AU2021102552A4

AU2021102552A4 - A Method For Determining Optimal Operating Parameters Of Dual-Field Coupled Dewatering Device

Info

Publication number: AU2021102552A4
Application number: AU2021102552A
Authority: AU
Inventors: Haifeng GONG; Wenlong Li; Ye PENG; Xianming ZHANG
Original assignee: Chongqing Technology And Business University Technology Development Co Ltd; Chongqing University; Chongqing Technology and Business University
Current assignee: Chongqing Technology And Business University Technology Development Co Ltd; Chongqing Technology and Business University
Priority date: 2021-05-13
Filing date: 2021-05-13
Publication date: 2021-07-01
Anticipated expiration: 2029-05-13

Abstract

The present invention discloses a method for determining optimal operating parameters of a dual-field coupled dewatering device, including the following steps of: comprehensively considering the effects of a swirling flow centrifugal field and a high-voltage electric field; using a computational fluid dynamics method; combining a flow field control equation, an electric field control equation, and a population balance equation; constructing a dynamic coalescence model of emulsified oil droplets under dual-field coupled enhancement, using the population balance model to simulate the coalescence and crushing process of the emulsified droplets in the device; calculating the particle size of the droplets distribution, an average particle size and separation efficiency under different operating parameters, and determining the operating parameters when the coupled device achieves the optimal separation effect. I s 2 3 Lu DiG. FIG.1 FIG. 2

Description

2 3 I s

Lu DiG. FIG.1

FIG. 2

Description

A METHOD FOR DETERMINING OPTIMAL OPERATING PARAMETERS OF DUAL-FIELD COUPLED DEWATERING DEVICE TECHNICAL FIELD

[0001] The present invention relates to the field of waste oil treatment technology, and particularly to a method for determining optimal operating parameters of a dual-field coupled dewatering device.

BACKGROUNDTECHNOLOGY

[0002] In the field of waste oil resource recovery, demulsification and dewatering treatment of emulsified oil is a relatively common process link. However, it is often difficult to effectively and quickly realize the demulsification and dewatering treatment of the emulsified oil by using a single process method. The combined use of two or more demulsification processes or operation units can greatly improve the efficiency of emulsified oil demulsification and dewatering, which is the direction of the development of demulsification and dewatering technology in the future. A dual field coupled dewatering device uses a swirling flow centrifugal device with a double cone section and a double tangential inlet as its body structure. The high-voltage electrode is cleverly embedded. An overflow tube is connected to a positive electrode of a high-voltage power supply. A barrel body is connected to a negative pole of the power supply. A coaxial cylindrical high-voltage electric field is formed in a swirling flow chamber The device combines the advantages of an electric demulsification method and a hydroswirl, makes the small droplets agglomerate and increase in an electric field of a cavity, and uses a swirling flow centrifugal field to separate large diameter droplets to realize the rapid separation of oil and water.

[0003] The emulsified droplets are acted on by electric field coalescence in the coupled device, which increases the size of the droplets, and at the same time are acted on by a centrifugal shearing force of the swirling flow centrifugal field, which causes the droplets with larger diameters to be broken. Therefore, the coalescence and crushing of the emulsified droplets in the coupled field is a dynamic process. The particle size of the droplets is directly related to the centrifugal force provided by the swirling flow field, which affects the oil-water separation effect of the device. Therefore, it is very important to clarify the coalescence and crushing process of the emulsified droplets in the device, as well as the particle size of the droplets distribution. The electric field

Description

strength and the flow rate of the inlet are important operating parameters of the dual-field coupled dewatering device. The intensity of the electric field directly affects the coalescence effect of the emulsified droplets. The flow rate of the inlet is directly related to the action time of the droplets in the electric field and the oil-water separation efficiency.

SUMMARY OF INVENTION

[0004] In view of this, the objective of the present invention is to provide a dual-field coupled dewatering device and a method for optimizing parameters. The device is a coupled demulsification dewatering device that integrates a high-voltage electric field and a swirling flow centrifugal field to achieve highly efficient and fast processing of a waste oil emulsified liquid.

[0005] In order to reach the forgoing objective, the present invention provides following technical solutions:

[0006] A method for determining optimal operating parameters of a dual-field coupled dewatering device includes the following steps of:

[0007] establishing a grid model of the dual-field coupled dewatering device;

[0008] constructing a dynamic coalescence model of emulsified oil droplets under the action of the dual-field coupled dewatering device;

[0009] setting the initial conditions for the calculation of the dual-field coupled dewatering device;

[0010] setting operating parameters of the coalescence and crushing process of the emulsified droplets in the dual-field coupled dewatering device;

[0011] calculating the separation efficiency of the emulsified droplets under the different operating parameters according to the grid model; and

[0012] determining the operating parameters when the coupled device achieves the optimal separation effect according to the separation efficiency;

[0013] Further, when the separation efficiency of the emulsified droplets under the different operating parameters is calculated according to the grid model, the particle size distribution and the average particle size of the emulsified droplets are still calculated.

[0014] Further, the grid model is established according to the following steps:

[0015] using tetrahedral and hexahedral hybrid grids to perform grid division for a model of the dual-field coupled dewatering device;

[0016] densifying a grid at which the electric field and the flow field are coupled; and

[0017] densifying a grid at a tangent point of an inlet end and a swirling flow cavity.

