The dynamics of a plant-scale cyclone/ejector system have been studied numerically. The purpose of said system is to separate and evacuate solid particles from a highly dense vapor stream involved in polyethylene production. Complexity arises from the fact that the transient pressure field within the Lappel cyclone governs the operation of the annular ejector, and vice versa. Specifically, the cyclone’s asymmetrically dancing vortex dips well into the ejector suction; therefore the two units cannot be computationally uncoupled. Compressible, time-dependent CFD results were surprisingly sensitive to the pressure discretization approach. Results had a mixed dependency on the slow pressure strain formulation in the differential Reynolds Stress calculations, while they were insensitive to the pressure-velocity coupling routine. Interesting results from earlier researchers regarding particle orbit radius, as well as particle bypassing were confirmed. Six geometric configurations for improving the system operation were evaluated. Pressure differential and solids collection efficiency were the two primary measures. Since said system is an integral part of a complex commercial operation, cost and physical space constraints severely limit the extent to which the geometry can be modified. Simple geometric changes were shown numerically to make operational improvements while only incrementally improving particle collection efficiency.

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