AMF #13 - Onboard Carbon Capture System (OCCS): A Technical Review
Muammer Akturk
Advancing a Greener Future: Specializing in Alternative Fuels, Decarbonization, and Gas Carriers
1. Introduction to the Challenge of Maritime Emissions and Decarbonization Goals
The shipping industry faces a significant challenge as stricter MARPOL regulations come into effect, coupled with upcoming measures to achieve future climate targets. This challenge will become increasingly complex as we approach 2050 targets. While clean energy technologies are technically viable alternatives to fossil fuels, they must become commercially accessible and globally available.
The transition to green technologies will involve a period where different options coexist. This is unavoidable due to the interdependence of fuel supply, distribution, and demand, as well as the time required for ships and bunkering infrastructure to adapt to globally available new technologies. This coexistence should be embraced to avoid penalizing early adopters and preventing others from wasting valuable time in choosing the right path.
Given this scenario, it's crucial to assess and potentially incorporate transition-facilitating technologies into the IMO regulatory framework. These technologies should contribute to achieving climate targets, and any new requirements should be universally applicable, avoiding preferential treatment of specific technologies and preventing the use of others.
1.1. Onboard Carbon Capture (OCCS) as a Decarbonization Strategy
Carbon Capture, Utilization and Storage (CCUS) is a technology already in use across various industries, including oil & gas, cement production, and power generation. Statistics from the Global CCS Institute show a significant increase in CCUS projects between 2010 and 2020 (60 projects) compared to the previous decade. This indicates steady global growth in CCUS, with ongoing research and development happening in Europe, America, and China.
There's positive news regarding the growth of CCUS projects. As of July 2023, there's a record number of projects in development (392 projects). New facilities are constantly being built and put into operation (11 new facilities operational and 15 under construction since 2022 report). The capture capacity of these projects has also seen significant growth (48% increase since 2022 report).
Implementing OCCS on ships offers several advantages:
Despite these benefits, the positive impact of OCCS on reducing emissions (projected to be 100 to 400 million tons per year in 2030 and 3 billion to 6.8 billion tons per year in 2050 according to the Intersessional Panel on Climate Change (IPCC) Special Report on Global Warming of 1.5°C) isn't currently factored into the IMO's framework for reducing ship emissions (EEDI/EEXI/CII). This needs to be addressed to incentivize the use of OCCS technology.
2. OCCS Technology Overview
There are two main approaches to capturing CO2 onboard ships: pre-combustion and post-combustion.
a)??? Chemical absorption is a prime example of a heat-driven approach. Here, chemical solvents in the capture unit absorb CO2 from the exhaust stream. Then, the solvent is heated to release the captured CO2 in a highly purified form. This method is advantageous for ships because the waste heat from the engine exhaust can be directly used to power the capture process.
b)??? Membrane separation offers a compact and electricity-driven alternative with moderate energy consumption. However, its energy efficiency suffers when aiming for very high CO2 capture rates, limiting its applicability in certain scenarios.
c)??? Calcium looping is another technology in the early stages of exploration for ships, with some pilot projects already conducted (reference 5.3.c). This material-driven process employs calcium oxide to capture CO2, generating a considerable amount of heat in the process. As a result, the operational energy cost of the capture unit might be minimal. However, challenges remain for its shipboard application, including the high operating temperatures, the large volume required to store the solid calcium oxide, and the additional cost of onshore sorbent regeneration.
d)??? Cryogenic capture utilizes extremely low temperatures to solidify CO2 from the exhaust gas, requiring significant energy input. This approach is still under early development.
Chemical Absorption: Widely Used Option
Among post-combustion capture methods, liquid amine absorption with liquid CO2 storage is a popular option with numerous designs based on this concept. A complete OCC system using this approach typically consists of three main components (as shown in Figure 3):
Solvent Selection: Finding the Right Option
Traditional land-based power plants often employ solvent-based carbon capture. The feed gas, or flue gas, enters a solvent wash column under specific temperature and pressure settings. To be effective, a suitable solvent need to possess several key characteristics:
Due to these desired properties, the industry standard solvent is typically amine-based. Examples include aqueous solutions of:
The captured CO2 dissolves in the solvent within the column. Steam, generated by reboiling liquid from the desorption column, then strips the CO2 from the solvent. Finally, the captured CO2 is compressed, cooled, and stored as a liquid. However, the reboiling process for solvent regeneration requires additional energy, which can be a drawback for shipboard applications.
