Avedøreværket, Denmark

Straw-fired CHP plant

Avedøreværket generates electricity for the Sealand electricity grid and heat for one of the largest metropolitan district heating systems in Northern Europe. The plant was commissioned in 1990.

Avedøre straw-fired plant

The world’s largest straw-fired supercritical boiler

The new Combined Heat and Power (CHP) block, Avedøre 2, represents a completely new technology and is the world’s largest plant of its kind. It is also the world’s most advanced straw-fired CHP plant.

In 1998 we were awarded the contract for the construction of the steam turbine and in 1999 we signed a contract for the ultra supercritical straw-fired boiler plant, featuring a new advanced straw-feeding system.

Straw-fired CHP plant Avedøre, Denmark

The Avedøre 2 plant, which can fire gas, oil, and biomass, began operation at the end of 2001.

The biomass plant contributes up to 35 MW electricity and 50 MJ/s heat. The plant accounts for about 10% of the annual fuel consumption, or approximately 150,000 tonnes of straw per year.

The boiler is designed for 100 percent straw firing, and is the world’s largest and most effective straw-fired boiler with ultra supercritical steam parameters. The boiler generates steam for the main steam turbine of the CHP block.

The technology

The advanced combustion system consists of two straw feeder systems which include:

  • Conveyor system from straw storage to boiler house
  • Fire damper for prevention of backfire
  • Control system for straw supply
  • Newly developed straw shredder which reduces the straw density from 100 kg/m3 to 30 kg/m3
  • Double screw feeders built into the water-cooling feeding ducts mounted on the boiler front
  • Water-cooled vibrating grate

The straw is fed into the furnace by screw feeders onto a water-cooled vibrating grate where up to 80 percent of the energy content is released by pyrolysis and gasification. The remaining straw/carbon will burn out on the water-cooled vibrating grate.

A bag filter system removes more than 99 percent of the particulates from the flue gas leaving the boiler. Slag and ash is carried to containers by a submerged slag conveyor system.

Fuel pre-treament and boiler - straw - Avedøre

Pre-treament system and boiler at the Avedøre straw-fired plant. 

Plant design data

Process parameters Values Units
Steam flow  144  t/h
Steam pressure  310  bar
Steam temperature  583  °C
Energy input  105  MW
Fuel input  26.5  t/h
Feedwater temperature  230  °C
Flue gas temperature after air heater  115  °C
Thermal efficiency  93.2 %
Electrical efficiency, total  49.5  %
Total plant output     
Maximum electrical output  535  MW
Maximum thermal output  620  MJ/s
Local flue gas limits     
 CO, max.    625   mg/Nm3
 NOx (calculated as NO2  240   mg/Nm3
     

*Based on 6% O2 in dry flue gas