Post-Combustion Carbon Capture: How Does It Work?

Post-combustion carbon capture is a theoretical solution to climate change. The anthropogenic release of greenhouse gases into the atmosphere causes climate change.¹ These gases prevent heat from escaping and cause the planet’s temperature to increase.²

Carbon dioxide (CO2), produced when fossil fuels are burned or deforestation occurs, is a major driver of global warming.³ Carbon capture and storage (CCS) reduces emissions by preventing CO2 from being released by heavy industry or power production.

What is post-combustion carbon capture?

Post-combustion carbon capture is one of three CCS methods currently in use. It involves removing diluted CO2 from flue gases after the combustion of fossil fuels, such as coal or natural gas.⁴ It is easy to modify existing power plants and heavy industry complexes to incorporate this technology.⁵ Designs for new plants can also include end-of-pipe technology.⁶

The other methods are pre-combustion and oxy-fuel combustion.⁷ As their names suggest, pre-combustion captures carbon before it is burned whilst oxy-fuel combustion uses oxygen to capture CO2.⁸ 

How does post-combustion carbon capture work?

Post-combustion carbon capture works in two different ways. Burning fossil fuels produces flue gases.⁹ CO2, water vapour, sulfur dioxides and nitrogen oxides comprise flue gases.¹⁰ Passing the flue gas through a solvent is one way to separate the CO2.¹¹ The solvent absorbs the CO2. Heating the solvent releases water vapour and leaves a concentrated steam of CO2.¹² Post-combustion capture can decrease a power plant’s CO2 emissions by as much as 80 to 90 per cent.¹³ 

Another technique in development is called calcium cycle capture.¹⁴ Lime is used as a solvent for this process.¹⁵ It captures CO2 and produces limestone. Heating the limestone drives off the CO2.¹⁶ Both processes require lots of energy to separate the CO2 and compress it sufficiently for storage.¹⁷ For example, the Boundary Dam power plant’s CCS facilities account for almost 25 per cent of the plant’s total output to operate.¹⁸ Burning even more fossil fuels is necessary to use CCS. This is expensive, harmful to the environment, and a further contributor to global warming.

Why is post-combustion carbon capture the most common?

Post-combustion carbon capture is the most common CCS technology because it is easy to apply to existing power plants.¹⁹ The pre-combustion process is actually cheaper than post-combustion, and it provides a much higher concentration of CO2.²⁰ However, it is not easy to modify older power plant generators to accommodate this technology, and therefore post-combustion is more common.²¹

Post-combustion carbon capture is also cheaper than oxy-fuel.²² This is because the oxy-fuel combustion method uses lots of oxygen to separate the CO2.²³ As a result, it increases costs. Though research is developing new techniques to make it cheaper, at present oxy-fuel is a less attractive CCS option than post-combustion.²⁴

Can carbon capture prevent climate change?

The application of CCS technology as a solution to climate change has so far been a failure. There are just two commercial power plants with working CCS facilities in the world.²⁵ They have a combined capture capacity of just 2.4 million tons of CO2 per year.²⁶ One of these facilities, the Petra Nova plant, has temporarily suspended its CCS capability due to low oil prices.²⁷ The target provided by the UN’s sustainable development strategy for the energy sector is 310 million tons per year by 2030.²⁸ To meet the net-zero goals of the Paris Agreement, about 2,000 CCS facilities will be needed by 2040.²⁹

Future investments should go towards clean energy sources. The average annual rate of global growth for renewable energy consumption has been 13.7 per cent over the past decade.³⁰ Almost two-thirds of all new power generation capacity added in 2018 was from renewables.³¹ There is both an urgent need and a clear economic incentive for development efforts to boost renewables, instead of trying to mitigate the damage caused by dirty fossil fuels.

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