Lush Grass Becomes Lush Green for UK Biogas Project

Deep in the gently rolling Mendip Hills of Somerset, in the southwest of England, nestles a dairy farm with 150 years of cheese making heritage. It lies only a few miles from the site of the world famous Glastonbury rock festival but the cows clearly dig the music, because they not only produce enough milk for some 14,000 metric tonnes of top quality cheese a year – they also power the farm.

Wyke Farms anaerobic digester units. Credit: David Appleyard.

Wyke Farms is the UK’s largest independent cheese producer and milk processor and is supplied by around 30 surrounding farms as well as its own three dairy units. In a £5 million (US$8 million) project that took five years to plan and construct, an on-site anaerobic digestor (AD) system together with two gas engines and associated ancillaries now power the farm and dairy.

With Ermintrude’s help, the operation supplies both process heat and electricity, enough to make this thriving business entirely supplied with renewable energy.

Featuring three 4,600 m3 biogas digesters, which are supplied up to 48 times over any 24 hour period, some 150 tonnes of material per day are fed into the cylindrical tanks.  The installation is licensed to convert up to 75,000 tonnes of biodegradable waste material from the farm and dairy per year, but currently the farm processes only 55,000 tonnes annually and there are no plans to increase throughput capacity at this time.

The feedstock includes both cow and pig slurry from the Wyke farms dairy operation and piggery as well as dry materials such as rapeseed plant stalks. These act as a substrate for the microorganisms to cling to in order to support their growth.

In addition, whey permeate derived from the cheese-making process is also used to generate biogas. However, as this material – aside from water comprising largely of lactose and minerals – is relatively high in sugar it must be fed in slowly to avoid a subsequent surge in gas production.

Under normal operation the AD is expected to produce some 250 m3 of gas per hour.

Grass clippings and cow slurry are used to create electricity and power at Wyke Farms. Credit: David Appleyard.

Gas produced through the anaerobic digestion process is dehydrated and scrubbed for H2S compounds before combustion to prevent excessive corrosion associated with the production of sulphuric acid. As part of this process, some oxygen is injected into the digester header tanks to encourage the growth of bacteria that can consume such compounds before the gas is passed through a carbon filter.

Alongside the digester units, which were installed by Germany-based Nord Biogas, there are two 670-hp gas engines with capacities of 499 kWe and about 700 kWth each, manufactured by MWM and supplied and installed by Pro2.

One engine has a heat recovery system that is used to aid the process of digestion as well as to pasteurize the digestate.

Within the cast concrete walls of the digester tanks, plastic tubes circulate heated water from the cooling jacket and the heat recovery exchanger from one of the engines. This heats the slurry within the digester tanks to some 40°C to promote biological activity, while feed water and other source materials are also pre-warmed.

Currently two of the three digester tanks are being used to process material.  The third is being used to store digestate and could potentially be available for gas production after this material is stored at a location central to the farm sites. However, with no plans to increase capacity it is likely that its use as a storage facility will continue.

This digestate is used as a rich organic fertilizer and goes back on the land. It is even given to local farms contracted to supply milk to the Wyke Farms dairy and reduces the requirement for additional nitrogen fertilizer, which is typically chemically produced. Excess heat is also used to pasteurize the digestate, eliminating any potential pathogens before distribution on the agricultural land.

The second engine, on a different though nearby site, receives its fuel from the digesters via a gas line. Heat from this unit is used in the cheese making process, supplying steam to the dairy and farm for example.

Alongside the gas engines are a number of gas burners to flare excess gas in the event of say, an engine failure.

The whole system is computer controlled and can be operated remotely via an internet connection. Furthermore, as it is grid-connected, the system can also be controlled remotely by the local distribution company or network operator. In the event of a repair to the local network, the generators may be taken off line and then resynchronized once required.

Tom Clothier, one of the family members still working in the business after four generations, is both the production director at the cheese makers and is the lead driver behind the company’s green ambitions. He explained that the project is supported under the UK’s renewable energy feed-in tariff support scheme and that the company receives 14.02p/kWh (US $0.087/kWh) of energy produced. With an anticipated load factor of 96 percetn or more, this equates to annual support to the tune of around £1.2 million ($2 million)

The project was financed through an extension to the farm’s existing loan facility arranged through Barclays Bank and Clothier said he expects the project to deliver a return on investment within five or six years. The project has a 20-year feed-in tariff agreement in place.

Speaking at the official commissioning of the facility Richard Clothier, another scion of the cheese-making dynasty, declared the project made the company the greenest brand in grocery with 100% green energy supplying the farm and dairy. However, he also called upon other manufacturers to take advantage of the support schemes that make such projects desirable and economically attractive. The tariff schemes that support project like this, “ are generous and they won’t be around forever,” he said.

“We’re committed to energy efficiency and we’re proud to be one of the first national food brands to be self-sufficient. Sustainability and environmental issues are increasing in importance to each and every consumer in the UK and green energy makes both emotional and practical sense,” Clothier said.  Using an AD at dairy farms closes a cycle, according to Clothier.  “We can now take the cow waste [which has inherently been a problem] and turn it into pure, clean energy to drive all our own needs and more.”

The AD project is part of the cheese brand’s £10 million ($16 million) green energy venture and in addition to the new biogas unit the company has also invested in a 49-kW and 39-kW solar power installation. It has also taken other environmental measures such as water recovery from the dairy operations.

Wyke Farm solar panels. Credit: Wyke Farms.

Another project under consideration is the development of a gas upgrading system that will purify the biogas by extracting carbon dioxide and also add an odor to allow direct injection into the national gas distribution grid. Clothier is also considering heat recovery systems from the water used in the dairy process and the company has also opened its Green Visitor Centre dedicated to educating others about sustainability in action.

Wyke Farms also recently announced that it has acquired a Nissan Leaf electric vehicle that will be used for local deliveries and will be charged using the solar PV on Wyke’s dairy farm buildings.

Overall, the environmental program will enable the farm to make claimed savings of 4000 tonnes of carbon dioxide emissions per annum.

Wyke Farms cheddar is a brand with heritage and quality at its heart, but sustainability is also a core value. Its biogas investment is designed to mean that the Clothier family can create at least another 150 years of cheese making history.

This article also appears in the November/December 2013 issue of Renewable Energy World magazine.  Click here to view the issue and subscribe!

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