HYDRODYNAMICS STUDY OF GAS-SOLID FLOW PATTERN IN AN INTERNALLY CIRCULATING FLUIDIZED BED WITH A DRAFT TUBE

摘要

Circulating fluidized beds (CFB) are widely used in coal combustion and gasification processes.These CFBs suffer from having very tall column as a solids raiser and accompanying additional external circulation of solids through cyclone.To avoid the external circulation accessories a compact internally circulating fluidized bed (IFCB) is developed.ICFB represent a modified spouted fluidized bed with a draft tube inside to avoid problem of gas bypassing.The hydrodynamics of ICFB have studied using combination of experiments and CFD simulations.Solids circulation rate and bed pressure drop were measured using high speed camera and pressure manometers for a wide range of particle sizes and bed heights.3D Two-fluid Eulerian granular flow model was adopted to predict the hydrodynamic behavior of ICFB.Effect of gas velocity, presence of draft tube on solid hold-up distribution, solid circulation pattern and variations in gas bypassing fraction in the ICFB have been investigated with the help of CFD simulations.CFD validation against the experimental data is made.