Carbon Dioxide Removal - NETS

 

Carbon Dioxide Removal (CDR) is a term used to refer to the removal or absorption of carbon from the air and storing it away safely. Climate change mitigation is the reduction, avoidance or removal of greenhouse gas emissions. CDR therefore encompasses forestry and the climate services of all green plants as well as the use of negative emission technologies.

When done mechanically, CDR is carried out through artificial (manmade) means. In a more in-depth way, these methods are known as negative emission technologies (NETS), because they absorb carbon from the air without re-releasing it. Thus they are “negative”. The goal of the Paris Agreement is to keep warming below 2 degrees above preindustrial levels this century and better still 1.5. To attain 1.5 degrees, emissions will have to reach “net zero” to mean that the amounts released into the atmosphere equal the amounts likewise removed. This should happen by 2050.

From then on, in the second half of the 21^st century, the world in whole will have to absorb increasingly more carbon from the air than emitted and so tilt the scales heavily in favor of removal. That is “net-negative”. The Intergovernmental Panel on Climate Change notes that for this to be successful, we not only need to cut our emissions radically but also remove to a considerable extent what is already in the atmosphere. And so, this is where negative emission technologies come in. NETS are a large scale use of carbon capture and storage (CCS). CCS is used in power plants and industries to capture carbon dioxide at source.

Mechanical CDR is classified into two technologies. One is Direct Air Carbon Capture and Storage (DACCS) and the other is Bioenergy with Carbon Capture and Storage (BECCS).

Direct air carbon capture and storage is whereby systems are used to selectively absorb carbon dioxide from the atmosphere and release the rest of the air back. Now, carbon dioxide (CO2) is the chief greenhouse gas especially in terms of long-term warming. This is because it is the most abundant and has a long lifetime. And so it is a priority.

A DACCS plant in Switzerland - source Climeworks

The earth shares one global atmosphere, and all gases, including greenhouse gases, are evenly and finely mixed all over despite their place of origin. Therefore, measurements are the same everywhere. Despite its climate effect, carbon dioxide is a small component of the air, in percentage being only 0.04% of the total. Because of this, large volumes of air have to be processed and so significantly more energy is used in DACCS to capture CO2.

DACCS captures CO2 through two main ways. The use of solid substances (sorbents) that absorb only carbon dioxide, or liquid solutions (solvents) that likewise react with carbon dioxide only.

That is, air is drawn in using fans and the stream of air is passed through the liquid or solid. The carbon dioxide is removed by the subsequent chemical reaction. The rest of the air is returned to the atmosphere. These absorbing substances are then taken off separately and heated where they release a stream of pure carbon dioxide.

The gas is captured and pressurized, and injected deep beneath the ground into rock formations. The sorbents are then returned to the main chambers and the process is repeated. The gas is stored in saline (salt water) aquifers or volcanic rock where it reacts with the rocks to form stable carbonates. It can also be packed into coal beds which are difficult to exploit, or decommissioned oil and natural gas fields.

DACCS is only net negative if the carbon is stored away permanently in the earth’s crust. If the CO2 is used elsewhere and the materials later on decompose, then the process is carbon neutral.

Notably, this technology can be used to counterbalance sectors that are difficult to decarbonize, like the cement, steel or chemicals industry. It is advantageous in that it can be located anywhere in the world, even in unhospitable places because it just needs the air and energy as a resource and porous rock storage.

DACCS has some shortcomings, and this includes the large amounts of electricity used to power the system- drawing in the air or heating the sorbents. The liquid systems use far more energy than the solids one, reaching a high of 800 degrees Celsius. However, if possible DACCS can be paired with solar or wind energy which are renewables and will produce clean electricity.

Bioenergy with carbon capture and storage is another system of removing carbon from the atmosphere. The term refers to the process of making bioenergy in combination with carbon capture and storage. Bioenergy is made from organic sources, primarily green plants. Here, woody plants, agricultural and organic municipal waste is burnt to generate energy I.e. heat or electricity. Alternatively, the biomass is turned to biofuels like biogas or ethanol through fermentation. The resultant carbon emissions from the process are captured and stored underground.

This process has more benefits than DACCS because not only does it absorb and lock away carbon emissions from the green plants, it also produces energy instead of using it, unlike DACCS. All green plants absorb carbon dioxide during photosynthesis to make food. They do this in the presence of sunlight. In absorbing CO2, they mitigate climate. This is the carbon dioxide that is released when organic matter is burnt or decomposed. In BECCS, it is captured, then transported via pipelines or vehicles to storage in geological formations.

In other cases, the captured carbon dioxide is sold to the fossil fuel sector, where it is used in enhanced oil recovery to increase yields of oil. It is also bought by the industrial beverages sector. There are possibilities for use in making plastic, curing concrete or in the chemicals and steel industries.

BECCS however needs a lot of organic matter and that means big chunks of land for purposely planting these crops. This would be in direct competition with other land uses, primarily agriculture and forests. Growing crops for energy also puts in jeopardy food security, because actually more land than is presently being used is needed for agriculture alone, to satisfy the needs of a growing world population. Likewise, more acreage needs to be put under forests.

BECCS also threatens biodiversity because selectively planting crops for energy imperils natural ecosystems. Water, already a scarce resource partially because of climate change, is needed in large quantities for irrigation in BECCS. The method also requires time, because plants take time to mature.

BECCS has additional transport costs, because the plant needs to be situated near the plantations but the storage sites may be elsewhere.

BECCS is considerably cheaper than DACCS if all greenhouse gas emissions are evaluated down the chain; from setting up the plant, growing crops to storing CO2 underground.

BECCS has other advantages too. One is that the process produces water instead of using it. Two is that it produces fuel, electricity or heat instead of consuming it. Three is that it is climate friendly. It sequesters carbon.

Both BECCS and DACCS are a sort of climate engineering but are necessary for reaching the goals of the Paris Agreement. These techniques though a part of climate mitigation, are significantly more expensive than natural solutions.

These systems need to be used in combination with energy efficiency, ecosystem adaptation and renewable energy. They are a way of removing carbon but the world must reduce emissions. They are not an excuse for neglecting emissions reduction, or decarbonizing our way of life.

There are concerns that big polluters might take advantage of these technologies to continue climate polluting, because their emissions can be removed from the atmosphere.

There are also questions around leakage, that is, is the carbon stored in the ground safe or will it eventually make its way out into the atmosphere? Some stakeholders are worried about the safety of underground storage e.g. in case of earthquakes, and the impacts on vegetation or underground aquifers which produce drinking water.

These two technologies are still in their infancy and only a handful of these plants exist worldwide.

To remedy this, there needs to be a lot of deliberate financial investment in this sector for advancement to occur. Currently, corporations like Microsoft and Shopify have invested in one such initiative, called Climeworks, in order to balance their carbon footprint.

More research is needed into cheaper and more efficient technology that does not have such a high energy requirement and is easily available.

Laws and policies are needed to regulate this nascent sector, and they need to encourage and define the boundaries around ethics, land rights and protection of natural resources.

Carbon markets for the services of DACCS and BECCS would go a long way to bolster growth because more buyers would spur progress.

Political goodwill is one of the most important drivers that would accelerate this sector. In fact, climate action as a whole is either propelled or held back by politicians and leaders of the whole world. In particular, NETS would be a good idea to diversify the climate mitigation efforts of a business or national entity without a substantial negative impact on the economy.

It would greatly aid meeting climate pledges and obligations

Social acceptability is also necessary, because these plants require space and therefore the agreement and favor from local communities.