A Matching Method for Electric Field Demulsification Parameters of Waste Oil Emulsion

Abstract

The present invention discloses a method for matching the electric field demulsification parameters of waste oil emulsion. The main idea is as follows: based on the droplet size, the optimal electric field parameters are matched. The electric field parameters are the electric field strength and the electric field frequency. The electric field frequency is divided into the pulse width and the pulse rest width for separate matching. First, a direct current electric field is applied to the droplets to determine the optimal electric field strength and the optimal pulse width of the droplets. Then, based on the optimal electric field strength and the optimal pulse width, a pulse electric field that outputs only one pulse is constructed and applied to the droplets to determine the optimal pulse rest width. The obtained electric field frequency can make the average deformation degree of the droplets slightly higher than the optimal deformation degree. On the premise of avoiding droplet rupture, the collision probability between droplets is maximized, which can effectively weaken the strength of the droplet interfacial film and achieve efficient coalescence demulsification of waste oil emulsion. It can effectively solve the technical problem of how to obtain the optimal electric field demulsification parameters and achieve the effect of improving the demulsification efficiency of waste oil emulsion.

Description

Technical Field

[0001] The present invention belongs to the technical field of separating liquids from each other by electricity in physical methods, and particularly relates to a method for matching parameters of electric field demulsification of waste oil emulsion. Background Art

[0002] In the resource recovery processes of numerous industrial waste oil emulsions, the primary link is to perform demulsification and dehydration treatment on the waste oil emulsion; currently, conventional demulsification and dehydration methods include sedimentation method, centrifugation method, chemical method, vacuum heating method, and electric field demulsification method, etc. Among them, the electric field demulsification method is widely used due to advantages such as fast demulsification speed and low working energy consumption. The main mechanism of electric field demulsification is that the droplets in the oil vibrate and deform under the action of a pulsed electric field, greatly weakening the strength of the oil-water interfacial film, making it easier for droplets to coalesce with each other. Electric field demulsification generally adopts a pulsed electric field demulsification device as shown in Figure 1 Figure 1, which includes a housing 1 with a chamber inside. The upper end of the housing has an oil outlet 2 communicating with the chamber, the lower end of the housing has an oil inlet 3 and a drain outlet 4 communicating with the chamber. In the middle of the chamber, several electrode plate groups 5 are provided. The electrode plate group includes two horizontally facing electrode plates. A pulse is applied to the two electrode plates to form a pulsed electric field between the two electrode plates; the waste oil emulsion in the area where several electrode plate groups are located is demulsified by the pulsed electric field. The less dense oil phase floats up and accumulates in the upper part of the chamber and is discharged through the oil outlet, and the denser water phase sinks and accumulates in the lower part of the chamber and is discharged through the drain outlet, thereby realizing the demulsification and dehydration treatment of the waste oil emulsion.

[0003] It has been found through research that if the electric field strength is too large, the deformation degree of the droplets (water droplets) in the waste oil emulsion will be too large, which will cause the droplets to rupture and disperse into smaller droplets, which is contrary to the purpose of demulsification; if the electric field strength is too small, the deformation degree of the droplets in the waste oil emulsion will be too small, which will lead to a decrease in the contact probability between the droplets; also, due to the different deformation degrees of droplets with different particle sizes under the same electric field strength, therefore, for any droplet with a certain particle size, there is an optimal electric field strength that can make the droplet reach a relatively large deformation degree without droplet rupture; the droplets will undergo harmonic resonance under the action of the electric field. Therefore, in order to achieve the deformation degree corresponding to the optimal electric field strength and a relatively high resonance frequency, there is a corresponding optimal electric field frequency; at the optimal electric field strength and frequency, the collision probability between adjacent droplets is relatively large, which can effectively weaken the strength of the droplet interfacial film, thereby achieving the best demulsification efficiency and realizing the efficient coalescence and demulsification of the waste oil emulsion. Therefore, it is necessary to propose a method for matching parameters of electric field demulsification of waste oil emulsion, and obtain the optimal electric field demulsification parameters for any droplet with a certain particle size through matching, so as to give full play to the maximum efficiency of electric field demulsification. Summary of the Invention

