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.