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Silent sentinel role for fixed biogas analyser at United Utilities

Biogas produced by the United Utilities anaerobic digestion sludge plant at Lancaster (Stodday) waste water-treatment runs a brand new 525 kW combined heat and power (CHP) engine generating electricity and now operating 24/7. It joins an existing 325 kW engine already in service for three years.

In addition to biogas from the Stodday mesophilic anaerobic digester, a new enzymic hydrolyser increases methane production further. Analysing all the biogas is a Geotech GA3000 static biogas analyser.

Before the combined streams of biogas reach the gas engines a Geotech GA3000 static biogas analyser is set to automatically and continuously measure and analyse the concentrations of methane (CH4), carbon dioxide (CO2), oxygen (O2) every minute, and hydrogen sulphide (H2S) every thirty minutes.

The gas analysis findings are stored in a data logger so that the North West’s water company United Utilities has its own precise, detailed and accurate record of the gas it is sending to its two Jenbacher CHP engines.

Dave Bega, Installation and Commissioning Manager for GCA at Stodday, said

The reason we are looking at the data is so we can see the details if we ever have any spikes of increase in the CO2 or H2S or any reductions in the CH4.

Each engine has its own CH4 monitor and will auto shutdown outside stipulated bands and the engines are running 24/7 on auto-control.

The plant receives 1,000 m3 of sludge per day, which produces 40,000 m3 of gas a week. This is enough power to make the site self-sufficient and feed excess power back into the national grid.

Dave Bega added,

We plan to run the larger engine at full load most of the time and both engines when the gas supply is adequate.

Another major part of the £13m project has been to boost the treatment of sewage sludge – the solid by product of the treatment process. A new enhanced enzymic hydrolyser kills almost all bugs such as e.coli and salmonella, in addition to increasing methane production to make even more power. The total process also supplies steam to heat water for the site offices.

Site Process Controller, Phil Smith:

The resulting treated sewage is then used as nitrogen-rich organic fertiliser for agriculture. There is no shortage of outlets – the farmers love it,

It’s free, full of nutrients and we even deliver it and spread it for nothing.

The upgraded facility is part of a £3.6bn investment programme from United Utilities designed to improve water quality and reduce the company’s environmental impact by 2015.

Highly reliable in service the GA3000 uses Geotech’s robust, field-proven technology to bring low-cost to automated fixed-position monitoring of methane-rich biogas. Easily operator installed, user field-calibrated and zeroed, the compact, self-contained GA3000 has gas conditioning as standard. It continuously analyses CH4, CO2, O2 and optionally, H2S at 0-5000ppm.

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