Abstract
Traveling thermal transients have been observed in deep-bed catalytic reactors. With certain combina tions of parameters and stimuli, these transients can increase in amplitude with increasing axial distance into the bed. The resulting peak temperatures can exceed structural equipment limitations and cause catalyst deactivation or physical deterioration. Reaction systems in which abrupt changes in operating parameters can occur are particularly susceptible. An understanding of the causes of such transients is important not only for design but also in operations where optimization of output and product quality is essential.
This paper describes a numerical procedure that effi ciently simulates thermal transients on a digital computer. Results are shown for a generalized reactior, scheme that includes the effects of reaction rate, activation energy, absorption, heat of reaction, heat capacities of gas and solids, and catalyst bed depth. Also covered is initiation through various stimuli such as feed rate, composition and temperature dis continuities, pressure variations, and abrupt activity changes.
The transients travel because the solid fixed-bed heat capacity causes temperature to lag concentration re sponses with step changes in operating conditions. An interesting result is that temperatures in the bed move in the direction opposite to the initiating stimulus. A decrease in feed temperature, for example, produces a positive peak wave temperature. A computer simulation of the phenomenon can aid in developing effective control strategies and operating procedures.
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