Sentinel keeps tabs on methane

The advance of methane recovery monitoring equipment technology is helping industry to safely capture methane for energy conversion and generate new revenue. Phil McLean at gas sensing specialist Trolex highlights the opportunities.

Landfills are the third largest human-induced emissions source globally, accounting for 12% of global methane emissions or nearly 750 million tonnes of CO2 equivalent. Many organisations are seeing the benefits of reducing methane emissions by capturing landfill gas (LFG) and using it as an energy source to yield substantial energy, economic and environmental benefits.

LFG comprises about 50% methane (CH4), the primary component of natural gas, and about 50% carbon dioxide (CO2) and a trace of non-methane organic compounds.

The implementation of landfill gas energy (LFG) projects reduces greenhouse gases and air pollutants, leading to improved local air quality and reduced possible health risks. LFG projects also improve energy and independence, produce cost savings, create jobs and help local economies.

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. Accurate continuous monitoring is crucial as changes in gas composition in a system can lead to engine down time and possibly even damage, reducing revenue and endangering both plant and personnel.

Current methane monitoring systems have several limitations. They use either thermal conductivity or infrared detectors. 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.

Infrared detection specifically looks for carbon-hydrogen bonds in hydrocarbon that provides an ideal means of measuring the methane content. Unfortunately any other hydrocarbon components or volatile organic compounds (VOCs) within the sample will also contribute to the response in an infrared detector.

Gas chromatography is often used to analyse the LFG stream, periodically measuring individual amounts of each component gas. Because samples have to be collected from the gas stream and sent to a laboratory for analysis, and the results sent back to site, this takes too much time and is far from a continuous measurement process.

After much research and development at Trolex a new methane monitoring system has been introduced that uses infrared detection coupled with a method to measure the methane content from the sample on a continuous basis. The 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.

Called Sentinel, the new system for methane recovery monitoring is a huge step forward in addressing methane recovery, either as a stand-alone gas-to-energy project, or as part of the Clean Development Mechanism (CDM) and the Joint Initiative (JI) flexible mechanisms agreed under the Kyoto Protocol. It is a fully integrated system with the advantages of maximising safety, meeting legal and regulatory requirements as well as generating new revenue streams, all in parallel.

So what are the wider opportunities which this method of methane monitoring is now helping to facilitate? Captured methane can be used for electric power generation, co-firing in boilers, district heating, vehicle fuel, and manufacturing uses such as feedstock for carbon black, methanol, and dimethyl ether production.

Even though Sentinel is new, the technology has already been installed in two UK schemes, two in South Africa and one in China and the US. Most schemes are approved or registered with the UNFCCC Clean Development Mechanism for gas-to-energy generation, and the system has been proven in testing conditions by independent authorities.

Phil McLean is senior engineer at Trolex. T: 0161 483 143

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