Cheltenham-based Andigestion Ltd is one of the UK’s largest gas-to-grid (G2G) anaerobic digestion (AD) facilities of its kind. Opened in November 2014, the site recycles more than 34,000 tonnes of food waste every year.
Collecting plate scrapings, leftovers and out-of-date produce from homes and businesses across Gloucestershire, Andigestion recycles these materials at its facility in Bishops Cleeve, via the AD process. Similar to composting, this sees food waste degrade naturally, while capturing the biogas produced during the process.
Using gas-to-grid (G2G) technology, this gas is purified and upgraded to reflect the properties of natural gas. By doing so, Andigestion can send 100% of the gas generated from recycling food waste straight to the national grid – allowing the power to be used almost immediately in homes nationwide.
As part of initial site development plans, Andigestion’s owners made the decision to operate grid-free. Simply, this meant that no mains power (electricity or gas) would be used on site. Instead, the plant was to be completely self-sufficient – effectively repurposing the energy it created.
Andigestion therefore looked towards gas engine specification and maintenance expert – CooperÖstlund – to specify and install a 350Kw, 8-cylinder combined heat & power (CHP) engine. Working alongside G2G technology, this would convert a nominal percentage of the captured biogas into electricity, which would be used to power the site’s lighting, de-packaging plant, air compressors and water pumps, with all surplus electricity sold back to the National Grid.
In addition to creating renewable electricity, heat produced by the CHP engine would also be utilised to firstly pasteurise the digestate, as well as keep it warm during the digestion process. This would ensure that the microorganisms present were kept at an optimum temperature – maximising the gas yield collected from recycling organic waste – as well as ensuring the resulting digestate could be repurposed as sustainable biofertiliser for local farmers.
But that’s not all. As the generation of renewable electricity is subsidised by the government’s Feed-In-Tariff (FIT), installing the system would guarantee a token financial return – simply for generating energy via CHP. Combine this with the Renewable Heat Incentive (RHI) subsidy for generating and utilising renewable heat, as well as injecting biomethane directly into the National Gas Grid via G2G, and the true financial benefit of CooperÖstlund’s engine solution becomes clear.
Delivering significant results
Following Andigestion’s official opening earlier this year, operation has been carried out in a highly sustainable fashion – utilising renewable electricity and heat to power the plant, while exporting biomethane to the National Gas Grid. Furthermore, the facility is now one of the only AD sites in the country to boast ‘island mode’ – meaning that it can continue to operate even in the event of the National Grid going down.
Jon Stait, operations manager at Andigestion, commented: “As one of the country’s most advanced AD facilities, our Bishops Cleeve site provides a sustainable waste management solution for homes and businesses across the Gloucestershire region. Operating entirely free of mains power, the site is as environmentally-friendly as it could be!
“However, this wouldn’t have been achievable without the assistance of CooperÖstlund, whose knowledge, expertise and creative thinking were a critical part of site development. The team delivered the perfect solution for our requirements and we can’t thank them enough.”
Johan Östlund, director at CooperÖstlund, added: “Working with AD sites nationwide, we have unparalleled experience in the specification, installation, commissioning and servicing of CHP gas engines.
“Although we typically fit and service gas engines on site looking to convert organic waste to electricity using CHP, working with Andigestion on such an innovative project demonstrated our capabilities on a more intricate scale.
“Using electricity to power the site and heat to pasteurised the digestate ensures that Andigestion can run its entire operations via recycled waste – setting the standard for other facilities across the UK.”