Читать книгу Coal-Fired Power Generation Handbook - James Speight G., James G. Speight - Страница 77

When there is need for simultaneous conveying and heating or cooling, a screw conveyor can be easily converted to a dryer or heat exchanger by providing the necessary heat to the moving solids either directly or indirectly and by removing the evaporated moisture by gentle gas flow or by application of vacuum (Osman et al., 2011).

Typically, a screw conveyor dryer consists of a jacketed vessel (generally cylinder or U-trough) in which material is simultaneously heated and dried as it is conveyed. The heating medium, usually hot water, steam, or any thermal fluid, may also flow through the hollow flights and shaft to provide high heat transfer area without the need for additional space or material.

The screw conveyor dryer is essentially a modified screw conveyor system. Therefore successful implementation of the screw conveyer dryer not only depends on the target output properties of the processed coal, but also on the screw dynamics and physical attributes. To determine a suitable screw configuration, physical characteristics of the material to be handled such as flow pattern (related to angle of repose), abrasiveness, and size must be known beforehand. Subsequently, the volumetric feed rate, screw speed, screw size, power requirement, heat requirement, and length of screw can be determined.