Drying Loss

As it happens so often in the paper mill, a machine that was performing to center line, quickly, in a span of about two hours, lost drying and had to slow down by 200 fpm. Since the machine was normally drying limited there was no alternative to the loss in drying except to slow the machine down. The operators checked all the obvious things such as steam flow, furnish change, hood temperature, etc. Fortunately PROdry engineers had previously performed a baseline survey on this hood. When they returned to the mill to trouble shoot the problem several anomalies were identified. Absolute humidities had generally increased. Wet end recirculation flow had increased. Calculated nozzle velocity had decreased. Supply airflow static pressures had decreased. Make-up and exhaust airflows were equally reduced. The hood balance did not change.

By identifying measured changes from the previous survey, a very valuable troubleshooting technique, it was decided to shut the machine down and perform an internal inspection of the Yankee hood particularly the recirculation damper. The inspection showed that the damper spun on its shaft to the 100% open position. This increased the recirculation airflow, raised system humidities, lowered nozzle velocities and resulted in a loss of drying.

A good baseline survey, done while the machine is running well, of any machine component is a valuable troubleshooting tool.

© 2007 PROdry Technology, Inc. Site last updated 3/7/07