CO2 and Supercritical CO2 (sCO2) has it’s use in the industry for decades. However, CO2 produced during a manufacturing process cannot be emitted in the atmosphere anymore. Therefore it is captured, stored or utilized more and more. For valve specification and valve sizing additional challenges arise.
Mokveld axial flow valves playing their part in the sustainable solutions for CC(U)S, as they are highly suitable for applications with CO2 and sCO2. This may be anti-surge valves, zero emission valves, axial choke valves, check valves, basically the complete scope of the Mokveld products. The axial flow design providing streamlined and low pressure loss flow path, the lack of cavities and the usage of elastomers insensitive to explosive decompression are inherent advantages.
During capture and storage process minimization of leakages is of paramount importance as CO2 is a potent GHG. The single-piece design of Mokveld axial flow valves reduces leak paths, reducing Scope 1, and weight in comparison to other valve designs. Mokveld's manufacturing processes are low in energy consumption reducing GHG Scope 3 emissions for our clients.
Mokveld supplied the first valves for CO2 service in the late 80’s. Worldwide deliveries to our clients covered high pressure anti-surge valves, check valves and injection choke valves. Experience gained on these deliveries have been incorporated into the current designs.
Carbon capture processes usually extract CO2 in the gas phase. It may be transported in the gas phase for utilization, for example in The Netherlands CO2 gas is used to improve plant growth in the greenhouses. Often however, CO2 is used in the supercritical phase (sCO2), where applications vary, e.g. degreasing, but also as replacement for steam in power generation.
In Carbon Capture and Storage projects the CO2 is compressed to liquid for transport by ship or compressed to sCO2 for injection in aquifers or (depleted) hydrocarbon reservoirs. For the latter this may be either Enhanced Oil Recovery (EOR) or lifetime storage.
The supercritical state of CO2 occurs at a low pressure and temperature (73.8 bar, 31.3 °C). sCO2 behaves like a compressible fluid, however with a density of a liquid. Close to the critical point, known as the Widom area, the fluid exhibits large anomalies in behaviour. necessitating valve outlet conditions to be evaluated and taken into account during valve sizing and selection. Phase changes, Joule-Thomson effect, can result in multiphase flow, CO2 clathrate formation (similar to hydrate formation in natural gas production) and possibly even dry ice depending on impurities in the gas.
To properly size a valve and select the correct Cv and cage type, it is of utmost importance that the correct fluid properties at the inlet as well as the outlet of the valve are used. This includes values upstream and downstream for temperature, density, compressibility and k-factor (cp/cv).
The axial flow concept, where the flow enters the pipe line directly after exiting the cage and thus avoiding extra turbulences is a good solution.
Understanding the phase diagram and fluid behaviour under supercritical or dense conditions is required for the best valve selection. For example, the vast changes in density are the reason that valves with cavities, where the fluid can be 'trapped', are best avoided. Changes in the pressure or temperature within the cavity may result in a change of the fluid density and lead to excessive pressures in the cavity.
CO2 containing water, even in very low concentrations, can form carbonic acid and is corrossive to carbon steel. 13% Cr 4% Ni stainless steel materials have very good corrosion resistance to CO2. As indicated above the temperatures that may occur require attention related to the material selection.
Applications on sCO2 also require attention for the selection of seals. As indicated above sCO2 has degreasing capabilities which might affect for instance ‘O’-ring performance and any seal system requiring grease lubrication / injection.
There is also an increased risk of Rapid Gas Decompression in elastomers due to the solubility of sCO2.
Mokveld valves applied 13% Cr 4% Ni stainless steel for decades, both for the valve body as well as the internals. Our the sealing technology consists only of thermoplastics assuring a valve solution of longevity.
Mokveld engineers can provide assistance at an early stage of the project. We can assist you in selecting suitable valves for your (s)CO2 application, defining the process layout, correct valve sizing and material selection. All to help you achieve the best possible valve solution for your CCS or CCUS application.
If you would like to have more information about our valve solutions for your carbon capture (utilization) and storage projects, please contact us. As experts in engineered valve systems, we are capable of providing reliable customer services and can support you with valve sizing and selection, process engineering, material selection and budget pricing.
For questions regarding our installed equipment you can contact our product support team. Our product support team is at your service for all queries regarding our installed base.
