Char-Wall Interaction and Properties of Slag Waste in Entrained-Flow Gasification of Coal Paola Brachi 1 , Fabio Montagnaro 1 , Piero Salatino 2,* 1 Dipartimento di Chimica, Università degli Studi di Napoli Federico II, Complesso Universitario di Monte Sant’Angelo, 80126 Napoli (Italy) 2 Dipartimento di Ingegneria Chimica, Università degli Studi di Napoli Federico II, Istituto di Ricerche sulla Combustione, Consiglio Nazionale delle Ricerche, Piazzale Vincenzo Tecchio 80, 80125 Napoli (Italy) Abstract 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-to- wall transfer and partitioning of solids during entrained-flow gasification of coal developed in a recently-published theoretical paper. Overview Entrained-flow coal gasifiers of new generation are often characterized by operating conditions (high operating temperatures and multi-stage feedings of coal and gaseous reactants) so as to favor ash migration/deposition onto the reactor walls, whence the molten ash (slag) flows and is eventually collected at the bottom of the gasifier [1,2]. Detailed studies concerning the fate of char particles as they impinge the wall slag layer have been only recently developed [3–6]. In a recently-published paper, Montagnaro and Salatino [7] have highlighted the relative importance of the parallel pathways of coal conversion consisting of entrained-flow of carbon particles in a lean-dispersed gas phase vs. segregated flow of the particles in the near-wall region of the gasifier promoted by particle migration and interaction with the molten slag. In particular, by taking into account characteristics such as char density, particle diameter and impact velocity, slag viscosity, interfacial particle-slag tension, theoretical criteria for both char particle entrapment inside and carbon-coverage of the wall ash layer have been developed. * This is represented in Figure 1, which depicts the following plausible regimes of C-slag micromechanical interaction: regime E) (entrapment), in which char particles reaching the slag surface are permanently embodied into the layer and further course of combustion/gasification is hindered; regime S) (segregation), in which char particles reaching the wall adhere to the slag layer’s * Corresponding author: piero.salatino@unina.it Proceedings of the European Combustion Meeting 2011 surface without being fully engulfed, so that the progress of combustion/gasification is permitted; regime SC) (segregation and coverage), in which the coverage of the slag layer with carbon particles is extensive. In this last regime a dense-dispersed annular phase is established in the close proximity of the wall ash layer, where the excess impinging char particles which cannot be accommodated on the slag surface accumulate. This phase is likely to be characterized by a velocity that is intermediate between that of the fast lean-dispersed phase and that of the slowly moving wall ash layer. This feature is beneficial to C conversion due to the longer mean residence time of carbon particles belonging to this phase. Consistently, a schematic diagram of the entrained-flow gasifier is presented in Figure 2 in which, in particular, the presence of three different sources of solid wastes is underlined, that is: slag phase, yielding coarse slag granules upon interaction with the quench bath at the bottom of the gasifier; dense-dispersed phase, giving rise to slag fines upon interaction with the quench bath; lean-dispersed phase, giving rise to fly ash escaping the gasifier in the gas stream. Rationale of the Present Investigation This investigation was stimulated by the operational experience from an industrial-scale pressurized (25 bar; cf. [8,9]) entrained-flow gasifier, operated in the slagging regime (at temperatures around 1700–1900 K; cf. [9,10]). The gasification chamber has an internal diameter of 3.8 m and a length of 13 m. Mass feeding ratios are: W OX /W F =0.8; W S /W F =0.1. Solid fuel feed rate is