Beyond keeping the engines running, Westwood’s CHPs have an impressive 99 percent uptime at 41 percent biogas to electricity and useable-heat efficiency.
These high rates will make substantially positive profit impact over the several years of investment payback. Watching the biogas as it comes from the gasholder and travels towards the CHPs and water heating boilers is a Geotech fixed gas analyser. This equipment, like the whole site is powered by the electricity the CHPs produce, and it plays a key role in keeping the CHP engines running.
Westwood’s biogas averages 60 percent methane (CH4), 40 percent carbon dioxide (CO2), about one percent oxygen (O2) with hydrogen sulphide (H2S) at trace levels below 100ppm. The static gas analysis unit is set to take a biogas reading every five minutes, 288 times a day. It feeds the data via Ethernet to Westwood’s central monitoring and control systems. Minimising the H2S in the biogas while keeping the O2 below critical levels helps keep the CHP engines running. They have a safety threshold engine-stop cut-off H2S level far higher than those ever reached.
In addition to Westwood’s technical staff checking digester and engine performance, the CHP and the Geotech system are set to keep watch on the biogas and on themselves and have down-the-line remote access by Geotech to the analyser’s panels and by the CHP manufactures to their engines. The two systems communicate with the central Westwood systems. So close is the system integration that when a Jenbacher CHP engine is to restart, for example after an oil change, it interrogates the AEMS data for the current percent CH4 content and adjusts its throttle setting for a start sequence at that level ensuring a safe, damage free and faultless engine restart.
The Geotech system is in use on many UK sites and others around the world. Applications include farm and food waste AD / biogas production, sewage sludge AD treatment, biogas harvesting and PPC compliance. With landfill gas and biogas energy-from-waste projects Geotech’s fixed analyser assists landfills and farmers in South America, Africa and Asia. The company can earn valuable carbon credits under the Clean Development Mechanism, through a combination of robust and reliable performance coupled with easily auditable, secure and verifiable data collection and storage systems. Based on Geotech’s continuously developing gas analysis technology, tested and proven in robust portable gas analysers for more than 20 years, AEMS operation is fully automated. It can analyse gas every six seconds. It self-purges and self-calibrates logs data and transfers it via Internet modem, Ethernet or both.
Servicing the analyser means that the inner unit is simply swapped. According to David Woolgar, it is easy with a service-exchange analyser inserted in moments and the Westwood unit sent for service and calibration within Geotech’s seven-day turnaround. Westwood technicians also use a Geotech GA5000 portable gas analyser to check biogas from each of the digesters at tapping points and to double check the automated readings of the fixedc gas analyser.