[0018] Further, the dynamic coalescence model is established by combining a flow field control equation, an electric field control equation, and a coalescence and crushing kernel function; and is

Description

established according to the following steps:

[0019] The flow field control equation is established according to the following formula:

[0020] V-pu=0(1)

[pu +V -(puu)= V -[p,,(u, -u)(u -U)+p+p 0 (u - u)(u0 - u)]

[00211]at -VP+Vu +pg+F (2)

[0022] Where,

[0023] U represents the speed of the mixed liquid; Uw represents the speed of a water phase; and Uo represents the speed of an oil phase;

[ 0 0 2 4 ]pw represents the density of water; po represents the density of oil; and p represents the density of the mixed liquid;

[0025] <pw represents the volume fraction of water;

[0026] <po represents the volume fraction of oil;

[0027] P represents a pressure;

[0028] represents a viscous stress tensor;

[0029] Fe represents an electric field force experienced by the droplets in the coupled dewatering device;

[0030] g represents an acceleration of gravity;

[0031] The electric field control equation is established according to the following formula:

[0032] F =V eEE - E -El(3)

[0033] Where,

[0034] , represents the relative dielectric constant of the emulsified liquid;

[0035] where, co represents a vacuum dielectric constant;

[0036] E represents an electric field strength;

[0037] I represents a unit tensor;

[0038] The coalescence kernel function is established according to the following steps:

[0039] The coalescence rate is calculated according to the following formula:

[0040] (di,dj)=h(di,dj)e(di,dj) (9)

[0041] Where,

[0042] represents a coalescence rate;

[0043] di represents the particle size of the i-th droplet;

[0044] dj represents the particle size of the j-th droplet;

[0045] h (di, dj) represents the collision frequency of droplets with diameters di and dj, respectively;

Description

[0046] e represents coalescence efficiency;

[0047] A collision frequency function is established according to the following formula:

[0048] h(di,d,) =C, C13(di +d) X di /3+ d|"/) 1 + (0 (10)

[0049] Where, Cl represents a constant;

[0050] A liquid film drain model is used to calculate the coalescence efficiency of the emulsified droplets in a turbulent flow field according to the following formula:

0 .71p.{(h|" -hj2) 3 1

[0051] A(dj,dj)=exp - 0 ." d(" d1 2 12 dj51 ) p EI/"dil/d 1/ (d,.+

[0052] Where,

[0053] hi is the initial thickness of the liquid film;

[0054] hf is the critical thickness at which the liquid film ruptures;

[0055] The dipole coalescence of the emulsified droplets in the electric field is calculated according to the following formula: 0.7(d +d) 3 (d| +dj 2 )ecs.E 2

[0056] K(didj)=

[0057] Where,

[0058] represents the viscosity of the mixed liquid;

[0059] co represents the relative dielectric constant of the oil phase;

[0060] The coalescence kernel function of the emulsified droplets is calculated under the dual-field coupled condition according to the following formula:

[0061] a(didj)=4didj)+K(di4j); (13)

[0062] Where,

[0063] K (di, dj) represents the coalescence kernel function of the emulsified droplets in the electric

field.

[0064] , (di, dj) represents the coalescence kernel function of the emulsified droplets in the electric field.

[0065] Further, the crushing kernel function is a product of the crushing frequency of the emulsified droplets and the probability density function of the droplets. The crushing frequency of the emulsified droplets is calculated according to the following formula:

[0066] g(d)= C3 exp -C4 (1+ 9 )d2 /3 L pE23 d513 (14)

[0067] Where,

Description

[0068] g(d) represents the crushing frequency;

[0069] C 3 represents a constant;

[0070] C4 represents a constant;

[0071]y represents an interfacial tension;

[0072] d represents the diameter of the droplet;

[0073] Further, the probability density function of the particle size of the droplets of the droplet is specifically as follows:

[0074] 8(d',d)=

[0074 46exp 4.5(2d' 3 2 ) (15)

( d'6

[0075] Where,

[0076]p(d', d) represents a probability density function of a droplet with a diameter of d' that crushes into a droplet with a diameter of d.

[0077]d' represents a diameter

[0078] Further, the initial conditions of the dual-field coupled dewatering device set boundary conditions and operating parameters in the following manner, specifically as follows:

[0079] setting inlet boundary conditions of the dual-field coupled dewatering device;

[0080] setting outlet boundary conditions of the dual-field coupled dewatering device;

[00 8 1]setting wall boundary conditions of the dual-field coupled dewatering device;

[0082] setting the physical parameters of oil and water;

[0083] setting the initial particle size and distribution of the droplets; and

[0084] setting the duty cycle, the voltage amplitude and the frequency of the electric field

[0085] Further, the operating parameters include electric field strength parameters acting on the dual-field coupled dewatering device; and an electric field strength is determined according to the following steps:

[0086] determining flow rate parameters of the inlet of the coupled device;

[0087] adjusting the electric field strength;

[0088] obtaining the cloud diagram of the distribution of the particle size of the droplets of the coupled device;

[0089] determining the separation efficiency of the emulsified droplets in the electric field; and

[0090] obtaining an electric field intensity at the maximum separation efficiency as an optimal electric field intensity parameter.

