A method for determining the optimum filter medium rating for a filter device

Abstract

The application discloses a kind of filtering device optimal filtering medium precision solving method, this method includes the following steps: step 1, establish theoretical analysis calculation model;Step 2, test verification;And step 3, data analysis and processing;The application has the advantages that: improve the filtering efficiency of filtering device can bring higher product quality, equipment life, production efficiency and environmental health protection.

Description

Technical Field

[0001] This invention belongs to the field of filtration device reliability technology, specifically, it designs a method for determining the optimal filtration medium accuracy of a filtration device. Background Technology

[0002] Separation and purification technologies have wide applications, covering fields such as chemical engineering, environmental science, biochemistry, pharmaceuticals, food, electronics, and aerospace. Filtration is a common separation technology that uses filter media to separate solid particles or suspended matter from a mixture, while allowing gases or liquids to pass through. Examples include air purifiers, water filters, oil filters, food filters, and gas filters.

[0003] Filtration efficiency is a key parameter of filtration devices. Generally speaking, the higher the precision of the filter medium, the higher the filtration efficiency of the filtration device. However, due to factors such as loose screws, poor welding, particle impact, uneven dust removal, aging of the filter medium, needle punching of synthetic felt during production, and stitching between filter bags, leakage problems are unavoidable in filtration devices, leading to a decrease in filtration efficiency and causing harm to the environment and the equipment itself.

[0004] Currently, Chinese patent "CN219744080U," entitled "A Filter," improves filtration efficiency by increasing the frequency of filter media replacement; Chinese patent "CN209967961U," entitled "A Diverter-Type Pulse-Jet Air Filter and a Dust Removal Device Using the Filter," improves filtration efficiency by enhancing the uniformity of dust removal; and Chinese patent "CN105126416A," entitled "A High-Efficiency Filtration Device," improves filtration efficiency by increasing the filter area. None of these patents address the issue of leakage in improving filtration efficiency. Scholars both domestically and internationally, such as Mouret G, Thomas D, Chazelet S, et al. Penetration of nanoparticles through fibrous filters perforated with defined pinholes[J]. Journal of Aerosol Science, 2009, 40(9): 762-775 and Bach B, Schmidt E. Influence of leaks in surface filters on particulate emissions[J]. Journal of hazardous materials, 2007, 144(3): 673-676, have conducted a series of studies on filtration processes with leaks. They found that the higher the precision of the filter medium, the more serious the consequences of leakage, but they did not provide a method for selecting the optimal precision of the filter medium.

[0005] When filtration efficiency declines and purification results fail to meet standards, companies often resort to replacing the filter media with higher precision ones. This not only increases filtration power consumption but may also lead to more particulate impurities leaking from the leak points, thus reducing filtration efficiency. Therefore, selecting a filter media with appropriate precision is of significant practical importance for improving the filtration efficiency of filtration devices and saving filtration and purification costs. Summary of the Invention

[0006] In view of the above-mentioned prior art, the purpose of this invention is to overcome the shortcomings of the prior art, adapt to the needs of reality, and thus provide a method for finding the optimal filter medium accuracy of a filter device under leakage conditions, providing a reference for improving the purification performance of the filter device.

[0007] To achieve the objective of this invention, the technical solution adopted is as follows: a method for determining the optimal filter medium accuracy of a filtration device, the method comprising the following steps:

[0008] Step 1: Establish a theoretical analysis and calculation model:

[0009] This calculation model is applicable to the filtration process of particulate matter or suspended solids in gases or liquids using filter media. The filtration device contains a leakage zone and a filtration zone. The filtration zone captures particulate matter or suspended solids in the gas or liquid, forming a filter cake of a certain thickness. Therefore, the resistance ΔP of the filtration zone... F The sum of the filter media resistance and the filter cake resistance is given by the following formula:

[0010] ΔP F (t)=k F ·v F (t)+m·(v F (t)) n+1 ·W(t) (1)

[0011] Where: ΔP F Resistance of the filtration zone

[0012] k F The filter medium resistance coefficient is expressed in Pa·s / m.

[0013] v F The velocity of gas or liquid passing through the filtration zone, expressed in m / s;

[0014] Both m and n are compressibility coefficients that reflect the change of filter cake with flow rate, and are constants.

[0015] W represents the filter cake surface density, the mass of particulate matter or suspended solids accumulated per unit area of ​​the filter medium, expressed in kg / m³. 2 ;

[0016] t is time, ΔP F (t) represents the resistance of the filter zone at time t, v F W(t) is the flow velocity of gas or liquid through the filtration zone at time t, and W(t) is the surface density of the filter cake at time t.

