Optimal program of sheet moisture control system for paper machine dryer section.

In order to overcome the large inertia of moisture control and stabilize the drying curve in paper machine dryer section, valve position control system was studied with dry air intake control as the main-loop, dryer vapor pressure control as the sub-loop together with feed-forward control. And further, a new control strategy was established in which hood supply air moisture and zero-level were respectively controlled by circulating load of exhaust air and exhaust rate of fan and dew point was controlled under the upper constraint. The results show that in comparation of conventional sheet moisture control system using the cylinder vapor pressure, the valve position control system with feed-forward control can stable sheet moisture fast. The influence of disturbance to exhaust air dew point is so low that its optimal value can be used for system design. The rapidity of dry air intake control and timeliness of feed-forward control make moisture fluctuation in sheet so small that the amount of steam and water resources can be effectively saved by optimizing the dryness setting in the quality control system of paper machine.