QUALITY CONTROL OF POLYETHYLENE POLYMERIZATION REACTOR M. Al-haj Ali, Emad M. Ali CHEMICAL ENGINEERING DEPARTMENT KING SAUD UNIVERSITY

Motivation Production of Various Grades of Polymer Optimum Grade Transition Methods: Open-loop optimization Feedforward-feedback control

Motivation Industrial Practice: Grade is maintained by controlling p M2 /p M1 and p H2 /p M1 Different grades have different gas ratios Direct Measurement of MI and Density Cost effectiveness Soft sensors

Process

Process Model McAuely Model Partial pressure dynamics Bed Temperature dynamics Recycle Temperature dynamics Benda correlation Instantaneous MI and Density correlation Sato et al Model Dynamic MI and Density

Mathematical Equations

Mathematical Equations … (1) (2) (3) (4)

Nonlinear Model Predictive Controller P: Prediction horizon M: Control Horizon  : output weights  : Input weights

Control Horizon

Robustness Additive correction: Kalman filter:

Control Objective Controlled Variables: MI Density Production rate Manipulated Variables: F M1 F M2 F H2 F c

Simulation Results Perfect model  M=1, P=2,  T  hr   =[ ]   =[ ]

Manipulated Variables

Simulation Results Imperfect Model: +10% error in reaction rate constant +5% error in  parameters

Manipulated Variables

Conclusions The settling time for MI ranges between 15 to 26 hours. The settling time for the polymer density ranges between 16 to 18 hours. Fastest response: T=0.1, P=M,  =[ ] large gas inventory, long residence times, and broad residence time distributions Molecular weight distribution control

Thank you

Supplementary results