2.1. CO2 Classification and Storage on Board Ships
Legal Status of Captured CO2:
The legal classification of CO2 captured on ships depends on its stage in the process and destination. Here are some possibilities:
Transporting Captured CO2:
Moving captured CO2 from the capture site to storage requires specialized ships. The International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code) governs the transport of carbon dioxide. Chapter 19 of the Code lists two applicable entries: "Carbon Dioxide (high purity)" and "Carbon Dioxide (reclaimed quality)".
Both entries require a type 3G ship, which is the simplest gas carrier designed for products needing "moderate preventive measures to preclude their escape" (Chapter 19, IGC Code).
Gas carriers are the best candidates to be the first vessels equipped with carbon capture technology, as they already have systems for safely handling and managing captured CO2. IMO regulations or Class rules will need to address specific requirements for ships with onboard carbon capture.
Ensuring Environmental Integrity:
Environmental safeguards for onboard CO2 capture systems should match those used in land-based industries to ensure captured CO2 isn't released into the atmosphere.
Ships using onboard CO2 capture to comply with regulations could develop and maintain an approved CO2 management plan. This plan should detail safe handling procedures for captured CO2, aligning with international environmental regulations and standards to prevent atmospheric release.
Captured CO2 will eventually be discharged at a CO2 terminal for storage or utilization. The transfer quantity ideally be documented through a receipt or certificate from the terminal operator and recorded in a designated log, such as a CO2 record book.
All those items should be considered by IMO as part of regulatory development for OCCS.
3. Regulatory Overview
LCO2 cannot be directly dumped into the sea due to its potential to evaporate into the air unless it remains in the form of dry ice. This aligns with Article 195 of the United Nations Convention on the Law of the Sea (UNCLOS), which prohibits the transformation of one type of pollution into another. The relevant excerpt is provided below:
"In taking measures to prevent, reduce and control pollution of the marine environment, States shall act so as not to transfer, directly or indirectly, damage or hazards from one area to another or transform one type of pollution into another."
Consequently, LCO2 storage tanks within the OCCS must be appropriately sized, based on calculations, to hold LCO2 until it can be transferred to a suitable reception facility.? ?
3.1.?London Protocol & London Convention for the Geological Storage of Carbon Dioxide
Captured carbon dioxide offloaded for storage or at any CO2 receiving facility for onward geological storage must comply with the London Protocol.
The London Protocol's primary objective is safeguarding the marine environment from all pollution sources by prohibiting unregulated waste dumping. Annex 1 of the Protocol lists materials considered permissible for ocean dumping with a permit. A 2006 amendment included carbon dioxide in Annex 1, allowing its storage under the seabed (Resolution LP.1(1)). To comply with Annex 1, paragraph 1.8, the exported material must be "carbon dioxide streams from carbon dioxide capture processes for sequestration." Additionally, per Annex 1, paragraph 4, disposal must occur in a sub-seabed geological formation.
While primarily aimed at preventing waste export to non-Parties, Article 6 of the London Protocol also prohibits the transboundary transfer of carbon dioxide for geological storage. However, an amendment to Article 6 (Resolution LP-3(4)) adopted in 2009 allows exporting carbon dioxide for storage in sub-seabed geological formations.
Since the Article 6 amendment hasn't been ratified by enough Contracting Parties, a temporary solution was established (Resolution LP.5(14)). This allows for the provisional application of the 2009 amendment by Contracting Parties who have deposited a declaration for its provisional application, pending its formal entry into force.
As per Article 6, paragraph 2, exporting carbon dioxide for geological storage requires an agreement between the involved countries. This agreement must confirm and allocate permitting responsibilities between the exporting and receiving countries, consistent with the Protocol and other applicable international law.
Article 9 outlines permit issuance and reporting obligations. Paragraph 2 specifies that a Contracting Party is responsible for issuing a permit when a CO2 stream is loaded in its territory or when a vessel registered in its territory loads a CO2 stream in a non-Contracting Party's territory for export to other countries for sub-seabed geological disposal.
During several IMO meetings it was also stated that the application of Articles 6 and 9 for delivering captured shipboard CO2 for permanent storage requires clarification.
