Concepts in Coalmine Ventilation and Development of the VamTurBurner© for Extraction of Thermal Energy from Underground Ventilation Air Methane

Abstract

Climate change is emerging as a significant challenge in terms of the response needed to mitigate or adapt to the predicted global changes. Severe impacts due to rising sea-level, seasonal shifts, increased frequency and intensity of extreme weather events such as storms, floods or droughts have become accepted by the scientific community as a real and present threat to civilisation. The most significant impacts are expected in the Arctic, the Asian mega-deltas, Small Island Developing States (SIDS) and sub-Saharan Africa (IPCC 2007). There are two approaches to global climate change either mitigation or adaptation. This dissertation aims to provide the initial design concepts for a system to mitigate methane, a significant Greenhouse Gas (GHG), emitted from coalmines by ventilation air circulated through the underground workings. The VamTurBurner©, a Ventilation Air Methane (VAM) gas turbine based methane burning system, is proposed as a method of extracting the thermal energy from the VAM. A key aspect of the problem responsible for the difficulty in extracting the energy from VAM is the low concentration of methane in the high volume ventilation airflow. This approach recasts the concepts of combustion dynamics of a premixed fuel flow to that expected for VAM to ascertain the conditions conducive to combustion or oxidation of the methane in the ventilation air. A numerical model using Large Eddy Simulation (LES) to study the combustion dynamics revealed that the temperature of the incoming ventilation air is a key variable related to the concentration of the VAM. Computational Fluid Dynamics modeling was used to study the design features needed to engineer a system capable of providing the required temperature of the incoming ventilation air. Applications for the available thermal energy are discussed in terms of the potential to generate electricity with steam turbines, provide space heating, produce hot water for many uses, and use the heat for industrial drying or as desired. The efficiency of the energy system is enhanced when the output from the amount of natural gas or electricity purchased is compared to the output enhanced by the addition of methane, considered as free. The VamTurBurner© concept, as described in this dissertation, appears to be a viable method of mitigating atmospheric methane in the pursuit greenhouse gas reduction.