Type of CHP system: CFB boiler

Plant owner:

Elsam A/S

Overgade 45

DK-7000 Fredericia


Commissioned: 1992

Status of plant: Commercial

Contractor details:

Boiler unit: consortie of Aalborg Ciserv and

Ahlström Boilers.

Turbine unit: ABB Turbinen Nürnberg

Precipitator:  FLS miljø

Controlsystem: ABB Industri

Boiler feed pumps: KSB

Power generation: Steam turbine

The turbine unit is designed for both heat- and process steam production. The max. power production is achieved at max. heat production.

The process steam supply is maintained at a constant pressure of 8,3 bar in the steam header. The pressure is controlled by means of control valves upsteam to the low pressure turbine.

Main fuel: Co-firing (fossil + biofuel)

The boiler is designed for straw and coal mixtures up to 60% and 100% respectively. The straw can be substituted by other biomass. The boiler is designed in all ranges of coal and straw mixtures for a moisture content up to 23 %

The anual fuel consumption at a 50:50% fuel mix is in average 70000 ton of straw plus 38000 ton of coal.

Nominal capacities & efficiencies:

Thermal input, biomass & waste: 52,8 MW

Total thermal input, incl. fossil fuels: 88 MW

Gross electrical output: 19,6 MWe

Net electrical output: 17 MWe

Heat output: 57 MJ/s

Electrical efficiency, gross: 22,3 %

Electrical efficiency, net: 19,3 %

Overall efficiency, gross: 87 %

Power to heat ratio: 0,3

Max. 60% of the coal can be substituted by straw or biomass.

The gross electricity production is obtained at 32 MJ/s heat + 25 MJ/s proces steam

The max. proces steam production is 52 MJ/s at 9 MJ/s heat and 16,1 MW power gross (overall efficiency, gross = 87,6%)

How is plant controlled: The plant is controlled by the heat demand in the district heating network of Grenaa and the surrounding industies.

Heat usage: Heating and process steam

Energy usage:

The power produced is fed into the electricity grid.

The heat is supplied to the district heating network of Grenaa  Varmeværk.

The proces steam is supplied to a paper recycling plant.

District heat coverage (% of total demand in DH network): 82 %

DH inlet temperature: 85 °C

DH return temperature: 50°C

Heat storage size: 3700 m3 m3

Fuel storage: The coal is stored in 2 silos, each 500 tonnes.

Straw storage capacity: 1,800 bales/2 x 400 tonnes, equal to 72 hours of operation with max. straw input.

Waste water: In 2001 26442 m3 waste water were sent to the municipal sewage system.

Ash discharge: In 2001 15195 ton of flyash were produced.

Solid particles are removed from the exhaust gas by an electrofilter. Mixing biomass and fossil fuels means that the rest products in the gas must be disposed of at a suitable facility. Special for this boiler plant is the direct injection of calcium in the combustion chamber, that way the desulpuhurisation takes place simultaneously with the combustion. The desulphurisation products is afterwards treated as a part of the fly ashes.

Plant description:

The idea with the plant is to exploit the energy of the straw in the region in combination with coal.

The coal and straw fired CHP plant provides electric power, district heat and industrial process steam from a Circulating Fluidized Bed (CFB) boiler and steam turbine plant. The fuel mix of coal and straw is an average of 50:50% energy input to the boiler.

The CFB boiler concept was adopted due to its capability of multi-fuel combustion and favourable environmental characteristics.

The plant is equipped with a heat storage tank to compensate for deviations between heat demand and heat production.

Fuel feeding system:

The crushed coal is extracted from the silos and conveyed to the lower part of the boiler where it is fed into the combustion zone at 4 locations.

The straw bales are processed in shredders and fed pneumatically into the boiler.

Boiler: CFB boiler, drum type.

Turbine: Back pressure turbine with separat low pressure turbine and 2 extractions for heat production in 2 stages.

Steam data:

104,4 t/hr

91 bar/505 oC

Flue gas cleaning:

The unit is equipped with an electrostatic precipitator.

SO2 is absorbed by in-bed desulphurization by limestone injection.

NOx is kept low by a low combustion temperature (850 oC) and step by step adding of combustion air.

Cooling system: Cooling by district heating water

Staff: Staff: 30 persons during day time and 2 persons outside normal working hours

Data collected and quality assured by: FORCE Technology.

Contact person: Anders Evald