An advanced multivariable controller (MVC) was recently implemented at the ethylene unit of the Condea Vista chemical plant in Lake Charles, Louisiana. This article discusses the "lessons learned" while implementing the system, which greatly improved the performance of the ethylene unit. First, the different project phases are profiled, from an initial benefit study through commissioning and training. Then we list and describe critical MVC success criteria, such as production increase, application uptime and operator acceptance. We also summarize the common mistakes to be avoided for a successful MVC project. The scope of the project included the ethylene cracking furnaces, refrigeration system and the product recovery train. A "Feed Maximizer" or "Composite Linear Program" (CLP) was implemented to help run the entire unit at maximum feed. The MVC application improved unit operations, substantially increased production while reducing steam and fuel gas usage, achieving or exceeding the expected benefits determined from the initial study. While the final implementation was successful, some lessons learned from this implementation will make future applications even more efficient.
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