Type of CHP system: BFB boiler

Plant owner: Owned by the Eskilstuna Municipality

Commissioned: 2000

Status of plant: Commercial

Contractor details:

Boiler delivered by Kvaerner Power.

Turbine by Siemens (former ABB Stal ).

Fuel handling system delivered by Essverk

Power generation: Steam turbine

The plant has a recently invented high tension generator (136 kv), Powerformer, which is direct coupled with the primary network. The flue gas condenser is a scrubber with three emits heat level and supplied with a moistening. Two levels emit heat the district heating grid and one level emits heat to the heat exchanger.

Main fuel: Wood chips

The fuel consists of forest residual (50%) and sawdust and bark from sawmills (50%). The annual use amount to around 270 000 tones (890 000 m3)

Nominal capacities & efficiencies:

Thermal input, biomass & waste: 120 MW

Total thermal input, incl. fossil fuels: 120 MW

Gross electrical output: 38,7 MWe

Net electrical output: 36,2 MWe

Heat output: 96 MJ/s

Electrical efficiency, gross: 32 %

Electrical efficiency, net: 30 %

Overall efficiency, gross: 112 %

The flue gas condenser reduce the efficiency of electricity with about 1 MW when the district heating return temperature is above 54 C due to higher condensation temperature.  Flue gas condenser is on 25 MW

How is plant controlled: By heat demand

Heat backup:

The plant consist of a CHP plant on 57 MW, 4 oil fired boilers all together on 310 MW, 2 heat exchanger all together on 25 MW and 2 electric boiler all together on 32 MW.

Furthermore is there a flue gas condenser (15 MW) and a accumulator on 60 MW, which can storage 1 200 MWh. Along the district heating grind is it also plants which are oil fired (60 MW)

Heat usage: Heating only

Energy usage:

4 160 district heating customers. The connected capacity is 394 MW, use around 690 MWh per year. Around 90% are connected to district heating. The division is multi dwelling houses 53%, industry 8%, one dwelling house 10 % and others 29 %

District heat coverage (% of total demand in DH network): 90 %

DH inlet temperature: 75-120 °C

DH return temperature: 45- 56°C

Heat storage size: 27000 m3

Hours of full load that the heat storage can meet: 60 MW in 20 hours

Fuel storage: 6000 m3 indoor and around 10 000 outside which is sufficient for 4 days

Waste water:

95 000 m3 per year of the condensing water from the flue gas condenser is distributed to the sewage treatment plant, which is owned by the municipality, where a wetland reduce the ammonium nitrogen

Ash discharge:

Ash treatment, both from the boiler and dust collector, occur in sealed system. The ash sells to the company Econova, which use it in the production of fertiliser

Plant description:

The CHP-plant was commissioned year 2000. Heat output is 71 MW, excluding flue gas condenser which is 25 MW. Gross power output is 38 MW

Chipped forest fuel is used, which mainly consist of forest residual and byproducts from sawmills.

The boiler is  a bubbling fluidized-bed

The turbine is a ABB Stal VAX mark with the high tension generator “Powerformer” (136 kv).

Electrostatic precipitator separates dust from the flue gases. The steam in the flue gases is condensing in a flue gas condenser (scrubber), recoverd heat is delivered to  the district haeting grid

Combustion air is moistening by the recovered condensation from the flue gas condenser in order to increase the efficiency of the condenser (10MW).

Fuel feeding system:

The fuel feeding system is sealed and the fuel is storage at the plant. Two feeding systems supply the storage with fuel. One feeding system was erected year 1986 and one 2000. At the fuel preparation is fuel rejected which have faulty size and dross. The rejected fuel has the seller to take care of.

Boiler: The BFB P has a efficiency of  91,5 %

Turbine: VAX turbine, 148 tons /hour

Steam data: 140 bar, 540 degree Celcius, 148 tons /hr

Flue gas cleaning:

Electrostatic precipitator separates dust from the flue gases. NOx is reduced by a SNCR which is installed at the boiler in order to reduce emit of nitrogen. A solution of 25% Ammonium hydrate is sprayed into the boiler, where the temperature of the flue gases is convenient. The quantity of the solution of ammonium hydrate is around 90 litre per hour. At the continuous control measurement is the then emitting to the air less than 2 ppm. Condensing water is also control measurement.

Cooling system: Own district cooling does air and water cooling of the generator

Convetional steam cycleBefore 140 bar, 540 C and after the condenser 0,7 bar

Staff: The company employ 37 persons including the CHP plant. Three persons per shift to run the plant

Electricity sale info: Sells to Nordpool

Total capital cost: € 52,000,000

Amortisation 20 year. Grant from the government € 12,4 million. Net investment € 39,4 milllion.  Costs for leasing and interest 3,4 million per year.

Boiler € 21 million, Turbine € 9 million, Supplement external fuel feeding system € 4 million, Building and ground € 8,3 million, District heating and other connections € 2,2 million, El- and controlling system € 4 million, projecting, purchasing, putting into service € 4,4 million.

Data collected and quality assured by: Swedish Biomass Association.

Contact person: Johan Vinterbäck