CONCENTRIC-TUBE AIRLIFT BIOREACTORS - PART I - EFFECTS OF GEOMETRY ONGAS HOLDUP

Gas holdup investigations were performed in three concentric-tube airl ift reactors of different scales of operation (RIMP: 0.070 m(3); RIS-1 : 2.5 m(3); RIS-2: 5.2 m(3); nominal volumes). The influences of the t op and bottom clearances and the flow resistances at the downcomer ent rance were studied using tap water as liquid phase and air as gaseous phase, at atmospheric pressure. It was found that the gas holdup in th e individual zone of the reactor: riser, downcomer and gas-separator, as well as that in the overall reactor is affected by the analyzed geo metrical parameters in different ways, depending on their effects on l iquid circulation velocity. Gas holdup was satisfactorily correlated w ith Pr, Ga, bottom spatial ratio (B), top spatial ratio (T), gas separ ation ratio (Y) and downcomer flow resistance ratio (A(d)/A(R)) Correl ations are presented for gas holdup in riser, downcomer, gas separator and for the total gas holdup in the reactor. All the above stressed t he importance of the geometry in dynamic behaviour of airlift reactors .