Dual-Stage Drying Process of Lignite Using Pilot Scale Coal Rotary Dryer

In conventional rotary drying process, lignite is fed into the drum with rotary-valve feeder and hot flue gas is injected concurrently at the bottom of the feeder. It is called single-stage drying since lignite is passed through one-step drying process. This study presents dual-stage drying process in which the primary dried coal is reintroduced into the rotary drum which results in secondary dried coal. Its effect on particle size distribution and total moisture at various feed mass flow rates ranging from 325 to 500 kg/h were investigated. The results show that total moisture of lignite decreased significantly for both single-stage (23.9%) and dual-stage drying (11.7%) without any spontaneous combustion even at excessive temperature as high as 188°C. Recirculation of flue gas creates less oxidative air which ranged from 16.5% to 19.7% inside the rotary drum. Standard deviation of moisture content implies that dual-stage drying process is able to reduce variation in moisture content which means better drying consistency.