**5. Conclusions**

Within this work, it was possible to demonstrate a suitable approach for determining gasification kinetics of one char with thermogravimetric analysis by the followings steps: determination of the mass influence; determination of possible influence of mineral matter or conversion model; non-isothermal measurement of a representative set of gas compositions; evaluation of measurement error; fitting results to possible models and assessment of model quality.

Hence, the char of a Rhenish lignite was gasified in a TGA at atmospheric pressure under non-isothermal conditions in order to determine the gasification kinetics for steam and CO2 gasification with the inhibiting effect of H2 and CO respectively. The measurement data were filtered with a first order Savitzky–Golay-Filter and an optimal integration time determined by means of the Allan variance.

Two reactions models, Arrhenius and Langmuir–Hinshelwood, and four conversion models, the volumetric model (VM), the grain model (GM), the random pore model (RPM) and the Johnson model (JM), were investigated. Furthermore, a model for the influence of the sample mass in a TGA was incorporated to account for mass transfer e ffects.

With this rigorous approach, it was found that the reaction is best described by the L–H rate equation together with the JM as the conversion model. For both, steam and CO2 gasification, the activation energies of the reverse reactions are negative. This is a hint that the L–H model does not completely describe the underlying reaction mechanism. Still, for typical environments of fluidized bed gasifiers, the L–H model can be used to predict the reactions rates.

**Author Contributions:** C.H. is responsible for administration, conceptualization, the original draft, and developed the applied methodology. The experimental investigation were conducted by E.L. J.M. supported the writing process with his reviews and edits. B.E. supervised the research progress and the presented work. All authors have read and agreed to the published version of the manuscript.

**Funding:** The research leading to these results has received funding from the COORETEC initiative as part of the 6th Program on Energy Research of the Federal Ministry for Economic A ffairs and Energy of Germany under gran<sup>t</sup> agreemen<sup>t</sup> No. 03ET7048A (FABIENE; Flexible Supply of Electricity and Fuels from Gasification of Lignite in a Fluidized Bed). The funding is gratefully acknowledged.

**Conflicts of Interest:** The authors declare no conflict of interest.
