Particle scale study on gasification of char in molten salt under carbon dioxide atmosphere

Abstract

Gasification in molten salt provides a promising way for the direct carbon fuel cell. Using visualization and surface analysis approaches, the interactions between char particles, coal, coal ash and molten salt during gasification in molten salt were examined in this work. It was discovered that the gasification rate of char particles without molten salt coverage gradually slowed down due to the blocking of ash in the pore structure of char after a period of gasification reaction (the shrinkage rate was about 60%). At this time, the char particles covered by molten salt reacted rapidly, which accelerated the gasification rate and the conversion of char particles. It was because that ash in the pores of the char particles was absorbed by the molten salt, accelerating the reaction. The char particles (the shrinkage rate was about 15%) could not react quickly after being covered by molten salt and they mainly underwent the processes of being covered, corroded and broken. The char particles covered by molten salt were cut to observe the morphology of char particles using Focused Ion Beam (FIB) combined with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis. It was found that the traces of diffusion of gas products in the molten salt and the entry of molten salt into the char had a dissolving and pore-expanding effect on the char particles. Further analysis about the gasification reactivity of char particles was conducted by Raman analysis, and it was discovered that dissolved (broken) char particles were more active than undissolved (unbroken) char particles.