REACTION OF CO2 WITH CLEAN-COAL TECHNOLOGY ASH TO REDUCE TRACE-ELEMENT MOBILITY

The combustion of coal in power plants generates solids (e.g., fly ash , bottom ash) and flue gas (e.g., SOx, CO2). New Clean Air Act mandate d reduction of SOx emissions from coal burning power plants. As a resu lt, a variety of Clean Coal Technologies (CCT) are implemented to comp ly with these amendments. However, most of the CCT processes transfer environmentally sensitive elements (e.g., As, Cd, Pb, Se) from flue ga s to CCT ash. The objective of this study was to determine the effect of a pressurized CO2 treatment on the chemistry of CCT ash. Three CCT ash samples, produced from lime injection, atmospheric fluidized bed c ombustion, and sodium carbonate injection processes were reacted under different CO2 pressure treatment conditions. Treated and untreated sa mples were subjected to various experiments including, X-ray diffracti on (XRD) analysis, calcium carbonate solubility studies, and trace ele ment extraction studies. Factors influencing the efficiency of a CO2 t reatment for CCT ash samples include combustion process, moisture, CO2 concentration, and pressure. The CO2 pressure treatment resulted in t he precipitation of calcite in CCT ash samples, and thus lowered the p H and the concentration of extractable trace elements (e.g., Cd, Pb, C r, As, Se). Furthermore, we found that CO2 pressure treatment was more effective for lime injection and atmospheric fluidized bed combustion processed samples than for sodium carbonate injection processed sampl es.