ND ethanol plant installing demo-scale anaerobic digester
Hankinson Renewable Energy LLC, a 120 MMgy ethanol plant in Hankinson, N.D., is in the process of starting up an anaerobic digester to produce 54 million Btu (MMBtu) of biogas a year, according to David Rein, a process engineer with Rein & Associates of Moorhead, Minn. Rein spoke about producing biogas from thin stillage from ethanol plants July 27 at the Biomass ’11: Renewable Power, Fuels and Chemicals Conference in Grand Forks, N.D.
Rein & Associates has been conducting bench and pilot studies of biogas production from thin stillage since 2006, he told the audience. The company has also completed feasibility studies resulting in three separate grants for more than $1 million being offered to ethanol plants through the USDA Repowering Assistance Program. “All those grants were turned down in the end by the ethanol plant,” he said, adding that it was heartbreaking. “It seems so wonderful and no one wants to do it.”
Asked by an audience member why the ethanol plants turned down the grant money Rein said he wasn’t sure. He speculated that it was because it’s something new. People want to see anaerobic digestion in operation at an ethanol plant and walk through to “kick the tires,” so to speak. “It seems to me, everybody wants to be first to be second,” he said.
Hankinson is one of three ethanol plants that elected not to build a full-scale digester. However, it is moving forward with the demo plant project in partnership with Rein & Associates. The engineering company will be paid based on the biogas produced and is offering this same deal to other ethanol plants. If the project in Hankinson goes well it can be easily expanded.
A 6 million gallon digester at Hankinson, as specified in the feasibility study, would have produced 1,380 MMBtu of renewable energy daily. That adds up to 16 percent of the plant’s current fossil fuel energy consumption and 14 percent of its design maximum energy consumption. The process would also produce ammonia and sulfuric acid for use in fermentation, Rein said.
The project would cost about $9.5 million to build, which is many times the $1.6 million grant offered the plant by the USDA. On the other hand, estimates were that it would have a 3.19 year payback rate while USDA said it had a 3.56 year rate of return on investment.
Using the thin stillage for biogas production means significantly cleaner backset, which many producers have told Rein & Associates will increase throughput at the ethanol plant. It may take a bit more corn but the ethanol plant will produce the same amount of distillers grains, he said.