Method for designing and optimizing structure of vocs buffer tank based on computational fluid dynamics

Abstract

The application provides a VOCs buffer tank structure design and optimization method based on computational fluid dynamics, comprising S1 establishing a three-dimensional entity model of a target buffer tank and setting initial structure; S2 adopting a computational fluid dynamics method to carry out transient numerical simulation on the internal flow field and VOCs component concentration distribution of the target buffer tank; S3 identifying internal defects of the target buffer tank according to the simulation result; S4 adjusting the structure parameters of the internal baffle based on the identified defects; S5 cyclically executing steps S2 to S4 to form a closed loop iterative optimization until the performance indicators of the target buffer tank meet the preset requirements, and obtaining a target structure parameter combination; and S6 outputting the target structure parameter combination for constructing a VOCs buffer tank entity structure. The application takes computational fluid dynamics simulation as a core to quantitatively identify and eliminate flow field defects through iterative optimization, greatly improves the effective volume utilization rate and dynamic concentration decay capacity of the buffer tank, and can effectively overcome the blindness of the existing experience design.

Description

Technical Field

[0001] This invention belongs to the field of volatile organic compound (VOCs) waste gas treatment and industrial ventilation, and particularly relates to a method for the structural design and optimization of VOCs buffer tanks based on computational fluid dynamics. Background Technology

[0002] As environmental standards continue to tighten, relevant regulations require that the concentration of VOCs entering back-end treatment equipment (such as regenerative thermal oxidizers (RTO) and activated carbon adsorption devices) must be consistently below 25% of the lower explosive limit. In intermittent production processes such as coating industry (automotive paint and furniture paint spraying lines), chemical storage and transportation, and printing and packaging, VOCs exhaust gas exhibits periodic and drastic fluctuations in air volume and concentration, with fluctuation ranges reaching several times or even tens of times.

[0003] Currently, waste gas dilution or simple buffer tanks are commonly used in engineering projects for temporary storage. Existing buffer tanks are mostly cylindrical tanks with straight inlet and outlet, and in some cases, multiple tanks are combined or built-in baffles are used. Common baffle types include: simple flat plate type (simple structure but prone to dead zones behind), anti-impact plate (local turbulence or sedimentation dead zones), perforated baffle (the opening ratio needs to be accurately calculated, otherwise it will fail or the resistance will increase sharply), guide plate / guide cylinder (complex structure, easy to accumulate particles), staggered multi-layer baffle (high resistance, easy to accumulate dust), spiral baffle (high cost, high resistance), adjustable baffle (high investment, easy to wear of moving parts), and combined baffle (high design difficulty, internal congestion).

[0004] In general, existing baffle designs rely heavily on empirical layout and lack quantitative design basis for specific exhaust gas characteristics (density, fluctuation frequency, dust content). This makes it difficult to achieve an optimal balance between mixing effect, flow resistance, and manufacturing cost, and their design approach suffers from the following systemic defects: (1) Existing designs rely solely on experience to estimate volume (e.g., "not less than the maximum exhaust gas emission in 1 hour"), assuming the entire tank is effective. However, in actual operation, due to short-circuiting and dead zones, the effective volume utilization rate is usually only 60%~70%. Existing standards do not provide quantitative assessment methods, leading to over-design that wastes investment or insufficient buffering that affects downstream applications; (2) The existing solution can only take action after the concentration exceeds the standard and the event is detected, and cannot proactively predict and prepare in advance. It can cope with the scenario where the fluctuating concentration of exhaust gas is slow, but in the scenario of intermittent production and frequent concentration pulses, its defects of delayed response, lack of quantification and inability to predict dynamic decay are exposed. High concentration gas masses may "penetrate" the tank and directly impact downstream equipment, causing RTO overheating, accelerated activated carbon penetration, and even safety accidents such as explosions. (3) The inlet and outlet positions and the shape of the guide vanes are determined intuitively without considering the differences in exhaust gas density and flow details. An unreasonable structure not only fails to eliminate short-circuiting, but may also exacerbate dead zones or generate additional resistance. The existing design cannot visualize the flow field, and modifying the structure is done blindly.

[0005] Therefore, there is an urgent need in this field for a design method that can quantitatively optimize the structure of buffer tanks, eliminate short-circuiting and dead zones, and improve dynamic adaptability. Summary of the Invention

[0006] In view of the problems existing in the prior art, the main objective of this invention is to provide a VOCs buffer tank structure design and optimization method based on computational fluid dynamics. By simulating and identifying short-flow channels, dead zones and recirculation zones using computational fluid dynamics (CFD) methods, the internal baffle structure is iteratively optimized to obtain the optimal combination of structural parameters, thereby achieving predictability, optimizability and verifiability of VOCs buffer tank performance.

[0007] The objective of this invention is achieved through the following technical solution: This invention provides a method for designing and optimizing VOCs buffer tank structures based on computational fluid dynamics, comprising the following steps: S1: Establish a three-dimensional solid model based on the geometric dimensions of the target buffer tank, and determine the tank shape, inlet position, outlet position, and the initial structure of its internal baffles; S2: The computational fluid dynamics method is used to conduct transient numerical simulations of the flow field and VOCs component concentration distribution inside the target buffer tank, and the simulation results include velocity field, concentration field and outlet dynamic response data. S3: Identify the short-flow channels and / or dead zones and / or recirculation zones within the target buffer tank based on the simulation results; S4: Based on the identified short-flow channels and / or dead zone locations and / or recirculation zones, adjust the structural parameters of the internal baffle; S5: Repeat steps S2 to S4, and optimize through closed-loop iteration until the performance indicators of the target buffer tank meet the preset requirements, and obtain the target structural parameter combination; S6: Output the target structural parameter combination, which includes the target inlet position, target outlet position, and target structural parameters of the internal baffle of the target buffer tank.

