Study: methane loss from biogas plants

According to the United Nations Economic Commission for Europe, methane is one of the most potent greenhouse gasses, with a global warming potential roughly thirty times that of CO2.

In November 2018 the Danish Government initiated a targeted effort to reduce methane leakage from biogas plants. This aimed both at assisting the participating biogas plants to identify and reduce methane leaks, and at quantifying the methane loss from the plants.

Ramboll assisted the Danish Energy Agency in documenting methane loss from biogas plants. The final report showed an average methane loss of 2.5% from the plants that participated in the project with some plants having a relatively high loss. The lowest average methane loss was seen at co-digestion biogas plants (1.9%), while the highest average loss was measured at wastewater treatment plants (7.7%).

Need for regulation

The study concludes that there is a need for regulation of methane emissions. Reducing methane leaks is key in ensuring biogas can positively contribute to the green transition. At the same time, there is also an economic incentive for biogas plants to reduce methane loss, as leaks reduce the overall gas yield.

Of the specific sources of methane leakage, the report highlights leaky pressure and vacuum valves as well as the lack of coverage and gas collection from post-storage tanks and sludge storage. This is important knowledge that the Danish Energy Agency will use to assess how a future regulation of methane emissions from biogas plants can best be designed.

Significance for historical derivation and projection

The report may have implications both for historical emissions and for future climate projects. In the climate projection for 2021 by the Danish Energy Agency, the average methane loss from biogas plants is calculated at 1%, while the Danish National Centre for Environment and Energy (DCE) has so far calculated a leakage rate of approximately 4.2% in the inventory of historical Danish emissions. Therefore, a dialogue with DCE has been initiated to discuss how this new knowledge can be included in the calculation of historical emissions and in future climate projections.

Ramboll’s report contains recommendations for technical solutions and maintenance to avoid methane loss. Furthermore, the report illustrates that reducing methane loss from biogas plants goes hand in hand with greater profitability as measures that reduce leakages and increase the amount of biogas collected directly lead to greater biogas output.