Computational fluid dynamics (CFD) study of a commercial-scale methanol-to-olefins (MTO) fluidized bed reactor

Abstract

Methanol-to-olefins (MTO) has been widely commercialized, yet the complex in-furnace phenomena still lack understanding. The flow characteristics and thermochemical behaviours in a commercial-scale MTO reactor are investigated by a reactive multi-phase particle-in-cell model. The spatial distribution of gas species and the impacts of key operating variables (e.g., mass flow rate, methanol to steam ratio, and wall temperature) on gas properties and reactor performance are analyzed. The results indicate the non-uniform distribution of gas variables. Methanol (i.e., CH3OH) is completely converted in a very short distance above the distributor. C2H4 and C3H6 have the largest concentrations, followed by C4H8, C3H8, CH4, and C5H10. The increased mass flow rate significantly elevates the concentration of C2H4 but highly declines the concentrations of C3H6, C3H8, CH4, and C5H10. The gas temperature rapidly rises below the gas distributor (z < 15 m) due to exothermic reactions and then shows almost no change in the axial direction (z > 15 m), demonstrating good temperature control in the reactor. Elevating the given operating parameters increases the temperature, viscosity, specific heat capacity, and thermal conductivity of gas phase but declines gas density. The vertical dispersion intensity of catalyst particles is one order of magnitude larger than the horizontal one. Heat transfer coefficient (HTC) distributions show three distinct parts, the small HTC in the lower region, the sharply increased HTC in the medium region, and the large HTC in the upper region.