A method for predicting mass transfer performance of multi-channel ceramic membranes for absorbing low-concentration gases in a wetting mode

Abstract

The present invention discloses a method for predicting the mass transfer performance of a multi-channel ceramic membrane for absorbing low-concentration gases in a wetting mode, which belongs to the technical field of separating low-concentration gases, and more importantly, belongs to the field of membrane structure calculation. Traditional membrane absorption is mainly based on hydrophobic membrane absorption, but when membrane wetting exists, it will cause the absorption resistance to increase significantly. Therefore, it is proposed to absorb in a wetting mode to enhance the absorption capacity of the membrane contactor. In view of the fact that traditional one-dimensional and two-dimensional modeling methods are unable to simulate the mass transfer performance of multi-channel ceramic membranes with complex geometric structures, this method predicts the mass transfer performance of multi-channel ceramic membranes with different structures by establishing a three-dimensional simplified model, and then optimizes the configuration of the multi-channel ceramic membrane. It is found that the average error between the calculation results of the simplified model and the original three-dimensional model is less than 3%, proving the feasibility of the model.

Description

Technical Field

[0001] The invention relates to a method for predicting mass transfer performance of a multi-channel ceramic membrane for absorbing low-concentration gas in a wetting mode, and belongs to the field of gas capture technology and membrane absorption technology. Background Art

[0002] The separation of acidic gases such as carbon dioxide (CO2) or sulfur dioxide (SO2) has always been one of the topics of concern for scholars at home and abroad. In particular, low-concentration acidic gases have extremely low driving forces for mass transfer, resulting in huge separation costs. Therefore, there is an urgent need to develop efficient low-concentration acidic gas separation technology. Chemical absorbents with high selectivity have been widely used in the field of acid gas absorption in recent years. The absorption equipment used in traditional chemical absorption processes is a packed tower, but there are problems such as small specific surface area and low mass transfer efficiency. Compared with absorption towers, membrane contactors have the advantages of higher gas-liquid ratio, operational flexibility, stable mass transfer interface, high mass transfer specific surface area, easy modular design and scale-up, and can effectively solve problems such as mist entrainment and unstable gas-liquid contact interface. In recent years, they have been widely studied and applied to the absorption of CO2 and SO2.

[0003] Considering that the molecular diffusion rate of the gas phase is much greater than that of the liquid phase during the separation process, the research on membrane absorption is mainly focused on hydrophobic membrane contactors. Studies have shown that hydrophobic membrane contactors have good application prospects for the absorption of high or medium concentrations of CO2 and SO2, but for the absorption of low concentrations of CO2 and SO2, the concentration of acidic gases in the gas to be treated is already very low. After diffusing through the pores of the hydrophobic membrane to the liquid-membrane boundary, the concentration will become even lower, thereby limiting the mass transfer of CO2. Therefore, it is proposed to use hydrophilic membrane contactors for the absorption of low-concentration gases. When chemical absorbents are used to absorb low-concentration gases in a hydrophilic mode (liquid fills the pores), the unreacted absorbents filling the pores are consumed slowly. At the same time, unreacted reactants and products diffuse in the liquid through the membrane pores and are continuously renewed between the pores and the liquid phase body, which not only solves the problem of membrane wetting in hydrophobic membrane contactors, but also improves the absorption efficiency. The feasibility of hydrophilic membrane contactors in low-concentration gas absorption has been demonstrated in our previous work, including the absorption of low-concentration SO2 (1000ppm) and direct air carbon capture (420ppm CO2).

[0004] Ceramic membranes have high mechanical strength and chemical stability, and are hydrophilic, which is beneficial for handling corrosive chemical absorption liquids to absorb CO2. The single-tube ceramic membrane has a simple geometry but a low specific surface area. The multi-channel ceramic membrane has a larger stacking area and higher mechanical strength than the single-tube ceramic membrane, which is more advantageous than the single-tube ceramic membrane, but the geometric structure is relatively complex. Currently, commercial multi-channel ceramic membranes are mainly used for interception and are not suitable for gas absorption. The contribution of specific channels in the multi-channel ceramic membrane to the total mass transfer flux is unequal. The distance from the central channel to the outer surface of the membrane tube is longer than that of other channels. Therefore, the membrane phase mass transfer resistance is higher, resulting in poor absorption effect of the central channel. Therefore, increasing the number of channels in the multi-channel ceramic membrane, that is, increasing the contact area, does not mean that the absorption performance is improved. Therefore, for low-concentration gas absorption systems, how to design and optimize the configuration of multi-channel ceramic membranes is a bottleneck for its further development.

