Launched in 2012, Lahti Energy’s Kymijärvi II power plant is the world’s first gasification power plant to use waste-based solid recovered fuel (SRF) and waste wood to generate electricity and district heat. The fuel is made from plastic, wood and paper waste collected from industrial, commercial and household sources. The 160 MW plant has the capacity for up to 250,000 tonnes of SRF and waste wood per year, which amounts to about 170,000 tonnes of coal and produces about 280-300 GWh of electricity as well as 680-700 GWh of heat annually. Kymijärvi II produces 110,000 tonnes of carbon dioxide annually, whereas the same amount of energy generated with coal would produce 410,000 tonnes more.
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Experimenting with gasification
Lahti Energy has used gasified biofuel and SRF as complementary fuel in their coal-fired Kymijärvi I since 1998, with positive results. At that time, the local company Päijät-Häme Waste Management was looking for ways to reduce landfill waste and started to provide waste for Kymijärvi’s new gasifier. Waste incineration plants (that can only utilize waste) are exempt from carbon dioxide emissions trade, which in part encouraged the company to specialize more in developing gasification technology. After some innovative measures, the idea of Kymijärvi II was born. Lahti Energy started promoting it as a new kind of demonstration plant, and applied for aid from the EU and the Finnish state in 2006. The €160.5 million project received €15 million from the Ministry of Employment and the Economy as well as €7 million from the EU. Construction started in 2009.
Complex automation controls eco-gas production
The preparation of SRF includes excluding unsuitable materials, such as aluminium and biowaste, and shredding the waste into small strips. SRF is prepared by waste management companies in Southern Finland and sent to Kymijärvi II. The SRF is gasified, and then the gas is cooled and cleansed. The resulting “eco-gas” is nearly equivalent to natural gas in purity. Because the energy content of the SRF varies, a complex automation system provided by Metso Ltd was constructed. The automation keeps the electricity and heat generation constant with about 200 guided motors, almost 1,000 measuring points and a price tag of nearly €10 million. In addition to SRF, the plant uses some actual natural gas, e.g., to start up the gasifier, and ignite the burners of the boiler as well as during situations when the plant malfunctions.
Unparalleled capacity with gas cooling and filtration
Crude waste-based gasification gas contains various impurities, such as metals, sodium and chloride, which, in addition to their environmental impacts, can damage plant machinery. The equipment corrosion problem generally related to waste-based fuels was solved in Kymijärvi II with an unprecedented gas cooling and filtration process. The gas coolers and cleaners are new technologies that enable gasification of SRF at unseen scales. After gasification, the temperature of the gas is lowered from 900 °C to 400 °C, which causes its impurities to solidify into ash. The gas is led to ceramic filter pipes in which unwanted particles stick to the pipe walls. During regular intervals, the sediment is removed using so-called nitrogen pulses. After this, the resulting pure eco-gas is ready to be sent to an ordinary natural gas boiler to be combusted. The purification process has had some problems, which is why the plant has not been able to generate energy at full power.
Regional dimension
In 2012, the Forum for Sustainable Development selected Kymijärvi II as the “Climate Deed of the Year”, praising its innovativeness and replicability. The plant also won a special commendation in the Nordic Energy Municipality Competition during the same year. Energy solutions have an important role in the strategy of the city of Lahti, which includes halving the carbon dioxide emission levels of 1990 by 2025. Kymijärvi II has reduced the use of the older Kymijärvi I combustion plant, which will soon become obsolete. Before long, Lahti Energy will fully replace Kymijärvi I and increase the usage of renewable energy, mainly biofuels from wood, with the coming Kymijärvi III.
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