The Role of Onboard Carbon Capture in Maritime Decarbonization
Published — September 30, 2022
This report examines the role of onboard carbon capture (OCC) in decarbonizing the maritime industry using a series of case studies. The case studies analyze the impacts of full or partial application of OCC on container, bulk and tanker vessels using carbon-based fuels, as part of a newbuild or retrofit. The following executive summary provides a summary of the report highlights.
Onboard carbon capture (OCC) is being considered as a technology that will play a role in decarbonizing shipping, in combination with energy efficiency and alternative fuels. OCC can be applied to all carbon-containing fossil, electro, and biofuels and, as a result, could play a mid- to long-term role in maritime decarbonization. However, the applicability of OCC depends on several factors including OCC technology development, commercial viability, alternative fuel prices and availability, and future emission-related regulatory requirements.
To gain a better understanding of the role of OCC in maritime decarbonization and assess OCC’s business case for different vessel types and sizes, we analyzed the applicability of OCC to the largest shipping segments (container, bulk, and tanker), main carbon-based fuels and full and partial application as part of a retrofit or newbuild.
CO2
can be separated or captured both pre- and post-combustion. Pre-combustion capture uses reforming to separate gases into mainly hydrogen and CO2. This process is used when reforming carbon-containing fuels to hydrogen for onboard use in fuel cells. Post-combustion capture utilizes the exhaust gas to capture and store the CO2. There are several different exhaust gas (post-combustion) carbon capture technologies and CO2 storage types, which could be considered for onboard use. Preconditioning to increase CO2 concentration is needed for some carbon capture technologies. For this study, post-combustion liquid amine absorption with liquid CO2 storage was used. The full OCC system consists of a liquid amine absorption capture unit, liquefaction unit and storage tank (Figure 1).
We completed a series of case studies covering the installation of OCC on low sulfur fuel oil (LSFO)-, LNG- and methanol (MeOH)-fueled vessels within the three largest segments (container, bulk, and tanker). Figure 2 provides an overview of the vessel types and sizes considered and the associated fuel as well as if the study was focused on retrofitting an existing vessel or a newbuild design. While most of our studies focus on newbuild integration, the VLCC case study also includes a study of retrofitting a partial and full OCC system on an existing vessel. We did not consider integration of OCC on LNG bulk carriers due to significant cargo losses. As endurance and ship speed (propulsion energy) have a major impact on the ship’s arrangement, these were carefully defined before starting each case study. Next, we considered the required dimensions for CO2 storage tanks and their ideal location. Loss of cargo (volume and weight) when installing an OCC system was also an important consideration. In some cases, CO2 storage tanks must be installed in cargo holds, resulting in cargo loss. For this study, loss of cargo weight was calculated as the increase of lightweight due to the carbon capture system plus the weight of captured CO2 minus the weight of consumed fuel.
For a very large crude carrier (VLCC) newbuild, the best business case studied, CO2 abatement cost ranges from $220-290/tonCO2 with a tank-to-wake effective CO2 emission reduction of 74-78%. The VLCC’s endurance was based on a Persian Gulf (PG)-Japan round trip (13,400nm, 41days) at a speed of 14.5 knots. We assumed that CO2 would be discharged in PG for the VLCC case. Carbon reduction performance for the VLCC case is provided in Figure 3. For the LSFO fuel type, the OCC system increases CO2 emissions by 42% due to the additional energy demand. In case of LSFO version and maximum carbon capture, about 55% of the additional energy is required for electricity (for circulation pump, liquefaction, etc.) and another 45% for steam (for separation of CO2). With an 82% capture rate, the effective emission reduction compared to the base ship CO2 emissions is 74%, which is like the MeOH version at 75% effective emission reduction. The LNG-fueled version can achieve 78% effective emission reduction due to a lower baseline CO2 emissions and lower additional energy requirements.
Figure 4 shows the VLCC’s vessel arrangement and the major modifications areas in the machinery, casing and deckhouse areas. For the VLCC, there is no cargo volume loss, however, the lightweight increase leads to a deadweight decrease of 3-4% (2,800-3,600 tons). There is a small impact on the vessel’s bending moment that can be mitigated by adjusting loading conditions without strengthening the hull structure. As the CO2 storage tanks are placed on deck, the bridge height needs to be increased 4-5 meters.
Based on the case studies completed, we concluded that:
- OCC with chemical absorption is technically feasible and expected to reach commercial availability by 2030,
- Additional OCC energy requirements lead to higher total fuel consumption (up to a 45% increase),
- Potential application of OCC shows the most promise for newbuilds as retrofits are costly and can require major modifications,
- Partial carbon capture typically leads to higher CO2 abatement costs due to high initial CAPEX, and
- OCC on large tankers has the best business cases while small bulk carriers have the most challenges.
Although the emissions reduction potential of OCC is significant, currently its CO2 abatement costs are high. Still, with further development OCC could play a role in the mid-term to reduce the emission intensity of existing fossil-fueled vessels. Further analyses and developments are required to maximize OCC emission reduction and minimize costs, as well as developing business models that would allow utilization and/or storage of the carbon captured onboard vessels. As a continuation of this work, the MMMCZCS has initiated an onboard carbon capture working group to study additional OCC technologies, applications, and business models.
Although OCC technologies are still in development, they will be commercially available soon and can provide significant emission reductions. As a result, ship owners aiming to decarbonize should assess their mid-term emission reduction targets and consider including OCC if it is an option for their vessel types, sizes, and trades.