[0005] The establishment of models and simulations can help predict the absorption performance of multi-channel ceramic membranes and optimize the structure of multi-channel ceramic membranes. Traditional one-dimensional and two-dimensional modeling methods cannot model the mass transfer performance of multi-channel ceramic membranes with complex geometric structures. Although the establishment of three-dimensional models can effectively predict the mass transfer performance of multi-channel hydrophilic ceramic membrane contactors, there are also some disadvantages, including the high computational cost of establishing three-dimensional models and the inability to intuitively display the relationship between geometric configuration and its mass transfer performance. Therefore, it is very important to propose a simplified model to predict the mass transfer performance of multi-channel ceramic membranes. Summary of the invention

[0006] In view of the defects of existing multi-channel ceramic membranes in gas absorption, the present invention provides a method for calculating the structure of a multi-channel ceramic membrane for wetting mode membrane absorption of low-concentration gas. By proposing a simplified three-dimensional model to predict the mass transfer efficiency of the multi-channel ceramic membrane, the model helps to reduce model calculation time and calculation cost, optimize the currently available multi-channel ceramic membrane structure, construct a multi-channel ceramic membrane configuration suitable for low-concentration gas absorption, and provide theoretical guidance and technical support for the structural optimization of multi-channel ceramic membranes.

[0007] The technical solution adopted by the present invention is:

[0008] A method for predicting mass transfer performance of a multi-channel ceramic membrane for absorbing low-concentration gas in a wetting mode comprises the following steps:

[0009] Step 1: construct a simplified three-dimensional geometric model of a single-tube ceramic membrane according to the size of the multi-channel ceramic membrane;

[0010] Step 2: Calculate the correction factor F, which satisfies the following formula:

[0011]

[0012] Where, L is the average distance from the center of each channel of the multi-channel ceramic membrane model to the outer boundary of the membrane, mm; r is the radius of the outer channel of the multi-channel ceramic membrane model, mm; n is the number of channels of the multi-channel ceramic membrane; a~d are all constants;

[0013] Step 3: Calculate the mass transfer coefficient k L , mass transfer coefficient k L Satisfy the following formula:

[0014]

[0015] Where D A-Liquid is the diffusion coefficient of absorbent A in the liquid, m 2 ·s -1 ; ε is the porosity; τ is the tortuosity factor; l m is the membrane thickness, mm; the mass transfer coefficient k L It is the absorbent mass transfer coefficient of the multi-channel ceramic membrane.

[0016] Preferably, the membrane materials of the multi-channel ceramic membrane and the single-tube ceramic membrane are porous aluminum oxide, porous titanium oxide, porous zirconium oxide or porous silicon oxide.

[0017] Preferably, the multi-channel ceramic membrane is an asymmetric multi-channel ceramic membrane.

[0018] Preferably, the three-dimensional geometric model of the single-tube ceramic membrane includes a membrane layer configuration and a tube layer configuration.

[0019] Preferably, the outer diameter and membrane length of the three-dimensional geometric model of the single-tube ceramic membrane are the same as the outer diameter and membrane length of the multi-tube ceramic membrane.

[0020] Preferably, the inner diameter of the three-dimensional geometric model of the single-tube ceramic membrane satisfies the following formula:

[0021]

[0022] Where R is the channel radius of the single-tube ceramic membrane three-dimensional geometric model, mm; r1 is the middle channel radius of the multi-channel ceramic membrane model, mm; r2~r n is the radius of other channels of the multi-channel ceramic membrane model, mm; n is the number of channels of the multi-channel ceramic membrane.

[0023] The beneficial effects of the present invention are:

[0024] The membrane material used in the present invention is a ceramic membrane, which has good hydrophilicity. The ceramic material has good alkali-resistant absorbent ability, and the pore structure and properties can maintain stability in the absorption system.

[0025] In response to the problem that current one-dimensional and two-dimensional modeling methods are unable to model the mass transfer performance of multi-channel ceramic membranes with complex geometric structures, the present invention proposes a three-dimensional simplified model, which can, on the one hand, predict the mass transfer performance of multi-channel ceramic membranes with less computing time and cost, and on the other hand, can intuitively show the influence of the multi-channel ceramic membrane structure on the mass transfer performance through the three-dimensional model.