[0008] As a further description of the above technical solution, the transient numerical simulation adopts the k-ε turbulence model, based on the finite volume method to discrete control equations, activates the component transport model, and sets the physical properties of VOCs components; the physical properties include diffusion coefficient and density.

[0009] As a further description of the above technical solution, in step S3, the outlet concentration change curve over time is extracted and compared with the inlet concentration fluctuation curve; combined with streamline visualization, velocity vector diagram or residence time distribution of VOCs waste gas in the tank, analysis is carried out to quantitatively identify the short-flow channels, dead zone locations and recirculation zone range in the target buffer tank.

[0010] As a further description of the above technical solution, in step S3, at least one of the following performance indicators is calculated: peak concentration attenuation coefficient at the inlet and outlet, dead zone volume ratio, and effective volume utilization rate. Wherein, the peak concentration attenuation coefficient is the ratio of the peak concentration at the outlet to the peak concentration at the inlet of the target buffer tank; The dead zone volume ratio is calculated based on the airflow velocity threshold or the residence time distribution of VOCs exhaust gas in the target buffer tank.

[0011] As a further description of the above technical solution, in step S4, the method of adjusting the structural parameters of the internal baffle includes at least one of the following: changing the installation position of the internal baffle, adjusting the opening ratio and opening distribution of the internal baffle, or adding multiple levels of internal baffles or guide vanes.

[0012] As a further description of the above technical solution, the inlet boundary of the transient numerical simulation is set as the volumetric flow rate and VOCs component concentration parameters that change dynamically with time; the outlet boundary is a pressure outlet or a volumetric flow rate outlet.

[0013] As a further description of the above technical solution, the fluctuation form of the VOCs component concentration is pulse fluctuation, periodic fluctuation or random fluctuation.

[0014] As a further description of the above technical solution, in step S5, the judgment index for iterative optimization includes at least one of the following: the peak concentration attenuation coefficient at the inlet and outlet is not greater than the set upper limit, the dead zone volume ratio is not greater than the set upper limit, the effective volume utilization rate is not less than the set lower limit, and the outlet concentration fluctuation amplitude is not greater than the set upper limit.

[0015] As a further description of the above technical solution, while outputting the target structural parameter combination in step S6, the corresponding dynamic response prediction results are simultaneously output; the dynamic response prediction results include the outlet concentration curve, outlet velocity curve, peak attenuation coefficient, time lag, dead zone volume ratio, and effective volume utilization rate under different inlet fluctuation conditions.

[0016] As a further description of the above technical solution, a comparison and verification step is also included: under the same simulation conditions, three-dimensional solid models of target buffer tanks with different tank shapes are established, and the structural parameters of the internal baffles of each three-dimensional solid model are the same; different inlet parameters are switched to perform multiple simulations, and the inlet and outlet concentration peak attenuation coefficients and effective volume utilization rates of each model are calculated and compared to quantitatively verify the performance differences of the tank configuration.

