In this work the simulation of a foaming molten slag gasification reactor was performed with a commercially available Computational Fluid Dynamics code. In the standard body of the code appropriate User-Defined Subroutines were devised and incorporated for the complete description of the process. The flow field and heat transfer equations were solved together with the simulation of the coal gasification phenomena. The model results are in good agreement with the respective experimental data, indicating the validity of the proposed model and thus providing a useful tool for the analysis of the molten slag gasifier operation.