[0026] The present invention proposes a simplified model to predict the mass transfer performance of a multi-channel ceramic membrane. The correction factor F is introduced into a single-tube ceramic membrane model to calculate and predict the mass transfer performance of the multi-channel ceramic membrane, thereby saving model calculation time and calculation cost.

[0027] The present invention can be used to calculate and optimize a multi-channel ceramic membrane structure through a simplified model, and can perform modular design on the membrane assembly, which is beneficial to the enlarged application of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the commercial 7-channel, 19-channel, and 37-channel ceramic membrane configuration in the embodiment;

[0029] Figure 2 is a cross-sectional view of the 19-channel ceramic membrane and the simplified three-dimensional geometric model of the single-tube ceramic membrane in Example 1;

[0030] Figure 3 It is a NaOH concentration distribution diagram in the 19-channel ceramic membrane model and the simplified three-dimensional geometric model of the single-tube ceramic membrane in Example 1;

[0031] Figure 4 is a cross-sectional view of the three-dimensional geometric model of the seven-channel ceramic membrane and the simplified single-tube ceramic membrane in Example 2;

[0032] Figure 5 It is a NaOH concentration distribution diagram in the 7-channel ceramic membrane model and the simplified three-dimensional geometric model of the single-tube ceramic membrane in Example 2;

[0033] Figure 6 is a cross-sectional view of the three-dimensional geometric model of the 37-channel ceramic membrane and the simplified single-tube ceramic membrane in Example 3;

[0034] Figure 7 is a NaOH concentration distribution diagram in the 37-channel ceramic membrane model and the simplified three-dimensional geometric model of the single-tube ceramic membrane in Example 3;

[0035] Figure 8 It is a comparison chart of the SO2 removal rate experimental values ​​of the ceramic membrane models of each channel in Examples 1-3, the calculated values ​​of the three-dimensional model and the SO2 removal rate of the corresponding simplified single-tube ceramic membrane;

[0036] Fig. 9It is a comparison chart of the calculation results of the simplified single-tube ceramic membrane three-dimensional geometric model and the original multi-channel ceramic membrane model under different channels and configurations. DETAILED DESCRIPTION

[0037] The present invention is specifically introduced below in conjunction with the accompanying drawings and embodiments (NaOH solution absorbs low-concentration SO2 gas).

[0038] In the following embodiments, the calculation formula for the radius of the three-dimensional geometric model of a single-tube ceramic tube (calculated from a multi-channel ceramic membrane) is:

[0039]

[0040] Where R is the channel radius of the single-tube ceramic membrane three-dimensional geometric model, mm; r1 is the middle channel radius of the multi-channel ceramic membrane model, mm; r2~r n is the radius of other channels of the multi-channel ceramic membrane model, mm; n is the number of channels of the multi-channel ceramic membrane.

[0041] The mass transfer coefficient equation of the absorbent NaOH in the hydrophilic membrane is:

[0042]

[0043] Where D A-Liquid is the diffusion coefficient of absorbent A in the liquid, m 2 ·s -1 ; ε is the porosity; τ is the tortuosity factor; l m is the film thickness, mm.

[0044] In the three-dimensional geometric model of a single-tube ceramic tube, a correction factor F is introduced to simplify the mass transfer coefficient of the absorbent NaOH in the hydrophilic membrane phase in the model. The mass transfer coefficient k L The calculation formula is:

[0045]

[0046] Where D A-Liquid is the diffusion coefficient of absorbent A in the liquid, m 2 ·s -1 ; ε is the porosity; τ is the tortuosity factor; l m is the membrane thickness, mm; F ​​is the correction factor; because the liquid phase that reacts with the gas is the NaOH solution in the membrane pores, the NaOH concentration will significantly affect the mass transfer and reaction rate, and the position and radius of the channels in the multi-channel ceramic membrane will affect the concentration distribution of the NaOH solution in the membrane layers of different channels. Therefore, the approximate solution of the correction factor F can be analogous to the dimensionless Hatta number form, and at the same time act on the mass transfer coefficient of the NaOH membrane phase in the hydrophilic membrane, and satisfy the following formula:

[0047]

[0048]

[0049] F1 represents the influence of the total mass transfer area of ​​multiple channels and the total mass transfer area of ​​a single tube on the mass transfer rate.

[0050]

[0051] F2 represents the influence of the radius of each channel and the location of the channel on the mass transfer rate.