[0017] Based on the above technical solutions, the beneficial effects of the present invention are as follows: 1. This invention uses CFD numerical simulation as its core to quantitatively analyze the velocity field, concentration field, and residence time distribution of VOCs inside the tank, so that the optimization process of VOC buffer tank structure has a clear flow mechanism basis and overcomes the blindness of empirical design. 2. This invention can simulate the pulsed, periodic and random fluctuations in the concentration of VOCs components at the inlet, quantitatively output the outlet concentration attenuation coefficient, evaluate the dynamic adaptability of the buffer tank to actual intermittent waste gas, predict the equipment operating status under extreme conditions in advance, and avoid safety and operational risks such as RTO overheating and activated carbon penetration. 3. This invention adopts a closed-loop iterative optimization process of "simulation-identification-adjustment" to eliminate short-circuiting, dead zones and backflow defects in the tank in a targeted manner, which can significantly improve the volume utilization rate of VOCs buffer tanks; 4. This invention adds a comparison and verification step for tanks with different configurations under the same working conditions, and performs simulation comparisons by switching inlet parameters multiple times to quantify the performance differences of different structures, which can provide objective data support for tank selection. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall process of the VOCs buffer tank structure design and optimization method based on computational fluid dynamics in an embodiment of the present invention. Figure 2 This is a local VOCs component concentration (including the inlet) distribution cloud map of a cubic VOCs buffer tank (baffle aperture 15mm) obtained without closed-loop iterative optimization in the third embodiment of the present invention; Figure 3 This is a local VOCs component concentration (including the outlet) distribution cloud map of a cubic VOCs buffer tank (baffle aperture 15mm) obtained without closed-loop iterative optimization in the third embodiment of the present invention; Figure 4 This is a local velocity (including inlet) distribution cloud map of a cubic VOCs buffer tank (baffle aperture 15mm) obtained without closed-loop iterative optimization in the third embodiment of the present invention; Figure 5 This is a local velocity (including outlet) distribution cloud map of a cubic VOCs buffer tank (baffle aperture 15mm) obtained without closed-loop iterative optimization in the third embodiment of the present invention; Figure 6 This is a local VOCs component concentration (including the inlet) distribution cloud map of a cubic VOCs buffer tank (baffle aperture 30mm) obtained through closed-loop iterative optimization in the third embodiment of the present invention; Figure 7 This is a local VOCs component concentration (including outlet) distribution cloud map of a cubic VOCs buffer tank (baffle aperture 30mm) obtained through closed-loop iterative optimization in the third embodiment of the present invention; Figure 8 This is a local velocity (including inlet) distribution cloud map of a cubic VOCs buffer tank (baffle aperture 30mm) obtained through closed-loop iterative optimization in the third embodiment of the present invention; Figure 9 This is a local velocity (including outlet) distribution cloud map of a cubic VOCs buffer tank (baffle aperture 30mm) obtained through closed-loop iterative optimization in the third embodiment of the present invention. Figure 10 This is a local VOCs component concentration (including the inlet) distribution cloud map of a cylindrical VOCs buffer tank (without perforated baffle) obtained without closed-loop iterative optimization in the third embodiment of the present invention; Figure 11 This is a local VOCs component concentration (including outlet) distribution cloud map of a cylindrical VOCs buffer tank (without perforated baffle) obtained without closed-loop iterative optimization in the third embodiment of the present invention; Figure 12 This is a local velocity (including inlet) distribution cloud map of a cylindrical VOCs buffer tank (without perforated baffle) obtained without closed-loop iterative optimization in the third embodiment of the present invention; Figure 13 This is a local velocity (including outlet) distribution cloud map of a cylindrical VOCs buffer tank (without perforated baffle) obtained without closed-loop iterative optimization in the third embodiment of the present invention; Figure 14 This is a local VOCs component concentration (including the inlet) distribution cloud map of a cylindrical VOCs buffer tank (baffle aperture 15mm) obtained through closed-loop iterative optimization in the third embodiment of the present invention; Figure 15 This is a local VOCs component concentration (including the outlet) distribution cloud map of a cylindrical VOCs buffer tank (baffle aperture 15mm) obtained through closed-loop iterative optimization in the third embodiment of the present invention; Figure 16 This is a local velocity (including inlet) distribution cloud map of a cylindrical VOCs buffer tank (baffle aperture 15mm) obtained through closed-loop iterative optimization in the third embodiment of the present invention. Figure 17 This is a local velocity (including outlet) distribution cloud map of a cylindrical VOCs buffer tank (baffle aperture 15mm) obtained through closed-loop iterative optimization in the third embodiment of the present invention.

[0019] Explanation of icon numbers: 1. Entrance; 2. Exit. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be noted that the terms "upper," "middle," "lower," "inner," "outer," "front," "rear," "left," and "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The embodiments of this invention will now be described according to its overall structure.

[0022] Please see Figures 1 to 17 This invention discloses a method for designing and optimizing VOCs buffer tank structures based on computational fluid dynamics. The disclosed method for designing and optimizing VOCs buffer tank structures based on computational fluid dynamics includes the following steps: S1: Establish a three-dimensional solid model based on the geometric dimensions of the target buffer tank, and determine the tank shape, inlet position, outlet position, and the initial structure of its internal baffles; S2: The computational fluid dynamics method is used to conduct transient numerical simulations of the flow field and VOCs component concentration distribution inside the target buffer tank, and the simulation results include velocity field, concentration field and outlet dynamic response data. S3: Identify the short-flow channels and / or dead zones and / or recirculation zones within the target buffer tank based on the simulation results; S4: Based on the identified short-flow channels and / or dead zone locations and / or recirculation zones, adjust the structural parameters of the internal baffle; S5: Repeat steps S2 to S4, and optimize through closed-loop iteration until the performance indicators of the target buffer tank meet the preset requirements, and obtain the target structural parameter combination; S6: Output the target structural parameter combination, which includes the target inlet position, target outlet position, and target structural parameters of the internal baffle of the target buffer tank.

[0023] Using the above method, firstly, in step S1, a three-dimensional solid model including the tank shape, inlet and outlet positions, and the initial structure of the internal baffles is established to provide a geometric basis for subsequent numerical simulations. Then, in step S2, computational fluid dynamics (CFD) is used to perform transient numerical simulations of the flow field and VOCs component concentration distribution inside the tank, obtaining velocity field, concentration field, and outlet dynamic response data, thereby quantitatively revealing the flow and mixing characteristics inside the tank. Subsequently, in step S3, based on the simulation results, the short-flow channels, dead zones, and backflow zones inside the tank are accurately identified, clarifying the structural defects. To address these defects, in step S4, the structural parameters of the internal baffles are adjusted (such as installation position, opening ratio and opening distribution, adding multi-stage baffles or guides). The design incorporates various structural parameters, including internal baffles, to achieve targeted improvements. In step S5, steps S2 to S4 are iteratively executed (re-substituting the modified internal baffle parameters into step S2 for CFD simulation, then performing defect identification in step S3, and finally adjusting according to step S4). This process forms a closed-loop iterative optimization of "simulation-identification-adjustment" until all performance indicators (such as inlet / outlet concentration peak attenuation coefficient, dead zone volume ratio, and effective volume utilization rate) meet preset requirements, obtaining the target structural parameter combination (i.e., the optimal structural parameter combination). Finally, in step S6, the output includes the target structural parameters (optimal structural parameters) of the internal baffles and the (optimal) target structural parameter combination formed by the tank shape and inlet / outlet positions. Thus, in the VOCs buffer tank structural design, the traditional experience-based design method is transformed into a quantitative iterative optimization based on flow mechanisms, effectively eliminating internal short-circuiting and dead zones, significantly improving its effective volume utilization rate and dynamic concentration attenuation capability. After the buffer tank is formed, it avoids the situation where high-concentration VOCs gas clouds penetrate and impact downstream equipment, thereby effectively ensuring the safe and stable operation of downstream RTO and activated carbon adsorption devices.

