Carbon Capture & Sequestration

Climate change due to Global warming is a major concern of the current world in maintaining a balance of technology and sustainability. The increasing quantity of greenhouses gases like  Carbon dioxide (CO₂), methane, water vapour, chlorofluorocarbon, ozone, etc. is resulting in the escalation of this global challenge. CO₂ accounts to 82% of the total greenhouse gases and are continuously released into the atmosphere due to burning of fossil fuel, industrial activities, forest fires, etc. Hence, to prevent global warming and achieve a sustainable world, expulsion of the CO₂ from the atmosphere is mandatory and Carbon Capture & Sequestration, CCS, is considered to be the most effective green engineering technique.

What is CCS?

CCS is the process of capturing the CO₂ released into the atmosphere as a result of various human activities and storing it deep underground in geological formation, locking it out of atmosphere.

CCS: A Net Zero Energy Strategy

Climate Change Intergovernmental Panel on Climate Change, IPCC, during its Climate Change report on 2023, highlighted that, to achieve the ambitions of the Paris Agreement and limit future temperature increases to 1.5°C (2.7°F), effort to reduce the emission is not sufficient, but, technologies to remove CO₂ from atmosphere is to be deployed. They announced CCS as one of the major strategies to achieve net zero energy system, i.e. the CO₂ emitted is equal to the CO₂ removed from the atmosphere.

Components of CCS     

Capture:

The separation of the CO₂ from the effluent stream or directly from atmosphere using following techniques:

a)      Pre-combustion: The fossil fuel is initially burnt in a gasifier to form a relatively pure exhaust stream of CO_2. It is a cheaper option but is difficulty to incorporate into existing facilities.

b)      Post-combustion: The CO₂ is captured from the exhaust stream after the combustion of the fossil fuel.  This method is well understood and is commonly use in industries as it can be retrofitted to conventional power plants.

c)      Oxy-combustion: The fossil fuel is burnt in pure oxygen instead of air resulting in production of pure CO₂ and water. It is the most effective method but is energy intensive.

d)      Direct air capture: The CO₂ from the atmosphere is scrubbed directly from the open atmosphere. This technology is still under research. This technology can be expensive but can be effective with diffused sources.

2.      Transport:

After capture the CO₂ is compressed into liquid form and is carried from the source to the reservoir site. Train, truck and ship are used for small scale carbon industries but application of pipelines are cheaper and is commonly used. Further studies related to pipeline transport for large scale project are under progress.

3.      Storage:

The CO₂ is stored deep underground isolating it from the atmosphere. The storage is mainly in 2 forms:

a)      Geological sequestration: The CO₂ is converted into high pressure liquid like form called as supercritical CO₂ and which is injected directly into sedimentary rocks, coal seams which are unapt for mining, and some volcanic rocks.  

b)      Mineral carbonation: The CO₂ is reacted with naturally occurring Iron (Fe), Magnesium (Mg) and Calcium (Ca) minerals. These reactions are time-consuming when performed at normal condition or else require high temperature & pressure, which will be highly energy consuming. 

CCS Current Progress

According to the report of Annual Global status of CCS released in November 2024 by  Global CCS Institute, in addition to the previous year facilities,  237 new pipeline facilities had been introduced, totalizing it to 628. Out of these 247 are in Front End Engineering and Design (FEED) stage and contribute to 64% raise in carbon capture and storage projects in comparison to preceding year. Furthermore, 79 capture facilities are operational, 212 CO₂ transport and/or storage projects are in FEED studies, 20 Direct Air Capture projects are either in operational or developmental phase.