[0091] Further, the operating parameters include flow rate parameters of the inlet acting on the dual-field coupled dewatering device; and the flow rate parameters of the inlet are determined according to the following steps:

Description

[0092] determining the electric field strength of the coupled device;

[0093] adjusting an flow rate of the inlet;

[0094] obtaining the cloud diagram of the distribution of the particle size of the droplets of the coupled device;

[0095] determining the separation efficiency of the emulsified droplets in the electric field; and

[0096] obtaining an flow rate of the inlet at the maximum separation efficiency as an optimal flow rate parameter of the inlet.

[0097] The present invention has the following beneficial effects:

[0098] The present invention provides a method for determining optimal operating parameters of a dual-field coupled dewatering device, including the following steps of: comprehensively considering the effects of a swirling flow centrifugal field and a high-voltage electric field; using a computational fluid dynamics method; combining a flow field control equation, an electric field control equation, and a population balance equation; constructing a dynamic coalescence model of emulsified oil droplets under dual-field coupled enhancement, using the population balance model to simulate the coalescence and crushing process of the emulsified droplets in the device; calculating the particle size of the droplets distribution, an average particle size and separation efficiency under different operating parameters, and determining the operating parameters when the coupled device achieves the optimal separation effect.

BRIEF DESCRIPTION OF THE DRAWINGS

[0099] In order to make the objectives, technical solutions and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0100] FIG. 1 is a flowchart of a model of a dual-field coupled dewatering device.

[0101] FIG. 2 is a flowchart of a calculation grid of a dual-field coupled dewatering device.

[0102] FIG. 3 is a flowchart of a method for determining optimal operating parameters of dual-field coupled dewatering device.

[0103] FIG. 4 is a principle diagram of a method for determining optimal operating parameters of dual-field coupled dewatering device.

[0104] FIG. 5 is the size distribution of cumulative droplets of inlet droplets.

[0105] FIG. 6 is a cloud diagram of Sauter average particle size on a longitudinal section of a coupled device.

[0106] FIG. 7 is a schematic diagram of droplet volume fraction distribution under different voltages.

[0107] FIG. 8 is the separation efficiency and average particle size of the coupled device under

Description

different voltages.

[0108] FIG. 9 is a cloud diagram of Sauter average particle size distribution on a longitudinal section of a coupled device.

[0109] FIG. 10 is a schematic diagram of the volume fraction distribution of droplets at different flow rates of the inlet.

[0110] FIG. 11 is the separation efficiency and average the particle size of the droplets of droplets of the coupled device at different flow rates of the inlet.

[0111] In the drawings: 1: Overflow tube, 2: Oil inlet, 3: swirling flow chamber, 4: Large cone section, 5: Small cone section; 6: Underflow tube.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0112] The present invention is further described below with reference to the drawings and specific embodiments, so that the person skilled in the art can better understand and implement the present invention, but the embodiments cited are not intended to limit the present invention.

[0113] Embodiment 1

[0114] As shown in FIG. 1, FIG. 1 is a model of a dual-field coupled dewatering device model, FIG. 1 shows a multi-physics field coupled model of the dewatering device. The dual-field coupled dewatering device includes an overflow tube, an oil inlet, a swirling flow chamber, a large cone section, a small cone section and an underflow tube. The overflow tube is connected to a positive electrode of a power supply. The outer surface of the swirling flow chamber is grounded as a negative electrode. A coaxial cylindrical electric field (a red area in the drawings) is formed in the swirling flow chamber. The emulsified droplets coalesce and increase under the action of the electric field, and realize rapid oil-water separation under the action of the swirling flowing field.

[0115] The overflow pipe and the oil inlet are arranged on the swirling flow chamber. The oil inlet is arranged on the outer wall of the swirling flow chamber. The oil inlet is arranged tangentially to the pipe wall of the swirling flow chamber so as to be suitable for a liquid flow to enter the swirling flow chamber at a certain speed and to be able to be rotationally flowed along the inner wall of the swirling flow chamber. The overflow pipe is arranged along an axial direction of the swirling flow chamber. The overflow pipe is located between the outer wall of the swirling flow chamber and the inner wall of the swirling flow chamber and arranged as a high-voltage electric field. The other side of the swirling flow chamber is connected to the large cone section. The other side of the large cone section is connected to the small cone section, and the other side of the small cone section is connected to the underflow pipe.

[0116] The outer wall of the overflow pipe is provided with a positive electrode of a high-voltage

Description

power supply. The inner wall of the swirling flow chamber is provided with a negative electrode of the high-voltage power supply, so as to be suitable for forming a high-voltage electric field in a region between the outer wall of the overflow pipe and the inner wall of the swirling flow chamber. At least two oil inlet are symmetrically rotationally arranged on the swirling flow chamber. The swirling flow chamber, the large cone section, the small cone section, and the underflow pipe are connected as a whole by welding, and the overflow pipe and the straight pipe are connected by a bolt.

[0117] The dual-field coupled dewatering device provided in this embodiment uses a liquid flow with a certain speed to enter the swirling flow chamber, and the flow liquid rotationally flows along the inner wall of the swirling flow chamber to form a hydrocyclone liquid. The device can be placed at a certain angle.

