CO2 capture and transport-conditioning through liquefaction (Task 4)

The Task looks at using low-temperature liquefaction and phase separation for the purification and transport conditioning of CO₂.

Deployment Case 1 (DC1) in NCCS, as well as the full-scale Norwegian CCS value chain, is very likely to be based on transporting liquefied CO2 by ship. Therefore, liquefaction will be a mandatory processing stage between capture and transport. As such, ensuring energy- and cost-efficient liquefaction that adheres to transport specifications is of the utmost importance. If the transport pressure can be reduced from 15 bar(g) (which is currently typical) to, for example, 5-6 bar(g), the transport capacity can be increased and the transportation costs decreased.

However, there are several questions and concerns related to low-pressure CO2 liquefaction and transport that must be addressed in order for this to be a viable option. Task 4 addresses several of these research questions through modelling and experiments.

Task 4 is related to other NCCS activities, for instance, as a potential complementary CO2 purification technology for retentate streams from proton-conducting membranes, thereby enabling the recovery of potential residues in form of volatile and combustible components. The MACH-2 spin-off project is closely linked to Task 4.

Experiments are conducted using the SEPPIL pilot rig for CO2 liquefaction with a capacity of 10–15 t CO2/day. The rig is financed under the ECCSEL programme.

Results 2021

In the period 2019-2021, low-pressure liquefaction experiments with pure CO₂ and CO₂/N₂ mixtures were performed at the ECCSEL SEPPIL facility, located in the thermal engineering laboratories at Gløshaugen, Trondheim. From 2019-2020, experiments were conducted, wherein the final separation pressure was continuously lowered until dry ice was observed and finally clogged the product liquid CO₂ line. This was done to establish the temperature and pressure at which dry ice would form, and to investigate the robustness of the process towards clogging.

In 2021, two experiments were conducted, one with high purity CO₂ and one with a CO₂/N₂ mixture, where the liquefaction process was operated in a steady state for five hours, at a pressure slightly higher than where dry ice were observed in the first experiments. This was to ensure that there was no undetected formation and accumulation of dry ice in parts of the system that could cause issues over time. The scale of experiments is in the range of 3.6-4.8 tons of CO₂ per day, or approximately 150-200 kg per hour. These experiments demonstrate that pure CO₂ can be safely liquefied at a pressure of 5.8 bar(a) and a CO₂/ N₂ mixture can be liquefied at 6.5 bar(a) without issues related to dry ice formation. Results from six of the low-pressure liquefaction experiments conducted have been selected and published in a journal article in the Energies Special Issue "Advances in Carbon Capture and Storage (CCS) Deployment" (DOI: 10.3390/ en14248220).

To qualify a complete low-pressure liquid CO₂ chain, all chain links, such as liquefaction, transfer to temporary storage, temporary storage, loading, transport, unloading, etc. must be investigated. Theoretical investigation can increase the TRL to 2-3 (theoretical verification).

In 2021, dynamic simulations of a low-pressure liquid CO₂ terminal for ship transport were started. This activity investigates the different phases of the storage and loading cycle, taking the different transient phenomena as well as the process control measures into account. This activity is expected to provide valuable insight into the rating, design and process control, and thereby contribute to the further TRL advancement of low-pressure liquid CO₂ loading systems. A functioning dynamic model was made in 2021 and will be further developed in 2022.

Figure 1: Liquid temperature and pressure in separator during the continuous reduction in pressure down to freeze out of CO₂ for a CO₂/N₂ mixture.
Figure 1: Liquid temperature and pressure in separator during the continuous reduction in pressure down to freeze out of CO₂ for a CO₂/N₂ mixture.

Results 2020

In 2020, low-pressure liquefaction experiments have been conducted in the Cold Carbon Capture Pilot (CCCP) experimental facility. Four experiments using a CO2/N2 mixture with 97 % CO2 as feed gas, and one experimental series using pure CO2 (99.992 %), have been performed. In the CO2/N2 mixture experiments, the final separation pressure was gradually lowered until the liquid outlet from the second separator was clogged by solid CO2. In the experiments with pure CO2, liquid CO2 was produced for an extended period at pressures from 6.5 bar(a) down to 5.4 bar(a). Figure 1 shows the stepwise reduction in pressure in the final separator for part of the CO2 liquefaction experiment. The scale of experiments is around 3.6 – 6.0 tonnes CO2 per day or approximately 150 - 250 kg per hour. 

The goal of the experiments is to demonstrate the feasible pressures at which liquid CO2 can be produced and the practical limit with respect to solid CO2 formation. The experiments will increase the confidence in low-pressure liquid CO2 transport chains. A lower CO2 transport pressure has several benefits (e.g. increased liquid CO2 density, possibility to use larger and lighter tanks, better ship hull utilization) that can reduce the transport costs significantly. 

Pressure and temperature in the final separation stage for liquefaction of pure CO2
Pressure and temperature in the final separation stage for liquefaction of pure CO2

In the MACH2 spinoff project, the CCCP rig will be used to investigate syngas/retentate separation in hydrogen production. The required upgrades of the experimental facility to enable these experiments, which will include flammable and poisonous components, have been completed, and a new risk assessment of the rig have been approved. The planned MACH2 experiments will be the first proof-of-concept for efficient CO2 separation and purification from H2-selective membrane retentate gas mixtures and will serve to pave the way for further development towards an integrated membrane/ low-temperature pilot.