[0017] Wherein, the filter medium resistance coefficient k F The filter media quality factor (QF) can be used to determine the filter media quality factor. filte Calculations show that the filter media quality factor (QF) is related to the material and structure of the filter media and is a property of the filter media itself. It is defined as the QF at a fixed airflow rate. filte The value is calculated using the following formula:

[0018]

[0019] In the formula: QF filte The quality factor of the filter medium is expressed in Pa. -1 ;

[0020] e F The filter media precision refers to the filtration efficiency of the filter media.

[0021] ΔP F * (0) represents the initial filtration resistance at a fixed air volume, in Pa;

[0022] v F * (0) is the initial filtration velocity under a certain fixed air volume, in m / s.

[0023] As filtration proceeds, the surface density W of the filter cake increases over time, and the rate of change is:

[0024] dW(t) / dt=c i ·e F ·v F (t) (3)

[0025] In the formula: c i The concentration of particulate matter or suspended solids in the inlet gas or liquid, expressed in kg / m³. 3 .

[0026] The resistance ΔP in the leakage zone L It is a multiple of the dynamic pressure, and its formula is:

[0027]

[0028] In the formula: k L The leakage resistance coefficient is dimensionless.

[0029] ρ gDensity of a gas or liquid containing particulate matter or suspended matter, expressed in kg / m³ 3 ;

[0030] v L The velocity of gas or liquid through the leak area, expressed in m / s;

[0031] v L (t) represents the flow velocity of the gas or liquid through the leak area at time t;

[0032] The filtration zone and leakage zone are connected in parallel, and the filtration resistance ΔP F With leakage resistance ΔP L The airflow in the filter zone and the leakage zone are equal; the sum of the airflow in the filter zone and the leakage zone is the total airflow. Therefore, a system of equations can be set up to calculate the flow velocities in the filter zone and the leakage zone at the initial moment. The system of equations is as follows:

[0033]

[0034] In the formula: A L The area of ​​the leak zone is expressed in meters (m²). 2 ;

[0035] A F The area of ​​the filtration zone is expressed in meters (m²). 2 ;

[0036] Q T Total flow rate, in cubic meters (m³). 3 / s;

[0037] A T Total area, in m² 2 ;

[0038] v T Total wind speed, in m / s;

[0039] Discretize equations (5) and (3), and iterate by taking the same time step Δt (Δt→0) to obtain the flow velocity at different times;

[0040] Total mass of particulate matter emitted by the filtration device (m) o The sum of the emissions from the filtration zone and the leakage zone is expressed as:

[0041]

[0042] Where: m o The total mass of particulate matter emitted by the filtration device, expressed in kg.

[0043] m o (t) represents the total mass of particulate matter emitted by the filtration device at time t, in kg;

[0044] Total volume of emitted gas V o(t) represents the sum of the processing volumes of the filtration zone and the leakage zone, and its expression is:

[0045]

[0046] In the formula: V o Total volume of emitted gas / liquid, in m³ 3 ,

[0047] V o (t) represents the total volume of gas / liquid discharged by the filtration device at time t, in cubic meters. 3 ;

[0048] Instantaneous particulate matter emission concentration c o (t) is the ratio of particulate matter mass emission velocity to gas / liquid volume emission velocity, therefore c can be calculated using equations (6) and (7). o (t), is:

[0049]

[0050] In the formula: c o The particulate matter concentration at the emission outlet.

[0051] m o ′(t) is m o The derivative of (t) with respect to t represents the particulate matter mass emission rate at time t.

[0052] V o ′(t) is V o The derivative of (t) with respect to t represents the gas / liquid volume emission rate at time t.

[0053] c o (t) represents the particulate matter emission concentration at time t.

[0054] Average particulate matter emission concentration The ratio of the total mass of emitted particulate matter to the total volume of emitted gas / liquid is expressed as:

[0055]

[0056] In the formula: The average particulate matter emission concentration over the time period from 0 to t.

[0057] Let the same time step Δt be used, and let By discretizing the expression in equation (9), the average outlet concentration during the time period from 0 to t can be calculated. for:

[0058]

[0059] Therefore, the instantaneous filtration efficiency e of the filtration device at time t can be calculated. T (t) and the average filtration efficiency during the time period from 0 to t They are respectively:

[0060]

[0061]

[0062] In the formula: e T For filtration efficiency;

[0063] e T (t) represents the filtering efficiency at time t;

[0064] The average filtration efficiency is given by the time interval from 0 to t.

