Hydrodynamic And Mass Transfer Characteristics In A Fixed Bed Under Gas-liquid Concurrent Upflow

A three-phase fixed bed reactor with concurrent gas-liquid upward flow,also called a flooded bed reactor(FBR),is widely used in petrochemical industry,wastewater treatment and other fields.In this paper,the hydrodynamic and mass transfer characteristics of the reactor were studied in flooded bed reactors with internal diameters of 5 cm,14 cm and 28 cm.Pressure drop and liquid holdup are important parameters for the design and operation of a flooded bed reactor.The effects of gas and liquid flow rates,particle diameter,and particle wettability on pressure drop and liquid holdup were investigated in a FBR with internal diameter of 5 cm.The packing used in this paper are Al2O3 particles(2.0 mm,4.0 mm,6.0 mm)and glass bead particles(2.0 mm,4.0 mm,9.0 mm).It is found that the effect of liquid velocity on pressure drop and liquid holdup is more obvious than the effect of gas velocity;the increase of particle diameter will reduce the pressure drop and liquid holdup of the bed;the wettability of particles will only have a significant effect on the pressure drop and the liquid holdup when the liquid flow rate is large.Residence time distribution is an important parameter for investigating the flow state in the reactor.The influence of the reactor diameter on the flow state was studied and the results show that the average residence time of the liquid phase in the bed becomes longer as the reactor diameter increases;the axial backmixing degree of the liquid phase in the bed increases as the reactor diameter increases;and the flow state in the reactor with internal diameter of 5 cm is closer to plug flow.The mean bubble diameter is a key factor for the mass transfer in a reactor.In this paper,the influence of the packing size on the mean bubble diameter was investigated in the reactor with internal diameter of 14 cm.The results show that the mean bubble diameter is approached to the pore size for the packing of 9.3 mm.An empirical correlation was proposed for the mean bubble diameter prediction and the predicted values agree well with the experimental values and the data in literature.