Why Carbon Capture and Storage (CCS)?
According to the Intergovernmental Panel on Climate Change (IPCC), global warming of more than 2°C would have serious consequences, such as an increase in the number of extreme climate events. The Paris agreement from the Paris climate conference (COP21) in December 2015 sets out a global action plan to limit global warming to bell below 2°C. The agreement is the first ever universal, legally binding global climate deal.
To reach this target, climate experts estimate that global greenhouse gas (GHG) emissions need to be reduced by 40-70% by 2050 and that carbon neutrality (zero emissions) needs to be reached by the end of the century at the latest. The International Energy Agency (IEA) has furthermore estimated that carbon capture and storage is vital if the world is to limit global temperature increase to 2°C.
How does CarbFix differ from other CCS projects?
The most commonly applied CCS method involves supercritical CO2 storage in sedimentary basins, depleted oil and gas reservoirs and coal beds. This method relies on an impermeable cap rock to hold buoyant gaseous and/or supercritical CO2 in the subsurface as the CO2 is less dense than formation waters providing a driving force for it to escape back to the surface via fractures, or abandoned wells.
The CarbFix project mainly differs from these typical CCS projects in two parts. Firstly, the CarbFix injection method eradicates the buoyancy effect by the dissolution of CO2 into water prior to, or during its injection into the subsurface. Secondly, CarbFix focuses on injecting CO2 into basalts which are reactive and contain high amounts of divalent cations like Ca, Mg and Fe. Chemical reactions between surrounding host rock and injected CO2 loaded fluids result in the formation of carbonate minerals that react with dissolved CO2 and form carbonate minerals.
How safe and efficient is the CarbFix injection method?
The CarbFix method is safer than conventional CCS methods because it involves immediate solubility storage as well as rapid mineral storage which permanently immobilizes CO2.
The largest risk of geologic carbon storage is believed to be leakage of the carbon either into the atmosphere or into overlying fresh-water aquifers. Leakage may be promoted by the presence of abandoned wells, or fluid-caprock interaction. Much of this risk is eliminated once the injected CO2 is dissolved into the aqueous phase, as CO2 saturated water is denser than CO2-free water. The CarbFix injection method was designed to dissolve CO2 into water during its injection to overcome the risks associated with the presence of buoyant CO2 gas or supercritical fluid in the subsurface.
Chemical reactions between the basaltic host rock and CO2 loaded injection water have also been shown to be rapid, resulting in over 95% permanent mineral CO2 sequestration in under two years.
Why is carbon mineralization so rapid in CarbFix?
Dissolution of CO2 prior to or during injection ensures that chemical reactions between host rock and injected fluid begin to take place immediately after injection. The high reactivity and chemical composition of the basaltic host rock (up to 25% by weight of calcium, magnesium and iron) play an even larger role in the efficiency of permanent mineral storage in basalts.
What is so special about basalts?
Basalts contain up to 25% by weight of calcium, magnesium, and iron, the chemicals needed for permanently immobilizing CO2 through formation of carbonate minerals. Basaltic rocks are highly reactive and are one of the most common rock types on Earth, covering ~10% of continental surface area and most of the ocean floor.
It has been estimated that the active rift zone in Iceland could store over 400 Gt CO2. The theoretical mineral capacity of the ocean ridges, using the Icelandic analogue, is of the order of 100,000-250,000 Gt CO2. This theoretical storage capacity is significantly larger than the estimated 18,500 Gt CO2 stemming from burning of all fossil fuel carbon on Earth.
Can the CarbFix method be applied elsewhere?
The CarbFix method can be applied wherever a CO2 source is located near basalt formations and a water source (fresh water or sea water).
Basaltic rocks cover about 10% of continental surface area and most of the ocean floor. It has been estimated that the active rift zone in Iceland could store over 400 Gt CO2. The theoretical mineral capacity of the ocean ridges, using the Icelandic analogue, is of the order of 100,000-250,000 Gt CO2. This theoretical storage capacity is significantly larger than the estimated 18,500 Gt CO2 stemming from burning of all fossil fuel carbon on Earth.
