(39d) Large Scale Ethylene Unit APC Using Shell Multivariable Optimizing Controller (SMOCPro)

Implementation of large, unit-wide APC controllers on Olefins units has
always been a challenge because it entails combining the dynamically
fast-response-time hot side controllers and the slow-response-time cold side
controller into a single controller.  In this paper we present experiences
using SMOCPro framework to address various Olefins
unit control objectives. SMOC^Pro computes
the dynamic solution of the whole controller each execution cycle. This
solution enables the Olefins Feed Pusher to better synchronize hot and cold
side move plans in order to hold cold-side targets more robustly and optimize
more smoothly. The implementation also involves  a furnace feed transition package that
automatically updates controller model gains, manipulated/controlled variable
limits, and other feed related parameters when a furnace switches feed type.
Online 1^st principle-based furnace effluent yield and TMT
calculations are integrated within the package. The use of Intermediate
Variables (IV) to improve dynamic model identification will also be discussed.