Hydrodynamic behaviour and gas-liquid mass transfer in a three-phase inverse turbulent bed reactor
Advancing the chemical engineering fundamentals
Multifase Flows (T2-5P)
Keywords: Bioreactor, three-phase fluidization, bed expansion, gas hold-up, mass transfer coefficient
Biofilm reactors with microorganisms immobilized on small suspended particles e.g. fluidized bed, airlift, inverse fluidized bed and circulating bed reactors have been used for organic matter and ammonia removal from industrial wastewaters. They allow higher biomass concentrations to be obtained, and higher volumetric loading rate of pollutants can be treated at the required removal efficiency. In this work, hydrodynamic characteristics and gas-liquid mass transfer in a laboratory scale inverse turbulent bed reactor were studied. In order to characterize internal flow in the reactor, the residence time distribution (RTD) was obtained by the stimulus-response technique using sodium chloride as tracer. The bed expansion - bed, the gas hold-up - g, and the volumetric gas-liquid mass transfer coefficient - kla were evaluated for a range of fluid dynamic conditions including different solid hold-up (0-0.2), air superficial velocities (0-0.014 m/s), liquid superficial velocities (0-0.05), and surface tensions (32 – 72 mNm as well as surface roughness. The parameters that characterize the RTD curve: mean residence time and variance were independent on the studied parameters, thus they do not influence the liquid mixing in the reactor. The hydrodynamic of the inverse turbulent bed was well described by a model that considers the reactor as two-mixed tank of different volumes. The volumetric gas-liquid mass transfer coefficient was found independent on the solid hold-up but it was influenced by the solid phase roughness and the surface tension. Increasing the former, up to 30% increase in the kla was observed, while up to 50% decrease in the same parameter was detected with the decrease in surface tension. The results enhance a previously suggested hypothesis which considers that the solid and liquid form a pseudo-fluid in the inverse turbulent bed reactor. On the basis of dimensionless analysis relationships are given, which allow calculating bed expansion, gas hold-up and volumetric gas-liquid mass transfer coefficient in three-phase inverse turbulent bed reactor.
Presented Tuesday 18, 13:30 to 15:00, in session Multifase Flows (T2-5P).
