What is Carbon Capture and Storage?

Carbon capture and storage (CSS) is the process of extracting carbon from the atmosphere – either as it is being emitted from a power plant or factory or at a later date – and storing it in a safe and controlled manner.

The practice has long been in use on a small scale in certain factories and industrial settings, but recently it has been suggested as a viable means of preventing climate change. This suggestion has been championed by environmental scientists for many years, but only recently has it gained much traction with governments and big business.

This is most likely due to the rising concerns about global warming and to the COP21 summit talks which took place in Paris last month, where 196 nations around the world pledged to avoid a global temperature hike of 2°C as an absolute and 1.5°C as an ideal target figure.

How Does CCS Work?

CCS relies on three basic stages of execution: capture, transport and storage. The use of CCS in energy production could avoid up to 90% of carbon reaching the atmosphere, and since 40% of all carbon in our atmosphere comes from industry, employing CCS in large-scale industrial settings is of the utmost importance.

There are three existing methods of carbon capture. Pre-combustion involves preparation of the fuel by adding oxygen to it to convert it into a mixture comprised mainly of carbon dioxide (CO2) and hydrogen (H). By using solid absorbents or liquid solvents, these two properties can be separated, meaning that only the hydrogen goes through the energy-production process, leaving the CO2 to be safely partitioned and stored elsewhere. However, the complex procedures involved in preparing the fuel mean that this technique is better suited to more modern power plants.

The second type of carbon capture is post-combustion. This works in a similar method as pre-combustion, using liquid solvents to separate the CO2 from the fuel source, but does not require treatment prior to combustion. It does, however, require the use of heat and steam to collect the CO2, meaning it can hamper the power generation capacity of a plant.

Oxyfiring is the final method of carbon capture. This involves combusting the fuel source in pure oxygen, as opposed to air. This leads to a relatively pure output gas of CO2, though the expense and amount of energy involved in creating the pure oxygen are drawbacks.

All of these techniques are currently in use, though none on a large, climate change-fighting scale. As such, it’s still unknown whether they could have potentially dangerous side effects in terms of the amount of other greenhouse gases (GHGs) they engender. In order to avoid this scenario, further research involving instrumentation such as FTIR gas analysers is imperative.

Where the Carbon is Stored

After being captured, the CO2 is compressed and transported to a suitable storage site. These storage sites are ideally located at least 800m below the Earth’s surface and are carefully selected to have the right blend of permeability and porosity.

The compressed CO2 is then injected into the rock via the use of wells, where it remains in a liquid-like state and permeates slowly through the surrounding rock area harmlessly. Again, more research is required to conclusively prove just how safe these CO2 deposit sites are and to find out more about their long-term effects on our environment.