CN118821503B - Simulation method for flow characteristics of polyvinyl alcohol resin polymerization kettle - Google Patents
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- 238000006116 polymerization reaction Methods 0.000 title claims abstract description 119
- 238000004088 simulation Methods 0.000 title claims abstract description 67
- 238000000034 method Methods 0.000 title claims abstract description 28
- 239000004372 Polyvinyl alcohol Substances 0.000 title claims abstract description 23
- 229920002451 polyvinyl alcohol Polymers 0.000 title claims abstract description 23
- 239000011347 resin Substances 0.000 title claims abstract description 19
- 229920005989 resin Polymers 0.000 title claims abstract description 19
- 238000003756 stirring Methods 0.000 claims abstract description 62
- 239000000463 material Substances 0.000 claims abstract description 38
- 238000004364 calculation method Methods 0.000 claims abstract description 31
- 239000012530 fluid Substances 0.000 claims abstract description 31
- 238000002474 experimental method Methods 0.000 claims abstract description 15
- 229920000642 polymer Polymers 0.000 claims abstract description 15
- 230000008878 coupling Effects 0.000 claims abstract description 7
- 238000010168 coupling process Methods 0.000 claims abstract description 7
- 238000005859 coupling reaction Methods 0.000 claims abstract description 7
- 239000000700 radioactive tracer Substances 0.000 claims description 38
- 238000002156 mixing Methods 0.000 claims description 28
- 238000004422 calculation algorithm Methods 0.000 claims description 6
- 239000006185 dispersion Substances 0.000 claims description 5
- 238000012544 monitoring process Methods 0.000 claims description 5
- 238000012546 transfer Methods 0.000 abstract description 4
- 239000013064 chemical raw material Substances 0.000 abstract description 2
- 238000012545 processing Methods 0.000 abstract description 2
- 230000008569 process Effects 0.000 description 11
- 239000010410 layer Substances 0.000 description 7
- 239000007788 liquid Substances 0.000 description 5
- 230000008859 change Effects 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 3
- 239000005977 Ethylene Substances 0.000 description 3
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- HGXJDMCMYLEZMJ-UHFFFAOYSA-N (2-methylpropan-2-yl)oxy 2,2-dimethylpropaneperoxoate Chemical compound CC(C)(C)OOOC(=O)C(C)(C)C HGXJDMCMYLEZMJ-UHFFFAOYSA-N 0.000 description 2
- XTXRWKRVRITETP-UHFFFAOYSA-N Vinyl acetate Chemical compound CC(=O)OC=C XTXRWKRVRITETP-UHFFFAOYSA-N 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000003111 delayed effect Effects 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- 239000003999 initiator Substances 0.000 description 2
- 229920002689 polyvinyl acetate Polymers 0.000 description 2
- 239000011118 polyvinyl acetate Substances 0.000 description 2
- 238000012795 verification Methods 0.000 description 2
- 239000005997 Calcium carbide Substances 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 238000006136 alcoholysis reaction Methods 0.000 description 1
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000010528 free radical solution polymerization reaction Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000011229 interlayer Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000003908 quality control method Methods 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 239000006188 syrup Substances 0.000 description 1
- 235000020357 syrup Nutrition 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/20—Design optimisation, verification or simulation
- G06F30/28—Design optimisation, verification or simulation using fluid dynamics, e.g. using Navier-Stokes equations or computational fluid dynamics [CFD]
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2113/00—Details relating to the application field
- G06F2113/08—Fluids
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
- G06F2119/14—Force analysis or force optimisation, e.g. static or dynamic forces
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Abstract
The application discloses a simulation method of flow characteristics in a polyvinyl alcohol resin polymerization kettle, which belongs to the technical field of chemical raw material processing, and comprises the following steps of obtaining a plurality of groups of different polymerization kettle-stirring paddle combinations and constructing a corresponding three-dimensional simulation model; and (3) selecting a material model and a fluid model to carry out pressure-speed coupling solution on the obtained polymerization kettle-stirring paddle combination, calculating a steady-state flow field with only the polymer as a medium based on the obtained polymerization kettle-stirring paddle combination with the optimal performance, carrying out unsteady-state calculation with the obtained steady-state flow field as an initial value to further obtain the residence time distribution of the material model, and verifying a simulation result through experiments. The continuous stirring type polymerization kettle and stirring paddle structure for producing the medium-high viscosity special PVA resin is designed by carrying out simulation on the flow characteristics of fluid in the polymerization kettle, so that the stirring uniformity of materials can be realized, and the heat transfer efficiency is high.
