Study of gas-liquid mass transfer in bubble and spray column adding solid media

Abstract

Gas absorption is a separation process that transfers substances from gas phase to liquid phases due to the different concentrations. The operation can be applied in many treatments or purifying processes e.g. CO2 absorption from biogas or volatile organic compounds (VOCs) recovery from petroleum emission air. The conventional unit operation using for the gas absorption process are bubble column and spray column. Although there are several literatures reporting the efficiency of spray columns and bubble columns, those were done separately. Therefore, this research projected to investigate both hydrodynamics and mass transfer in both spray and bubble columns and comparing their specific power consumptions in order to develop the selection a guideline for industrial usages. The results indicated that the bubble column had larger specific interfacial area than the spray column when using at small gas loading rate. At this range of operation, the bubble column yielded higher overall mass transfer coefficient with the same specific power consumption. However, when operating at high gas loading rate, the spray column was the one better than the bubble column since the bubble column consumed larger power consumption as the pressure drop of the bubble column was mostly due to the gas flow.

In addition, this research also studied the effect of solid phase on the hydrodynamics and mass transfer in the bubble column and spray column. By using the colorimetric method of “red bottle” experiment, it was found that the bubble-particles collision diminished the mass transfer of bubbles because the collision slowed down the bubbles especially for the small bubbles due to the fact that the small bubble simply lost their velocities from the collision. However, there was an advantage of introducing the particles since solid particles could obstruct the rising bubble and reduced its rising velocity. Consequently, the contact time between gas and liquid is increased and resulted in higher gas hold up and specific interfacial area. Therefore, with the appropriate conditions for which solid promoted specific interfacial area higher than diminished the mass transfer coefficient, the higher mass transfer rate was achieved. For the experimental setup using in this research, the enhance of mass transfer rate was occurred when the movable ring-shaped particles were introduced into the column that had large orifice sizes of gas sparger.

In addition, this thesis also developed a colorimetric method to determine the overall mass transfer coefficient of oxygen without using other equipment rather than measuring the time which color of the solution changed from colorless to saturated red. This technique is very useful in the aspect of education since it does not require another equipment for measurement rather than visually observation. Nevertheless, the performance of optical fiber probes for hydrodynamics determination of droplets were also investigated.