In the United States (US), Germany-headed biogas specialist Weltec Biopower GmbH has announced the successful completion, commissioning and handover of a dairy biomethane aka renewable natural gas (RNG) plant in Barron County, Wisconsin (WI).
After just four months of construction, the dairy farm now can produce up to 2.36 million Nm3 (86,600 MMBTU) of RNG per annum.
The biogas on the farm is processed using advanced membrane-based gas upgrading technology to deliver 272 Nm3 per hour (159 SCFM), 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 transportation fleets.
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 anaerobic digestion (AD) plant producing biogas for on-site heat and power needs, so the concept was not new for them.
For years, we have been utilizing cattle manure to generate biogas, meeting our farms electricity and heating needs while also fertilizing our fields with digestate. 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, said the owner.
Modular design
Weltec Biopower constructed three 6,850 m3 (1.8 million US gallons) 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, explained Carsten Hesselfeld, COO of Weltec Biopower North America.
With a diameter of 31.48 meters, the 8.8 meter 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, emphasized Carsten Hesselfeld.
The plant is designed to process 207,000 tonnes of cattle manure annually (150,000 gallons per day), 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 gallons) 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 the Weltec Biopower contract – into high-quality RNG at gas grid specifications.
The digestate is pumped from the RNG plant to the existing lagoons.
Weltec Biopower designed and supplied key components for the Barron County RNG project, including digesters, a prefabricated containerised 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 CO2eq and tax benefits
By utilizing RNG as a fuel source the dairy achieves substantial environmental benefits, reducing carbon emissions by approximately 11,200 tonnes of carbon dioxide equivalents (CO2eq) annually.
Additionally, the plant owners capitalize on financial incentives such as RNG tax credits and fuel tax allowances.
According to Weltec Biopower, this project – with a strongly negative RNG, the fast construction time, and the relatively low CAPEX – is a great example of the huge potential that still exists for biogas/RNG development at some of the smaller dairy farms in the United States.
Projects like Barron County RNG have a key part to play in decarbonizing North American agriculture while decarbonizing truck fleets.
