CO2 transport
Results 2021
How CO₂ flows through restrictions
Model to predict running-ductile fractures in CO₂ pipelines
We are working to improve our ability to predict running-ductile fractures in CO2 pipelines. The work has progressed along three main lines of research.
The first is to improve methods for describing the steel and crack behaviour in a finite-element modelling framework, including the consistent calibration of model parameters based on limited input from material tests. The second line of research is to describe the pressure load on the pipe walls from the escaping CO2, properly taking non-equilibrium effects into account (see also the previous paragraph). The third line of research is to “distil” the knowledge obtained into an engineering tool.
We have previously assessed pipeline designs for the Northern Lights project. This year we wrote an update of this work together with Equinor, which will be presented at the TFAP Conference in March 2022.
Educating the next generation of CCS scientists
This year, we co-supervised a master’s candidate from the Department of Structural Engineering at NTNU on modelling ductile fracture in steel structures. Our two PhD candidates who work on the topic of fracture mechanics related to fracture-propagation control in pipes, and on the topic of depressurization of CO₂ in pipes, have both successfully completed their first year. Both candidates are co-supervised by NTNU and SINTEF.
Understanding CO2 depressurization in pipes
Depressurization of CO2 in pipes in one of the keys to obtain the quantitative models that are needed by engineers to design efficient and safe CO2-transportation systems, and to devise how to best operate them. In 2020, the first results from the ECCSEL depressurization facility were published in the form of a journal article and dataset. They yielded new insight into the pressure and temperature development as a pipe filled with CO2 is emptied through a full-bore opening. In particular, these experiments are the first of their kind published with dense and accurate temperature measurements. The experiments also showed that the first instants of depressurization are out of equilibrium (see figure). This has implications on assessment methods for running-ductile fracture – one of the design criteria for pipelines transporting highly pressurized and compressible fluids.Model to predict running-ductile fracture in CO2 pipelines
SINTEF’s coupled fluid-structure (FE-CFD) model to predict running-ductile fracture (RDF) in CO2 pipelines was further developed, both with respect to thermodynamics (implementation of accurate equations of state for CO2-rich mixtures) and material mechanics (how to accurately calculate the steel behaviour and the crack propagation). We are testing these improvements by comparing to published data from full-scale tests. The work is in progress and will be published next year. This year, our work on fracture propagation control for the Northern Lights project was published at the IPC 2020 conference, jointly with Equinor. One result from that work is shown below, namely, an illustration of the perhaps non-intuitive effect that a higher operating pressure is less severe with respect to running-ductile fracture.Educating the next generation of CCS scientists
This year, we co-supervised a master’s candidate at the Physics Department at NTNU on the topic of accurate numerical methods for two-phase flow in pipes or channels with abruptly varying cross sections. This candidate was then employed to pursue her PhD in NCCS on the topic of depressurization of CO2 in pipes. A second PhD was also employed this year, on the topic of fracture mechanics related to fracture-propagation control in pipes. Both candidates are supervised jointly between SINTEF and NTNU.
ECCSEL depressurization facility and improved models
The ECCSEL depressurization facility became operational in 2019. This facility is specifically instrumented to record fast changes in pressure and temperature as pressure waves propagate in a pipe. These data contribute to safe and efficient CO2 transport through validation of numerical models which enable us to better design and operate CO2-transport systems.
Gas and liquid experiments have been conducted with the rig and we obtained preliminary results with high resolution and consistency. The data will be used to validate and improve the fluid part of our coupled fluid-structure (FE-CFD) running-ductile-fracture (RDF) prediction model, as well as models for transient (time-varying) multiphase (gas-liquid and gas-liquid- solid) flow of CO2 in general. The data will be further analysed and published in 2020.
In addition, we improved our coupled FE-CFD model for predicting running-ductile fracture in CO2 pipelines by improving our material-model calibration method and by more efficient thermodynamics calculations.
The RDF model can be made available to industry. A way to do this is outlined in the document ‘Fracture-propagation-control tool for industry – proposal for a pre-project’ submitted to the Task Family. Putting the model into industrial use could lead to benefits including reduced cost and design margins and lowered project risk.
More efficient simulation of multiphase flow
Our postdoc at the University of Zürich has developed a new numerical method for compressible (‘low-Mach’) multiphase flow. This could lead to more efficient simulation tools for multiphase flow of CO2, that is, simulation tools that can handle a large range of flow situations in a robust and numerically efficient way.
Interest outside of NCCS
A work package on model-based design tools for fracture design and control was part of a bilateral Norway-China application entitled “Digital solutions for predictive maintenance and structural integrity assessment of energy pipelines – Doorstep”. This shows that the work attracts interest outside NCCS.
Main results
- Commissioning of the ECCSEL depressurization facility brought much closer.
- Further validation of SINTEF coupled FE-CFD model for fracture-propagation control, published at IPC2018.
- Battelle two-curve tool software updated with new functionality, including GERG-2008 and EOS-CG equations of state.
The work focused on CO2 transport by pipelines. We established a roadmap for the development of an engineering tool for fracture propagation control in CO2-transport pipelines, which can help ensure safe and cost-efficient CO2 transport. By engineering tool, we mean a tool that can be used with relative ease and with short runtimes by an engineer using a desktop computer, as opposed to heavier finite-element (FE) and computational fluid dynamics (CFD) simulations. The SINTEF coupled FE-CFD code is an essential part of the development, due to the physical insights that can be gained through its use.
Several publications have hypothesized that the CO2 flow exiting the pipeline through a fracture is not in equilibrium. We made some progress in the modelling of non-equilibrium flow.
Work was also performed on the validation of our procedure for calibrating the material model in the FE-CFD code.
The NCCS industry partners, in particular Aker Solutions, Gassco, Larvik Shipping, Shell, Statoil and Total are following up and providing input to the work.