Guidelines (2012 Specific Guidelines for the assessment of carbon dioxide for disposal into sub-seabed geological formations (LC 34/15, annex 8)) have been developed for the activity allowed under the amended Article 6. One aspect addressed in the guidelines is a specific characterization of the carbon dioxide stream, including any associated incidental substances. This characterization should include, as appropriate: origin, amount, form, composition, physical and chemical properties, toxicity, persistence, and bioaccumulation potential. The guidelines further state that "if the carbon dioxide stream is so poorly characterized that proper assessment cannot be made of the risks of potential impacts on human health and the environment, that carbon dioxide stream shall not be dumped."
Regarding the CO2 stream characterization, different geological storage locations have their own specifications for the accepted CO2 purity. For ships using carbon capture technology, it's crucial to consider how the CO2 delivered to a CO2 terminal or reception facility can be characterized. This could be done during carbon capture technology certification, followed by annual CO2 analysis once added into the regulatory framework by IMO.
3.2.?EU ETS Requirements and Understanding of Carbon Capture Usage
The EU Emissions Trading System (EU ETS) Directive addresses Carbon Capture, Utilization, and Storage (CCUS) technologies through specific provisions. Companies are exempt from surrendering allowances for:
3.3. ISO Standard Development
ISO/TC 265, focused on Carbon Dioxide Capture, Transportation, and Geological Storage (CCUS), has published 10 ISO standards. These documents provide review and recommendations for various aspects of CCUS, including:
3.4.?IMO Regulations and Progress for OCCS
Prior to the implementation of regulations for onboard carbon capture technology, maritime Administrations may need to grant exemptions to facilitate trials of these systems.
Regulation 3 of MARPOL Annex VI addresses exceptions and exemptions, with paragraph 2 specifically allowing for "Trials for ship emission reduction and control technology research." This regulation permits Administrations to grant exemptions from specific Annex VI provisions for ships conducting trials on emission reduction and control technologies, including engine design programs.
Ships testing carbon capture systems might require exemptions from:
Onboard carbon capture systems necessitate additional fuel for operation, potentially causing ships to exceed applicable design indexes, which could qualify as a major conversion. This would also result in a higher annual CII compared to regular operation without the system.
Currently, no guidelines exist for applying Regulation 3.2. The granting of such exemptions falls entirely under the discretion of the relevant Administration. A more standardized approach to granting these exemptions would be beneficial and to enhance transparency regarding Regulation 3.2 application, submitting notifications on relevant exemptions to the Organization might be appropriate.
The duration of sea trials, and consequently the exemption permit under Regulation 3.2, is subject to provisions that vary based on the per-cylinder displacement volume of the marine diesel engine. The Committee may consider amending this approach in the future.
4. Permanent Storage, Utilization, and Transport of CO2
Once captured and transported to land, CO2 finds application in numerous industrial sectors. Globally, an estimated 230 million tonnes (Mt) of CO2 are utilized annually. The fertilizer industry is the primary consumer, utilizing 130 Mt of CO2 in urea production. The oil and gas sector follows closely, consuming 70 to 80 Mt of CO2 for enhanced oil recovery. Food and beverage production, metal fabrication, cooling, fire suppression, and greenhouse plant growth stimulation are additional commercial applications. Notably, the carbon in CO2 can facilitate converting hydrogen into a more manageable and usable fuel, such as aviation fuel. Furthermore, CO2-cured concrete offers potential cost reductions and improved performance compared to conventional concrete production.
4.1 Utilization of CO2
CO2 is a vital input material for numerous industries. Global demand for CO2 currently sits around 230 Mt annually, with the fertilizer industry alone consuming 125 Mt per year as a raw material for urea production. Oil and gas producers utilize approximately 70-80 Mt per year for enhanced oil recovery (EOR). CO2 also plays a role in food and beverage production, cooling, water treatment, and agriculture, though the demand in these sectors is comparatively smaller. Processing requirements for the CO2 stream vary depending on the intended use. For instance, CO2 suitable for EOR or other industrial applications might not be appropriate for food and beverage production. These varying uses also impact transportation requirements due to purity specifications. Emerging opportunities include CO2 utilization and fuel production for methane and methanol, potentially forming a future energy chain.
4.2 Permanent Storage/Injection into Wells
For many years, the oil and gas industry has injected CO2 during hydrocarbon production as an Enhanced Oil Recovery (EOR) method to increase well yield. A similar application exists for enhanced coal bed methane (ECBM) recovery. However, the long-term goal is to store CO2 deep underground as a dedicated process, separate from associated production activities.
