Carbon capture, use and storage (CCUS)

In the last edition of this column we looked at the opportunities for non-destructive evaluation (NDE) in the wind sector. This month, we are looking at a sector that is perhaps less familiar but is gaining increasing traction in the journey to net zero: carbon capture, use and storage (CCUS). CCUS is particularly applicable to industrial processes that emit carbon dioxide and where electrification or low-carbon fuels are not feasible; it is also applicable to power stations that use hydrocarbons to generate electricity.

There are seven so-called industrial clusters in the UK, which together produce 50% of all UK industry emissions. The government supports CCUS development in these clusters with the aim of achieving high-impact emissions reductions and reducing risk by enabling the sector to share transport and storage infrastructure^[1]. This will be done in a series of ‘Tracks’, with Track-1 underway (HyNet in the North West of England and North Wales and the East Coast Cluster in Teesside) and Track-2 initiated.

There are three main types of carbon capture: capturing carbon dioxide after fuel is burnt (‘post combustion’), removing carbon dioxide from fuel before it is burnt (‘pre combustion’) and capturing carbon dioxide directly from the atmosphere, ie not from fuel or emissions. The latter type results in a carbon-negative process because carbon is removed from the atmosphere.

In the term ‘CCUS’, the term after ‘carbon capture’ is ‘use’ or ‘utilisation’. However, while there do exist various uses for carbon dioxide (for example in the food industry, the synthetic fuel industry, etc), it is estimated that it is not efficient or perhaps possible to put all the captured carbon dioxide to use. Therefore, we are typically talking about ‘carbon capture and storage’, sometimes referred to as ‘carbon sequestration’.

The next step is ‘transport’, which is not assigned a letter in the ‘CCUS’ term but is the most important when it comes to NDE. The captured carbon dioxide is compressed to make transportation more efficient. It is transported in purpose-built or repurposed pipelines onshore and/or offshore and sometimes also via sea or land vehicles. This necessitates similar NDE to that in the hydrocarbon sector, including crack detection (with features such as inlets being particularly susceptible), weld inspection and corrosion mapping. As with other pipelines, applicable techniques include ultrasonic testing, phased array ultrasonic testing and magnetic flux leakage amongst others; however, some things are different.

Carbon dioxide is transported at higher pressures than hydrocarbons and pipe walls may be thicker. This may therefore limit the options for NDE techniques and the equipment that can be used. Pure, dry carbon dioxide is non-corrosive, but impurities (the presence of which is partly dependent on the capture technique) and water can lead to acid formation and thus corrosion. Therefore, monitoring for moisture and inspecting for corrosion are essential. Pipelines are typically metal because of the high pressure, though increasingly flexible non-metallic pipes are being considered, especially for offshore transportation. In CCUS operations, carbon dioxide will be handled close to, or above, its critical pressure (73.82 bar) and temperature (31.04°C)^[2]. In this state, carbon dioxide displays liquid-like properties and is referred to as ‘dense phase’ or supercritical. Significant hazards can occur if carbon dioxide in such a phase experiences a rapid or total loss of pressure.

Finally, ‘storage’. The carbon dioxide is stored onshore or offshore, typically in porous geological formations, for example saline aquifers or depleted oil and gas reserves, where an impermeable top layer traps the carbon dioxide. These storage facilities require inspection at various life stages and monitoring for carbon dioxide leakage.

Many readers will have heard of ‘hydrogen and CCUS’ as a pair of terms. Hydrogen is an alternative fuel to fossil fuels for some industrial processes and power generation and it can be considered the ‘partner’ of CCUS because they are both strong pillars of industrial decarbonisation, especially where electrification is not feasible. Another important link is that so-called ‘blue’ hydrogen is produced from methane and the resulting carbon dioxide emissions are captured and stored. Similarly, bioenergy with carbon capture and storage (BECCS) generates renewable energy from biomass and the resulting carbon dioxide emissions are captured and stored.

In summary, CCUS brings with it a host of varied infrastructure, with demanding and critical NDE requirements. Readers are encouraged to watch this exciting space. For those interested in reading more, the Carbon Capture and Storage Association (CCSA) provides case studies from across the world^[3] – 77 projects are already in operation, and counting!

The NDE for Clean Energy Industries column will be back in September with a look at NDE for another of the clean energy industries. Please send any comments or queries to editor Corinne Mackle at ndtnews@bindt.org

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