A simplified model for management of resonance exotherms in fixed-bed reactors using liquid carriers

Abstract Resonance exotherms in fixed-bed reactors are less common than typical runaway reaction exotherms and standard mitigation procedures may not have been designed to manage them. Although resonance exotherms are transient phenomena, eventually leaving the reactor in a steady state, they can be quite catastrophic in the process, leading to very large temperature excursions if not properly handled. Transient exotherms have been studied under various names (travelling temperature waves, creeping profiles, reaction wave fronts, propagating waves, convective instabilities…). In this paper, we will focus on resonance exotherms resulting from a change in the state of the catalyst in the fixed bed, after interaction with the fluid. Typical examples are catalyst sulfiding and catalyst regeneration. Our objectives and new contributions are: 1. to identify hydrocarbon adsorption during oil-in as a potential cause of high-temperature resonance exotherms, 2. to raise the level of awareness about resonance exotherms by reviewing existing theory and practice on vapor/catalyst systems, and 3. to propose simple and systematized methods to manage and mitigate these exotherms by adding liquid carriers. The literature offers simplified analysis for vapor/catalyst systems, resulting in correlations that are successful in the initial definition of the operating envelope. We review this methodology and apply it to study the effect of adding the liquid as carrier, and to extend the practice to exotherm management using the liquid. In addition, we developed a generalized numerical transient fixed-bed model that includes vapor/liquid/catalyst interactions. Animations based on the results of that model were presented at the meeting. The numerical model confirmed the findings of the simplified models and will be discussed in a future publication.