[0065] Step 2: Experimental Verification

[0066] By setting the model parameters to be consistent with the experimental parameters, the model can be verified by comparing the experimental values ​​and the calculated values.

[0067] Step 3: Data Analysis and Processing

[0068] Calculating the curves of filtration efficiency and filtration resistance as a function of filter media precision and airflow under different leakage rates reveals that: increasing airflow velocity increases filtration efficiency; increasing filter media precision increases filtration resistance, while filtration efficiency initially increases and then decreases, indicating an optimal filter media precision e. F,opt To achieve maximum filtration efficiency e T,max ;

[0069] Optimal filter media accuracy under different leakage rate conditions F,opt and maximum filtration efficiency e T,max The values ​​are extracted and curve-fitted with the leakage rate to obtain the optimal filter media accuracy e at a certain airflow rate. F,opt and maximum filtration efficiency e T,max The relationship between the leakage rate Lr and the expression for e F,opt (Lr) and e T,max (Lr);

[0070] To obtain a more general formula, the calculation model from step 1 is used to calculate different flow rates Q. T Optimal filter media accuracy e under different leakage rates (Lr) F,opt and maximum filtration efficiency e T,max By fitting these values ​​to surface parameters and the flow rate and leakage rate respectively, different air volumes Q can be obtained. T Optimal filter media accuracy under different leakage rates (Lr) F,optand maximum filtration efficiency e T,max The relational expression, i.e., e F,opt (Lr,Q T ) and e T,max (Lr,Q T );

[0071] Optimal filter media accuracy e F,opt The fitted calculation expression can provide a reference for selecting the optimal filter medium and improving filtration efficiency in filtration devices; maximum filtration efficiency e T,max The fitted calculation expression can be used to estimate the filtration efficiency under a certain leakage condition, or to estimate the size of the leakage based on the filtration efficiency, or to determine whether the filtration efficiency has reached its maximum value under a certain leakage condition. It can also calculate how much the filtration efficiency will improve after replacing it with the filter medium with the optimal precision, providing a basis for decision-making on whether to replace it with the optimal filter medium.

[0072] Furthermore, the leakage rate Lr refers to the proportion of the leakage area to the total area, specifically: A L / (A F +A L )×100%.

[0073] Furthermore, the total flow Q T For the total area A T Total wind speed v T The product of, i.e., Q T =A T ·v T The unit is m 3 / s.

[0074] Furthermore, the total area A T For the effective filter media area A F and leakage area A L The sum of, i.e., A T =A F +A L The unit is m 2 .

[0075] This invention establishes a mathematical calculation model for predicting the filtration process based on the principles of equal parallel resistance and conserved airflow. The calculation model reveals an equilibrium point in the effect of filter media precision on filtration efficiency. Before this equilibrium point, the positive effect of increased filter media precision on filtration efficiency is dominant; after the equilibrium point, the negative effect is dominant; and at the equilibrium point, filtration efficiency reaches its maximum value. This invention defines the precision corresponding to the equilibrium point as the optimal filter media precision e. F,opt The filtration efficiency achieved is called the maximum filtration efficiency e. T,max .

[0076] By using a computational model, the optimal filter media precision and maximum filtration efficiency under different conditions can be obtained. Through fitting, calculation expressions for the optimal filter media precision and maximum filtration efficiency can be derived, providing a reference for evaluating and controlling leaks and improving the purification performance of filtration devices.

[0077] The beneficial effects of this invention are as follows:

[0078] Improving the filtration efficiency of a filtration device can lead to higher product quality, equipment lifespan, production efficiency, and environmental health protection. This invention, through experiments and a computational model, discovers that changing the precision of the filter medium can improve the filtration efficiency of the filtration device, and that an optimal filter medium precision, e, exists. F,opt This maximizes the filtration efficiency. T,max .

[0079] In situations where leakage is unavoidable, using filter media with optimal precision not only improves the filtration efficiency of the filtration device with minimal changes to the original equipment, but also saves on filtration and purification costs by reducing the precision of the filter media and filtration resistance.

[0080] The calculation model of this invention yields the relationship between the optimal filter media precision and operating conditions, enabling the optimal filter media precision to be calculated relatively quickly, thus providing a reference for selecting the optimal filter media precision and improving filtration efficiency in filtration devices. Attached Figure Description

[0081] Figure 1 Figure (a) is a simplified schematic diagram of the leakage zone, Figure (b) is a schematic diagram of particle aggregation and permeation during the filtration process, and Figure (c) is a schematic diagram of the distribution of filter cake on the filter media.

