Char-wall interaction and properties of slag waste in entrained-flow gasification of coal

The aim of this paper is to investigate the properties of solid wastes coming from an industrial-scale pressurized entrained-flow gasifier, by means of a combination of techniques: elemental, granulometric and X-ray diffraction analyses, scanning electron microscopy and energy dispersive X-ray analysis. The results are critically discussed in the light of the different regimes of char-slag micromechanical interaction and of the different phases that are established in the gasification chamber. The discussion allows to give useful insights concerning the properties and partitioning of carbon among the three main sources (coarse slag, slag fines, fly ash) of solid residues coming from the gasifier: in particular, differences between coarse slag and slag fines are highlighted, though these wastes are generated from the same main-stream. Furthermore, it is observed that residual carbon in slag granules is present in a segregated embedded form, while slag fines are composed of both porous (high-carbon) and compact (low-carbon) material. Altogether, the properties of the three residues are consistent with a mechanistic framework of the bulk-towall transfer and partitioning of solids during entrained-flow gasification of coal developed in a recently-published theoretical paper.