Assessment of Greenhouse Gas Emissions from Low Temperature Oxidation and Spontaneous Combustion at Surface Coal Mines in Australia

Greenhouse gas emissions from low temperature oxidation and spontaneous combustion from surface coal mines continue to be difficult to quantify and, as a result, are not included in the Intergovernmental Panel on Climate Change (IPCC) inventory of greenhouse emissions. However, this situation may change and in anticipation of this possibility, ACARP has funded research in this area over the past five years.

The first of these projects was ACARP Project C8059 (Carras et al., 2000) in which emissions were measured by placing a specially built chamber over areas of spontaneous combustion in coal mine waste material. The results from that study
provided the first direct measurements of greenhouse gas emissions from spontaneous combustion and low temperature oxidation but the technique was extremely labour intensive and required many measurements to estimate emissions over an entire mine.

During Project C8059, a loose correlation between ground temperature and greenhouse gas emissions rate was observed and this led to the development of Project C9062 (Carras et al., 2002) which sought to use airborne infrared thermography to measure ground temperature and thereby estimate emissions over large areas. Although thermography proved to be very effective at identifying areas of spontaneous combustion, emissions determined by this technique were still subject to large uncertainty. Consequently, the most recent project, which is currently underway, C13073 - Determination of the greenhouse gas emissions from spontaneous combustion, was established to investigate the use of inverse methods to determine emissions from spontaneous combustion. In this approach, CO2 concentrations in the air downwind of areas affected by spontaneous combustion are being monitored over extended periods and air pollution modelling techniques applied to estimate the flux of CO2 from the source.

While past and current research has focussed on methods for estimating emissions from spontaneous combustion there is at present little quantitative information on the relative size of these emissions compared with other greenhouse gas sources within individual coal mines or the coal industry overall. To address this situation, the project described in this report was established with two objectives:

• to assess the significance of greenhouse gas emissions from spontaneous combustion for individual coal mines and
• to investigate the suitability of satellite imaging as a means of estimating the significance of spontaneous combustion across the coal industry.

This study provides the first estimates, based on actual mine data, of the significance of greenhouse gas emissions from spontaneous combustion for a number of individual surface coal mines. These estimates place this emission source in context for individual mines. The study also provides a scoping document on the feasibility of using satellite data to estimate the significance of spontaneous combustion across the entire black coal industry.