This study involved the analysis and characterization of the multiphase flow phenomenon inside the lower stage cyclone separator used in the clinker burning process. The analysis was performed using both CFD and experimental research methods. Very few studies are devoted to such types of cyclone separators, which in addition to their basic functions are also responsible for the technological process. Due to the atypical working conditions of these cyclone separators, they are characterized with a complex geometry, which significantly differs from that of the traditional separators. Furthermore, the evaluation of the accuracy and level of reliability of the two models of turbulence closure-k-epsilon RNG and RSM (RANS), and the LES. The results obtained led to the conclusion that for the lower stage cyclone separators, the LES model proved to be the most accurate (both in the case of forecasting the separation efficiency and pressure drop). The performance parameter (in particular the separation efficiency) values obtained for the RSM model were also characterized by high accuracy. The k-epsilon RNG model was characterized by significantly larger deviations. (C) 2018 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.