[0118] As shown in FIG. 2, FIG. 2 is a calculation grid of the dual-field coupled dewatering device model, where the model grid is divided in the following manner: a tetrahedral and hexahedral hybrid grid is used to perform grid division for the model of the dual-field coupled dewatering device. A schematic diagram of grids is formed. Grids have the number of 312344, 1.1 of the maximum growth rate, and 0.7 of a curvature factor. The quality of the grid at a coupled place of the electric field and the flow field has the most obvious influence on coupled simulation results. Therefore, when dividing the grids, densification should be carried out reasonably. In addition, a grid at a tangent point of the inlet end and a swirling flow cavity should be appropriately densified to ensure the quality of the grids.

[0119] FIG. 3 is a flowchart of a method for determining the optimal operating parameters of a dual-field coupled dewatering device, and FIG. 4 is a schematic diagram of a method for determining the optimal operating parameters of a dual-field coupled dewatering device. The method includes the following steps:

[0120]establishing a grid model of the dual-field coupled dewatering device;

[0121] constructing a dynamic coalescence model of emulsified oil droplets under the action of the dual-field coupled dewatering device;

[0122] setting the initial conditions and simulation conditions for the grid model calculation of the dual-field coupled dewatering device, which are used to simulate the crushing and coalescence process of the emulsified droplets in the dual-field coupled dewatering device under different operating parameters;

[0123] setting operating parameters of the coalescence and crushing process of the emulsified droplets in the dual-field coupled dewatering device;

[0124] calculating the particle size distribution, the average particle size and the separation

Description

efficiency of the emulsified droplets under different operating parameters according to a grid model; and

[0125] determining the operating parameters when the coupled device achieves the optimal separation effect according to the separation efficiency;

[0126] The grid model is established according to the following steps:

[0127] using tetrahedral and hexahedral hybrid grids to perform grid division for a model of the dual-field coupled dewatering device;

[0128] sealing and treating a grid at which the electric field and the flow field are coupled; and

[0129] sealing and treating a grid at a tangent point of an inlet end and a swirling flow cavity.

[0130] The dynamic coalescence model is established by combining a flow field control equation, an electric field control equation, and a coalescence and crushing kernel function; and is established according to the following steps:

[0131] (1) establishing a population balance equation according to the following formula, which is specifically as follows:

[0132] Flow field control equation (N-S equation)

[01 3 3 ]n a dual-field coupled separation device, an incompressible fluid satisfies the following continuity equation and the following momentum conservation equation:

[0134] V-pu=0(1)

pu +V-(puu)=V[qpgp,(u, -u)(u, -u)+ p,(u.-u)(u,- u)]

[0135] at -VP+V.a+pg+F (2)

[0136] U represents the speed of the mixed liquid; where Uw represents the speed of a water phase;

and Uo represents the speed of an oil phase;

[0137]pw represents the density of water; po represents the density of oil; and p represents the

density of the mixed liquid;

[0138] pw represents the volume fraction of water;

[0139] po represents the volume fraction of oil;

[0140] P represents a pressure;

[0141] represents a viscous stress tensor;

[0142] Fe represents an electric field force experienced by the droplets in the coupled dewatering

device;

[0143] g represents an acceleration of gravity;

[0144] Electric field control equation

[0145] Because there is no corresponding electric field coupled module in the Fluent (ANSYS 16.0) software, the present invention uses a user-defined function to convert the electric field force

Description

into an external volume force as a source term and add the source term to the N-S equation. The electric field force Fe experienced by the droplets inside the coupled dewatering unit can be expressed as:

[0146] gg 2 )(3)

[0147] E represents the relative dielectric constant of the emulsified liquid;

[01 4 8 ]so represents a vacuum dielectric constant;

[0149] E represents an electric field strength;

[0150] I represents a unit tensor;

[0151] Coalescence kernel function

[0152] It is assumed that the collision of the droplets in a coupled unit is a binary collision, the size of the droplets is a coalescence rate ) between di and dj, which can be expressed as a product of a collision frequency h and coalescence efficiency e. That is:

[0153] )L(di ,dj)=h(di ,dj)e(di ,dj) (4)

[0154] The collision of droplets in a swirling flow centrifugal device is mainly caused by turbulent fluctuations. The collision frequency function can be expressed as:

[0155] h(di,d,)=C I (d,+d) (di2/3+d2/ 3 )1/2 1+ (5)

[0156] Where C 1 represents a constant;

[0157] Collision between the droplets can lead to two results-coalescence and rebound, so coalescence efficiency is used to describe the results of droplet collisions. The coalescence efficiency of the emulsified droplets in a turbulent flow field is calculated using a liquid film drain model:

[0158]

[05 dj~dj = -,)exp r 0.7lp (h|1 12 3 -h/2) d 2d 2 (d,+d)) (6)

[0159] where hi and hfare the initial thickness of the liquid film and the critical thickness at which rupture occurs, respectively, and p, is the viscosity of water. In the electric field, the emulsified droplets undergo dipole coalescence, and the coalescence rate is calculated as follows: 3 (d 2 )ceE2

[0160] K(d,,dj)=0.7(d+dj) +d| pdd,(7)

[0161] so represents the relative dielectric constant of the oil;

[0162] Therefore, the coalescence kernel function of the emulsified droplets is calculated under the

Description

dual-field coupled condition as follows:

[0163] a(dij)--)(di4j)+K(didj) (8)

[0164] The crushing kernel function

[0165] The crushing frequency formula of the emulsified droplets is as follows:

[0166] g(d)=C3 (1+q )d2 3 x a(I+ -C 4

(

[0167] 5 represents the surface tension of the emulsified droplets;

[0168] The particle size probability distribution function of the droplets can be used to calculate distribution of the particle size of the droplets, which is expressed as follows:

[0169] f$(d',d) =T exp -4.5(2dd.)I (10)

[0170] A product of formulas (9) and (10) in this embodiment represents the crushing kernel function.

