Abstract
Thermal drying from a wet solid to a dry solid is an essential intermediate step in many solids processing plants. Humidity has a major effect on dryer performance and ability to meet quality specifications, particularly for convective dryers. Humidity calculations using a psychrometric chart give an excellent short-cut method for dryer sizing. Ambient and inlet humidity affects both drying kinetics and equilibrium moisture content, especially at lower drying temperatures, and is also important in storage. Exhaust humidity measurement is also useful for tracking and controlling the progress of drying, especially as direct moisture content measurement is often difficult. However, accurate and reliable measurements are difficult due to the hot, damp and dusty environment. The recent revision of British Standard BS 1339 has helped to clarify definitions and improve calculation methods.