Molecular hydrogen evolution as a consequence of atmospheric oxidation of coal: 3. Thermogravimetric flow reactor studies

Large bituminous coal piles stored outdoors for long periods of time can undergo autocatalytic autogenous heating. Associated with the low temperature (50-150 °C) oxidation of the coal is the chemisorption of oxygen and the emission of CO and H₂O. This process is accompanied by residual gas evolution, mainly CO and low molecular weight hydrocarbons. Low temperature simulations in the laboratory (50-150 °C) have shown that an appreciable amount of molecular hydrogen, H₂ (few hundred ppm volume), is also evolved. Flow reactor thermogravimetric analysis of the low temperature coal oxidation process has been performed with two different bituminous coals; one from Northern Appalachia in the USA, and the other from the Ruhr Basin of Germany. It has been observed that the emission of H₂ occurs at temperatures as low as 50 °C and that, as has been previously suggested, this reaction is an oxidation correlated process. Furthermore the emission of H₂ is a fast process, occurring within a few minutes from the onset of heating the coal sample. Prior to the evolution of the aforementioned gases, an increase in the coal sample weight is observed due to oxygen chemisorption. The mechanism and a parameter study is discussed in detail.