Large-diameter chimney traceable flue gas flow measurement system and method

Abstract

The invention discloses a traceable flue gas flow measurement system and method for a large-diameter chimney, and belongs to the field of flue gas flow measurement. The system comprises a tracer gas cylinder used for containing a tracer; the flow controller is used for controlling the output flow of the tracer agent; the tracer agent output from the flow controller is injected into the upstream position of the chimney pipeline through the tracer agent injection probe so as to be mixed with the flue gas; the tracer sampling probe is mounted at the downstream position of the chimney pipeline and is used for extracting a mixed gas sample through a gas pump; and the gas analyzer is used for analyzing the obtained gas sample and calculating the volume flow rate of the flue gas in the chimney pipeline. According to the invention, the volume flow of the flue gas in the chimney is directly calculated by monitoring the concentration change of the tracer agent in the flowing process in the pipe, so that the accuracy of flow measurement is improved, and the measurement result has traceability.

Description

Technical Field

[0001] The invention relates to the field of flue gas flow measurement, and in particular to a traceable flue gas flow measurement system and method for a large-diameter chimney. Background Art

[0002] Carbon dioxide emissions from the thermal power industry account for about 40% of total carbon dioxide emissions, so it is of great practical significance to achieve accurate measurement of carbon emissions in the thermal power industry. The largest error in carbon emission measurement in thermal power companies comes from flue gas flow measurement. Currently, the commonly used flue gas flow measurement methods include differential pressure method and ultrasonic method, all of which are based on the principle of velocity area method. In the measurement of chimney flue gas flow, these methods have very high requirements for the length of the straight pipe section at the installation position of the flow meter, and often require a straight pipe section 10-20 times the length of the pipe diameter upstream. However, in actual applications, thermal power plants are limited by factors such as site and economy, and the installation position of the flow meter often cannot meet the above requirements, resulting in the inability to fully develop the flue gas in the pipe, resulting in strong turbulence, backflow, asymmetric flow and secondary flow. In addition, the diameter of the chimney of the thermal power plant is large, and the flow velocity measured by the above measurement method is difficult to represent the average flow velocity of the cross section, resulting in a large flow measurement error. According to research, the complex flow characteristics of flue gas can cause the measurement error of conventional flow measurement methods to reach 25% or even more. In addition, the measurement accuracy and stability of the flow meter cannot be guaranteed in the long term in large-diameter chimneys, and the country lacks standard equipment and a complete traceability system for calibrating the flue gas flow in large-diameter chimneys, which further limits the improvement of the flue gas flow measurement accuracy. Summary of the invention

[0003] In order to solve at least one of the technical problems existing in the prior art to a certain extent, the object of the present invention is to provide a traceable flue gas flow measurement system and method for a large-diameter chimney based on a tracer gas dilution method.

[0004] The first technical solution adopted by the present invention is:

[0005] A traceable flue gas flow measurement system for a large diameter chimney, comprising:

[0006] Tracer gas cylinder, used to hold tracer;

[0007] A flow controller, used to control the output flow of the tracer;

[0008] A tracer injection probe, wherein the tracer output from the flow controller is injected into an upstream position of the chimney duct through the tracer injection probe to mix with the flue gas;

[0009] The tracer sampling probe is installed in the downstream position of the chimney duct and extracts the mixed gas sample through the air pump;

[0010] A gas analyzer is used to analyze the obtained gas samples for calculating the flue gas volume flow in the chimney duct.

[0011] Furthermore, the calculation formula of the flue gas volume flow rate is as follows:

[0012]

[0013] Where, X T,1 is the concentration of the injected tracer, V T,1 is the volume flow rate of the injected tracer; X T,D is the concentration of the tracer in the gas sample collected downstream; X T,U is the tracer concentration measured upstream of the injection point.

[0014] Furthermore, the tracer is sulfur hexafluoride (SF6), and the tracer dilution ratio is 1:500,000.

[0015] Furthermore, the tracer is injected into the chimney pipe by flue injection or chimney injection; and / or,

[0016] The tracer sampling probe adopts a three-point sampling method for sampling.