[0004] Aiming at the above deficiencies of the prior art, the purpose of the present invention is to provide a method for matching the parameters of electric field demulsification of waste oil emulsion, to solve the technical problem of how to obtain the optimal electric field demulsification parameters, and to achieve the effect of improving the demulsification efficiency of waste oil emulsion.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for matching the parameters of electric field demulsification of waste oil emulsion includes the following steps:

[0007] 1) Establish a two-dimensional physical model of the droplets in the oil-water mixture under the action of an electric field in a pulsed electric field demulsification device;

[0008] 2) Construct a two-dimensional dynamic deformation model of the droplets under the action of an electric field in the two-dimensional physical model, and set the boundary conditions and the physical parameters of the oil-water mixture;

[0009] 3) Set the electric field type of the two-dimensional physical model as a direct current electric field, add multiple groups of operating parameters, and the operating parameters include the electric field intensity, and the electric field intensity in each group of operating parameters increases sequentially;

[0010] 4) The two-dimensional dynamic deformation model respectively draws the droplet deformation curves under each group of operating parameters according to the two-dimensional physical model after grid division, and selects the droplet deformation curve with the peak value of the droplet deformation degree equal to the optimal deformation degree;

[0011] 5) Take the electric field intensity corresponding to the droplet deformation curve selected in step 4) as the optimal electric field intensity, and determine the optimal pulse width according to the droplet deformation curve selected in step 4);

[0012] 6) Set the electric field type of the two-dimensional physical model as a pulsed electric field and only output one pulse, add a group of operating parameters, and the operating parameters include the optimal electric field intensity and the optimal pulse width determined in step 5);

[0013] 7) The two-dimensional dynamic deformation model draws the droplet deformation curve under the operating parameters added in step 6) according to the two-dimensional physical model after grid division;

[0014] 8) Determine the optimal pulse rest width according to the droplet deformation curve obtained in step 7).

[0015] Further, step 1) includes the following sub-steps:

[0016] 11) In the pulsed electric field demulsification device, take the cross-section of the region between two electrode plates belonging to the same electrode plate group as the flow field;

[0017] 12) Fill the flow field with the oil-water mixture, place the only droplet in the oil-water mixture at the center of the flow field, define the particle size of the droplet as R, and the size of the flow field as 16R×16R.

[0018] Furthermore, the two-dimensional dynamic deformation model described in step 2) is established by combining the flow field control equation, the interface tracking equation, and the electric field control equation. The flow field control equation is as follows:

[0019]

[0020] where u is the velocity vector of the oil-water mixture, ρ is the density of the oil-water mixture, p is the pressure of the oil-water mixture, μ is the viscous shear stress tensor of the oil-water mixture, F st is the oil-water interfacial tension, F e is the electric field force, I is the identity matrix; t is time;

[0021] The interface tracking equation is as follows:

[0022]

[0023] where is the phase field variable, represents the oil phase, represents the water phase, represents the oil-water interface; γ is the mobility; G is the chemical potential;

[0024] The formula for the chemical potential G is as follows:

[0025]

[0026] where λ is the mixed energy density, h is the oil-water interface thickness;

[0027] The volume fractions of the oil and water phases are respectively expressed as:

[0028]

[0029] where Vf0 is the volume fraction of the continuous phase oil, and Vf1 is the volume fraction of the discrete phase droplets;

[0030] The relationship between the oil-water interfacial tension F st and the chemical potential G is as follows:

[0031]

[0032] The electric field control equation is as follows:

[0033]

[0034] ε r = Vf0 × ε oil + Vf1 × ε water

[0035] where εr represents the relative permittivity of the oil-water mixture, ε0 represents the permittivity of vacuum, E represents the electric field strength, and ε oil is the relative permittivity of the oil phase; ε water is the relative permittivity of the water phase.

[0036] Further, the operation of setting boundary conditions in step 2) is as follows: Connect the two boundaries corresponding to the two electrode plates in the flow field to the positive pole of the power supply and ground respectively, and both boundaries are set to no-slip; Set the other two boundaries in the flow field as the inlet boundary and the outlet boundary respectively, and set both the inlet flow velocity and the outlet flow velocity to 0.

[0037] Further, the physical parameters of the oil-water mixture in step 2) include the density, viscosity, relative permittivity, oil-water interfacial tension, and permittivity of vacuum of the water phase and the oil phase.

[0038] Further, the operation of meshing the two-dimensional physical model in step 4) is as follows: Mesh the two-dimensional physical model with triangular meshes; Refine the meshes of the droplet and around the droplet.