Long-term CO2 storage is achieved through injection into naturally occurring porous rock formations, such as depleted oil or gas reservoirs, coal beds, or saline aquifers. Depleted reservoirs and non-extractable coal beds around the world hold potential for storage, provided the geological formations meet the necessary criteria. Deep saline aquifers are also considered suitable locations for long-term CO2 storage.
Geological sequestration of CO2 utilizes the substance in a supercritical fluid state, meaning it exists above its critical temperature and pressure on the phase diagram.
Evaluating a proposed storage location is crucial. This assessment ensures the site has adequate capacity for the planned CO2 volume, the formations can absorb CO2 at the desired injection rate, and the stored material remains permanently underground over the long term, without migrating into surrounding soil, groundwater, or the atmosphere. Migration can occur naturally or through abandoned wells, faults, and fractures. Key parameters for evaluation include depth (influencing pressure), salinity, temperature, and the porosity and permeability of the storage reservoir rock, along with geophysical features like faults.
Several mechanisms contribute to retaining injected CO2. Physical barriers to migration, such as domes, faults, or variations in rock type and permeability, trap CO2 within the formation. Additionally, the CO2 becomes trapped within voids in the rock material, like water held in a sponge. Over time, stored CO2 may interact chemically with minerals to form a solid or dissolve into the formation's saltwater and settle downward. Estimates suggest that over 98% of the injected CO2 will be permanently sequestered and unable to escape the injection site.
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For offshore injection activities, existing oil and gas platforms and facilities (fixed or floating) can be repurposed for CO2 injection, whether for EOR or storage. In the storage scenario, additional considerations include powering and operating the facility (both operating expenses - OPEX and capital expenditures - CAPEX). This might involve new or upgraded equipment, potential life extension for the structure and mooring system (if floating), and injection risers. These costs come on top of expenses incurred for plugging and abandoning depleted wells. Infrastructure reuse may not be feasible if it wasn't originally designed and constructed for CO2 injection service due to differences in fluid pressure, temperature, and necessary material properties. These properties are crucial to prevent potential corrosion, pitting, or cracking, as previously mentioned.
A good example to the above approach is the Norwegian government’s full-scale CCS project called "Longship." This project captures CO2 from two industrial sites near Oslo and transports the liquefied CO2 to an onshore terminal on Norway's west coast. From there, a pipeline carries the CO2 to a permanent subsea storage location in the North Sea. "Northern Lights" is a component of the Longship project responsible for CO2 transport and storage. Its objective is to develop a cross-border, open-source CO2 transport and storage infrastructure network. This network would accommodate CO2 transport by ships from relevant capture sites across Europe to a CO2 receiving terminal in Norway for intermediate storage before final, permanent storage in the North Sea.
5. Technical Considerations for OCCS on Ships
5.1 Review of Current Status and Maturity Level of OCCS Technology
A study by MMMCZCS suggests that amine-based absorption OCC systems are expected to achieve Technology Readiness Level (TRL) 9 by 2028-2030 (Figure 4). While onboard capture technology has been tested on vessels, a fully integrated system including onboard liquefaction and storage hasn't been demonstrated in the marine environment. However, ongoing liquefied CO2 carrier projects incorporating onboard liquefaction and storage are expected to showcase these onboard technologies by 2025. The need for exhaust cleaning before carbon capture is identified as a potential challenge for heavy fuel oil use and would necessitate development based on existing technologies.
Traditional solvent-based carbon capture commonly used in land-based power plants involves feeding the flue gas into a solvent wash column at specific temperature and pressure. Ideal solvent properties include high thermodynamic capacity, fast absorption rate, low regeneration energy, minimal degradation, low volatility, and low corrosivity. Amine-based solvents, such as aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), methyl diethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP), and blended amine AMP and piperazine, are preferred in industry due to these desirable characteristics. Dissolved CO2 is then stripped from the solvent in a column using steam. This steam is generated by reboiling liquid from the desorption column, followed by compression and cooling for storage as a liquid. However, re-boiling the liquid requires additional energy, posing a challenge for onboard ship applications.
Alternative Solvent-Based Systems: To address the drawbacks of tall columns with high capital and operating costs, significant energy demands, and intercooling needs, alternative approaches utilize improved gas-liquid reactors employing new principles and technologies for CO2 capture. One such technology is the Rotating Packed Bed (RPB). This system resembles a spinning donut that utilizes centrifugal force to promote micro-mixing and enhance mass transfer, exceeding the capabilities of gravity-driven conventional static absorption columns. The RPB's compact size allows for lower construction costs compared to traditional fixed-bed reactors, which require substantial packed volume. Pilot plants have shown promise for the RPB's potential to minimize both operating and capital expenses for CO2 capture compared to conventional columns.
