Steam gasification of Miscanthus derived char: the reaction kinetics and reactivity with correlation to the material composition and microstructure

Abstract

This work presents a comprehensive study on the steam gasification kinetics and reactivity of Miscanthus chars (MC) prepared at different temperatures (600 °C, 800 °C and 1000 °C) with the correlations to their composition and microstructure. The results showed that the order of gasification reactivity was MC600 > MC800 > MC1000, and the microcrystalline structure and the content of inherent alkali and alkaline earth metals in the MC were the main factors affecting their reactivity under steam gasification. The reactivity also increased with the increase of gasification temperature, and the effect of gasification temperature on the reactivity of MC was far greater than that of the char production temperature. High heating rate could also effectively promote the gasification reactivity of MC. The kinetics of the steam gasification process were analyzed by different modelling methods. The Random pore model (RPM), among the three methods compared, was the most suitable one to describe the kinetics of isothermal gasification process, of which, the activation energies were in the range of 176-203 kJ/mol with a good kinetic compensation effect between activation energy and pre-exponential factor. The master-plots method proved that the F 2 mechanism was suitable for describing the early stage (X<50%) of the MC gasification reaction, and the D 1 mechanism was suitable to the late stage (X >50%) of the MC gasification process.

Kinetic study on the CO2 gasification of biochar derived from Miscanthus at different processing conditions

“…The quantitative description of index S was used to evaluate the effect heating rate on the reactivity of the biochar. A high S value means that the biochar has a high gasification reactivity [18].…”

“…As shown in Eq.10, in the whole range of gasification reaction, comparing the experimental value of ( ) ( 0.5 ) ⁄ with the theoretical value of ( ) ( 0.5 ) ⁄ , the mechanism function (corresponding to the theoretical curve) that best matches the experimental curve can be considered as the most probable mechanism function of the biochar gasification reaction. It is considered that the kinetic model function ( ) (corresponding to the theoretical curve) is the kinetic model function of the biochar gasification experimental curve [18].…”

“…Nevertheless, the gasification reactivity is very difficult to predict because of the difference in their physicochemical properties. Tian et al [18] reported that the microcrystalline structure and the alkali and alkaline earth metal content in the miscanthus derived biochar were the dominant factors for the change of gasification reactivity.…”

“…The reaction kinetics are critical in process development, as they provide important parameters for reactor design and process modelling [22]. Some research showed that the kinetic parameters of different biochar produced by different conditions are not the same [3,18,23]. Wang et al [6] obtained the CO 2 gasification kinetic parameters of biochar prepared at N 2 , H 2 , CO and CO 2 atmosphere by a number of kinetic modelling methods.…”

“…In our previously work [18], it was discovered that the biochar preparation temperature resulted in significant differences in material microstructure, composition, and gasification reactivity of the biochar prepared at N 2 atmospheres. In order to further study the microstructure characteristic and gasification reactivity of biochar for optimisation, it is important to comprehensively understand the parametric factors that can influence the gasification mechanism under a variety of processing atmospheres.…”