Investigation on the Characteristics of the Mixed Bed Materials in a CFB Boiler

The mixed bed materials of charcoal and quartz sand were used in a circulating fluidized bed boiler, which was a subsidiary reactor in a bio-oil production system using wood sawdust as raw material. The understanding of fluidization and combustion characteristics of the mixed bed materials is very important to enhance heat transfer and improve the performance of the whole bio-oil production system. Based on experimental results, the average diameter of charcoal and quartz sand are 0.098 mm and 0.142 mm respectively. Both minimum fluidized velocity and terminal velocity have great differences between charcoal and quartz sand at the same conditions according to theoretically calculated results. The Layered phenomena may appear due to the big density difference, which will weak the heat transfer between them. At a certain chamber temperature, the heating time of quartz sand increases with increasing the particle diameter. For a certain particle diameter, the heating time will be shortened when increasing the chamber temperature. The burning-out time of charcoal increases with the increasing of diameter, and will be shortened significantly when increasing the chamber temperature. Increasing the temperature of hot wind properly and selecting reasonable fluidization velocity of wind may improve the performance of the bio-oil production system.