[0171] The method for determining the optimal operating parameters of the dual-field coupled dewatering device provided in this embodiment is specifically implemented according to a user defined function udf (a user defined function), which is specifically as follows:

[0172] Step1: defining the coalescence rate according to the coalescence kernel function

[0173] The emulsified droplets are simultaneously acted on by the electric field and the centrifugal field in the device, so the coalescence kernel function of the emulsified droplets under the dual field coupled action is a sum of the coalescence functions under the separate action of the electric field and the swirling flow field, that is, a (di ,dj) =) (di ,dj) +K (di ,dj) . The macro DEFINEPBCOALESCENCERATE is used to define a coalescence rate of the emulsified droplets. The electric field intensity is solved by using the macro C_UDSIG (c, t, 0), and the macro C_UDMI (c, t, 0) is used to store the electric field strength for subsequent UDF calls.

[0174] The macro DEFINEPBCOALESCENCERATE is defined according to formula (8).

[0175] The C_UDMI (c, t, 0) is a macro of a value of a user-defined memory in an accessing unit or a storage unit.

[0176] The C_UDSIG(c, t, 0) is a macro that accesses a unit variable for calculating a gradient of a user-defined scalar transmission equation.

[0177] Step2: defining a crushing rate according to a crushing frequency and a probability distribution function

[0178] According to equations 9 and 10, two macros are used to define the crushing frequency and the probability distribution of the emulsified droplets, one of which is macro DEFINEPBBREAKUPRATEFREQ, and the other macro is

Description

DEFINEPBBREAKUP_RATEPDF.

[0179] The DEFINEPBBREAKUPRATEFREQ is defined according to formula (9).

[0180] The DEFINEPBBREAKUPRATEPDF is defined according to formula (10).

[0181] Specifically, the followings are provided:

[0182] In the UDF function, the macro C_UDSIG (c, t, 0) is used to calculate the electric field strength of each unit in x, y, and z directions, and the Number of User-Defined Memory Locations is set to 4, that is, the macro C_UDMI (c ,t,0) provides four storage locations to store the electric field strength and total electric field strength in three directions for access and calls by subsequent UDF program.

[0183] Program compilation process: Define--User-Defined--Function--Compiled. coalesced and crushing kernel function codes are added to sourcefiles for compilation.

[0184] Population balance model (PBM) setting: opening Population Balance, checking Discrete Method, setting the number of dispersed phase groups, RatioExponent, and the maximum diameter and the minimum diameter, checking the Aggregation Kernel option, selecting User-Defined, and loading the coalescence function into PBM; similarly, checking the Breakage Kernel option, selecting User-Defined, and loading the crushing frequency function and a probability density function into the PBM.

[0185] Step3: outputting the particle size of the droplets in the form of Sauter average diameter to the flow field equation.

[0186] Specifically, the followings are provided:

[0187] Define-Phases-Secondary Phase is executed to change the diameter of the dispersed phase to sauter-mean to realize communication between the PBM and the flow field equation.

[0188] The boundary conditions and parameter settings are determined in the following manner, specifically as follows:

[0189] (1) Entry boundary conditions:

[0190] An inlet boundary is a speed inlet. The flow rate of the two inlets is the same, Qi=2.4, 3.2, 4, 4.8m 3/h. A normal speed is calculated to be 6 m/s, 8 m/s, 10 m/s, and 12 m/s, and the normal speed in the other two directions is 0.

[0191] (2) Outlet boundary conditions: an outlet boundary is free outflow, and the underflow fraction is set to 10 %.

[0192] (3) Wall boundary conditions: no-slip boundary conditions are used at a wall, and a region near the wall is processed using a standard wall function.

[0193] (4) The particle size of the droplets is divided into 10 groups. The median diameter of the emulsified droplets is 100 tm. The size distribution of cumulative droplets at the inlet droplets is

Description

shown in FIG. 5, and FIG. 5 is a schematic diagram of size distribution of the cumulative droplets of the inlet droplets.

[0194] (5) The physical properties of oil and water are shown in Table 1.

[0195] Table 1: Physical properties of oil and water at 20 °C

g(kg.m 3 ) p,(kg.m-3 ) p(mPa.s) p,(mPa-s) e,(F -m-) c,(F-m-')

[0196] 863 988.2 16.8 1.3 2.8 81.5

[0197] The electric field is set to have 50% of a duty ratio, t 0 kV, 8 kV, 11 kV, and 13 kV of a voltage amplitude, and 6 Hz of a frequency. For the transient state of the model, the size distribution and separation efficiency of the droplets in the coupled device at 15 s are studied. Pressure-speed coupling adopts SIMPLEC algorithm. A gradient item chooses Least Squares Cell Based algorithm. A pressure item chooses PRESTO algorithm. Momentum, Volume Fraction, Turbulent Kinetic Energy, Turbulent Dissipation Rate and Reynold Stresses choose QUICK algorithm.