[0024] Specifically, the transient numerical simulation uses the standard k-ε turbulence model commonly used in the engineering field (it should be understood that other turbulence models can also be selected according to factors such as the actual fluid type, flow velocity characteristics and boundary condition complexity) to accurately simulate the turbulent motion inside the buffer tank (standard wall functions can be used to handle the flow in the near-wall region of the tank and baffle). Based on the finite volume method, the flow control equation, turbulent transport equation and component transport equation are discretely solved. At the same time, the component transport model is activated, and the physical properties of VOCs components such as density and diffusion coefficient are entered. The entire process of airflow, turbulent evolution and VOCs component convection and diffusion is solved simultaneously.

[0025] Specifically, in step S3, the outlet concentration change curve over time is extracted and compared with the inlet concentration fluctuation curve; combined with streamline visualization, velocity vector diagram or residence time distribution of VOCs exhaust gas in the tank, analysis is carried out to quantitatively identify the short-flow channels, dead zone locations and recirculation zone range in the target buffer tank.

[0026] Specifically, in step S3, at least one of the following performance indicators is calculated: peak concentration attenuation coefficient at the inlet and outlet, dead zone volume ratio, and effective volume utilization rate; wherein, the peak concentration attenuation coefficient at the inlet and outlet is the ratio of the peak concentration at the outlet to the peak concentration at the inlet of the target buffer tank; the dead zone volume ratio is calculated based on the airflow velocity threshold or the residence time distribution of VOCs waste gas in the tank.

[0027] Specifically, in step S4, adjusting the structural parameters of the internal baffle includes at least one of the following: changing the installation position of the internal baffle, adjusting the opening ratio and opening distribution of the internal baffle, or adding multiple levels of internal baffles or guide vanes. It should be understood that each round of adjustment modifies only one or a few parameters to allow for a clear comparison of the optimization results.

[0028] Specifically, the inlet boundary of the transient numerical simulation is set as the volumetric flow rate and VOCs component concentration parameters that change dynamically with time; the outlet boundary is a pressure outlet or a volumetric flow rate outlet.

[0029] Specifically, the fluctuations in the concentrations of the VOCs components can be pulse-like, periodic, or random.

[0030] Specifically, in step S5, the judgment indicators for iterative optimization include: the peak concentration attenuation coefficient at the inlet and outlet is not greater than the set upper limit, the dead zone volume ratio is not greater than the set upper limit, the effective volume utilization rate is not less than the set lower limit, and the outlet concentration fluctuation amplitude is not greater than the set upper limit.

[0031] Specifically, while outputting the target structural parameter combination in step S6, the corresponding dynamic response prediction results are output simultaneously; the dynamic response prediction results include the outlet concentration curve, outlet velocity curve, peak attenuation coefficient, time lag, dead zone volume ratio, and effective volume utilization rate under different inlet fluctuation conditions.

[0032] Specifically, it also includes a comparison and verification step: under the same simulation conditions, three-dimensional solid models of target buffer tanks with different tank shapes are established, and the structural parameters of the internal baffles of each three-dimensional solid model are the same; different inlet parameters are switched to perform multiple simulations, and the inlet and outlet concentration peak attenuation coefficients and effective volume utilization rates of each model are calculated and compared to quantitatively verify the performance differences of tank configurations.

[0033] The present invention will be further described in detail below with reference to specific embodiments. In a specific embodiment, a VOCs waste gas buffer tank in an automotive painting workshop is used as the application object. The waste gas exhibits periodic fluctuations in concentration and flow rate. According to current environmental protection regulations, the concentration of VOCs components entering the downstream RTO incineration equipment must be consistently lower than 25% of the lower explosive limit.

[0034] The implementation plan includes a standardized performance evaluation: peak concentration attenuation coefficient at the inlet and outlet ≤ 0.8, dead zone volume ratio ≤ 10%, effective volume utilization rate ≥ 90%, and outlet concentration fluctuation ≤ 1500 mg / m³. 3 .

[0035] The simulation uses general-purpose CFD numerical simulation software, and the standard k-ε turbulence model, finite volume method, and component transport model are used uniformly throughout the simulation. The simulation medium is a mixture of air and coating VOCs at normal temperature and pressure.

[0036] Example 1: Initial Simulation, Defect Identification, and Iterative Optimization of a Cubic Buffer Tank (15mm Baffle Orifice) This embodiment designs and optimizes the above-mentioned VOCs buffer tank structure based on computational fluid dynamics to achieve the above design specifications. Specifically, it includes the following steps: S1: Establish a 3D model and determine the initial structure. (1) Tank parameters The tank has a cubic shape, with net external dimensions of 2450mm (length) × 2450mm (width) × 4725mm (height), and an effective volume of 23m³. 3 The inner wall of the tank is designed to be smooth and non-slip.

[0037] (2) Import and export layout It adopts an air intake on the upper left and an air outlet on the lower right. The nominal diameter of the inlet pipe is 1050mm and the nominal diameter of the outlet pipe is 900mm. The height of the pipe centerline from the bottom of the tank is 2350mm, the length of the pipe extending into the tank is 150mm, and the horizontal distance between the center of the inlet and outlet is 1025mm.

