Presented paper

IMWA2019 Students work

Hydrogen Generation in Underground Mines

Declercq, Julien (1); Oelkers, Eric (2); Griffiths, Ruth (1); Bowell, Rob (1)
1: SRK Consulting, United Kingdom; 2: University College London, United Kingdom

Mine gas explosions present a serious safety threat in the worldwide mining industry, causing potential loss of life, production loss and financial loss. The production of hydrogen, a common explosive gas, by serpentinisation in ultramafic‐hosted hydrothermal systems is a well-documented process that has been studied in the context of the origin of life, exotic habitats and astrobiology, and hydrothermal alteration of the ocean floor. However, hydrogen generation can also occur in underground mines, with potential disastrous consequences, and this scenario has not been studied in details. This study aims to model hydrogen generation and potential explosibility associated to the case study of an underground mine hosted within mafic rocks.

Hydrogen generation in the underground mine has been calculated by 1/ determining the exposed surface area of mafic minerals, e.g. serpentine and olivine, within the mine workings during life of mine. This has been achieved using the mineralogical description of the different exposed lithologies coupled with the 3D mine design and geological block model. 2/ by applying experimentally determined alteration rates to those exposed minerals allowing us to define a kinetic predictive model of hydrogen release by serpentinisation.

Subsequently hydrogen explosivity has been determined by tracking, within the gas mixture present in the stopes, the predicted hydrogen proportion in a hydrogen, nitrogen and oxygen ternary diagram with respect to their flammability envelope (Dwyer et al, 2003). This potential was further explored in the case of a simplified atmosphere (O2, N2, H2 and CO2) using the revised Le Chartier method (Cheng et al. 2012).

It has been recognized that the potential for hydrogen generation in subsurface systems is a rate-controlled process and as such sensitive to various parameters, e.g. temperature, pressure, pCO2, redox, mineralogical variations. The explosibility of the underground mine gas mixture has been explored in a sensitivity study and the results compared to other real-world examples.

References:

Cheng, J., Wang, C., & Zhang, S. (2012). Methods to determine the mine gas explosibility–An overview. Journal of Loss Prevention in the Process Industries, 25(3), 425-435.

Dwyer Jr, J., Hansel, J. G., & Philips, T. (2003). Temperature influence on the flammability limits of heat treating atmospheres. In Proceedings of the 22nd heat treating society conference and the 2nd international surface engineering congress. Indianapolis (pp. 24-28).

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