Enhanced control structure design for an industrial off-gas system: Simple reconfigurations benefit the economy

Abstract

For control structure design of the industrial off-gas benchmark system, application of the Skogestad's state-of-art design procedure has suggested the scrubber inlet pressure (Psi in the roaster) and one of the fan speeds (Nfan1 or N_fan2 in the furnace) as the self-optimizing controlled variables CVs. In this study, we stress and advocate the gSOC-plus-BAB approach as an enhanced design toolkit for the classical and systematical design procedure. The gSOC (global self-optimizing control) is able to efficiently solve measurement combinations as CVs with improved economic performances, while the BAB (branch and bound) algorithm serves to fast screen promising measurement subsets for large-scale problems. Using the enhanced design for the off-gas system, our new findings are to control the combination of roaster's ID fan outlet pressures, 0.494PIDfan1+0.506PIDfan2 (setpoint: −257.04 Pa), and the furnace's fan pressure difference, PIDfan1- PIDfan2 (setpoint: 0). Such simple reconfigurations can dramatically reduce the average economic loss by 53.3% for the roaster and even achieve perfect optimal control for the furnace. Both steady state and dynamic evaluations are carried out to validate the reconfigured control structures.© 2017 Elsevier Inc. All rights reserved.

Keywords

• Off-gas process
• Energy saving
• Control structure design
• Self-optimizing control
• Controlled variable