The possibility of drying in superheated steam or superheated solvent vapour has been realized for a long time but practiced very little. The advantages and disadvantages of such drying are discussed. Knowledge of equilibrium moisture content and drying rates is necessary when designing equipment for drying in superheated vapour, and some aspects of these are presented. A short discussion on large scale application of steam drying is included.
Removal of moisture in steam-fluidized, mainly steam-heated, fluidized beds makes possible significant energy savings over conventional forms of large-scale drying. The systems are described and their application to brown coal is reviewed. In this application the use of the system to permit meeting diurnal variation in power-station output, and the use of triple-effect drying to minimise coal usage and to avoid the necessity of recovering in the turbines the energy in the steam from the last dryer are discussed. Moisture-equilibrium of brown coal in superheated steam is reported. To facilitate the rapid adoption of the systems proposed, studies are being made of heat-transfer -to dried coal, of moisture equilibrium in pressurized and vacuum Downloaded by [New York University] at 01:27 17 June 2015 220 POlTER ET AL. systems, and of the use of carrier solids for drying lump materials.
I PROD IJ C T FINES Flgure 1. Pllot-plant dryer used for heat transfer measurements. When steam is not employed but air, the condenser is replaced by a bag filter.
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