A streamlined demister design method based on probability model

Abstract

The present invention relates to the technical field of streamlined demister design, and in particular to a streamlined demister design method based on a probability model, comprising the following steps: step S1: analyzing and calculating the demisting rate λ and the total pressure loss Δp of a single bend in a single channel; step S2: determining the gas flow rate, bend spacing, bend angle, demisting rate λ, and total pressure loss Δp with the highest demisting efficiency i; step S3: equating the demisting rate λ to the absorption probability P of droplets; step S4: equating the process of n bends absorbing droplets to a series of independent random events; and step S5: calculating the demisting failure probability 1-P(A) for each bend. i ); Step S6: After the droplet passes through the n folding plates, the absorption probability of the droplet is 1-(1-P) n ; Step S7: Let 1-(1-P) n ≥99%, and the number of bends n required for the demister is calculated; this solves the problems of large computational complexity and low efficiency in the existing design of streamlined demisters using the Euler-Lagrange coupling numerical method.

Description

Technical Field

[0001] The invention relates to the technical field of streamlined demister design, in particular to a streamlined demister design method based on a probability model. Background Art

[0002] Streamlined demister is an effective and widely used gas-liquid separation device. Its main function is to properly handle the mist entrained in the gas to prevent harmful mist from being discharged into the air, thereby causing immeasurable damage to the environment. At the same time, it is also necessary to avoid the impact of mist on other equipment. Therefore, designing a streamlined demister that can efficiently remove mist is a hot research issue.

[0003] The Euler-Lagrange coupling numerical method is often used to solve the streamlined demister during the design process. The streamlined demister consists of multiple bends and has a complex structure. The direct Euler-Lagrange coupling method is computationally intensive to perform design analysis on the streamlined demister, resulting in low analysis and solution efficiency for the streamlined demister.

[0004] Therefore, it is necessary to invent a streamlined demister design method based on a probability model to solve the above problems. Summary of the Invention

[0005] In order to solve the problems of large computational complexity and low efficiency in designing a streamlined demister using the existing Euler-Lagrange coupling numerical method, the present invention provides a streamlined demister design method based on a probability model.

[0006] The present invention is achieved by adopting the following technical solutions:

[0007] A streamlined demister design method based on a probability model comprises the following steps:

[0008] Step S1: using the Euler-Lagrange coupling method to analyze and calculate the demisting rate λ and the total pressure loss Δp of a single bend in a single channel of a streamlined demister under different gas flow rates, different bend plate spacings, and different bend angles multiple times, and calculate the ratio of the demisting rate λ to the total pressure loss Δp: demisting efficiency i = λ / Δp;

[0009] Step S2: Select a single channel single bend with the highest demisting efficiency i, and determine its corresponding demisting rate λ, gas flow rate, bend spacing and bend angle θ;

[0010] Step S3: The demisting rate λ is equivalent to the absorption probability P of a single bend in a single channel for droplets, and the probability of demisting failure of a single bend is calculated as 1-P;

[0011] Step S4: For a streamlined demister with n bends in a single channel, the process of the n bends absorbing droplets is equivalent to a series of independent random events A1, A2, ..., A n , then the absorption probability of the droplets at each bend is calculated as P(A1), P(A2), ..., P(A n ), where P(A i )≥0, and n≥i≥1;

[0012] Step S5: Calculate the probability of failure of defogging at each bend as 1-P(A i ), then the probability that the droplet is not absorbed by any bend is On the contrary, the probability that a droplet is absorbed by any of the n bends is

[0013] Step S6: Since the streamlined demister is often manufactured with the same bends, it is assumed that the absorption probability of the mist droplets at each bend is the same and is P, that is, P(A1)=P(A2)=...=P(A n )=P, then the absorption probability of the droplet after passing through n bends is 1-(1-P) n ;

[0014] Step S7: Assume that the absorption probability of the streamlined demister droplets needs to reach 99%, then let 1-(1-P) n ≥99%, calculate the value of n, which is the number of bends required for a single channel of the streamlined demister;

[0015] Step S8: Calculate the total pressure loss Δp×n of n bends based on the total pressure loss Δp of a single bend to ensure that the total pressure loss of gas flowing through the n bends is less than the rated wind pressure of the fan.

[0016] In step S1, the demisting rate λ is the ratio of the mass of the droplets captured by the wall to the mass of the incoming droplets, that is, the difference between the inlet droplet mass and the outlet droplet mass divided by the inlet droplet mass; the total pressure loss Δp is equal to the inlet total pressure minus the outlet total pressure; and the demisting efficiency i is the ratio of the demisting rate λ to the total pressure loss Δp.

[0017] The method of the present invention is reasonable, reliable and efficient. Compared with the Euler-Lagrange coupling method, the present invention is based on a brand-new principle. This new principle can quickly analyze the demisting efficiency of a streamlined demister containing many bends through the demisting rate of a single bend in a single channel, greatly reducing the calculation amount of the numerical simulation of the streamlined demister, thereby significantly accelerating the design process of the streamlined demister. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1is the concentration of inlet and outlet droplets at different bending angles of a single channel calculated by the Euler-Lagrange coupling method in the embodiment.

