Control System Design for Furnaces with Multiple Parallel Passes

Abstract

Systematic control system design for process furnaces with multiple parallel tube-passes is addressed. The control objectives are to regulate furnace outlet temperature while holding the temperature rise across the individual tubes to be the same (tube-pass heat load balancing). With respect to furnace throughput (Ftot), two operating scenarios are considered: (1) Ftot is held constant, and (2) short-term transient variability in Ftot is acceptable. Alternative control structures, CS1 for scenario 1 and CS2–CS3 for scenario 2, are synthesized and quantitatively evaluated for their closed-loop dynamic performance to expected load/servo changes. The scenario 1 heat load balancing problem is shown to exhibit strong multivariable dynamic interaction, and the control benefit of dynamic matrix control is quantified. On the basis of the results, the suitability of the alternative control systems in industrial settings is discussed.