superheated steam drying.pdf

Arun S Mujumdar, National University of Singapore and Sakamon Devahastin KMUTT, Bangkok, Thailand 2008 Superheated Steam Drying An Emerging Drying Technology OUTLINE ? Introduction to S uperheated S team D rying (SSD) ? Basic principles ? Classification and selection of SSD ? Selected applications of SSD ? Closure Resources ? See chapter on Superheated Steam Drying In handbook of Industrial Drying. Ed. . Mujumdar, CRC Press, USA, 2006, 1280 pp ? See chapter in Guide to Industrial Drying, . Mujumdar, Color Publications, 2004? Special issues on SHSD of Drying Technology journal, 2007. SUPERHEATED STEAM DRYING (SSD) ? Proposed over 100 years ago; received serious attention only during the past 20-30 years ? Uses superheated steam instead of hot air or combustion/flue gases in a direct (convection) dryer ? plex equipment than hot-air drying system;leak- proofing needed; feed/discharge can be difficult ? energy consumption (if exhausted steam can be used elsewhere in the process and not charged to dryer) ? Better product quality (in most cases);Safe operation, no fire/explosion hazard; no oxidation SUPERHEATED STEAM DRYER (Contd) ? If steam pressure is kept constant and more energy is added, its temperature increases and saturated steam es superheated steam (SHS) ? If extra heat can be transferred to an available heat sink, SHS returns to saturated conditions ? Any convection dryer can be made into SHSD . fluidized bed, flash, rotary, conveyor type, spray, impinging jet; opposing jets (impinging streams) etc. Additional heat sources . radiation, conduction, MW etc can also be added ? Low, near-atmopsheric or high pressure operation possible Closed steam drying system Recycled steam Fan/blower Direct use of steam Energy recovery via heat exchanger Removal of condensate Heater purged steam steam from boiler Typical SSD schematic SUPERHEATED STEAM DRYER Saturated Steam Feed Saturated Steam Feed Assume 100°C, 1 bar; H = 2,690 kJ/kg Ste