- David Berstad
- Research Scientist
- 411 44 876
- Gas Technology
- SINTEF Energi AS
CO2 capture and transport-conditioning through liquefaction (Task 4)
The task is looking to use liquefaction to optimise the transport condition of CO2, thus making liquification a mandatory processing stage in the interface between capture and transport. To do this, an efficient CO2 liquefier process will be derived. Important criteria are energy- and cost efficiency adhering to transport specifications and safety.
As describes in CO2 value chain and legal aspects (Task 1) , CO2 transport is an important piece of the value CCS value chain. We are looking to use liquefaction to optimise the transport condition of CO2. To do this, we need to derive an efficient CO2 liquefier process designs.
As described in Task 1, shipping of CO2 is most likely to be the preferred mean of transport. Hence, liquefaction will be a mandatory processing stage in the interface between capture and transport, thus playing an imperative role in the CSS value chain. Important design criteria are therefore energy- and cost efficiency adhering to transport specifications, and safety.
As a proof of concept, a pilot rig for CO2 liquefaction with 10–15 t CO2/day capacity is under commissioning, financed under the ECCSEL programme.
Through its research, the this task will provide other tasks with important insight like:
- Input to value chain assessments - Task 1
- Solvent technology – environmental issues - Task 2
- Low emission H2 production -Task 3
- Gas turbines - Task 5
Several of our activities, such as process modelling and simulation, is of relevance to potential suppliers of post-, oxy- and pre-combustion capture units, as well as critical components thereof. Further, it is also of general relevance to shipping companies that are potential shippers of liquid CO2 between the points of capture and unloading.
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.
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.
- 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.
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.