[0082] Figure 2 This is a comparison chart of the experimental values ​​and model calculation values ​​of the filtration resistance of the present invention;

[0083] Figure 3 This is a comparison chart of the experimental values ​​and model calculation values ​​of the filtration efficiency of this invention;

[0084] Figure 4 This is a graph showing the change in filtration efficiency of the present invention with the precision of the filter media (Lr = 0.3%).

[0085] Figure 5 This is a graph showing the change in filtration efficiency of the present invention with the precision of the filter media;

[0086] Figure 6 This is a graph showing the change in filtration resistance as a function of filter media precision according to the present invention.

[0087] Figure 7This is a graph showing the variation of the optimal filter media precision, maximum filtration efficiency, and filtration efficiency of the high-precision filter media as a function of leakage rate.

[0088] Figure 8 For the optimal filter media accuracy e of this invention F,opt (Lr,Q T A schematic diagram of the fitting results;

[0089] Figure 9 e represents the maximum filtration efficiency of this invention. T,max (Lr,Q T A schematic diagram of the fitting situation. Detailed Implementation

[0090] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0091] Example

[0092] In specific production practices and experiments, the following problem was encountered: During filtration and purification, the higher the precision of the filter medium, the better the filtration efficiency; high-precision filter media often brings good filtration results. However, since leakage is unavoidable, when a leakage rate of 0.3% occurs, is using the highest precision filter media still the best option? If not, then what should the optimal precision be? How much does using the optimal precision filter media improve filtration efficiency? Does the optimal precision save precision compared to high-precision filter media (assuming a filter media precision of 99.99%)? Does it reduce filtration resistance (energy consumption)?

[0093] This implementation takes the purification of dust-laden gas as an example. Under the filtration parameters shown in Table 1 and an airflow of 20 L / min, the above problem is solved. Figures 1 to 9 As shown, the present invention provides a method for determining the optimal filter medium accuracy of a filtration device, the method comprising the following steps:

[0094] Step 1: Establish a theoretical analysis and calculation model:

[0095] Table 1 Filtration Operating Parameters

[0096]

[0097] Leaks may be randomly distributed, occurring as internal or external leaks. Studies have shown that the distribution of leak points only initially affects the filtration parameters, and subsequently has almost no effect. Therefore, leaks can be simplified as being concentrated in one area, divided into a leak zone L and a filtration zone F, such as... Figure 1 As shown in Figure (a);

[0098] As filtration continues, a dust layer of a certain thickness will accumulate in the filtration zone, such as... Figure 1As shown in Figures (b) and (c), the resistance ΔP of the filter zone is therefore... F The sum of the filter media resistance and the dust layer resistance is given by the following formula:

[0099] ΔP F (t)=k F ·v F (t)+m·(v F (t)) n+1 ·W(t) (1)

[0100] Where: ΔP F The resistance of the filtration zone;

[0101] k F The filter medium resistance coefficient is expressed in Pa·s / m.

[0102] v F The velocity of gas or liquid passing through the filtration zone, expressed in m / s;

[0103] Both m and n are compressibility coefficients that reflect the change of filter cake with flow rate, and are constants.

[0104] W represents the filter cake surface density, the mass of particulate matter or suspended solids accumulated per unit area of ​​the filter medium, expressed in kg / m³. 2 ;

[0105] t is time, ΔP F (t) represents the resistance of the filter zone at time t, v F W(t) is the flow velocity of gas or liquid through the filtration zone at time t, and W(t) is the surface density of the filter cake at time t.

[0106] Among them, the filter media resistance coefficient k F Filter media quality factor (QF) filte The calculated formula is as follows:

[0107]

[0108] In the formula: QF filte —Filter media quality factor, in Pa -1 ;

[0109] e F For — filter media precision, that is, the filtration efficiency of the filter media;

[0110] ΔP F * (0) represents the initial filtration resistance at a fixed airflow rate. In this embodiment, it represents the initial filtration resistance at an airflow rate of 20 L / min, in Pa.

[0111] v F* (0)——Initial filtration velocity at a certain fixed air volume. In this embodiment, it is the initial filtration velocity when the air volume is 20L / min, and the unit is m / s.

