Indirect thermal drying of lignite: Design aspects of a rotary dryer

An investigation of the thermal drying of lignite has been carried out, by using an indirect heat pilot rotary drum. The process aims at the productio n of dry lignite and clean steam as part of a gasification procedure. Both flighted and bare drum modes have been employed. Temperature profiles along the dryer length, the amount of evaporation (moisture conversion) and the solids residence time distribution (RTD) were measured. A non-isothermal mo del was tested under three different regimes of solids flow. Model integrat ion, by taking account of experimental amount of evaporation at dryer exit and temperature profiles along the dryer length, has been utilized in the v alidation of drying kinetics and heat transfer correlations. Model predicti ons compare satisfactorily with the operating data of an indirect heat indu strial lignite dryer. Overall heat transfer coefficients of the pilot rotar y dryer were found to agree well with those reported for direct heat dryers .