Description
Technical Field
The application relates to the technical field of chemical raw material processing, in particular to a simulation method for the flow characteristics of a polyvinyl alcohol resin polymerization kettle.
Background
At present, most of polyvinyl alcohol production adopts a calcium carbide acetylene method process route, and the process route has high energy consumption, large pollution and low product quality. The special polyvinyl alcohol (PVA) resin by the ethylene method has the advantages of good quality, high purity, low energy consumption and the like. The ethylene process polyvinyl alcohol device uses azo or tert-Butyl Peroxypivalate (BPV) as an initiator, methanol as a solvent, vinyl Acetate (VAC) and ethylene are subjected to solution polymerization by the initiator to generate polyvinyl acetate, and the polymerization liquid is subjected to an alcoholysis process to produce a polyvinyl alcohol product.
The polymerization process of polyvinyl acetate is one of the key points of quality control, and determines the distribution of the molecular weight of the polymer, the uniformity of the particle size, the impurity content and the stability of the quality. The stirring type polymerizer is a place for polymerization reaction, and the problems of uneven mass and heat transfer, difficult control of the reaction process, uneven product quality and the like caused by the increase of viscosity often occur in the synthesis process of the high molecular polymer, so the flow field characteristic of the polymerizer plays a key role in the product quality. Many factors influence the flow characteristics of the flow field in the polymerization kettle, and a method for accurately measuring the flow characteristics of the flow field in the polymerization kettle based on the influence of various factors is lacking in the prior art.
Disclosure of Invention
One of the objects of the present application is to provide a method for simulating the flow characteristics in a polyvinyl alcohol resin polymerization vessel, which can solve at least one of the above-mentioned drawbacks of the prior art.
In order to achieve at least one of the purposes, the application adopts the technical scheme that the method for simulating the flow characteristics of the polyvinyl alcohol resin polymerization kettle comprises the following steps:
S100, combining polymerization kettles with different structures and stirring paddles of various types to obtain a plurality of groups of different polymerization kettles-stirring paddles combinations and constructing corresponding three-dimensional simulation models;
s200, selecting a material model and a fluid model which meet the requirements, and carrying out pressure-speed coupling solution on the obtained polymerization kettle-stirring paddle combination through an algorithm to obtain the polymerization kettle-stirring paddle combination with the optimal performance;
s300, calculating a steady-state flow field with only polymer as a medium based on the obtained polymerization kettle-stirring paddle combination with the optimal performance, and performing unsteady-state calculation with the obtained steady-state flow field as an initial value to further obtain the residence time distribution of a material model;
And S400, verifying a simulation result through experiments.
In the step S200, the top of the polymerization kettle with the optimal performance is a standard elliptical head, the bottom of the polymerization kettle is a W-bottom elliptical head, the stirring paddle combination with the optimal performance comprises double-folded paddles and curved-edge straight paddles, wherein the curved-edge straight paddles are positioned at the bottom of the polymerization kettle, the number of the double-folded paddles is at least one, and the double-folded paddles are arranged above the curved-edge straight paddles at intervals.
Preferably, in step S200, the material model is a single material model, the fluid model is a kappa-epsilon standard turbulence model, the blade motion of the stirring paddle is a multiple reference system, and the pressure-velocity coupling solution is performed by using a SIMPLE algorithm, wherein the inlet boundary of the polymerization kettle is inlet flow, the outlet boundary is outlet pressure, and the wall surface is processed by using a standard wall surface function.
Preferably, the step S300 is performed by adding the tracer to perform a simulated calculation of the residence time distribution, the tracer is added instantaneously at the inlet of the steady-state flow field after the calculation of the steady-state flow field converges, the concentration of the tracer at the outlet of the flow field is monitored while the unsteady-state calculation is performed, and the calculation of the residence time distribution is performed based on the duration of the tracer from the addition to the concentration towards the set value.
Preferably, the calculation of the residence time distribution is performed by monitoring the duration of time for the tracer to be added to a concentration approaching 0.
Preferably, the concentration of the tracer is monitored every time at i time within the duration from the beginning of the tracer addition to the time when the concentration tends to be set, so as to obtain the corresponding concentration c i of the tracer, and the residence time distribution is represented by a residence time distribution density function E (t), and the specific calculation formula is as follows:
。
Preferably, in step S300, after the residence time distribution is obtained, the accuracy of the simulation result is determined by calculating the dispersion σ t 2 of the residence time distribution and the number m of equivalent total mixing tanks, and the specific calculation formula is as follows:
;
;
;
Wherein, Indicating the average residence time.
