This paper presents a numerical study of the gas–powder flow in a typical Lapple cyclone with division of gas and particle flow in a vortex finder. The Navier-Stokes equations along with the RNG k-ε turbulent model are solved numerically. The separation efficiency and the trajectory of particles are simulated and the effects of the particle size on the separation efficiency and the particle residence time are investigated. The effect of the particle density on the particle size in the range which results 100% cyclone separation efficiency and particle residence time is investigated. Large particles generally have a higher concentration in the wall region and small particles have a higher concentration in the inner vortex region. The particles enter from different sides give different separation efficiency and trajectory. A particle with a size exceeding a critical diameter or a critical density would stagnate on the wall of the cyclone’s cone. This phenomenon is regarded as a main reason for the deposition on the inner conical surface in such cyclones used in the cement industry.

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