[0039] Further, the operation of plotting the droplet deformation curve in step 4) is as follows:

[0040] Establish a rectangular coordinate system with the center of the droplet as the origin, define the distance between the two endpoints where the droplet intersects the y-axis as the major axis of the droplet deformation, and denote it as a; Define the distance between the two endpoints where the droplet intersects the x-axis as the minor axis of the droplet deformation, and denote it as b; Define the deformation degree of the droplet as D, and

[0041] According to the two-dimensional physical model after meshing, use the interface tracking equation in the two-dimensional dynamic deformation model to track the oil-water interface, obtain the two endpoints where the droplet intersects the y-axis and the two endpoints where the droplet intersects the x-axis at each moment during the droplet deformation process, calculate the major axis and minor axis of the droplet deformation at each moment, then calculate the deformation degree of the droplet at each moment, and finally plot the droplet deformation curve showing the variation of the deformation degree of the droplet with the time of the applied electric field.

[0042] Further, the optimal deformation degree is 1.9.

[0043] Further, the operation of determining the optimal pulse width according to the droplet deformation curve selected in step 4) in step 5) is: In the droplet deformation curve selected in step 4), take the time duration that the droplet experiences from the initial state to the optimal deformation degree as the optimal pulse width.

[0044] Further, the specific operation of step 8) is: In the droplet deformation curve obtained in step 7), take the time duration that the droplet experiences from the optimal deformation degree to the minimum deformation degree as the optimal pulse rest width.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The main idea of the method for matching the electric field demulsification parameters of waste oil emulsion in the present invention is: based on the droplet size, the optimal electric field parameters are matched. The electric field parameters are the electric field strength (E) and the electric field frequency. The electric field frequency is divided into the pulse width (T) and the pulse rest width (τ) for separate matching. First, a DC electric field is applied to the droplets to determine the optimal electric field strength and the optimal pulse width of the droplets. Then, based on the optimal electric field strength and the optimal pulse width, a pulse electric field that outputs only one pulse is constructed to act on the droplets to determine the optimal pulse rest width. The obtained electric field frequency can make the average deformation degree of the droplets slightly higher than the optimal deformation degree. On the premise of avoiding droplet rupture, the collision probability between droplets is maximized, which can effectively weaken the strength of the droplet interfacial film, thereby achieving the best demulsification efficiency and realizing the efficient aggregation and demulsification of waste oil emulsion. It can effectively solve the technical problem of how to obtain the optimal electric field demulsification parameters and achieve the effect of improving the demulsification efficiency of waste oil emulsion. Description of the Drawings

[0047] Figure 1 It is a partial cross-sectional view of the pulse electric field demulsification device described in the background art;

[0048] Figure 2 It is a logic block diagram of a method for matching the electric field demulsification parameters of waste oil emulsion in an embodiment;

[0049] Figure 3 It is a schematic diagram of the two-dimensional physical model described in the embodiment;

[0050] Figure 4 It is a schematic diagram of the two-dimensional grid model obtained by meshing the two-dimensional physical model described in the embodiment;

[0051] Figure 5 It is a comparison diagram of droplet deformation curves of droplets with the same particle size under different electric field strengths in Experiment 1 described in the embodiment;

[0052] Figure 6 It is a droplet deformation curve diagram corresponding to the optimal deformation degree in Experiment 1 described in the embodiment;

[0053] Figure 7 It is a droplet deformation curve diagram corresponding to the optimal electric field parameters in Experiment 1 described in the embodiment;

[0054] Figure 8 It is a schematic diagram of dividing the time of electric field action according to the deformation of droplets in Experiment 1 described in the embodiment;

[0055] Figure 9 It is a droplet deformation curve diagram corresponding to the pulse rest width τ1 = 7 ms in Experiment 1 described in the embodiment;

[0056] Figure 10 It is the droplet deformation curve diagram corresponding to the pulse rest width τ2 = 17 ms in Experiment 1 described in the embodiment;

[0057] Figure 11 It is the droplet deformation curve diagram corresponding to the pulse rest width τ3 = 57 ms in Experiment 1 described in the embodiment;

[0058] Figure 12 It is the droplet deformation curve diagram corresponding to four kinds of particle size droplets in Experiment 2 described in the embodiment;

