Effects of temperature and particle size on minimum fluidization and transport velocities in a dual fluidized bed

Prior to operating a dual fluidized bed gasifier (DFBG) using a riser (0.078 m-I.D × 8.5 m-high) as a combustor and a bubbling bed as a gasifier (0.2 m-I.D. × 2.1 m-high), the hydrodynamic properties such as minimum fluidizing velocity and transport velocity of silica sand (270μm) as a bed material in a DFBG were determined at different temperature (25-800°C). The minimum fluidization velocity decreases from 0.065 m/s to 0.036m/s with increasing temperature. But the transport velocity, a boundary velocity between the turbulent and fast fluidization flow regimes, increases from 2.55 m/s at 25°C to 4.47 m/s at 600°C. The effect of particle size on the minimum fluidization and transport velocities was determined and correlations are proposed to predict both velocities at different temperature. The relationship between the operating variables and solid circulation rate was also determined. The obtained data can be utilized to determine the operating conditions in the hot DFBG system.