[0198] Finally, results of the numerical simulation are carried out as follows:

[0199] (1) determining the optimal electric field strength

[0200] When the inlet has a flow rate of 10 m/s, the particle size distribution of a longitudinal section (x=0 mm) of the coupled device under different voltages is shown in FIG. 6. It can be seen from the drawings that there are many tiny droplets that are difficult to separate in an axis region of the coupled device. These tiny droplets are dispersed in the oil and gathered in the axis region of the device. As the electric field strength increases, a region of the particle diameter of the small droplets gradually decreases, which shows that the electric field makes the small droplets in the emulsified oil coalesce to increase, reduce the water content in the oil phase, and improve the separation efficiency. Compared with FIG. 6(a), after the electric field is applied, the particle size of the droplets in the swirling flow chamber section of the device increases obviously. The higher the voltage, the larger the particle size. This is because the electric field increases the coalescence rate of the emulsified droplets, which increases the particle size of the droplets, thereby facilitating the subsequent swirling flow separation. In addition, because the electric field is a coaxial cylindrical electric field, in the electric field region, the particle size of the droplets gradually decreases in a radial direction.

[0201] FIGS 6(a)-(d)show a cloud diagram of the Sauter average particle size on a longitudinal section when different voltages are applied to the coupled device, respectively, where FIG. 6(a) OkV, FIG. 6(b) 8kV, FIG. 6(c) 11kV, FIG. 6(d) 13kV.

[0202] FIG. 7(a)-(d) shows the volume fraction distribution of the droplets inside the coupled

Description

device with cross-sections z=812 mm, 700 mm, 600 mm and 100 mm under different voltages. In FIG. 7(a), compared with the case of no electric field, when U=13 kV, the volume fraction of large droplets (greater than 400 m) are approximately doubled, while the volume fraction of small droplets (less than 100 m) is reduced by 40%. This is because the application of the electric field causes dipole coalescence of the droplets, and the coalescence rate increases with an increase in the electric field strength. At the z=700 mm section, because the large cone section is a swirling flow acceleration section of the coupled device, a turbulence intensity and a shear force are relatively large, which causes the droplets to crush, and the volume fraction of the large droplets is slightly reduced. The small cone section of the device is a section formed by a secondary swirling flow acceleration section and a reverse flow. Because a cone angle is relatively small, a swirling flow acceleration effect is relatively small, which is not enough to form a large turbulence intensity, but slightly increases the collision frequency between the droplets and causes the particle size of the droplets to increase. In addition, although the collision frequency of the droplets in a tail tube section is relatively small, the particle size is relatively large, and a large agglomeration rate can still be obtained, so that the size distribution of the droplets does not change much with an increase in voltage, as shown in FIG. 7(d) .

[0203] FIGS 7(a)-(d) show the volume fraction distribution of the droplets under different voltages, respectively. FIG. 7(a) z=812 mm, FIG. 7(b) z=700 mm, FIG. 7(c) z= 600 mm, FIG. 7(d) z=100 mm.

[0204] As shown in FIG. 8, FIG. 8 shows the separation efficiency and the average particle size of the coupled device under four different voltages. It is not difficult to see from the drawings that as the voltage increases, the dewatering efficiency of the device gradually increases. When U=11kV, the dewatering efficiency reaches its peak value at the time, and then stays steady. This is because higher voltage can get more large droplets, but an increase in the particle size of the droplets also increases the crushing rate of the droplets, causing the separation efficiency not to continue to increase as the voltage rises. In addition, a change trend of the particle size of the droplets with change in the voltage is basically consistent with a change trend of separation efficiency, which further proves that the particle size of the droplets is one of the important factors affecting the separation efficiency. Compared with the case of no electric field, when U=11kV, the average particle size increases by 60%, and the separation efficiency increases by 27.5%.

[0205](2) Determining the optimal flow rate of the inlet

[0206] When U=11 kV and the inlet has 6 m/s , 8 m/s , 10 m/s , and 12 m/s of a flow speed, respectively, FIG. 9 shows the cloud diagram of the distribution of the particle size of the droplets of the longitudinal section of the coupled device. It can be seen from FIG. 9 that as the flow rate of

Description

the inlet decreases, the particle size of the droplets in the electricfield region gradually increases. This is because the flow rate of the inlet is reduced, which reduces the axial speed of the emulsified oil in the coupled device and increases the coalescence time of the oil in the electric field, so that the coalescence of the droplets increases as much as possible. Moreover, a smaller flow rate of the inlet causes a smaller turbulence intensity, so that the large droplets are broken as few as possible, which is beneficial to the separation of oil and water. However, because of the decrease of the flow rate of the inlet the tangential speed of the fluid inside the device is directly reduced. The oil-water separation performance of the coupled device is reduced, resulting in an increase in the droplets in an axis region of the coupled device, an increase in the water content of the oil in the overflow port, and a decrease in the separation efficiency of the device.

[0207] FIGS. 9(a) - (d) show cloud diagrams of the Sauter average particle size distribution on the longitudinal section of the coupled device at different flow rates of the inlet, respectively. FIG. 9(a) 6 m/s, FIG. 9(b) 8 m/s, FIG. 9(c) 10 m/s, FIG. 9(d) 12 m/s.