[0059] Figure 13 It is the comparison diagram of the droplet deformation curves obtained from the real experiment and Experiment 1 in Experiment 3 described in the embodiment;

[0060] Among them, there are a housing 1, an oil outlet 2, an oil inlet 3, a drain outlet 4, and an electrode plate group 5. Specific implementation manners

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Components of the embodiments of the present invention described and illustrated herein usually can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0062] It should be noted that similar reference numerals and letters denote similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship in which the product of the invention is usually placed during use. It is 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 thus cannot be construed as a limitation on the present invention. In addition, the terms "first", "second", "third", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance. In addition, terms such as "horizontal" and "vertical" do not mean that the components are required to be absolutely horizontal or hanging, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined. In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, the terms "set", "install", "connect", and "couple" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0063] Embodiment:

[0064] Please refer to Figure 2 , a method for matching the parameters of electric field demulsification of waste oil emulsion, comprising the following steps:

[0065] 1) Establish a two-dimensional physical model of the droplets in the oil-water mixture under the action of an electric field in a pulsed electric field demulsification device; including the following sub-steps:

[0066] 11) In the pulsed electric field demulsification device, take the cross-section of the region between two electrode plates belonging to the same electrode plate group as the flow field;

[0067] 12) Fill the flow field with the oil-water mixture, and place the only droplet in the oil-water mixture at the center of the flow field. Define the particle size of the droplet as R, and the size of the flow field as 16R×16R, as Figure 3 shown;

[0068] For the convenience of calculation and analysis, in the method for matching the parameters of electric field demulsification of waste oil emulsion of the present invention, a simulation experiment of the deformation of droplets in waste oil emulsion under the action of an electric field is characterized by an oil-water mixture containing only one droplet (water droplet).

[0069] 2) Construct a two-dimensional dynamic deformation model of the droplet under the action of an electric field in a two-dimensional physical model, and set the boundary conditions and physical parameters of the oil-water mixture.

[0070] In step 2), the two-dimensional dynamic deformation model is established by combining the flow field control equation, the interface tracking equation, and the electric field control equation. The flow field control equation is as follows:

[0071]

[0072] where u is the velocity vector of the oil-water mixture, ρ is the density of the oil-water mixture, p is the pressure of the oil-water mixture, μ is the viscous shear stress tensor of the oil-water mixture, F st is the oil-water interfacial tension, F e is the electric field force, I is the identity matrix; t is the time;

[0073] The interface tracking equation is as follows:

[0074]

[0075] where is the phase field variable, represents the oil phase, represents the water phase, represents the oil-water interface; γ is the mobility; G is the chemical potential;

[0076] The formula for the chemical potential G is as follows:

[0077]

[0078] where λ is the mixed energy density and h is the oil-water interface thickness;

[0079] The volume fractions of the oil and water phases are respectively expressed as:

[0080]

[0081] where Vf0 is the volume fraction of the continuous phase oil and Vf1 is the volume fraction of the discrete phase droplet;

[0082] The relationship between the oil-water interfacial tension F st and the chemical potential G is as follows:

[0083]

[0084] The electric field control equation is as follows:

[0085]

[0086] ε r= Vf0×ε oil + Vf1×ε water

[0087] where ε r represents the relative permittivity of the oil-water mixture, ε0 represents the permittivity of vacuum, E represents the electric field strength, and ε oil is the relative permittivity of the oil phase; ε water is the relative permittivity of the water phase.

[0088] The operation of setting the boundary conditions in step 2) is as follows: Connect the two boundaries corresponding to the two electrode plates in the flow field to the positive pole of the power supply and ground respectively, and both boundaries are set to no-slip; Set the other two boundaries in the flow field as the inlet boundary and the outlet boundary respectively, and set both the inlet flow rate and the outlet flow rate to 0.

[0089] The physical parameters of the oil-water mixture described in step 2) include the density, viscosity, relative permittivity, oil-water interfacial tension, and permittivity of vacuum of the water phase and the oil phase.