Preferably, the factors influencing the flow characteristics in the polymerization kettle include the flow field distribution structure in the polymerization kettle, the rotation speed of the stirring paddles, the flow rate of the fluid in the polymerization kettle and the viscosity of the polymer, and in step S400, all the polymerization kettle-stirring paddle combinations are tested to verify the simulation results through four aspects of the flow field distribution structure in the polymerization kettle, the rotation speed of the stirring paddles, the flow rate of the fluid in the polymerization kettle and the viscosity of the polymer.
Compared with the prior art, the application has the beneficial effects that:
According to the application, through carrying out simulation on the flow characteristics of fluid in the polymerization kettle, the continuous stirring type polymerization kettle and stirring paddle structure which are in line with the production of medium-high viscosity special PVA resin are designed, so that the stirring uniformity of materials can be realized, and the heat transfer efficiency is high.
Drawings
FIG. 1 is a schematic of the overall workflow of the present application.
FIG. 2 is a schematic diagram of a three-dimensional simulation model of a conventional polymerizer according to the present application.
FIG. 3 is a schematic diagram of a three-dimensional simulation model of an optimal polymerizer according to the application.
FIG. 4 is a simulated cloud image of the flow field distribution obtained by simulation of the polymerizer shown in FIG. 2 in the present application.
FIG. 5 is a simulated cloud image of the flow field distribution obtained by simulation of the polymerizer shown in FIG. 3 in the present application.
FIG. 6 is a schematic diagram showing residence time distribution of the polymerizers shown in FIGS. 2 and 3 at different rotational speeds in accordance with the present application.
FIG. 7 is a schematic illustration of residence time distribution at various flows for the polymerizers shown in FIGS. 2 and 3 according to the present application.
FIG. 8 is a schematic diagram showing residence time distribution of the polymerizers shown in FIGS. 2 and 3 at different viscosities in accordance with the present application.
FIG. 9 is a graph showing residence time distribution obtained by simulation and experiment of the polymerizer shown in FIG. 3 in the present application.
Detailed Description
The present application will be further described with reference to the following specific embodiments, and it should be noted that, on the premise of no conflict, new embodiments may be formed by any combination of the embodiments or technical features described below.
In the description of the present application, it should be noted that, for the azimuth words such as terms "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., the azimuth and positional relationships are based on the azimuth or positional relationships shown in the drawings, it is merely for convenience of describing the present application and simplifying the description, and it is not to be construed as limiting the specific scope of protection of the present application that the device or element referred to must have a specific azimuth configuration and operation.
It should be noted that the terms "first," "second," and the like in the description and in the claims are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order.
The terms "comprises" and "comprising," along with any variations thereof, in the description and claims of the present application are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements that are expressly listed or inherent to such process, method, article, or apparatus.
In one preferred embodiment of the present application, as shown in fig. 1, a method for simulating the flow characteristics in a polyvinyl alcohol resin polymerization kettle comprises the following steps:
And S100, combining polymerization kettles with different structures and stirring paddles of various types to obtain a plurality of groups of different polymerization kettles-stirring paddles combinations and constructing corresponding three-dimensional simulation models.
And S200, selecting a material model and a fluid model which meet the requirements, and carrying out pressure speed coupling solution on the obtained polymerization kettle-stirring paddle combination through an algorithm to obtain the polymerization kettle-stirring paddle combination with the optimal performance.
S300, calculating a steady-state flow field with only polymer as a medium based on the obtained polymerization kettle-stirring paddle combination with the optimal performance, and performing unsteady-state calculation by taking the obtained steady-state flow field as an initial value to further obtain the residence time distribution of the material model.
And S400, verifying a simulation result through experiments.
It will be appreciated that the present application provides for the selection of a polymerizer-paddle combination having optimal performance through simulation of the flow characteristics of the fluid in the polymerizer. It should be noted that there are various structural types of the polymerizer, and various structural types of the stirring paddles, and different types and number combinations of stirring paddles can be adapted to a polymerizer of a single structure. Different flow characteristics can be generated when different polymerization kettles correspond to different stirring paddles, so that the optimal polymerization kettle-stirring paddle combination is found by carrying out simulation on the flow characteristics of the polymerization kettles. Therefore, the continuous stirring type polymerizer and stirring paddle structure which accords with the production of the medium-high viscosity special PVA resin is designed, the stirring uniformity of materials can be realized, and the heat transfer efficiency is higher. Of course, in order to ensure the accuracy of the simulation result, the accuracy of the simulation result can be verified by setting a comparison experiment.
