Wisconsin dairy gets RNG plant

In February, German biogas specialist Weltec Biopower completed the commissioning and handover of a dairy RNG (renewable natural gas) plant in Barron County, Wisconsin, after four months of construction. The company said the dairy farm will be able to produce 2.36 million standard cubic meters of RNG annually (86,600 million BTU per year).

The RNG is processed using membrane-based gas upgrading technology to deliver 272 standard cubic meters per hour (159 standard CFM), which is compressed, bottled and transported to a gas grid injection point. The carbon-negative RNG is drawn off the gas grid elsewhere to enhance the sustainability of the transportation fleets of the buyers.

German biogas specialist Weltec Biopower has completed the commissioning and handover of a dairy RNG plant in northern Wisconsin, shown here under construction. (Photo: Weltec Biopower)

Sustainable agricultural practices

The farm in northern Wisconsin currently has a herd of 3,400 cattle, primarily Holsteins along with a number of Swiss cows. The owners previously operated an anaerobic digestion plant producing electricity for on-site use, so the concept was not new for them.

“For years, we have been utilizing cattle manure to generate biogas, meeting our farm’s electricity and heating needs while also fertilizing our fields with digestate,” said the owner of Norswiss Farms. “With the new RNG facility, we have expanded our digestate utilization on a larger scale and now store it in our dedicated lagoon for optimal land application.”

Weltec Biopower built three 6850 cubic meter (1.8 million gal.) duplex stainless steel digesters for the new biomethane plant near Rice Lake, Wis.

“We constructed the tanks using a ring-by-ring assembly approach, with the final step involving the installation of a gas-tight membrane storage roof,” said Weltec Biopower North America COO Carsten Hesselfeld.

With a diameter of 31.48 m, the 8.8 m high, insulated stainless steel tanks each have a gas storage volume of 3320 cubic meters.

“Our modular construction method, tried and tested worldwide over the past 20-plus years, contributed significantly to the short construction time of the plant,” said Hesselfeld. The plant is designed to process 207,000 metric tonnes of cattle manure annually (150,000 USG per day), with some flexibility to incorporate future increases in herd size.

Biomass processing, energy output

The company said the facility employs a streamlined process flow, with manure fed from the barns into a 1,543 cubic meter (408,000 gal.) stainless steel pre-storage tank before being pumped into the digesters. The digestion system has a retention time of 34 days before the biogas is upgraded in a membrane-based system into high-quality RNG at gas grid specifications. Digestate is pumped from the RNG plant to the existing manure lagoons.

Weltec Biopower designed and supplied key components for the project, including digesters, a prefabricated containerized pump-block system, heating and boiler containers and a prefabricated factory-tested control container to simplify works on site, enhance the fast construction time and ensure optimal operational efficiency.

By utilizing biomethane as a fuel source, Weltec Biopower said the dairy can achieve substantial environmental benefits, reducing carbon emissions by approximately 11,200 tonnes of CO2 equivalents annually. Additionally, the plant owners capitalize on financial incentives such as RNG tax credits and fuel tax allowances. The company said the project is an example of the potential that still exists for biogas/RNG development at smaller dairy farms in U.S., and the role they can play in de-carbonizing North American agriculture as well as truck fleets.