[0038] (3) Initial structure of internal baffle A single integral flat baffle is vertically installed inside the tank. The baffle is 20mm thick and has a surface size of 4425mm × 3232mm. The bottom of the baffle is 250mm from the bottom of the tank and the top is 50mm from the top of the tank. The baffle has circular through holes with an initial diameter of 15mm, and the holes are evenly distributed in a matrix. The baffle is located at the horizontal mid-section of the tank body, 1150mm from the inlet end face 1.

[0039] (4) Model simplification Only the fluid region inside the tank is retained as the computational domain, and non-flowing auxiliary structures such as flanges and supports are deleted to complete a 1:1 three-dimensional solid model.

[0040] S2: Transient Numerical Simulation Setup and Calculation (1) Grid division A hybrid mesh approach is adopted, with structured meshes used in the main flow regions and local mesh refinement used in areas with abrupt flow changes, such as inlets and outlets, baffle openings, and wall corners. The total number of global meshes is approximately 1.01 million, with a mesh skewness of <0.85 and an orthogonality quality of >0.3, which meets the computational convergence requirements.

[0041] (2) Solver and physical model Solver: A pressure-based transient solver is selected, with the medium set as an incompressible fluid, suitable for the flow characteristics of low-speed exhaust gas at normal temperature and pressure. Turbulence Model: The standard k-ε turbulence model is used, combined with standard wall functions to handle near-wall flow; the empirical constants of the model adopt industry-standard methods. = 1.0、 = 1.3、 = =1.44、 = 1.92.

[0042] Discretization method: The finite volume method is used to discretize the governing equations over the entire domain. The convection term adopts the second-order upwind scheme, and the diffusion term adopts the central difference scheme.

[0043] Component model: Activate the component transport model and define air and coating VOCs as the gas phase.

[0044] (3) Boundary conditions and initial conditions Inlet 1 boundary (velocity inlet 1): average air volume is 12000 m³ / h 3 The concentration of VOC components fluctuated periodically at inlet 1, with a peak concentration of 17796 mg / m³. 3 The fluctuation period is 60s; the turbulence intensity at inlet 1 is 5%, and the hydraulic diameter is 1050mm.

[0045] Outlet 2 boundary (pressure outlet 2): The gauge pressure of outlet 2 is set to 0 Pa (atmospheric pressure), and the reflux component is air by default.

[0046] Wall boundaries: The tank wall, baffle wall, and pipe wall are all designed as non-slip solid walls.

[0047] Initial conditions for the entire field: initial flow velocity inside the tank is 0 m / s, and background VOCs concentration is 0 mg / m³. 3 The pressure is standard atmospheric pressure.

[0048] (4) Time and Iteration Control Time step =0.5s, maximum number of iterations per time step: 30; convergence residuals for continuity equation, momentum equation, k equation, ε equation, and component equation are uniformly set to 10.-6 The total calculation time is 600 seconds, covering 10 complete concentration fluctuation cycles, ensuring that the flow field and concentration field reach a stable periodic state.

[0049] (5) Data output A monitoring point is set at the center of the outlet section to record the instantaneous VOCs component concentration and instantaneous flow velocity at the outlet in real time; the entire field data, including velocity contour plot, velocity vector plot, streamline plot, and VOCs concentration contour plot, is automatically saved every 2 seconds. After the calculation is completed, the entire flow field, concentration field, and time series data are exported.

[0050] S3: Defect Identification and Performance Index Calculation (1) Import and export operating data Under this operating condition, the VOC concentration at inlet 1 of the cubic buffer tank is 17796 mg / m³. 3 The airflow velocity at inlet 1 is 7.3 m / s; after passing through a 15 mm diameter baffle, the VOC concentration at outlet 2 is 15457 mg / m³. 3 The airflow velocity at outlet 2 is 21.5 m / s.

[0051] Flow mechanism analysis: The perforated baffle forces the airflow through the small hole, effectively blocking the jet from directly impacting the outlet 2 and suppressing the formation of short flow; after the gas flows through the small hole, it forms a high-speed jet and local vortex, which enhances the turbulent mixing of gas masses of different concentrations, making the airflow distribution in the tank more uniform, effectively improving the tank volume utilization rate, and achieving the smoothing of the concentration fluctuation at the inlet 1.

[0052] (2) Flow field defect identification Analysis combining concentration cloud map, velocity vector map and streamline diagram: There are still local straight flow channels in the upper part of the tank, which are short flow channels that have not been completely eliminated; After the airflow passes through the baffle, two low-speed vortex zones are formed in the upper and lower areas on the leeward side of the baffle. The airflow velocity in the area is less than 0.1m / s, the fluid renewal is slow, and it is a typical flow dead zone and backflow zone; The overall flow field distribution is uneven, and there is still a risk of high-concentration gas clouds penetrating.

[0053] (3) Calculation of core performance indicators Peak concentration decay coefficient: Peak concentration at outlet 2 / Peak concentration at inlet 1 = 15457 / 17796 ≈ 0.869; Dead zone volume percentage: Using an airflow velocity of less than 0.1 m / s as the threshold for determining the dead zone, and combined with the residence time distribution statistics, the dead zone volume accounts for 22% of the total tank volume; Effective volume utilization rate: Calculated, the effective volume utilization rate of the tank is 69%.

[0054] (4) Result determination The peak concentration decay coefficient was 0.869 > 0.8, the dead zone volume ratio was 22% > 10%, and the effective volume utilization rate was 68% < 90%. All three core indicators failed to meet the preset requirements, and the baffle structure needs to be optimized and adjusted.

