Every year, 237 million tonnes of carbon dioxide are released to the atmosphere from the world’s underground coal mines through exhaust vented air, according to CSIRO Exploration and Mining project leader Dr Shi Su.

The main greenhouse culprit in coal mining is methane, which is 23 times more potent than carbon dioxide as a greenhouse gas (over a 100-year time frame) and accounts for about 70% of all coal mining-related methane emissions.

China was responsible for about 45% of these emissions, he said. In a major Australia-China initiative to mitigate methane emissions and backed by the Australian and Chinese coal industries, Su and his team have spent the past three years developing a new methane-based power system that would both mitigate emissions and provide a valuable source of clean, green energy.

The result is VAMCAT – Ventilation Air Methane Catalytic Turbine – a low-heating value gas turbine powered by about 1% methane from ventilated air.

The stumbling block in the technology’s development, Su said, had been that although gas drainage efficiency in China has increased from 15% in 1998 to 26% in 2004, much of the captured gas was poor in quality, limiting its re-use capability.

He estimates that more than 70-80% of the drainage gas has a methane concentration of less than 30%, which cannot be used by conventional technologies.

“This low concentration of methane in mine ventilation air presents a major challenge for utilisation and mitigation,” he said.

"It requires either treatment in its dilute state, or concentration up to levels that can be used in conventional methane-fuelled engines.

“VAMCAT is the first technology to overcome the concentration level issue using a new catalytic combustor. The combustor has been integrated into a CSIRO-patented, lean burn gas turbine system, currently emerging from a trial phase.”

With the combustion testing phase now over, the pilot phase launched in May is now concentrating on developing a 20-30kW prototype demonstration unit. The case studies at two Australian and one Chinese coal mines have shown methane cuts of up to 90% using VAMCAT in these mines.

CSIRO and the Australian Greenhouse Office, together with China’s Shanghai Jiaotong University and Huainan Coal Mining Group, will construct the first pilot-scale demonstration unit, and operate it in a coal mine in China.

Su said a prototype demonstration unit with a power output of 20-30kW would first be demonstrated in 2008, and the operational performance data and experience gained from this small unit would be used to design a second-generation turbine of at least 1MW output.

Eventually, it is expected that VAMCAT would be a long-term solution to emissions, particularly in China, which is the largest potential market for technologies mitigating those emissions.

Su said the VAMCAT technology would also have uses to mitigate methane from landfill, livestock and combustibles in industrial offgas – making the technology and exciting development outside the minerals industry.

Several companies have already expressed interest in the technology, which is compact and inexpensive.

The project was supported by the Australian Government’s Bilateral Climate Change Partnerships Program and an Australia-China special fund grant under the Australian Government International Science Linkage Program. The initial investigation of catalytic combustion performance was supported by a grant from the Australian Coal Association.

Australia's Mining Monthly