Reducing moisture transients in the paper-machine drying section with the mid-ranging control technique

A new control strategy using feedback control has been developed for the multi-cylinder paper dryer configuration to reduce moisture transients in the drying section. The air system in the blow boxes was used to control the fast moisture transients in the paper machine. The new control system was combined with a previously developed physical model and was then compared with a conventional moisture control system. The comparison concerned the ability to restore the moisture ratio for two different dynamic changes, a moisture disturbance and a paper grade change. By combining the conventional steam control loop with an air loop, it was possible to significantly decrease the transient of the moisture disturbance.