The thermodynamic Model "Gibbs Free Energy Gradient Method" (GMM), published on the Vol. 90 (2011) of this Journal and validated with literature data, is now applied to the simulation of an experimental campaign realized at the ENEA Research Centre of Trisaia (Italy). The GMM well reproduces the experimental results of steam gasification of refuse-derived fuel (RDF) obtained on two laboratory and pilot scale rotary kilns. Consequently, the experimental syngas composition is put in relation to the main process parameters through a new approach incorporating the GMM for identifying a reliable correlation between the extent of reactions and the gasifier temperature. This correlation appears independent from the scale of the rotary kiln and the residence time in the investigated range of variables. On this basis, the GMM is adapted to become a tool for designing industrial gasifiers starting from experimental data since the required final composition of the syngas and the required performances may be obtained by designing a gasification zone operating at the temperature calculated by the proposed method. It is believed that this procedure is extendable to other geometries and different type of apparatus by studying and including the effect of other parameters. (C) 2016 Elsevier Ltd. All rights reserved.