[0055] S4: Adjust the structural parameters of the tank's internal baffle. Throughout the process, the tank's shape, inlet and outlet positions, and pipe dimensions remain constant. Internal baffles are adjusted following a single variable principle, including changing the baffle installation height, adjusting the baffle orifice diameter and distribution, and adding multi-stage baffles or guide vanes. This embodiment prioritizes optimizing the orifice parameters before fine-tuning the installation position.

[0056] S5: Closed-loop iterative optimization Steps S2 to S4 (i.e., the "simulation-identification-adjustment" process) are executed repeatedly for a total of 6 iterations. In each round of simulation, the model, physical parameters, boundary conditions, and solution parameters are kept consistent with the initial conditions. The iteration process and indicators are shown in Table 1 below: Table 1. Iteration process and indicators for 6 rounds Iteration Termination Determination After the 6th iteration: the peak concentration attenuation coefficient at the inlet and outlet is 0.750 < 0.8, the dead zone volume ratio is 8.3% < 10%, the effective volume utilization rate is 92.1% > 90%, and the concentration fluctuation range at outlet 2 is 1120 mg / m³. 3 <1500 mg / m 3 Once all indicators meet the design requirements, the iteration terminates, and the current structure is determined as the target structure (i.e., the optimal structure).

[0057] S6: Output target mechanism parameters and dynamic response prediction results (1) Final combination of structural parameters Tank body: cubic shape, with external dimensions of 2450mm×2450mm×4725mm, and the overall structure remains unchanged; Inlet and outlet: left inlet and right outlet layout, inlet pipe diameter 1050mm, outlet pipe diameter 900mm, installation height and pipe extension length remain in the initial position; Internal baffle: The bottom is 250mm from the bottom of the tank and the top is the top of the tank; it adopts non-uniform opening, with a lower hole diameter of 18mm and an upper hole diameter of 12mm, and a total opening rate of 14%; guide vanes with a length of 400mm are added to the left and right sides of the baffle.

[0058] (2) Dynamic response prediction results The system synchronously outputs the outlet 2 concentration curve and outlet 2 velocity curve under periodic fluctuation conditions; characteristic parameters: the peak concentration attenuation coefficient at the inlet and outlet is 0.75, the average airflow time lag is 18s, the dead zone volume ratio is 8.3%, and the effective volume utilization rate is 92.1%; at the same time, it exports the optimized global velocity cloud map, concentration cloud map, and streamline map as technical basis for equipment processing, on-site installation, and operation and maintenance.

[0059] Example 2: Simulation comparison of a traditional cylindrical buffer tank (elliptical inclined baffle + bent pipe outlet 2). In this embodiment, a cylindrical buffer tank model with the same effective volume as in Embodiment 1 is established. The simulation model, physical property parameters, boundary conditions, and solution settings are completely unified, while the tank body adopts the classic structural form of elliptical inclined baffle + bent pipe outlet 2.

[0060] (1) Initial structure of the tank Tank body: Cylindrical tank, inner diameter 2500mm, cylinder height 4000mm, effective volume is equal to that of a cubic tank; Internal baffle: An elliptical inclined baffle is installed inside the tank. The baffle is arranged at an angle, and the plate surface is an elliptical structure without openings. The installation position is consistent with the axial position of the initial baffle in Example 1. Outlet 2 structure: Abandon the straight pipe outlet 2 and adopt the bent pipe outlet 2 structure to change the airflow direction, thereby attempting to weaken the straight short flow.

[0061] Inlet 1 structure: The air intake is a horizontal straight pipe on the upper right side with a nominal pipe diameter of 1050mm. The installation height and extension length are consistent with those of Example 1.

[0062] (2) Simulation results and data analysis Under the same operating conditions, the VOCs concentration at inlet 1 of the cylindrical buffer tank is 13649 mg / m³. 3 The VOCs concentration at the two outlets was 13649 mg / m³. 3 There was no decrease in concentration at the inlet and outlet; the airflow velocity at inlet 1 was 8.8 m / s, and the airflow velocity at outlet 2 was 13.2 m / s.

[0063] (3) Flow field and performance analysis When a cylindrical tank is combined with an elliptical inclined baffle and a curved outlet 2, although the curved outlet changes the direction of airflow, the main flow inside the tank still forms a clear short-flow channel along the side wall of the tank. The elliptical inclined baffle can only slightly change the local flow direction and cannot prevent high-concentration gas masses from flowing directly to outlet 2. The gas mixing effect inside the tank is extremely poor, and it has no concentration suppression capability whatsoever. The dead zone and reflux zone inside the tank are large, and the effective volume utilization rate is far lower than that of a cubic buffer tank with a 15mm perforated baffle.

[0064] The comparison shows that, under the same working conditions, even with the optimization of the structure using elliptical inclined baffles and bent pipe outlet 2, the overall performance of the cylindrical tank is still significantly inferior to that of the cubic tank.

[0065] Example 3: Comparison Experiment with Different Baffle Orifice Diameters Please see Figures 2 to 17 Based on the two types of tanks mentioned above, comparative simulations were conducted by changing the baffle opening parameters: the baffle opening diameter of the cubic buffer tank was increased from 15mm to 30mm; at the same time, a 15mm small hole was opened on the inclined baffle of the original elliptical inclined baffle cylindrical buffer tank, while the rest of the geometry, mesh, model parameters, and boundary conditions remained unchanged. The simulation results and analysis are as follows.

