CO₂ (CCS) Flow Metering

Carbon capture and storage (CCS) processes capture carbon dioxide (CO₂) emissions from industrial processes, power generation, and other sources, and then store them underground. Although it offers significant potential to reduce greenhouse gas emissions, as a relatively new technology, CCS faces several challenges.

Key carbon capture and storage challenges include cost, technical difficulties, safety, storage capacity, and regulatory requirements. Public perception can also be an issue, with critics raising concerns about its safety and effectiveness. In addition, CCS is sometimes seen as detracting from efforts to reduce emissions through renewable energy and better energy efficiency.

Commercial challenges
As a relatively new and expensive technology, CCS faces several commercial challenges that have limited its widespread adoption. The current cost of capturing and storing CO₂ can be prohibitively high, particularly for smaller industrial facilities or power plants. As a result, many companies are, at present, hesitant to invest in CCS technology due to concerns about its economic viability. While some governments have provided funding for CCS projects, many companies argue that additional incentives, such as tax credits or subsidies, are needed.

Storage challenges
Captured CO₂ is typically stored underground, usually in former oil and gas reservoirs which have been proven to have held their resources in place for millions of years. The capacity of these underground geological formations to store CO₂ is limited, and not all sites may be suitable for long-term storage. There is also a need to identify and assess potential storage sites, which can be time-consuming and expensive.

Infrastructure challenges
Suitable storage sites can be remote, so captured CO₂ may need to be transported across large distances, requiring a network of pipelines. The cost of building and maintaining these pipelines can be high, and there may be public resistance to their construction. These cost issues may also apply to the storage infrastructure itself, as even existing geological sites are likely to need to be adapted for the safe storage of CO₂ and monitored to ensure there is no leakage. Additionally, CCS infrastructure must be integrated with existing infrastructure, such as power plants or industrial facilities, which can be a complex and expensive undertaking.

CO₂ and its impact on material
Carbon dioxide can have significant adverse effects on materials, including corrosion, degradation, scaling, and embrittlement. These effects can be seen in a variety of industries, including oil and gas, power generation, and transportation, and so are likely to create challenges for any CCS process. Understanding and mitigating these effects is essential for maintaining safe and efficient operations.

Corrosion
When CO₂ reacts with water, it can form carbonic acid. So, when moisture contaminates pipelines transporting CO₂, it can lead to corrosion in metal components and pipes, particularly those made from carbon steel or copper alloys. This, in turn, can lead to leakage, which is often difficult to detect, and can be dangerous and expensive to repair.

Degradation
The presence of CO₂ can cause the degradation of materials such as polymers and rubber. Again, this is often caused by CO₂ reacting with moisture to create carbonic acid, and leads to an adverse effect on the material’s mechanical strength, stiffness, and other properties. CO₂ can also react with the calcium hydroxide present in concrete, leading to degradation and cracking.

Scaling
Scaling is the build-up of mineral deposits on equipment surfaces. When CO₂ dissolves in water, it can react with minerals to form scale. This can occur in pipelines, heat exchangers, and other equipment, leading to reduced efficiency and increased maintenance costs. Calcium-based materials, such as limestone and concrete used in storage sites, are also susceptible to scaling in the presence of CO₂.

Embrittlement
When CO₂ dissolves in some materials, particularly polymers and elastomers, it can cause them to become brittle and more prone to cracking or breaking under stress. This can affect components such as seals, gaskets, and coatings.

Despite the challenges involved, carbon capture and storage is a promising technology for reducing greenhouse gas emissions, particularly from large industrial sources such as power plants and cement factories.

Further research and development are likely to improve the efficiency and reliability of CCS processes, while delivering more cost-effective and scalable technologies.

With an increasing focus on the environmental impacts of CO₂ emissions, public perception is shifting in favour of carbon capture schemes, driven by greater engagement and discussion. This is backed by policy support from governments and regulatory bodies looking to fund and incentivise CCS projects globally.

Additionally, CCS is often the only realistic option open to many industrial applications looking to secure a significant reduction in their emissions rapidly.

