Why materials selection is so important for carbon capture and storage

In Elsevier’s Becoming Net Zero webinar series, experts in the field talk about technical and engineering aspects related to the achievement of net zero and decarbonization goals. In the first webinar — Carbon Capture and Storage – Materials Selection Considerations opens in new tab/window — the discussion was led by Gary Coates opens in new tab/window, Technical and Market Development Manager at the Nickel Institute opens in new tab/window. He explained the various aspects of Carbon Capture, Utilization and Storage (CCUS) and the role it will play as one of many tools needed to achieve net-zero greenhouse gas (GHG) emissions.

“Many organizations are committed to either becoming carbon neutral or carbon negative, but most only have a vague idea of how to accomplish these goals,” Coates said. “While eliminating carbon dioxide emissions is the ideal result, it may not be possible, so capturing and storing carbon is necessary, at least in the short term.”

Carbon capture technologies

“As the technology is developed, the challenge is achieving cost-effectiveness,” Coates said.

One aspect of the economic equation is profitable use of the carbon. CO2 is already being used as a raw material in some processes. These include beverage carbonization, various food industry processes, and in fabricated metal products such as welding gases. But the primary usage of carbon dioxide today, comprising 88% of the market, is in Enhanced Oil Recovery (EOR).

EOR involves injecting gas, water or chemicals into a well to change the makeup and location of the oil in it to improve recovery rates. In some places, such as the Canadian oil sands, EOR is the only way to extract the oil because it’s too heavy to flow.

Waterflooding is the simplest EOR approach. When water is pumped down the well, it sweeps the oil up the reservoir. But water is scarce in many locations, and water restrictions are becoming more common.

Instead of water, gases of various kinds can be used to push hydrocarbons to the surface if the internal pressure of the oil well fades. Carbon dioxide comes into play here. If CO2 becomes more plentiful due to stepped up carbon capture efforts, this helps the viability of CCUS. Note, too, that flaring of CO2 is commonplace at many well sites. Utilizing that carbon in EOR is far less destructive to the environment than flaring.

Other plans for carbon are to permanently store it underground, and to cause it to react with another substance to form an inert carbon compound that is easy to store.

“There is a high cost to capturing carbon and dumping it into a cavern, so its use in EOR makes economic sense,” Coates said.

Regardless of which technology is deployed or which approach to CCUS is preferred, materials considerations must remain at the fore due to the corrosive nature of some forms of carbon dioxide.

Material selection is critical

There are a great many corrosion issues that need to be considered when separating CO2 from other gases. As Coates explained:

If CO2 is dry, it is non-corrosive, and it is a matter of economically transporting it to its storage site. But if liquified or compressed, higher strength materials may be needed.   

Dry CO2, then, can be channeled, stored and transported using traditional carbon steel. But even in those cases, a low-alloyed, higher strength steel may be beneficial. When the carbon dioxide is humid, though, an acidic liquid is often produced, which is corrosive to carbon steel. The solution is either to add a coating to carbon steel or specify stainless steel.

“In many cases, raw CO2 gases may contain other more corrosive gases which must be removed first,” Coates said. “Special equipment can be used to ensure a higher CO2 concentration with fewer impurities.”

Removing CO2 in the real world

SaskPower Boundary Dam is a coal-fired power plant with flue gases that contain much ash, some sulfur, and many other elements generated by the burning of coal. Low NOx (nitrous oxide) burners are used to limit the oversupply of air to contain emissions. An electrostatic precipitator helps to reduce ash, but SO2 must be removed first. At SaskPower, SO2 is converted to sulfuric acid for sale to industry. In addition, a solvent process removes about 90% of the CO2. 6% Molybdenum stainless steel alloys are used during many of these processes to prevent corrosion. Following that, the CO2 is dried and sent via a carbon steel pipeline to an oilfield for EOR.

“For many components, 316L, 317L and 2205 duplex stainless steel are used, and occasionally higher alloyed stainless steel,” Coates said. “Sometimes stainless clad on carbon steel can be used.”

In CCUS, two major types of solid absorbent recovery systems are used. Pressure Swing Adsorption (PSA) requires dry feed gas and typically runs under a vacuum. In this case, carbon steel or low alloyed stainless steels can be used. Alternatively, Temperature Swing Adsorption (TSA) is done at higher temperatures under humid conditions. Stainless steel such as 304L is needed, but sometimes 316L is used for certain parts of the process.

Supercritical (gas that behaves like a liquid) CO2 can sometimes pose additional challenges. Take the case of the Northern Lights Project in Norway opens in new tab/window. Carbon dioxide from several sources in Oslo is taken by pipeline to a port where it is compressed and shipped by boat to the Bergen area. It is stored temporarily onshore before being taken by pipeline to a permanent offshore subsea storage area (a previous oil production site). Because much of the pipeline and ship transport is done with dry CO2 in a supercritical state, carbon steel can be used. But low alloyed, higher strength steels are preferred for ship transport as they can cope better with higher levels of humidity. Further, storage of supercritical CO2 is often done in the liquid state in tanks at higher pressures and low temperatures. Again, low alloyed steel is advised.

Materials research needs

There are many different processes being developed today for carbon capture. The most challenging ones involve taking different flue gases and removing contaminants such as sulfur, nitrogen oxides, fluorides and chlorides to obtain to relatively pure CO2 so it can be easily transported and stored. For material engineers, various factors must be considered, Coates said:

There are many technologies being trialed and in development to reduce the industrial carbon footprint, and many different materials will be used. It is up to us as material engineers to ensure that the most cost-effective alloys giving the expected life are used, and they are fabricated and maintained correctly.

Engineers working with materials specialists need to find ways of removing the various contaminants cost-effectively using environmentally friendly methods. The Knovel material property search engine is a resource that can help engineers and researchers find numeric data hidden in handbooks, manuals, and databases. There are thousands of materials and substances (metals, polymers, ceramics, chemicals, etc) and more than 100 properties (physical, thermodynamic, electrical, corrosion, toxicity, etc) to search. As Coates explained:

The Knovel databases contain key information that gives clues to optimal and cost-effective material selection for the variety of CCUS processes. Knovel and other Elsevier sources help engineers find vital materials information and data quickly.  

These are just a few of the highlights of the Carbon Capture and Storage, Materials Selection Considerations webinar.