This work presents a study on a gas-solid cyclone separator used in a complex cement production plant. The objective of the study consists on the performance evaluation and optimization of the cyclone separator in terms of particle separation and heat transfer efficiencies, while keeping pressure losses under control. The thermal interaction is between two gas-solid mixtures, one feeded at 850 degrees C and the other at 600 degrees C, respectively. The solid phase consists, mostly, of calcium carbonate subsequently intended to the so-called baking process for the production of clinker and then cement. The main goal of the study is maximizing the separation efficiency, minimizing the temperature at the exit of the plant and maintain the pressure drop not far from its value in the running plant. In a previous study, the authors defined the suitable setup of the mesh, physical models and turbulence; the same setup has been adopted in the present work during all the optimization phase. Vortex finder length (initially of cylindrical shape), its conicity angle and the pressure losses are the parameters (independent variables), taken into account to optimize the separation efficiency and the temperature of the gas at the exit of the plant. The optimization process was started with the base case that replies the geometric shape of the plant in operation. A detailed overview of the classical and recent optimization methods, is included in the Appendix, together with a brief illustration of a general pattern concerning an optimal design procedure. The numerical approach, for all the cases, is based on implicit unsteady simulations using the Eulerian Multiphase model. (C) 2017 Elsevier B.V. All rights reserved.