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Abstract
The hydrodynamic (gas holdup, ϵG, bubble size distribution, db, and the Sauter-mean bubble diameter, d 32), gas solubility (C*) and mass parameters (gas-liquid interfacial area, a, and volumetric liquid-side mass transfer coefficient, kLa) were measured for various gases (H2, CO, N2, CH 4 and He) in an organic liquid (Isopar-M) in the absence and presence of two different solids (glass beads and alumina powder) in two large-scale SBCRs of 0.316 and 0.289 m ID. The data were obtained under wide ranges of pressures (1–27 bar), superficial gas velocities (0.08–0.4 m/s), temperatures (323–453K), and solid concentrations (0–36 vol.%).
The experimental data obtained showed that ϵG and k La increased with pressure due to the increase of small gas bubbles holdup; increased with superficial gas velocity due to the increase of the gas momentum; and significantly decreased with solid concentration due to a reduction of small gas bubble population. ϵG and k La values were found to increase with temperature due to the decrease of the Sauter mean bubble diameter and increase of the mass transfer coefficient (kL). The gas holdup, however, was found to decrease with temperature when the solid concentration was greater or equal 15 vol.% due to the reduction of froth stability under such conditions.
Empirical and back propagation neural network (BPNN) models were developed to correlate the hydrodynamic and mass transfer parameters in BCRs and SBCRs obtained in our laboratory and those from the literature. The developed models were then used to predict the effects of pressure, superficial gas velocity, temperature and catalyst loading on the total syngas holdup and mass transfer coefficients for the Low-Temperature Fischer-Tropsch (LTFT) synthesis carried out in a 5 m ID SBCR with iron oxides and cobalt-based catalysts. Under typical LTFT operating conditions (30 bar, 513 K, 30 and 50 wt%), the total syngas holdup and mass transfer coefficients predicted for H2/CO ratio of 2:1 with cobalt-based catalyst were consistently lower than those obtained for H2/CO ratio of 1:1 with iron oxide catalyst in the superficial gas velocity range from 0.005 to 0.4 m/s.
