Competition and Inhibition Effects during Coal Char Gasification in the Mixture of H2O and CO2

The mechanisms of char gasification in the mixture of H2O and CO2 are not clear, and some problems are yet to be solved. The Langmuir-Hinshelwood (L-H) model of char gasification in the mixture of H2O and CO2 and the inhibition effect between char-H2O and char-CO2 reactions are two controversial issues among these problems. This paper presented new data to elucidate these two issues. Experiments were carried out at atmospheric pressure using a modified thermogravimetric analyzer (TGA) system at various reactant partial pressures and within a temperature range of 1173-1273 K. The kinetic parameters in the L-H model were determined from pure H2O and CO2 gasification (N-2 as a diluent). The experimental results showed that the L-H model based on common active site assumption is applicable to describe the experimental data and the pressure is not the reason leading to different results in validity experiments of common or separate active site assumptions. Including H-2 and CO in the reactant gas does not change the reaction mechanisms from common active sites to separate active sites either. It was also found that the reaction rate first decreases and then increases as the CO2 concentration increases at a fixed H2O concentration, while the reaction rate continuously increases as the H2O concentration increases at a fixed CO2 concentration. This means that the char-H2O reaction is inhibited by the char-CO2 reaction. Finally, the specific surface area tests of char samples at 20% carbon conversion confirm the common active site assumption.