Particle-liquid heat transfer in trickle-bed reactors

One of the major disadvantages of trickle-bed reactors is their poor capability to eliminate the heat involved in reaction. Knowledge of particle-fluid heat transfer rates in trickle-bed reactors assesses the possibility to prevent the formation of hot spots. Safely problems, deactivation of the catalyst and less than optimal selectivities in catalytic reactions can be avoided. In this contribution, experimental results on particle-liquid heat transfer rates in trickle-bed reactors are presented. Local time-averaged particle-liquid heat transfer fates are determined with custom-made probes in the trickle and pulsing flow regime. In the trickle flow regime, the local heat transfer coefficient increases both with increasing liquid flow rate and, to a lesser extent, with increasing gas flow rate. The transition to pulsing flow results in a substantial increase in heat transfer rates. In both flow regimes, heat transfer rates are governed by the linear liquid velocity. No principal difference exists between the trickle and pulsing flow regime, although the hydrodynamic behavior is very different. Local heat transfer rates are strongly dependent on the local structure of the packed bed. Virtually instantaneous measurements of particle-liquid heat transfer rates are conducted using constant temperature anemometry. During pulsing flow, heat transfer rates inside the pulses are roughly 3 to 4 times higher with respect to heat transfer rates in between the pulses. Constant temperature anemometry is an accurate experimental method to determine instantaneous particle-liquid heat transfer rates in trickle-bed reactors. (C) 2001 Elsevier Science Ltd. All rights reserved.