Viscosity and crystal morphology data of anorthite bearing synthetic coal slag systems. (15th November 2020)

• Record Type: Journal Article
• Authors: Schupsky, Jan Peter; Saar, Olga; Wu, Guixuan; Dohrn, Matthias; Müller, Michael
• Is Part Of: Fuel. Volume 280(2020)
• Publication Date: 2020-11-15
• Subjects: Entrained flow gasification -- Coal slag -- Slag viscosity, crystallisation -- Anorthite -- Crystal morphology; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2020.118663
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: Viscosity measurements of three synthetic coal slags. Non-Newtonian behaviour was found, based on crystallisation of anorthite in the slag. Crystallisation of slag investigated via quenching experiments. Anorthite is the major crystallising phase and was defined as a tetragonal prism. Anorthite morphology data were gathered from the quenching experiment results. Abstract: In this study, three synthetic SiO2 -Al2 O3 -CaO-Fe2 O3 (-MgO) coal slag systems (ST-D-2, HKT, SOM-1) with varying basicity were investigated on their viscosity and the dominant crystallisation product: anorthite (CaAl2 Si2 O8 ). To predict crystallisation products, thermodynamic equilibrium calculations were executed using FactSage and the GTox database. Anorthite is predicted as a major crystallising phase in the slags. High temperature viscosimetry revealed non-Newtonian behaviour of the slags below 1275 °C. Additional viscosity measurements revealed viscosity deviations, based on crystallisation. Post-experimental analysis of the slags revealed the presence of elongated crystals with anorthite composition. Additional quenching experiments were performed and crystallisation results of the HKT slag were exemplarily shown in this study. Quenched samples were analysed by XRD and SEM-EDX to determine the crystallised phases and the crystal structure. Anorthite was identified as the dominant phase in the HKT slag but also in the ST-D-2 and SOM-1 slag system. As crystallisation strongly influences slag viscosity, a phase analysis of anorthite was conducted. The crystal morphology of anorthite displayed a common elongated characteristic and was generalised as a tetragonal prism with variations in its dimensions. Crystal size measurements ascertained constant small crystal sizes at temperatures below 1100 °C, and exhibited an increase of anorthite length with increasing temperatures above 1100 °C. Additionally, the aspect ratio was examined to ensure a complete three-dimensional characterisation of the anorthite phase. Crystal morphology data can be used in a future viscosity model as enhancing parameters to enable the calculation of viscosities for partly crystallised slags.