Impurities challenging for CO₂ transport
It is difficult to capture CO2 from flue gas, for example, without capturing other gases or water at the same time. Even small amounts of the other gases can create major problems when CO2 is to be transported to the storage site.
“If the CO2 gas comes from a gas fired power plant, coal-fired power plant or industry, it is almost never 100 per cent pure CO2”Gaute Svenningsen,Institute for Energy Technology at Kjeller outside of Oslo
Depending on how well the CO2 gas is purified, it will contain a greater or lesser degree of impurities in the form of particles, water, sulphur or nitrogen compounds
CO2 in various mixtures
In the project that Svenningsen is managing,the goal is to determine what degree of impurities can be accepted. Many of the impurities can react and form products that can destroy the steel pipes that are to transport the CO2.“
If we envision an infrastructurefor CO2 transport with many different sources, the CO2 may contain various impurities that both separately and in mixture can result in destructive reactions,” says Svenningsen.
“CO2 captured from a coal-fired power plant may, for example, contain small amounts of sulphuric gas. If this is exposed to water and oxygen, sulphuric acid can form and corrode the steel in a pipeline. CO2 from other sources may contain other impurities that can result in other reaction products, including solid particles.
Particles in the gas or detachedparticles from corrosion processes can also create problems, especially at the final station where the CO2 is injected into the underground storage site.
All the experiments are conducted at a laboratory at Kjeller, where different types of impurities from separate sources are added to the CO2 in very exact doses and at specific time intervals Then the effect on steel corresponding to what is used in pipelines is measured over time.
“Corrosion and cross chemical reactions are studied in autoclave and flowlabs in which all of the variables are under precise control,” Svenningsen explains.
Spectrometers, laser light and infrared light are used to measure the content of impurities and reaction products. If impurities disappear from a gas mixture, it is an indication that a chemical reaction is taking place,which is generally not desirable.
Small volumes, large consequences
“What we have seen is what would normally be regarded as very small amounts of impurities, but which can have large consequences over time. CO2 with sulphuric acid can eat through 40 mm steel pipe in the course of a year,” says Svenningsen.“
When there are plans to transport many millions of tonnes of CO2 over many kilometres for many years to come, it is important that costly pipelines do not rust away in a short period of time. With knowledge of how much, and which, impurities the infrastructure can withstand over time, it is possible to stipulate precise requirements for the purification of CO2 from different sources before transport and storage.
The project will establish a basis for the recommendation of limit values for various types of impurities in CO2 mixtures that are transported in pipelines. This knowledge will be of decisive importance to anyone who is responsible for the operation of pipelines and other plants that handle impure CO2.