Modeling of Oxidative Coupling of Methane for Manufacture of Olefins—Part I: CFD Simulations

Abstract

This paper presents a comprehensive computational fluid dynamics (CFD) model for describing the oxidative coupling of methane (OCM) carried out in fixed-bed reactors for olefin production. Initially, a single pellet model was developed and implemented to describe the heat and mass transfer within the pellet and between the gaseous and solid phases. Subsequently, sensitivity analyses were performed to assess the impact of pellet arrangement and feed conditions on the heat and mass transfer rates, subsequently affecting concentration and temperature profiles. As indicated by the simulations, a high ethylene content could be obtained with the increase in the CH4/O2 ratio, aligning well with previous experimental studies. Furthermore, it was observed that pellet arrangement can significantly affect the reactor performance. Additionally, the behavior of temperature and concentration in the gaseous and solid phases can be very different, such that pseudo-homogeneous modeling approaches should not be assumed a priori. Finally, the simulated temperature differences between the gaseous and solid phases were very substantial and above 100 °C, indicating the occurrence of catalyst auto-ignition behavior.

Numerical Investigation of the Effect of Inhomogeneous Flow Behaviors inside a Particle Cluster in the OCM Reaction

“…Therefore, we simplified our models by assuming that the particle clusters were structurally stable in the flow field, regardless of any deformation or breakage behaviors. This approach was consistent with methodologies employed in similar studies. ,, …”

“…This approach was consistent with methodologies employed in similar studies. 32,33,44 The SIMPLE algorithm was utilized for the pressure− velocity coupling scheme. The format of spatial discretization for gradient and pressure terms was set as the least squares cellbased format and PRESTO format, respectively.…”

“…However, it is noteworthy that the current research studies on particle clusters are mainly focused on macroscopic average characteristics, such as the size, number, and spatial distribution of clusters . By homogenizing the flow characteristics of particle clusters, simplified and equivalent flow information on clusters was obtained. , This equalizing treatment ignored the nonuniform flow behaviors inside the clusters, weakening the inhibition effect of the nonuniformity on gas–solid contact and heat transfer. , Fontoura et al suggested that it was unreasonable to assume a pseudohomogeneous distribution of flow fields within clusters. They found that there was an uneven flow characteristic inside the cluster, which changed the spatial distribution of temperature and particle concentration, resulting in the autoignition behavior of particles.…”

“…30,31 This equalizing treatment ignored the nonuniform flow behaviors inside the clusters, weakening the inhibition effect of the nonuniformity on gas−solid contact and heat transfer. 32,33 Fontoura et al 33 suggested that it was unreasonable to assume a pseudohomogeneous distribution of flow fields within clusters. They found that there was an uneven flow characteristic inside the cluster, which changed the spatial distribution of temperature and particle concentration, resulting in the autoignition behavior of particles.…”