Type of CHP system: BFB boiler

Plant owner: Plant owner is Termia Oy, part of the Atro Group (Formerly Savon Voima Oy)

Commissioned: 2002

Status of plant: Commercial

Contractor details:

The main boiler (48 MW) of Iisalmi plant was commissioned by Foster Wheeler Oy in 2002. BMH Wood technology Oy delivered the fuel handling and feeding system.

Power generation: Steam turbine

Process optimisation and plant design included an innovative steam turbine solution which improved the power/heat ratio to 0.49 when it typically has been 0.40 in similar type and size plants.

Main fuel: Multifuel (more biofuels and/or peat)

Iisalmi power plant was designed for wood and peat fuels. The main fuels are peat and by-products from sawmills. In 2002 the total use of solid fuels was about 127 GWh from which about 70 % was peat and 30 % wood fuels. Year 2002 was the starting year of the plant and it was not used during whole year.

Nominal capacities & efficiencies:

Thermal input, biomass & waste: 49 MW

Total thermal input, incl. fossil fuels: 49 MW

Gross electrical output: 14,7 MWe

Net electrical output: 13,7 MWe

Heat output: 30 MJ/s

Electrical efficiency, gross: 30 %

Electrical efficiency, net: 28 %

Power to heat ratio: 0,49

The bubbling fluidised bed unit can be fired on up to 70 % wood fuels, and up to 30 % green chips. The remainder is accounted for by milled peat.

How is plant controlled:

By heat demand. Theoretical minimum heat load is 10 MW. If the load of the district heating network is less than 10 MW, heat is produced in other units and the plant is shut down.

Heat backup:

Termia Oy has several oil fired boilers coupled with the district heating network. There are two oil fired boilers (2×12 MW) and a fluidised bed boiler (15 MW) at the old Parkatti’s heating plant located next to Iisalmi power plant.

Heat usage: Heating only

Energy usage: Heat produced at the plant is used for supply district heating network of the city of Iisalmi.

District heat coverage (% of total demand in DH network): 85 %

DH inlet temperature: 85 – 115 °C

DH return temperature: 45 – 55°C

Fuel storage:

Peat and wood fuels are handled using the old fuel receiving and handling station and storage silo. From there fuel is fed into a 2000 m3 intermediate storage silo. Fuel storage capacity is about 30 hours.

Ash discharge: Ash is used for landscaping of the Iisalmi airport for the next 10 years.

Plant description:

The power plant was built next to the old Iisalmi heating plant. Old plant was connected to the new power plant block with pipes. The steam boiler of the plant was designed to be a multi-fuel-fired boiler, which is able to use all domestic fuels.

When the construction decision was made the main objective was to utilise indigenous fuels, peat and biomass, as much and possible with high efficiency. Environmental impact analysis was made according to the Finnish regulations taking into account the impact of various fuels and emissions from their combustion and the increased traffic because of fuel transportation.

Heat production is typically around 170 000 MWh and electricity production 60 000 MWh annually. Sources: Termia and “Iisalmi district heating power plant – High cogeneration performance and environmentally friendly by utilisation of biofuels” in Bioenergy 2003 Proceedings by Anssi Kalmari.

Fuel feeding system:

Fuel is conveyed from storage silo by an elevator into a screw feeder and into two feeder bins of 100 m3 volume each. From there the fuel is then fed into the fluidised bed.

Boiler: 48MW BFB boiler by Foster Wheeler.

Turbine:

The steam turbine is a new single casing, two-stage model, with a double flow district heating tail. The steam flow is distributed to separate turbine flow sections in such way that steam is distributed evenly between both heat exchangers at higher DH-waster exhaust temperatures and at partial loads too. This technical advancement in turbine technology enables a clearly higher power generation output on wintertime compared to conventional backpressure turbine. The steam turbine has been supplied by Blohm&Voss Industrietechnik GmbH.

Steam data: 17,3 kg/s, 515°C, 93 bar

Flue gas cleaning: Electric precipitator by ABB.

Staff: O&M personnel of 5 persons operate the power plant and the Parkatti heating plant. The number of other personnel at the plant is 9 persons.

Electricity sale info: Atro group sells the electricity.

Total capital cost: € 22,400,000

Data collected and quality assured by: VTT Processes.

Contact person: Kati Veijonen