Multiphase Flow And Mass Transfer Properties In Low And High Pressure Trickle Beds

Trickle bed reactors are widely used as multiphase contactors in petroleum processing and chemical industry. In the design of such reactors, evaluation of the liquid hold up, pressure drop, and mass transfer coefficient is needed to account for the close link between the global hydrodynamics and the mass transfer and reaction performances of reactors. During past decades, though the three critical parameters have been the subject of many experimental and modeling investigations, a predictive estimate of the parameters remains difficult with good accuracy.In this paper, a trickle-bed of 0.025m I.D. and 0.6m height packed with three-robed catalyst and glass beads was set up for hydrodynamics and mass transfer studies. Data of two phase pressure drop and liquid film mass transfer coefficient were obtained in different operation conditions, including operation pressures (up to 4 MPa) and different gas and liquid superficial velocities. Based on the experimental work, related influencing factors were discussed. The main finding of the present work is that under certain conditions, the characteristics of packings (particle size and packing voidage) and operation pressures play a decisive role in increasing inertial effects of flows. As a result of such cases, there is an increase in form drags between phases, which leads to higher pressure drops and thus improvement of mass transfer conditions.Secondly, we have shown that based on the Ergun equation used for single phase flow in a packed bed, length scales and two phase friction factors can be constructed in a logical manner for an equivalent representation for gas-liquid two phase flows in low and high pressures trickle beds. In terms of the scales and two phase friction factors, based on available data by different authors, new improved correlations for evaluation of two phase pressure drop and phase holdups are suggested for porous and non-porous packings with equivalent diameters of 1.5-6 mm, and for modified Reynolds numberfrom 3.3 to 88, operation pressures up to 6 MPa and superficial gas velocities up to 8.8 cm/s.Finally, a new correlation for prediction of liquid film mass transfer coefficients was also derived based on the concept of two phase friction factors and experimental data obtained in the present work.The proposed new correlations are tested with a variety of available experimental data from the literature and new experimental results obtained in the present work. It is demonstrated that the new correlations improve model predictions of pressure drop, holdup, and mass transfer coefficients. The advantage of our approach is that estimation of the basic parameters in the design of trickle bed reactor can be obtained in a consistent and predictive way.