The approach
Exergi will retrofit a state-of-the-art district heating facility in downtown Stockholm. The KVV8 power station combusts woody biomass waste (i.e., treetops, branches, saw mill dust) sourced from Sweden and nearby countries in Europe to produce heat and electricity for 800k Stockholm residents.
After biomass combustion, the CO₂ concentration in the flue gas is 18-19%. The retrofit involves reacting this CO₂ with potassium carbonate at high pressure, heating the resulting potassium bicarbonate, and then condensing out the water vapor to leave the CO₂, which is then transported via ship and permanently sequestered deep underground.
The case for Exergi
Near-term tons at affordable prices, with a trajectory to <$100 per ton: Exergi’s facility has the capacity to deliver 800,000 tons of carbon removal per year, starting in 2028. Further reductions in capex and transportation costs offer a demonstrable path to <$100/ton at scale.
A track record of robust execution: Exergi has been providing heat and power to Stockholm for over 150 years. Their track record of building and executing large industrial processes will be critical to the success of this first-of-a-kind retrofit.
Sustainable source of biomass: Exergi uses biomass wastes and residues diverted from Swedish and neighboring countries’ forestry systems where they would otherwise rapidly decay, re-releasing CO₂ into the atmosphere. The retrofit unit is net-energy generating, so the plant will require no additional biomass. Frontier has a set of Biomass Sourcing Principles that Exergi must meet as a condition of its contract, which is elaborated on below.
Strong community engagement: Based in downtown Stockholm, Exergi has a robust, multi-decade strong relationship with the local community. This community has been highly engaged in the design and build of this project.
Retrofit of a state-of-the-art district heat facility: KVV8 is a relatively new biomass-based facility in Stockholm that is expected to generate heat and power for many decades to come. Thanks to its advanced heat recovery, the process is extremely energy efficient, and without it, local energy needs would likely be met by carbon-intensive alternatives.
Highly efficient capture system: Exergi’s HPC (hot potassium carbonate) capture system has demonstrated 90% capture efficiency.
Operating in a well regulated jurisdiction with strong environmental conduct laws and policies: Exergi is subject to the rules of regulations of Sweden and the European Union, including legislation over the appropriate use of biomass.
Pricing and delivery
Exergi’s bioenergy facility retrofit will remove 800,000 tons of CO₂ per year in total starting in 2028. Frontier members will buy $48.6M of the facility's removal output between 2028 and 2030. The exact volume of tons going to Frontier buyers, and the price per ton, will be announced pending the outcome of a competitive reverse auction being conducted by the Swedish government, in which Exergi hopes to win subsidies. Once finalized, Frontier will report the tons and prices.
The illustration shows a possible design of Stockholm Exergi’s planned facility.