From coal to biomass: Asnæs power plant

Converting a coal fired plant to renewable sources of energy, in line with client Ørsted’s decision to cut coal out of its power stations by 2023, helping bring renewable heat and power to homes in Kalundborg, Denmark.
Asnæsværket (ASV), Blok 6/Unit 6, Flisplads Dato: 3. oktober 2019
Ørsted, the leading energy company in Denmark and the world’s most sustainable energy company according to Corporate Knights, has decided that coal will no longer be used as a fuel at the company’s power stations by 2023.
The decision is a result of the company’s vision to lead the path towards a sustainable transformation of the energy system and the core reason for converting one of the largest coal-fired power plants in Denmark, Asnæs, to renewable energy.
In 2020, a new biomass-sourced unit came to life, designed as a high-efficient combined heat and power plant. The wood chip-fired unit works in synergy with the power station’s electric and standby boilers and a large heat pump owned by Kalundborg municipality’s heat supplying company. This setup gives a high degree of flexibility and reliability of supply as the intermittent renewable energy from wind and solar is used when available at competitive prices, while the energy from biomass delivers power to the grid and process steam for district heating and nearby industries.
Commonly known as Unit 6, the new plant has a power capacity of 25MW and a thermal capacity of 129MW including 28MWth generated by a flue gas condensing plant. This can power approximately 24,000 homes with green electricity and feed another 37,000 homes with green heat. The switch from coal to biomass brings an annual saving of 800,000 tonnes of CO2, equivalent to the emissions from 400,000 cars.
Ramboll was the Owner’s Engineer for technical consultancy and advisory. First, we conducted a feasibility study for the new unit and in the following planning phase and execution provided engineering, design, and construction services. During the installation of the new unit, we were responsible for health, safety, and environment coordination and supervision of the contractor’s work.
A traditional but flexible setup
The selected concept covers facilities for receiving, screening, conveying, and storing wood chips from sustainable forestry, in addition to fresh biomass feedstock. The energy is converted in a traditional steam generator/turbine setup but is designed to accommodate multiple operating modes, including a complex mix of process steam, district heating and power production.
To meet the stringent environmental requirements and a high efficiency target, the plant has a state-of-the-art flue gas cleaner, and a flue gas condensation and combustion air humidification. The condensate is cleaned and used as makeup water for the water-steam cycle.
The work on Asnæs Power Plant Unit 6 started in 2016 and finished in 2019. The plant became operational in 2020.

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