It should be appreciated that there are a variety of software for performing simulations of flow characteristics in a polymerization vessel, for example Star-CD software may be used to simulate the residence time distribution of the fluid in a stirred tank polymerization vessel. For the establishment of the three-dimensional simulation model of each polymerization kettle-stirring paddle combination, the three-dimensional model of each polymerization kettle-stirring paddle combination can be firstly constructed through three-dimensional software, and the three-dimensional software used for constructing the three-dimensional model has various types, such as Solidworks, creo and the like. And then, carrying out grid division on the three-dimensional model through simulation software, wherein the grid type can be unstructured tetrahedral grids, and the number of grids needs to meet the requirement of grid independence.
In this embodiment, factors influencing the flow characteristics in the polymerizer include the flow field distribution structure in the polymerizer, the rotational speed of the stirring paddle, the flow rate of the fluid in the polymerizer, the viscosity of the polymer, and the like. In step S200, based on the material (PVA resin) used for polymerization, simulation is performed through four aspects of flow field distribution structure in the polymerization kettle, rotation speed of the stirring paddle, flow rate of fluid in the polymerization kettle and viscosity of the polymer, and a specific structure of the final polymerization kettle-stirring paddle combination with optimal performance is shown in fig. 3. Wherein, the top of the polymerization kettle is a standard elliptical head (not shown), and the bottom is a W-bottom elliptical head. The blades corresponding to the stirring blade combination of the polymerization kettle comprise double-folded blade paddles and bent-edge straight blade paddles. The number of the bent-edge straight blade paddles is one and is arranged at the bottom of the polymerization kettle, and the number of the double-folded blade paddles is at least one and is arranged above the bent-edge straight blade paddles at intervals.
It is noted that, because the bottom of the polymerization kettle is the W-bottom elliptical head, the bending of the straight blade paddles with the curved edges is W-shaped, thereby ensuring that the straight blade paddles with the curved edges can also sufficiently stir the bottom of the polymerization kettle. The specific number of the double-folded blades above the straight blade paddles with the bent edges can be selected according to actual needs, wherein one specific example is shown in fig. 3, the number of the double-folded blades is three, the adjacent double-folded blades are axially equidistantly arranged, and an included angle of 90 degrees exists between the adjacent double-folded blades in the axial projection, so that the dynamic balance stability of the double-folded blades in the stirring process is ensured.
In the embodiment, the material model comprises a single material model and a multi-material model, wherein the single material model only needs to consider one material, and the multi-material model correspondingly needs to consider multiple materials. Since the present application is directed only to the case of PVA resin polymerization, in step S200, a single material model, that is, a model in which only PVA resin polymer is considered, is used for the material model.
Meanwhile, the types of the fluid models are also various, specific choices can be determined according to the actual needs of the person skilled in the art, and in the embodiment, a kappa-epsilon standard turbulence model is preferably adopted, wherein the kappa-epsilon standard turbulence model is one of the most widely used turbulence models in the fluid mechanics, and two equations respectively describing turbulence energy and turbulence dissipation rate are adopted for simulating the turbulence motion under the high Reynolds number, and the specific principle and model structure of the kappa-epsilon standard turbulence model are known to the person skilled in the art and are not explained in detail herein. Correspondingly, in order to further improve the accuracy of the simulation result, the blade motion of the stirring paddle adopts a multiple reference system, and the pressure velocity coupling solution is carried out through a SIMPLE algorithm. Wherein, the inlet boundary of the polymerization kettle is inlet flow, the outlet boundary is outlet pressure, the wall surface is processed by adopting a standard wall surface function, and the calculated residual error is 1 multiplied by 10 -4.
In this embodiment, in order to facilitate non-steady state calculation to obtain the residence time distribution, in step S300, a tracer may be added to the fluid model, and in the simulation, the tracer is a custom-defined additional amount, and the concentration change of the tracer may be monitored to calculate the residence time distribution. Specifically, the tracer is instantaneously added at the inlet of the steady-state flow field after the calculation convergence of the steady-state flow field, and the influence of the addition time on the calculation of the residence time distribution can be reduced or avoided through the instantaneous addition of the tracer. The concentration of the tracer at the outlet of the flow field is monitored while the unsteady state calculation is performed, and the calculation of the residence time distribution is performed based on the duration of time the tracer is added from the addition to the concentration toward the set point.