How much water is needed for dissolving CO2?
At 25 bar CO2 pressure, the water demand to fully dissolve CO2 is 27 tons of pure water for each ton of CO2, but 31 tons of seawater are required at the same temperature. The amount of water required for dissolving CO2 decreases with increasing CO2 partial pressure, lower temperature and lower salinity.
The groundwater used for dissolving CO2 at the CarbFix pilot injection site has a temperature of around 20°C. At that temperature, 22 tons of groundwater are required to fully dissolve CO2 at 25 bar of pressure, but only 13 tons are required at 2°C.
Can seawater be used instead of freshwater?
Yes, seawater can be used for dissolving CO2 instead of freshwater. The basaltic ocean ridges are porous and vast amounts of seawater are circulated annually through them by natural processes. Every year, about 100 Gton of water is circulated through the oceanic ridges; this is about three times greater than the present mass of anthropogenic release of CO2 to the atmosphere.
Can the water used for dissolving CO2 be reused or is it contaminated?
Yes, the water can be circulated and reused after CO2 has been removed from it via carbonate formation. At our pilot injection site in Iceland we can even drink the water after the CO2 is gone. A positive side effect of the carbonation process is that heavy metals tend to precipitate into the carbonates along with Ca, Mg, Fe and CO2, providing a potential method for purifying groundwater.
Is CarbFix the ultimate solution to climate change?
CarbFix is not the ultimate solution to climate change but rather a new tool in the fight against global warming. The International Energy Agency (IEA) has furthermore estimated that carbon capture and storage is vital if the world is to limit global temperature increase to 2°C and the CarbFix method provides a safe, efficient way to permanently immobilize CO2 where basalts and water sources are located near CO2 sources and thus contributing to reducing greenhouse gas emissions.
Who are involved with the project?
CarbFix was founded by four partners in 2007: the University of Iceland, CNRS in Toulouse, the Earth Institute at Columbia University in New York and Reykjavik Energy. Several universities and research institutes, and over 100 people have contributed to the project, thereof a number of PhD and MS students as well as engineers and technicians. Current partners, working on the CarbFix2 project, are Reykjavik Energy, CNRS, University of Iceland, Amphos21 and Climeworks.
Where is the CarbFix injection located?
The CarbFix injection is located at Hellisheidi geothermal power plant. The power plant co-produces electricity and hot water from the Hengill central volcano and installed capacity of 300 MW electricity and 120 MW thermal. Without gas capture and injection, the power plant would emit about 40,000 tons CO2 and 12,000 tons H2S. The CO2 emissions amount to about 5% of what a coal fired power plant of the same size would emit.
What is the current status of the project?
Based on successful pilot scale injections in 2012, experimental industrial scale injection began in June 2014. CO2 and H2S emissions from Hellisheidi power plant are captured in a gas abatement plant through a simple scrubbing process, dissolved in condensate from the power plant and returned back home to the geothermal system within the basaltic bedrock where they came from. At the end of 2015 about 10 thousand tons of gases had been injected, thereof 6300 tons of CO2. In 2016 the injection was further scaled up, doubling the amount of the injected gases. The capturing capacity of the gas abatement plant after the scale up is up now about 10,000 of CO2 and 7,000 tons H2S annually, or about 25% and 50% of the emissions from the power plant, respectively.
The fate of the injected gases is monitored through a tracer and geochemical monitoring program but first results indicate rapid and permanent mineralisation as was to be expected based on results from pilot injections.
What is the energy penalty for adding CarbFix to a power plant?
The energy penalty of the CarbFix injection method depends on the type and efficiency of the power plant. The Hellisheidi power plant emits 21.6 g of CO2per kWh of electricity produced. In contrast,CO2 emissions from typical coal and gas fired power plants range from 385 to 1000 g of CO2 per kWh electricity produced. Thus the energy penalty associated with injecting CO2 as a dissolved phase into the subsurface is on the order of 0.2% for the ase of the Hellisheidi power plant and ranges from 3 to 10% for typical coal and gas-fired power plants.