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, including increased draughts, floods, and storms. Millions would lose their livelihoods and have to migrate, causing increased tensions and the risk of war. The Paris agreement from the Paris climate conference (COP21) in December 2015 sets out a global action plan to limit global warming to well 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 less than 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 such as Ca, Mg and Fe. Chemical reactions between surrounding host rock and injected CO2 loaded fluids result in the formation of carbonate minerals for permanent storage of the injected CO2.

How safe and efficient is the CarbFix injection method?

The CarbFix method is considered 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. 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 basalt is the most common rock type on the surface of Earth, covering ~5% of the 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. The question remains, how much of this theoretical storage capacity is feasible to use for mineral storage of CO2.

Other reactive rocks can also do the job and that is among the studies undertaken in CarbFix2 and the related GECO project.

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). The most feasible formations are young formations, where faults and fractures are still open, and pore space not yet filled with secondary minerals.

How much water is needed for dissolving CO2?

At 25 bar CO2 pressure and 25°C, 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.

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.

One of the aims of the EU-funded CarbFix2 project is to optimize the use of seawater for injection of CO2. This is an important step in the development of CarbFix which can increase the geographical applicability of the method.

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, resulting in even lower concentrations.

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 large scale application of carbon capture and storage is vital if the world is to limit global temperature increase to below 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 current operations of the CarbFix project are taking place 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. 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 12,000 of CO2 and 7,000 tons H2S annually, or about 33% and 75% of the emissions from the power plant, respectively

At the end of 2018 about 66 thousand tons of gases had been injected, thereof about 43 thousand tons of CO2.

The fate of the injected gases is monitored through injection of tracers and geochemical monitoring program, but 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 case of the Hellisheidi power plant and ranges from 3 to 10% for typical coal and gas-fired power plants.