[0090] 3) Set the electric field type of the two-dimensional physical model as a direct current electric field, and add multiple sets of operating parameters. The operating parameters include the electric field strength, and the electric field strength in each set of operating parameters increases sequentially;

[0091] 4) The two-dimensional dynamic deformation model respectively draws the droplet deformation curves under each set of operating parameters according to the two-dimensional physical model after grid division, and selects the droplet deformation curve whose peak deformation degree is equal to the optimal deformation degree;

[0092] The operation of grid division of the two-dimensional physical model in step 4) is as follows: Use triangular grids to divide the two-dimensional physical model; Perform encryption processing on the grids of the droplet and around the droplet, as Figure 4 shown;

[0093] The operation of drawing the droplet deformation curve in step 4) is as follows:

[0094] Establish a rectangular coordinate system with the center of the droplet as the origin, define the distance between the two endpoints where the droplet intersects the y-axis as the major axis of the droplet deformation, and denote it as a; Define the distance between the two endpoints where the droplet intersects the x-axis as the minor axis of the droplet deformation, and denote it as b; Define the deformation degree of the droplet as D, and

[0095] According to the two-dimensional physical model after grid division, the interface tracking equation in the two-dimensional dynamic deformation model is used to track the oil-water interface, and the two end points where the droplet intersects the y-axis and the two end points where the droplet intersects the x-axis at each moment during the droplet deformation process are obtained. The major axis and minor axis of the droplet deformation at each moment are calculated, and then the deformation degree of the droplet at each moment is calculated. Finally, the droplet deformation curve showing the change of the deformation degree of the droplet with the time of the applied electric field is plotted.

[0096] Currently, it has been found through research that when the ratio of the major axis to the minor axis of the droplet deformation exceeds 1.9, the droplet will begin to become unstable. Therefore, in the present invention, the droplet deformation ratio of 1.9 is used as a constraint condition, that is, the optimal deformation degree is set to 1.9; after applying a DC electric field, when the peak value of the droplet deformation curve reaches 1.9, the corresponding electric field strength and time at this time are respectively used as the optimal electric field strength and the optimal width.

[0097] 5) Take the electric field strength corresponding to the droplet deformation curve selected in step 4) as the optimal electric field strength, and determine the optimal pulse width according to the droplet deformation curve selected in step 4);

[0098] The operation of determining the optimal pulse width according to the droplet deformation curve selected in step 4) in step 5) is as follows: in the droplet deformation curve selected in step 4), the time duration experienced by the droplet from the initial state to the optimal deformation degree is used as the optimal pulse width.

[0099] 6) Set the electric field type of the two-dimensional physical model to a pulsed electric field and output only one pulse, and add a set of operating parameters, where the operating parameters include the optimal electric field strength and the optimal pulse width determined in step 5).

[0100] 7) The two-dimensional dynamic deformation model plots the droplet deformation curve under the operating parameters added in step 6) according to the two-dimensional physical model after grid division; the operation of plotting the droplet deformation curve in step 7) is the same as that in step 4).

[0101] 8) Determine the optimal pulse rest width according to the droplet deformation curve obtained in step 7); the specific operation is as follows: in the droplet deformation curve obtained in step 7), the time duration experienced by the droplet from the optimal deformation degree to the minimum deformation degree is used as the optimal pulse rest width.

[0102] The main idea of the method for matching the electric field demulsification parameters of waste oil emulsion in the present invention is as follows: Based on the droplet size, the optimal electric field parameters are matched. The electric field parameters are the electric field strength (E) and the electric field frequency. The electric field frequency is divided into the pulse width (T) and the pulse rest width (τ) for separate matching. First, a DC electric field is applied to the droplets to determine the optimal electric field strength and the optimal pulse width. Then, based on the optimal electric field strength and the optimal pulse width, a pulse electric field that outputs only one pulse is constructed and applied to the droplets to determine the optimal pulse rest width. The obtained electric field frequency can make the average deformation degree of the droplets slightly higher than the optimal deformation degree. On the premise of avoiding droplet rupture, the collision probability between droplets is maximized, which can effectively weaken the strength of the droplet interfacial film, thereby achieving the best demulsification efficiency and realizing the efficient aggregation and demulsification of waste oil emulsion. It can effectively solve the technical problem of how to obtain the optimal electric field demulsification parameters and achieve the effect of improving the demulsification efficiency of waste oil emulsion.

[0103] To prove the feasibility of the electric field parameters matched by the present invention and the effectiveness in improving the demulsification efficiency, a simulation experiment is carried out according to the method for matching the electric field demulsification parameters of waste oil emulsion as follows:

[0104] Experiment 1: Electric field parameter matching is carried out for an oil-water mixture with a droplet size of 1.0×10 -3 m.

