Impacts of char structure evolution and inherent alkali and alkaline earth metallic species catalysis on reactivity during the coal char gasification with CO₂ /H₂ O

Abstract

Summary In this work, we studied the effects of char structural evolution and alkali and alkaline earth metallic species (AAEMs) catalysis on the reactivity during the char gasification with CO2, H2O, and their mixture. The gasified chars with different carbon conversion levels were prepared, and their physicochemical structures were characterized via nitrogen adsorption and FT‐Raman techniques. The concentrations of AAEMs in different modes were obtained by the sequential chemical extraction method. The reactivities of the raw and gasified chars were analyzed by the thermogravimetric analysis. The gasification atmospheres had varied effects on the physicochemical structure of coal char. The gasified char obtained in the CO2 atmosphere had a lower aromatic condensation degree compared with that obtained in the H2O atmosphere, irrespective of the temperature. The impact of the atmospheres on the specific surface area of the char varied with the temperature because H2O and CO2 have different routes of development of pore structure with coal char. A large specific surface area facilitates the exposure and dispersion of more AAEMs on the surface of the channel, which is conducive to their contact with the gasification agent to play the catalytic role. Thus, the reactivity of the gasified char is well correlated with its specific surface area at different gasification temperatures. In the absence of AAEMs, the chemical structure of coal char becomes the dominant factor affecting the reactivity.

Study on CO 2 gasification kinetics of biomass char based on pore structure analysis: Theoretical modelling of structural parameter ψ in random pore model

“…However, it is not an easy task to realize the theoretical modelling of the structural parameter model issues. The influence of many factors, such as the pore structure, 39,40 catalytic elements, 41,42 heat transfer 43 and mass transfer, 44,45 should be considered. Among these factors, the pore structure of char is an important factor for the accuracy of the model because the pore structure is not only the primary attachment site of the catalytic elements but also the primary site of the gas-solid reaction.…”