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

The properties of solid wastes (fly and bottom ashes) generated from an industrial-scale pressurized entrained-flow gasifier were investigated. Bottom ashes consist of coarse slag granules and fine slag particles, both retrieved from the quench bath but characterized by distinctively different morphological and physicochemical properties. Characterization of fly ash, coarse slag, and fine slag has been accomplished by a combination of experimental techniques: elemental, granulometric, and X-ray diffractometric analyses, scanning electron microscopy, and energy-dispersive X-ray analysis. Analysis of results gives useful information on the properties and partitioning of carbon among the three main ash streams (coarse slag, slag fines, and fly ash). 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. Carbon partitioning and properties of the different phases of which bottom ashes are composed are further analyzed in light of the flow patterns that establish the gasification chamber, with a focus on char-slag micromechanical interaction and char segregation. The properties of the three ash residues are consistent with a mechanistic framework, developed in a recent study (Montagnaro, F.; Salatino, P.Combust. Flame 2010, 157, 874-883), according to which extensive bulk-to-wall transfer of char is followed by the establishment of a segregated dense-dispersed char phase in the near-wall region of the gasification chamber.