It will be appreciated that the residence time distribution after the tracer is added is a function of the concentration of the tracer, so that the concentration of the tracer may be measured a number of times in succession over a period of time after the tracer has been added to the flow field to calculate a corresponding residence time distribution. The duration of the tracer measurement for the calculation of the residence time distribution may be chosen by the person skilled in the art according to his actual needs, for example the duration of the tracer from the addition to the concentration decreasing to half may be chosen for the calculation of the residence time distribution, and the duration of the tracer from the addition to the concentration tending to 0 may be chosen for the calculation of the residence time distribution. In order to ensure the accuracy of calculation of the residence time distribution, it is necessary to acquire as much tracer concentration data as possible, so for calculation of the residence time distribution in this embodiment, the duration of time for which the tracer is added to the concentration of 0 to be used as calculation of the residence time distribution may be preferable.
In this embodiment, the residence time distribution may be represented by a residence time distribution density function E (t), and then the concentration of the tracer is monitored once every Δt i time within the duration of the beginning of the addition of the tracer to the concentration trend set value, so as to obtain a corresponding tracer concentration c i for calculating the residence time distribution density function E (t), where a specific calculation formula is as follows:
。
It should be appreciated that the specific value of the interval Δt i for monitoring the concentration of the tracer may be chosen according to the actual needs of the person skilled in the art, for example, 0.5s, 1s, 10s, etc.
In this embodiment, after the residence time distribution is obtained, in order to further ensure the accuracy of the simulation result, the precision of the simulation result may be determined by calculating the dispersion σ t 2 of the residence time distribution and the equivalent total mixing tank number m, where a specific calculation formula is as follows:
。
。
。
Wherein, Indicating the average residence time.
It should be noted that the dispersion of the dwell-time distribution is used to characterize the degree of divergence of the vector field at various points in space, the smaller the value of the dispersion σ t 2 of the dwell-time distribution, the more concentrated the calculated dwell-time distribution. The equivalent total number m is a parameter describing the degree of mixing in the polymerizer and indicates how close the polymerizer is to the ideal polymerizer. The larger the value of the number m of the equivalent total mixing kettle is, the higher the mixing degree in the polymerization kettle is, the more uniform the residence time distribution of materials in the polymerization kettle is, and the improvement of the selectivity and the yield of the reaction is facilitated.
In this embodiment, as can be seen from the foregoing, factors affecting the flow characteristics in the polymerizer mainly include the flow field distribution structure in the polymerizer, the rotational speed of the stirring paddle, the flow rate of the fluid in the polymerizer, and the viscosity of the polymer. Therefore, in step S400, experiments can be performed on all the combinations of the polymerizer and the stirring paddles from four aspects of the flow field distribution structure in the polymerizer, the rotation speed of the stirring paddles, the flow rate of the fluid in the polymerizer and the viscosity of the polymer, so as to realize verification of simulation results. For ease of understanding, the process of the experiment will be described in detail below.
Specifically, in order to simplify the verification process, only experimental comparison of the optimal polymerizer-paddle combination shown in fig. 3 with the conventional polymerizer-paddle combination shown in fig. 2 will be described in detail. For convenience of description to follow, a conventional polymerizer-paddle combination is defined as an original polymerizer, and an optimal polymerizer-paddle combination is defined as a new polymerizer.
1. Defining the structural parameters of the original polymerization kettle and the new polymerization kettle.
For the raw polymerizer, it is shown in FIG. 2. The inner diameter T of the polymerization kettle is 2891.5mm, the straight Duan Gaodu is 9269mm, the bottom is flat bottom, the top is standard elliptical seal head, the diameter d of the inlet and outlet pipe is 150mm, and the liquid level height H in the polymerization kettle is 9100mm. Adopt the frame-type stirring rake FFKS, paddle diameter D is 2132mm, and the diameter of two frames is 408mm, and the bracing piece width of top and bottom is 360mm, and the diameter of two inside bracing pieces is 219mm.