[0019] Figure 2 It is the demisting rate of a single channel at different bending angles calculated by the Euler-Lagrange coupling method in the embodiment.

[0020] Figure 3 It is the total pressure loss of a single channel at different bending angles calculated by the Euler-Lagrange coupling method in the embodiment.

[0021] Figure 4 It is the demisting efficiency of a single channel at different bending angles calculated by the Euler-Lagrange coupling method in the embodiment.

[0022] Figure 5 3 is a comparison chart of the effect of the number of bends on the water vapor absorption rate calculated by the present method and the Euler-Lagrange coupling method in the embodiment.

[0023] Figure 6 3 is a comparison diagram of the effect of the number of bends on the total pressure loss calculated by the present method and the Euler-Lagrange coupling method in the embodiment.

[0024] Figure 7 3 is a diagram of droplet concentration distribution when the Euler-Lagrange coupling method is used to calculate different numbers of bends in the embodiment.

[0025] Figure 8 3 is a diagram of pressure loss distribution when calculating different numbers of bends using the Euler-Lagrange coupling method in an embodiment. DETAILED DESCRIPTION

[0026] Example

[0027] As attached Figure 1 ~Attached Figure 8 As shown, a streamlined demister with a folding plate spacing of 20 mm, a gas flow rate of 6 m / s, and an unknown bending angle is taken as an example;

[0028] A streamlined demister design method based on a probability model comprises the following steps:

[0029] Step S1: using the Euler-Lagrange coupling method to analyze and calculate the demisting rate λ and total pressure loss Δp of a single bend of the streamlined demister at different bend angles multiple times, and calculating the demisting efficiency i=λ / Δp;

[0030] The Euler-Lagrange coupling method is used to analyze the motion trajectory of each droplet in a single bend of the streamlined demister, and the demisting rate λ and total pressure loss Δp of a single bend are analyzed. Fluid mechanics is used to analyze the movement of the continuous phase air in the streamlined demister at each moment, and the air force acting on each droplet is calculated based on the airflow pressure distribution, the position and diameter of each droplet at each moment. The particle motion equation is used to calculate the motion trajectory and position of the discrete phase droplets at each moment, and the above steps are repeated to calculate the movement of the droplets. If a droplet reaches the wall, outlet and inlet of the streamlined demister at a certain moment, it is considered that the droplet is adsorbed or overflowed, and the droplet is removed from the calculation model. The continuous phase in the simulation is air with a density of 1.225 kg / m 3 , dynamic viscosity is 1.7894×10 -5 N·s / ㎡; the dispersed phase is droplets with a density of 998.2kg / m 3 The droplet mass flow rate entering the streamlined demister is 50 kg / (m2·s). The droplet size is uniformly distributed, ranging from 1 μm to 50 μm. The droplets are evenly distributed across the inlet cross-section, and the droplet incidence velocity is consistent with the gas flow rate in both magnitude and direction. Velocity inlet and pressure outlet boundary conditions are adopted: the inlet is a velocity inlet with an air velocity of 6 m / s; the outlet is a pressure outlet with a pressure of 0 Pa. The folded plate wall is a non-slip adiabatic wall, and the wall liquid film is ignored when capturing droplets. The air flow field model uses structured grid CFD.

[0031] Step S2: Select a single channel single bend with the highest demisting efficiency i, and determine its corresponding demisting rate λ and bending angle θ;

[0032] Under the premise of determining the gas flow rate and the spacing between the folded plates, folded plates with bending angles θ of 20°, 45°, 90°, 110°, 135° and 160° were selected. Then, the Euler-Lagrange coupling method was used to analyze and calculate the demisting efficiency i of a single bend at various bending angles θ. The influence of the bending angle θ on the demisting efficiency i was obtained. The influence of the bending angle θ on the inlet droplet concentration, outlet droplet concentration, demisting rate λ and total pressure loss Δp is shown in the attached figure. Figure 1 , Attachment Figure 2 , Attachment Figure 3 As shown in the following figure, the demisting efficiency i under different bending angles θ is Figure 4 As shown;

[0033] The calculation results and the attached Figure 4 As shown, when the bend angle θ is 110°, the demisting rate λ of a single bend per unit energy consumption is the highest. Therefore, under the working conditions of this embodiment, the streamlined demister should use a bend angle θ of 110°. At this time, the demisting rate λ is 0.197, the total pressure loss Δp is 12.05 Pa, and the ratio of the demisting rate to the total pressure loss, that is, the demisting efficiency i = λ / Δp = 0.016, is calculated to three decimal places.

