CO2 systems, studies and solutions

The global energy system is undergoing a profound transformation as the world strives to reduce greenhouse gas emissions and mitigate climate change. Renewable energies, such as wind and solar, are expected to play a major role in the future energy mix, but they also pose challenges for the stability and reliability of the grid. Hydrogen, as a clean and versatile energy carrier, can offer solutions for storing and transporting excess renewable energy, as well as for decarbonising hard-to-abate sectors, such as heavy industry and transport.

Carbon Capture, Utilisation and Storage (CCUS) technologies can also help reduce the carbon footprint of fossil fuels, especially natural gas, which can serve as a flexible and low-carbon backup for variable renewables. CCUS involves capturing the carbon dioxide (CO₂) emitted from power plants or industrial facilities, transporting it to a suitable location, and either utilising it for various products, such as chemicals, fuels, or building materials, or storing it permanently in geological formations, such as depleted oil and gas fields or saline aquifers.

Pipelines can play an essential role in the implementation of CCUS, by providing a safe and reliable way of transporting large volumes of CO₂ from capture sites to utilisation or storage sites. Pipelines can also enable the development of regional and international CCUS networks by connecting different sources and sinks of CO₂ and facilitating cross-border trade. However, pipelines need to be designed and operated to handle CO₂, as it has different physical and chemical properties than natural gas, such as higher density, higher corrosivity, and more complex operating phase envelope characteristics. This can be done by retrofitting existing natural gas pipelines, or by building new dedicated CO₂ pipelines, depending on the technical and economic feasibility.

For years, Saipem has played an active role in the development of technologies and solutions for the safe and reliable transportation of CO₂ via pipelines. This article will illustrate a couple of design cases, namely: a repurposing exercise applied to an existing sealine system to transport CO₂ offshore and conceptual studies for new on-land CO₂ pipeline transportation.

Repurposing existing sealines to CO₂ transport offshore: a case study

The design of offshore pipelines for CO₂ transportation is a relatively new topic, which requires specific knowledge and skills. The main aspects that differentiate CO₂ pipelines from conventional hydrocarbon pipelines are the following:

• The fluid properties and phase behaviour, which depend on the CO₂ composition, purity, temperature, and pressure. CO₂ can exist in gas, liquid, or supercritical state, with different densities, viscosities, and compressibility. Moreover, CO₂ can form solid hydrates under certain conditions, which can pose operational challenges and safety risks.
• The corrosion phenomena, which can affect the pipeline’s integrity and durability. CO₂ is a highly corrosive agent, especially when water is present in the stream. Therefore, the pipeline material selection, coating, cathodic protection, and corrosion inhibitors are crucial aspects to consider in the design and operation of CO₂ pipelines.
• The decompression behaviour, which influences the fracture propagation and arrest mechanisms. CO₂ undergoes a rapid pressure drop and temperature decrease during decompression, which can lead to brittle or ductile fracture initiation and propagation along the pipeline. The decompression behaviour depends on the fluid properties, the pipeline geometry, and the initial and final pressure and temperature.

The development of a case study for repurposing existing offshore pipelines to CO₂ transport, as part of a carbon capture and storage (CCS) project, needs to cover as minimum:

• The conceptual steps for the requalification of an existing pipeline system.
• The selection of design and operating conditions.
• The application of relevant standards and guidelines.
• The assessment of risks and environmental impacts.

A recent case study developed by Saipem involves two existing offshore platforms linked to shore by two 12 in. pipelines, which have already terminated their design life (Figure 2).1 The analysis considers a two-phase development process: Phase 1, where the existing pipeline is reused as much as possible to transport CO₂ in gas phase; and Phase 2, where the pipeline system is replaced to transport CO₂ in dense phase, due to the increase of reservoir pressure.

The main design challenges for repurposing the existing pipeline are the pressure containment and the running shear…

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Read the article online at: https://www.worldpipelines.com/special-reports/22042024/co2-systems-studies-and-solutions/