Biogas monitoring yields rewards


Source: Geotechnical Instruments (UK) Ltd

Whilst there is increasing interest in generating power from waste gas, this has been central to one company for years. Based in the UK, Geotech has been helping water utilities, agricultural and landfill operators and food waste processors worldwide offset energy costs or generate income from waste-generated biogas, manufacturing portable and fixed monitoring equipment.

Geotech has over 200 fixed gas monitoring systems installed around the world, and thousands of portables. One system is installed on the oldest anaerobic digestion (AD) plant in the UK. At South West Water's Countess Wear Sewage Treatment, built in 1895, a Geotech AEMS monitors gases produced from two anaerobic digesters fuelling four 165KW combined heat and power (CHP) engines generating electricity to grid and heat. UK water utilities now routinely use data from biogas monitoring systems as input to sophisticated control systems.

Sewage AD has been common in many countries for years but increasing energy costs now drive efficiency. In Turkey, at the $150m Antalya wastewater plant, over 3,000,000m3 of wastewater are treated daily, and a Geotech AEMS system analyses the biogas before it goes to the CHP engine.

Protecting engines

There is a strong business case to use gas monitoring to protect an engine. CHP engines generally cost between £250,000 and £750,000. Gas monitoring protects the CHP engine from expensive unplanned downtime due to sudden gas level changes, as well as engine repairs (a sudden change in methane % can cause a valve to blow) and unnecessary maintenance. On a small 0.5MW plant, at around 4% of the CHP cost, an analyser may take 5 days to pay for itself in avoiding lost downtime. On a 1MW site it could pay for itself in half-a-day's downtime.

Biogas monitoring for large scale agriculture

Many large agricultural processors install an AD plant to generate revenue and dispose of waste. This is usually from a single crop, such as molasses in India, palm oil in Malaysia or potato in the UK. McCain Foods built a covered anaerobic treatment lagoon producing methane (CH4) for burning from 77,000m3 of wastewater rich in potato starch. The lagoon's cover keeps out oxygen (O2) and enables collection of CH4 for burning in the CHP engine to produce electricity. Monitoring the process with the Geotech analyser enables McCain to ensure the protection of their CHP engine from dangerous hydrogen sulphide (H2S) levels, as well as verifying the H2S scrubber's performance.

Checking the biogas de-sulphurisation process

H2S scrubbing (desulphurisation) is the process of removing H2S from the gas mix before it goes to CHP. Biogas often contains significant levels of H2S which is corrosive and can cause extensive CHP damage. 'Levels of H2S are dependent on the feedstock used', according to Tim Wilson, Senior Technical Support Engineer. 'Geotech's fixed biogas monitoring system, the GA3000 PLUS, is designed to monitor before and after desulphurisation, with H2S sensors for high and low ranges.'

Monitoring the digestion process

Biogas monitoring is also key for process control. Geotech is working with leading edge AD operators to investigate how monitoring very low levels of gases produced at different stages of the process can be used to control the process, and early signs are promising. 'We have recognised that hydrogen can be released during the AD process and monitoring these very low levels, possibly up to 300ppm H2, may help in process management. We are currently gathering information about how H2 levels correlate with volatile fatty acid (VFA) levels from lab samples', commented Geotech's Graham Sanders, UK Sales & Development Engineer. 'A spot check with a portable BIOGAS 5000 could provide vital real-time information to help process optimisation.'

Big business on landfills

Landfill sites also produce large amounts of CH4. This should be destroyed to minimise greenhouse gas emissions but it is also a valuable fuel. Careful management across a landfill gas field can optimise the gas yield and the power it generates. Initially a bonus in the UK, where compliance with environmental legislation is central to landfill gas monitoring, the heat and power from landfill gas is now a valuable revenue stream. The calorific value of landfill gas is routinely measured on typically massive US landfill sites, using the portable GEM5000.

'The shift in focus from compliance to generating power is a trend we are seeing all over the world', says Amanda Randle, Geotech's Commercial Manager. 'Increasingly we pick up details of schemes to incentivise productive use of biogas. For example, the GA3000 PLUS has recently been installed on a number of sites where biogas - typically around 60% methane - is being upgraded to over 95% methane. This higher concentration is more valuable fuel as it can be used more flexibly.'

Based in the UK, Geotech designs, develops, sells and supports gas monitoring equipment worldwide.

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