[0034] Step S3: The demisting rate λ of a single bend with a bending angle θ of 110° is equivalent to the probability P of the bend absorbing droplets, that is, P = λ = 0.197. Then the probability of failure of demisting for a single bend is 1-P = 1-0.197 = 0.803;

[0035] Step S4: The process of n bends absorbing droplets is equivalent to a series of independent random events A1, A2, ..., A n The absorption probabilities of the droplets at n bends are P(A1)=P(A2)=……=P(A n )=P=0.197, and n≥i≥1, then the absorption probability of the droplet after passing through n bends is 1-(1-P) n =1-(1-0.197) n ;

[0036] Step S5: Assuming that the absorption probability of the streamlined demister droplets needs to reach 99%, then let 1-(1-0.197) n ≥99%, calculated and attached Figure 7 As shown in the figure, when n is greater than 20, the demisting efficiency of the streamlined demister with a bending angle θ of 110° can reach 99%;

[0037] Step S6: By calculation and attachment Figure 3 As shown, the total pressure loss of a single bend with a bending angle θ of 110° is Δp=12.05Pa. The total pressure loss of 20 bends is calculated to be Δp×n=12.05*20=241Pa, which meets the requirement of being less than the rated wind pressure of the fan.

[0038] In order to verify the correctness of this method, a streamlined demister with a folding plate spacing of 20 mm, a gas flow rate of 6 m / s, and a bending angle θ of 110° was selected. The Euler-Lagrange coupling method was used to calculate the demisting efficiency when the number of bends in a single channel was 5, 10, 15, and 20. The calculated droplet concentration distribution and pressure loss are shown in the attached figure. Figure 7 and attached Figure 8 As shown in the figure, the demisting rate and total pressure value are calculated from the figure. The results are shown in the attached Figure 5 and attached Figure 6 From the figure, we can see that the results of this method are close to those of the Euler-Lagrange coupling method, which shows that this method is correct.

[0039] From the attached Figure 5 , Attachment Figure 6The figure also shows some differences between this method and the Euler-Lagrange coupling method. This is because this method assumes that total pressure loss and demisting are entirely achieved by the bends. However, when analyzing the demisting rate and total pressure loss of a single bend using the Euler-Lagrange coupling method, there is a straight section at the entrance and exit of the bend. This section's total pressure loss and demisting rate are also incorporated into the probabilistic demisting model. However, in the multi-bend analysis, this straight section is not present. Therefore, the demisting rate and total pressure loss of this method are higher than those of the Euler-Lagrange coupling method.

[0040] The above embodiment only describes the situation where the bending angle θ and the number of bends are selected under the premise that the gas flow rate and the fold plate spacing are determined; in the specific implementation process, this method can be used to calculate and analyze different gas flow rates, different fold plate spacings, different bending angles θ and different numbers of bends, and then design a streamlined demister with the highest demisting efficiency.

[0041] In the description of the present invention, it should be understood that the indicated orientations or positional relationships 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, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0042] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A streamlined demister design method based on a probability model, characterized by: The steps include: Step S1: using the Euler-Lagrange coupling method to analyze and calculate the demisting rate λ and the total pressure loss Δp of a single bend in a single channel of a streamlined demister under different gas flow rates, different bend plate spacings, and different bend angles multiple times, and calculate the ratio of the demisting rate λ to the total pressure loss Δp: that is, the demisting efficiency i = λ / Δp; Step S2: Select a single channel single bend with the highest demisting efficiency i, and determine its corresponding demisting rate λ, gas flow rate, bend spacing and bend angle θ; Step S3: The demisting rate λ is equivalent to the absorption probability P of a single bend in a single channel for droplets, and the probability of demisting failure of a single bend is calculated as 1-P; Step S4: For a streamlined demister with n bends in a single channel, the process of the n bends absorbing droplets is equivalent to a series of independent random events A1, A2, ..., A n , then the absorption probability of the droplets at each bend is calculated as P(A1), P(A2), ..., P(A n ), where P(A i )≥0, and n≥i≥1; Step S5: Calculate the probability of failure of defogging at each bend as 1-P(A i ), then the probability that the droplet is not absorbed by any bend is On the contrary, the probability that a droplet is absorbed by any of the n bends is Step S6: Since the streamlined demister is often manufactured with the same bends, it is assumed that the absorption probability of the mist droplets at each bend is the same and is P, that is, P(A1)=P(A2)=...=P(A n )=P, then the absorption probability of the droplet after passing through n bends is 1-(1-P) n ; Step S7: Assume that the absorption probability of the streamlined demister droplets needs to reach 99%, then let 1-(1-P) n ≥99%, calculate the value of n, which is the number of bends required for a single channel of the streamlined demister; Step S8: Calculate the total pressure loss Δp×n of n bends based on the total pressure loss Δp of a single bend to ensure that the total pressure loss of gas flowing through the n bends is less than the rated wind pressure of the fan.

2. The method for designing a streamlined demister based on a probability model according to claim 1, wherein: In step S1, the demisting rate λ is the ratio of the mass of the droplets captured by the wall to the mass of the incoming droplets, that is, the difference between the inlet droplet mass and the outlet droplet mass divided by the inlet droplet mass; the total pressure loss Δp is equal to the inlet total pressure minus the outlet total pressure; and the demisting efficiency i is the ratio of the demisting rate λ to the total pressure loss Δp.

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