13.07.2015 Views

Assessment and Future Directions of Nonlinear Model Predictive ...

Assessment and Future Directions of Nonlinear Model Predictive ...

Assessment and Future Directions of Nonlinear Model Predictive ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

408 B.A. Foss <strong>and</strong> T.S. Scheicritical areas: modelling, state estimation, formulation <strong>of</strong> the control problemitself <strong>and</strong> implementation issues. The paper ends with some conclusions.2 Reference BaseThe reference base contains a number <strong>of</strong> industrial applications <strong>of</strong> NMPC in avariety <strong>of</strong> processes. Some examples are:• A system for optimization <strong>of</strong> suspension PVC polymerization processes hasbeen implemented on two large (140 m3) autoclaves located at Hydro Polymers’plant in Porsgrunn, Norway. The system is characterized as follows: Itcontains a rather detailed nonlinear model <strong>of</strong> the polymerization reactor. Thereactor model includes reaction kinetics, thermodynamic calculations for thefour-phase suspension process, quality parameters <strong>and</strong> energy balances forthe suspension <strong>and</strong> cooling systems. The application optimizes the temperaturereference trajectory <strong>and</strong> the amount <strong>of</strong> initiators charged to the reactorin order to initiate the polymerization process. The optimization is based onan economic criterion which includes the batch time as well as cost <strong>of</strong> initiators.The process is highly exothermic, <strong>and</strong> the purpose <strong>of</strong> the optimizationis to minimize the batch time without exceeding available cooling capacity<strong>and</strong> without using an inhibitor to slow down the polymerization process.The optimization is performed once for each batch cycle, <strong>and</strong> the temperaturepr<strong>of</strong>ile, which consists <strong>of</strong> approximately 80 ”straight line segments”, isoptimised for the entire batch under a number <strong>of</strong> constraints imposed by thequality specifications <strong>of</strong> the various PVC products. Based on logged data afew model parameters are estimated as functions <strong>of</strong> conversion. The systemis implemented using Cybernetica’s NMPC <strong>and</strong> batch optimisation platform.• Three NMPC applications for stabilization <strong>and</strong> quality control <strong>of</strong> the Borealispolypropolyne plant in Schwechat, Austria have been developed <strong>and</strong> implementedin cooperation with Borealis’ personnel. The implementations arebased on nonlinear first-principles models <strong>of</strong> the polyolefine plant (includingthree different polymerization reactors), <strong>and</strong> on Borealis in-house system formodel predictive control (BorAPC). The system is characterized as follows:The three MPC applications comprise a multivariable control system with alltogether 11 control inputs <strong>and</strong> 19 controlled outputs. The nonlinear modelconsists <strong>of</strong> 77 states which are estimated on-line together with a few modelparameters.• NMPC <strong>of</strong> a base-catalyzed phenol-formaldehyde batch polymerization processhas been implemented. The system is based on a rigorous model <strong>of</strong>the polymerization reactor. The system is implemented at Dynea’s plant inSpringfield, Oregon, USA. The model for this condensation polymerizationprocess includes reaction kinetics, thermodynamics, population balances forfunctional groups <strong>and</strong> energy balance for the reactor <strong>and</strong> cooling system.Safety is an important issue <strong>and</strong> one driving force for implementing NMPC.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!