WELTEC BIOPOWER hands over dairy RNG plant in Wisconsin (U.S.)
The German biogas specialist WELTEC BIOPOWER has successfully completed the commissioning and handover of a dairy renewable natural gas (RNG)/ biomethane plant in Barron County, Wisconsin (U.S.).
After just four months of construction, the dairy farm produces 2.36 MMm3y of RNG/biomethane (86,600 MMBtu per year). This RNG, above gas grid specifications, is processed using advanced membrane-based gas upgrading technology to deliver 272 sm3 per hour (159 sft3/min), which is compressed, bottled and transported to a gas grid injection point. This strongly carbon-negative RNG is drawn off the gas grid elsewhere, significantly enhancing the sustainability of the transportation fleets of the buyers.
Sustainable agricultural practices. The farm currently has a herd of 3,400 cattle, primarily Holsteins along with a select number of Swiss cows. The owners previously operated an AD plant producing electricity for onsite 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. “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.”
Four-months construction time thanks to modular design. WELTEC BIOPOWER constructed three 6,850-m3 (1.8-MMgal) duplex stainless-steel digesters for the new biomethane plant near Rice Lake.
“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,” explains responsible WELTEC BIOPOWER North America COO Carsten Hesselfeld. With a diameter of 31.48 mm, the 8.8-m high, insulated stainless-steel tanks each have a gas storage volume of 3,320 m3. “Our modular construction method, tried and tested worldwide over the past 20+ years, contributed significantly to the short construction time of the plant,” emphasizes Hesselfeld. The plant is designed to process 207,000 metric tpy of cattle manure (150,000 gal/d), with some flexibility to incorporate future increases in herd size.
Efficient biomass processing and energy output. The facility employs a streamlined process flow, with manure fed from the barns into a 1,543-m3 (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 (specified, purchased and integrated into the central SCADA system under WELTEC BIOPOWER contract) into high-quality RNG at gas grid specifications.
Digestate is pumped from the RNG plant to the existing 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.
Savings through CO2 equivalents and tax benefits. By utilizing biomethane as a fuel source, the dairy achieves substantial environmental benefits, reducing carbon emissions by approximately 11,200 metric tpy of CO2 equivalents. Additionally, the plant owners capitalize on financial incentives such as RNG tax credits and fuel tax allowances.
This project (particularly the strongly negative RNG, the fast construction time and the relatively low CAPEX for such a project) is a great example of the huge potential that still exists for biogas/RNG development at some of the smaller dairy farms in the U.S.
Projects like this have a key part to play in de-carbonizing North American agriculture, and de-carbonizing U.S. truck fleets. With the successful implementation of this dairy RNG project, WELTEC BIOPOWER continues to drive innovation, quality and cost-effective solutions for dairy RNG developers, as well as continuously developing market-leading expertise in the co-digestion market.
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