[0112] The mass W of the dust layer accumulated on a unit area of ​​filter media will change over time, and the rate of change is:

[0113] dW(t) / dt=c i ·e F ·v F (t) (3)

[0114] In the formula: c i —Inlet dust concentration, unit: kg / m³ 3 .

[0115] The resistance ΔP in the leakage zone L It is a multiple of the dynamic pressure, and its formula is:

[0116]

[0117] In the formula: k L —Leakage resistance coefficient, dimensionless;

[0118] ρ g —Density of dust-laden gas, in kg / m³ 3 ;

[0119] v L —Leakage velocity, in m / s.

[0120] v L (t)——Leakage wind speed at time t, in m / s.

[0121] The leakage zone and the filter zone are connected in parallel, and the leakage resistance ΔP L With filter resistance ΔP F The airflow is equal before and after the filter; therefore, a system of equations can be set up to calculate the airflow velocity in each region at the initial moment. The system of equations is as follows:

[0122]

[0123] In the formula: A L —Leakage area, in m 2 .

[0124] A F —Effective filter media area, according to the filtration parameters in Table 1, A in this embodiment F The value is fixed at 0.0177m 2 ;

[0125] Q T —Total flow, total flow QT For the total area A T Total wind speed v T The product of, i.e., Q T =A T ·v T The unit is m 3 / s;

[0126] A T —Total area, total area A T For the effective filter media area A F and leakage area A L The sum of, i.e., A T =A F +A L The unit is m 2 ;

[0127] v T —Total wind speed, in m / s.

[0128] Discretize equations (5) and (3), and iterate by taking the same time step Δt to obtain the filtration wind speed and leakage wind speed at different times. In this embodiment, Δt is taken as 0.001s.

[0129] Total mass of particulate matter emitted by the filtration device (m) o The sum of the emissions from the filtration zone and the leakage zone is expressed as:

[0130]

[0131] Where: m o The total mass of particulate matter emitted by the filtration device, expressed in kg.

[0132] m o (t) represents the total mass of particulate matter emitted by the filtration device at time t, in kg.

[0133] Total volume of emitted gas V o (t) represents the sum of the treatment volumes of the filtration zone and the leakage zone, and its formula is:

[0134]

[0135] In the formula: V o Total volume of emitted gas / liquid, in m³ 3 ,

[0136] V o (t) represents the total volume of gas / liquid discharged by the filtration device at time t, in cubic meters. 3 ,

[0137] Instantaneous particulate matter emission concentration c o(t) is the ratio of particulate matter mass emission velocity to gas / liquid volume emission velocity, therefore c can be calculated using equations (6) and (7). o (t), is:

[0138]

[0139] In the formula: c o The particulate matter concentration at the emission outlet.

[0140] c o (t) represents the particulate matter emission concentration at time t.

[0141] m o ′(t) is m o The derivative of (t) with respect to t represents the particulate matter mass emission rate at time t.

[0142] V o ′(t) is V o The derivative of (t) with respect to t represents the gas / liquid volume emission rate at time t.

[0143] Average particulate matter emission concentration The ratio of the total mass of emitted particulate matter to the total volume of emitted gas / liquid is expressed as:

[0144]

[0145] In the formula: The average particulate matter emission concentration over the time period from 0 to t.

[0146] Let the same time step Δt be used, and let By discretizing the expression in equation (9), the average outlet concentration during the time period from 0 to t can be calculated. for:

[0147]

[0148] Therefore, the instantaneous filtration efficiency e of the filtration device at time t can be calculated. T (t) and the average filtration efficiency during the time period from 0 to t They are respectively:

[0149]

[0150]

[0151] In the formula: e T For filtration efficiency,

[0152] e T (t) represents the filtering efficiency at time t.

[0153] The average filtration efficiency over the time period from 0 to t;

[0154] Step 2: Experimental Verification

[0155] By setting the model parameters to be consistent with the experimental parameters and comparing the calculated values ​​with the experimental values, the accuracy of the computational model was verified. Figure 2 and Figure 3 As shown;

[0156] Step 3: Data Analysis and Processing

[0157] The leakage rate Lr refers to the proportion of the leaked area to the total area, that is: Lr = A L / (A F +A L Calculate the filtration efficiency as a function of filter media precision under a certain leakage rate condition. When the leakage rate is 0.3%, the filtration efficiency changes with filter media precision as shown below. Figure 4 As shown in the figure, the filtration efficiency first increases and then decreases with the increase of filter media precision. It is not that higher filter media precision necessarily leads to higher filtration efficiency; rather, there exists an optimal filter media precision e. F,opt To achieve maximum filtration efficiency e T,max ,like Figure 4 As shown in the annotation,

[0158] This is because, when there is a leak, the high precision of the filter media, while increasing the filtration efficiency of the filtration zone, suppresses the flow rate in the filtration zone and increases the flow rate in the leak zone. The latter plays a major role, resulting in low filtration efficiency.

