MANAGING THE SPONTANEOUS COMBUSTION HAZARD IN SUB-BITUMINOUS UNDERGROUND COAL MINE

Testing and analysis of New Zealand's sub-bituminous coals has highlighted a characteristic of very high to extreme inherent propensity for spontaneous Combustibility. A number of geological geotechnical and operational factors specific to Huntly Fast Mine Further aggravate the risks associated with self heating. In the past the colliery relied on natural inertisation to control the spontaneous combustion hazard in sealed areas. This process was dependent on using the natural disorption of seam methane to develop a fuel rich, but oxygen deficient atmosphere. Following a serious goaf heating resulting in an organised mine evacuation, some significant changes were introduced to the site spontaneous combustion management system. The concept of nitrogen injection, as a method of rapidly inducing oxygen depletion in newly sealed areas, was trialed. Encouraging results from the trial led to further operational use of the technique and resulted in the decision being maid to establish a permanent site based nitrogen facility, This paper presents the additional measures taken by Huntly East Mine, from a mine design, operational process control and gas management perspective, to enhance safety procedures and minimize the risks imposed by the specific characteristics of this coal and its extreme propensity to spontaneously combust. Further, a comparison is made between the gas ratios and trends, from the mine's tube bundle gas monitoring system and gas chromatograph analysis, under normal operating conditions and during the goaf. selfheating incident. The results of the nitrogen injection trial are used to illustrate the proof positive of a simple, efficient and cost effective means of improving safety through the proactive management of the goaf atmosphere. The influence of the nitrogen injection into the goaf is most graphically displayed in the time resolved graphs and Ellicott's diagrams.