Stockholm Exergi, the utility supplying district heat to the city of Stockholm, made a commitment in June 2020 to become climate positive by 2025. The goal is to reach “negative emissions”, primarily by deploying bio-CCS (bioenergy + carbon capture and storage) to the large biomass fueled combined heat and power plant at Värtan in central Stockholm. This plant is one of the world’s largest of its kind, and it uses woodchips from Sweden and the whole Baltic region to supply the city of Stockholm with heat and power.
This large CHP (combined heat and power plant) was inaugurated in 2016, and has a total capacity of 380 MW, with a biomass fuel use of over 2 TWh. The fuel is primarily forest residues, tops and branches, collected from felling and thinning operations and transported to Stockholm either by train or by boat. If left in the forest, these residues would decompose within a few years and release large amounts of carbon dioxide. Instead, they are used to substitute fossil fuels. Stockholm Exergi closed down its last coal boiler in April 2020. This unit had not been used during the preceding winter due to relative warm winter weather and low heat demand. From now on, the only fossil fuels used by Stockholm Exergi is the fossil plastics in municipal waste used in two other heat plants.
In December 2019 a pilot unit for carbon capture was started at the Värtan plant. After successful results Stockholm Exergi is ready to invest in a full-scale installation, capturing 800 000 tons of carbon dioxide yearly – creating a very large carbon sink. This unit can be up and running by 2025. Capacity for storage of this CO2 in the North Sea can be in place 2024, according to Stockholm Exergi. This will be a cooperation between Swedish and Norwegian actors.
New legislation and a governmental support scheme will be necessary to implement the bio-CCS technology at such a large scale. A governmental study on how to make this possible was published in January 2020, and the reactions to the proposals have been positive. If implemented at all Swedish major biobased CHP plants and large pulp mills, bio-CCS could mean storage of up to 30 million tonnes per year of biogenic CO2 from Swedish sources. This is more than half of the total greenhouse gas emissions in Sweden today. Large-scale deployment of bio-CCS will be needed to reach ambitious climate targets by mid-century. The total cost will be 60 – 100 €/ton CO2, according to the Swedish study.
Besides bio-CCS at the Värtan plant, Stockholm Exergi will also produce bio-char to improve soils in parks and gardens and thus create additional carbon sinks. The company is also investing in improved technology for plastic recycling from municipal waste. Also these measures will contribute to making Stockholm the first global city with negative emissions – truly positive for the climate.