USE OF COAL DRYING TO REDUCE WATER CONSUMED IN PULVERIZED COAL POWER PLANTS

This is the third Quarterly Report for this project. The background and technical justification for the project are described, including potential benefits of reducing fuel moisture, prior to firing in a pulverized coal boiler. A description is given of the equipment, instrumentation and procedures being used for the fluidized bed drying experiments. Laboratory data are presented on the effects of bed depth on drying rate. These show that drying rate decreased strongly with an increase in bed depth as the settled bed depth varied from 0.25 to 0.65 m. These tests were performed with North Dakota lignite having a 6.35 mm (1/4 inch) top size, constant inlet air and heater surface temperatures, constant rate of heat addition per unit initial mass of wet coal and constant superficial air velocity. A theoretical model of the batch dryer is described. This model uses the equations for conservation of mass and energy and empirical data on the relationship between relative humidity of the air and coal moisture content at equilibrium. Outputs of the model are coal moisture content, bed temperature, and specific humidity of the outlet air as functions of time. Preliminary comparisons of the model to laboratory drying data show very good agreement