For the new polymerizer, it is shown in FIG. 3. The inner diameter T of the polymerization kettle is 2800mm, the diameter of straight Duan Gaodu is 4800mm, the top is a standard elliptical head, the bottom is a W bottom elliptical head, the diameter d of an inlet and an outlet is 150mm, the height H of the liquid level in the polymerization kettle is 4066mm, the two rings of 12 groups of inner cooling pipes are uniformly distributed circumferentially, 24 groups are total, the outer diameter of an outer pipe is 133mm, and the outer diameter of an inner pipe is 114mm. Four layers of paddles are arranged, wherein the upper three layers are double-folded-blade paddles CCJ, the diameters of the paddles are 1550 mm, the bottom layers are curved-edge straight-blade paddles PTJ, the diameters of the paddles are 1400mm, and the interlayer spacing of the paddles is 950mm.
2. And defining experimental conditions.
TABLE 1 parameter Table for simulation of original polymerizer and New polymerizer
As shown in Table 1 above, eight simulated conditions 1 to 8 were defined, and the original and new polymerizers corresponded to four conditions. The four working conditions of the original polymerization kettle are respectively a simulation working condition 1, a rotation speed of a blade is 18r/min, a flow rate is 59.8m 3/h, a viscosity of a material is 2.5 Pa.s, a simulation working condition 2, a rotation speed of the blade is 28r/min, a flow rate is 59.8m 3/h, a viscosity of the material is 2.5 Pa.s, a simulation working condition 3, a rotation speed of the blade is 28r/min, a flow rate is 119.5m 3/h, a viscosity of the material is 2.5 Pa.s, a simulation working condition 7, a rotation speed of the blade is 20r/min, a flow rate is 59.8m3/h and a viscosity of the material is 10 Pa.s. The four working conditions of the new polymerization kettle are respectively simulated working condition 4, the rotating speed of a blade is 46r/min, the flow is 22m 3/h, the viscosity of a material is 2.5 Pa.s, the rotating speed of the blade is 69r/min, the flow is 22m 3/h, the viscosity of the material is 2.5 Pa.s, the simulated working condition 6, the rotating speed of the blade is 69r/min, the flow is 44m 3/h, the viscosity of the material is 2.5 Pa.s, the rotating speed of the blade is 63r/min, the flow is 22m 3/h, and the viscosity of the material is 10 Pa.s.
3. Experimental results and analysis.
(1) Results and analysis of flow field distribution experiments.
Under the working condition simulation working condition 1 of the original polymerization kettle, a speed vector field and a speed cloud chart formed by the offset frame type stirring are shown in figure 4. In the figure, the flow direction of the fluid is mainly circumferential rotation, and part of the fluid flows from the frame to the center of the shaft, so that the flow velocity of the region of the inner frame outwards is higher, and the flow velocity of the central region in the kettle is lower.
Under the simulation working condition 4 of the new polymerization kettle, a speed vector field and a speed cloud chart formed by the combined stirring paddles are shown in fig. 5. From the figure, it is found that the outer edge blades of the upper three layers of CCJ paddles discharge fluid upwards, the central position of the paddles discharge fluid downwards, the bottom paddles PTJ discharge fluid outwards along the edges, move upwards after being blocked by the heat exchange tubes, and return downwards along the axial direction, so that local fluid circulation is formed. The flow rate in the area between the upper three layers of double-hinge paddles CCJ is larger, and the flow rate in the area between the bottom layer curved-edge straight-blade paddles PTJ and the double-hinge paddles CCJ of the penultimate layer is smaller.
Comparing the speed and distribution in the original polymerization kettle and the new polymerization kettle, the original polymerization kettle mainly takes radial flow as main, the new polymerization kettle has more axial circulation, and the area with small flow velocity of the new polymerization kettle is obviously less than that of the original polymerization kettle, so the flow field distribution state of the new polymerization kettle is better than that of the original polymerization kettle.
(2) Influence of the rotational speed of the stirring paddles on the residence time distribution.
And respectively selecting different rotating speeds of the original polymerization kettle and the new polymerization kettle under fixed flow to perform experimental simulation of residence time distribution, namely selecting a working condition simulation working condition 1 and a simulation working condition 2 for the original polymerization kettle and selecting a working condition simulation working condition 4 and a simulation working condition 5 for the new polymerization kettle. The results of the experiment are shown in fig. 6 and table 2, and it can be seen from fig. 6 that the time for peak formation is advanced, i.e. the mixing rate is faster and the mixing time is shorter, by increasing the rotation speed of the original polymerizer. As can be seen from the statistics table shown in Table 2, the equivalent total mixing kettle number m of the original polymerization kettle is reduced from 1.452 to 1.326 by 8.68% with the increase of the rotating speed. Although the peak time is slightly advanced after the rotation speed of the new mixing kettle is increased, the equivalent total mixing kettle number m is reduced from 1.051 to 1.037, and only 1.33 percent is reduced. The influence of the rotating speed on the original polymerization kettle is far greater than that of the new polymerization kettle, probably because the original polymerization kettle is stirred to form radial flow mainly, the rotating speed is increased, the turbulence is enhanced, the back mixing in the kettle is enhanced, the new polymerization kettle mainly flows in the axial direction, the back mixing degree is high, the rotating speed is increased, and the liquid flowing speed is accelerated.
