Carbon capture and storage, often referred to as carbon sequestration, is attracting substantial investments worldwide due to environmental, social and governance initiatives. In the United States, the Department of Energy recently announced $3.7 billion of funding to sequester carbon dioxide in enhanced oil recovery (EOR) and other projects. But as our article in the March 2023 issue of Hydrocarbon Processing magazine, titled Control Valves for Carbon Sequestration Applications, relates, these projects are challenging.
One technique offering promise is geological carbon capture and storage, which captures carbon dioxide from a variety of sources and sequesters it deep underground. While conceptually easy to understand, the logistics of handling carbon dioxide for these applications is not so straight forward.
To understand the issue, let’s look at one of the most promising technologies, geologic carbon sequestration, which seeks to capture and store carbon dioxide in underground porous rock formations.
The worldwide potential for storage is enormous, with an estimated 3,000 gigatons of potential storage capacity in the United States alone. This injected carbon dioxide can also be used as part of EOR methods, which use the carbon dioxide to reduce the viscosity of hydrocarbons and drive them towards existing well heads.
Geologic carbon sequestration process is composed of three major tasks, as detailed below.
Various processes are used for carbon capture, with amine separation the most popular:
Amine separation remains the most widely used method for carbon capture, and control valves used in these applications face significant challenges. These valves are subjected to high pressure drop and outgassing conditions as the entrained carbon dioxide separates from the amine solution while passing through valves.
There is no international control valve sizing standard for these applications, but Fisher can assist with sizing and selection.
Carbon dioxide compression
After separation comes compression, with centrifugal compressors typically used to boost low gas pressures to a supercritical state for pipeline transport, creating another major issue:
Centrifugal compressors are prone to a catastrophic condition known as surge at low flow rates. If flow is not restored through the compressor immediately, the internals of the compressor can be destroyed in a matter of seconds. To prevent this condition from occurring, anti-surge valves are installed between the discharge and suction of the compressor, and they open very quickly to establish forward flow the moment compressor surge is detected.
These large valves have specialized actuators and positioner components to provide extremely fast and accurate response, and valve trims are specially designed to handle the very high pressure drop and high flow conditions common in this service.
Carbon dioxide injection
The last carbon sequestration step is injection into abandoned aquifers, salt domes, or depleted gas and oil fields. Carbon dioxide can also be utilized for EOR.
The carbon dioxide readily enters the hydrocarbon in the target zone, lowering its viscosity and increasing its volume to drive it toward surface wells. Enhanced oil recovery has the dual potential of sequestering carbon dioxide while increasing oil production, so the economics are very favorable. For this reason, the bulk of carbon sequestration injection projects were initially focused in this area.
Injection pressures depend greatly upon the depth and type of geologic formation, but in all cases the automated injection valves can be subjected to thousands of pounds of pressure, high vibration, and high noise—as well as corrosive conditions created when trace amounts of water or hydrogen sulfide remain in the carbon dioxide. Body, trim, and seal material selection is a critical aspect of valve sizing and selection.
When faced with the task of specifying automated valves for a carbon sequestration project, users should consult with a knowledgeable valve vendor experienced with these types of applications. The wide range of potential conditions—as well as challenges associated with body and trim material selection, elastomer seal problems, and difficulties with sizing supercritical valve applications—warrants careful consideration.