Mass transit coefficient and pressure fluctuations in trickle bed



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This work is an experimental study of flow patterns and solid-liquid mass transfer coefficients in trickle bed. Flow patterns investigated include gas-continuous, transition, and pulsing flows. In the study of flow patterns, liquids with different physical properties were used, with air the gas phase for all cases. The results obtained with air-ethanol mixtures indicate that liquid viscosity has a strong influence on location of the transition boundary. Other system parameters (such as bed porosity, packing wettability, packing method, etc.) were found to have influence on location of the boundary. The investigation of pressure drop across a pulse led to the conclusion that frictional pressure drop in the liquidrich phase is the main contribution to the pressure fluctuations. A simple model can be used to predict the amplitude of pressure oscillation. The phase distribution of the pulses (liquid-rich and gasrich phases) were determined from time-traces of pressure fluctuations. An electrochemical method was used to measure the local instantaneous solid-liquid mass transfer coefficient. These coefficients were determined for the different flow regimes and are in good agreement with those measured by Sato (9). A comparison of the time-traces of the instantaneous mass transfer coefficient and wall pressure indicates that an immediate increase in mass transfer coefficient occurs, when a pellet is in the liquid-rich phase, while the pressure increase is much slower and depends on the length of liquidrich phase and pulse velocity. Complete wetting of the pellets was found in the pulsing flow regime indicating that in this flow regime the catalyst utilization may be better than in the gas-continuous flow regime.