Maximising efficiency of AD plants with gas analysers

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Source: QED Environmental Systems Ltd.

As focus around the globe is increasingly shifting towards renewable energy, anaerobic digestion (AD) has become an economically viable energy source that capitalizes on reusing our wasted materials. It is a relatively easy and natural means of turning a broad variety of complex waste into a simple fuel gas.

It’s no surprise therefore, that the number of AD plants across the UK has risen in recent years. These plants have a significant role to play in helping the country meet the Government’s target of generating 15 per cent of the UK’s energy from renewable sources by 2020. It is therefore of increasing importance that the quality of gases produced by these plants is maintained and monitored efficiently.

Avril Banks, Director of AB-EN Environment & Energy – an independent AD advisor on optimising biogas production and longstanding customer of QED’s Geotech gas analysers – is of the opinion that an essential part of maintaining and improving the quality of gas in AD plants today is to have state of the art gas analysers in place.

Avril states that the use of gas analysers in AD plants has sometimes been overlooked as “an added extra” – but in reality, this equipment is essential in improving the quality of the biogas being produced and making plants safer.

In order for AD plants to run smoothly and effectively, there needs to be efficient management procedures in place but also a high level of understanding of the biological processes within the tanks and how to monitor these. Individual feedstock gives off differing methane and H2S quantities and it’s important to be able to monitor the process of these gas productions throughout the feed cycle.

In some plants there is a lack of understanding about the importance of process monitoring equipment. This may not be the fault of a plant’s owners or management team but ironically – at the hands of AD plant technology providers. Gas analysers, aeration and odour controls are very often the things that go first in price negotiations, yet they are key to operational success and efficiency.

A gas analyser comes into its own in an AD plant in many ways. Primarily, it allows a plant to manage their feed systems and profile in real time, giving accurate data on the methane and hydrogen sulphide levels being produced to allow operators to fine tune how they feed their digester. They also give advance warning of overfeed or process inhibition by the way the ration of CH4 to CO2 changes and can indicate blockages and fissures in a plant by monitoring the oxygen levels.

Some operators use the real time data from an analyser in conjunction with historical data to hone their AD process for the best quality biogas, produced in the most efficient way. Others use the data to react quickly to changes in the gas make up.

As well as improving gas quality, there is an important safety aspect to using gas analysers. Hydrogen sulphide released in the AD process can damage equipment and be harmful to people. The only reliable way to monitor the levels of H2S within the gas going to an engine is through regular in-line monitoring of the gas and this can ensure engine longevity.

To get accurate readings, gas analysers must be properly calibrated, and this is where some users fall down or get frustrated with using them. Gas analysers from some providers don’t have regular service systems in place and will be sent internationally to get calibrated which can often take months.

Calibration is important as the H2S cells in all systems become exhausted with time and concentration and so for an analyser to be effective it must undergo regular calibration. Geotech instruments are calibrated on a fixed system, using the ISO17025 audited automated calibration rigs, reducing the process to just a few hours of downtime.

With better monitoring in place, we as a sector can be both more efficient, more productive and safer, to establish biogas as a reliable and clean alternative to natural gas.

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