Quality inferential control of an industrial high density polyethylene process

The melt index (MI) is an important quality variable of control in polyolefin processes. However, it is difficult to measure this variable at frequent and regular sample intervals. A practical on-line inferential scheme is proposed in this paper for predicting the MI using secondary on-line measurements. This on-line MI inferential estimation scheme is combined with a quality control system that utilizes a two-degree of freedom cascaded model predictive controller. The proposed system has been successfully evaluated, under regulatory as well as tracking conditions, on an industrial poly olefin operation.