Captured Carbon: How Does CCUS Work?

Carbon capture, utilisation and storage (CCUS) refers to a group of technologies that trap carbon dioxide (CO2) at the source of emissions. They subsequently transport the CO2 to a location where it can be utilised or stored.1 Artificial sequestration of captured carbon, for instance, by injecting it deep underground prevents it from entering the atmosphere.2 This is a useful climate change mitigation method, as CO2 is the most important driver of climate change.3

However, 80 per cent of the carbon captured today is used for enhanced oil recovery.4 What’s more, burning this oil results in more CO2 emissions and contributes to further global warming.

What is carbon?

Carbon is an important chemical. It forms more compounds than all the other elements combined.5 In its natural gaseous state, CO2 enters the atmosphere and blocks heat from escaping.6 This helps to keep our planet warm. In fact, it is what makes the Earth hospitable for life. 

However, humans have increased the atmospheric concentration of CO2 by 47 per cent since the Industrial Revolution.7 Deforestation, land-use changes and burning fossil fuels8 have brought the level of CO2 to its highest point in at least 800,000 years.9 This has subsequently raised average global temperatures by 1°C.10

How is carbon captured?

There are three methods of capturing carbon from power plants and industrial facilities: pre-combustion, post-combustion and oxy-fuel capture.11 

Pre-combustion carbon capture

Pre-combustion technologies involve oxidising fuel into a syngas before combustion. Then, this syngas undergoes a water-gas shift reaction to produce hydrogen and a CO2-rich gas mixture. The CO2 can then be captured and transported. This leaves the hydrogen gas available for combustion – carbon emission-free.12

Post-combustion carbon capture

Post-combustion capture is the most commonly used CCUS technology.13 When fossil fuels are burned, they produce flue gases of different compounds, including CO2.14 This flue gas is passed through a solvent to absorb the carbon dioxide.15 It is then heated to release water vapour and leave a concentrated stream of CO2, ready to be compressed for transportation.16 

This last stage of the process can be highly energy-intensive. For example, the CCUS facilities at Boundary Dam power station in Canada use 25 per cent of the total power output to operate.17 

Oxy-fuel combustion

Oxy-fuel combustion is a complex way of capturing carbon. This makes it more difficult to apply to existing power plants.18 The method requires the fuel to be burned in oxygen instead of air.19 This facilitates combustion at a higher temperature, increasing the efficiency of the reaction.20 It also produces a flue gas that is predominantly H2O and CO2.21 As a result, it is easier to capture, compress and store the CO2 stream. However, the process is still under development.22

Does carbon capture actually work?

CCUS has attracted interest for decades. The first large-scale project to successfully inject captured carbon into the ground was in Texas in 1972.23 Since then, governments across the globe have invested billions of dollars into CCUS projects.24 Yet, despite all the funding, there are just 65 commercial CCUS facilities worldwide. Only 26 of these are in operation.25 

Collectively, the facilities in operation can capture 40 million tonnes of CO2 per year. However, the International Energy Agency (IEA), IPCC and other groups estimate that 1.5 gigatonnes of carbon must be captured every year by 2030. This is the amount of mitigation required to stay on a 1.5°C increase climate trajectory. To reach this figure, an increase in CCUS capacity by a factor of 35 from today is needed.26 

Given the large capital involved, CCUS projects and related infrastructure take six to 10 years from conception to commissioning.27 Currently, there are a mere 20 additional projects in the pipeline.28 Carbon capture may work in the few instances where it is in use. But, it is highly unlikely to achieve sufficient capacity to mitigate global warming. Therefore, it could be seen as a failure in this regard.

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