Conversion to renewables: Avedøre plant

Avedøre is one of the most energy efficient combined heat and power (CHP) plants in the world. Owned by Ørsted, the largest energy company in Denmark, and located less than ten kilometres from downtown Copenhagen, the plant’s unparalleled flexibility is what makes Avedøre stand out. Initially designed as a conventional fossil fuel plant, it has gradually been upgraded to 100% biomass.

Ramboll has been involved in the development of Avedøre since conception and construction in the 1980s, regularly providing the client with expertise on a wide range of specialist issues.

Avedøre consists of two units. Unit 1 was built in 1990, using coal as a fuel source. Since then, Unit 1 has undergone a lifetime extension and a bioconversion, enabling the plant to produce heat and power solely from biomass in the form of wood pellets.

Even though it takes more power to retrieve the same amount of energy from wood pellets than from coal, Unit 1 is still able to function at full capacity without the need to downgrade the plant in any way. In addition, it is possible to change fuel types without shutting down operation. The unit’s capacity when using biomass is 254 MW electricity and 359 MWth heat.

Prior to the bioconversion of Unit 1 in 2016, Ramboll was the Owner’s Engineer for the lifetime extension of the power plant. This included preparing a feasibility study and assessing the building structure, boiler, electric installations, and flue gas cleaner. We were also the Owner’s Engineer for

the bioconversion itself. This included assessing combustion systems, fuel storage, and fuel transportation with the use of 3D models to minimise the risk of broken wood pellets, which can lead to spontaneous combustion or explosions due to wood dust.

Unit 2 was built in 2002 as a multi-fuel unit to run on coal, oil, gas, and biomass. In 2008, the unit was converted to 100% biomass, and it now runs on wood pellets and straw in two separate boilers. Running on biomass, the unit has a capacity of 394 MW electricity and 497 MWth heat.

Since the construction of Unit 2 in 2002, Ramboll has taken part in the development of the plant’s flexible and continuous adaptations to new fuel types. Ramboll assisted Ørsted in converting Unit 2 from 80% to 100% biomass, which involved planning, managing, and supervising the implementation of a new wood pellet mill.

• Supplying heat and power for Copenhagen citizens: Avedøre generates heat for more than 215,000 households in the Danish capital area and enough power to supply annual electricity for over 1.3 million households.
• A major biomass conversion scheme: Avedøre is connected to a complex flue logistics system plant with silos holding up to 100,000 tonnes of biomass. The adjoining harbour facilities allow for biomass to be shipped by sea from abroad or from a pelletation plant further down the coast, also designed and constructed by Ramboll. After the conversion in 2016, Avedøre power plant has consumed 1.2 million tonnes of wood pellets annually.
• High efficiency with fewer CO2 emissions: Unit 1 attains an energy conversion efficiency of up to 91% by reusing excess heat from the power production for district heating. A high energy efficiency results in better fuel economy and a reduction in CO2 emission per produced kWh.
• One of the world’s largest straw-fired boilers: Unit 2 has an additional separate dedicated biomass boiler operating on straw which is innovatively connected directly to the main boiler steam cycle. It can fire up to 25 tonnes of straw per hour, supplying more than 120MW high pressure steam.