[0017] The second technical solution adopted by the present invention is:

[0018] A method for measuring the traceable flue gas flow rate of a large-diameter chimney comprises the following steps:

[0019] Build a physical model of the chimney, mesh the physical model, and simulate the model;

[0020] The final tracer type is determined based on the mixing effect of the tracer with the flue gas, the gas detection level, and the cost;

[0021] Determine the tracer dilution ratio based on the gas mixing effect;

[0022] Determine the injection cross section of the tracer based on the mixing effect of the gas;

[0023] A flue gas flow measurement system is built based on the information determined by the simulation to measure the flue gas flow.

[0024] Furthermore, the physical model of the chimney is constructed, the physical model is meshed, and the model is simulated, including:

[0025] Determine the chimney diameter and build a chimney model;

[0026] Fluent meshing was used to mesh the model, and the mesh around the tracer injection port was encrypted.

[0027] It is assumed that the flow of flue gas in the chimney duct is steady and incompressible, and the standard k-ε turbulence model is used;

[0028] The component transport model in the FLUENT numerical simulation software is used to reflect the diffusion of the tracer and the mixing of the tracer with the flue gas during the transportation process. The material transport equation and the mass diffusion equation are as follows:

[0029]

[0030] In the formula, R i Indicates the net generation rate of substances involved in chemical reactions; S i Represents a discrete term; Sc t represents the turbulent Schmidt number; ρ represents the density of the mixed fluid, in kg / m 3 , Y i represents the mass fraction of component i, Represents the velocity vector of the mixed fluid in m / s, D i,m It represents the molecular diffusion coefficient of component i in the mixture, with the unit of m 2 / s,μ t It represents the turbulent viscosity of the mixture.

[0031] Furthermore, the final tracer type is determined according to the mixing effect of the tracer and the flue gas, including:

[0032] Under the preset conditions, simulate the mixing effects of various tracers with flue gas in the chimney, and obtain the main factors affecting the mixing effect of tracers and flue gas;

[0033] The final tracer type is selected based on the simulation results, gas detection level, and cost.

[0034] Furthermore, determining the tracer dilution ratio according to the mixing effect of the gas includes:

[0035] Set the flow rate of flue gas in the chimney;

[0036] Set a variety of tracer dilution ratios to simulate the effect of tracer dilution ratios on tracer injection speed;

[0037] According to the simulation results, the influence of tracer dilution ratio on the mixing effect of tracer and flue gas is analyzed.

[0038] Further, determining the injection cross section of the tracer according to the mixing effect of the gas includes:

[0039] Two tracer injection sections, chimney injection and flue injection, were set to simulate the effects of chimney and flue section injection on the mixing of tracer and flue gas and flow measurement error.

[0040] The final tracer injection cross section is selected based on the simulation results and flow measurement errors.

[0041] Furthermore, the large-diameter chimney traceable flue gas flow measurement method further includes the step of setting tracer sampling:

[0042] Three sampling sections were set up, which were located at the downstream of the pipeline at 3D, 8D, and 12D away from the tracer injection position. When the flue was injected, the upper plane of the flue in front of the chimney inlet was defined as 0D, and 3D and 8D were the two original measurement sections close to the chimney of the power plant. D represented the chimney pipe diameter.

[0043] The beneficial effects of the present invention are as follows: the present invention provides a system for measuring the flue gas flow rate of a large-diameter chimney by applying the tracer gas dilution method, and directly calculates the volume flow rate of the flue gas in the chimney by monitoring the concentration change of the tracer in the process of flowing in the pipe, so as to improve the accuracy of the flow measurement, and the measurement result is traceable. In addition, the measurement accuracy mainly depends on the mixing of the tracer and the flue gas, and the strong turbulence and various complex flow characteristics of the flue gas in the chimney flow process can well promote the mixing of the tracer and the flue gas, so the best solution for implementing the method is studied based on the numerical simulation method, so as to achieve the effect of greatly reducing the length of the straight pipe section required for measurement and increasing the accuracy of flow measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the embodiments of the present invention or the drawings of related technical solutions in the prior art are introduced below. It should be understood that the drawings introduced below are only for the convenience of clearly describing 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 work.

