Title page for ETD etd-11112008-125913

Document Type Doctoral Thesis
Author Matjie, Ratale Henry
Email henry.matjie@sasol.com
URN etd-11112008-125913
Document Title Sintering and slagging of mineral matter in South African coals during the coal gasification process
Degree PhD
Department Materials Science and Metallurgical Engineering
Advisor Name Title
Prof P C Pistorius Supervisor
  • computer controlled scanning electron microscopy
  • energy dispersive spectrometer
  • X-ray diffraction
  • electron microprobe
  • particle morphology
  • low temperature ashing
  • pyrolysis
  • sequential leaching
  • pyrometallurgy
  • screening
  • density separation
  • coal analysis
  • coal sintering and slagging
  • Lurgi gasification
  • coal ash analysis
  • mineral matter
  • petrology
  • scanning electron microscope
  • quantitative evaluation
  • macerals
  • FactSage modeling
  • glass analysis
  • scanning electron microscopy
Date 2008-09-02
Availability unrestricted

Coals, from mines in the Highveld coalfield, as well as gasification ash samples were characterised, in order to understand the mineralogical and chemical properties of the individual components in the gasification feedstocks.

X-ray diffraction of low temperature oxygen-plasma ash indicates that the coals contain significant proportions of kaolinite, quartz and a fluxing elements-bearing mineral (dolomite), plus minor concentrations of illite and other fluxing elements-bearing minerals namely calcite, pyrite and siderite.

Of the feed coal, the -75+53 mm size fraction has a high pyrite, and to a lesser extent a high calcite and dolomite content. However, the small proportion of iron-bearing phases (from the reaction between kaolinite and pyrite) in samples taken from the gasifier implies that pyrite contributes minimally to sintering or slagging in this case.

Calcite is mainly present in the >1.8 g/cm3 density fraction of the feed coal, whereas dolomite is mainly present in the 1.5-1.8 g/cm3 density fraction, as inclusions or fine cleats in the coal matrix.

Electron microprobe analyses of coals from the six different South African mines confirmed that some Ca, Mg, Al, Si, Na, K, Ti and Fe are present in the organic matrix in the coal samples tested in this study, but the amounts of these are small compared with the fluxing elements in minerals.

XRD and microprobe analyses indicate that the ash clinker samples taken from the gasifiers contain a number of crystalline high temperature phases, including anorthite, mullite, cristobalite, quartz and diopside. FactSage confirmed that anorthite and mullite are equilibrium phases at elevated temperatures in the ash clinkers and heated rock fragments. Limited reaction takes place between the included coal minerals and the extraneous rock fragments.

ŠUniversity of Pretoria 2008

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