Effect of circulation pipe diam. on the selected flow parameters of the hybrid airlift reactor was computed from a developed math. hydrodynamic model and exptl. verified. The apparatus consisted of a fluidized bed reactor and an airlift reactor. It was not a typical 3-phase airlift reactor, because the contact between solid and gas phases did not occur. The developed model was based on the global momentum balance and mass balances of the gas and liq. Exptl. verification of the model was carried out by the measurements of gas hold-up in the bubbling zone (manometric method), liq. flow velocity in the downcomer and fluidized bed height.