Addressing carbon dioxide emissions by capture & trapping mechanisms

Climate change and global warming are of great international concern, as the last 20 years have seen a significant rise in global air temperatures. Global warming is caused mainly by the emission of greenhouse gases, including water vapour, carbon dioxide (CO₂), methane, nitrous oxide, and chlorofluorocarbons. CO₂ is now regarded as a leading cause of global warming, with the construction industry a major source of CO₂ emissions. Together, building and construction are responsible for 39% of all carbon emissions in the world, with operational emissions (from energy used to heat, cool and light buildings) accounting for 28%. The remaining 11% comes from embodied carbon emissions, or ‘upfront’ carbon that is associated with materials and construction processes throughout the whole building lifecycle.

The transition towards mainstream net zero carbon standards requires immediate action to achieve greater awareness, innovation, improved processes to calculate, track and report embodied carbon, voluntary reduction targets from industry and roll out of new legislation at city, national and regional level. Approaches such as maximising the use of existing assets, promoting renovation instead of demolition and seeking new circular business models that reduce reliance on carbon intensive raw materials are also needed. Therefore it is essential to know about the methods to trap. Geological carbon sequestration involves the separation and capture of carbon dioxide at the point of emissions followed by the storage in deep underground geologic formations This process is also known as Carbon capture and storage (CCS).

Carbon capture and storage for addressing the challenges of carbon dioxide by capture and trapping mechanisms

Carbon capture and storage (CCS) (or carbon capture and sequestration or carbon control and sequestration is the process of capturing waste carbon dioxide usually from large point sources, such as a cement factory or biomass power plant, transporting it to a storage site, and depositing it where it will not enter the atmosphere, normally an underground geological formation. The aim is to prevent the release of large quantities of CO₂ into the atmosphere from heavy industry. It is a potential means of mitigating the contribution to global warming and ocean acidification of carbon dioxide emissions from industry and heating. Although CO₂ has been injected into geological formations for several decades for various purposes, including enhanced oil recovery, the long term storage of CO₂ is a relatively new concept. Direct air capture is a type of CCS which scrubs CO₂ from ambient air rather than a point source.

There are three main steps to carbon capture and storage (CCS) – trapping and separating the CO₂ from other gases, transporting this captured CO₂ to a storage location, and storing that CO₂ far away from the atmosphere. Carbon is taken from a power plant source in three basic ways – post-combustion, pre combustion and oxy-fuel combustion.

With post-combustion ­carbon capture, the CO₂ is grabbed after the fossil fuel is burned. The burning of fossil fuels­ produces something called flue gase­s, which include CO₂, water vapor, sulfur dioxides and nitrogen oxides. In a post-combustion process, CO₂ is separated and captured from the flue gases that result from the combustion of fossil fuel. This process is currently in use to remove CO₂ from natural gas. The biggest benefit to using this process is that it allows us to retrofit older power plants, by adding a “filter” that helps trap the CO₂ as it travels up a chimney or smokestack. This filter is actually a solvent that absorbs carbon dioxide.

With pre-combustion carbon capture,­ CO₂ is trapped before the fossil fuel is burned. That means the CO₂ is trapped before it’s diluted by other flue gases. Coal, oil or natural gas is heated in pure oxygen, resulting in a mix of carbon monoxide and hydrogen. This mix is then treated in a catalytic converter with steam, which then produces more hyd­rogen, along with carbon dioxide. These gases are fed into the bottom of a flask. The gases in the flask will naturally begin to rise, so a chemical called amine is poured into the top. The amine binds with the CO₂, falling to the bottom of the flask. The hydrogen continues rising, up and out of the flask.

With oxy-fuel combustion carbon capture, the power plant burns fossil fuel in oxygen. This results in a gas mixture comprising mostly steam and CO₂. The steam and carbon dioxide are separated by cooling and compressing the gas stream. The oxygen required for this technique increases costs, but researchers are developing new techniques in hopes of bringing this cost down. Oxy-fuel combustion can prevent 90 percent of a power plant’s emissions from entering the atmosphere.

Trapping mechanisms for addressing the challenges of carbon dioxide by capture and trapping mechanisms

Now the processes are discovered it is time to explore Trapping mechanisms of Carbon Dioxide collection and storage which are explained below.

Structural Trapping

The single most important factor for securing CO₂ is the presence of a thick and fine-textured rock that serves as a seal above the sequestration reservoir. The seal should provide an effective permeability and capillary barrier to upward migration.

Capillary Trapping

Sometimes referred to as residual-phase trapping, this process traps CO₂ primarily after injection stops and water begins to imbibe into the CO₂ plume. The trailing edge of the CO₂ is immobilized, slowing up-dip migration. Capillary trapping is particularly important for sequestration in dipping aquifers that do not have structural closure.

Residual trapping

This phase of trapping happens very quickly as the porous rock acts like a tight, rigid sponge. As the supercritical CO₂ is injected into the formation it displaces fluid as it moves through the porous rock. As the CO₂ continues to move, fluid again replaces it, but some of the CO₂ will be left behind as disconnected – or residual – droplets in the pore spaces which are immobile, just like water in a sponge. This is often how the oil was held for millions of years.

Solubility trapping

Just as sugar dissolves in tea, CO₂ dissolves in other fluids in its gaseous and supercritical state. This phase in the trapping process involves the CO₂ dissolving into the salt water (or brine) already present in the porous rock. Just as a bottle of fizzy water is actually slightly heavier than the same bottle filled with still water, so this salt water containing CO₂ is denser than the surrounding fluids and so will sink to the bottom of the rock formation over time, trapping the CO₂ even more securely.

Mineral Trapping

This mechanism occurs when dissolved CO₂ reacts directly or indirectly with minerals in the geologic formation, promoting precipitation of carbonate minerals. Mineral trapping is attractive because it could immobilize CO₂ for very long periods. However, the process is thought to be comparatively slow because it depends on dissolution of silicate minerals, so the overall impact may not be realized for tens to hundreds of years or longer.

These trapping processes take place over many years at different rates from days to years to thousands of years, but in general, geologically stored CO₂ becomes more securely trapped with time.

Favourable geological factors required

A fundamental understanding of the geologic, hydrologic, geomechanical, and geochemical processes controlling the fate and migration of CO₂ in the subsurface is necessary to provide a base for developing methods to characterize storage sites and to select sites with minimal leakage risk. However, even at a good storage site, engineering practices must be optimized to ensure reservoir integrity. Monitoring will play a key role in observing CO₂ behavior, in calibrating and validating predictive models, and in providing early warning that leakage may be imminent. In the event of threatened or actual leakage, remediation measures, such as plugging abandoned wells, would be needed. A regulatory infrastructure would be required to ensure due diligence in locating, engineering, operating, monitoring, and remediating CO₂ storage projects. Finally, private- and public-sector frameworks would be needed to ensure financial responsibility for covering short- and long-term liabilities.

India is fast adopting practices for addressing the challenges of carbon dioxide by capture and trapping mechanisms . With big names forming partnership for carbon emission, it is quite evident it is the need of time. Given below are few landmark projects and some projects which are in production in India related carbon dioxide capture.

Conclusion

Fast urbanization and industrial growth boosts up the need of habitat for more people in urban areas. It also results in an enhanced lifestyle of the people. Both industry and elevated lifestyles demand more energy, as a result, power demand has drastically increased after the industrial revolution. But we need to control it for sustainability and ecosystem preservation. The processes and trap mechanisms will up to prevent the challenge of addressing carbon dioxide.