[0052]

[0053]

[0054] Where L1, L2, ..., L n is the distance from the center of each channel of the multi-channel ceramic membrane model to the outer boundary of the membrane, mm; r is the radius of the outer channel of the multi-channel ceramic membrane model, mm; n is the number of channels of the multi-channel ceramic membrane; a~d are all constants.

[0055] Hydroxyl ions diffuse in water. Under the conditions of pressure of 1 atm and temperature of about 25°C, the diffusion coefficient D A-Liquid 5.25×10 -9 m 2 ·s -1 .

[0056] When a high concentration absorbent is used to absorb a low concentration gas, assuming that the components at the gas-liquid interface can be fully reacted, the Fick law shows that under the same absorbent concentration (OH in the hydrophilic membrane) - It is the "carrier" for SO2 mass transfer in the membrane phase), and its maximum absorption flux can be obtained by the following formula:

[0057]

[0058] in is the hydroxide ion concentration in the absorbent, is the hydroxide ion concentration at the interface. When the mass transfer coefficient of NaOH in the membrane phase of the hydrophilic membrane increases, its absorption performance becomes better and the removal rate increases.

[0059] For the gas absorption experiment of the membrane contactor, we usually use the more intuitive gas removal rate to evaluate the absorption performance of the membrane contactor. Considering that the SO2 mole fraction in the gas phase is very low (≤0.1vol%), the difference in gas flow inflow and outflow of the membrane contactor can be ignored. Therefore, the SO2 removal rate can be calculated by the following formula:

[0060]

[0061] Where, η is the SO2 removal rate; Y g,in , Y g,out Represent the SO2 concentrations at the inlet and outlet of the membrane contactor gas respectively.

[0062] Example 1

[0063] A commercial 32 mm diameter, 19-channel ceramic membrane was used for simulation and optimization.

[0064] Step 1, construct a three-dimensional geometric model of a 19-channel ceramic membrane and a single-tube ceramic membrane of the same size that need to be solved;

[0065] In this example, the outer diameter of the commercial multi-channel ceramic membrane is 32mm, the number of channels is 19, the channel aperture is 4mm, the distance between the second circle of channels and the outer wall of the membrane tube is 10.1mm, and the distance between the third circle of channels and the outer wall of the membrane tube is 4.3mm; the outer diameter of the single-tube ceramic membrane of the same size is 32mm, and the inner diameter is calculated by the formula to be 17.4mm; the cross-section of the constructed membrane tube is shown in the figure below. Figure 1 shown.

[0066] The operating conditions of the two models are defined, including operating temperature, pressure, gas throughput, and gas-liquid concentration; the operating temperature is 303K, the pressure is 1atm, the gas throughput is 3L / min, the absorbent NaOH concentration is 0.2mol / L, and the low-concentration gas SO2 concentration is 1000ppm.

[0067] Based on the above mass transfer coefficient equation, a multi-channel ceramic membrane model was constructed using COMSOL to verify the calculation process.

[0068] The multi-channel model structure during the verification process includes membrane layer and tube layer, wherein the membrane layer includes "chemistry (chem)" and "transport of diluted species (tds)" physical fields, and the tube layer includes "laminar flow (spf)" and "transport of diluted species (tds)" physical fields.

[0069] The reaction equation in the model is defined as:

[0070] SO2+2OH≥SO3+H2O

[0071] The reaction rate is defined as:

[0072] r j =k(T)*chem.c_SO2*chem.c_OH

[0073] k(T)=exp(2851.1 / T-9.3795)

[0074] Where chem.c_SO2 and chem.c_OH are the set concentrations of SO2 and OH respectively, k(T) is the reaction rate constant, and T is the absolute temperature.

[0075] The diffusion coefficient of hydroxide ions in the membrane is defined as: D C_OH =5.25×10 -9 [m 2 / s];

[0076] The film sulfur dioxide gas diffusion coefficient is defined as:

[0077] The diffusion coefficient of sulfur dioxide gas in the tube layer is defined as:

[0078] The gas flow mode in the tube layer is defined as laminar flow, and the boundary conditions are set to fully developed flow, with the same gas flow rate in each channel.

[0079] The model mesh is drawn with free triangle mesh, and the mesh size is corrected to the fluid dynamics size, with the maximum unit size of 0.2 mm. At the same time, three boundary layers are set at the tube membrane boundary.

