Investigation of cold flow hydrodynamics in a dual fluidized bed for gasification of high-ash coal

Abstract

The hydrodynamics of a compact dual fluidized bed (DFB) gasifier, consisting of a short riser and a bubbling fluidized bed (BFB), designed for high-ash coal, has been investigated. The effects of fluidization numbers from various aeration ports, and secondary aeration (SA) in the riser have been examined on solids circulation rate and solids holdup in the DFB. The performance of solids recycle systems has been investigated for on-bed and in-bed solids discharge from the BFB to the riser resulting in a low- and high- bed density operation in the riser. For high superficial gas velocity and high-density operation of the riser, an intense solids backmixing is noticed near the riser-exit, which decreases when SA is used. SA is found to be more effective in maintaining a proper balance between solids holdup and solids circulation rate when the bottom riser bed is operated in the fast fluidized bed regime for in-bed solids discharge.