Beating the heat

The CSIRO is working to develop a fire-suppressant gel as a potential solution to the risk of spontaneous combustion in underground coal mines.

Working in an underground coal mine brings with it inherent risks.

While many of the traditional risks have been eliminated through

improved knowledge and technology, others still remain.

Of all of the safety concerns that are faced by coal miners, the most pressing is the spontaneous heating and combustion of coal that comes from the reaction of coal and coal dust with oxygen.

Beyond the obvious safety fears

that come from the possibility of

spontaneous combustion, including the potential loss of life, other factors are of concern.

It can have severe financial implications by causing lengthy production delays, as well as the damage to or loss of machinery and coal resource.

With this knowledge firmly in mind, scientists from CSIRO Exploration and Mining (now CSIRO Earth Science and Resource Engineering) have embarked on a research project sponsored by the Australian Coal Association Research Program (ACARP) to develop effective composite gels that can be used as barriers to fight against heating and combustion in underground coal mines.

According to CSIRO’s Dr. Sheng Xue, the objective of the study, Controlling Underground Heatings Using Innovative Fire-Suppressant Injection, was to identify suitable gel-forming mixtures that can be injected as a low viscosity fluid mixture into the ground of a coal mine through boreholes.

The gel is designed to form a barrier that is able to either block air/oxygen from areas undergoing heating, or stop the loss of other fire suppressants, such as water, that have been put in the at-risk areas.

The study also featured a number of additional objectives to do with finding the correct type of gel.

“A gel suitable for controlling and extinguishing heating needs to meet the requirements of easy preparation, no or low toxicity, adjustable gelling time, low sensitivity to dissolved salts, controllable viscosity, long gel life, relatively high thermal stability and incombustibility,” Xue said.

Results of the study have proved to be very positive, showing that the gels can successfully be used to control heating at various points of an underground coal mine, including the longwall face, the roof of a gate road and a sealed longwall face.

With results of these tests,

researchers are confident that the gels will be able to make significant contributions to reducing spontaneous combustion within a few years.

An extension project proposal has been submitted to ACARP to consider developing commercially applicable delivery systems.

The two methods under consideration are a mobile delivery system which is best suited to smaller-scale heating, and a surface-based system for large-scale situations.

The other main components of the new research will include developing injection approaches that would maximise air-blocking area for a given volume of gel; undertaking field tests at known heating sites exposed during open cut mining of old workings; and developing operational procedures and guidelines for the gel injection technique.

“If an extension of the project is granted it may take two or three years to complete,” Xue said.

“Then mine operators can begin to make the changes to incorporate the new mobile gel preparation and injection system.”

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