Formation rates of characteristic carbon phases during fuel-water slurry injection in a hot fluidized bed

Abstract

Abstract The interaction of fuel-water slurries (FWS) with a hot fluidized bed has been studied and the allocation of fixed carbon resulting after FWS dehydration and devolatilization has been investigated. An experimental technique has been purposely set up. A pneumatic injector has been used to disperse FWS into an atmospheric fluidized bed reactor, 140 mm ID. Silica sand has been used as bed material. The experiments have been carried out at typical temperatures of atmospheric fluidized bed combustion (AFBC), but under inert conditions to prevent combustion. Nitrogen as inert gas has been used for fluidization and for dispersion of FWS. Experiments provide results in terms of relative formation rates of carbon aggregates (A-phase), tiny carbon deposits on individual sand particles (S-phase) and carbon fines (F-phase). Relative formation rates are controlled by injection conditions, i.e. by the velocity of dispersing gas at the nozzle and the gas-to-slurry mass feed ration. A further operating parameter is the hydrodynamics of the bed. Finally, the nature of the parent fuel in FWS is also of great importance. The above findings are critically reviewed in the paper in order to determine the rates controlling the formation of carbon phases in an actual FWS-fired FBC unit.