Low-Temperature CO2 Capture: Low-temperature CO2 capture technology, currently under development (TRL 5/6 based on Sustainable Energy Solutions (IEAGHG, 2019)), involves cooling the flue gas to separate CO2 in liquid or solid form. Hybrid solutions also exist, where a membrane step pre-concentrates CO2 before flue gas cooling. Membrane separation offers advantages due to its compact size, low environmental impact, ease of scaling, minimal moving parts, and operational simplicity. Hybrid capture systems like Hybrid Membrane Cryogenic (HMC) and Low-Temperature Membrane Cryogenic (LTMC) combine the benefits of membrane and cryogenic techniques.
The provided Figure 5 highlights the global TRL status of CCS technologies. This information highlights the potential for adopting CO2 circular economy processes in the shipping sector. Further Life-Cycle Analysis of the process, considering both technological and economic aspects, is crucial for successful implementation.
5.2 Risks Associated with Onboard OCCS Installations
Several exhaust gas (post-combustion) carbon capture technologies and CO2 storage options are being considered for onboard use. Liquid amine absorption with liquid CO2 storage is one of the more prevalent technologies with existing designs available. A full onboard carbon capture system (OCCS) typically comprises a liquid amine absorption capture unit, a liquefaction unit, and a storage tank.
Despite advancements in carbon capture technology development, significant risks need to be mitigated before widespread commercial adoption onboard ships. The key challenges include:
Table 1 provides an overview of the main risks associated with onboard OCCS and potential mitigation measures that can contribute to advancing the development of this technology for ships.
Table 1: Main Risks and Mitigation Measures for OCCS (Source: MMMCZCS)
5.3 System Integration Onboard
Compared to onshore facilities, installing CCS technology on ships presents a more complex challenge due to several specific requirements such as limited space, crew safety considerations, accelerated material degradation in a marine environment, vibrations, constant motion, and accelerations.
Integrating onboard carbon capture systems (OCCS) with the existing machinery system can significantly impact a ship's overall performance and operations. Therefore, a thorough evaluation of key parameters is crucial for successful integration.
To determine the most suitable onboard CO2 capture technology, a comprehensive analysis considering all critical elements is necessary. These elements include:
Impact on Different Vessel Types:
Tankers: Tankers are generally less affected by OCC system installations. CO2 storage tanks can be placed on deck, minimizing impact on cargo capacity. To minimize the impact on longitudinal strength, two tanks can be positioned at the forward part of the deck depending on the size and configuration. However, this placement may necessitates raising the navigation bridge from its original design to meet visibility requirements. CO2 tanks can also increase the maximum longitudinal bending moment of a vessel by 5-10%. Depending on the strength margin of the original design, hull reinforcement or operational limitations may be necessary. In a conventional fuel VLCC case, the total CO2 tank capacity is typically around 10,000 cubic meters.
Bulk Carriers: Integrating OCCS onboard bulk carriers presents the greatest challenges due to space constraints, especially when considering additional space requirements for alternative fuel installations.
Container Vessels: Large container vessels rely heavily on the availability of suitable CO2 receiving facilities at ports they visit. This directly impacts on the required tank capacities onboard. For longer voyages without onshore CO2 discharge capabilities, larger tanks can be considered. However, this approach leads to a significant increase in hull girder shear force and potential stability issues due to the increased CO2 storage requirements. These factors necessitate detailed evaluations.
Overall, tankers offer the easiest integration due to the ability to place CO2 tanks on deck with minimal impact on cargo capacity. Bulk carriers and container vessels present more significant integration challenges that can lead to substantial cargo loss. Ship integration and cost considerations become more prominent for smaller vessels, making larger tankers the most commercially viable option for OCCS implementation.
In the context of OCCS applications, various levels of preparation and conversion serve as milestones in the process of retrofitting or constructing vessels with carbon capture technologies. These levels represent a step-by-step approach, progressing from initial planning and space allocation to full integration of capture units, liquefaction systems, and associated infrastructure into the vessel's design. Each level signifies an advancement in readiness, with increasing complexity and capability for effective onboard capture and management of carbon emissions. A typical example of these levels is presented in Table 2.
