Automatic minimum differential pressure control for dryer cylinders

Abstract

A supply of steam is fed to a drying cylinder (10) from a steam line (20) through a steam pressure control valve (22). Condensate and steam are removed from the drying cylinder to a separator (32). The pressure of the removed steam is controlled by a steam pressure control valve (36) and the rate of condensate removal is monitored by a condensate removal monitor (48). A computer controller (16) adjusts the steam feed and removal pressure control valves to maintain the smallest differential pressure therebetween which will maintain the condensate removal rate substantially constant. The computer controller sets an initial pressure differential during an initializing step (50). In a first pressure differential adjustment step (52), the computer decreases the pressured differential in first increments until the condensate removal rate begins to decrease. In response to the decrease, the first pressure differential adjusting step increases the pressure differential by the first increment. A second pressure differential adjusting step (54) functions like the first pressure differential adjusting step but uses a smaller increment. A checking step (56) periodically increases the pressure differential by the second increment and returns the program to the second pressure differential adjusting step to reestablish an optimal pressure differential.