[0208] FIGS 10 (a)-(d) are the volume fraction distribution of the droplets at four different flow rates of the inlet when cross-sections z=812 mm, 700 mm, 600 mm and 100 mm and U=11 kV. In the swirling flow chamber section of the device, because of the increase in the flow rate of the inlet, the axial speed of the fluid inside the device is increased, the residence time of the emulsified droplets in the electric field is reduced, and the volume fraction of large droplets is gradually reduced. By comparison, it is found that compared with the situation when v=12 m/s, when v=6 m/s, the volume fraction of the small droplets is reduced by about 45%, and the volume fraction of the large droplets is increased by about 40%. In FIG. 10(b), the volume fraction of the large droplets is slightly reduced compared to the swirling flow chamber section. This is because the turbulence intensity and the turbulent diffusion rate of the large cone section are larger, which increases the possibility of crushing of the large droplets. Compared with the large cone section in FIG. 10(c), because of the smaller turbulence intensity of the small cone section, the droplets collide and coalesce, and the volume fraction of the large droplet increases slightly. The volume fraction distributions of the droplets at the four inlet speeds in the tail tube section are similar, which is consistent with the reason mentioned in FIG. 7(d).

[0209] FIGS. 10(a)-(d) show diagrams of the volume fraction distribution of the droplets of different flow rates of the inlet, FIG. 10(a) z=812 mm, FIG. 10(b) z=700 mm, FIG. 10(c) z =600 mm, FIG. 10 (d) z = 100 mm.

[0210] As shown in FIG. 11, FIG. 11 shows the separation efficiency and the average particle size of the droplets of the coupled device at different flow rates of the inlet. As the flow rate of the inlet increases, the separation efficiency of the coupled device first increases, reaches a peak at 10 m/s

Description

and then decreases. This is because the increase in the flow rate of the inlet increases the tangential speed of the fluid inside the device in a low-speed section, which improves the separation performance. The flow rate of the inlet continues to increase, which increases the intensity of turbulence inside the device and increases the crushing rate of large droplets, resulting in a decrease in separation efficiency. And the average the particle size of the droplets gradually decreases with an increase in the flow rate of the inlet, which is consistent with the conclusion obtained by analyzing the particle size distribution inside the coupled device.

[0211] From the above analysis, it can be concluded that the electric field has a more obvious influence on the distribution of particle size of the droplets. When U=11kV, the separation performance of the coupled device is the optimal. Compared with the case of no electric field, the average particle size of the droplets increases by 60%, and the separation efficiency increases by 27.5%. The flow rate of the inlet is directly related to the coalescence time of the emulsified droplets in the electric field and the oil-water separation efficiency. When the flow rate of the inlet is 10 m/s, the separation efficiency is the maximum.

[0212] The method provided in this embodiment is verified by the following tests, which are specifically as follows:

[0213] No. 46 turbine oil was selected as the continuous phase. Water was a dispersed phase, and Span-80 was taken as the emulsifier, added to a mixed solution at 5 g/L of a concentration to prepare an oil-water mixture with 10 % of a water content. In a configuration process, intermittent stirring was used. When an agitator did not work, real-time sampling and analysis of the particle size of the droplets were carried out. When ddsd,50=100pm, the agitator stopped working, and pus the configured emulsified liquid into a storage tank for later use. The dewatering tests under different voltages and the different flow rates of the inlet were carried out by adjusting a screw pump inverter and a high-voltage pulse power supply. After the separation was ended, samples were taken from an overflow tank. A petroleum water content meter (SYD2122C) is used to detect the water content of the sample, and formula (7) was finally used to calculate the dewatering efficiency of the device. In order to eliminate the influence of short-term fluctuations and a sampling depth on the water content of the sample, a liquid level was divided into 3 layers, and the samples were taken from each layer every 3 min with a total of three times, and its average value was the water content of the oil in the overflow tank.

[0214] r (

[0215] where 9wis the water content of the emulsified liquid.

[0216] Table 2: Separation efficiency of the device under different voltages

Description

[02171

Voltage kV 0 8 11 13 Separation 60.8 77.3 90.5 89.6 efficiency %

[0218] Table 3: the separation efficiency of the device under different flow rate of the inlets,

[02191

The flow rate of 6 8 10 12 the inlet m/s Separation 68.1 80.7 90.5 85.9 efficiency %

[0220] Tables 2 and 3 are test results of the dual-field coupled dewatering device at different voltages and the different flow rates of the inlet, respectively. Compared with FIGS 8 and 11, it can be seen that numerical results are consistent with experimental results, indicating that the method of determining the optimal operating parameters of the dual-field coupled dewatering device proposed in the present invention is reasonable and feasible.

[0221] The forgoing embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or alterations made by the person skilled in the art on the basis of the present invention are all within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to claims.

