Liquid-induced pulsing flow in trickle-bed reactors

This contribution describes the experiments on pulse induction by cycling the liquid feed in a column of 3.2 m height. Based on a square-wave cycled liquid feed, two feed strategies are developed that involve the artificial induction of natural pulses and a separation of the wetting efficiency in time. The feed strategies aim at increasing the mass transfer rate of the limiting reactant and to prevent flow maldistribution and hot spot formation. The feed strategies are categorized upon a relatively fast and slow cycling of the liquid feed. The potential consequences of the developed feed strategies on reactor performance are evaluated. Cycling the liquid feed results in the formation of continuity shock waves in the column. The shock waves decay by leaving liquid behind their tail. This decaying process limits the frequency of the cycled liquid feed to rather low values since at relatively high frequencies, total collapse of the shock waves occurs. By the induction of natural pulses inside the shock waves, the integral mass and heat transfer rates during the liquid flush will be improved. Shorter flushes can therefore be applied and the usual encountered periodic operation is optimized. This feed strategy is termed the slow mode of liquid-induced pulsing flow. The second feed strategy termed the fast mode of liquid-induced pulsing flow may be viewed as an extension of natural pulsing flow. Individual natural pulses are induced at an externally set pulse frequency less than 1 Hz. This feed strategy is the only fast mode of periodic operation possible since pulses are stable while shock waves decay. The characteristics of the induced pulses equal the pulse characteristics of natural pulsing flow at equivalent gas flow rates. A critical liquid holdup in between pulses is necessary for the induced pulses to remain stable. (C) 2002 Elsevier Science Ltd. All rights reserved.