[0159] If the filter media is too low in precision, it will reduce the filtration efficiency of the filtration zone. Although the flow rate in the filtration zone is increased and the flow rate in the leakage zone is reduced, the former plays the main role, resulting in low filtration efficiency.

[0160] The optimal precision filter media balances the positive and negative effects of increased filter media precision, thus maximizing the filtration efficiency.

[0161] from Figure 4 and Figure 6 It can be concluded that when the leakage rate is 0.3%, the high-precision filter media (99.99% precision) is not the optimal precision filter media, but rather the 98% precision filter media. The filtration efficiency of the optimal precision filter media is 4% higher than that of the high-precision filter media, and the filtration resistance is reduced by 40Pa, saving 2% of the filter media precision.

[0162] The changes in filtration efficiency and filtration resistance with filter media precision under different leakage rates are as follows: Figure 5 and Figure 6As shown, under leakage conditions, using excessively high-precision filter media not only fails to improve filtration efficiency but also increases filtration resistance, which in turn increases energy consumption.

[0163] Obtain the optimal filter media accuracy under different leakage rate conditions. F,opt and maximum filtration efficiency e T,max The results were obtained by fitting the data to the leakage rate using exponential and polynomial functions, respectively. Figure 7 As shown, the results were obtained at an air volume Q. T At a flow rate of 20 L / min, the optimal filter media accuracy is e. F,opt and maximum filtration efficiency e T,max The relationship between the leakage rate Lr and the expression for e F,opt (Lr) and e T,max (Lr), respectively:

[0164] e F,opt (Lr)=e -7.796Lr R 2 =0.9954 (13)

[0165] e T,max (Lr)=-990791Lr 3 +22290Lr 2 -197.2Lr+1, R 2 =0.9987 (14)

[0166] In the formula: e F,opt The optimal filter media precision means that, under the same conditions, the filtration efficiency of the filtration device is maximized when using filter media of this precision.

[0167] e T,max The maximum filtration efficiency is the filtration efficiency achieved using the optimal filter media precision.

[0168] e F,opt (Lr) represents the optimal filter media precision at the leakage rate Lr;

[0169] e T,max (Lr) represents the maximum filtration efficiency at a leakage rate of Lr;

[0170] e is the natural constant, with a value of approximately 2.71828;

[0171] R 2 This represents the fitting correlation coefficient for the corresponding formula;

[0172] As shown in the figure, when the leakage rate is 1.00%, the filtration efficiency of the optimal precision filter media is 7.50% higher than that of the high precision filter media (99.99% precision).

[0173] The above results were obtained at an airflow rate of 20 L / min. Therefore, to further consider the influence of airflow rate and derive a more general calculation formula, the optimal filter media accuracy e under different airflow rates and leakage rates can be calculated. F,opt and maximum filtration efficiency e T,max And perform polynomial fitting on it, the fitting result is as follows Figure 8 and Figure 9 As shown, different air volumes Q were obtained. T Optimal filter media accuracy under different leakage rates (Lr) F,opt and maximum filtration efficiency e T,max That is, e F,opt (Lr,Q T ) and e T,max (Lr,Q T ), respectively:

[0174] e F,opt (Lr,Q T = 0.9807 - 10.75Lr + 0.001422Q T -70.17Lr 2 +0.1753Lr×Q T -2.236×10 -5 ×Q T 2 ,R 2 =0.989 (15)

[0175] e T,max (Lr,Q T = 0.9343 - 141.2Lr + 0.00174Q T -7394Lr 2 +0.08363Lr×Q T -2.273×10 -5 ×Q T 2 ,R 2 =0.9933 (16)

[0176] In the formula: e F,opt (Lr,Q T Leakage rate Lr and air volume Q are the following parameters: T Optimal filter media accuracy at that time

[0177] e T,max (Lr,Q T Leakage rate Lr and air volume Q are the following parameters: T The maximum filtration efficiency at that time.

[0178] R 2 This is the fitting correlation coefficient for the corresponding formula.