[0105] According to the two-dimensional physical model established in step 1) and the boundary conditions set in step 2), as Figure 3 shown.

[0106] The physical parameters of the oil-water mixture set in step 2) are shown in the following table;

[0107]

[0108] The two-dimensional grid model obtained by meshing the two-dimensional physical model according to step 4) is as Figure 4 shown.

[0109] The droplet deformation curves at different electric field strengths obtained according to step 3) and step 4) are as Figure 5 shown; Through research, it is found that when the ratio of the major axis to the minor axis of droplet deformation exceeds 1.9, the droplets will start to become unstable. Therefore, the present invention takes the droplet deformation ratio of 1.9 as a constraint condition, that is, the optimal deformation degree is set to 1.9; Therefore, select from Figure 5 the droplet deformation curve corresponding to the optimal deformation degree, as Figure 6 shown.

[0110] According to step 5), based on Figure 5 and Figure 6 , the optimal electric field E = 612 Kv / m is determined. Based on Figure 6It is obtained that the time duration for the droplet to reach the optimal deformation degree from the initial state is 23 ms, that is, the optimal pulse width T = 23 ms is determined.

[0111] According to steps 6) and 7), with the optimal electric field strength E = 612 Kv / m and the optimal pulse width T = 23 ms as the parameters of the pulsed electric field, and only outputting one pulse, the droplet deformation curve corresponding to the optimal electric field parameters is obtained as Figure 7 shown, based on Figure 7 It is obtained that the time duration for the droplet to reach the minimum deformation degree from the optimal deformation degree is 17 ms, that is, the optimal pulse rest width τ = 17 ms is determined.

[0112] To verify the effectiveness of the optimal pulse rest width τ = 17 ms, the time of the electric field action is divided into a stretching stage, a contraction stage, a recovery stage, and a stable stage according to the deformation of the droplet, as Figure 8 shown; three points are taken respectively in the contraction stage, the minimum deformation degree, and the stable stage of the droplet deformation curve, and the time length between them and the point where the optimal deformation degree is located is taken as the pulse rest width, that is, the pulse rest widths τ1 = 7 ms, τ2 = 17 ms, and τ3 = 57 ms;

[0113] With the same electric field strength E = 612 Kv / m and pulse width T = 23 ms, and different pulse rest widths τ1 = 7 ms, τ2 = 17 ms, and τ3 = 57 ms, pulsed electric fields are applied to the droplets respectively, and the corresponding droplet deformation curves are obtained as Figure 9 、 Figure 10 and Figure 11 shown; according to Figure 9 It can be seen that when the pulse rest width is 7 ms, the average deformation degree of the droplet is the smallest. Because when the second pulse arrives, the droplet is still in the contraction stage, and under the inertial action of the droplet deformation, part of the electric field force is offset, and the average deformation degree of the droplet is lower than the optimal deformation degree, resulting in a lower collision probability between droplets, which is not conducive to demulsification; according to Figure 10 It can be seen that when the pulse rest width is 17 ms, when the second pulse arrives, the droplet is exactly at the minimum of the contraction stage, and the electric field force and the inertial force in the recovery stage will promote the stretching deformation of the droplet together, making the average deformation degree of the droplet slightly higher than the optimal deformation degree (although higher than the optimal deformation degree, the droplet will become unstable, but slightly higher than the optimal deformation degree will not cause the droplet to break and can still be used for demulsification and dehydration; of course, in actual operation, the electric field strength corresponding to the point slightly lower than the optimal deformation degree can also be used as the optimal electric field strength and the corresponding optimal pulse width can be determined), making the collision probability between droplets higher, which is conducive to demulsification; according to Figure 11It can be seen that when the pulse pause width is 57 ms, the average value of droplet deformation is also smaller than that when the pulse pause width is 17 ms, and the droplet vibration frequency is also smaller, which is not conducive to demulsification. In summary, it is correct and effective to determine the duration from the optimal deformation degree to the minimum deformation degree of the droplet as the optimal pulse pause width, which is conducive to increasing the collision probability between droplets, thereby improving the efficiency of demulsification and dehydration.

