Gasification is a thermochemical process devoted to the production of syngas, starting from a solid fuel such as coal, biomass, or refuse-derived fuel (RDF). The gasification efficiency and the chemical composition of the produced syngas are strongly affected by the feedstock and the operating conditions of the process. Besides the direct use as a fuel for power generation, downstream applications of syngas for chemical production demand specific H-2/CO ratios, as extensively reported in the literature. For this reason, in the present work, a comprehensive mechanistic approach is applied to the description of the coal gasification process, highlighting the sensitivity of key operating parameters on syngas quality. The solution of this multi-scale, multi-phase, and multi-component problem requires careful attention to the kinetics in the solid and the gas phase as well as the heterogeneous gas solid reactions. The kinetic model is validated with experimental data obtained in updraft gasifiers (including the Sotacarbo pilot gasification plant), and the catalytic effects of ash on the reactivity of low-rank coals are also addressed and quantified.