Upgrading biogas derived from food waste
Customer: ReFood Ltd - division of SARIA Group
Location: Widnes, Cheshire, UK
Purpose: biogas-to- biomethane upgrading for pipeline injection (gas-to- grid)
Order date: September 2013
Plan commissioned: August 2014
ReFood is a large commercial producer of renewable energy from food waste. It has published its vision for zero waste to landfill in the UK by 2020. The Widnes facility was the company’s first site specifically designed to produce upgraded biogas for injection into the UK natural gas network, so benefitting ReFood both from the network gate price and available government incentives, in particular the Renewable Heat Incentive (RHI).
Purpose-built facility to receive and separate food waste collected under contract mainly from commercial food processing, retailing and hospitality businesses in the north-west region, but also health and education premises. The key economic driver for the waste producers in making their contractual arrangements with ReFood is the elimination of payment of landfill taxes.
The food waste is the primary feedstock from which the raw biogas is produced in concrete anaerobic digesters. Greenlane supplied a complete biogas-to- biomethane upgrading system with an advanced de-sulphurisation package.
The technical challenge
Food waste is distinguished from many other organic feedstocks by abnormally high levels of H2S and volatile organic components (VOC’s).
Stripping out H2S is necessary to lesser or greater degree for biogas from all ADs. But high concentrations of VOCs are prevalent in food waste, due to kitchen food preparation and cleaning processes. Some, such as d-limonene, can alter the safe odour of the output biomethane.
Also present are silicon compounds known as siloxanes deriving from detergents, cosmetics and even migration from paper packaging. These can seriously clog and corrode gas-burning appliances if allowed into the gas network.
Failure to suppress these elements to minimal acceptable levels (eg H2S at <1ppm) would render the upgraded biomethane non-compliant for network/ pipeline entry.
Greenlane supplied pre-wash activated carbon filters feeding gas to a Greenlane ‘Totara’ water-wash unit with a gas throughput capacity (flow rate) of 650-2,000 Nm3/hr; plus a Siemens HMI sensor controlled operating system with 24/7 remote monitoring and gas analysis, as part of a comprehensive aftercare package.
Design & engineering development
Continual advances in water-wash technology mean that this process is now highly efficient at removing H2S. The efficient range of the ‘Totara’ upgrader enabled the customer to start benefiting from the system at the earliest stage of biogas production.
The plug-and- go design of Greenlane upgraders makes them highly adaptable to constraints in site size and shape.
The dual-channel filter allows the filtration media to be periodically replaced without interrupting the operation of the main gas throughput system.
These features are understood to have contributed to the customer’s decision to choose Greenlane.
The plant has been operating successfully and has been described by industry experts as one of the most efficient plants of its type in Europe. 120,000 tonnes of food waste are processed annually. 5MWh of renewable energy is produced.
The operational outcome has resulted in the customer ordering a very similar Greenlane plant for installation on a site in the London area in 2016.
“We are proud of our food waste processing site at Widnes and the Greenlane upgrading system within it. We are looking forward to achieving the same success with our Dagenham project.”
Philip Simpson, Commercial Director, ReFood
The biogas upgrading technology used in this project conclusively disproved the idea that food waste presented too many technical challenges to make a network-compliant gas for injection into national or local natural gas grids.
The payback period for the investment required was shown to make a strong commercial case to proceed. The environmental benefits included a reduction in food waste, for which UK landfill charges are escalating year on year.
As with most chemical processing systems, optimising efficiency by assessing the right configuration of processing functions is key. OPEX is low and the aftercare package provided helps maintain the plant at high efficiency.