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The mode of occurrence of the ionisable salt minerals in coals is investigated, together with their release during combustion. Three UK bituminous coals used in the study have been fully characterised and their mineralogical composition established. The most abundant mineral components are the kaolinite and mica groups of aluminosilicates, ankerite, dolomite, calcite, pyrite and quartz. Sodium and chlorine appear to be present as ions attached to surfaces within the coals' porous structure. As the ionisable salt content of the coals decreases, so the melting temperatures of the resultant ashes increases. Increasing chlorine, sodium and calcium contents are correlated with increasing ash fouling and corrosion propensities. The importance of condensing inorganic salts and possibly low melting point eutectic mixtures in providing an initial adhesion layer causing build-up of deposits has been established. Initial deposits on above-bed surfaces are particularly affected by surface temperature and the use of sulphur sorbent bed materials. Chlorine and sulphur anions are recovered primarily as volatile products of combustion. Natural sulphur retention is greatest for the coal with the highest calcium content.

Additional information

Authors: COAL RESEARCH ESTABLISHMENT BCC, British Coal Corporation, Cheltenham (GB)
Bibliographic Reference: EUR 12081 EN (1990) 149 pp., MF, ECU 8
Availability: (2)
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