[0114] Experiment 2: Taking Experiment 1 as an example, the electric field parameters were matched for oil-water mixtures with droplet diameters of 0.8×10 -3 m, 1.2×10 -3 m, and 1.4×10 -3 m respectively. The matched electric field parameters are shown in the following table;

[0115]

[0116] According to the matched electric field parameters, the pulsed electric field was optimized for droplets of different diameters. As Figure 12 shown, for droplets of the same diameter under the condition of the same optimal electric field strength, the deformation of the droplets under the action of the pulsed electric field with matched pulse width and pulse pause width was compared with that under the action of the pulsed electric field without electric field parameter matching. It can be seen that the amplitude of the pulsed electric field optimized by this method to stimulate droplet deformation is greater than that of the non-optimized pulsed electric field. Therefore, this method is also effective for droplets of different diameters.

[0117] Experiment 3: A real experiment was carried out. The waste oil emulsion, electric field strength, pulse width, and pulse pause width used in the real experiment were the same as those in Experiment 1. The effectiveness of the simulation was verified by comparing the real experimental results with the simulation results;

[0118] The device used in the real experiment includes two parts: one part is a chaotic pulse group electric field generation device, which includes an arbitrary waveform generation device (DG1022Z, Rigol, China) used to generate chaotic pulse group signals, a high-voltage pulse power supply (TP3090, Teslaman, China), and a digital oscilloscope (TDS1002C-EDU, Tektronix, USA); the other part is a droplet deformation observation device, which includes a stereomicroscope (SZX7, Olympus, Japan), a high-speed camera (FR-800, PC0, Germany) connected to the microscope, a droplet deformation observation chamber designed with plexiglass, two copper sheets used as electrodes, and a notebook with image recording software TroublePix;

[0119] Experimental procedure: An arbitrary waveform generator is used to generate a chaotic pulse train signal, which is input into a high-voltage pulse power supply to generate a chaotic pulse train electric field, and the electric field parameters are detected by a digital oscilloscope; the positive pole of the high-voltage pulse power supply is connected to the right copper plate of the droplet observation chamber, and the negative pole of the high-voltage pulse power supply is connected to the left copper plate of the droplet observation chamber. The deformed images of the droplets are transmitted to a notebook through a microscope equipped with a high-speed camera for observation.

[0120] Result comparison: The comparison graph of the droplet deformation curves obtained from the real experiment and Experiment 1 is as Figure 13 shown;

[0121] Result analysis: The simulation results lag slightly behind the experimental results because the simulation results are obtained under ideal conditions, and the experimental results are affected by a series of factors such as instrument accuracy, environmental factors, and measurement errors; however, the overall error is small. Based on the two-dimensional physical model and two-dimensional dynamic deformation model described in the present invention, the deformation of droplets in waste oil emulsion can be accurately reflected. Therefore, the method for matching the demulsification parameters of the waste oil emulsion electric field can be used to study the matching of electric field parameters for demulsification and dehydration of pulsed electric fields.

[0122] 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 the technical solutions. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the spirit and scope of the present technical solutions shall be covered by the scope of the claims of the present invention.