So, while further innovation and investment are required to fulfil its full potential, CCS is already an effective and realistic solution for mitigating the large-scale emissions of CO₂.

Efficiency of carbon capture and storage
The efficiency of CCS depends on a number of factors, including the type of technology used, the energy requirements for capture and compression, and the efficiency of the power plant or industrial process from which the CO₂ is captured.

However, in general, CCS projects can capture up to 90% of the CO₂ emissions from industrial processes and power plants, and this figure is likely to improve as technologies develop further. Some experts have postulated that capture rates of 98% to 99% are possible.

In addition, the capture process is quite energy-intensive, and can increase the cost and environmental footprint of CCS, as well as make the power generation or industrial process application less efficient.

Even so, the efficiency of CCS is not the sole consideration. Other factors, such as cost, reliability, and environmental impact, are also critical. CCS has the potential to play a vital role in reducing greenhouse gas emissions and mitigating climate change.

Carbon capture and storage is generally considered to be a safe technology. Nevertheless, there are some risks associated with it that must be managed and addressed, including leakage, groundwater contamination, pipeline incidents, and health risks to personnel. Generally, however, these risks can be managed and mitigated through careful project design, implementation, and monitoring.

What are the risks?

Carbon dioxide leakage 
If CO₂ leaks into the atmosphere, it could contribute to climate change or pose a risk to human health, undoing the benefits of the CCS project. To mitigate this risk, storage sites must be carefully selected to ensure their suitability for long-term storage, and monitored regularly to detect any leakage.

Groundwater contamination
If CO₂ leaks into groundwater, it can acidify the water and cause contamination. To prevent this, CCS projects must conduct thorough site assessments to identify potential risks to groundwater and implement measures to protect it.

Pipeline accidents
Transporting CO₂ from capture sites to storage sites via pipelines often takes place over large distances, and can pose a risk of accidents or leaks. For this reason, pipelines must be designed, constructed, and maintained to high safety standards.

Health and safety risks
The capture and compression of CO₂ can pose health and safety risks to workers if not handled properly. Effective and robust safety measures, along with training for workers, are needed to reduce the likelihood of any problems occurring.

In process industries when CO₂ is going to be recovered and sold on for use in other processes, it will generally be in a pure state (ie 99.995% pure). With the emerging Carbon Capture and Storage projects, the quality of the CO₂ to be transported and stored will more likely be at a purity of between 95% and 99%. This is due to contaminants left in the CO₂ during the capture process. It will vary depending on the capture process and industry. For example, coal power stations may produce more contaminants than a gas field equivalent.This impure CO₂ stream in known as “Rich CO₂”. A typical example of this would be as per the published CO₂ make up for the Porthos CCS Project in the Netherlands. This quotes only a better than 95% CO₂ purity.

Typical contaminants can be nitrogen, hydrogen, methane, oxygen and trace amines from the capture process (Click here for Porthos page). The reason that the knowledge of these contaminants is important is that they may have an impact on the integrity and operational safety of the transport system (corrosion and embrittlement are examples of the possible effect). In addition, where there ais tax credit to be paid as an incentive for the storage, the relevant regulatory body will only want to pay for the actual CO₂ element of the rich stream. 

(a) For financial accounting and emissions-trading purposes, bulk quantities of CO₂ sequestrated must be quantified to a level of uncertainty defined by the relevant trading scheme (e.g. the European Emissions Trading System (EU-ETS) or the United Kingdom Emissions Trading Scheme (UK-ETS) from which carbon credits will accrue. This takes place in two stages:

- Measurement of bulk fluid quantities. This provides a method for the Transport and Storage Company to charge the CO₂ emitter for transporting and then storing the “rich CO₂” 

- Determination of CO₂ concentration. This provides the relevant regulatory body a way of quantifying the actual mass of CO₂ stored and value of carbon credit awarded. 

(b )The quantity of CO₂ delivered at each injection point must be determined at a level of uncertainty that is low enough to meet the requirements of the relevant reservoir models.