A review of required modifications and cost estimates for upgrading the rig to enable experiments with small concentrations of water in the feed gas mixture in the liquefaction rig have also been conducted.

Main results 2019

During 2019, we made a theoretical basis for CO2 liquefaction experiments relevant for full-scale cases for low-pressure transport of liquid CO2. From this we know how to operate the rig to obtain the desired test conditions, and what to expect in the experiments. An outline of an experimental plan for low-pressure CO2 liquefaction was also made.

In the MACH2 spinoff project (a spinoff from Task 4) we worked out the necessary upgrades of the CO2 liquefaction facility to run experiments with flammable

and poisonous components, which is required to investigate syngas/retentate separation in hydrogen production. Most of the upgrades were also completed in 2019 and January 2020, except some electrical work and implementation of safety systems that has been postponed until after the first NCCS Task 4 experiments are finished. Moreover, an external refrigeration cycle was installed and various upgrades to increase the rigs flexibility and accuracy have been implemented. These upgrades allow us to operate the rig such that we obtain the desired test conditions in both NCCS and MACH2, and increases the accuracy of the results.

Now that the rig is back in operation, several experiments will be conducted. Task 4 will demonstrate the feasible pressures at which liquid CO2 can be produced and the practical limit with respect to solid CO2 formation. The experiments will increase the confidence in low-pressure liquid CO2 transport chains. A lower CO2 transport pressure has several benefits (e.g. increased liquid CO2 density, possibility to use larger and lighter tanks, better ship hull utilization) that can reduce the transport costs significantly. In MACH2, the first proof-of-concept for efficient CO2 separation and purification from H2-selective membrane retentate gas mixtures is being prepared to pave the way for further development towards an integrated membrane/low-temperature pilot.

Picture: The experimental facility. Figure: Liquefaction process diagram showing included parts of the process in the experimental Throttling valve Compressor stage 2 Separator 3 Low-pressure liquid CO2 for ship transport Compressor stage 1 setup relative to an assumed full CO2 liquefaction process located between capture plant and ship loading terminal.

Results 2018

Main Results

  • Due to extremely high activity on commissioning the laboratory pilot facility, we have asked for very low budgets so far, with the aim of expanding on experimental activity beyond 2018
  • Other work ongoing until the end of 2018 (comparison of two different processing routes for CO2 liquefaction), not concluded at the time of reporting. KPIs to be compared comprise: Specific energy usage, total swept compressor volume, CO2 purity, CO2 recovery and more.

Impact and innovations

  • In parallel with NCCS, but with high relevance to potential future NCCS work, we have successfully commissioned the 10 t/d CO2 liquefaction pilot plant and run several tests for separation of N2 and CO2. This infrastructure can be very useful for NCCS in the coming years.
Interior of the 10 t/d CO2 liquefaction and separation pilot facility

Results 2017

The main activity was to provide an overview of the relevant inlet and outlet boundary conditions and specifications (compositions, temperature, pressure etc.) to which CO2 liquefaction processes must adhere. The gathering of information was done by data collection from other deliverables where available, as well as by communication with other NCCS tasks.

Examples of inlet boundary specifications are: CO2 captured from post-combustion capture with relatively high purity, and CO2-enriched synthesis gas retentate from protonic membrane reforming (PMR). Outlet specifications are mainly high-pressure CO2 for pipeline transport and liquid CO2 for ship transport. Low-temperature CO2 processing and its adherence to the various boundary conditions in post- and pre-combustion applications was given an initial consideration.

In parallel with the NCCS work, the task core group is involved in the construction and commissioning of a laboratory pilot infrastructure for low-temperature CO2 separation and liquefaction, funded through the ECCSEL infrastructure programme. The infrastructure has a capacity in the range 5–15 ton CO2 per day, and can operate down to around -55°C temperature range and up to 120 bar pressure. Upon completion, the infrastructure will be available for experimental activities relevant for NCCS.

Task leader

Stian Trædal

Stian Trædal

Research Scientist
934 47 877
Name
Stian Trædal
Title
Research Scientist
Phone
934 47 877
Department
Gas Technology
Office
Trondheim
Company
SINTEF Energi AS

Publications

Publications listed below are not in registered in Cristin.

See all other NCCS Publications registered in Cristin, the Norwegian Research Information system.

  • CO2 Capture from IGCC by Low-Temperature Synthesis Gas Separation
    David Berstad*, SINTEF Energy Research, Geir Skaugen ,SINTEF Energy Research, Simon Roussanaly, SINTEF Energy Research, Rahul Anantharaman, SINTEF Energy Research, Petter Nekså, SINTEF Energy Research,Kristin Jordal, SINTEF Energy Research,Stian Trædal, SINTEF Energy Research andTruls Gundersen, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU)
  • CO2 liquefaction close to the triple point pressure
    Stian Trædal*, Jacob Hans Georg Stang, Ingrid Snustad,Martin Viktor Johansson and David Berstad all SINTEF Energy Research