[0066] (1) Simulation data of each group of working conditions Cubic buffer tank (baffle aperture 30mm): VOCs concentration at inlet 1 is 17796mg / m³ 3 The airflow velocity at inlet 1 is 7.3 m / s; the VOCs concentration at outlet 2 is 14876 mg / m³. 3 The airflow velocity at outlet 2 is 18.0 m / s.

[0067] Cylindrical buffer tank (elliptical inclined baffle with 15 mm small hole + 2 bends at outlet): VOCs concentration at inlet 1 is 13649 mg / m³ 3 Inlet 1 airflow velocity: 8.8 m / s; Outlet 2 VOCs concentration: 13649 mg / m³ 3 The airflow velocity at outlet 2 is 14.4 m / s.

[0068] (2) Comparative analysis of working conditions Cubic buffer tank (30mm baffle orifice diameter): Compared to the 15mm orifice diameter condition, the increased baffle orifice area weakens the airflow throttling effect, reduces the intensity of the jet and vortex formed by the small orifice, and results in insufficient turbulent mixing of VOCs. This manifests as a simultaneous decrease in outlet 2 concentration and outlet 2 flow velocity, a decline in concentration suppression efficiency, and a deterioration in the overall performance of the buffer tank, proving that the baffle orifice diameter is a key sensitive parameter; an excessively large orifice diameter will weaken the equipment performance.

[0069] Cylindrical buffer tank (elliptical inclined baffle with 15mm opening + elbow outlet 2): After adding an opening to the original elliptical inclined baffle, the flow field and concentration field inside the tank did not improve significantly. The inlet and outlet concentrations remained unchanged, with only a slight increase in the flow velocity at outlet 2. Simply adding an opening to the elliptical inclined baffle of the cylindrical tank, along with elbow outlet 2, cannot fundamentally solve its inherent flow field defects, and its performance remains far inferior to that of the cubic buffer tank.

[0070] (3) Experimental conclusions For cubic VOCs buffer tanks, the baffle aperture needs to be set within a reasonable range; an excessively large aperture will reduce the turbulent mixing effect. At the same time, the tank configuration is the core factor determining the buffer tank's ability to homogenize concentration and stabilize flow. Even if a cylindrical tank is equipped with an elliptical inclined baffle, a bent outlet 2, and the baffle openings are modified, it is difficult to achieve the ideal performance. In addition, a cubic tank with a baffle with an appropriate aperture is the preferred structure for treating intermittent, high-concentration fluctuating VOCs waste gas.

[0071] Example 4: Adaptability verification under various concentration fluctuation conditions Based on the optimal structural model optimized in Example 1, keeping all geometric parameters, simulation model, and physical parameters unchanged, the boundary of the inlet 1 for three types of typical industrial VOCs concentrations—pulse fluctuation, periodic fluctuation, and random fluctuation—was set to verify the structure's adaptability to operating conditions.

[0072] (1) Pulsating concentration fluctuation: instantaneous peak concentration 20000 mg / m³ 3 The pulse duration was 10 s; the simulation showed that the concentration peak attenuation coefficient was 0.73, and there was no high-concentration gas mass penetration phenomenon.

[0073] (2) Periodic concentration fluctuations: Using the basic operating conditions of Example 1, all performance indicators are stable and meet the standards.

[0074] (3) Random concentration fluctuations: VOCs concentrations range from 8000 to 19000 mg / m³ 2 The concentration at outlet 2 fluctuates irregularly within the range, and the fluctuation range is always controlled within the preset threshold.

[0075] Verification conclusion: The optimized buffer tank structure of this invention can fully adapt to three types of complex exhaust gas fluctuation conditions: pulse, periodic, and random. It has strong dynamic anti-interference ability and can effectively avoid problems such as RTO overheating and activated carbon adsorption penetration. It has excellent operational safety and stability.

[0076] Example 5: Alternative Implementation Alternative Solution 1 (Experimental Scheme for Similarity Criterion in Scaled-Down Models) (1) Model making: According to a suitable geometric similarity ratio, a scaled-down model of the buffer tank is made using transparent plexiglass to completely replicate the cubic tank body, inlet and outlet positions, and optimize the back baffle structure; the test wind speed is matched according to the Reynolds similarity criterion to ensure that the model and the prototype flow state are similar in dynamics.

[0077] (2) Experimental system setup: A ventilation system, a VOCs gas mixing system and a detection system were set up. The flow field was visualized by using the staining solution tracer method and the hydrogen bubble tracer method. The concentration of VOCs components in different areas of the tank was quantitatively detected by using planar laser-induced fluorescence technology.

[0078] (3) Experimentation and iteration: By visualizing images, short flow, dead zone and recirculation zone are identified, and the concentration peak attenuation coefficient, dead zone ratio and effective volume utilization rate of inlet 1 are calculated. The process of "experimentation-analysis-structure modification" is followed in a closed loop iteration until the indicators meet the standards.

[0079] (4) Result conversion: Based on the similarity criterion, the parameters of the scaled-down model are converted into the dimensions of the prototype equipment, and the final design scheme is output. The advantages of this scheme are that the flow field is intuitive and there is no numerical calculation error; the disadvantages are that the model processing and testing cycle is long and the cost is high. It is suitable for physical verification of simulation results.

[0080] Alternative Solution 2 (Analytical / Semi-Analytical Model Solution) (1) Model simplification: The internal flow channel of the buffer tank is simplified into a multi-stage ideal mixing vessel series model, and the flow unit is divided according to the structural form.

