It was shown that tangential velocity, axial velocity and turbulent kinetic energy in the settling tank decreased significantly when the dipleg length was extended. This means that a dust collector with a dipleg can effectively prevent the re-entrainment of already separated dust. In addition, the elongated part of dipleg increases dust separation space, and thus separation efficiency increases, at the expense of a slightly increased pressure drop. Authors [36] investigated experimentally cyclones with three different geometries of dust outlet from cyclone: a cyclone with a dust trap, with a cone at cyclone outlet, and a cyclone with a cylindrical dipleg. They found that in the case of a cyclone with only a dust trap, the swirling stream passes from the cyclone cone to the settler, which will cause the collected particles to be entrained again. In case of cyclone with a tip cone, efficiency improvement in cyclone has been achieved. They showed that separation efficiency can be significantly improved by changing dust collector geometry. One of the methods of increasing cyclone separation efficiency is to attach an additional element (cone) at the dust outlet from the cyclone to the settling tank. The task of this element, also known as the apex cone, is to limit the secondary circulation of the separated dust particles. It is very important to precisely select cone diameter, the apex angle and its proper position. Incorrect selection of these parameters may block the bottom outlet of the cyclone and make it difficult for dust to fall into the tank, and thus reduce cyclone separation efficiency. Therefore, [37] influence of fifteen variants of the geometrical configurations of the counter-cone on cyclone efficiency was analyzed. The cone geometry was determined by the following parameters (Figure 5): cone diameter \(D_{S}\), apex angle \(\alpha\), and distance from the cone base to the cyclone bottom outlet with diameter \(B_{h}\), for cyclone outlet diameter \(B\). Figure 4: Diplegs and dust settler’s geometry. Drawing made on the base [33]. It was found that cone use in each of investigated geometric variants led to cyclone efficiency increase. The results show that the optimal position of the cone (assuming separation efficiency is maximized) should be above the bottom outlet of the cyclone at a distance of \(B_{h}=0.15B\) (82.5 mm). The apex angle of the cone should be \(\alpha=85^{\circ}\). Improvement in separation efficiency was observed for particles smaller than 60 \(\upmu\)m, and, in particular, for particles up to 15 \(\upmu\)m in diameter. The authors of [38; 39; 40] investigated the apex angle of the counter-cone at the dust outlet from the cyclone in the range of \(\alpha=40\)-\(80^{\circ}\). They found that the optimal value of the angle regarding the maximum separation efficiency is \(\alpha=70^{\circ}\). Moreover, they observed that increasing the gap between the cone and the wall of the cyclone conical part increased the number of small particles that entered the dust tank. Two design variants of the cone were analyzed [36]. In the first variant, the cone (apical angle \(\alpha=90^{\circ}\)) was located under the cyclone lower outlet. In the second variant, the cone (\(\alpha=120^{\circ}\)) was located above the cyclone lower outlet. The latter solution led to an increase in the separation efficiency by 2%, and an increase in the pressure drop from about 1200 Pa to 1400 Pa. The author of [41] compared with CFD the two suggested locations of the cone (below the outlet of the cyclone and in cyclone conical part). He concluded that placing the cone below the cyclone conical portion is more beneficial, as it helps to increase the particle separation efficiency. The above-mentioned examples show that single cyclone operation is significantly influenced by appropriate dimensions selection of dust collector and attachment of an additional element (cone) at cyclone dust outlet.