[0045] Figure 1 is a three-dimensional model diagram of a flue-chimney in an embodiment of the present invention;

[0046] Figure 2 is a schematic diagram of a traceable flue gas flow measurement system for a large-diameter chimney in an embodiment of the present invention;

[0047] Figure 3 is a schematic diagram of a chimney model and a straight pipe model in an embodiment of the present invention; wherein, Figure 3 (a) is a schematic diagram of the chimney model. Figure 3 (b) is a schematic diagram of the straight tube model;

[0048] Figure 4 is a schematic diagram of cross-sectional mesh division in an embodiment of the present invention;

[0049] Figure 5 Schematic diagram of the relative standard deviation of the cross-sectional tracer concentration changing with the chimney height in an embodiment of the present invention; wherein, Figure 5 (a) is a schematic diagram of the mixing effect in the chimney model. Figure 5 (b) is a schematic diagram of the mixing effect in the straight tube model;

[0050] Figure 6 Schematic diagram of two tracer injection schemes in the embodiment of the present invention; wherein, Figure 6 (a) is a schematic diagram of chimney injection. Figure 6 (b) is a schematic diagram of flue injection;

[0051] Figure 7 Schematic diagram of six tracer sampling schemes in the embodiments of the present invention;

[0052] Figure 8 1 is a comparison diagram of the mixing effect of the tracer and the flue gas when the tracer is injected into the chimney and the flue respectively under a certain working condition in an embodiment of the present invention (in the figure, D represents the diameter of the chimney pipe);

[0053] Fig. 9 Schematic diagram of the flue gas flow measurement error of each sampling scheme under three working conditions in the embodiment of the present invention when the tracer is injected into the chimney and the flue; wherein, Fig. 9 (a) is a schematic diagram of the flue gas flow measurement error at 60% load. Fig. 9 (b) is a schematic diagram of the flue gas flow measurement error under 80% load. Fig. 9 (c) is a schematic diagram of the flue gas flow measurement error under 100% load.

[0054] Figure 2 Figure numerals: 1 - tracer gas cylinder; 2 - Ethernet; 3 - flow controller; 4 - tracer injection probe; 5 - chimney pipe; 6 - tracer sampling probe; 7 - gas pump; 8 - gas analyzer; 9 - data acquisition and control equipment. DETAILED DESCRIPTION

[0055] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limitations of the present invention. For the step numbers in the following embodiments, they are only provided for the convenience of explanation, and the order between the steps is not limited in any way, and the execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0056] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0057] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0058] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0059] In order to solve the existing technical problems, the present invention applies the tracer gas dilution method to the measurement of flue gas flow in large diameter chimneys, and studies the best solution for implementing the method based on the numerical simulation method. The tracer gas dilution method can overcome the flow measurement error caused by uneven velocity distribution, and its measurement results are traceable. It has good application prospects when applied to the measurement of flue gas flow in large diameter chimneys or as a field calibration method. Among them, the tracer gas dilution method has the following advantages: (1) It does not need to measure the cross-sectional area of ​​the pipeline, so the flow measurement error caused by the size error can be avoided; (2) It can overcome the problem of overestimation of the flow measurement result caused by the wall effect; (3) The concentration of the injected tracer is known, and the determination of the flue gas volume flow only requires the measurement of the volume flow of the tracer and the sample tracer concentration collected at the sampling positions upstream and downstream of the injection port. These three measurement variables are all well traceable, so the final flue gas flow measurement result is also traceable.

[0060] like Figure 1 and Figure 2 As shown, this embodiment provides a large-diameter chimney traceable flue gas flow measurement system, including:

[0061] Tracer gas cylinder 1, used for containing tracer;

[0062] A flow controller 3, used to control the output flow of the tracer;

[0063] The tracer injection probe 4 is used to inject the tracer output from the flow controller into the upstream position of the chimney pipe 5 through the tracer injection probe to mix with the flue gas;

[0064] The tracer sampling probe 6 is installed at the downstream position of the chimney pipe, and the mixed gas sample is extracted by the air pump 7;

[0065] The gas analyzer 8 is used to analyze the obtained gas sample so as to calculate the flue gas volume flow rate in the chimney duct.

[0066] As an optional implementation, see Figure 2 The measurement system also includes a data acquisition and control device 9, which is connected to a gas analyzer 8 and a flow controller 3 via an Ethernet 2.

