What is biogas?

Primarily consisting of methane and carbon dioxide, biogas is a combustible mixture of gases, convertible into energy. Biogas can be extracted by a biological process which converts organic material into biogas in an oxygen-deficient environment. The biomass is made up by biological residual products, seaweed and algal sludge removed from beaches as well as livestock manure from adjacent farms.

The main constituents of raw biogas is about two-thirds methane and one third carbon dioxide. They can be utilised directly as fuel in, for instance, a gas generator to generate electricity. Gas generators need cooling, a process that produces heated cooling water. A heat exchanger transfers the heat of the cooling water to water, which can be used as district heating to households and offices or for industrial production.

Environment & Climate

Biogas from livestock manure and organic residual is a carbon-neutral fuel. When replacing fossil fuels such as coal, oil or natural gas, it contributes to reducing greenhouse gas emission.

But that is not all. Biogas production represents better use of agricultural livestock manure, further reducing greenhouse gas emission and leaching of nutrients to the aquatic environment.

Carbon-neutral fuel
When plants grow, they absorb carbon dioxide from the atmosphere and use the carbon of carbon dioxide as a building stone. Later, the plants will perhaps be converted to animal feed and be eaten by a pig. The carbon is now inside a pig, and some of it will be transported into the liquid manure and then to the biogas facility, there to be converted into methane and carbon dioxide. Once biogas is used as fuel, the carbon dioxide will be emitted to the atmosphere again.

In this way, the emitted carbon dioxide will be offset by the carbon dioxide absorbed by the plants from the atmosphere when they grew.

The process makes biogas a carbon-neutral fuel, and when it replaces fossil fuels, it recirculates carbon dioxide and counteracts accumulation of greenhouse gases in the atmosphere.

Reduced leaching and accumulation of nutrients
Nutrients like nitrogen leach from liquid manure and fertiliser to the aquatic environment, and subsequently seeps from the soil to streams, lakes and coastal waters.

When nutrients leach to the aquatic environment or seaweed is left to decompose on beaches, the processes add nutrients to algae which begins to grow. If sufficient nutrients are added, the algae may grow to the extent that they consume all oxygen in the water surrounding them, leading to oxygen deficiency. In turn, this process may cause dead zones in the water, both in the water column and at the bottom.
Thus, reuse of seaweed and collection of liquid manure for use in the biogas facility solve two problems at once – both leaching and accumulation of nutrients from farms and beaches.


Environmental benefits

Underlying technology

Solrød Biogas uses a well-known technology, in which raw material – seaweed from the beach, organic residual from the food industry and liquid manure from farms – decompose in tanks in an oxygen-deficient environment. The key process in the biogas facility happens in the reactor tanks. There, bacteria are added, and, at a temperature of about 52 degrees, they convert the organic matter into biogas. Once the biomass has degassed in the reactor tanks, it will be stored and later returned to the farms as fertiliser.

The produced gas is transmitted to Solrød District Heating and used in a gas engine, producing about 25 GWh electricity and about 30 GWh heat annually. The electricity is sold in the electricity market, while the heat is sold to the district heating company Vestegnens Kraftvarmeselskab (VEKS).


How we do it

Biogas production
Via the heat recovery process and the heating system, liquid biomass is pumped into decomposition tanks. Solid biomass is added by means of an automatic loader. The biomass is heated before being pumped in, and the temperature remains at a constant level by recirculation through heat exchangers.

Storage and transportation
The produced biogas is collected and cleaned of hydrogen sulphide (H2S) in a gas processing facility and stored in a gas storage facility. From there, we transmit the gas to, for instance, Solrød District Heating to be used to generate electricity and heat.

We transfer the degassed biomass to storage tanks, dimensioned for 5-days’ production. Once trucks have delivered liquid manure to the facility, they are filled with the degassed biomass and return to the farms where the biomass is used as biological fertiliser.

Solrød Biogas extracts sustainable energy from organic material – biomass – in a controlled process, and the residual is ideal as fertiliser at farms. The illustration shows the various steps of the process.

Transport to the facility
Residual from the companies CP Kelco and Chr. Hansen, seaweed from Køge Bay and livestock manure from pigs and cattle are transported to and from the facility in tankers and closed containers – a total of about 28 loads – on weekdays between 6 am and 6 pm and Saturdays between 6 am and 3 pm.

Reception facilities
We store sufficient biomass from farms to cover five days’ supply. CP Kelco will have its own storage facility with a capacity of 2-3 days’ production. Seaweed is collected from spring to autumn and stored as silage, allowing it to be used all year round.