Linear Analysis of the In-Phase and Out-of-Phase Stability Behavior of a Natural Circulation Reactor: Upscaling Effects

Abstract

This study focuses on the stability behavior of a natural circulation chemical reactor. The reactor contains many heat-generating ethylene oxide catalyst tubes where the spaces between the tubes constitute parallel boiling channels connected between two plenums. In-phase and out-of-phase flow oscillations can occur in these channels. In this paper, these oscillations were analyzed under natural circulation conditions using a linearized frequency domain model. The results indicate that the out-of-phase mode of instability is more dominant than the in-phase mode instability. The model predictions for the in-phase mode oscillation were compared with those of the time-domain code MONA. The effect of the radial non-uniformity in the flow distribution in the parallel boiling channels on the flow stability was investigated. The model was further applied to investigate the effects of upscaling the reactor (increase in reactor area with constant power density) on the channel flow distribution and stability. It was found that with an increasing reactor diameter, the channel flow distribution is greatly affected even though the power density remains constant. This increases the out-of-phase instability of the reactor. The results are important for the design of future reactor systems.