Gas-Liquid Mass Transfer in High-Pressure Bubble Columns

Volumetric gas-liquid mass-transfer coefficients are investigated in bubble columns under high-pressure and moderate-temperature conditions by utilizing an oxygen desorption method. The oxygen concentration in the liquid phase, water or Paratherm NF heat-transfer fluid, is monitored with a high-pressure optical fiber oxygen probe. The study covers operating conditions up to pressures of 4.24 MPa and up to temperatures of 92 °C. The superficial gas and liquid velocities vary up to 40 and 0.89 cm/s, respectively. Experimental results show that system pressure, temperature, gas and liquid velocities, liquid properties, and column dimensions are major factors affecting mass transfer. The mass-transfer coefficient increases with both pressure and temperature. Both gas and liquid velocities improve mass transfer due to higher turbulence at high-velocity conditions. Liquid properties and column dimensions also have significant effects on mass transfer. The effect of liquid velocity on k_la is mainly due to the change in k_l, while other variables affect k_la mainly through the change in gas holdup, which directly affect the interfacial area, a. A consideration of the dispersion term on the determination of k_la gives results similar to those of the continuous stirred tank reactor model, which was used to determine k_la in this study.