Mining Publication: A Comparison Between Ignition Behaviours of 7 Different UK and World-Traded Coals in Air, and in a Mixture of Oxygen and Carbon Dioxide Gases Representative of Oxy-Combustion Conditions

A 20L ignition test chamber has been used to test suspensions of 7 UK and world traded coals in air and O₂/CO₂ mixtures typical of oxy-combustion conditions. The coals varied in rank from sub-bituminous to bituminous and were tested in varying concentrations from the ignition limit to 400g/m³. Following each successful test the combustion residue was collected, weighed and analysed within a thermogravimetric analyser, allowing Q factors to be estimated. The ignition limit varied slightly in air, but was mostly around the 200g/m³ level. With the exception of Coal C, which was much harder to ignite, it correlated roughly with coal rank. The ignition limit changed significantly with O₂ concentration when in mixed O₂/CO₂ gases. Only a few high volatile coals ignited in 21% O₂/CO₂ v/v, and then only with a 2500 J, rather than a 1000J, igniter. An increase in O₂/CO₂ levels to 30 or 35% gave ignition patterns similar to those carried out in air with a further increase to 40% having little additional effect. In addition the minimum ignition concentration decreased with increase in O₂. Heterogeneous combustion or gasification of the coal by CO₂ appears to be confirmed by comparing weight loss results for air and O₂/CO₂ mixtures respectively for an equivalent peak pressure rise.