AVK knife gate valves installed at large biogas plant in Denmark

GrønGas Vraa is a large Danish biogas plant receiving slurry from 50 local farmers. AVK has delivered 36 knife gate valves to the plant.

The plant in Vraa produces biogas from cattle and pig manure, industrial waste products and food leftovers. The plant can treat 365,000 tons of biomass every year and can supply the natural gas network with approximately 13 million cubic meters of bio methane. This corresponds to the consumption of gas in 6,500 residences or the annual consumption of 4,300 cars or 250 buses. The establishment of the plant has created new jobs in the local area, and today there are five people hired to maintain the plant, whilst there are eight drivers delivering manure and picking up fertilizer from the plant.

Biogas manufacturing

Biogas is manufactured from organic waste which is biodegraded in sealed-off containers by means of bacteria. The bacteria that break down the biomass emit gas which is used for energy purposes. In this form, gas can be used directly as fuel for e.g. gas generators that produce electricity. Additionally, gas can also be cleansed of CO2 and hydrogen sulfide, so it is converted into methane. Like methane, gas can be used in the natural gas network.

The process

The production of biogas is initiated when fresh manure is mixed with industrial waste and food leftovers in the recipient container. Biomass is then pumped into the reactors and heated to approx. 52 degrees. Biomass is kept in the reactors while manure is fermented and gas is formed. The gas is discharged from the reactor containers and degassed manure is pumped into storage containers from which farmers can pick it up. This process, starting when the manure arrives at the plant until the farmers pick up the fertilizer, lasts approximately 40 days.

Use of by-product

The production of biogas minimises the emission of nitrogen. When manure is being degassed, the dry matter of manure is decomposed. Consequently, manure contains a lower amount of organic nitrogen and a higher amount of inorganic convertible nitrogen. This means that a larger part of the nitrogen is obtained by plants and a smaller part of the nitrogen is washed out in the water environment. Therefore, degassed manure is also of interest to farmers, and the use of the degassed manure also has a positive effect on the harvest yield.

Knife gate valves help manure through the process

AVK has delivered 36 knife gate valves to the plant in Vraa. 30 of these valves are installed in the manifold where manure is picked up and conveyed through the plant. A few of the valves are located on the outside of the containers and are used to transport beets (the preferred food resource) directly into the process. Furthermore, six valves are installed to fill and empty the plant’s three heating modules.

The excess heat produced by the plant is delivered to the city of Vraa and Vraa heating plant. GrønGas Vraa plant was built in cooperation between the energy company E.ON Danmark and farmer Jens Peter Lunden, who also runs GrønGas Hjørring not far away from the plant in Vraa.