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    Biogas leakage – how to protect your AD plant from the silent killer

    The UK’s anaerobic digestion (AD) industry has come a long way in a short space of time, growing by 350% in a decade. Over 300 AD plants have been built in the last five years alone, taking the current total to 648 operational facilities with a total capacity of 1 GWe-e . During this time, owners and operators have been on a steep learning curve and the sector’s operational efficiency and health & safety records are both on an upward trajectory. But while advancements have been made in many areas, there remains room for improvement in others.

    In particular, the issue of biogas leakage is one which many AD operators are still failing to address; often because the problem is invisible. However, the dangers associated with it – from diminished profits to environmental pollution and Health and Safety risk – should not be underestimated. Here, Tim Elsome, General Manager for AD specialists FM BioEnergy, outlines the real cost of unidentified biogas leaks – and the inexpensive steps you can take to reduce the risks on your plant…

    The scale of the problem
    While most responsible plant operators will be monitoring key parameters such as temperature, pH and biogas production on a regular basis, the vast majority are not checking for gas leaks, believing it’s an issue which doesn’t affect their plant.

    The evidence proves otherwise. Over the last 10 years, 85% of the plants we have surveyed in the UK and Germany were suffering from a biogas leakage – a quarter of these were deemed ‘significant’, causing serious financial losses and safety concerns. 

    Translating this to the UK as a whole could mean that 550 plants are currently at risk; with 137 in danger of a serious financial or safety breach. Furthermore, if each of these 550 plants was to leak an average of just 0.5% of their capacity, it could equate to a potential loss of 4.25 MW of energy a year, resulting in 6670 tonnes of methane escaping into the atmosphere each year.

    The risks of doing nothing
    The implications of this volume of methane being released are significant. According to the latest IPCC Assessment Report, methane is 34 times more potent than CO2 as a greenhouse gas over a 100-year period. For any industry to be emitting this volume of methane would be a concern; but for a renewable sector, whose entire premise is based on being green, this is catastrophic.

    Aside from the considerable environmental impact, biogas leaks bring other risks. In the worst-case scenario, biogas in combination with air can form an explosive gas mixture which, in a confined space near an ignition source, can result in explosion. While 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 H2S which is toxic and has been the cause the deaths in the UK agricultural industry in ralatin to slurry tank management. As H2S is heavier than air it will fall to the ground and in confined poorly ventilated spaces can accumulate and remain unnoticed until someone enters which can have 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 of methane per hour will result in a financial loss in the region of £5,000 per year. 

    There is also the issue of sustainability criteria to consider. In order 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. This is area of that regulators have considered clamping down as some industry reports mention very high levels of fugitive emmissions. Site can use gas leakage surveys as a way to protect against potential loss of incentives and prove to the aurthorities that their sites are well managed and keep leaks to a minimum.

    Leakage hotspots
    While an AD operator may believe that their plant is operating at a high standard, all anaerobic digesters have inherent weak points which make them susceptible to biogas leakage. Potential hotspots include:
    •    Gas membrane connections
    •    Viewing window and stirrers
    •    Carbon filters
    •    Any areas where maintenance is carried out

    Reducing your risk
    The risks of gas leakage are clearly significant and often expensive. However, identifying a leak is a simple and affordable process which 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 camera and infra-red devices, including:
    •    Survey of digester, CHP, biogas upgrading equipment, roof membranes, pipes and flanges;
    •    Analysis of emissions from CHP and double-membrane covers;
    •    Analysis of diffusions through biolene membranes;
    •    Report with images, videos and repair priority table.

    While 25% of our audits to date have uncovered serious failings, the majority (60%) were found to have only minor leaks; fixing these not only prevents a more serious and costly incident from occurring, it often results in a 12-month payback on the price of the survey. 

    The 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. 
     

    ForFarmers