AM-96-42 ONE MULTIVARIABLE CONTROLLER INCREASED CAPACITY OF AN OLEFLEX”/MTBE COMPLEX

Description:

Capacity increased by more than 4.6% when one dynamic matrix controller began operating in Valero Refining Company’s MTBE production complex in Corpus Christi, Texas. This was on a plant that was already running well above design capacity due to process changes previously made on the plant. A single controller was developed to cover an OleflexTM isobutane dehydrogenation unit and an MTBE reaction and fractionation plant with the intermediate isobutylene surge drum. The overall benefit is realized by a comprehensive constrained multivariable predictive controller which properly handles all sets of limits experienced by the complex, whether limited by the front-end OleflexT” or back-end MTBE unit. The controller has 20 manipulated, 6 disturbance and 44 controlled variables, and covers widely varying dynamics with settling times ranging from twenty minutes to six hours. The controller executes each minute with a six hour time horizon. A unique achievement is intelligent handling of the surge drum level by the controller for higher average daily capacity of the complex as a whole. The OleflexTM often operates at simultaneous limits on reactor effluent compressor capacity, cold box temperature and hydrogen/hydrocarbon ratio and the MTBE at impurity in butene column overhead as well as impurity in MTBE product.