TABLE 2 statistical table of residence time distribution for the original and New polymerizers
(3) The effect of the flow of the fluid on the residence time distribution.
And respectively selecting different flow rates for experimental simulation of residence time distribution of the original polymerization kettle and the new polymerization kettle at a fixed rotating speed, namely selecting a working condition simulation working condition 2 and a working condition simulation working condition 3 for the original polymerization kettle and selecting a working condition simulation working condition 5 and a working condition simulation working condition 6 for the new polymerization kettle. As shown in fig. 7 and table 2, it can be seen from fig. 7 that the peak of the residence time distribution density function becomes narrower gradually by increasing the original flow rate with the fixed stirring rotation speed. When the flow is small, the curve tailing is more obvious. As can be seen from the statistics table shown in Table 2, as the flow rate increases, the equivalent total mixing kettle number m of the original polymerizer increases from 1.326 to 1.622 by 22.3%. After the flow rate of the new mixing kettle is increased, the equivalent total mixing kettle number m is reduced from 1.037 to 1.034, and the change is very small and can be basically ignored. Therefore, the influence of the flow on the original polymerization kettle is far greater than that of the new polymerization kettle, probably because the back mixing degree of the original polymerization kettle is not high, after the flow is increased, the back mixing degree of materials is further reduced under the action of radial flow, the number m of equivalent total mixing kettles is increased, the new polymerization kettle is close to the state of total mixing flow, and the influence of flow change on the mixing degree is small.
(4) Influence of material viscosity on residence time distribution.
And respectively selecting different material viscosities of the original polymerization kettle and the new polymerization kettle under the condition of keeping the unit power consumption relatively close, and performing experimental simulation of residence time distribution, namely selecting a working condition simulation working condition 2 and a simulation working condition 7 for the original polymerization kettle and selecting a working condition simulation working condition 5 and a simulation working condition 8 for the new polymerization kettle. The results of the experiments are shown in fig. 8 and table 2, and it can be seen from fig. 8 that the viscosity of the original polymerization kettle is increased, and the peak-out time is delayed, namely, the mixing rate is slower and the mixing time is longer. As can be seen from the statistics table shown in Table 2, as the viscosity increases, the equivalent total mixing kettle number m of the original polymerizer increases from 1.326 to 1.416 by 6.79%. The new mixing kettle is slightly delayed in peak time after the viscosity is increased, but the equivalent total mixing kettle number m is increased from 1.037 to 1.039, only 0.19 percent is increased, and the change is small. Therefore, the influence of viscosity on the original polymerization kettle is far greater than that of the new polymerization kettle, probably because the original polymerization kettle is stirred to form radial flow, the viscosity is increased, the turbulence of fluid is weakened, the back mixing in the kettle is weakened, the new polymerization kettle is mainly axially flowing, the back mixing degree is high, the viscosity is increased, and the flow speed of fluid is weakened.
In this embodiment, in order to further ensure the accuracy of the residence time distribution calculated by the simulation, in step S400, an experiment of residence time distribution of the tracer based on the optimal polymerization vessel-stirring paddle combination shown in fig. 3 may be performed and compared with the simulation result, and the experimental process will be described in detail below.
Specifically, parameters of a polymerization kettle and a stirring paddle are set, wherein the inner diameter T=0.5m of the stirring tank of the polymerization kettle, the ratio of the liquid level in the tank to the tank diameter is 0.7, the inlet and outlet pipe diameters are 0.02m, the stirring paddle is a double-leaf 45-degree inclined-blade paddle, the diameter of the paddle is 0.35m, the distance from the bottom of the tank to the lowest double-leaf 45-degree inclined-blade paddle is 0.18m, the flow is 5.1L/min, the stirring rotating speed is 70r/min, the experimentally simulated material adopts a mixed solution of water and syrup, the viscosity is 0.146 Pa.s, the density is 1280kg/m 3, and the concentration of the tracer is monitored at the outlet of the polymerization kettle every 10 s. Based on the parameters, the tracer concentration data of 10 seconds per interval can be obtained, the corresponding residence time distribution can be obtained through calculation, the residence time distribution obtained through experiments is compared with the simulation result, and the residence time distribution curve graph of the experiments and the simulation shown in fig. 9 can be obtained. As can be seen from fig. 9, the results of the simulation and the experimental values are relatively close, so that the results of the simulation can be considered to be more close to the real situation.