[0179] Among them, equations (13) and (15) represent the optimal filter media precision e. F,opt The fitting calculation expression can provide a reference for selecting the optimal filter media under leakage conditions. For example, according to formula (13), when the leakage rate Lr = 0%, the optimal filter media accuracy is 100%; when the leakage rate Lr = 0.3%, the optimal filter media accuracy is 98%.

[0180] Using the best precision filter media can not only improve the filtration efficiency of the filtration device, but also save on filter media precision and reduce filtration resistance, thereby reducing filtration and purification costs.

[0181] Equations (14) and (16) represent the maximum filtration efficiency e. T,max The fitting calculation expression can be used to estimate the filtration efficiency under a certain leakage condition, or to estimate the size of the leakage based on the filtration efficiency, or to determine whether the filtration efficiency has reached its maximum value under a certain leakage condition, and to calculate how much the filtration efficiency will be improved after replacing it with the optimal precision filter media, providing a basis for decision-making on whether to replace the filter media.

[0182] For example, according to formula (14), when the filtration efficiency is only 58%, the leakage rate is not less than 0.3%; when the leakage rate is 0.3% and the filtration efficiency is 54%, by using the filter media with the best precision, that is, by changing to the filter media with 98% precision, the filtration efficiency can be increased to 58%, which is 4% higher.

