Installing an AD plant in 2012 provided a new income stream for an arable farm that wanted to reduce risk through diversification. Today, it exports more than three quarters of the energy it produces, whilst powering the whole farm and benefitting from both the solid and liquid waste product.
W.H. Gittins & Sons has a cropped area of 3,800 acres. The land is largely planted with cereals including winter wheat, barley, maize and sugar beet.
25 per cent of the crops grown are fed to the digester, which also requires bought-in feedstock in the form of chicken muck, and whey supplied by neighbouring farms.
“50 per cent of the feedstock for the digester is grown on farm and the other 50 per cent is bought-in. 25 per cent of our cropped acreage is fed to the digester,” explains renewables manager, Sam Dutton.
The outcome of feeding a tank of this size is 1.9Mwh of power generation. This is largely sold back to the grid, with the farm exporting 76 percent of the energy produced.
“We use 24 percent to run the farm. That electricity powers the farm buildings which use about 6% and the digester which uses 4%. We also have two ground source heat pumps which provide the energy needed for our drying floors. There are also 3.5 acres of solar panels generating 100kw/h from a one-megawatt system,” he adds.
The farm has developed a crop rotation that suits the digester but also puts an emphasis on high yielding cereal crops. Maize, sugar beet and chicken litter, along with whey from local dairies, is mixed and fed every hour, on the hour.
“Consistency is the key. If we change the balance of the mix, we need to do so slowly. Some digesters use water as the liquid element, but we prefer to use a waste product in the form of whey. Recycling the whey is one benefit, but, unlike water, it also provides energy too,” he says.
The digester has two distinct areas for materials to be used. An outer ring is fed from the hopper, which sends material through a Vogelsang PreMix solid matter feeder. The PreMix is a 4-in-1 feed system which separates and removes any foreign matter such as stones, mashes the feedstock, mixes it into a homogenous liquid and pumps it into the digester.
“We bring liquid through from the back end of the digester, through a macerator, to mix with the fresh feed. This mixture is then pumped into the centre of the digester where it does its work,” he adds.
The expended mixture is pasteurised and sent through two separators before the liquid portion is stored for applying to crops using dribble bars and a trailing shoe. The solid fraction is applied as a dressing.
“We generate between 30 and 40,000 cubes of total biomass. Understanding the nutrient value has helped us to reduce our bought-in fertiliser and make best use of both the solid and liquid fractions,” he says.
The liquid is largely applied through a dribble bar umbilical system. A local contractor handles 80 per cent of the application whilst the farm uses a Joskin tanker with a 15-metre trailing shoe to apply areas that can’t be reached by umbilical.
The system is almost entirely closed off and self-sufficient. This has lowered the cost of producing the high-quality cereal crops and makes best use of less productive land or land more suited to spring sowing for crops that feed the digester.
Learn more about the PreMix