By vessel and by pipeline – achieving our CCUS ambitions

By Jørg Aarnes, Global Lead, DNV

DNV secures CCS pipeline materials study for Neptune Energy in the Dutch North Sea (photo: DNV)
DNV secures CCS pipeline materials study for Neptune Energy in the Dutch North Sea (photo: DNV)

In the race to accelerate the energy transition and reach ever more ambitious climate targets, carbon capture utilisation and storage (CCUS) is recognised as a crucial element in the race to net-zero. According to the Intergovernmental Panel on Climate Change (IPCC), CCUS is essential to global economies achieving their emissions-cutting commitments at low cost.

The impact of CCUS technology is immense, with the UN estimating that it could mitigate between 1.5 and 6.3 gigatons of CO2 equivalent per year [1]. In the DNV Energy Transition Outlook 2020 [2], it was predicted that the scaling of CCUS will not happen to a significant level until 2040, without government intervention and a more concerted effort to reduce the cost of the technology.

To spur the development of CCUS projects and scale-up its transition to a cost-competitive technology, the safety aspects of carbon dioxide (CO2) transport by pipeline and by sea need to be addressed. With a track record developed over the last 30 years, DNV is a pioneer in the field of CCUS and is today conducting work across the global CO2 capture market to provide solutions to overcome these challenges.

CO2 pipeline transport for storage
There are two primary transport options for CO2, by ship or by pipeline. For small volumes and long distances offshore, transfer by ship is considered as the cheapest option, whilst for larger volumes and short distances, pipelines are most suited.

Steel pipelines, as used for natural gas, can transport CO2 in dense phase. By controlling the pressure and temperature within the pipeline, the volume that needs to be transported is reduced and the pipeline capacity is maximised.

There are challenges associated with the use of pipelines. For instance, there is the risk of the pipe running ductile fractures in both directions, with the potential to rupture the pipe along a distance of hundreds of metres with eventual leaks if not arrested. In this case, a pressure plateau would develop (Figure 1), where the escaping fluid expands to CO2gas and the pressure in the region of the crack tip remains high.

Figure 1: A pressure plateau during a full-scale burst arrest test at DNV’s Research and Development Centre in Cumbria, UK (photo: DNV)
Figure 1: A pressure plateau during a full-scale burst arrest test at DNV’s Research and Development Centre in Cumbria, UK (photo: DNV)

Acting in response to this issue, DNV set up a joint industry project (JIP) named CO2SafeArrest and in February 2021, used the findings to update the recommended practice (RP), DNVGL-RP-F104 “Design and operation of carbon dioxide pipelines.”

Under the Carbon Capture & Storage Research Development and Demonstration Fund, the JIP work was supported by the Australian Commonwealth Government and the Norwegian funding body CLIMIT.

As part of the JIP, DNV and the Australian Energy Pipelines Cooperative Research Centre (EPCRC) came together to improve understanding around what governs running ductile fractures. At DNV’s Research and Development Facility in Cumbria, UK, two large-scale CO2 crack arrest tests were conducted on 24-inch X65 pipes with wall thickness of 13.5 to 15 mm. These tests investigated fracture propagation and arrest characteristics of steel pipelines carrying CO2 and investigated the dispersion of CO2 following its release into the atmosphere.

The first test was carried out along the full-length of a specially constructed pipeline, consisting of eight pipe sections, part-buried under ca. 1m clay. In the second test, half of the test was left exposed, with the other half part-buried in a similar way as in the first test. An explosive charge, cutting a slit ca. 1 metre into each of the two pipes in the middle of the test layout, was set off to trigger a running fracture.

In the first test, the crack propagated through the two first pipe sections on each side and arrested in the third pipe section on each side. In the second test (Figure 2), the fracture propagated in the three first pipe sections on each side and arrested in the fourth pipe section. The crack velocity and pressure decompression were captured in both successful tests.

