In-situ reaction between arsenic/selenium and minerals in fly ash at high temperature during blended coal combustion

Abstract

Blended coal combustion technology was extensively used in coal-fired power plants in China. In order to investigate the in-situ reaction between trace elements and minerals in fly ash during blended coal combustion, a bituminous (HLH), anthracite (ZW) and the blended coal of these two parent coals were combusted in a drop tube furnace at 1150°C. The ash gathered at high temperature segment (HTA) and low temperature segment (LTA) of the furnace were analyzed, respectively. The results indicated that the retention rates of arsenic in HTA were lower than that in LTA, which suggested that arsenic would be re-absorbed by ash during cooling down of flue gas. For HTA the retention rates of arsenic in ash of ZW, Z3H1, Z1H1, Z1H3, HLH were 60.31%, 26.85%, 13.29%, 20.23% and 36.11%, respectively. The arsenic was more difficult to be captured by HTA of blended coal than that of parent coal. As for selenium, the retention rates in HTA of five coal samples were 24.68%, 23.60%, 20.58%, 15.19% and 38.13%, which had the same retention law as arsenic. The results of X-ray diffraction (XRD) demonstrated that the mineral morphology was changed obviously during blended coal combustion. Unlike parent coal, mullite appeared in HTA of blended coal, and peak of mullite was enhanced with proportion of ZW increased in blended coal. It was consistent with the trend of retention of As and Se in HTA. It illustrated that change of mineral species and in-situ reaction between minerals and trace elements significantly affected emission of arsenic and selenium during blended coal combustion.