Underground » Ventilation, Gas Drainage and Monitoring
It is important to understand the influence of mine ventilation on the likelihood of developing of a spontaneous combustion event in a longwall mining environment. To date there has been a general concept proposed for a “critical velocity zone” to exist where conditions are ideal for the development of a heating. However, practical demonstration of this concept by laboratory experimentation is lacking. The main objective of this project is to physically validate the “critical velocity zone” concept by investigating the self heating behaviours of a wide range of Australian coals using incubation testing. A suite of 10 coal samples from New South Wales and 11 coal samples from Queensland covering different coal measure sequences within the various coal basin settings have been used for repeat incubation testing at different flow rates from sluggish ventilation conditons to high ventilation conditions. These samples cover a range of R70 self-heating rate values from 0.15°C/h to 11.13°C/h.
The results of the incubation testing show that under ideal conditions a “critical velocity zone” exists for a heating to develop that is dependent on the interaction between the moisture/reactivity heat balance and the ventilation flow rate. This has been demonstrated for coals covering a rank range from high volatile C bituminous to medium volatile bituminous in mining conditions representative of both New South Wales and Queensland. For coals with a low reactivity the “critical velocity zone” corresponds to an area in the goaf where the ventilation flow rate is sluggish. As the coal reactivity increases the location of the “critical velocity zone” may become shallower or wider depending on the moisture/reactivity heat balance.
The wide range of coals and mine site boundary conditions used in this project provides a practical benchmark of coal incubation behaviour for assessing spontaneous combustion hazard likelihood under variable ventilation flow rates.