Swedish biomass CHP plant
by M Rydehell, KanEnergi Sweden AB
As a consequence of governmental incentives and the need for clean and cheap energy, the municipalities of Sigtuna and Upplands Väsby, outside Stockholm, established the utility Brista Kraft AB with the aim of supplying the area from the Arlanda airport to Stockholm with renewable energy. Today the company supplies approximately 65% of the district heating and 25% of the electricity needed in the area from a combined heat and power plant based on biomass.
The Brista Kraft CHP plant
Prompted by their high dependence on oil and electricity for heating purposes, the municipalities of Sigtuna and Upplands Väsby, slightly north of Stockholm, searched for a renewable solution for their common supply area.
The political decision in Sweden to phase out nuclear power, and the incentives in the form of grants for electricity production based on biomass, influenced the municipalities in their choice. Their chosen solution was to establish a jointly-owned utility, Brista Kraft AB, and to build a combined heat and power (CHP) plant to supply the area with clean energy, and to utilise the resources available in the area. As the project developed, another goal was to utilise economically viable technology for flexible fuel use.
The fuel is taken from forests around the plant ­ chipped residues from cutting of forests, like bark, treetops and branches. Only 10% of the energy content in the annual growth of the forests around the plant are used. A smaller amount of fuel is shipped in from Estonia.
At the plant the chipped biofuel, with a moisture content of 55%, is transported to a storage building with room for 13,000m3 of fuel. The technology used in the plant is optimised for the moisture content in the fuel used, therefore no drying process is needed. The fuel is fed automatically to the boiler when required.
The steam boiler is a fluidised bed type delivered by Foster Wheeler Energi Oy, with a capacity of 122 MWth, steam pressure of 144 bar and a steam temperature of 540°C. The particle collection equipment comprises an electrostatic precipitator to separate dust from the flue gases (99.5% is collected). Ashes are taken back to the forest, to keep the nutrient balance.
The VAX II steam turbine, delivered by ABB Stal, has both high- and low-pressure parts, connected to a generator with a capacity of 44 MWe, 10 kV. The electricity produced is fed to the grid. After the steam turbine, the steam is brought to a heat exchanger for district heating (capacity: 85 MWth). The temperature of the water when fed to the district heating system is 90-120°C, and it is returned at 40-60°C.
The Brista plant is situated between Stockholm and Arlanda airport, in the middle of Sweden. The plant was commissioned in December 1996 and has been in full operation since February 1997. Brista Kraft AB operates the CHP plant.
The total investment needed for the plant was 80.5 million ECU and it was financed by the municipalities of Upplands Väsby and Sigtuna in co-operation with ABB Credit AB. The plant is expected to have a payback period of around 15 years.
The expected energy production was 360 GWh of heat and 190 GWh of electricity. In a normal year the production amounts to about 390 GWh of heat and 160 GWh of electricity. From January to April 1998 the electricity production was 80 GWh. No problems besides normal start-up difficulties have occurred.
The production of heat has replaced an annual oil consumption of 25,000 m3 of oil (264 GWh). The CO2 emissions are thereby reduced by 73,000 tonnes/year. Transportation of the fuel adds CO2 to the atmosphere, but this is negligible compared to the amounts saved by converting from fossil fuels to biomass.
By bringing ashes back to the forests a natural cycle is closed, and nutrients are returned. In addition, the ashes are basic and thus keep acidification at a lower level.
The plant delivers 65­70% of the heat needed in neighbouring Upplands Väsby, Rosersberg, Märsta and Arlanda. The remaining heat comes from a heat pump in Vilunda, Upplands Väsby, which extracts heat from the sea. The customers of Brista Kraft include smaller and larger industries, households and residential blocks. The distance from the plant to Upplands Väsby is 12 km, to Märsta 6.5 km, and to Arlanda airport 1.7 km. It may be possible to connect this district heating system with the district heating system of Stockholm in the future.
The electricity is fed to the grid and covers approximately 25% of the electricity demand in the municipalities.
For more information please contact Göran Eriksson at:
Brista Kraft AB, S-195 84 Märsta, Sweden
Tel: +46 8 592 588 00
or the CADDET Swedish National Team in Stockholm.
The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.