CN-121540592-B - On-line viscosity monitoring method for regenerated polyester homogenization kettle based on ultrasonic transmission

CN121540592BCN 121540592 BCN121540592 BCN 121540592BCN-121540592-B

Abstract

The invention relates to the technical field of high polymer material processing and process detection, and discloses an ultrasonic transmission-based on-line viscosity monitoring method for a regenerated polyester homogenization kettle, which comprises the steps of constructing a multi-channel ultrasonic transmission sensing array in the homogenization kettle, acquiring the acoustic propagation characteristics of a melt in real time, and dynamically analyzing the intrinsic viscosity based on an acoustic velocity-attenuation joint inversion model; and further, the viscosity data is in closed-loop linkage with an executing unit such as stirring, heating and the like, and the technological parameters are regulated and controlled in a grading manner according to the deviation and the duration. The method realizes non-contact, real-time and accurate monitoring and active regulation and control of the melt viscosity of the regenerated polyester, and remarkably improves the batch consistency of the product and the intelligent production level.

Inventors

ZHANG JIAHONG
ZHANG FEIPENG
XIE LIFENG
XU ZHONG

Assignees

福建省百川资源再生科技股份有限公司

Dates

Publication Date: 20260508
Application Date: 20260121

Claims (8)

1. The method for monitoring the on-line viscosity of the regenerated polyester homogenization kettle based on ultrasonic transmission is characterized by comprising the following steps of: uniformly arranging at least 4 ultrasonic transmitting transducers on the wall surface of the barrel of the homogenizing kettle along the circumferential direction, and correspondingly arranging the same number of ultrasonic receiving transducers on the inner wall positions opposite to the ultrasonic transmitting transducers to form a multipath cross transmission sensing network; Controlling the ultrasonic transmitting transducer to transmit ultrasonic signals in a pulse modulation mode, penetrating the regenerated polyester melt and capturing the regenerated polyester melt by the ultrasonic receiving transducer; carrying out time domain envelope extraction and frequency domain spectrum analysis on the ultrasonic signals received by each transmission path, and respectively calculating ultrasonic propagation time and energy attenuation coefficient under the path; Based on the propagation time data of all transmission paths, fitting a sound velocity space distribution field in the melt by adopting a least square method; Inputting the sound velocity space distribution field and the attenuation coefficient space distribution field into an acoustic-rheological coupling inversion model which is trained in advance, and outputting an intrinsic viscosity three-dimensional distribution map of the regenerated polyester melt at the current moment; performing volume weighted average on the intrinsic viscosity three-dimensional distribution map to obtain a global intrinsic viscosity value representing the homogenization state of the whole kettle melt; Comparing the global intrinsic viscosity value with a preset target viscosity value, if the absolute value of the deviation is larger than a preset first threshold value, starting a first-stage regulation strategy to adjust the rotating speed of a stirring paddle at the bottom of the homogenization kettle, if the absolute value of the deviation is larger than a preset second threshold value and the duration exceeds 30 seconds, starting a second-stage regulation strategy to adjust the stirring rotating speed, and simultaneously, adjusting the flow of heating medium of a jacket heating system, and if the absolute value of the deviation is within a tolerance band of +/-0.5% of the target viscosity value for 60 seconds continuously, judging that the current batch reaches the homogenization endpoint and triggering a discharging control signal; in the first-stage regulation strategy, the regulating quantity delta N of the rotating speed of the stirring paddle is represented by the formula Determining, wherein dt is a derivative of time, η target is a target intrinsic viscosity value, η current is a current global intrinsic viscosity value, K p is a proportionality coefficient, a value of 15 revolutions per minute liter per gram, K i is an integral coefficient, a value of 0.5 revolutions per minute liter per gram per second; in the second-stage regulation strategy, the regulation of the flow rate of the heating medium is based on Arrhenius relation between the temperature and the viscosity of the melt Wherein eta is the intrinsic viscosity of the melt, exp is the expression form of a natural exponential function, B is a factor before referring to E a is the activation energy, R is the gas constant, T is the absolute temperature, and the required temperature correction quantity DeltaT lm is reversely deduced according to the current viscosity deviation and then the required temperature correction quantity DeltaT lm is transferred through a jacket heat transfer equation Calculating the required heat load variation, and further adjusting the opening of a heat medium control valve, wherein the heat medium is a biphenyl-biphenyl ether mixture, Q is the required heat load variation, and U is the heat transfer coefficient.