[0080] Step 2, optimize the parameters of the single-tube ceramic membrane model and introduce the correction factor F, establish a simplified three-dimensional model to predict the mass transfer performance of the corresponding multi-channel ceramic membrane, the cross-sectional diagram of the original model and the simplified model is shown in Figure 2 As shown;

[0081] The constructed correction factor F is:

[0082]

[0083]

[0084]

[0085] Substituting the specific geometric parameters, we obtain: L=6.76; r=2; F=50.03.

[0086] The parameters of the simplified single-tube model are the same as those of the multi-channel model, where the hydroxide ion diffusion coefficient in the membrane layer is defined as:

[0087] D C_OH =F*5.25×10 -9 =2.63×10 -7 [m 2 / s]

[0088] According to the above operating conditions, the SO2 removal rate of the 19-channel ceramic membrane obtained in the experiment is 63%, and the SO2 removal rate obtained by the 19-channel three-dimensional model is 61.8%. After introducing the correction factor F, the SO2 removal rate obtained by the simplified single-tube three-dimensional model is 63.4%, which has an error of 1.6% with the original three-dimensional model and 0.4% with the experimental value. The NaOH concentration distribution of the membrane layer of the simplified model and the original model is as follows Figure 3 shown.

[0089] Example 2

[0090] A commercial 32 mm diameter, 7-channel ceramic membrane was used for simulation and optimization.

[0091] Step 1, construct a three-dimensional geometric model of a 7-channel ceramic membrane and a single-tube ceramic membrane of the same size that need to be solved;

[0092] In this example, the outer diameter of the commercial multi-channel ceramic membrane is 32mm, the number of channels is 7, the channel aperture is 6.6mm, and the distance between the second circle channel and the outer wall of the membrane tube is 6.35mm; the outer diameter of the single-tube ceramic membrane with the same size is 32mm, and the inner diameter is calculated by the formula to be 17.5mm; the cross-section of the constructed membrane tube is shown in the figure below Figure 1 As shown;

[0093] The operating conditions of the two models are defined, including operating temperature, pressure, gas throughput, and gas-liquid concentration; the operating temperature is 303K, the pressure is 1atm, the gas throughput is 3L / min, the absorbent NaOH concentration is 0.2mol / L, and the low-concentration gas SO2 concentration is 1000ppm.

[0094] The multi-channel model structure includes a membrane layer and a tube layer, wherein the membrane layer includes the "chemistry (chem)" and "transport of diluted species (tds)" physical fields, and the tube layer includes the "laminar flow (spf)" and "transport of diluted species (tds)" physical fields.

[0095] The reaction equation in the model is defined as:

[0096] SO2+2OH≥SO3+H2O

[0097] The reaction rate is defined as:

[0098] r j =k(T)*chem.c_SO2*chem.c_OH

[0099] k(T)=exp(2851.1 / T-9.3795)

[0100] Where chem.c_SO2 and chem.c_OH are the set concentrations of SO2 and OH respectively, k(T) is the reaction rate constant, and T is the absolute temperature.

[0101] The diffusion coefficient of hydroxide ions in the membrane is defined as: D C_OH =5.25×10 -9 [m 2 / s];

[0102] The film sulfur dioxide gas diffusion coefficient is defined as:

[0103] The diffusion coefficient of sulfur dioxide gas in the tube layer is defined as:

[0104] The gas flow mode in the tube layer is defined as laminar flow, and the boundary conditions are set to fully developed flow, with the same gas flow rate in each channel.

[0105] The model mesh is drawn with free triangle mesh, and the mesh size is corrected to the fluid dynamics size, with the maximum unit size of 0.2 mm. At the same time, three boundary layers are set at the tube membrane boundary.

[0106] Step 2, optimize the parameters of the single-tube ceramic membrane model and introduce the correction factor F, establish a simplified three-dimensional model to predict the mass transfer performance of the corresponding multi-channel ceramic membrane, the cross-sectional diagram of the original model and the simplified model is shown in Figure 4 As shown;

[0107] The constructed correction factor F is:

[0108]

[0109]

[0110]

[0111] Substituting the specific geometric parameters, we obtain: L = 7.73; r = 3.3; F = 7.2.

