scenario, biogas in combination with air can form an explosive gas mixture that, in a confined space near an ignition source, can result in explosion. Although explosions are thankfully extremely rare, they bring a high risk of serious injuries and fatalities and, as a result, are something no plant owner ever wants to experience on their site. Biogas also contains hydrogen sulphide


air, it will fall to the ground. In confined, poorly ventilated spaces it can accumulate and remain unnoticed until someone enters, resulting in sometimes fatal effects. Gas leaks on AD plants also have a financial impact. Any volume of biogas leaking into the atmosphere will subsequently reduce a plant’s gas yield; and therefore, the owner’s profit margin. In fact, losing just 1m3

S), a toxic gas that has been the cause of a number of deaths in the UK agricultural industry in relation to slurry tank management. As H2

of methane per

hour will result in a financial loss in the region of £5,000 per year. Tere is also the issue of sustainability criteria to consider. To receive payments through either the feed-in tariff (FIT) or renewable heat incentive (RHI) schemes, AD operators must demonstrate that their plant is operating sustainably. Regulators have considered clamping down on this area, as some industry reports mention very high levels of fugitive emissions. Site operators can therefore use gas leakage surveys as a way to protect against potential loss of incentives and demonstrate to the authorities that their

S is heavier than

AD plants have inherent weak spots, which make them

susceptible to biogas leakage

plant is well-managed, with leaks kept to a minimum.


Although an AD operator may believe that their plant is operating at a high standard, all anaerobic digesters have inherent weak points that make them susceptible to biogas leakage. Potential hotspots include: gas membrane connections; cable grommets (where a submersible stirrer cable passes through the digester wall); flange connections; viewing windows; carbon filters; and any areas where maintenance is carried out.

REDUCING YOUR RISK Te risks of gas leakage are clearly significant and often expensive. However,

identifying a leak is a simple and affordable process that can help prevent a serious incident from occurring. A gas leakage detection service should therefore form part of any responsible plant operator’s ongoing maintenance programme. For example, the FM BioEnergy

service covers a full AD plant survey with a methane-sensitive monitor and laser, as well as infrared devices, including: survey of all tanks, CHP, biogas upgrading equipment, roof membranes, pipes and flanges; analysis of emissions from CHP and double-membrane covers; and report with images, videos and repair priority table.

Although the majority of its audits to

date have uncovered minor leaks, 25% were found to have serious failings; fixing these not only prevents a more serious and costly incident from occurring, it also often results in a 12-month payback on the price of the survey.

Te best times to conduct a detection

survey are at the start of full operation; after significant maintenance work; if your feed-to-gas conversion is lower than expected (and the biology remains stable); and of course, if you can smell biogas. After all, the cost of detecting a potential leak is minimal but the implications of leaving it to chance could be massive.

A detection survey using a methane-sensitive monitor and laser, as well as infrared devices, can spot biogas leaks invisible to the naked eye

Tim Elsome is general manager for FM BioEnergy. 39

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