Underground » Ventilation, Gas Drainage and Monitoring
The study addresses Hydrogen Sulphide (H2S) in coal seams. The objectives of the project were to undertake a comprehensive series of interrelated studies to gain a full understanding of this complex problem. The goal was to understand how, where and why high concentration zones of H2S occur, how does gas release from the coal mass, can concentrations be diluted or neutralised through improved ventilation, water, chemical or microbiological solution sprays or infusion and can mining approaches be modified to contain the problem efficiently? A multidisciplined approach has been used for related investigations.
Co-initiators of the project were the Queensland Oaky Creek and Southern Collieries. Both these operations had experienced significant modification to mining practice and slowing down of development rates due to H2S in coal seam gas and both were scheduled to mine through further high concentration H2S affected panels.
Prior to the study there was virtually nothing published on the topic within the international literature and few overseas studies that have addressed the problem. H2S is an extremely toxic gas and can cause death at exposures above 500 ppm. Coal cutting within H2S affected seams can release airborne contamination levels of over 100 ppm H2S during mining.
An initial section examined background issues including H2S occurrence, properties, reaction chemistry, physiological effects and safety and legislated statutory considerations.
The mine ventilation system can be modified to allow safe production through H2S affected zones. Designs for maximising safe production through affected mine panel or development headings have been tested. Mining options to reduce H2S emissions have also been examined.
A major program of in-seam chemical neutralisation infusion trials was undertaken at Southern Colliery. The basic aim of the chemical infusion process is to prestrip a significant proportion of H2S to allow coal mining at a production rate that ensures a safe working environment at all times. Some approaches to analysis of results and evaluating the efficiency of the approach have been given. However it has not been possible to complete a thorough analysis and to arrive at a value for infusion neutralisation efficiency that can be supported with confidence. It is strongly recommended that mines facing a H2S problem and contemplating use of infusion neutralisation consider investing employee and management resources in a full evaluation study to allow quantification of efficiency and benefits. Despite these hesitations, results particularly from the 703 Longwall trial indicated that the infusion program did have a measurable beneficial effect on face atmospheric conditions during mining of the H2S zone subsequent to infusion.
A comprehensive study of a major impediment to mining in a number of areas in Queensland, Australia is described. The study was the first of its kind. Prediction of future occurrences of H2S zones can occur with greater reliability. A major benefit has been that mines facing extraction in H2S coal seam zones have greater confidence due to the findings of studies and trials undertaken. Safety risk assessments can be undertaken from a base of objective data. There is a greater ability to quantify the cost of not mining through or sterilising H2S affected coal compared to the cost of proactively altering (and possibly slowing down) the mining system and incorporating aspects such as changed ventilation, chemical sprays and seam neutralisation to ameliorate the problem.