Compositional Variations in Pilot Gasifier and Laboratory-Produced Slags and their Impacts on Slag Viscosity and Coal Assessment

Abstract

The flow behaviour of coal mineral matter at high temperatures is an important parameter for coal use in entrained-flow gasification technologies. Recently, gasification performance data was obtained from a series of pilot-scale gasification tests on a suite of well-characterised Australian black coals. Evaluation of the results of the pilot tests and the detailed laboratory investigations provided the opportunity for evaluation of the practical applicability of different laboratory and modelling techniques for coal assessment in terms of mineral matter behaviour in entrained flow gasification. A series of viscosity measurements was made over the range 1200–1600uC using slags produced in a pilot scale gasifier at temperatures between 1200 and 1700 uC, and laboratory-produced slags. These data were compared with viscosity predictions based on an empirical model developed from an extensive database of slag viscosity measurements. Major differences between predicted and measured viscosities were investigated and, where appropriate, related to slag composition and microstructure. There were some significant differences (in some cases up to 100% of the viscosity values) in the viscosity behaviour of laboratory-prepared slags and those produced during the pilot-scale gasification test runs. These differences were attributable to differences between the composition of the laboratory-produced slags and those tapped from the pilot scale gasifier. The major source of these compositional variations appears to be a result of partitioning of mineral matter components into fly ash and slag in the gasifier, and the possible subsequent interaction of this slag with slag already present on the wall of the gasifier. These observations have implications for the manner in which coal mineral matter is assessed for its likely behaviour, and ultimate suitability for use, in entrained flow gasification systems. In order to improve the reliability of coal slag assessment procedures, test procedures should include preliminary modelling based on expected coal ash and slag compositions, viscosity measurements of laboratory-produced slags, and analyses of ash and slag compositions where possible to ascertain the degree of compositional partitioning and its impact on slag behaviour. Ongoing work is required to better understand the nature of mineral matter transformations under gasification conditions and the impact of this on coal and gasifier performance. f 2011 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association All rights reserved. A R T I C L E I N F O Article history: Received 8 November 2010; Received in revised form 21 March 2011; Accepted 24 March 2011