examples are only used to illustrate the technical solutions of the application, rather than limit the same; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of each embodiment of the application.

Claims

1. A method for optimizing a nozzle of a urea direct injection system for denitration of a waste heat boiler, characterized by, The method comprises the following steps: Based on the flue structure of the waste heat boiler, the design working condition parameters and the physical parameters of urea, a three-dimensional parameterized CFD nozzle model is established; Through the CFD solver, the three-dimensional parameterized CFD nozzle model is iteratively calculated to generate the flue gas flow field distribution diagram, the urea droplet trajectory cloud picture and the concentration field distribution diagram under different nozzle geometric sizes, and a candidate scheme set is screened out; According to the nozzle geometric size parameters of the candidate scheme set, a replaceable nozzle physical prototype set is manufactured; The replaceable nozzle physical prototype set is installed on the waste heat boiler denitration experiment platform, and the denitration efficiency value and the ammonia escape rate value of each nozzle prototype under actual operating conditions are measured respectively; The flue gas flow field distribution diagram, the urea droplet trajectory cloud picture and the concentration field distribution diagram are analyzed in association with the denitration efficiency value and the ammonia escape rate value, and the optimal nozzle geometric size parameter is output.

2. The method of claim 1, wherein the method is characterized by: It comprises: Based on the flue structure of the waste heat boiler, the design working condition parameters and the physical parameters of urea, a three-dimensional geometric model of the basic nozzle is generated; The nozzle throat diameter, the outlet diffusion angle and the length-diameter ratio are selected as adjustable geometric parameters to establish a geometric parameter library; In the CFD pre-processing software, the geometric parameter library is bound to the topological structure of the three-dimensional geometric model of the basic nozzle through geometric association rules to form a three-dimensional parameterized CFD nozzle model.

3. The method of claim 1, wherein the method is characterized by: It comprises: Based on the three independent parameters of the nozzle throat diameter, the outlet diffusion angle and the length-diameter ratio in the geometric parameter library, an orthogonal experimental design method is used to generate a characteristic size combination matrix; The characteristic size combination matrix is input into the CFD solver to drive the three-dimensional parameterized CFD nozzle model to automatically deform and iteratively solve, and the flue gas flow field distribution diagram, the urea droplet trajectory cloud picture and the concentration field distribution diagram corresponding to each group of parameters are output; The standard deviation of urea concentration in all concentration field distribution diagrams is extracted, and the area ratio of the region with a standard deviation ≤5% is defined as the mixing uniformity quantification value; With the constraint condition that the mixing uniformity quantification value ≥90%, the qualified parameter group is extracted from the characteristic size combination matrix to form a candidate scheme set.

4. The method of claim 1, wherein the method is characterized by: It comprises: Based on the geometric size parameter table of the candidate scheme set, three groups of parameters of the throat diameter, the outlet diffusion angle and the length-diameter ratio are extracted, and are regrouped according to the gradient rule that the parameter value difference amplitude ≥15% to generate a gradientized nozzle three-dimensional model group.

5. The method of claim 4, wherein the method is characterized by: A unified buckle type quick mounting interface is integrated on the flange end of the gradientized nozzle three-dimensional model group to ensure the physical interchangeability of all prototypes and the experimental platform spray gun seat; A five-axis numerical control machine tool is used for cutting processing according to the gradientized nozzle three-dimensional model group, and a hole diameter processing precision compensation of +0.1mm~+0.15mm is applied to the prototype with a throat diameter <10mm to output a replaceable nozzle physical prototype set.

6. The method of claim 1, wherein the method is characterized by: It comprises: In the flue of the experimental platform, a first detection section and a second detection section are arranged downstream of the nozzle; The physical prototype of the replaceable nozzle is installed in sequence to the experimental platform lance seat, the boiler load is controlled in the range of 80%~110% design value with 10% gradient change, after stable operation for 30 minutes at each load point, the ammonia concentration and NO x concentration data of two sections are collected synchronously; The flue temperature fluctuation is monitored in real time, and when the temperature change exceeds ±5℃, standard concentration ammonia gas is injected into the ammonia concentration analyzer for online calibration, and the original measurement value of the ammonia escape rate at the load point is corrected based on the calibration result; According to the first cross section NO x The concentration C1 and the second cross section NO x The concentration C2, the denitration efficiency value of the current prototype at the current load point is calculated, the denitration efficiency=(C1-C2) / C1*100%, and the average value of the ammonia concentration of the four measuring points of the second cross section is taken as the ammonia escape rate value of the working condition; The denitration efficiency values and ammonia escape rate values of all the prototypes under full load gradient are summarized to form a steady-state working condition performance data set.

7. The method of claim 6, wherein the method is characterized by: In the flue of the experimental platform, a first detection section is arranged 1.5 m downstream of the nozzle, and a second detection section is arranged 3 m downstream of the nozzle. Four laser ammonia concentration analyzers and flue gas sampling probes are evenly distributed in the circumferential direction of each section.

8. The nozzle optimization method for the urea direct injection system for waste heat boiler denitrification according to claim 1, characterized in that, The method comprises the following steps: Based on the flue gas flow velocity field distribution map, the region with a flow velocity of 0.5-3 m / s is marked as a low-speed mixing zone; Based on the urea droplet trajectory cloud map, the region with a droplet residence time of greater than or equal to 0.8 s is marked as an effective reaction zone; the spatial intersection of the low-speed mixing zone and the effective reaction zone is defined as the boundary of the effective mixing zone; Within the boundary of the effective mixing zone, the standard deviation σ of the urea concentration field distribution map is extracted, and the area ratio of the region with σ less than or equal to 2.5% is recorded as the effective uniformity index; In the steady-state working condition performance data set, the working conditions with a denitration efficiency greater than 95% and an ammonia escape rate less than 3 ppm are marked as qualified working conditions, and the corresponding nozzle geometric dimensions, effective uniformity index and measured ammonia escape rate value of each qualified working condition are associated to generate a three-dimensional performance matrix; In the three-dimensional performance matrix, the working condition point with an effective uniformity index greater than or equal to 92% and the lowest ammonia escape rate is selected, and the nozzle throat diameter, outlet diffusion angle and length-diameter ratio corresponding to the working condition point are output as the optimal nozzle geometric dimension parameters.

Images