Some char particles are entrained in the raw syngas as its leaves the top of the gasifier, but are recovered and recycled back to the reactor via a cyclone. Ash particles, removed below the bed, give up heat to the incoming steam and recycle gas. At startup, the bed is heated externally before the feedstock is introduced.
Fluidized-bed gasifiers may differ in ash conditions (dry or agglomerated/slagging) and in design configurations for improving char use. Also, depending on the degree of fluidization and bed height, these types of reactors sometimes are also named as circulating fluidized bed reactors, and/or transport reactors.
Fluidized-bed gasifiers display these characteristics: