The development of a new plasma process involving high temperature gas-solid interaction makes necessary the analysis of hydrodynamic phenomena. In this context, CFD modelling appeared as a key tool for the design, the control and the optimisation of the process. In a previous step, the general flow inside the reactor in the absence of carbon particles has been studied. A simplified approach to take into account the influence of the rotating electromagnetic forces (3-phase AC) has been developed. In the next step, whose preliminary results are presented in this paper, the injection of a gaseous hydrocarbon must be considered. We present in this paper a simple approach considering the plasma-particle system as a homogeneous continuous semi-transparent absorbent gas. The influence of the absorption coefficient is discussed.