[0081] (2) Tracer experiment: Tracer gas was instantaneously injected into inlet 1, and the tracer concentration change curve at outlet 2 was continuously monitored. The axial curve was fitted based on the residence time distribution theory. Characteristic parameters such as diffusion coefficient and number of reactors in series.

[0082] (3) Calculation and optimization: The dead zone volume ratio and effective volume utilization rate are calculated using the fitted parameters. The baffle and inlet / outlet structure are adjusted in accordance with the empirical correlation between the structure and flow parameters. After multiple experiments and iterations until the performance meets the standards, the final design scheme is output. This scheme is simple to implement, has a small amount of calculation, and low cost. It is suitable for preliminary scheme estimation and rapid selection in the early stage of the project. The disadvantage is that it cannot realize three-dimensional visualization of the flow field and cannot accurately locate local defects.

[0083] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any changes, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for structural design and optimization of VOCs buffer tanks based on computational fluid dynamics, characterized in that, Includes the following steps: S1: Establish a three-dimensional solid model based on the geometric dimensions of the target buffer tank, and determine the tank shape, inlet position, outlet position, and the initial structure of its internal baffles; S2: The computational fluid dynamics method is used to conduct transient numerical simulations of the flow field and VOCs component concentration distribution inside the target buffer tank, and the simulation results include velocity field, concentration field and outlet dynamic response data. S3: Identify the short-flow channels and / or dead zones and / or recirculation zones within the target buffer tank based on the simulation results; S4: Based on the identified short-flow channels and / or dead zone locations and / or recirculation zones, adjust the structural parameters of the internal baffle; S5: Repeat steps S2 to S4, and optimize through closed-loop iteration until the performance indicators of the target buffer tank meet the preset requirements, and obtain the target structural parameter combination; S6: Output the target structural parameter combination, which includes the target inlet position, target outlet position, and target structural parameters of the internal baffle of the target buffer tank.

2. The method for VOCs buffer tank structure design and optimization based on computational fluid dynamics according to claim 1, characterized in that, The transient numerical simulation employs a k-ε turbulence model, based on the finite volume method to discretely determine the control equations, activates the component transport model, and sets the physical properties of the VOCs components, including diffusion coefficient and density.

3. The method for VOCs buffer tank structure design and optimization based on computational fluid dynamics according to claim 1, characterized in that, In step S3, the outlet concentration change curve over time is extracted and compared with the inlet concentration fluctuation curve; combined with streamline visualization, velocity vector diagram or residence time distribution of VOCs exhaust gas in the tank, analysis is carried out to quantitatively identify the short-flow channels, dead zone locations and recirculation zone range in the target buffer tank.

4. The method for designing and optimizing VOCs buffer tank structures based on computational fluid dynamics according to claim 1, characterized in that, In step S3, at least one of the following performance indicators shall be calculated: peak concentration attenuation coefficient at inlet and outlet, dead zone volume ratio, and effective volume utilization rate; Wherein, the peak concentration attenuation coefficient is the ratio of the peak concentration at the outlet to the peak concentration at the inlet of the target buffer tank; The dead zone volume ratio is calculated based on the airflow velocity threshold or the residence time distribution of VOCs exhaust gas in the target buffer tank.

5. The method for VOCs buffer tank structure design and optimization based on computational fluid dynamics according to claim 1, characterized in that, In step S4, the method of adjusting the structural parameters of the internal baffle includes at least one of the following: changing the installation position of the internal baffle, adjusting the opening ratio and opening distribution of the internal baffle, or adding multiple levels of internal baffles or guide vanes.

6. The method for VOCs buffer tank structure design and optimization based on computational fluid dynamics according to claim 1, characterized in that, The inlet boundary of the transient numerical simulation is set as the volumetric flow rate and VOCs component concentration parameters that change dynamically with time; the outlet boundary is a pressure outlet or a volumetric flow rate outlet.

7. The method for designing and optimizing VOCs buffer tank structures based on computational fluid dynamics according to claim 6, characterized in that, The fluctuations in the concentrations of the VOCs components can be pulse-like, periodic, or random.

8. The method for designing and optimizing VOCs buffer tank structures based on computational fluid dynamics according to claim 1, characterized in that, In step S5, the judgment index for iterative optimization includes at least one of the following: the peak concentration attenuation coefficient at the inlet and outlet is not greater than the set upper limit, the dead zone volume ratio is not greater than the set upper limit, the effective volume utilization rate is not less than the set lower limit, and the outlet concentration fluctuation amplitude is not greater than the set upper limit.

9. The method for designing and optimizing VOCs buffer tank structures based on computational fluid dynamics according to claim 1, characterized in that, While outputting the target structural parameter combination in step S6, the corresponding dynamic response prediction results are simultaneously output; the dynamic response prediction results include the outlet concentration curve, outlet velocity curve, peak attenuation coefficient, time lag, dead zone volume ratio, and effective volume utilization rate under different inlet fluctuation conditions.

10. The method for designing and optimizing VOCs buffer tank structures based on computational fluid dynamics according to claim 1, characterized in that, It also includes a comparison and verification step: under the same simulation conditions, three-dimensional solid models of target buffer tanks with different tank shapes are established, and the structural parameters of the internal baffles of each three-dimensional solid model are the same; different inlet parameters are switched to perform multiple simulations, and the inlet and outlet concentration peak attenuation coefficients and effective volume utilization rates of each model are calculated and compared to quantitatively verify the performance differences of the tank configuration.

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