[0112] The parameters of the simplified single-tube model are the same as those of the multi-channel model, where the hydroxide ion diffusion coefficient in the membrane layer is defined as:

[0113] D C_OH =F*5.25×10 -9 =3.78×10 -8 [m 2 / s]

[0114] According to the above operating conditions, the SO2 removal rate of the 7-channel ceramic membrane obtained by the experiment is 49.34%, and the SO2 removal rate obtained by the 7-channel three-dimensional model is 49.29%. After introducing the correction factor F, the SO2 removal rate obtained by the simplified single-tube three-dimensional model is 49.36%, with an error of 0.07% from the original three-dimensional model and 0.02% from the experimental value. The NaOH concentration distribution of the membrane layer of the simplified model and the original model is shown in Figure 5shown.

[0115] Example 3

[0116] A commercial 32 mm diameter, 37-channel ceramic membrane was used for simulation and optimization.

[0117] Step 1, construct a three-dimensional geometric model of a 37-channel ceramic membrane and a single-tube ceramic membrane of the same size that need to be solved;

[0118] In this example, the outer diameter of the commercial multi-channel ceramic membrane is 32mm, the number of channels is 37, the channel aperture is 2.9mm, the distance between the second circle of channels and the outer wall of the membrane tube is 11.8mm, the distance between the third circle of channels and the outer wall of the membrane tube is 7.3mm, and the distance between the fourth circle of channels and the outer wall of the membrane tube is 2.9mm. The outer diameter of the single-tube ceramic membrane with the same size is 32mm, and the inner diameter is calculated by the formula to be 13.6mm; the cross-section of the constructed membrane tube is shown in the figure below: Figure 1 As shown;

[0119] The operating conditions of the two models are defined, including operating temperature, pressure, gas throughput, and gas-liquid concentration; the operating temperature is 303K, the pressure is 1atm, the gas throughput is 3L / min, the absorbent NaOH concentration is 0.2mol / L, and the low-concentration gas SO2 concentration is 1000ppm.

[0120] The multi-channel model structure includes a membrane layer and a tube layer, wherein the membrane layer includes the "chemistry (chem)" and "transport of diluted species (tds)" physical fields, and the tube layer includes the "laminar flow (spf)" and "transport of diluted species (tds)" physical fields.

[0121] The reaction equation in the model is defined as:

[0122] SO2+2OH≥SO3+H2O

[0123] The reaction rate is defined as:

[0124] r j =k(T)*chem.c_SO2*chem.c_OH

[0125] k(T)=exp(2851.1 / T-9.3795)

[0126] Where chem.c_SO2 and chem.c_OH are the set concentrations of SO2 and OH respectively, k(T) is the reaction rate constant, and T is the absolute temperature.

[0127] The diffusion coefficient of hydroxide ions in the membrane is defined as: D C_OH =5.25×10 -9 [m 2 / s];

[0128] The film sulfur dioxide gas diffusion coefficient is defined as:

[0129] The diffusion coefficient of sulfur dioxide gas in the tube layer is defined as:

[0130] The gas flow mode in the tube layer is defined as laminar flow, and the boundary conditions are set to fully developed flow, with the same gas flow rate in each channel.

[0131] The model mesh is drawn with free triangle mesh, and the mesh size is corrected to the fluid dynamics size, with the maximum unit size of 0.2 mm. At the same time, three boundary layers are set at the tube membrane boundary.

[0132] Step 2, optimize the parameters of the single-tube ceramic membrane model and introduce the correction factor F, establish a simplified three-dimensional model to predict the mass transfer performance of the corresponding multi-channel ceramic membrane, the cross-sectional diagram of the original model and the simplified model is shown in Figure 6 As shown;

[0133] The constructed correction factor F is:

[0134]

[0135]

[0136]

[0137] Substituting the specific geometric parameters, we obtain: L = 6.13; r = 1.435; F = 190.6.

[0138] The parameters of the simplified single-tube model are the same as those of the multi-channel model, where the hydroxide ion diffusion coefficient in the membrane layer is defined as:

[0139] D C_OH =F*5.25×10 -9 =1×10 -6 [m 2 / s]

[0140] According to the above operating conditions, the SO2 removal rate of the 37-channel ceramic membrane obtained by the experiment is 69.3%, and the SO2 removal rate obtained by the 37-channel three-dimensional model is 69.5%. After introducing the correction factor F, the SO2 removal rate obtained by the simplified single-tube three-dimensional model is 69.2%, which has an error of 0.3% with the original three-dimensional model and 0.1% with the experimental value. The NaOH concentration distribution of the membrane layer of the simplified model and the original model is shown in Figure 7 shown.

