Abstract This paper presents the CFD calculations of a large cyclone (the diameter of the cylindrical part is 0.7 m) equipped with a counter-cone. Three cases of different locations and diameters of the counter-cone base were investigated. The Reynolds-averaged Navier–Stokes equations with the Reynolds stress turbulence model (RSM) were used in the analysis. The Lagrangian method was employed to track the particle motion and calculate the cyclone efficiency. The applied model correctly reflects the flow through the device and facilitates the estimation of the separation efficiency. In the presented case, displacement of the counter-cone into the dust bin improved the separation efficiency with a slight increase in pressure loss.