Claims

1. A method for matching the parameters of electric field demulsification of waste oil emulsion, characterized in that: It includes the following steps: 1) Establish a two-dimensional physical model of the droplets in the oil-water mixture under the action of an electric field in the pulsed electric field demulsification device; 2) Construct a two-dimensional dynamic deformation model of the droplets under the action of an electric field in the two-dimensional physical model, and set the boundary conditions and physical parameters of the oil-water mixture; 3) Set the electric field type of the two-dimensional physical model as a direct current electric field, add multiple sets of operating parameters, where the operating parameters include the electric field intensity, and the electric field intensity in each set of operating parameters increases sequentially; 4) The two-dimensional dynamic deformation model respectively draws the droplet deformation curves under each set of operating parameters according to the two-dimensional physical model after grid division, and selects the droplet deformation curve with the peak deformation degree of the droplet equal to the optimal deformation degree; 5) Take the electric field intensity corresponding to the droplet deformation curve selected in step 4) as the optimal electric field intensity, and determine the optimal pulse width according to the droplet deformation curve selected in step 4); 6) Set the electric field type of the two-dimensional physical model as a pulsed electric field and output only one pulse, add a set of operating parameters, where the operating parameters include the optimal electric field intensity and the optimal pulse width determined in step 5); 7) The two-dimensional dynamic deformation model draws the droplet deformation curve under the operating parameters added in step 6) according to the two-dimensional physical model after grid division; 8) Determine the optimal pulse rest width according to the droplet deformation curve obtained in step 7); Step 1) includes the following sub-steps: 11) In the pulsed electric field demulsification device, take the cross-section of the region between two electrode plates belonging to the same electrode plate group as the flow field; 12) Fill the flow field with the oil-water mixture, place the only droplet in the oil-water mixture at the center of the flow field, define the particle size of the droplet as R, and the size of the flow field as 16R×16R; In step 2), the two-dimensional dynamic deformation model is established by combining the flow field control equation, the interface tracking equation and the electric field control equation. The flow field control equation is as follows: where, u is the velocity vector of the oil-water mixture, ρ is the density of the oil-water mixture, p is the pressure of the oil-water mixture, μ is the viscous shear stress tensor of the oil-water mixture, F st is the oil-water interfacial tension, F e is the electric field force, I is the identity matrix; t is time; The interface tracking equation is as follows: wherein, is a phase field variable, represents the oil phase, represents the water phase, represents the oil-water interface; γ is the mobility; G is the chemical potential; The formula for the chemical potential G is as follows: Among them, λ is the mixed energy density, and h is the oil-water interface thickness; The volume fractions of the oil and water phases are respectively expressed as: Among them, Vf0 is the volume fraction of the continuous phase oil, and Vf1 is the volume fraction of the discrete phase droplets; The interfacial tension F between oil and water st The relationship with the chemical potential G is as follows: The electric field control equation is as follows: ε r = Vf0 × ε oil + Vf1 × ε water Among them, ε r represents the relative permittivity of the oil-water mixture, ε0 represents the permittivity of vacuum, E represents the electric field strength, and ε oil is the relative permittivity of the oil phase; ε water is the relative permittivity of the water phase; The operation of drawing the droplet deformation curve in step 4) is as follows: Taking the center of the droplet as the origin, a rectangular coordinate system is established. The distance between the two endpoints where the droplet intersects the y-axis is defined as the major axis of the droplet deformation, denoted as a; the distance between the two endpoints where the droplet intersects the x-axis is defined as the minor axis of the droplet deformation, denoted as b; the degree of deformation of the droplet is defined as D, and According to the two-dimensional physical model after grid division, use the interface tracking equation in the two-dimensional dynamic deformation model to track the oil-water interface, obtain the two end points where the droplet intersects the y-axis and the two end points where the droplet intersects the x-axis at each moment during the droplet deformation process, calculate the major axis and minor axis of the droplet deformation at each moment, and then calculate the deformation degree of the droplet at each moment. Finally, draw the droplet deformation curve showing the change of the deformation degree of the droplet with the application time of the electric field; The specific operation of step 8) is: in the droplet deformation curve obtained in step 7), take the time duration from the optimal deformation degree to the minimum deformation degree of the droplet as the optimal pulse rest width.

2. The matching method of the electric field demulsification parameters of the waste oil emulsion according to claim 1, characterized in that: The operations of setting boundary conditions described in step 2) are as follows: Connect the two boundaries corresponding to the two electrode plates in the flow field to the positive pole of the power supply and ground respectively, and both boundaries are set as no-slip; Set the other two boundaries in the flow field as the inlet boundary and the outlet boundary respectively, and set both the inlet flow velocity and the outlet flow velocity to 0.

3. The matching method for the electric field demulsification parameters of waste oil emulsion according to claim 1, wherein: The physical parameters of the oil-water mixture described in step 2) include the densities, viscosities, relative dielectric constants, oil-water interfacial tensions, and vacuum dielectric constants of the water phase and the oil phase.

4. The matching method of the electric field demulsification parameters of waste oil emulsion according to claim 1, characterized in that: The operations of meshing the two-dimensional physical model in step 4) are as follows: Mesh the two-dimensional physical model using triangular meshes; Refine the meshes of the droplets and around the droplets.

5. The matching method for the electric field demulsification parameters of waste oil emulsion according to claim 1, characterized in that: The optimal degree of deformation is 1.

9.

6. The matching method for the electric field demulsification parameters of waste oil emulsion according to claim 1, characterized in that: The operation of determining the optimal pulse width according to the droplet deformation curve selected in step 4) in step 5) is: In the droplet deformation curve selected in step 4), take the time duration experienced by the droplet from the initial state to the optimal degree of deformation as the optimal pulse width.

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