[0141] The calculation results of the simplified model are compared with those of the original model and the experimental results to verify the accuracy of the correction factor F. The results are as follows: Figure 8As shown in the figure, it can be seen that after the correction factor F is introduced, the calculation results of the simplified model are slightly different from the calculation results of the original model and the experimental calculation results; in order to test whether the correction factor F is applicable, multiple simulations of asymmetric channel ceramic membranes were carried out, and the results are shown in Fig. 9 As shown in the figure, it can be seen that the calculation results of the simplified model have a good fit with the calculation results of the original model, and the average absolute error is within 3%.

[0142] The above is only a preferred implementation of the patent of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the patent of the present invention. These improvements and modifications should also be regarded as the protection scope of the patent of the present invention.

Claims

1. A method for predicting the mass transfer performance of a multi-channel ceramic membrane for absorbing low-concentration gas in a wetting mode, characterized in that: The steps include: Step 1: construct a simplified three-dimensional geometric model of a single-tube ceramic membrane according to the size of the multi-channel ceramic membrane; wherein the inner diameter of the three-dimensional geometric model of the single-tube ceramic membrane satisfies the following formula: Where R is the channel radius of the single-tube ceramic membrane three-dimensional geometric model, mm; r1 is the middle channel radius of the multi-channel ceramic membrane model, mm; r2~r n is the radius of other channels of the multi-channel ceramic membrane model, mm; n is the number of channels of the multi-channel ceramic membrane; Step 2, calculate the correction factor F; the liquid phase that reacts with the gas is the absorbent in the membrane pores. The absorbent concentration will affect the mass transfer and reaction rate, and the position and radius of the channel in the multi-channel ceramic membrane will affect the absorbent concentration distribution in different channel membrane layers. Therefore, the approximate solution of the correction factor F can be analogous to the dimensionless Hatta number form, and at the same time act on the mass transfer coefficient of the absorbent in the hydrophilic membrane. The correction factor F satisfies the following formula: F1 represents the effect of the total mass transfer area of ​​multiple channels and the total mass transfer area of ​​a single tube on the mass transfer rate; F2 represents the influence of the radius of each channel and the location of the channel on the mass transfer rate; Where L1, L2, ..., L n is the distance from the center of each channel of the multi-channel ceramic membrane model to the outer boundary of the membrane, mm; L is the average distance from the center of each channel of the multi-channel ceramic membrane model to the outer boundary of the membrane, mm; r is the radius of the outer channel of the multi-channel ceramic membrane model, mm; n is the number of channels of the multi-channel ceramic membrane; a~d are all constants; Step 3: Calculate the mass transfer coefficient k L ; In the three-dimensional geometric model of the single-tube ceramic tube, the correction factor F is introduced to simplify the mass transfer coefficient of the absorbent in the hydrophilic membrane phase in the model; the mass transfer coefficient k L Satisfy the following formula: Where D A-Liquid is the diffusion coefficient of absorbent A in the liquid, m 2 ·s -1 ; ε is the porosity; τ is the tortuosity factor; l m is the membrane thickness, mm; the mass transfer coefficient k L It is the absorbent mass transfer coefficient of the multi-channel ceramic membrane.

2. The method for predicting mass transfer performance of a multi-channel ceramic membrane for absorbing low-concentration gas in a wetting mode according to claim 1, characterized in that: The membrane materials of the multi-channel ceramic membrane and the single-tube ceramic membrane are porous aluminum oxide, porous titanium oxide, porous zirconium oxide or porous silicon oxide.

3. A method for predicting mass transfer performance of a multi-channel ceramic membrane for absorbing low-concentration gas in a wetting mode according to claim 1 or 2, characterized in that: The multi-channel ceramic membrane is an asymmetric multi-channel ceramic membrane.

4. The method for predicting mass transfer performance of a multi-channel ceramic membrane for absorbing low-concentration gas in a wetting mode according to claim 1, characterized in that: The three-dimensional geometric model of the single-tube ceramic membrane includes a membrane layer configuration and a tube layer configuration.

5. A method for predicting mass transfer performance of a multi-channel ceramic membrane for absorbing low-concentration gas in a wetting mode according to claim 1 or 4, characterized in that: The outer diameter and membrane length of the three-dimensional geometric model of the single-tube ceramic membrane are the same as those of the multi-tube ceramic membrane.

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