Making the best of methane: The latest look at methane abatement in coal mining

In a climate of political turmoil, when we don’t know which way the climate tax is going to go, one thing is for sure: Investing in cleaner mining techniques is a safe way to go, no matter the political outcome.

The good news is the mining industry in the Hunter Valley will soon be leading the way for cleaner emissions thanks to a history-making grant, the biggest ever seen by the University of Newcastle – which is funding a research project from which all mining companies and other industries stand to benefit.

The new project is headed up by the internationally-renowned energy researcher and chemical engineer Professor Behdad Moghtaderi, funded to the tune of $30 million split between the Department of Industry and ACA Low Emissions Technologies Ltd.

Professor Moghtaderi has already made a public name for himself with a geothermal power and waste heat recovery project named GRANEX, which was shown on ABC television program The New Inventors.

But now the Iranian-Australian researcher is taking the clean emissions game a step further in a research program to reduce the greenhouse gas effects of ventilation air methane (VAM) from underground coal mining.

According to Moghtaderi, research and development of a new gas abatement technology will be carried out in partnership with several multi-national mining companies, including Glencore Xstrata, which is the major partner.

“The fact that we have the support of our industrial partners, as well as the Federal Government is an indicator that the whole coal mining sector is supporting this research project,” Professor Moghtaderi said.

The basis of the research is to safely abate the greenhouse gas effects of waste methane from underground coal mining by converting the methane to carbon dioxide, without relying on combustion of the methane.

As Moghtaderi explained, in order for workers to operate safely in underground mine fresh air is pumped from the surface into the mine via a ventilation system.

The exhaust of this ventilation system, which is primarily a mixture of methane and air, is referred to as “VAM” or ventilation air methane, which under normal conditions is simply released into the atmosphere.

“But with the new suite of technologies we are developing, we’ll be able to convert the VAM into carbon dioxide,” Moghtaderi said.

“For this purpose we take the VAM from the ventilation exhaust and transfer it to an abatement unit using a ‘capture duct’ and the abatement unit which is installed at the back end of the capture duct then converts the methane to CO2 before releasing it into the atmosphere.”

Chemical Looping

 The new abatement technology under development is based on the concept of chemical looping.

Moghtaderi described it essentially as a chemical reaction.

“There are various types of chemical reactions, and combustion, a flame, is an example of one type of chemical reaction, a high temp fast oxidation,” he said.

“That’s normal combustion, what you see when you have a flame.

“Now, there are other chemical reactions which are essentially flameless, and the reaction that we have for chemical looping process is one of those.

“You have metal oxide in this case, like iron or copper oxide. These react with the methane, and they provide the necessary oxygen to oxidise the methane, which turns it into carbon dioxide. The whole process is happening at much lower temperatures than an ordinary combustion, you don’t see any visible flame or anything like that, but in principle it’s very similar, it’s just a chemical reaction.”

The whole chemical looping process reaches maximum temperatures around 500-600 degrees Celsius, whereas in a typical combustion elevated temperatures are recorded as high as 1100 degrees Celsius.

Difficulties with Methane

The main reason for trying to abate the effects of fugitive methane from coal mining without combustion is the difficulty of combusting such ventilation air methane (VAM).

“The biggest challenge is that methane is very easy to combust at certain levels of concentration…  lower concentrations are harder to convert, concentrations that are below the flammable limit, so normal combustion processes are no longer any help,” Moghtaderi said.

 “In waste management, the concentrations of methane are in excess of 10-15 per cent, so it can be burnt in a conventional gas engine without much difficulty.

“But the concentration of methane in VAM is typically about 1 per cent, so the methane must be converted using alternative methods such as thermal conversion and chemically conversion, like chemical looping.”

The maths of chemical conversion

In terms of global warming, the potential for atmospheric warming of methane is 25 times higher than that of carbon dioxide, so the goal of methane and VAM abatement is to turn methane into carbon dioxide, a simple enough process with the right tools, and therefore bring down the global warming potential of the fugitive exhaust emissions from underground coal mining.

