A Multivariable Controller for Hydrotreater Severity

A multivariable controller has been implemented to control reaction severity of the FCCU feed hydrotreater unit at the Houston, Texas refinery of Lyondell Petrochemical Company (a division of Atlantic Richfield) The controller uses four manipulated variables to control three dependent variables. Three feedforward variables are also included in the controller design, and the limits of three additional dependent variables are respected at steady state. The controller was implemented on a Honeywell 4500 process control computer using Dynamic Matrix Control (DMC), and uses commercially available software for both process identification and process control.