At this very moment across the entire planet, there are machines pushing carbon out into the atmosphere. Scientists estimate that the amount of carbon dioxide we produce has increased by around 80% in the years since 1970, and with the developing world continuing to increase its carbon output, those numbers look set to continue their upwards trajectory. But what is carbon, should we eliminate it entirely and how does carbon capture actually work? Read on to find out.
Before anything else, it’s useful to establish that carbon in our atmosphere is absolutely crucial to the continued survival of life on this planet. Carbon dioxide (CO2) is an entirely natural gas that allows sunlight to reach the earth but stops some of the sunlight from reflecting back in to space, thus warming the planet. Without carbon dioxide, our planet would have an average temperature of minus 22 degrees, which is far from ideal for anybody creature which wants to continue living. The problem occurs, however, when there’s too much carbon in the atmosphere. More carbon means more heat is stopped from reflecting out in to space, thus warming the planet. Currently, everything from our power plants to our cars produce carbon dioxide, and short of completely revolutionising the existing power infrastructure, there’s little we can do to stop this carbon from getting out into the atmosphere. There are ideas to help though, and one of them is carbon capture.
Carbon capture is exactly what its name sounds like, it involves trapping the carbon dioxide as it’s emitted from its source, transporting it to a storage location (typically held deep underground or underwater) and isolating it from the atmosphere. This would mean that whilst the fuels being burnt were neither green nor sustainable, their emissions would be drastically cut, leading to less damage to the environment. Many see this as a happy compromise between 100% renewable energy and utilising the remaining fossil fuels on Earth, but how does the process actually work?
There are three main types of capture:
1) Post-combustion capture is where the CO2 is captured after the fuel has been burned. When fossil fuels are burned they create flue gasses, which include many things other than CO2 like water vapour, nitrogen oxides and sulphur dioxides. In this procedure carbon is captured by adding a sort of filter made of a solvent to the chimney or smokestack during the burning of fossil fuels. Once the filter is full, it can be heated to remove the water vapour and leave only concentrated CO2. The advantage of this method is that it can function in existing power plants, meaning no expensive rebuilds, whilst the disadvantage is the amount of energy required to compress the gas for transport.
2) Pre-combustion capture is where the CO2 is trapped before the fossil fuels are burned. The fossil fuel is heated in a chamber of pure oxygen, which results in a mixture of carbon monoxide and hydrogen. This mixture is then fed in to a catalytic convertor (much like the one on your car) with steam, which produces yet more hydrogen along with carbon dioxide and is then fed in to a flask where the a chemical called amine is poured in to the top. The oxygen and amine bind together leaving the carbon to float to the top whilst the amine goes to the bottom for reuse. This form is already in use for natural gas, and is much more efficient than post-combustion capture.
3) Oxy-fuel combustion capture is when the power plant burns fossil fuel in oxygen, which results in a gas mixture made up of steam and CO2. The steam and carbon dioxide are then separated by cooling the gas and the carbon can then be captured. This is by far the most efficient, preventing around 90% of the carbon produced from entering the atmosphere.