[0183] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0184] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for determining the optimal filter medium accuracy of a filtration device, characterized in that: The method includes the following steps: Step 1: Establish a theoretical analysis and calculation model: This calculation model is applicable to the filtration process of a filter medium for particulate matter or suspended solids in a gas or liquid. The filter device contains a leakage zone and a filtration zone. The filtration zone captures particulate matter or suspended solids in the gas or liquid, forming a filter cake of a certain thickness. Therefore, the resistance ΔP of the filtration zone... F The sum of the filter media resistance and the filter cake resistance is given by the following formula: ΔP F (t)=k F ·v F (t)+m·(v F (t)) n+1 ·W(t) (1) Where: ΔP F Resistance of the filtration zone k F The filter medium resistance coefficient is expressed in Pa·s / m. v F The velocity of gas or liquid passing through the filtration zone, expressed in m / s; Both m and n are compressibility coefficients that reflect the change of filter cake with flow rate, and are constants. W represents the filter cake surface density, the mass of particulate matter or suspended solids accumulated per unit area of ​​the filter medium, expressed in kg / m³. 2 ; t is time, ΔP F (t) represents the resistance of the filter zone at time t, v F W(t) is the flow rate of gas or liquid through the filtration zone at time t, and W(t) is the surface density of the filter cake at time t. Wherein, the filter medium resistance coefficient k F The filter media quality factor (QF) can be used to determine the filter media quality factor. filter Calculations show that the filter media quality factor (QF) is related to the material and structure of the filter media and is a property of the filter media itself. It is defined as the QF at a fixed airflow rate. filter The value is calculated using the following formula: In the formula: QF filter The quality factor of the filter medium is expressed in Pa. -1 , e F The filter media precision refers to the filtration efficiency of the filter media. ΔP F * (0) represents the initial filtration resistance at a fixed airflow rate, in Pa. v F * (0) represents the initial filtration velocity at a fixed air volume, in m / s. As filtration proceeds, the surface density W of the filter cake increases over time, and the rate of change is: dW(t) / dt<c i ·e F ·v F (t) (3) In the formula: c i The concentration of particulate matter or suspended solids in the inlet gas or liquid, expressed in kg / m³. 3 , The resistance ΔP in the leakage zone L It is a multiple of the dynamic pressure, and its formula is: In the formula: k L The leakage resistance coefficient is dimensionless. ρ g Density of a gas or liquid containing particulate matter or suspended matter, expressed in kg / m³ 3 , v L The velocity of gas or liquid through the leak area, expressed in m / s. v L (t) represents the flow velocity of the gas or liquid through the leak area at time t. The filtration zone and leakage zone are connected in parallel, and the filtration resistance ΔP F With leakage resistance ΔP L The airflow in the filter zone and the leakage zone are equal; the sum of the airflow in the filter zone and the leakage zone is the total airflow. A system of equations is set up to calculate the initial flow velocities in the filter zone and the leakage zone. The system of equations is as follows: In the formula: A L The area of ​​the leak zone is expressed in meters (m²). 2 , A F The area of ​​the filtration zone is expressed in meters (m²). 2 , Q T Total flow rate, in cubic meters (m³). 3 / s, A T Total area, in m² 2 , v T Total wind speed, in m / s. Discretize equations (5) and (3), and solve them iteratively by taking the same time step Δt. When Δt→0, the flow velocity at different times can be obtained. Total mass of particulate matter emitted by the filtration device (m) o The sum of the emissions from the filtration zone and the leakage zone is expressed as: Where: m o The total mass of particulate matter emitted by the filtration device, expressed in kg. m o (t) represents the total mass of particulate matter emitted by the filtration device at time t, in kg. Total volume of exhaust gas / liquid V o (t) represents the sum of the processing volumes of the filtration zone and the leakage zone, and its expression is: In the formula: V o Total volume of emitted gas / liquid, in m³ 3 , V o (t) represents the total volume of gas / liquid discharged by the filtration device at time t, in m³. 3 , Instantaneous particulate matter emission concentration c o (t) is the ratio of particulate matter mass emission velocity to gas / liquid volume emission velocity, therefore c can be calculated using equations (6) and (7). o (t), is: In the formula: c o The particulate matter concentration at the emission outlet. m o ′(t) is m o The derivative of (t) with respect to t represents the particulate matter mass emission rate at time t. V o ′(t) is V o The derivative of (t) with respect to t represents the gas / liquid volume emission rate at time t. c o (t) represents the particulate matter emission concentration at time t. Average particulate matter emission concentration The ratio of the total mass of emitted particulate matter to the total volume of emitted gas / liquid is expressed as: In the formula: The average particulate matter emission concentration over the time period from 0 to t. Let the same time step Δt be used, and let By discretizing the expression in equation (9), the average outlet concentration during the time period from 0 to t can be calculated. ,for: Therefore, the instantaneous filtration efficiency e of the filtration device at time t can be calculated. T (t) and the average filtration efficiency during the time period from 0 to t They are respectively: In the formula: e T For filtration efficiency, e T (t) represents the filtering efficiency at time t. The average filtration efficiency over the time period from 0 to t; Step 2: Experimental Verification By setting the model parameters to be consistent with the experimental parameters, the model can be verified by comparing the experimental values ​​and the calculated values. Step 3: Data Analysis and Processing Calculating the curves of filtration efficiency and filtration resistance as a function of filter media precision and airflow under different leakage rates reveals that: increasing airflow velocity increases filtration efficiency; increasing filter media precision increases filtration resistance, while filtration efficiency initially increases and then decreases, indicating an optimal filter media precision e. F,opt To achieve maximum filtration efficiency e T,max ; Optimal filter media accuracy under different leakage rate conditions F,opt and maximum filtration efficiency e T,max The values ​​are extracted and curve-fitted with the leakage rate to obtain the optimal filter media accuracy e at a certain airflow rate. F,opt and maximum filtration efficiency e T,max The relationship between the leakage rate Lr and the expression for e F,opt (Lr) and e T,max (Lr); To obtain a more general formula, the calculation model from step 1 is used to calculate different flow rates Q. T Optimal filter media accuracy e under different leakage rates (Lr) F,opt and maximum filtration efficiency e T,max By fitting these values ​​to surface parameters and the flow rate and leakage rate respectively, different air volumes Q can be obtained. T Optimal filter media accuracy under different leakage rates (Lr) F,opt and maximum filtration efficiency e T,max The relational expression, i.e., e F,opt (Lr,Q T ) and e T,max (Lr,Q T ); Optimal filter media accuracy e F,opt The fitted calculation expression can provide a reference for selecting the filter medium with the best accuracy; maximum filtration efficiency e T,max The fitted calculation expression can be used to estimate the filtration efficiency under a certain leakage condition, or to estimate the size of the leakage based on the filtration efficiency, or to determine whether the filtration efficiency has reached its maximum value under a certain leakage condition. It can also calculate how much the filtration efficiency will improve after replacing it with the filter medium with the optimal precision, providing a basis for decision-making on whether to replace it with the optimal filter medium.

2. The method for determining the optimal filter medium accuracy of the filter device according to claim 1, characterized in that: Leakage rate Lr refers to the proportion of the leaked area to the total area, specifically: A L / (A F +A L )×100%.

3. The method for determining the optimal filter medium accuracy of the filter device according to claim 1, characterized in that: Total flow Q T For the total area A T Total wind speed v T The product of, i.e., Q T =A T ·v T The unit is m 3 / s.

4. The method for determining the optimal filter medium accuracy of the filter device according to claim 1, characterized in that: Total area A T For the effective filter media area A F and leakage area A L The sum of, i.e., A T =A F +A L The unit is m 2 .

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