2. The on-line viscosity monitoring method for the regenerated polyester homogenization tank based on ultrasonic transmission is characterized in that an ultrasonic transmitting transducer and a receiving transducer in the multi-path cross transmission sensing network are made of high-temperature-resistant piezoelectric ceramic materials, the transducers are connected with a homogenization tank body in a sealing mode through a flange plate, double-channel metal winding gaskets are arranged at the connection positions, electric leads of all the transducers are led out through a high-temperature ceramic insulating sleeve, and the electric leads are connected into a signal conditioning module located in an explosion-proof junction box.
3. The ultrasonic transmission-based on-line viscosity monitoring method for the regenerated polyester homogenization kettle is characterized in that the signal conditioning module performs pre-amplification, band-pass filtering and analog-to-digital conversion processing on an original received signal, and the digital signal after analog-to-digital conversion is transmitted to a central processing unit, and time domain envelope extraction and frequency domain spectrum analysis are performed by the central processing unit.
4. The ultrasonic transmission-based on-line viscosity monitoring method of a regenerated polyester homogenization kettle according to claim 3, wherein the time domain envelope extraction adopts a Hilbert transform method to construct an analysis signal for each received signal sequence x (n) Where j is an imaginary unit, H [ x (n) ] represents a Hilbert transform operator, the envelope signal e (n) is defined as |z (n) |, the ultrasonic propagation time is determined by detecting the starting zero-crossing of the envelope signal e (n), in particular by finding the point in time at which the amplitude of the envelope signal exceeds the noise floor by a factor of 3, the energy attenuation coefficient α is determined by the formula And calculating, wherein L is the transmission path length, P 0 is the received signal energy of the same path in the reference state, and P is the current received signal energy.
5. The ultrasonic transmission-based regenerated polyester homogenization kettle online viscosity monitoring method of claim 1, wherein fitting a sound velocity space distribution field inside a melt by a least square method based on propagation time data of all transmission paths comprises dividing an inner cavity of the homogenization kettle into N hexahedral grid cells, establishing an MxN path-cell correlation matrix A, wherein M is the number of transmission paths, and element A ik represents the length ratio of an ith path passing through a kth cell, wherein the propagation time of the ith path is t i , the path length is L i , and the average sound velocity on the ith path B is the M-dimensional observation vector, B i is the M-dimensional observation vector of the ith path, and the sound velocity vector is solved by the least square method And synchronously adopting the same grid division and an associated matrix, taking the attenuation coefficient of each path as an observation value, inverting the attenuation coefficient of each unit by a least square method to form the attenuation coefficient spatial distribution field.
6. The ultrasonic transmission-based online viscosity monitoring method for the regenerated polyester homogenization kettle is characterized in that the construction process of the acoustic-rheological coupling inversion model comprises the steps of collecting melt samples under different temperature, pressure, molecular weight distribution and impurity content conditions in the production process of not less than 500 batches of regenerated polyester; measuring the intrinsic viscosity of each batch of samples under the standard condition of a laboratory, and synchronously recording sound velocity and attenuation data obtained by an ultrasonic transmission sensing network under the same working condition, wherein the sound velocity mean value, the sound velocity standard deviation, the attenuation mean value and the attenuation standard deviation are used as input feature vectors, the intrinsic viscosity measured by the laboratory is used as an output label, and a support vector regression algorithm is adopted to train a nonlinear mapping relation; the support vector regression algorithm employs a radial basis function kernel.
7. The ultrasonic transmission-based on-line viscosity monitoring method of a recycled polyester homogenizer of claim 1, wherein the volume weighted averaging of the intrinsic viscosity three-dimensional distribution map to obtain a global intrinsic viscosity value indicative of the state of homogenization of the whole kettle melt comprises: dividing the inner cavity of the homogenizing kettle into a plurality of hexahedral grid units, wherein the viscosity value of each unit is obtained by inversion results of at least 4 transmission paths around the unit through inverse distance weighted interpolation; The unit volume weight is determined according to the ratio of the unit volume weight to the total melt volume, the viscosity of the kth unit is eta k , the volume is V k , the total melt volume is V total , and the global intrinsic viscosity value is obtained 。
8. The ultrasonic transmission-based on-line viscosity monitoring method of a recycled polyester homogenizer according to claim 1, wherein at the initial stage of the homogenization process start-up, the system performs a rapid modeling phase: during the first 10 minutes, ultrasonic data are collected at a frequency of once every 5 seconds and the intrinsic viscosity profile is updated while the stirring power consumption and the melt temperature change rate are recorded; When the global intrinsic viscosity value change rate of three consecutive calculations is less than 0.1% per minute, the system automatically switches to steady state monitoring mode, reducing the data acquisition frequency to once every 30 seconds.

