Carbon Capture Could Be the Next Offshore Trend

Quaim Choudhury is a senior managing principal engineer with ABS.

Carbon capture and storage (CCS) technology has been around for longer than many people think.

During the 1920s, CO₂ scrubbers were used to remove impurities from methane to make it a commercially viable product. This early CCS technology has stood the test of time and now provides the first step in modern carbon capture processes.

CCS took off in the 1970s when it was known as EOR. CO₂ captured from oil and gas production was reused by injecting it into depleted oil and gas reservoirs to re-pressurize them, enabling the extraction of more hydrocarbons.

As climate change and sustainability priorities have gained momentum, the process was rebranded as carbon capture and storage (CCS) and carbon capture, utilization and storage (CCUS). Despite the name change, most CCS projects are in EOR.

However, there is sizable potential for CCS and CCUS technologies to play an important role in meeting global emissions reduction targets. This is because they enable the mitigation of CO₂ emissions from large output generation industrial sites such as power plants and refineries. In addition, the technologies can remove existing CO₂ from the atmosphere.

There are several methods of CCS. Most new technologies and improvements center around three systems—post-combustion, pre-combustion and oxy-fuel combustion.

Post-combustion capture separates CO₂ from combustion flue gas. Chemical absorption using amine-based solvents is the most technologically mature CO₂ separation technique for power plants. This is also the technique most applicable to the marine and offshore sectors at present.

In the pre-combustion method, the fuel is processed with steam and/or oxygen to produce a gaseous mixture of carbon monoxide and hydrogen, known as syngas. Syngas is free of contaminants such as particulates, sulfur, ammonia, chlorides, mercury and other trace metals, and possibly carbon, depending on the source fuel and processes. Syngas can be a low-carbon or even a carbon-free substitute for fossil fuels. It is combustible and can be used as a fuel in gas turbines and internal combustion engines.

Finally, oxy-fuel combustion capture uses nearly pure oxygen (using air separation units) instead of air to combust fuel. This results in a flue gas composed of CO₂ and water vapor, and dehydrating the flue gas generates a high-purity CO₂ stream. This process reduces the carbon release in the atmosphere and is recognized as one of the solutions for decarbonization.

CCS and the offshore sector

How far down the track is the offshore industry with CCS?

There is growing interest regarding the use of CCS on oil and gas platforms and FPSO units, but key challenges remain around offshore storage in deepwater environments because of constraints caused by water pressure. These facilities often use large gas turbines that produce emissions around the clock, presenting a strong argument for some kind of CCS solution.

The key challenges include space, weight and power limitations, although the extent of the type of CCS system to be fitted will depend on the platform or site in question. Arguably, the most significant obstacle centers around how to remove captured CO₂. Offshore installations are stationary and require infrastructure for offloading via pipeline, or ships to transport it to appropriate reception facilities at a port or other offshore hub for sequestration.

Conversations are taking place about using captured CO₂ to synthesize methanol for platforms that produce e-fuels, a class of synthetic fuels in gas or liquid form made by synthesizing captured CO₂ and hydrogen produced from renewable power sources such as solar and wind power.

The most feasible scenario is a combined plant which processes water for generating hydrogen and can be used for other e-fuels such as ammonia. Offshore platforms already process chemicals and store various substances, so it is not a huge change to make this part of a processing facility subject to the same usual constraints on space, weight and power.

There is no one-size-fits-all CCS solution, especially for offshore applications. Any of the potential pathways could be suited for a particular project depending on the economics and technical aspects, and we have seen activity across several types of systems. Indeed, there have been encouraging results in several post-combustion concepts like amine absorption and CO₂ liquefaction, as well as chemical processes which produce calcium carbonate solids. Precombustion reactors are also in various stages of study, and some are very close to being adopted.

CCS onboard vessels—will it happen?

There is a lot of R&D taking place, especially around leveraging amine-based post-combustion techniques and adapting what has been used for land-based industries such as power generation and refining. Transfer of these land-based technologies onboard ships can be a way to remove CO₂ emissions from the exhaust of hydrocarbon fuel burning equipment. For existing ships, this will reduce vessel-specific CO₂ emissions and improve the Carbon Intensity Indicator (CII).

However, there are limitations and various challenges to installing these systems onboard existing ships such as: space constraints, additional power requirements, mitigation of risks affecting people on board, the structural strength and integrity of the vessel. Currently, some lower capacity systems (20% to 30% carbon capture) are installed onboard ships as pilot projects but it will take time for them to get to maturity.

The key issue is scale. Ships have more constraints than offshore platforms, and there are complex issues such as weight and center of gravity to consider. Likewise, ships already have onboard systems for applications such as electricity and water capacity. Indeed, CCS systems will use energy, which also needs to be considered—if a higher capacity CCS is installed then proportionately more of everything is needed.  

To overcome some of these issues, alternative CCS technologies to amine absorption are being evaluated, including membrane systems and processes that use chemicals to produce solid outputs. However, they are still very nascent concepts compared to amine-based processes, with very few systems installed on vessels or on land.

It is not just the practicalities of the vessel that need to be considered. Port infrastructure is another key challenge, as captured material, in whatever state, needs to be unloaded. Potential solutions include modularized offtakes in the form of containers which can be unloaded onto land. Facilities accommodating this idea could spring up in green ports and corridors initially, but these hubs are not likely to become mainstream assets in the near future.

As a part of global decarbonization efforts, ABS is actively engaged in work on vessel-based CCS systems. Several approvals in principle for vessel designs submitted by shipyards/designers in Asia and Europe have been completed, including amine-based designs and other types of CCS processes. Additionally, ABS has worked with other vendors to pilot technologies onboard ships, carrying out small-scale tests to analyze concepts and feasibility.  

There is a lot of interesting CCS work going on both offshore platforms and vessels. As the industry accelerates its efforts to decarbonize and transition to a net-zero future, it will be intriguing to see the extent to which carbon capture and storage plays a role.