Polymer Processing Laboratory University of Maryland Physics Based Modeling and Control of Extrusion Paul Elkouss David Bigio

Polymer Processing Laboratory University of Maryland Motivation Control extrudate quality – anything that can be measured online Use a physically based model Closed loop control using kinematic and additional plant models to regulate the product qualities Example vis-breaking of polypropylene: –Vis-breaking = cutting of polymer chain –MWD influences product properties –Control product properties: Viscosity, Yield strength, etc. –Peroxide has very high control influence

Polymer Processing Laboratory University of Maryland Experimental Approach Polymer Optical Analysis S D Mixing Section Probe DAQ/ PC ch gap cl ap

Polymer Processing Laboratory University of Maryland Experimental System

Polymer Processing Laboratory University of Maryland Research Diagram

Polymer Processing Laboratory University of Maryland Background – Summary Simple and Complex models of extruder behavior Different models of peroxide degradation, but most are based on work by Tzoganakis FEM has been used to model degradation in the extruder (computationally intensive), but none have used lamellar modeling yet. Most open loop model structures have been determined statistically (arbitrary), but Walsh et. al. are first to use model based on kinematics.

Polymer Processing Laboratory University of Maryland 3 rd Order Plant Model Like 3 CSTR’s with transport delay Model fits for each probe Deconvolve signals to get fits for individual probes

Polymer Processing Laboratory University of Maryland RTD’s and Model Fits

Polymer Processing Laboratory University of Maryland Mean Residence Measures Mean Residence Volume Mean Residence Revolution

Polymer Processing Laboratory University of Maryland RTDs at Different Operating Conditions

Polymer Processing Laboratory University of Maryland Model Validation

Polymer Processing Laboratory University of Maryland Other Kinematic Representations RRD - Residence Rotation Distribution –The same specific throughput (Q/N) gives the same curve. RVD – Residence Volume Distribution –The curves w/o volume delay collapse to one curve –One set of shape parameters describes all conditions

Polymer Processing Laboratory University of Maryland RRD

Polymer Processing Laboratory University of Maryland Model fits in Volume Domain (RVD)

Polymer Processing Laboratory University of Maryland 3 rd Order with Different Poles Like 3 CSTR’s of different volumes with transport delay

Polymer Processing Laboratory University of Maryland An important question: What frequency disturbances can be damped by mixing process given the screw geometry? Disturbance Rejection

Polymer Processing Laboratory University of Maryland Lamellar Model One dimensional model of material transfer (Ottino et. al.) Useful for studying laminar mixing, diffusion and reaction Three dimensional flows  one dimension. Example - simplified calculations. –Relate to operating conditions –Calculate diffusion and inter-material area growth –No need to calculate reaction, or geometry

Polymer Processing Laboratory University of Maryland Background – Lamellar Model  (x)=  V x =-  x

Polymer Processing Laboratory University of Maryland System ID For determining open-loop kinematic model of plant Determine volume delay, and shape factor for sensor

Polymer Processing Laboratory University of Maryland Closed Loop Control Issues Modeling the Plant Online property measurement –What to measure –Measurement delay Control Scheme –Simple, smith predictor –Advanced control: Robust, Adaptive control –Online parameter correction

Polymer Processing Laboratory University of Maryland What is currently being done Warp time model –Compare to steady state results –Relate to operating conditions to predict the DC Gain Control Scheme –Apply adaptive control to the plant –Verify with Experiments

Polymer Processing Laboratory University of Maryland Conclusions Kinematic model is main model for the extruder The model is applicable to many different measurable quantities Additional models can be added to provide better control