Story and photos by Kelsey Thalhofer
Capital Press | Dairy | July 31, 2012
When a digester caught fire at an Aumsville, Ore., dairy farm July 25, the unit’s owners in Washington, D.C., knew the second it happened.
Just before the accident, the digester — the second in a line of unique low-temperature units being introduced in the U.S. — had been running at capacity, producing 190 kilowatts of electricity per hour, said Alan Tank, head of Revolution Energy Solutions, which built and owns the unit and operates it from the company’s Washington, D.C., headquarters.
A “critical alarm” signaled the loss of biogas pressure in one of the bio-reactor processing tanks and the digester shut itself down, preventing further damage and perfectly executing its emergency defenses, he said.
The accident, which started when the rubber top of the digester began to leak methane, was the result of a “perfect mix” of unlikely events, said Tank, who founded Revolution Energy Solutions and serves as its CEO.
“You could have (the rubber top) fail 100 times and you’d probably never have a fire,” Tank said, as the rare combination of methane and oxygen produced by the leak would have to meet a spark within seconds to start a fire.
Other experts agree on the safety of the units.
“I personally believe they’re quite safe,” Mike Gamroth, professor emeritus of animal sciences at Oregon State University, said of the digesters. He likened the rarity of the incident to someone’s chance of being struck by lightning. “This is a very unusual case.”
Fire officials gave an initial estimate of $250,000 in damage, which was sustained to the machine’s membrane, insulation, plumbing and electrical systems.
Tank arrived in Aumsville July 27 to assess the damage and attempt to find out where the spark came from — though he concluded that they might never know — and said the most important thing was that no people, animals or equipment had been damaged or lost at Oakley Farms, which hosts the digester.
The digester’s flame arresters — designed to stop the fire — functioned correctly, and the engine automatically shut down.
“The system did everything it was supposed to do, and it worked,” Tank said of the emergency features. No manure was lost in the incident, and he hopes to have one of the machine’s bio-reactor processing tanks running again within a few weeks and the second within a few months.
Digesters have been used for years to convert manure into methane gas, which fuels generators that produce electricity. The RES digester is unique because it operates at about 70 degrees Fahrenheit, a much lower temperature than other designs.
The RES digesters, which cost about $2 million in tax credits and private equity to build, can process up to 30,000 gallons of manure a day, and convert it into nearly odorless liquid fertilizer, solid bedding and electricity. It uses about 2 percent of the energy it produces to power itself.
Digesters also lessen the manure smell dairies and other livestock operations produce.
“If you drive by on the highway, you can’t smell it anymore,” Buzz Gibson, owner of Lochmead Farms in Junction City, Ore., said. His 715-cow dairy farm hosts the first RES digester. Since it began operation in November 2010 the digester has generated more than 1.7 billion kilowatt-hours of electricity, he said.
“It’s way better than a windmill,” Betty Bielenberg, co-owner of Oakley farms, said. She said neighbors had commented on the reduced smell of her dairy farm — which milks 325 cows, each producing about 150 pounds of manure a day — and she was excited that the machine had been “outproducing” the owners’ electricity expectations.
“We feel like it’s a really good thing,” she said.
The Oakley digester had been in operation since January. Construction of a third unit is under way near Dayton, Ore. The company hopes to construct a fourth dairy digester in Oregon and two digesters at swine operations in North Carolina by the end of the year.
Many similar digesters are already in use in Europe, Tank said.
“It’s not a new technology; it’s not a new design,” Tank said. “I’m just hopeful that an event like this doesn’t discourage people from moving forward.”
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