Friday, 30 September 2011

Accidental combustion of a coal waste heap in Scotland burning since 2009

Researchers at the Universities of Edinburgh and Strathclyde have studied a burning Bing. A 30 m high waste heap at Bogside, North Lanarkshire, Scotland, started to smoulder (flameless combustion) in 2009, approximately 80 years after the closure of the pit.

 The work was presented at the Geological Society of America Annual Meeting in Minneapolis, USA. Presentation reference: Investigation of self-sustained combustion of a coal waste heap in Scotland. And it has featured in the The Scotsmant, Edinburgh website, Strathclyde website, and Vision Systems (on our use of thermal imaging).

Photo composition, clik to enlarge.


Coal mining was widespread in the central belt of Scotland from 1830 until the 1970’s and created a legacy of waste heaps or ‘bings’ that still dot the landscape. High content of coal fines and carbonaceous shales, make bings very prone to self-heating and smoldering combustion.

Chemical, geotechnical and physical parameters of the Bogside Bing have been studied. A combustion front is moving from west to east along the axis of the bing at an approximate rate of 1m/month. Three well-defined zones were identified and mapped using thermal imagery and temperature probes: the undisturbed zone, the preheating plus drying zone and the combustion zone. The subsurface fire results in a detrimental effect to the vegetation and structural integrity of the heap.

Spread of the combustion is accompanied by the development of vents ahead of the front, fissures that run parallel to the direction of heating and smaller landslips along the flanks. Changes to the heap's soil mechanics induced by the smouldering front create a network of fissures, some running deep, that supply the front with enough air to sustain the process.

Analysis of gas from the vents, show elevated CO2, CO, CH4 and SO2, and partially depleted in oxygen. All these are indicative of smouldering activity within the bing. The primary environmental concerns are likely to be from SO2 release and metals leaching from waste material (i.e. Pb, Se, Cr). The stability of the structure may be compromised as smouldering progresses. Bogside Bing continues to release products of combustion and represents an accidental source of fossil fuel burning.
Dr G Rein next to a water vapour vent on top of the Bogside Bing


Full reference of the presentation:
K Torrance, C Switzer, G Rein, R Hadden, C Belcher, R Carvel, Investigation of self-sustained combustion of a coal waste heap in Scotland, Paper No. 282-8, 2011 GSA Annual Meeting, Minneapolis 9–12 Oct. 2011.