Experimental investigation and empirical modeling of flow regimes and hydrodynamic characteristics of a cone-shaped bed using sand–biomass binary mixtures

Abstract

Flow regimes and hydrodynamic characteristics of a cone-shaped bed, the key element of a fluidized-bed combustor, were studied in this work. Prior to the cold-state experiments, the bed material (alumina sand/dolomite/limestone) was premixed with palm kernel shell in different proportions of the biomass in a binary mixture: 0, 2.5, 7.5, and 10 wt.%. In a test series with the selected bed material, the pressure drop across the bed and air distributor (Δp) was measured versus superficial air velocity at the air distributor exit (u), for three static bed heights (20, 30, and 40 cm). Four sequent flow regimes were found in the sand–biomass bed with for the selected range of u. The findings revealed the effects of operating variables on the major hydrodynamic characteristics: minimum velocity of partial fluidization (umpf), minimum velocity of full fluidization (umff) and corresponding pressure drops (Δpmax and Δpmff), and entire Δp–u diagram of the bed. The mathematical models for predicting umff and Δpmff, were empirically developed, both exhibiting good agreement with experimental data. A nomograph for the assessment of the pressure drop across the conical bed with the binary mixture at any arbitrary superficial air velocity has been proposed in this work.