On conventional paper and board machines, the energy required to dry the sheet to the desired moisture target at the reel is supplied by a series of rotating, steam-heated, dryer cylinders. These cylinders, or "cans," are grouped into multiple drive sections, which go progressively faster in order to adjust for machine direction stretch and to maintain sheet tension. This module will provide a general overview of the drying section of a paper machine.
Learning Objectives
At the end of this module, you will be able to:
- Describe the design and operation of a typical multi- cylinder dryer section
- List the objectives of paper machine drying
- Define the terms "latent heat," "boiling point," "evaporation," "condensation," "superheated," and "blow-through steam"
- Identify, describe, and state the purpose of dryer syphons, dryer fabrics, pocket ventilation systems, hood makeup air and exhaust systems, and blow boxes
- Describe heat transfer and mass transfer during sheet drying
- Describe the three phases of drying - sheet heating, constant rate, and falling rate
- List the factors that affect sheet drying
- Identify and describe single-tiered and double-tiered dryer sections
- Explain the purpose of blow-through steam
- Describe the two ways blow-through steam can be recovered for reuse
- Identify and describe safety hazards and safety guidelines for multi-cylinder dryer sections