Bottom ash samples were collected from four lignite power plants of Greece.
Granulometric analysis was executed and after homogenization four distinct
fractions (>1.25, 0.63-1.25, 0.18-0.63, <0.18 mm) were obtained. The samples
were analyzed by X-Ray Diffraction (XRD) and Energy Dispersive System (EDS),
while thermogravimetry (TG/DTG) and stereomicroscope viewing were applied
for the coarse fractions. Furthermore, proximate analysis (moisture, ash,
volatiles, fixed carbon) was undertaken and Loss on Ignition (LOI) and
calorific values were determined. The particle size distribution revealed
that bottom ash satisfies the gradation criteria for concrete and
geotechnical applications. The mineral composition included mainly amorphous
matter, quartz, plagioclase, calcite and gehlenite and minor amounts of
pyroxene, portlandite, hematite, micas etc.. The chemical analysis showed
Si, Ca, Al, Mg, Fe, S as major and Ti and K as minor chemical elements,
indicating high slagging and fouling potential within the thermal chambers.
Based on the chemistry and mineralogy of the bottom ash samples, a potential
utilization in concrete manufacturing is discussed, taking into account
certain limitations. Based on LOI, proximate analysis, calorific values and
TG/DTG profiles of the coarse fractions (>1.25 mm), certain differences in
the characteristics of the bottom ash of the younger and the three older
power plants were observed. High amounts of unburnt carbon were determined
in the coarse fraction (>1.25 mm) of all plants except the younger one,
indicating a problematic combustion within the chambers and a potential of
reburning these coarse material in a waste to energy application.
A comprehensive analytical characterization of Greek lignite bottom ash samples