Study on distribution, chemical states and binding energy shifts of elements on the surface of gasification fine ash

Abstract

Using feed coal as a reference, a series of modern advanced analysis and measurement technologies such as X-ray photoelectron spectroscopy, scanning electron microscopy–energy dispersive X-ray spectroscopy and X-ray diffraction have been used to analyze the gasification fine ash obtained from a pulverized coal gasification unit. The results show that the fine ash mainly consists of elemental carbon, oxygen, silicon, and aluminum. The elemental carbon distributes primarily on the foams structure, while the spherical particles mainly consisted of silicon and aluminum are embedded in the foams structure. The C1s spectrum is composed of five components in which the content of graphitized carbon is up to 38.36%, and the content of aromatic C–C or C–H, the main existing form on coal surface, is only 25.75%. The 67.31% of elemental silicon is combined with bridging oxygen (Si–O) and 32.69% of that connected to non-bridging oxygen (Si–O₂). The existence of aluminum is in the form of aluminum oxides with two coordinated modes ([AlO₆] and [AlO₄]), and the content of [AlO₆] group is nearly double that of [AlO₄]. Simultaneously, the binding energies of silicon and aluminum increase by approximately 3 eV, while that of carbon almost no change because of the number of carbon atoms is significantly higher than that of other elements. The silicon atoms and aluminum atoms are surrounded by masses of carbon atoms for the special microstructure of FA. The different chemical states of carbon with higher electronegativity along with the role of high temperature and pressure make the binding energies of silicon and aluminum changed dramatically.