[0067] The working principle of the above system is as follows: the tracer gas cylinder provides high-purity tracer gas, and the flow controller controls the tracer to be injected into the chimney duct from the tracer injection probe at a constant rate. A flue gas sampling probe is installed at the downstream position, and the mixed gas sample is extracted by a pump, and the flow rate of the gas sample is controlled to make it enter the gas analyzer stably. The data acquisition and control equipment can control the equipment in the system to achieve the above operations by connecting to Ethernet, and communicate with other equipment to achieve data synchronization, centralized monitoring and recording, and calculate the flue gas volume flow in the monitoring pipeline by the following formula:

[0068]

[0069] Where, X T,1 is the concentration of the injected tracer, V T,1 is the volume flow rate of the injected tracer; X T,D is the concentration of the tracer in the gas sample collected downstream; X T,U is the tracer concentration measured upstream of the injection point, which is taken as 0 in this embodiment.

[0070] The measurement accuracy of the tracer gas dilution method depends on the mixing degree of the tracer and the gas in the pipe. Therefore, the strong turbulence and complex flow characteristics of the airflow in the pipe will promote the mixing of the tracer and the flue gas, thereby improving the measurement accuracy of the method. In order to improve the measurement accuracy, the embodiment of the present invention is also studied based on numerical simulation, which is described in detail below in conjunction with the accompanying drawings and the specific application scenario of a large-diameter chimney in a thermal power plant. However, the application scenario of the present invention is not limited to a large-diameter chimney in a thermal power plant, and can be applied to various pipeline gas flow measurement scenarios.

[0071] (1) CFD model establishment and verification

[0072] 1.1) Geometric model and meshing

[0073] The chimney model of this embodiment is as follows Figure 3 The chimney has a diameter of 7.8m and a height of 210m. There are measurement platforms at the heights of 80m and 120m. However, since there is a 40m high platform at the bottom of the chimney, the actual length of the chimney is 170m. For the convenience of analysis, the bottom of the chimney is set at a height of 0m. At this time, the heights of the measurement platforms are 40m and 80m respectively. Figure 3 The straight tube model shown in (b) is used to compare with the above-mentioned real chimney model to study the influence of different flue gas flow characteristics on the mixing effect of tracer and flue gas. The values ​​of the straight tube model pipe diameter and length are the same as those of the chimney model.

[0074] In this embodiment, Fluent meshing is used to mesh the model, and Poly-hexcore is used to mesh the hexahedral mesh. In order to make the numerical simulation results more accurate, the mesh of the tracer injection port and its vicinity is encrypted. For details, see Figure 4 Example in. This embodiment sets 4 grid division schemes to verify the grid independence, and uses the relative standard deviation of the tracer concentration in the chimney section as the evaluation index to analyze the mixing effect of the tracer and the flue gas. The simulation results are: the simulation results with a grid number of 216w and 240w are almost the same, and the simulation results with a grid number of 156w and 180w are partially different from the simulation results with a grid number of 200w and 223w. Based on the above results, this embodiment selects a scheme with a grid number of 216w to carry out subsequent simulation work.

[0075] 1.2) Mathematical model and boundary conditions

[0076] The flow of flue gas in the duct can be assumed to be steady and incompressible flow, and its continuity equation, momentum equation and energy equation are shown in equation (2):

[0077]

[0078] Where: ρ is the smoke density, kg / m 3 ; u is the flue gas velocity, m / s; t is the time, s; Γ φ is the generalized diffusion coefficient, φ is a universal variable; S φ is a generalized source term.

[0079] This embodiment uses the standard k-ε turbulence model and uses the SIMPLEC algorithm to solve the flow field.

[0080] The turbulent kinetic energy equation is:

[0081]

[0082] The dissipation rate ε equation is:

[0083]

[0084] Where: G k is the turbulent kinetic energy; C 1ε , C 2ε is a constant; k and σ ε are the turbulent Planck numbers for the k equation and the ε equation, respectively.

[0085] This example uses the component transport model in the FLUENT numerical simulation software to reflect the diffusion of the tracer and the mixing of the tracer with the flue gas during the transportation process. The material transport equation and the mass diffusion equation are:

[0086]

[0087] Where: R i Indicates the net generation rate of substances involved in chemical reactions; S i Represents a discrete term; Sc t represents the turbulent Schmidt number.

[0088] The inlet of this simulation is a velocity inlet. According to the 60%, 80%, and 100% load of the power plant, the flue gas inlet velocity is set to 6.04m / s, 6.75m / s, and 7.45m / s respectively. The outlet is set to a pressure outlet. The wall surface is a standard no-slip wall surface condition.

