Published in the December 2009 Coal USA Magazine

Current methane monitoring systems have a number of limitations. According to gas sensing specialist Trolex, thermal conductivity detectors measure the thermal conductivity of the whole gas sample, giving a collective reading for all the constituents of the gas, not just methane, and are therefore unreliable.

Infra-red detection specifically looks for carbon-hydrogen bonds in hydrocarbon but any other hydrocarbon components within the sample will also contribute to the response.

Gas chromatography, where samples are taken in the gas stream before being sent to a laboratory, is lengthy and does not offer continuous measurement.

“With the practice of methane drainage for power generation now on the increase, it has become vital to ensure that effective methane recovery monitoring is in place,” Trolex senior engineer Phil McLean said.

“Methane can be a big revenue earner as demonstrated by UK Coal, which has pioneered the technology, and which in 2007 realised some £4.3 million profit from gas extracted from its mines, and generated enough electricity to power over 40,000 homes.”

Trolex’s new methane monitoring system uses infra-red detection coupled with a unique method to measure the methane content from the sample on a continuous basis.

“The way this works is that an initial gas analysis is used to train the system, and subsequent analysis can be used to fine-tune the system.

“The contributions to the overall signal from the detector caused by methane and other hydrocarbon gases are evaluated, and the methane content is derived from the overall signal and the individual contributions from the different gases.

“This technique provides a continuous online, high accuracy monitoring capability for methane drainage.

“It is a fully integrated system with the advantages of maximizing safety, meeting legal and regulatory requirements as well as generating new revenue streams, all in parallel,” McLean said.

Known as Sentinel, Trolex’s system can help address methane recovery in projects such as mine heating and coal drying.

“For the very low-concentration methane in mine ventilation air, technological development has progressed to the point that this CMM source can be oxidised and the resulting thermal energy used to produce heat, electricity, and refrigeration,” McLean said.

Despite its newness to the market, Sentinel has already been installed at two coal mines in the United Kingdom and one in China, and is being effectively used in a gold mine in South Africa.

“Now that there are significant advances in methane monitoring technology available, we will undoubtedly see many more projects around the world not only benefiting from increased site safety, but also protecting the environment and generating substantial additional revenue for their organizations at the same time,” McLean said.