GAS HOLD-UP AND BACKMIXING IN A BUBBLE-COLUMN REACTOR UNDER COAL-HYDROLIQUEFACTION CONDITIONS

Gas hold-up and the extent of liquid-phase backmixing have been investigated experimentally at room temperature and under coal hydroliquefaction conditions (viz. temperature 164 to 384 degrees C and pressure between 4.5 to 15 MPa) using a continuous tubular bubble-column reactor of small diameter (1.9 cm) and large length to diameter ratio. Gas hold-up is affected by superficial gas velocity and temperature particularly above 300 degrees C. The effects of superficial liquid velocity, gas molecular weight and pressure are negligible. Liquid-phase dispersion coefficient and Peclet number are strongly dependent on superficial gas velocity. The modified correlation of Hikita er al. (1980) for the fractional gas hold-up is found to fit the experimental data at high temperatures after corrections have been applied for dissolution of gas and liquid vaporization. Literature correlations derived from two-and three-phase systems are found to be inapplicable under coal hydroliquefaction conditions for delta(G) < 1 cm/s. E(L) is found to vary proportionally with delta(1.53)(G).