New technology optimises biomass utilisation

​New biomass-fired CHP plant in Aarhus, Denmark, contributes to achieving the Danish government’s target of reducing greenhouse gas emissions by 40 per cent by 2010 and converting to a fossil-free energy system by 2050.

​The first turf has been cut for a biomass-fired CHP plant, next to the waste incineration plant in Lisbjerg near Aarhus, Denmark. A total of DKK 1.3 billion has been allocated to construct the plant, which is scheduled to supply district heating and power by the end of 2016. The plant is established as part of the City of Aarhus’ ambitions to reduce its carbon footprint by means of extensive use of biofuels. Using biomass instead of coal and gas is a vital part of the Danish energy and climate policy, since biomass is considered carbon neutral by the climate accounts.

Produces heat when the electricity sale rate is low
The new biomass-fired CHP station helps future-proof the district heating supply in Aarhus by ensuring a multi-fuel energy production, which will mainly rely on waste, wood pellets, straw and wood chips. The plant will be able to adjust production to current demand and current electricity sale rates, consequently only produce district heating when the market price of electricity is low by fully or partially disconnecting the steam turbine, explains Niels Jakobsen, Project and Market Director in COWI’s department of Thermal Power. In his opinion, there is vast potential in exporting Danish expertise in the field: “In general, Denmark is at the forefront of developing biomass for energy production. This means that Danish projects may form the basis for increased export of Danish know-how in energy production, both for consulting companies such as COWI and for manufacturers producing the necessary equipment, since this knowledge is very unique,” explains Jakobsen.

New technology utilises waste gas
The Lisbjerg plant applies state-of-the-art technology to ensure optimum utilisation of the energy of waste gas. This is done through waste gas condensation, where the condensation heat of waste gas is recovered and used in the district heating system. Efficiency is further boosted by introducing moisture to the combustion air. The added moisture is recovered as heat during waste gas condensation.

The CHP plant features a highly efficient waste gas cleaning facility, which generates almost no wastewater since the majority of the condensate from the waste gas condensation is reused. Condensate is processed into makeup water, i.e. it is cleaned to a high quality level, and used in the station’s boiler and in the district heating network.

Plant key figures:

​Input effect: 110 MW equalling some 50 Heston bales of straw an hour.
Power production: Approximately 37 MW.
Heat production: Approximately 77 MW.
Efficiency: Approximately 103.6 per cent (calculated based on the fuel net calorific value).
Fuel consumption: Around 230,000 tonnes of straw a year.
Storage capacity: 67 hours or 3,168 bales of straw.
Designed to run on 100 per cent straw, but can take up to 50 per cent wood chips.
Total sum allocated for construction works: some DKK 1.3 billion.

COWI A/S is main consultant on the project and architectural firm Friis & Moltke A/S is sub-consultant.