Pre-combustion mercury removal potential of rapid pyrolysis in high ash coal and mode of occurrence

Mercury is a widely known pollutant, and coal combustion is one of the largest sources of anthropogenic Hg emission. Mercury reduction technologies globally rely on flue gas treatment. However, pre-combustion techniques show immense potential. Mild pyrolysis of coal offers a promising approach for mitigating mercury emissions. This study investigated the mercury distribution and its mode of occurrence in six high ash coal samples from the Jagannath area of eastern India. The findings revealed that Hg content in coal samples ranged from 0.154-0.308 mg/kg. Majority of the mercury was bound to pyrites (60–90 %) and organic matter (5–15 %). Rapid pyrolysis at temperatures ranging from 200 to 700 °C demonstrated significant mercury removal efficiency (up to 95 %). In particular, at 400 °C with minimal loss in calorific value and mass. Though the high-temperature pyrolysis (600 °C) resulted in maximum mercury removal, but with a notable loss in calorific value and product yield. The Hg content in raw coal, initially ranging from 9 to 20 μg Hg/MJ, was reduced to 3 to 11 μg Hg/MJ in char produced at 400 °C. Further reduction was observed in char produced at 600 °C, where the Hg content decreased to between 2–3 μg Hg/MJ. This research emphasizes the effectiveness of mild pyrolysis in reducing mercury content of high ash coal, thereby facilitating the generation of cleaner energy.