Full biomass conversion of Denmark’s largest power plant
About Avedøre Power Station
Avedøre is located just south of Copenhagen, Denmark.
It consists of two units: a 254 MW “unit 1” and a 543 MW “unit 2”, commissioned in 1990 and 2001, respectively. It supplies electricity to Eastern Denmark’s grid and heat to Greater Copenhagen’s district heating network.
As a result of a recent coal-to-biomass conversion project at unit 1, Avedøre Power Station is now able to run 100% on biomass.
The total production capacity for the two blocks on the Avedøre Power Station is 797 MW electricity and 932 MW district heating.
Of course, the amount of energy actually produced at Avedøre Power Station each year depends on weather conditions (which impacts demand) and fuel prices (which impacts supply economics).
Prior to the project, Avedøre 1 primarily used coal as fuel, but has now been completely converted to biomass. The unit’s capacity now using biomass is 254 MW electricity (down slightly from 253 MW) and 359 MW thermal (heat).
The conversion of unit 1 started in April 2015.
In December 2016, utility company DONG Energy announced the completion of the project; now using wood pellets and straw.
The plant is still able to burn coal should it be needed, but aims to process about 1.2 million tonnes of biomass per year.
The power station utilises 89% of the energy of its fuel (compared with 40-50% for the average electricity-only power station in the UK). That’s because it is a combined heat and power (CHP/cogeneration) facility.
The work on the Copenhagen cogeneration plant cost around DKK740m (€100m) to complete. The conversion was financed by DONG Energy and VEKS (more info on the latter organisation below).
The largest single component in the conversion was installed in June 2016: a 34-tonne air cooler installed in the boiler house at a height of 20 meters.
In operation, the wood pellets are crushed in roller mills before being blown into the boiler as dust, at a rate of about 38kg per second. The air cooler ensures that the crushed wood pellets do not ignite before reaching the boiler, keeping them below 130 degrees celsius.
Avedøre 2 was designed originally as a multi-fuel system.
Central to unit 2 is an 80m tower boiler linked to a steam turbine and a generator. This boiler and its supporting fuel logistic and combustion system allows fuel-flexible operation on either coal (at 100% load), oil (100%), natural gas (100%) or biomass (at a slightly reduced load of 70%).
A separate, dedicated biomass boiler operates on straw with an output capacity of 45 MW. It fires up to 25 tonnes of straw per hour and is also connected directly to the main boiler steam cycle (increasing efficiency of the overall plant output).
The plant also includes two gas-driven turbines, each with a capacity of 110 MW. These are connected to the main steam cycle as feed water heaters, allowing the plant operator (DONG Energy) to switch flexibly between heat or power driven operation.
Unit 2 fires at relatively high steam conditions of 300 bar pressure and a temperature of 600 degrees celsius.
Connected to the plant is a logistics system with two silos (100,000 tonnes capacity each) and adjoining harbour facilities. Biomass (wood pellets) can be shipped from abroad or from a pelletisation plant further down the coast.
In addition to its heat and power output, the exhaust smoke gives residuals useful in applications like plaster, concrete blocks and insulation.
Market & Policy Context
In Denmark the full bio-conversion of large coal fired units to wood pellets is helped by the fact that all the involved power stations are Combined Heat and Power (CHP). Denmark levies high taxes on heat production based on fossil fuels, while biomass based heat production for district heating is un-taxed.
Locally, Copenhagen has an ambition of being CO2 neutral in 2025, to which this project contributes.
VEKS, the other investor in the recent coal-to-biomass conversion project of unit 1, provides district heating in the western part of Copenhagen. It is a joint municipal partnership which is run as a non-profit company.
VEKS was founded in 1984 to utilize heat from CHP plants and surplus heat from waste incineration, major industrial facilities and so on. Since VEKS began, consumption of fuel reduced by two-thirds compared to when heat was generated in oil-fired boilers at the local district heating companies.
The VEKS system has a total of 104 twin pipes with seven pumping stations and 44 exchange stations transmitting heat to local district heating systems. It continues to expand.
In order to enable investment in the conversion, VEKS and DONG Energy signed a new agreement which means that from 2016 until 2033, unit 1 at Avedøre Power Station can supply green heat to VEKS’ customers.
For DONG Energy, the conversion work also prolongs the lifetime of the plant and is a major part of its commitment to stop all use of coal (i.e. in all its European power plants) by 2023.
[last update April 2017]