Professor Moghtaderi is careful to point out the errors often made in relation to reporting the reductions gained by converting methane to carbon dioxide.

“The mistake that people make, especially if they’re running a mining company and have liabilities to report for instance, they talk about this conversion making the methane go down by a factor of 25,” he said.

“That is incorrect, because you also have to consider the mass of methane, which is much lighter, as the molecular weight of methane is 16, whereas for CO2 it’s 44.

“Because you need other material to react with the carbon in methane to make the carbon dioxide, and that is the oxygen provided by metal oxides, so if you do the mass balances you realise that your reducing the liabilities by a factor of about nine.”

“So, with the chemical reactions always based on molecular basis, if one mole of methane, or 16 kg is reacted with the sufficient quantity of air, one mole of CO2, 44 kg will be produced.

“If you convert the above figures to mass base figures you could say that per kilogram of methane about 2.75 kilograms of CO2 is produced.

“Therefore, the real reduction in Global Warming Potential, if one converts methane to CO2, would be about nine (25/2.75 = 9.1).

“The mistake that is often made is that everyone assumes that one kg of methane converts to 1 kg of CO2 and thus the reduction in GWP is 25 (25/1 =25) or in the case of some miners claims, 21 (21/1 = 21)

“So, the true reduction in Global Warming Potential is about 9; which is still a significant figure for emissions reduction.”

Safety

As always, the most essential aspect of any new development in the mining industry is one of safety, and ensuring there is as little risk as possible introduced to an already dangerous industry.

 “One of our objectives in this project is to study the safety aspects of the capture duct, the professor said.

“In this context the project will answer two fundamental and overarching research questions: Can an accidental fire or explosion formed in the VAM capture duct (or VAM abatement unit) be prevented from reaching the mine shaft using properly designed prevention and mitigation measures fitted to the duct; and can the same prevention and mitigation measures interrupt or stop an accidental fire or explosion initiated in the mine shaft from reaching the VAM capture duct (or VAM abatement unit)?”

A spokesperson for the Department of Industry explained to Australian Mining that while this new technology is not specific to the coal mining industry, its application is specific to the circumstances and risks present at coal mines. 

“Approximately two thirds of methane emissions from Australian coal mining is emitted in dilute and variable concentrations through the ventilation air systems of underground black coal mines,” the spokesperson said. 

“These projects are focused on developing and testing innovative technology solutions to capture this Ventilation Air Methane, while addressing the safety challenges of incorporating VAM capture technologies into the ventilation systems of underground mines.”

 

Competition

Professor Moghtaderi said that there are other gas abatement technologies available off the shelf from overseas and within Australia, “but we believe that chemical looping will have the advantage over those,” he added.

“Our work on the capture ducts can be equally applied to any abatement unit that you put on the back end of the duct.”

Most importantly, the results of the research into methane abatement, done by University of Newcastle, will be made freely available to the public, including all sectors of industry, the professor said.

“We all agree, the partners, participants, and government, that what is found in this research project ought to be shared for the common good of the sector.”

Timeframe

Testing of the new VAM abatement hardware will be carried in Glencore Xstrata mines in the Hunter Valley, with rollouts commencing in 2016.

A Department of Industry spokesperson said new technology solutions should become available as a commercial reality within the next five to ten years.

“The projects include various stages to be undertaken over a four-year period, including laboratory and pilot-scale testing and demonstration, prior to the deployment of large-scale technologies and systems,” the spokesperson said.

“The development and commercialisation of this technology will assist the NSW coal industry to reduce its emissions footprint.”

In 2012 coal mining accounted for almost 29 mega-tonnes of carbon dioxide equivalent, or 4.6 per cent of Australia’s net greenhouse gas emissions, according to the Department of Industry.

“Fugitive methane emissions released from the coal seams during mining has to be removed from the mine through ventilation systems to protect the safety of workers, and capturing this methane, which represents two thirds of the methane emissions from mining activities, will have a significant impact on reducing the industry’s emissions footprint.”

Images: University of Newcastle

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