Secondary Processes on Coal Deposits Change Emissions of Greenhouse Gases

Abstract

Opencast coal mine Bilina (Czech Republic) produces eight million tons of subbituminous coal per year. Contrary to high CO₂ emissions (7.69 Gg/year), the measured CH₄ emissions are low (0.44 Gg/year). To evaluate greenhouse gas emissions from the mine, we measured gas desorption from fresh coals after coal crushing and milling, together with the atmosphere in the mine. Original coal bed methane, lost during basin evolution, was replaced by secondary microbial gas production of CH₄ (δ¹³C −70 to −55 ‰, δD −275 to 260 ‰) and CO₂ (δ¹³C -10 to -16 ‰). Most of the secondary CH₄ was released before excavation, and the recent coal seam emits only CO₂. Loss of CH₄ (0.27 m³ ton^-1) was calculated back from the isotope fractionation of residual CO₂. Excavated coal is rich in CO₂ (0.53 m³ ton^-1), which results in elevated atmospheric concentration on the sampling sites near working excavators (550–2000 ppm).

Keywords: coal, opencast coal mine, coal bed methane, secondary gas production, methane and carbon dioxide emissions, carbon and hydrogen isotopes