**1. Introduction**

The electric power sector contributes to about a quarter of the total CO2 emissions worldwide. Therefore, in most mitigation scenarios for climate change the share of low-carbon electricity supply (comprising renewable energy, nuclear and carbon capture and storage) increases from the current share of approximately 30% to more than 80% by 2050 [1].

A power plant based on integrated gasification combined cycle (IGCC) is a very suitable addition to any future power system, because it offers the possibility to capture CO2 in a very efficient pre-combustion process. Furthermore, in a poly-generation configuration, this technology is able to accommodate the intermittent renewable power generation from wind and solar and operate the gasification island at full load by producing synthetic chemical products like hydrogen, SNG, methanol, and Fischer–Tropsch fuels. For high-ash and low-rank coals, fluidized bed gasifiers are especially suitable [2].

The rate of char gasification is the limiting step in gasifiers and most relevant for determining residence times of the particles and size of the reactors. Therefore, an understanding of the mechanics of char gasification for the chosen fuel is essential for the design of gasifiers. Considerable work has been done already in the field of char gasification processes. Irfan et al. [3] did a comprehensive review on CO2 gasification of coal regarding different factors of influence like coal rank, pressure, gas composition, temperature, and mineral matter. In this study, it was concluded that CO2 gasification characteristics are hard to conclude with full authenticity and the researchers observed those differently for a variety of coals. Generally, the same is true for steam gasification [4]. Ye et al [5] investigated the kinetics and reactivity of two South Australian low-rank coals and quantified the reaction rate for steam and CO2 gasification as well as the influence of mineral content and particle size. Nevertheless, the carbon conversion in the presented data never exceeded 70% and the inhibiting effect of the products has not been included in the model. Another study by Huang et al. [6] focused on the influence of H2 and CO at different temperatures, but only worked with the reaction rate at 50% carbon conversion and omitted a comparison of different conversion models. Fermoso et al. [7] used non-isothermal experiments to determine a suitable conversion model and made statements on the errors of the models but again omitted any inhibiting influence of product gases. Everson et al. [8] assessed the gasification kinetics with steam and CO2 including the influence of the product gases of an inertinite-rich coal with isothermal measurements in a temperature range of 150 K. They used data for almost the complete carbon conversion and validated their assumed kinetic and conversion model with the measurement results but neglected to test other possible models.

It can be stated that most existing work focuses on analysis of single aspects of the gasification, and is not suitable to describe the conversion process in a gasifier completely with its changing gas compositions, temperatures, and particles of varying carbon conversion. For correct prediction of the gasifier behavior with Computational Fluid Dynamic (CFD), a sound modelling of the reaction properties of the fuel is imperative. Therefore, this work aims at demonstrating a methodology to find a complete model for the char conversion during gasification of one specific lignite char that takes into account all relevant temperatures and gas compositions for the full range of char conversion.
