Multivariable Non-linear Control of Industrial LDPE Autoclave Reactors

New methods for control of industrial LDPE (low density polyethene) autoclave reactors are presented in this paper. The control system is constructed to enhance product quality optimization and improve the operability and stability of the reactor. The new control is performed at two levels. At the basic level, the reactor pressure, the temperature profile and the production rates are controlled. Quality optimization is done at the supervisory level, where set points for the basic level controller are calculated. The paper contains details on the basic level system, which is a multivariable controller derived by use of nonlinear decoupling. The properties of this controller are shown in simulations. Comparisons are made with the conventional control that was used in the plant until recently. Finally, some results are presented from the use of the new controller at Statoil´s LDPE plant in Bamble, Norway.