Calculating fugitive emissions

AS speculation continues over whether the Carbon Pollution Reduction Scheme will pass Australia’s Senate, GeoGas chief reservoir geologist Joan Esterle discusses how coal operations can report fugitive greenhouse emissions.

Blair Price

Australia’s longwall mines already have to monitor and record gas streams to varying levels, but Esterle said the CPRS requirements would increase – and in some cases already had – the level and extent of monitoring.

“The increased diligence is partly for CPRS accounting needs but just as importantly for the purpose of increasing gas capture efficiencies,” she said.

“Going forward, operators will maximise the volumes of gas captured in purer, pre and post drainage streams, and in turn minimise gas volumes in the main ventilation system.”

She said this would reduce the greenhouse gas burden and optimise the underground work environment and gas utilisation opportunities.

“The increased monitoring will ensure the availability of robust data sets at mines, which will ultimately lead to improved gas emission forecasts and the ongoing development of gas management strategies.”

Surface operations face a bigger task in meeting the CPRS requirements as they haven’t had to test for gas before.

Esterle set out the main technical challenges facing open cut coal mines in assessing and auditing fugitive emissions from virgin coal to point of sale.

The first hurdle is the detection and accurate measurement of lower gas levels required for open cut mines.

“Open cut mines generally have lower gas contents than the deeper underground,” Esterle said.

“Smaller volumes, and the gas composition of smaller volumes, are more difficult to measure accurately so we are exploring some different methods for improving our techniques.”

Another hurdle is the assignment of gas content to “non-coal” stratigraphy and determining when or which rocks contain no gas and at what depths.

“Traditionally only coal, and maybe carbonaceous material, in the roof and floor are sampled,” she said.

“Estimations for open cut require an assessment of gas content and potential emissions for the complete stratigraphy of the overburden and the floor. Testing can be costly so we are working to optimise sampling without sacrificing information.”

Esterle said another challenge would be deciding on an approach to estimating carbon footprint across the value chain.

“Coal will lose gas as it fragments, exposing greater surface area to air, so one can assume a gas balance approach where ‘all gas is desorbed’ by the point of sale or try to model and monitor gas emissions as a function of comminution through the mining chain.

“The latter is difficult as every coal behaves differently. Some mines are running site audits from the face to the product stockpile to determine whether a simple gas balance approach defines the process or one needs to continuously test.”

She added that doing all this cheaply so the testing regime was not “onerous or a disincentive” was yet another challenge for surface operations to meet the CPRS requirements.

Lastly, auditing the accuracy of emissions estimates is a challenge because there is no current means of accurately monitoring emissions in open cut mines as there is in underground mines.

To Esterle’s knowledge, no other coal industry in the world is attempting to conduct a tough level of auditing and assessments for open cut coal operations as soon as Australia.

Should the CPRS pass the Senate in its present form, all operating and planned coal mines in Australia must report fugitive greenhouse emissions from coal mining by 2011.

Esterle said open cut emissions under the CPRS were based on a gas-in-place assessment, so GeoGas would look into improving the accuracy of GIP assessment for open cut mines.

She said this meant improving the lower detection limit for gas content and composition as the assessment of the gas reservoir underpinned any emissions model or development of gas management plan, whether for underground or open cut.

“We also have methods for assessing the cumulative gas reservoir size of the stratigraphy and we are determining whether these are directly applicable to open cuts or require some modification.

“We are also looking at the issue’s uncertainty across the process from sampling testing through to assignment of gas contents to the stratigraphy, and determining the optimal approach for the industry.”

GeoGas, a Runge subsidiary, already includes the estimation of carbon footprint as part of its gas management services.

“Gas reservoir characterisation is fundamental to all our work: it sets the data up for downstream modelling and provides direct input into coal seam gas statements, a requirement under Queensland legislation,” Esterle said.

“The proposed CPRS is seen as an extension of the underground emissions and gas management consulting services we currently provide.”

Of Australia’s 81 operating coal mines, 50 are open cut operations.

Esterle has 20 years of experience in coal research and its application to mining, materials and gas reservoir behaviour.

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