The foregoing has outlined the basic principles, features, and advantages of the present application. It will be understood by those skilled in the art that the present application is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present application, and various changes and modifications may be made therein without departing from the spirit and scope of the application, which is defined by the appended claims. The scope of the application is defined by the appended claims and equivalents thereof.
Claims (5)
1. A simulation method for the flow characteristics of a polyvinyl alcohol resin polymerization kettle is characterized by comprising the following steps:
S100, combining polymerization kettles with different structures and stirring paddles of various types to obtain a plurality of groups of different polymerization kettles-stirring paddles combinations and constructing corresponding three-dimensional simulation models;
s200, selecting a material model and a fluid model which meet the requirements, and carrying out pressure-speed coupling solution on the obtained polymerization kettle-stirring paddle combination through an algorithm to obtain the polymerization kettle-stirring paddle combination with the optimal performance;
s300, calculating a steady-state flow field with only polymer as a medium based on the obtained polymerization kettle-stirring paddle combination with the optimal performance, and performing unsteady-state calculation with the obtained steady-state flow field as an initial value to further obtain the residence time distribution of a material model;
S400, verifying a simulation result through experiments;
In performing step S300, a simulated calculation of the residence time distribution is performed by adding a tracer;
The tracer is instantaneously added at the inlet of the steady-state flow field after the calculation and convergence of the steady-state flow field;
Monitoring the concentration of the tracer at the outlet of the flow field while performing the unsteady state calculation;
every interval during the duration from the beginning of the tracer addition to the concentration towards the set point Monitoring the concentration of the tracer for one time to obtain the corresponding concentration of the tracer;
The residence time distribution is represented by a residence time distribution density function E (t), and the specific calculation formula is as follows:
;
in step S300, after the residence time distribution is obtained, the residence time distribution is distributed by dispersion And calculating the equivalent total mixing kettle number m to judge the accuracy of the simulation result, wherein the specific calculation formula is as follows:
;
;
;
Wherein, Indicating the average residence time.
2. The simulation method of the flow characteristics in the polyvinyl alcohol resin polymerizer according to claim 1, wherein in the step S200, the top of the polymerizer with the best performance is a standard elliptical head, and the bottom is a W-bottom elliptical head;
the stirring paddle combination with the optimal performance comprises double-folded-blade paddles and curved-edge straight-blade paddles, wherein the curved-edge straight-blade paddles are positioned at the bottom of the polymerization kettle, the number of the double-folded-blade paddles is at least one, and the double-folded-blade paddles are arranged above the curved-edge straight-blade paddles at intervals.
3. The simulation method of flow characteristics in a polyvinyl alcohol resin polymerizer according to claim 1, wherein in step S200, a material model is a single material model, and a fluid model is a fluid modelA standard turbulence model;
the blade movement of the stirring paddle adopts a multiple reference system, and pressure and speed coupling solution is carried out through a SIMPLE algorithm, wherein the inlet boundary of the polymerization kettle is inlet flow, the outlet boundary is outlet pressure, and the wall surface is processed by adopting a standard wall surface function.
4. The simulation method for flow characteristics in a polyvinyl alcohol resin polymerizer according to claim 1, wherein calculation of residence time distribution is performed by monitoring the duration of time for which the tracer is added to a concentration of 0.
5. The method for simulating the flow characteristics in a polyvinyl alcohol resin polymerization vessel according to claim 1, wherein the factors affecting the flow characteristics in the polymerization vessel include a flow field distribution structure in the polymerization vessel, a rotational speed of a stirring paddle, a flow rate of a fluid in the polymerization vessel, and a viscosity of a polymer;
Then in step S400, experiments were performed on all the polymerizer-paddle combinations to verify the simulation results through four aspects of flow field distribution structure in the polymerizer, rotational speed of the paddles, flow rate of fluid in the polymerizer, and viscosity of the polymer.
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