The purpose of dryer can warm-up/cooldown procedures is to permit uniform expansion or contraction of all components of the dryer system in order to minimize thermal stresses in the equipment. If the dryer section is heated or cooled too quickly, damage can occur to the dryer can, steam joints, bearings, etc.
A general warm-up procedure goes something like this:
- Verify that the lubrication oil supply is on for all dryer can and felt roll bearings.
- Start by adding low temperature steam (240 °F) to each section. This is approximately 5 psig steam with a few degrees of superheat. When steamfit heads start to warm, put dryer cans at crawl speed for 1.5 hours. This should increase can surface temperature by 1-1.5 °F per minute.
- Increase steam pressure to 15 psi for 1.0 hour to expel condensate. Dryer speed can be increased to run speed during this time.
- For low steam pressure systems (<50 psi), increase steam pressure to thread/run settings. For higher steam pressure systems, slowly increase the steam pressure over the course of the next 30-45 minutes to desired pressures.
- Total warm-up can range from two to four hours depending on the starting temperature of the cans.
A more specific warm-up procedure should be defined for each machine system.
If you need more information on dryer can warm-up procedures, contact your Valmet representative.