Hydrodynamics of two-phase flow in a deep airlift reactor.

摘要

Several hydrodynamic measurements are made inside a deep bubble column containing gas and liquid, including void ratio, bubble diameter, liquid dispersion, and gas transfer. The column is 26 meters tall and has a diameter of 1.06 meters and was modified so that it could run as either a bubble column or an external airlift reactor (EALR). Experiments were performed to determine the effects of sparger type, column type, total unaerated height, and superficial gas velocity. Void ratio measurements were calculated for five local sections of the column by measuring pressure differentials between pressure taps. Above 2 meters from the column bottom, gas void ratio was well described by a straightforward model that incorporates the influence of hydrostatic pressure, superficial gas velocity, and a fitted bulk bubble-rise velocity, which does not exhibit a strong dependence on sparger type. The fitted slip velocities compare well with literature measurements of single-bubble slip velocities.; Bubble diameter measurements were made throughout the entire height of the column using a submersible camera attached to a trolley. It was found that the average bubble diameter throughout the column did not change significantly with gas flow rate or depth. A relatively small change in bubble diameter was found with sparger type. The greatest difference was found between the bubble column and the air-lift reactor.; Dispersion measurements are taken for each gas flow rate using fluorescein dye as the conservative tracer and are used to determine a dispersion coefficient (DL) for several sets of operating conditions. Bubble-water gas transfer measurements are made for each flow rate at several heights using dissolved oxygen (DO) probes and a total dissolved gas (TDG) probe. A two-phase advective-dispersion model, which incorporates the DL values determined from the dispersion experiments, is fit to the DO measurements using the gas transfer coefficient ( kLa) as a fitting parameter. Using the results from these tests and calculated interfacial surface areas determined using the void ratio and bubble diameter measurements, the liquid film coefficient (k L) is computed. Results are compared to those from the literature.