Desulphurisation of South African coal using low power microwave energy
Date
2009-07-29T12:19:18Z
Authors
Mohamed, Waseela
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Abstract
The effect of microwave irradiation on South African bituminous coals has been
studied using various alkali solutions and particle sizes. Optimization of the
treatment process was carried out on both low and high sulphur coals at varying
power levels and retention times. Changes in structure and combustion
characteristics after desulphurisation using a strong caustic solution were
investigated.
The optimum sulphur removal time and microwave power for the high sulphur
(±3.3 %) coal were difficult to determine. This is possibly due to the uneven
distribution of pyrite within the coal structure and thus the samples may be biased.
Coal particles of sizes 212 μm and 74 μm showed optimum sulphur removal of 40
% after an exposure time of 10 min at a power of 650 W using a sodium
hydroxide solution. Decreased sulphur contents were noted with a decrease in
particle size. Structural characteristics were largely unaltered as determined by
XRD and Raman analysis. A slight decrease in calorific value and volatile matter
was noted.
The low sulphur coal yielded a 40 % sulphur decrease depicting independence of
the mode of occurrence of pyrite in the coal. Structural characteristics of the coal
were apparently unaffected whilst combustion characteristics decreased to some
extent.
Treatment with strong potassium hydroxide solutions as well as mixtures of
sodium chloride and sodium hydroxide yielded improved desulphurisation values
in comparison with that of the sodium hydroxide solution alone (40 % to 52 %
sulphur decrease obtained). Conventional leaching with sodium hydroxide was
found to show enhanced sulphur removal results than that of coals treated using
microwave energy. Further studies are needed on the desulphurization of South
African coals before a firm conclusion can be drawn.