Byung-Ho Song

CFD simulation with experiments in a dual circulating fluidized bed gasifier

Abstract Gas and particles hydrodynamic behaviors were investigated in a pilot-scale cold-mode riser and a bubbling fluidized bed gasifier by means of experiment and computational fluid dynamics (CFD). Six different experimental sets were conducted in the cold-rig dual fluidized bed (DFB) at different gas velocities in both the riser and the recycle chamber aeration. A two-dimensional (2D) multi-fluid Eulerian model incorporating the kinetic theory of granular flows was applied to identify unsteady-state behaviors of the fluidized bed. The CFD model predicts well the solid circulation rate in the cold-rig DFB for all the six experimental runs. A discrepancy between experiment and simulation is observed in the axial solid holdup along the riser. The simulation results demonstrate that the cold-bed simulation can be used to predict the solid circulation rate for the hot-bed operation of the DFB gasifier.

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 x 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 flmdizing 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.

Gas Yields from Coal Devolatilization in a Bench-Scale Fluidized Bed Reactor

Devolatilization behavior of Australian bituminous coal-gasification was determined in a 0.1 m diameter fluidized bed at 650-900 °C. To predict gas yields from devolatilization, several correlations reported for gas yields were evaluated with the present experimental data. The correlation of Goyal and Rehmat [1993] was found to be good one. Also, a correlation for the product gas yields has been proposed from devolatilization of bituminous coals as a linear function of temperature with constants from the experiment. The experimental yields of product gas show good agreement with the values calculated by the proposed correlation.