WWRC 95-13
Reaction of CO2 With Clean Coal Technology Ash to Reduce Trace Element Mobility
Abstract
The combustion of coal in power plants generates solids (e.g., fly ash, bottom ash)
and flue gas (e.g., SOX, C02). New Clean Air Act mandated reduction
of SOX emissions from coal burning power plants. As a result, a variety of Clean Coal
Technologies (CCT) are implemented to comply with these amendments. However, most of the CCT
processes transfer environmentally sensitive elements (e.g., As, Cd, Pb, Se) from flue gas to CCT ash.
The objective of this study was to determine the effect of a pressurized C02 treatment on
the chemistry of CCT ash. Three CCT ash samples, produced from lime injection, atmospheric fluidized
bed combustion, and sodium carbonate injection processes were reacted under different
C02 pressure treatment conditions. Treated and untreated samples were subjected to
various experiments including, X-ray diffraction (XRD) analysis, calcium carbonate solubility studies,
and trace element extraction studies. Factors influencing the efficiency of a C02
treatment for CCT ash samples include combustion process, moisture, C02
concentration, and pressure. The C02 pressure treatment resulted in the precipitation of
calcite in CCT ash samples, and thus lowered the pH and the concentration of extractable trace elements
(e.g., Cd, Pb, Cr, As, Se). Furthermore, we found that C02 pressure treatment was more
effective for lime injection and atmospheric fluidized bed combustion processed samples than for sodium
carbonate injection processed samples.
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