The CO2 problem remains one of the main environmental challenges to address in order to ensure the planet’s sustainability. For years, the focus has been on reducing carbon emissions and transitioning to an energy generation model based on renewables and other non-polluting sources.
However, despite the growing relevance of clean energy in the energy mix of different countries, we are still far from achieving a significant reduction in the carbon footprint. In this context, emerging solutions like CO2 capture and storage present a very interesting option to explore, as they focus on neutralizing carbon dioxide (and even reusing it, as we will see a bit later), shifting the perspective of the problem from emissions themselves to the capacity to neutralize them as a threat.
In any case, considering that there still seems to be a long way to go before achieving 100% green energy supply, CO2 capture and storage technologies will continue to make an essential contribution to mitigating the environmental impact of residual emissions.
What is CO2 capture and storage?
Carbon capture and storage (CCS) refers to any process by which CO2 is ‘trapped’ to prevent its presence in the atmosphere and is then directed to a safe location where it poses no threat, usually underground.
This involves capturing carbon dioxide at its original emission source, separating it from other gases, compressing it, and transporting it to keep it out of the atmosphere, either in underground geological strata or deep in the ocean. Another storage option is mineralization, which we will discuss a bit later.
Furthermore, with emerging technologies, capture can be done both after fossil fuels have been burned (i.e., once they have been used in industrial processes or in car engines), and in pre-combustion, through gasification processes that produce a synthetic gas from which carbon dioxide can be extracted.
Different systems for capturing and storing CO2
There are currently multiple methods being investigated and applied for capturing and storing carbon dioxide:
1-Direct air carbon capture (DAC)
This formula is the most developed at present and consists of the direct extraction of CO2 from the atmosphere, making it a very interesting way to respond to the emission of greenhouse gases on a large scale.
The most recent innovations include the use of advanced synthetic absorbent materials, such as ion exchange resins traditionally used for wastewater treatment, or molecular sieves frequently used in the hydrocarbon industry to dehydrate gas streams. Using these procedures, DAC is becoming a promising way to achieve efficient CO2 capture at an affordable cost.
2-Oxycombustion
Oxycombustion is also a promising technology for carbon capture, especially in fossil fuel-fired power plants, although some issues regarding its energy efficiency and implementation costs would still need to be resolved.
This method would operate by oxyfuel combustion, that is, by burning fuel in an oxygen-enriched environment instead of conventional air, giving rise to gases composed of CO2 and water vapour. When cooled and condensed, this is separated from the carbon dioxide, which is then isolated for capture and subsequent storage.
3-Carbon capture through artificial photosynthesis
This carbon capture technology is the most experimental of all, and would consist of replicating the natural process followed by plants to convert CO2 into chemical energy. To this end, systems are being tested that use advanced catalysts and semiconductor materials to generate reactions that would ultimately serve to transform carbon dioxide into chemical compounds such as methanol and ethanol, which, as we know, can be used as fuels and are much cleaner and more sustainable than hydrocarbons.
These would be the main technologies for capture, but the application of these procedures is inseparable from storage, for which there would also be different solutions:
Geological storage of CO2
This is an option that seems to be the most feasible in the long term. The captured CO2 would be injected into underground geological formations, ranging from deep marine aquifers to depleted gas, oil or coal deposits. Current research is focused on both identifying the most suitable locations and improving the efficiency, safety and control of the storage process.
CO2 storage through mineralization
This solution involves a chemical transformation of carbon dioxide to form stable minerals, which could be safely stored indefinitely. Currently, materials are being investigated that can accelerate the mineralization process to reduce time and costs.
Current development of carbon capture and storage systems
According to data from the Center for Climate and Energy Solutions (C2ES), at the end of 2021 there were only 26 active carbon capture projects worldwide, and 34 more in development. In addition, operational carbon capture and storage facilities would have a processing capacity of about 40 million tons of CO2 per year. These figures are clearly insufficient if we consider that in 2020 the volume of CO2 from fossil fuels was quantified at almost 35 billion tons
In Europe, the Nordic countries are the ones that are investing the most in capture and storage technologies. Currently, there are projects underway in Norway, Denmark, Sweden, Finland and Iceland, among others, that cover both the transport and geological storage of CO2 and the generation of synthetic fuels from it.
Spain has not included in its National Integrated Energy and Climate Plan (PNIEC) 2021-2030 R&D activities or the development of carbon capture and storage projects, which pushes back the horizon of application of these technologies, which require a development phase of between 8 and 10 years.
It should be noted that at a global level, most of the captured carbon is used in a process that in the oil industry is called enhanced oil recovery (EOR), which allows hydrocarbons to be extracted from previously inaccessible deposits.
With this, we see that it is not only feasible to capture CO2 to prevent it from having a harmful effect on the atmosphere, but it can also be reused, thus obtaining a perpetual virtuous circle of capture-storage-reuse.
In fact, there is already an incipient development of what is known as CCUS technologies: Carbon Capture, Use and Storage, which also includes those that would allow carbon dioxide to be transformed into chemical compounds such as methanol and ethanol, which are energy sources that, without being 100% green, have a fairly small carbon footprint.