ABSTRACT
The first feedforward control system was used in about 1925 to control boiler drum level. Feedback in the form of bias, or trim, corrects for any cumulative measurement or other error in the system. The potential applications of feedforward techniques are virtually endless, but they usually involve a distillation process. Several improvements are provided by feedforward control. The analog lead or lag unit is similar to a controller. Integral and derivative adjustments in conjunction with gain become the lead or lag adjustments. Control of the distillation process has needed improvement since the column became a key part of most chemical and petrochemical processes. The problems associated with the control of a distillation process are slow response and long dead times. Many feedforward systems have produced increased efficiencies in distillation processes and have justified their cost in a very short time. However, to achieve this, the process generally must be one that can demonstrate economic advantages through closer control.
