Reducing methane emissions in the biogas industry to fight climate change

Since its establishment, Assentech has been on a mission to bring awareness to the dangers of gas leakages and support the tank storage industry to mitigate risks posed by inefficient equipment. With the awareness that the biogas industry is a huge contributor to methane pollution, Assentech is focusing on how it can support operators to become more aware of leaks and how to prevent them in the future.
Biogas mainly consists of methane (40–75%) and carbon dioxide (15–60%) which are greenhouse gases (GHG). There are also several other trace gases that usually make up less than 2% in volume. These include hydrogen sulphide (H2S), ammonia (NH3), hydrogen (H2), and nitrogen (N2).

These trace gases also create the potential for air pollution and acid rain, which can adversely impact soils and public health.

Methane on its own is an odourless gas, however, when mixed with hydrogen sulphide it will create a foul ‘rotten egg’ smell. This gas is heavier than air and can be very dangerous because it is toxic, corrosive, flammable and explosive – so something you really do not want leaking from a biogas tank.

Methane is a far more potent greenhouse gas that can be up to 36 times more damaging than carbon dioxide. This is why it is imperative to focus on mitigating leakages to fight against climate change. If we are able to capture the potent greenhouse gases from landfills, food waste and manures, it can be converted into useful biofuel and also reduce fugitive emissions.

Pressure Vacuum Relief Valves (PVRVs) are designed to protect a tank from damage, like ruptures or explosions, created by overpressure or excessive vacuum. PVRVs are commonly found on top or adjacent to the digesters.

Pressure Vacuum Relief Valve & Flame Arrestors are combination units that will also protect a digester against over pressure and excessive vacuum, but also provide protection from externally cause sources of ignition and heat. Methane contributes of approximately 60% of biogas, of which is highly flammable and if left leaking from a digester can form an explosive atmosphere when mixed with oxygen in the air surrounding the tank

Emergency Relief Valves also protect the tank against rupture or explosion by providing emergency relief capacity over and above that provided by the normal operating pressure relief vale on the tank. All emergency vents are individually tested for calibration and leakage according to Section 5.4. API2000.

Patented Mobile Test Bench
Management of ageing plants or even checking new devices is important as you will read below. So, the Vent-Less test bench range by Assentech is good news for the industry. It will automatically run a functional test cycle on a tank breather vent and certify the results based on international standards.

Even with crucial equipment like these, the danger of fugitive emissions is still evident if they are not designed or tested in accordance with the international standards; API2000 and ISO28300. To ensure this it is important to insist on an individual leak test certificate. This must specify the serial number, flow recorded, calibrated equipment used and pressure achieved. Keep in mind that a batch certificate of conformance does not represent what functional tests was applied to the vent.

The Assentech designed range of Test Benches leaves the control of ensuring breather valves are venting efficiently is in the hands of the operator’s onsite. Each breather valve is required to be serviced every three years and inspected every year, so the test benches will make this process easier, and dramatically more accurate. With each test, a leak test certificate will be instantaneously generated to empower the operator with evidence for international standards that their breather vent is working within the regulations.

It’s going to require consistency across the biogas industry to ensure that harmful gases are kept inside tanks and utilised as biofuel instead of posing as a health and environmental threat. By understanding and acting upon the issue of fugitive emissions in the biogas industry, we can mitigate the risks and fight climate change.

Following COP21 in 2015 the IPCC drafted the Paris Agreement which set targets to keep global temperatures under 1.5 degrees over pre-industrial levels. This led all of the main accountancy firms to create a common reporting platform defining and declaring company activities affecting Environmental, Social and Governance (ESG) aspects.
Current predictions in 2021 ahead of COP26 indicate that we will exceed this target which will lead to increasingly adverse weather conditions and many other events that will affect all of us.
Mark Carney, UN Envoy for Climate Change has stated that those companies who adopt and invest in technology to reduce emissions will be seen as part of the solution and those that don’t will be seen as part of the problem.

Buyer beware!

The case study below shows actual test results showing the difference between low cost-inefficient valves and quality devices.

A low-cost vent manufacturer claimed leak tightness of less than 1 SCFH (standard cubic feet per hour) at 90% of setpoint (opening pressure). We purchased one of these vents. The manufacturer refused to issue an individual leak test certificate to evidence this claim. We tested the device and found it to be leaking more than 2 SCFH at 90% of the set point. This generated a loss equal to 496 cubic metres per year. That equates to 4.41 double-decker size gas clouds whereas a quality device was also tested and produced a leak rate of less than 0.01 SCFH or 2.4 cubic metres per year and 0.02 double-deckers.

These were new valves being compared. Once out in the field, we find poor quality vents that leak over 50 SCFH at 90% of the set point. With multiple valves, on-site the losses are immense but can be easily resolved.