"We are able to let our students experience a true heating and to show them how to recognise signs of a heating in practice rather than from a text book," said facility director, Basil Beamish.
Self-heating testing can be performed in the new laboratory at two scales, from grams up to kilograms. As-received coal is tested in a 2-metre column (60-litre capacity) and sub-samples are then tested in an adiabatic oven to obtain the R70 self-heating rate index of the coal. Collaboration with SIMTARS makes it possible to compare the results up to the tonnage scale using their 16-tonne chamber.
The laboratory is being used for both teaching and research. There are four research projects in progress this year, associated with different Australian mines that cover the range from low- to high-propensity to self-heat.
"The marked differences in self-heating development of these coals is helping the students to understand the mechanisms of spontaneous combustion and the effects coal quality has on the hazard", Beamish said.
One of the projects has, for example, already identified pyrite-driven spontaneous combustion. Due to the features of the 2-metre column, the effects of changing ventilation parameters can also be assessed. This has been successfully demonstrated by another project, which has monitored a complete goaf heating from the initial goaf fall through to inertisation.
Initially, the coal was allowed to equilibrate to a starting temperature of approximately 30 degrees C, with no airflow.
"This has provided valuable information on the seamgas bleed rate into the goaf", Beamish said.
As air was allowed to pass through the goaf coal, the temperature profile of the pile was recorded (see figure). An initial hotspot develops as a result of moisture redistribution in the pile and then progressively migrates towards the upwind surface, as it chases the air to feed it. Off-gas analysis was also monitored using both Minigas sensing and gasbag sampling. These results are used to correlate with the temperature history of the heating as it develops.
Once the heating was well established, changes were made to the air pressure and hence air flowrate, to record whether these had a positive or negative effect on the heating development. The heating was allowed to reach a maximum temperature of 220 degrees C, before being inertised with nitrogen. The rate of heating dissipation was monitored during this process.
Commenting on the implications of the research for the industry one of the students had this to say: "Understanding of spontanteous combustion is critical for successful risk management, and it is essential that people entering the coal mining industry have an idea of the complexities of the problem. The wealth of practical information from this form of testing allows students to follow the interaction of all the factors affecting the self heating process, and all in one test! As this is a new area of testing the results are quite exciting, and certainly useful to industry."
A workshop on "Progress in Spontaneous Combustion Testing" is being planned for early next year. This will be jointly hosted by UQ and SIMTARS and sponsored by ACARP. The main aim of the workshop is to provide industry people with the opportunity to see testing in action and discuss the validity and relevance of the techniques being used. Anyone interested in this workshop, which can be accredited as part of continuing professional development, should register to be included on the mailing list. For more information contact:
Dr Basil Beamish
Senior Lecturer in Mining Engineering
Division of Mining and Minerals Process Engineering
The University of Queensland
BRISBANE QLD 4072