Type of CHP system: BFB boiler
Plant owner: Vapo Oy
Status of plant: Commercial
Bubbling fluidised bed boiler delivered by Foster Wheeler Oy.
The fuel handling system was supplied by Vesme Oy and fuel feeding system by Raumaster.
Power generation: Steam turbine
The boiler is a conventional fluidised bed boiler with a maximum capacity of 66 MWth. The district heat water is heated in two stages. In the first stage hot water is generated with back pressure steam and the second stage with bleeding steam. The plant is equipped with an auxiliary water cooler (6 MWth max) to prime the power production and help to use plant in the summer when the heat demand is low.
Main fuel: Multifuel (more biofuels and/or peat)
Forssa power plant was designed for wood and peat fuels. The main fuels are by-products from sawmills, bark and sawdust, and wood chips. The total use of solid fuels was in 2002 275 GWh from which about 65 % was wood fuels, 31 % peat fuels and rest was 4 % was recovered fuels (REF)
Nominal capacities & efficiencies:
Thermal input, biomass & waste: 72 MW
Total thermal input, incl. fossil fuels: 72 MW
Gross electrical output: 17,2 MWe
Net electrical output: 15,5 MWe
Heat output: 48 MJ/s
Electrical efficiency, gross: 23 %
Electrical efficiency, net: 19,9 %
Overall efficiency, gross: 89 %
Power to heat ratio: 0,35
Electricity efficiency is calculated based on gross electricity generated divided by fuel power of the boiler. Nominal overall efficiency is approximated based on efficiency of the boiler (92%)
How is plant controlled: Plant is controlled by the heat demand. The plant is provided with an auxiliary water cooler to maximize the annual power production.
Heat backup: There are other heating plants in the city which can be used as back up and peak boilers (total of 56 MW). These boilers use heavy fuel oil.
Heat usage: Heating only
Heat is used for district heating in the city of Forssa. In 2002 district heat production was 185 GWh and net electricity generation was about 55 GWh in this power plant. Number of customers was in the end of year 2002 more than 500.
District heat coverage (% of total demand in DH network): 93 %
DH inlet temperature: 75 – 115 °C
DH return temperature: 45 – 75°C
The biofuels are transported by trailer lorries to the plant. The fuel is mainly stored in the large open storage field. The surface area of the asphalted field is about one hectare. The maximum size of the stockpile is about 70000 m3 in autumn. The storage field also serves as quality homogeniser, as different fuels are sorted as layers.
About 20 % of fuel loads are unloaded directly into the storage of the reception station. The reception station is an aboveground reception building compromising four separate reception pockets. The useful volume of the storeroom is 4×200 m3.
There are two big right circular boiler bins of 2×150 m3. Fuel feed is controlled in such way that the boiler load regulates the rotation speed of the discharge screws in the bins.
Ash discharge: Ash is used for landscaping the power plant area and for foundation of the fuel field.
Plant description: Forssa power plant was commissioned in 1996.Plant has fulfilled all the technical and economic expectations so far.
Fuel feeding system:
The fuel is discharged from each storage pocket directly onto a scraper conveyor that is located transversely at the end of storeroom and conveys the fuel to the screen. The design capacity of the fuel line between the reception station and the boiler bins is 250 bulk-m3/h. The fuel is screened with a disc screen. The riddlings are conveyed by the scraper conveyor direct to the boiler bin. The tailings fall after crushing down onto the same conveyor. The disc screen and the crusher are enclosed and designed for wood fuels. The crusher is a slowly rotation two-rotor shearing and necessary reversing roll crusher. The capacity of the crusher is 50 m3/h. There are two big right circular boiler bins of 2×150 m3. Fuel feed is controlled in such way that the boiler load regulates the rotation speed of the discharge screws in the bins.
Boiler: Conventional BFB boiler by Foster Wheeler.
Turbine: Back pressure turbine. ABB Turbinen Budabest, Hungary OT4206.
Steam data: 22.8 kg/s, 510°C, 66 bar
Back pressure of steam turbine is 0.585 bar. Extraction pressure for district heat load is 1.4 bar, and extraction pressure for feed water tank is 6.7 bar.
Flue gas cleaning: The boiler plant is equipped with a one-box and two field electric precipitator. Efficiency: 99.5%.
Staff: The company Forssan Energia employes a staff of 48 persons. The number of O&M personnel at the power plant is 8 and in the district heating department 5 persons.
Electricity sale info: Power plant sells the electricity to the department of electricity of Forssan Energia.
Total capital cost: € 15,900,000
Total costs (including boiler, fuel preparation system, civil works, instrumentations, control system and electrification) were about € 15.9 million (1996).
Boiler € 4.9 milllion, steam turbine and generator € 2,5 million, buildings € 1,7 million, fuel handling system € 1,1 million.
Data collected and quality assured by: VTT Processes.
Contact person: Kati Veijonen