Figure 2: The observations from the CO₂SafeArrest large-scale tests have been used to propose a new empirical model for assessment of running ductile fracture in CO₂ pipelines (photo: DNV)
Figure 2: The observations from the CO₂SafeArrest large-scale tests have been used to propose a new empirical model for assessment of running ductile fracture in CO₂ pipelines (photo: DNV)

A new empirical model for the assessment of running ductile fractures in CO2 pipelines, which is included in DNVGL-RP-F104, was developed from the findings of this study. The key outcomes included:

  • The crack propagated with almost constant pressure at the crack tip until arrest took place.
  • The decompression of CO2 did not follow a fully flat plateau as predicted for a theoretical model, but rather a “sloping” plateau (as has also been observed in previous tests).
  • Crack propagation was faster in the unburied compared to the buried pipes. However, the eventual arrest did take place in pipes with similar properties.

As part of a wider feasibility study into the development of a large-scale CCS facility in the Dutch North Sea, Neptune Energy Netherlands tasked DNV to assess the fracture and suitability of offshore pipelines for re-use in CO2 transport.

If the project is developed in the Neptune-operated L10-A, L10-B and L10-E areas, it will be one of the largest CCS facilities in the Dutch North Sea and could meet more than 50% of the CO2 reduction target by the Dutch industrial sector. The study will be completed by mid-August.

Using the sea for CO2 transportation
Transport of CO2 by ship is emerging as an essential link in the decarbonisation chain, potentially creating new industrial markets. The use of ships to provide flexibility to where CO2 is sourced is a key component of the Northern Lights project (Figure 3), part of a collaborative Norwegian initiative to achieve full-scale CCS involving Equinor, Shell and Total. DNV provided technical support to the approval of ship design for the Northern Lights projects, which transports CO2 at so-called medium pressures around 15-20 bar and temperatures at around -25° C to -30° C.

Figure 3: The Norwegian Ministry of Petroleum and Energy has approved the development plan for the storage part of the Longship carbon capture and storage project (source: Northern Lights)
Figure 3: The Norwegian Ministry of Petroleum and Energy has approved the development plan for the storage part of the Longship carbon capture and storage project (source: Northern Lights)

The tanks for the Northern Lights project have been designed to withstand pressure accumulation during laden voyages and the corrosive effects of liquid CO2. The chosen design resolves the competing demands of economical tank manufacturing while meeting strict safety requirements by replacing standard low-temperature steel for pressure vessels with a high tensile strength property to withstand higher extreme loading and ensure resistance to cracking.

DNV concluded the pre-class evaluation of the innovative type C containment tanks for liquefied CO2 in October 2019. The medium-pressure system reduces refrigeration requirements and provide relatively high-volume efficiency when applied on ships typically used for LPG transportation.

A new low-pressure concept to transport CO2 is also under development. In this concept, CO2 is kept at a temperature around -50° C, with a pressure of 7 bar, in line with LPG containment systems. Higher pressures combined with higher (ambient) temperatures is also possible.

Action is required now
Industrial-scale CCS has been defined as an integral part of the solution to reach the COP21 1.5° C target. Despite innovations within the CCS sector in recent years, CCS won’t move down the cost learning curve unless the industry significantly increases its roll-out of the technology. There are also several major challenges to address around social acceptance, environmental credentials and crucially, techno-economic issues.

In the near-term, there needs to be action to spend more and scale-up CCS to ensure that the technology fulfils its promise to accelerate the energy transition and significantly contribute to reaching our climate targets.

References
[1] https://www.hydrocarbonengineering.com/the-environment/23032021/idtechex-lessons-learned-from-the-closure-of-petra-nova-in-texas
[2] https://eto.dnv.com/2020

Jørg Aarnes, Global Lead – Low Carbon Energy Systems at DNVJørg Aarnes is the Global Lead – Low Carbon Energy Systems at DNV, based at the company’s headquarters in Høvik, Norway. He has spent more than a decade working in various functions for DNV, predominantly in the low carbon space. Aarnes has been involved in developing DNV’s Technology Outlook 2025, publishing a position paper on hydrogen as an energy carrier, developing a framework for certification of sites and projects for geological storage of carbon dioxide, and leading market analysis for climate adaptation services. Aarnes has a PhD in applied mathematics with emphasis on reservoir modelling and simulation.