Onboard Carbon Capture Utilization And Storage

Shipboard carbon capture is a technology that has the potential to play a significant role in maritime decarbonization. However, as with other new technologies, its success will depend on a number of factors, including: technical advancements (to produce systems compatible with shipboard operations and available space); commercial feasibility (which will in turn be impacted by the availability and cost of alternative fuels, as well as the price of carbon); availability; and the regulatory landscape.

Onboard Carbon Capture

Onboard Carbon Capture Utilisation and Storage (“OCCUS”) could assist in reducing the environmental impact by capturing carbon dioxide (CO2) emissions from ships before they are released into the atmosphere with exhaust gas. The captured CO2 emissions are then liquefied and transported away and stored deep underground or turned into value-added products. Although this process has been used by other industries, it has not yet been widely adopted by the marine industry. This is due to the additional costs and space constraints that make it difficult to install the necessary equipment on board. However, technological developments and innovative design solutions could potentially overcome these challenges and make OCCUS a viable option for existing ships where conversion to zero-carbon fuels is cost-prohibitive and provides a route to extending the asset lifetime of these vessels.

Methods Of Capturing

Carbon capture technology has been around for decades and is primarily used by land-based establishments. Among the several potential carbon-capturing technologies, the most successful approach for ship-based carbon capture is the application of the post-combustion method. This procedure entails cleaning exhaust gasses before they are released, typically by installing equipment within or near the vessel exhaust stack.

The following measures are being considered by the shipping industry for post-combustion carbon capture. These can either be retrofitted on existing ships or integrated into new ship designs.

1. Chemical absorption – This involves wet scrubbing of exhaust gas followed by the use of an absorber unit in which the chemical solvent (e.g., monoethanolamine (MEA), aqueous ammonia, or water-soluble amines) removes CO2. This solvent is then sent through a desorber, which separates CO2 from the solvent while also recovering the solvent for reuse. Such systems may require careful chemical handling consideration, e.g., solvents that need periodic replenishment or replacement may have specific requirements for the quantities or availability of extra solvent, used chemical residue treatment, and discharge protocols.
2. Membrane separation – This process uses membranes as a physical filtration device to absorb contaminants such as CO2. Conventional membrane technology consists of filters suited to certain molecular sizes. Gaseous membrane CO2 filters are composed of a semi-permeable fabric that allows certain molecules to pass through while preventing others from doing so. The presence of additional gasses, such as NOx and SOx, as well as moisture, may reduce the effectiveness of these systems. Membrane filters may require frequent maintenance, treatment, or replacement.
3. Cryogenic capture – It involves cooling exhaust gas to very low temperatures, which causes the CO2 to condense into a liquid that can be stored onboard in cryogenic storage tanks until the ship reaches port. The extreme temperatures required for cryogenic carbon capture necessitate interaction with other systems on board to optimize the heat exchange process.
4. Solid sorbent adsorption – Sorbents can be used in dry scrubber systems to adsorb CO2 molecules from the exhaust gas. However, dry scrubbers are not commonly used in the marine industry, as wet scrubbers outperform them in terms of efficiency, cost, and maintenance requirements.

Ways Of Carbon Utilization

The economic viability and scalability of carbon utilization technologies can vary depending on factors like the availability of low-cost carbon capture methods, the market demand for the end products, and the energy required for conversion processes. Here are some common ways of carbon utilization:

• Oil and gas industry: The process of injecting CO2 into existing oil fields is a well-known “enhanced oil recovery” (EOR) technique – the addition of CO2 increases the overall pressure of an oil reservoir, forcing the oil towards production wells. The CO2 can also blend with the oil, improving its mobility and allowing it to flow more easily. Some have even gone so far as to argue that such technology could be used to make the full lifecycle emissions intensity of oil carbon-neutral or even carbon-negative.
• Synthetic fuels: Similarly, captured carbon can be combined with hydrogen, which might itself be produced in a carbon efficient manner, such as by electrolysis powered by renewable energy, to create synthetic fuels like e-methanol and sustainable aviation fuel as low-carbon or even net-zero fuels that could be used to reduce the carbon footprint of the shipping and aviation sectors respectively.
• Construction industry: Carbon capture can be integrated into the production of building materials, such as concrete and aggregates.
• Carbonated beverages: Captured CO2 can be used in providing fizz in carbonated drinks.
• Agriculture and aquaculture: Captured CO2 can be used in controlled environments to enhance plant growth in agriculture or provide a source of carbon for aquaculture operations, which can lead to increased crop yields and more efficient food production. Captured carbon can also be used in the fertilizer industry for manufacturing urea.
• Algae cultivation: The captured CO2 can be used to stimulate the growth of algae, and that could assist in counteracting climate change as it can absorb CO2 faster than any other biomass. Algae can be used for various purposes, including biofuel production, wastewater treatment, and as a source of protein in aquaculture.

Additional Capital

OCCUS is technically feasible, but it may require significant additional capital expenses and some compromise on cargo space. The system is energy-intensive and the annual operating costs for the ships will go up considerably depending on the amount of carbon they capture. The regulations and technologies are still developing but the various pilot projects should provide an opportunity to assess the technical feasibility and to help assess the economic feasibility. The UK Club is committed to supporting its Members in their transition to alternative fuels and technologies. Further guidance regarding the decarbonization of shipping can be found in the Club’s Decarbonisation Roadmap and in various other articles published on the Club’s website. 

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Source: Ukpandi

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