BETTER APPROACH TO DISTILLATION CONTROL.

The article describes ″Fractionic″ , a modular fractionation (distillation) control system developed at the Texas City Refinery of the Amoco Oil Company. The material balance section is devoted solely to the determination of bottoms and overhead product flows. The energy balance section is devoted solely to the determination of heat input at the reboiler. The reflux section is devoted to the control of reflux only. It should be noted that there are no independent variables. All column parameters are determined by feed rate and composition, and product specifications. The Fractronic modules that make up the total system are asembled with the operator's panel, trend recorders, temperature converters, power supplies and field termination strips into a free-standing, self-contained cabinet. This system is then checked as a unit in the shop and usually used for operator training before installation. Due to the functional layout and the procedureless operation of the panel, operator training consisting of one 4-hour session has proven quite adequate. Most of the systems now in service have been installed during normal operations by transferring one loop at a time. This has typically taken about four hours to completely transfer to Fractronic control, and after a day or so of tuning, the systems are usually operating satisfactorily. The system is extremely tolerant of large feed rate and composition changes and usually maintains product specifications even during severe unit upsets.