Numerical investigation of the partial oxidation in a two-stage downdraft gasifier

This paper presents a 2D axisymmetric CFD model of the oxidation zone in a two-stage downdraft gasifier. The purpose of this study is to investigate in detail this zone, which is crucial for tar cracking. Results fit satisfactorily to the experimental data regarding temperature pattern and tar concentration. Simulations highlighted several crucial points of the process: (a) tertiary tar are mainly destructed by combustion; (b) pyrolysis gas composition significantly influences the process; (c) the air injector design is fundamental in gasification as the air velocity and the air/fuel ratio have a great influence on the process; and (d) there is a critical injection velocity (about 34 m s−1 in this case) that dramatically changes the flow pattern.