Fluidized bed gasification of lignite char with CO2 and H2O: A kinetic study

Gasification of a lignite char with either CO2 or H2O at atmospheric pressure was studied in a lab-scale fluidized bed apparatus at different bed temperatures (775-900 °C) and gas concentrations. CO2 concentrations in the range 20-100% and H2O concentrations in the range 10-70% were used in the batch experiments. The carbon conversion rate was measured by following the outlet CO and CO2 concentrations with time. A predictive kinetic model for both CO2 and H2O gasification of the lignite char was developed from the experimental results, that was able to correctly predict the evolution of carbon conversion versus time. Both gasification reactions kinetics followed a Langmuir-Hinshelwood (L-H)-type equation. The activation energy of the CO2 gasification reaction was larger than that of steam gasification, indicating a larger reactivity of the lignite char towards H2O in the investigated temperature range, as expected. Interestingly, the structure-related parameters of the kinetic expressions of the two gasification reactions were the same, suggesting that CO2 and H2O are likely to attack the same carbon surface sites on this char.