Claims

1. A method for determining optimal operating parameters of a dual-field coupled dewatering device,

comprising the following steps of: establishing a grid model of the dual-field coupled dewatering device;

constructing a dynamic coalescence model of emulsified oil droplets under a dual-field coupled action; setting the initial conditions and simulation conditions for the grid model calculation of the dual-field

coupled dewatering device;

setting operating parameters of the coalescence and crushing process of the emulsified droplets in the dual-field coupled dewatering device;

calculating the separation efficiency of the emulsified droplets under the different operating parameters

according to the grid model; and

determining the operating parameters when the coupled device achieves the optimal separation effect according to the separation efficiency;

the dynamic coalescence model is established by combining a flow field control equation, an electric field control equation, and coalescence and crushing kernel functions; and the coalescence kernel function is established according to the following steps: calculating a coalescence rate according to the following formula: (d,dj)=h(di,dj)e(di,dj) (1) where X(di , dj) represents the coalescence rate of two droplets with diameters di and dj;

h(di,i, dj) represents the collision frequency of droplets with diameters di and dj, respectively; e(di, dj) represents the coalescence efficiency of two droplets with diameters di and dj; di, dj represent the diameters of any two droplets; a collision frequency function is established according to the following formula:

h(di, d,)= C 1/3(d,+d) 2 d| +d|2)" I1+ rp, 2 , represents the relative dielectric constant of the emulsified liquid; and <pw represents the volume fraction of water; C 1 represents a constant; a liquid film drain model is used to calculate the coalescence efficiency of the emulsified droplets in a

turbulent flow field according to the following formula:

e(d,,d)=exp- 0.7Iii,(i1 2 ,hf12)(3) pOElI3d|ll dj[1(d,+d 2 )

where po represents the density of oil; hi is the initial thickness of a liquid film; hfis the critical thickness at which the liquid film ruptures; p, represents the viscosity of water; the coalescence rate of the emulsified droplets is calculated in an electric field according to the 3 2 2 2 K(djd) =0.7(d, +dj) (d +dj )eccsE udi dj (4) following formula: where, so represents a vacuum dielectric constant; p represents the viscosity of a mixed liquid; so represents the relative dielectric constant of the oil phase; E represents an electric field strength; the coalescence kernel function of the emulsified droplets is calculated under the dual-field coupled condition according to the following formula: a(di 4j) =(di Oj)+K(di j)0

2. The method for determining the optimal operating parameters of the dual-field coupled dewatering device according to claim 1, wherein when the separation efficiency of the emulsified droplets under the different operating parameters is calculated according to the grid model, the particle size distribution and the average particle size of the emulsified droplets are still calculated.

3. The method for determining the optimal operating parameters of the dual-field coupled dewatering device according to claim 1, wherein the grid model is established according to the following steps: using tetrahedral and hexahedral hybrid grids to perform grid division a model of the dual-field coupled dewatering device; densifying a grid at which the electric field and the flow field are coupled; densifying a grid at a tangent point of an inlet end and a swirling flow cavity.

4. The method for determining the optimal operating parameters of the dual-field coupled dewatering device according to claim 1, wherein the crushing kernel function of the emulsified droplets is a product of the droplet crushing frequency and the probability density function, the droplet crushing frequency is calculated according to the following formula: g(d)=C 3 ( exP[C4 /(6) (1p)d, pxe d =( where , represents the relative dielectric constant of the emulsified liquid; and <p, represents the volume fraction of water; pw represents the density of water; g(d) represents the crushing frequency of the droplets with diameter d; C 3 represents a constant; C4 represents a constant; a represents an interfacial tension; d represents the diameter of the droplet; the probability density function of the droplet distribution is calculated according to the following formula: pi(d',d) = 4.6~ex (2d3 d.3)21 4 exp -4.5(2'-d32 d 3d6 (7 where, p(d', d) represents a probability density function of a droplet with a diameter of d' that crushes into a droplet with a diameter of d; d' represents the diameter of the droplet.

5. The method for determining the optimal operating parameters of the dual-field coupled dewatering device according to claim 1, wherein the initial conditions of the dual-field coupled dewatering device set boundary conditions and operating parameters in the following manner, specifically as follows: setting inlet boundary conditions of the dual-field coupled dewatering device; setting outlet boundary conditions of the dual-field coupled dewatering device; setting wall boundary conditions of the dual-field coupled dewatering device; setting the physical parameters of oil and water; setting the initial particle size and distribution of the droplets; and setting the duty cycle, the voltage amplitude and the frequency of the electric field.

6. The method for determining the optimal operating parameters of the dual-field coupled dewatering device according to claim 2, the operating parameters include electric field strength parameters acting on the dual-field coupled dewatering device; and an electric field strength is determined according to the following steps: determining flow rate parameters of the inlet of the coupled device; adjusting the electric field strength; obtaining the cloud diagram of the distribution of the particle size of the droplets of the coupled device; determining the separation efficiency of the emulsified droplets in the electric field; and obtaining an electric field intensity at the maximum separation efficiency as an optimal electric field intensity parameter.

7. The method for determining the optimal operating parameters of the dual-field coupled dewatering device according to claim 2, the operating parameters include flow rate parameters of the inlet parameters acting on the dual-field coupled dewatering device; and the flow rate parameters of the inlet are determined according to the following steps: determining the electric field strength of the coupled device; adjusting an flow rate of the inlet; obtaining the cloud diagram of the distribution of the particle size of the droplets of the coupled device; determining the separation efficiency of the emulsified droplets in the electric field; and obtaining an flow rate of the inlet at the maximum separation efficiency as an optimal flow rate parameter of the inlet.