[0089] (2) Selection of tracers

[0090] According to the Maxwell-Gilliland formula, the diffusion coefficient between the two gases can be calculated by formula (7):

[0091]

[0092] Where T is temperature, K; p is pressure, kPa; M is molecular mass; v refers to the volume of 1 mol of substance in liquid state at its normal boiling point, cm 3 / mol; A and B represent two gases respectively.

[0093] In this example, in order to analyze the influence of the type of tracer on the mixing effect of the tracer and the flue gas, the mixing effect of two tracers, SF6 and He, and the flue gas is analyzed in the chimney model and the straight pipe model. It should be noted that this example only analyzes SF6 and He, but is not limited to these two substances. The simulation is carried out at 80% load, and the tracer is injected at a chimney height of 20m. Figure 5The relative standard deviation of the cross-sectional concentration of the chimney model and the straight tube model varies with height. The following conclusions can be drawn: First, whether in the chimney model or the straight tube model, the relative standard deviation of the cross-sectional concentration of SF6 is always greater than that of He, which is consistent with the above analysis of the diffusion coefficients of the two tracers, that is, He has better diffusivity and can further reduce the unevenness of the cross-sectional concentration distribution. Second, in the chimney model, the relative standard deviation of the cross-sectional concentration of the two tracers varies with height, while in the straight tube model, it shows a large difference. This is because in the chimney model, the turbulence intensity is large and the flow characteristics are complex after the flue gas flows through the corner. These flow conditions play a leading role in the mixing of the tracer and the flue gas, while in the straight tube, the flue gas does not have the above flow conditions. Therefore, the mixing effect of the tracer and the flue gas is mainly affected by the diffusion coefficient. Third, in the chimney model, the relative standard deviation of the tracer cross-sectional concentration drops below 10% at a height of about 9D. According to the description in the standard ASTM E2029-11 (2019), the tracer and flue gas have been fully mixed at this height, meeting the requirements of the tracer gas dilution method in pipeline flow measurement. In the straight pipe model, due to the lack of strong turbulence and complex flow promotion, the distribution of the tracer in the pipeline is still very uneven, which does not meet the requirements of the tracer gas dilution method in pipeline flow measurement.

[0094] Based on the above comparison, combined with the criteria for tracer selection and the properties of various common tracers, this embodiment selects SF6, which has a higher detection level and is more convenient and readily available in power plants, as a tracer for the subsequent research.

[0095] (3) Selection of tracer dilution ratio

[0096] The ratio of the tracer to the flue gas will affect the diffusion of the tracer in the pipe and the mixing effect with the flue gas. Therefore, in this embodiment, three schemes are set as shown in Table 1 to study the effect of the dilution ratio of the tracer in the flue gas on the mixing effect of the flue gas. This embodiment is simulated under the condition of 80% load, and the flow rate of the flue gas in the chimney is 14.34m / s.

[0097] Table 1 Different tracer dilution ratio schemes (flue gas volume flow rate 685.3m 3 / s)

[0098]

[0099] The simulation results are as follows: The mixing effects of the three tracer dilution ratio schemes have the same trend of change with the chimney height, but Scheme 2 has a better mixing effect of tracer and flue gas than the other two schemes. Compared with Scheme 2, the tracer injection speed of Scheme 1 is too small relative to the mainstream of flue gas in the pipe, and the disturbance imposed on the flue gas is insufficient. In addition, the kinetic energy carried by the tracer is low, so the diffusion of the tracer in the flue gas and the efficiency of mixing with the flue gas are low; and compared with Scheme 2, the tracer injection speed of Scheme 3 is very high. Excessive injection speed will cause the tracer to directly penetrate the flue gas and reach the far end of the pipe. In addition, a low-pressure area may be formed on the surface of the high-speed tracer jet, hindering the mixing of the tracer and the flue gas. Comparing the mixing effects of the tracer and the flue gas in the three schemes and taking into account the detection limit of the conventional gas analyzer, this embodiment selects Scheme 2 for subsequent research. In this case, the tracer dosage is moderate, and the concentration of the diluted tracer can also be easily detected.

