Farm-scale Farm-scale anaerobic digestion at anaerobic digestion at

Walford & North Shropshire Walford & North Shropshire CollegeCollege

Jon ParryJon ParryDirector of WalfordDirector of Walford

Walford FarmWalford Farm220 ha of ground220 ha of ground200 Holstein cows, averaging 7,800 l/cow/year200 Holstein cows, averaging 7,800 l/cow/year300 Lleyn ewes300 Lleyn ewes70 ha of cereal crops70 ha of cereal crops30 ha of forage maize30 ha of forage maize100 ha of grass100 ha of grass20 ha of woodland20 ha of woodland

A commercial unit required to produce annual A commercial unit required to produce annual profits but also serve as a teaching resourceprofits but also serve as a teaching resource

The Walford Farm DigesterThe Walford Farm Digester Commissioned in 1994 and run every year Commissioned in 1994 and run every year

sincesince ““Fed” a diet of cow slurry throughout the Fed” a diet of cow slurry throughout the

winter periodwinter period 330 m330 m33 capacity, which equates to 15 days capacity, which equates to 15 days

slurry production when all cows are housedslurry production when all cows are housed Chopper pump lifts slurry from slatted channel Chopper pump lifts slurry from slatted channel

directly in to the digesterdirectly in to the digester Digester agitated via circulating gas from the Digester agitated via circulating gas from the

top of the vessel through a series of pipes top of the vessel through a series of pipes across the flooracross the floor

Temperature increased to approx 38Temperature increased to approx 38oc oc by by circulating water heated from burning circulating water heated from burning harvested methaneharvested methane

The Walford Farm Digester The Walford Farm Digester (cont)(cont)

As gas quantity and quality improves CHP As gas quantity and quality improves CHP will produce heat that is re-circulated to will produce heat that is re-circulated to maintain the tempmaintain the temp

Digestate pumped from the bottom of the Digestate pumped from the bottom of the vessel over a separatorvessel over a separator

Solid waste is odourless and stored for use in Solid waste is odourless and stored for use in gardens/fieldsgardens/fields

Liquor is stored in a glass enamel tower, and Liquor is stored in a glass enamel tower, and spread on farmland via irrigation systemspread on farmland via irrigation system

CostingsCostingsWhere does slurry handling system stop and AD Where does slurry handling system stop and AD

system start ?system start ? Best guestimate is £3,000 maintenance and Best guestimate is £3,000 maintenance and

£3,000 staff time per year£3,000 staff time per year Electricity produced £10,000 - £8,000 per yearElectricity produced £10,000 - £8,000 per year Double ROCs £5,000 - £4,000 per yearDouble ROCs £5,000 - £4,000 per year Improved nutrient availability £3,000 per yearImproved nutrient availability £3,000 per year Compost sales £1,000 per year Compost sales £1,000 per year

What next ?What next ? Summer feedstock:Summer feedstock:

– Green wasteGreen waste– Animal manuresAnimal manures– Energy cropsEnergy crops– Gate feesGate fees

NVZ regulations NVZ regulations