Denmark has quickly become a world leader in biomethane production. There are now 75 operational AD plants in Denmark, most of which produce biomethane gas and have been developed over the past 10 years.

During a briefing at SEGES Innovation, a Danish independent agricultural research and innovation organisation, attendees of the recent Irish Farm Buildings Association (IFBA) tour to Denmark learned that 35% of Denmark’s gas-use is supplied by biomethane from those plants.

Many of these are connected directly to the gas grid, and by 2027, 100% of the country’s gas needs will be supplied by biomethane.

These AD plants process anywhere from 36,000t to upwards of 1,000,000t of feedstock per year to produce biomethane gas. The trend in Denmark is very much for AD plants to increase in size and use waste sources.

Slurry

Animal slurry is an important feedstock, with 33% of all slurry and manure produced in the country processed through AD. The country aims to reach 70% within a few years, which should be achievable, given their indoor livestock systems.

The plant was first built in 2015, but has expanded three times.

Denmark operates under the Nitrates Directive, which includes a derogation of up to 230kg N/ha. Many livestock farmers export slurry to AD plants to help with compliance.

As well as animal slurry, farmyard manure, litter and industrial wastes are also significant feedstocks. Energy crops make up just 4% of the total feedstock mix.

Straw from cereal crops has been identified as a significant new source of feedstock and is set to be used in many of the newest AD plants.

Contractors

The splash plate has been banned since 2001 in Denmark, but few farmers were still using it at the time anyway.

The feedstock is either collected from or delivered by 50 farmers in the area.

Farm contracting is a big business in Denmark, helped by larger farms and a thriving AD industry. Contractors typically spread digestate via an injection system, to reduce ammonia emissions at an average charge of €4/m3. Digestate can be spread from 1 February to 1 October.

Case study: Frijsenborg Biogas Plant

ADVERTISEMENT

The first site visit of the IFBA tour was to the Frijsenborg Biogas Plant, located outside of Aarhus in east Denmark.

The group was greeted by Frijsenborg’s operations manager, Christian Ejby, who showed us around the plant. The AD plant was first built in 2015, but has since expanded three times.

Frijsenborg’s operations manager, Christian Ejby.

The original feedstock capacity was 60,000t, producing 570m3/hr of biomethane, but today it processes over 250,000t, producing around 1,800m3/hr of biomethane.

For context, that’s enough gas to heat 6,000 homes per year.

Farm

ADVERTISEMENT

The AD plant is part of a significant farming business, split between two estates: Frijsenborg and Wedellsborg. The business is privately held, currently in its 13th generation of family ownership, with businessman Bendt Wedell at the helm.

The plant processes over 250,000t of feedstock every day.

Frijsenborg Biogas Plant is situated among 1,400ha of tillage land, which they farm, and around 5,000ha of forestry. Wedellsborg is approximately 1.5 hours away, where another 1,700ha of tillage land is farmed along with 2,000ha of forestry.

Feedstock is mixed before entering the tanks.

In addition to their tillage farms, which mostly produce seed crops, they also run a forestry operation, conduct game hunts, own extensive properties, operate a nursery, and have poultry houses where they produce over eight million chickens each year.

The idea for the AD plant originally came from the need for better poultry waste management. The company employs 100 people.

Feedstock

The 250,000t of feedstock for the plant consists of straw and manure from cows, chicken litter, slurry and wastes such as potato pulp, glycerine and fat from neighbouring Aarhus.

Obtaining planning permission for AD plants in Denmark can be challenging.

Due to increased competition from AD operators, livestock farmers are now being paid an average of €3.5/t for farmyard manure and chicken litter.

While slurry is a significant feedstock for AD in Denmark, it isn’t economical to pay for it, as its biomethane yield is too low.

Demand for digestate is strong, with a waiting list in place.

The feedstock is either collected from or delivered by 50 farmers in the area, and they have around 60 farmers who take the digestate. Demand for digestate is strong, with a waiting list in place. Digestate can be spread on any land, but stock must be kept off grassland for a minimum of 21 days after spreading.

Many farmers enter into long-term agreements with AD plants to supply slurry and manures, and take back digestate. The business has six HGV lorries, which deliver and collect materials.

As is now the trend with Danish AD plants, they don’t use any purpose-grown feedstock.

Design

When they were expanding the plant, the group identified that one of the main concerns for the local community was the odour that it could produce. To address this issue, they made the decision to house the feedstock intake hoppers inside a shed that’s pressurised to contain the air inside.

This enclosed air is then passed through a cleaning system, where it’s filtered through woodchips to eliminate any odours before being released.

The grid injection unit on site.

During the visit to the plant, there was no noticeable odour around the site, except in the vicinity of the hoppers inside the shed. Obtaining planning permission for AD plants in Denmark can be challenging, so consulting with the local community is crucial.

The site has two storage tanks.

The hoppers consist of two walking floors, which are filled up twice a day. The plant has five tanks that are used for anaerobic digestion, and also has two storage tanks.

Operation

The site is 700m away from the high-pressure gas transmission pipeline, which operates at around 580 PSI. They were able to connect directly to this line, meaning they are not limited in export volumes of biomethane.

They use a membrane gas upgrader to remove CO2 from the raw biogas.

They use a membrane gas upgrader to remove CO2 from the raw biogas. The upgrader increases the methane content of the gas to 97.4%.

The biomethane doesn’t have to be spiked with propane before grid injection.

Christian says the membrane upgrading system is simple to operate, although it is energy-intensive. They are currently looking into capturing the CO2 and selling it.

The plant is run using imported electricity at a price of around 10c/kWh. As biomethane gas is valuable, they try to export everything they produce. They use a biomass burner to supply the heat for the plant.

They use 10 8x4x4 square bales per day, which heats the tanks to 49oC.

This boiler was using woodchip until it became more economical to burn straw. They use 10 8x4x4 square bales per day, which heats the tanks to 49oC.

They directly employ six people to run the plant, with four on the technical side and two managing the feedstock. This doesn’t include the drivers for the six HGVs. They also built a shed onsite to house spares for all of the main wearing parts to keep downtime to a minimum.

Support

During the first phase of their AD development, they secured a 40% capital grant. Today, they receive the current market rate for gas and also receive additional green certificates on top of this.

The flare on the site.

To qualify for these certificates, they must maintain International Sustainability and Carbon Certification (ISCC) registration, which involves detailed accounting of energy and emissions used in the production and transportation of the feedstocks.

DCC partnership

Last year, Irish company DCC Energy became a co-owner of Frijsenborg Biogas. This partnership resulted in DCC, which also manages the Shell network in Denmark and owns Flogas Ireland, acquiring a 50% ownership stake in the biogas company.

The shed onsite to house spares for all of the main wearing parts keeps downtime to a minimum.

According to Christian, the motivation behind this move was to partner with a company capable of securing the best market rates for their biomethane gas.

Future plans

The construction of the plant cost around €26m, spread across various phases. It’s worth noting that if they were to build the project from scratch today, the cost would likely be significantly higher due to inflation.

The site is 700m away from the high-pressure gas transmission pipeline, which operates at around 40bar.

The entire plant was constructed by the provider EnviTec Biogas, as they preferred having a single supplier capable of handling all aspects of the project.

The author Stephen Robb is currently involved in a family/community proposal for an anaerobic digestion facility in Co Donegal.

In the near future, they are interested in expanding the plant further, and intend to build a solar farm to power the plant instead of importing electricity.