'Cow power' turning manure and food waste into electricity in England
Waste from the cows and food products are used to produce gas to power electric generators in a city in England, it has been revealed.
John Wintle monitors the engine inside the control room, where gas produced by mixing cow manure and food waste powers a generator and produces 5.2 million kilowatt-hours of electricity, at the Stonyvale Farm in Exeter.
Every day in rural Penobscot County, a large dairy farm harnesses clean-burning gas from cow manure and food waste, and it generates enough electricity to power 800 homes continuously.
The process, commonly known as cow power, has the potential to earn the facility USD 800,000 a year. It also creates byproducts -- animal bedding and a less-odorous fertilizer -- that save the farm about 100,000 dollars a year.
Cow power is more consistent than solar and wind energy, and it eliminates greenhouses gases that otherwise would enter the atmosphere.
For the past 13 months, Exeter Agri-Energy has been combining cow manure and industrial food waste at this location, the Morning Sentinel reported.
In its first year, the company generated 5,200 megawatt-hours for the grid, which earned the farm about 520,000 dollars from Bangor Hydro Electric. Now that the kinks have been worked out, the facility is on track to produce about 8,000 megawatt-hours a year. At 10 cents per kilowatt hour, that's 800,000 dollars.
The project was installed in four months beginning in August 2011. It cost 5.5 million dollars and received 2.8 million dollars in grants from Efficiency Maine, the U.S. Department of Agriculture and the U.S. Treasury Department.
The facility is a subsidiary of the Foglers' Stonyvale Farm, which hosts the project on its land.
Stonyvale also supplies the system with 20,000 gallons of raw cow manure every day.
The manure, which is produced by 1,800 cows, is plowed from the barn floors by a skid steer and diverted into a pump house. From there, the manure is pumped about 1,000 feet through underground pipes to Exeter Agri-Energy, where it enters the facility's anaerobic digesters -- two silolike containers that each hold about 400,000 gallons of manure and food waste.
The food waste arrives nearly every day in an 8,000-gallon tanker truck. The waste comes from grease traps and food processors throughout New England and is delivered by a subcontractor. From the trucks, the waste is pumped into holding tanks, where it flows into the digesters and mixes with the manure.
The digesters are heated to 104 degrees, which creates optimal conditions for the bacteria that are naturally present in cow manure. As the bacteria feed and multiply, the mixture exudes biogas -- about 60 percent methane and 40 percent carbon dioxide.
As the gas pressure builds, the containers' rubber tops expand like balloons and give the containers a domelike appearance. When pressure is sufficient, gas travels through pipes to a 1-megawatt generator.
The generator runs almost constantly throughout the year, except during maintenance periods. The exhaust leaves the generator through a short stainless steel stack, about the size of an exhaust pipe on a farm tractor.
Travis Fogler, operations manager for Stonyvale Farm, said the gas burns cleanly.
At the same time, spent material is pumped out of the containers, where it passes through a mechanical liquid separator. Plant fibres that aren't broken down during the anaerobic digestion process are separated from the water and reused.
All day long, the fibres churn out of the machine in bone-dry clumps that fall into large piles that are used for cow bedding or compost.
The liquid from the separator is pumped back to the farm, where it spills into lagoons that once held raw manure. The liquid contains all the same fertilizing nutrients found in raw manure, but it's better.
The liquid is easier to spread on fields than manure; plants absorb its nutrients more easily and it is virtually odourless, said Wintle.
Those two byproducts save the farm about 100,000 dollars a year, Fogler said.
The greatest savings are found in fertilizer costs. It's not that they produce more fertilizer; they can just use more of what they have.