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Clay and pyrite transformations during ignition of pulverised coal

Published online by Cambridge University Press:  05 July 2018

F. H. Hubbard ,
R. J. McGill ,
R. K . Dhir  and
M. S. Ellis
F. H. Hubbard
Affiliation:
Department of Geology, University of Dundee
R. J. McGill
Affiliation:
Department of Geology, University of Dundee
R. K . Dhir
Affiliation:
Department of Civil Engineering, University of Dundee
M. S. Ellis
Affiliation:
Department of Civil Engineering, University of Dundee
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Abstract

Clay minerals are the principal reactive, non-combustible, phases present in the pulverized coal burned in power station furnace units. Despite the short heating time involved, the clay mineral impurity is wholly transformed in the ignition.

Illitic clays are partially melted, fluxed by water and potash, to produce an alumino-silicate melt phase. The melt is frothed by the synchronous production of carbon dioxide in an iron oxide catalysed oxidation of associated carbonaceous matter. This produces the hollow, gasfilled, glass-walled spheres (cenospheres) characteristic of pulverized fuel ash (PFA). Partial, primary devitrification crystallization of mullite and quartz from the high-alumina glass is general and the extent of devitrification may influence the pozzolanic efficiency of the PFA cenospheres.

Without the advantage of potash fluxing, the kaolinite lattices are dehydrated and transformed, without melting, to amorphous aluminosilicate and crystalline mullite.

Oxidation of pyrite leads to coating of cenospheres by condensed magnetite and the emission of sulphur dioxide in the flue gases.

Type
Research Article
Information
Mineralogical Magazine , Volume 48 , Issue 347 , June 1984 , pp. 251 - 256
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1984

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