In the previous post about carbon capturing, we discussed the “what” and “how” of carbon capture. In this post, we’ll be talking about how this captured carbon is transported to its storage location.
Depending on the method responsible for generating CO2, in a lot of situations impurities exist in the flue gases. These impurities, such as sulfur oxides could react with the means of storage, leading to corrosion. Because of this, carbon is treated using the methods we discussed in the previous post.
TRANSPORTATION
Most times, the point of Carbon capture isn’t the same as that for sequestration. Usually, the storage site is quite far from the production plant and so, a viable means of transport is always necessary.
Just as with LPG and other gaseous fuels, CO2 is mostly transported via pipelines. This is because it is cheaper and more cost-effective. Carbon IV Oxide is compressed to a pressure above 8 MPa in order to avoid two-phase flow regimes and increase the density of the CO2.
These pipelines. are ideal for transporting carbon gases without reacting. This is because the pipeline material is designed and chemically treated to remain inert even under high pressure.
The United States boasts of over 2,500 km of pipeline that transports more than 40 Mega tonnes of CO2 per year, mainly to sites in Texas, where the CO2 is used for Enhanced Oil Recovery (EOR). In Norway, a 160 km pipeline exists, also for the transport of CO2.
Alternatively, ships are used to transport CO2 especially when the distance to be covered is too great to be covered by pipelines. When this is the case, CO2 is compressed to a pressure of 7 atmospheres for transportation.
Finally, road and rail tankers can also be used. They carry CO2 at transport CO2 at a temperature of -20ºC and at 2 MPa pressure. However, they are highly limited. The cost-to-benefit ratio is too low and so the option is least considered. Compared to other means, land-based tankers aren’t feasible.
STORAGE
The most feasible means of carbon storage is by injecting it into geological formations beneath the Earth. Usually, the gas is injected as a supercritical fluid- that is a gas that is subjected to high pressure till it exists as a liquid- and is trapped so that it doesn’t escape to the atmosphere.
Biological sequestration is also highly considered. This involves the use of living organisms such as vegetation, algae, and bacteria to absorb carbon dioxide. The rate at which this can be accomplished is far below the rate at which humans emit carbon dioxide, therefore, this means needs to be supported.
Making CO2 to react with metallic oxides is also a viable alternative. This occurs in nature; however, it also takes a while. Human and technological interventions have helped to speed up the rate. Unfortunately, the power demanded the process makes it a cause for concern.
Storage beneath the ocean is a possibility; however, such could lead to Ocean Acidification and is thus banned by major international bodies like OSPAR.
THE CCS PARADOX
According to the USGS in a 2013 report on the nationwide assessment of geologic carbon sequestration, an estimated mean storage potential of 3,000 metric gigatons of carbon dioxide is possible. This is quite encouraging.
However, from collecting to storing, CCS demands much energy be expended for proper execution. It is estimated that CCS would require 10 to 40% of a power plant’s output energy. If the source of this energy is a fossil fuel, then more Carbon dioxide will be released into the atmosphere.
Also, the cost of the processes involved makes it difficult to be implemented. Despite these restrictions, more than 75% of proposed CO2 gas processing projects had been implemented by 2019. Also, as of 2020, about one-thousandth of global CO2 emissions were captured by CCS. Currently, 22 CCS stations exist worldwide, some of which are still under construction.
Research is also being carried out to find new viable methods for storing carbon. The goal is to capture at least 2,000 million tonnes in 2030. Currently, we are at 40 million tonnes. New techniques such as Pyrogenic carbon capture and storage (PyCCS) are being developed.
If we keep pushing, we’ll be able to save our planet from dangerous warming and other harmful side effects of human activities.
