Application of a single multivariable controller to an FCCU

A number of significant benefits are realized from the design and operation of a single multivariable controller for a Fluid Catalytic Cracking Unit. A single controller has been built for the Star Enterprise FCCU No. 3 in Port Arthur, Texas. The controller includes the Feed Preheat System, the Reactor, the Regenerator, the Main Fractionator, and the Wet Gas Compression. The controller contains 17 manipulated variables, 41 controlled variables, and 1 disturbance variable. The elapse time between project initiation and final commissioning was four months including a one month delay for unit maintenance. After commissioning, it was determined in the post audit that the simple payout for the project was less than one month. The controller has maintained a high stream factor since its commissioning 8 months ago. The single large scale controller improves the reliability of the control system, permits the handling of all the interactions between independent variables, removes stability analysis from the controller design, increases the ability of the controller to address the economics of the operation, and increases the maintainability of the system relative to traditional heuristic combinations of PID controllers.