Focus on Coal
Peter Whitbread-Abrutat
growing energy crops than using existing agricultural land or clearing natural vegetation cover. Biomass crops (grown specifically to be burnt for fuel) typically include fast-growing trees planted at high densities and perennial tall grasses, while biofuel crops are subsequently processed to derive fuels. Jatropha for example produces an inedible oil that can be used to produce biodiesel and is the subject of much interest for growing on mined lands in China, the Philippines and elsewhere. Tere are also potential additional or combination benefits with less intensive energy crops, such as for biodiversity, and/ or providing a carbon sink or offset as forest biomass or soil improvement with ‘biochar’ which could qualify for
carbon credits.
Coal mine methane Atmospheric methane is a greenhouse gas 25 times more potent than CO2
emissions for 2010 were estimated at 6875 million metric tonnes of CO2
equivalent and
are expected to rise by 15 per cent by 2020. Te coal mining industry produces approximately 6 per cent of this total. Sound reasons then for using coal mine methane (CMM) technology to capture it from underground coal mines and use it to produce energy while simultaneously converting it to CO2
– a tried and tested Nick Coppin
technology in many developed country coal mining areas for working coal mines. Even in the case of abandoned mines there can be huge potential as a source of power, although the production of methane declines initially rapidly and then over an extended period. Leading countries in this technology include Australia, Germany, the UK and the USA.
China, the world’s largest emitter of coal mine methane, already captures methane and produces energy from it in working mines, but the potential for further development is enormous.
Bioreactor landfills Open pits and quarries have often been used for the landfill disposal of municipal and other biodegradable wastes. Today, these sites produce methane from anaerobic decay of the waste, which can be captured and burned to produce heat or electrical energy while being converted to carbon dioxide. If properly engineered for optimum gas production and recovery,
Experimental power generation Closed mine sites also provide ideal opportunities for research in alternative energy uses, with vertical shafts and large volume underground workings that are ideal for storing air or water and saline waters that can be used as chemical batteries. Experimental technologies include wave shaft, compressed air storage, acid mine drainage and osmotic power.
Promising future Although interest in these areas is on the increase, the re-use of mine sites for alternative energy generation remains at a small scale. Stringent planning or permitting conditions can affect many alternative energy developments, especially in relation to visual impact.
A more sensitive land and development planning and permitting regime, particularly relating to the re-use of brownfield sites and the re-deployment of labour, could be given a higher priority. Many of the new technologies, although developing
fast, are still in the early stages of commercial viability - often with assistance from government incentive or green energy subsidy schemes designed to encourage development and implementation of energy generation from low-carbon sources during the early years. As they become more commercially viable, and financial institutions more amenable to providing debt and equity finance, the long term future of mine sites could be very different and far more promising than the reality of today. ●
Peter Whitbread-Abrutat and Nick Coppin are with Wardell Armstrong International, Truro, Cornwall, UK, the independent engineering consultancy specialising in mineral resource development and management.
www.wardell-armstrong.com
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www.engineerlive.com
they can be very efficient bioreactors with sustainable supply for many years. Te Woodlawn Bioreactor in New South Wales, Australia, located in the 25 million cubic metre Woodlawn open cut base metal mine, has received over 600 000 tonnes of putrescible waste from Sydney since 2005. Methane is now being harvested to produce
electricity, and 25 wind turbines on the site will potentially generate electricity to power 17 000 homes.
Hydropower Pumped water storage for power generation in the underground workings of closed or abandoned mines or surface open pits are an emerging option for the generation of hydroelectricity. Tis technology is not yet operational, but projects are being planned or are in development. Tey generally involve high capital expense, but avoid the potential environmental impacts of storing water at the surface. Two underground pumped water storage projects
. Global anthropogenic methane
that have been proposed in recent years include an underground limestone mine in Ohio, USA, and the underground workings of an abandoned iron mine in New Jersey, USA.
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