Description

On-line viscosity monitoring method for regenerated polyester homogenization kettle based on ultrasonic transmission Technical Field The invention belongs to the technical field of high polymer material processing and process detection, and particularly relates to an on-line viscosity monitoring method of a regenerated polyester homogenization kettle based on ultrasonic transmission. Background With the large-scale application of the regenerated polyester in the fields of textile, packaging, engineering plastics and the like, the melt viscosity control in the production process becomes a key link for determining the consistency of the product performance. Viscosity is used as a core index for reflecting the molecular weight distribution and chain structure of the polymer, and directly influences spinning processability, mechanical strength and thermal stability. In the homogenization kettle process of the regenerated polyester, the components and molecular chains of the melt are reconstructed under the conditions of high temperature, high vacuum and strong shearing, and the viscosity is the comprehensive characterization of the dynamic chemical-physical coupling process. Therefore, the viscosity is accurately monitored and regulated in real time, and the method is a basic premise for guaranteeing the quality stability and the process economy of the regenerated polyester. The on-line viscosity monitoring technology based on the ultrasonic transmission principle gradually becomes an important means for detecting the rheological property of the melt due to the advantages of non-contact, quick response, high temperature resistance and the like. According to the method, the complex viscosity of the medium is inverted by measuring attenuation and speed change of ultrasonic wave propagation in polyester melt, so that the defects of easiness in abrasion, easiness in blockage and serious hysteresis of a traditional rotary viscometer are overcome. However, the current ultrasonic monitoring system is limited to data acquisition and display functions, and has not yet formed deep coupling with the production process, so that the monitoring result is difficult to be converted into an effective control instruction. The method has the following problems that an operator manually adjusts parameters such as stirring rotation speed, heating power and the like according to historical experience or offline laboratory data, dynamic response cannot be realized, meanwhile, polyester melt viscosity has obvious inertia to response of process disturbance, when ultrasonic waves detect that the viscosity deviates from a target value, the reaction enters an irreversible stage, so that intrinsic viscosity between batches fluctuates greatly and the qualification rate is reduced, in addition, a fixed time sequence or open-loop control strategy is generally adopted in a homogenization process, and influences of raw material batch differences, heat history accumulation and flow field non-uniformity on a homogenization effect are ignored, so that microstructure consistency of products of each kettle is difficult to guarantee. Disclosure of Invention The invention provides an on-line viscosity monitoring method of a regenerated polyester homogenizing kettle based on ultrasonic transmission, and aims to solve the technical problems of monitoring and controlling dislocation, process response lag and uncontrollable homogenizing effect in the prior art. The method comprises the steps of constructing a multichannel ultrasonic transmission sensing array in a homogenizing kettle, acquiring acoustic propagation characteristics of the regenerated polyester melt in different spatial positions and time dimensions in real time, dynamically analyzing the intrinsic viscosity of the melt based on an acoustic velocity-attenuation joint inversion model, and simultaneously, carrying out closed-loop linkage on viscosity data obtained by analysis and a process execution unit of the homogenizing kettle, and automatically generating regulation and control instructions of stirring rate, heating power and material residence time according to a preset viscosity target interval and a dynamic tolerance zone, so that integrated control of real-time sensing, accurate judgment and active intervention of the homogenizing process of the regenerated polyester melt is realized. The method for monitoring the online viscosity of the regenerated polyester homogenization kettle based on ultrasonic transmission comprises the following steps of uniformly arranging at least 4 ultrasonic transmitting transducers on the wall surface of a barrel of the homogenization kettle along the circumferential direction, correspondingly setting ultrasonic receiving transducers with the same number at the positions of the inner wall opposite to the ultrasonic transmitting transducers to form a multi-path cross transmission sensing network, transmitting ultrasonic signals with the center frequency o