[0100] (4) Tracer injection section plan setting

[0101] The measurement accuracy of the tracer gas dilution method depends on the mixing degree of the tracer and the flue gas. Although the increase of the pipeline length (mixing distance) can effectively improve the mixing degree of the tracer and the flue gas, in practical applications, we all hope that the tracer and the flue gas can be fully mixed in the shortest possible distance. To achieve this goal, this example simulates the effects of two situations of chimney and flue cross-section injection on the mixing of the tracer and the flue gas and the flow measurement error, such as Figure 6 As shown in the figure, the chimney injection section is located at a plane at a height of 20m, and the flue injection section is located 2m in front of the chimney entrance. At the same time, three sampling sections and six sampling measurement point arrangement schemes were set up to evaluate the consistency and stability of the measurement results under each injection scheme. The sampling schemes are as follows: Figure 7 As shown in the figure, the sampling sections are located at 3D, 8D, and 12D from the injection section (the upper plane of the chimney in front of the chimney entrance is defined as 0D when the chimney is injected). The 3D and 8D sections are located 40m and 80m from the chimney measurement platform respectively.

[0102] Table 2 shows the flow measurement errors of various cases simulated in this embodiment under different tracer sampling point arrangement schemes, and the calculation formula is as follows:

[0103]

[0104] Among them, Q 测量值 It is calculated by substituting the tracer concentration obtained at the sampling point into formula (1), Q 真实值 is the flue gas volume flow rate in the duct in the simulation case.

[0105] Table 2 Relative error of flow measurement under different conditions (%)

[0106]

[0107] Figure 8 The effect of different injection cross-sections on the mixing degree of tracer and flue gas under 80% load is shown. As can be seen from the figure, when injected into the flue, at the position of about 2D cross-section, the relative standard deviation of the tracer concentration drops to 10%, which meets the requirements of standard ASTM E2029-11 (2019) for sufficient mixing of tracers. Compared with chimney injection, the mixing effect of tracer and flue gas has been greatly enhanced, and the mixing distance required for full mixing is reduced by about 7D, and the relative standard deviation of the cross-sectional concentration at a height of about 5D has dropped to 5%. The results show that compared with chimney injection, the tracer can achieve more complete mixing with the flue gas at a shorter distance. This is because when injected into the flue, the tracer and the flue gas flow through the bend together, the flow direction changes sharply, the flue gas forms a secondary flow, and generates strong turbulence, which increases the mixing efficiency of the tracer and the flue gas. From this, we can also see that under the action of the bend, the tracer gas dilution method has greatly reduced requirements for the length of the straight pipe section compared to other flow measurement methods based on the velocity area method.

[0108] Fig. 9 The flow measurement errors of each sampling scheme at different sampling sections under different working conditions on two injection sections are shown. The results show that the measurement performance of each scheme under different working conditions is extremely similar, so the 80% load is taken as an example for analysis. As can be seen from the figure, under the chimney injection condition, the flow measurement error between the sampling schemes fluctuates widely, ranging from -32.02% to 49.75%, but when three-point sampling is performed, the measurement errors on the 3D, 8D, and 12D sections are only -3.59%, -0.69%, and -1.05%, respectively. The measurement error under the flue injection condition is smaller than that under the chimney injection, and the measurement error fluctuations between different sampling schemes are relatively stable, all within ±10%, which meets the requirement of the standard DL / T 2376-2021 that the velocity / flow measurement error does not exceed 10%. In addition, when sampling at three points, the measurement errors on the 3D, 8D, and 12D sections were only 0.98%, -0.52%, and 0.21%, respectively, all within ±1%. Compared with chimney injection, the measurement performance of flue injection has been greatly improved.

[0109] In summary, the present invention provides a traceable flue gas flow measurement method for large-diameter chimneys based on the tracer gas dilution method, and studies the best solution for implementing the method based on the numerical simulation method. The tracer gas dilution method calculates the volume flow of flue gas in the chimney directly by monitoring the concentration change of the tracer during the flow in the pipe. The measurement accuracy of this method mainly depends on the mixing of the tracer and the flue gas. The strong turbulence and various complex flow characteristics of the flue gas during the flow in the chimney can well promote the mixing of the tracer and the flue gas, thereby greatly reducing the length of the straight pipe section required for measurement and increasing the accuracy of flow measurement.

[0110] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0111] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A traceable flue gas flow measurement system for a large diameter chimney, characterized in that: include: Tracer gas cylinder, used to hold tracer; A flow controller, used to control the output flow of the tracer; A tracer injection probe, wherein the tracer output from the flow controller is injected into an upstream position of the chimney duct through the tracer injection probe to mix with the flue gas; The tracer sampling probe is installed in the downstream position of the chimney duct and extracts the mixed gas sample through the air pump; The gas analyzer is used to analyze the obtained gas sample and obtain the tracer concentration in the flue gas sample for calculating the flue gas volume flow in the chimney duct.

