Facilitating the transition

Despite minimal progress over the years, there is now a noticeable increase in global interest and investment in CCUS initiatives.

In the UK, CCUS is a pivotal aspect of the UK government’s 2020 ‘Energy White Paper: powering our net zero future’. As an integral component of the UK’s strategy for decarbonising industries, the government has committed to establishing two CCUS clusters by the mid-2020s (with an additional two by 2030). These clusters include the East Coast Cluster, which encompasses Teesside and Humberside, connected to the offshore storage site of the Northern Endurance Partnership. The other cluster is HyNet, covering the Merseyside region and North Wales, with storage sites located in the Irish Sea.

Studies indicate that the UK sector of the North Sea possesses substantial capacity to store approximately 78 gigatons (GT) of CO₂ in saline aquifers. This storage potential translates to over 200 years worth of capacity based on the UK’s 2021 CO₂ emissions. It is widely acknowledged that achieving net zero emissions without the implementation of CCUS is not deemed feasible.

Furthermore, nations around the world are presently committed to fostering a flourishing low-carbon hydrogen industry. CCUS will play a vital role in facilitating the rapid expansion of low-carbon hydrogen production through steam methane reforming. The integration of CCUS with methane reforming offers a viable pathway for cost-effective hydrogen generation, with net zero CO₂ emissions, and is anticipated to be widely embraced.

An often overlooked aspect of CCUS is the requirement for appropriate flow measurement technology for CO₂ streams. The ability to comprehend, monitor, and regulate the flow rate of CO₂ will be crucial for ensuring the effective functioning of CCUS operations.

At each stage in the CCUS infrastructure, accurate measurement of the CO₂ flow rate is required. These measurements can occur over a range of temperatures, pressures, flow rates and fluid phases, and must be validated through a credible traceability chain.

The traceability chain provides the underpinning confidence required to verify meter performance, financial and fiscal transactions, and environmental compliance. Unfortunately, there is currently a lack of traceable gas CO₂ and liquid CO₂ flow measurement facilities and associated flow measurement standards. This is a significant barrier to the successful implementation of CCUS projects worldwide.

Fluid properties of CO₂

CO₂ is a fairly unique fluid, and its properties present several measurement challenges. At ambient temperature and pressure, CO₂ is in a gaseous state and its flow measurement is relatively straightforward. However, above the critical point of 31.1°C, and 73.9 bar, CO₂ becomes supercritical, exhibiting properties which are hybrid between gas and liquid.

Operating near the critical point can present significant technical challenges as slight changes in temperature and pressure may result in large changes in fluid properties. The phase diagram for CO₂ and the anticipated operating range for the CCUS chain are shown in Figure 1. Each of the four phases may present different measurement challenges and maintaining the desired fluid phase may also be problematic.

The possibility of phase change is further exacerbated by the likelihood of impurities being present in the CO₂ stream, which may cause significant shifts in phase boundaries, the critical point, and specifically the two-phase region. Traces of impurities may also influence the density and compressibility of the process stream. Therefore, CO₂ streams across the CCUS chain will require careful modelling and regular sampling to ensure the desired operating conditions and/or fluid phase are maintained.

This article was originally published in the March 2024 issue of Hydrocarbon Engineering magazine. To read the full article, sign in or register for a free subscription.

Written by Dr Chris Mills, TÜV SÜD National Engineering Laboratory, UK.

Read the article online at: https://www.hydrocarbonengineering.com/special-reports/18042024/facilitating-the-transition/