Transformation Characteristics of Arsenic and Lead during Coal Combustion

The study of the transformation of heavy metals during the coal combustion process is of great significance to controlling their emission. In this study, three coals with different contents of arsenic (As), lead (Pb), and mineral elements were selected. The experiments were conducted at 900–1300 °C using a drop tube furnace system. The transformation of As and Pb during the combustion processes of the three coals was obtained. It was found that both the gaseous and particulate phases were important forms of As and Pb in the combustion products. As the temperature increased, the proportion of gaseous-phase As of the YBS (Yuan Baoshan) coal and JT (Jing Tai) coal first increased and then decreased, and the proportion of gaseous-phase As of the HLH (Huo Linhe) coal increased slightly. As the temperature increased, the proportion of gaseous-phase Pb of the three coals increased and reached approximately 65% at 1300 °C. For the particulate phase, As and Pb were mainly present in ultramicrometer particles after combustion. The differences in the three coal components caused the different distributions of As and Pb in the gaseous and solid combustion products. The coal with a high content of iron (Fe) and calcium (Ca) was more conducive to the migration of gaseous-phase As to solid-phase As during flue gas cooling, while the effects of Ca and sulfur (S) on Pb transformation in the coal were offset. The original modes of occurrence of As and Pb in the three coals were mainly organic-bound and residual forms. During the combustion process, the organic-bound As and Pb were completely released, the residual As and Pb were partially released, and small amounts of water-soluble and ion-exchangeable As and Pb were formed. The analysis of the distribution characteristics of As and Pb in the combustion products showed that the direct release ratios of As and Pb during high-temperature combustion were greater than 45%. During flue gas cooling, more than 60% of As and Pb in the submicrometer particle were produced by transformation from the gaseous phase to particulate phase.