Observations from Testing Dryer Section Performance, 1992 Engineering Conference Proceedings

Performance testing can be used to identify problem areas in the paper machine dryer section which affect sheet quality, moisture profiles, and production rates. Dryer surface temperatures and cross-machine profiles, sheet temperatures, and pocket humidity levels and profiles are some of the tools used for documenting dryer section performance. This paper provides examples of common drying problems which can be diagnosed by performance testing.

Dryer surface temperatures and profiles provide an indication of condensate removal and heat transfer from the dryers. The effects of improperly sized syphons and condensate drop piping, insufficient differential pressures, improper syphon clearance, unfelted dryers, insufficient dryer fabric tension, and improper dryer bar installation are demonstrated. Sheet temperatures can be used to determine drying zones and the effects of poor wet end graduation and overdrying into the size press.

High and non-uniform pocket humidities can reduce drying rates and affect reel moisture profiles. The effects of fabric permeability, pocket ventilator operation, air flows through the hood, opening and closing hood doors, and felt roll position in the pocket are discussed. The limited ability of profiling pocket ventilators to correct moisture profiles is also shown.