How Mineralization Works in Geologic Storage with BECCS
Carbon mineralization is a slow, yet effective process within the carbon cycle. Its ability to keep large amounts of carbon out of the atmosphere for millions of years makes mineralization an essential component of the cycle. Without it, there’d be no regulation of atmospheric carbon dioxide and no balance in the global temperature.
Mineralization facilitates long-term carbon storage by encasing carbon into a crystal structure of minerals. This is essential given that other reservoirs within the carbon cycle lack the ability to sequester carbon for an equivalent length of time. The carbon storage in soil and trees, for example, can be easily disrupted and release carbon dioxide back into the atmosphere.
When mineralized, carbon is guaranteed to remain out of the atmosphere for thousands of years.
Carbon mineralization can occur in two types of settings: above ground or below ground. Above-ground mineralization is known as ex-situ and is the method used for enhanced weathering and carbon capture with concrete. Underground, or in-situ, mineralization occurs when carbon dioxide reacts with alkaline rock and solidifies as carbonate. In-situ mineralization occurs with Carbon Capture & Storage (CCS) technologies like Direct Air Capture (DAC) and Bio-Energy with Carbon Capture & Storage (BECCS) when injecting carbon into geological formations.
Mineralization with BECCS
With the increase in anthropogenic carbon emissions, technologies like BECCS can combat the rising global temperature by removing carbon dioxide on a large scale. Transferring excess carbon from the atmosphere and sequestering it underground accelerates this journey within the carbon cycle so it may mineralize over time.
BECCS is the implementation of CCS to Bioenergy systems. For example, an industrial facility may combust organic matter to produce heat & power. BECCS technology then captures the carbon dioxide from these industrial processes and sequesters it permanently using geologic storage. Doing so creates a net negative system.
Once carbon dioxide is separated from the other emissions, it’s pressurized into a supercritical fluid. As a fluid, carbon dioxide can be easily stored in a larger quantity than in its gaseous state. It is then transported to a site where it will be taken out of contact with the atmosphere and placed in a subterranean reservoir. Once there, the carbon dioxide will solidify within two years. This is mineralization in geologic storage and it’s the last stage in the BECCS logistics chain.
Where is Carbon Stored?
Carbon dioxide may be stored in saline formations, unmineable coal seams, oil and natural gas reservoirs, shale rocks, or basalt formations. This geologic storage is the key element for carbon sequestration.
It is through geologic storage that carbon will mineralize.
Image: Closeup of Oslo shale rock.
Source: John Thoresen on Unsplash
To limit global warming to 1.5°C, the IPCC projects that carbon dioxide removal will be to be used on the order of 100–1000 GtCO2 throughout the remainder of the 21st century. Given that the global storage capacity for carbon is estimated between 8,000Gt and 55,000Gt, there is more than enough geologic storage space for carbon sequestration.
In North America alone there are over 200 identified sedimentary basins that may be utilized for the geologic storage of carbon dioxide. In Europe, there are an estimated 482 gigatonnes of storage available via saline aquifers.
Image: Carbon dioxide storage capacity in the United States.
Image source: Clean Air Task Force
What Makes Geoligc Storage Safe?
Carbon Capture & Storage (CCS) technologies have already incorporated geologic storage for decades. The technology and its components are not new, but rather they are well-established. In 1972 the first natural gas plants began operation using CCS and over the last fifty years CCS technology has proven to be safe and effective. The Global CCS Institute affirms that “no significant safety, health or environmental impacts have been documented from existing CCS projects.”
Geologic storage works because carbon dioxide is injected into locations that are already equipped to store it. The qualities of sedimentary basins and other geologic formations keep carbon dioxide securely in place. These features include pores that hold carbon dioxide, permeability to allow carbon dioxide to flow through the formation, and the presence of a cap rock that acts as a barrier and seal. Over 98% of injected carbon dioxide remains in the subsurface for over 10,000 years. In the low 2% chance that carbon dioxide is released from an underground reservoir, there is no environmental damage done. The carbon dioxide simply returns to the atmosphere.
Image: Geologic storage of carbon dioxide.
Source: The Global CCS Institute
Once supercritical carbon dioxide is inserted into a reservoir, there are four mechanisms by which the carbon dioxide is permanently prevented from reentering the atmosphere. Its confinement is either done through structural trapping, residual trapping, solubility trapping, or mineral trapping.
Structural trapping
This kind of sequestration locks in the largest amount of carbon dioxide by sealing it in under an impermeable layer of rock.
Residual Trapping
This occurs when carbon dioxide is placed in the pore spaces between rock grains. Due to its porous nature, the rock behaves like a sponge and when carbon dioxide is sequestered, it moves through the rock’s available spaces.
Solubility Trapping
When injected carbon dioxide dissolves in brine water found within the rock it’s known as solubility trapping. The dissolved carbon dioxide then reacts with hydrogen atoms to create HCO3-.
Mineral Trapping
After carbon dioxide dissolves in brine water, it can react with the mineral of the rock. Over time, the reaction creates solid carbonate minerals and permanently stores carbon dioxide.
Solving the Climate Crisis with BECCS Technology
Once carbon dioxide is successfully sequestered underground it can begin its mineralization process. Without CCS technologies, the natural mineralization process sequesters an estimated .7 billion tonnes of carbon dioxide per year. While there is more carbon stored in rock than there is in the atmosphere, it’s not enough to maintain a healthy global climate.
To avoid permanent changes to the global climate, 10 billion tonnes of atmospheric carbon must be removed each year by 2050.
This is where BECCS steps in to accelerate carbon dioxide removal. The global implementation of BECCS will help mitigate the excess carbon that natural mineralization can’t sequester on its own. Currently, the most common sequestration arrangement for BECCS facilities in Europe and the Nordics is through partnerships with storage operators sequestering carbon in the North Sea, Norwegian Sea, and Barents Sea. At these sites, carbon dioxide is trapped thousands of meters below the seafloor. In North America, carbon sequestration is done by utilizing land-based geologic storage that is widely available in the midwest. Collectively, these efforts will make a significant contribution to preventing the climate crisis from escalating and restoring the atmosphere to its pre-industrial levels.