2. A large diameter chimney traceable flue gas flow measurement system according to claim 1, characterized in that: The calculation formula of the flue gas volume flow rate is as follows: Where V T,1 is the concentration of the injected tracer, V T,1 is the volume flow rate of the injected tracer; V T,D is the concentration of the tracer in the gas sample collected downstream; X T,U is the tracer concentration measured upstream of the injection point.

3. A large diameter chimney traceable flue gas flow measurement system according to claim 1, characterized in that: The tracer is sulfur hexafluoride, and the tracer dilution ratio is 1:500,000.

4. A large diameter chimney traceable flue gas flow measurement system according to claim 1, characterized in that: The tracer is injected into the chimney pipe by flue injection or chimney injection; and / or, The tracer sampling probe adopts a three-point sampling method for sampling.

5. A method for measuring the traceable flue gas flow rate of a large diameter chimney, characterized in that: The following steps are involved: Build a physical model of the chimney and the flue in front of the chimney entrance, mesh the physical model, and simulate the model; Determine the type of tracer based on the mixing effect between the tracer and the flue gas; Determine the tracer dilution ratio based on the gas mixing effect; Determine the injection cross section of the tracer based on the mixing effect of the gas; A flue gas flow measurement system is built based on the information determined by the simulation to measure the flue gas flow.

6. A method for measuring the traceable flue gas flow rate of a large diameter chimney according to claim 5, characterized in that: The physical model of the chimney and the part of the flue in front of the chimney inlet is constructed, the physical model is meshed, and the model is simulated, including: Determine the size and layout of the chimney and the flue in front of the chimney entrance, and build a chimney model; Fluent meshing was used to mesh the model, and the mesh around the tracer injection port was encrypted. It is assumed that the flow of flue gas in the chimney duct is steady and incompressible, and the standard k-ε turbulence model is used; The component transport model in the FLUENT numerical simulation software is used to reflect the diffusion of the tracer and the mixing of the tracer with the flue gas during the transportation process. The material transport equation and the mass diffusion equation are as follows: In the formula, R i Indicates the net generation rate of substances involved in chemical reactions; S i Represents a discrete term; Sc t represents the turbulent Schmidt number; ρ represents the density of the mixed fluid, Y i represents the mass fraction of component i, represents the velocity vector of the mixed fluid, D i,m represents the molecular diffusion coefficient of component i in the mixture, μ t represents the turbulent viscosity of the mixture, is a vector differential operator.

7. A method for measuring the traceable flue gas flow rate of a large diameter chimney according to claim 5, characterized in that: The step of determining the type of tracer according to the mixing effect of the tracer and the flue gas comprises: Under the preset conditions, simulate the mixing effects of various tracers with flue gas in the chimney, and obtain the main factors affecting the mixing effect of tracers and flue gas; The final tracer type is selected based on the simulation results, gas detection level, and cost.

8. The method for measuring the traceable flue gas flow rate of a large diameter chimney according to claim 5, characterized in that: The step of determining the tracer dilution ratio according to the mixing effect of the gases comprises: Set a variety of tracer dilution ratios to simulate the effect of tracer dilution ratios on tracer injection speed; According to the simulation results, the influence of tracer dilution ratio on the mixing effect of tracer and flue gas is analyzed.

9. The method for measuring the traceable flue gas flow rate of a large diameter chimney according to claim 5, characterized in that: The step of determining the injection cross section of the tracer according to the mixing effect of the gas comprises: Two tracer injection sections, chimney injection and flue injection, were set to simulate the effects of chimney and flue section injection on the mixing of tracer and flue gas and flow measurement error. The final tracer injection cross section is selected based on the simulation results and flow measurement errors.

10. The method for measuring the traceable flue gas flow rate of a large diameter chimney according to claim 5, characterized in that: The traceable flue gas flow measurement method for a large diameter chimney further comprises the following steps: Three sampling sections were set up, which were located at the downstream of the pipeline at 3D, 8D, and 12D away from the tracer injection position. When the flue was injected, the upper plane of the flue in front of the chimney inlet was defined as 0D, and 3D and 8D were the two original measurement sections close to the chimney of the power plant. D represented the chimney pipe diameter.

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