Table 2: OCCS Leveling Concept for Installation & Preparation?
5.4 Impact on Ship Design and Performance (Space Requirements, Weight, Energy Consumption)
Impact on LCO2 Tank Location and Regulations, Packaged vs. Bulk Storage:
The classification and regulations for LCO2 storage depend on its form: packaged (e.g., freight containers) or bulk.
Bulk Storage (IGC Code): If LCO2 is stored in bulk, the International Gas Carrier (IGC) Code applies. Chapter 19 of the IGC Code specifies that CO2 must be carried in a Type 3G ship. Paragraph 2.4.1.4 of the IGC Code outlines the minimum safe location for cargo tanks in Type 3G ships, requiring a distance from the bottom centerline and outer shell as specified. Additionally, paragraph 2.4.4 prohibits LCO2 tank placement forward of the collision bulkhead.
Packaged Storage (IMDG Code): When CO2 is carried in packaged forms, it's classified as a dangerous good under the IMDG Code (Chapter 3.2). While Section 7.1.3.2 allows storage on both weather and under decks, the IMDG Code lacks detailed provisions for safe stowage locations of packaged CO2.
Summary of Applicable Regulations:
Table 3 summarizes damage stability requirements for different ship types based on subdivision location. However, these requirements might not address the specific safety concerns regarding the protective distance of LCO2 storage tanks from external damage, except in cases covered by the IGC Code.
Table 3: Damage Stability Requirement Summary
Table 4 summarizes the key points from paragraphs 2.4.1.4 and 2.4.4 of the IGC Code concerning the safe location of LCO2 storage tanks in bulk.
Table 4: Protective Distances per IGC Code
Table 5 summarizes the classification of CO2 as a dangerous good under the IMDG Code.
Table 5: IMDG Code Classification of CO2
LCO2 storage tanks need to be sized appropriately to hold captured CO2 until it can be transferred to a reception facility. Their placement can significantly impact a ship's intact and damage stability. Existing regulations in SOLAS, the International Code on Intact Stability (IS Code), and others might address LCO2 storage from a stability perspective; however, it may not be entirely clear which provisions are most applicable for determining the safest location for these tanks to ensure protection from external damage.
Table 6: CO2 Calculation on a 20MW Engine Vessel with LNG Fuel
Safety Considerations of CO2 Storage Onboard Ships:
Density and State Transitions: Due to its higher density than air, leaked CO2 can accumulate in low-lying confined spaces, posing a safety risk. CO2's critical point (73.8 bar and 31°C) and triple point (5.2 bar and -57°C) allow it to transition between solid, liquid, and gas states relatively easily based on environmental changes. Additionally, LCO2 boils at -78.5°C, and during vaporization, it can reach temperatures as low as -83°C (liquid CO2 release temperature).
Classification and Toxicity: While the IMDG Code classifies CO2 as a non-flammable and non-toxic gas transported in packaged forms, some countries consider it a toxic substance (e.g., China, Japan, UK, US, EU). These countries often have similar threshold values for CO2 toxicity. However, the current IGC Code focuses on asphyxiation hazards and the triple point rather than CO2 toxicity, outlining safety requirements based on these considerations (refer to Table 8 for details).
Table 7: Minimum Requirements for CO2 (High Purity)
SIGTTO proposed to amend IGC Code for the classification of "Carbon dioxide (high purity)" and "Carbon dioxide (reclaimed quality)" to include "toxic" in addition to "asphyxiant" and this proposal has not been finalized yet.
Chemical Risks: Capturing CO2 from exhaust gases involves a chemical solvent that selectively absorbs CO2 through chemical reactions. A liquefaction facility using a refrigerant is also required to convert captured CO2 gas into a liquid state. If these solvents or refrigerants have asphyxiating, toxic, or flammable properties, they may pose safety risks to the crew and the vessel. Table 9 provides examples of exposure limits for CO2 designated as a toxic product in some countries.
Table 8: CO2 Exposure Limits (Concentration in Volume)
Unregulated Tank Location and Potential Consequences: While captured LCO2 from onboard CCS can be considered a type of waste, MARPOL Annex VI lacks specific regulations regarding the safe location of storage tanks containing LCO2 emissions from ships. This lack of regulation could lead to unsafe situations or catastrophic casualties if external damage occurs from a collision or grounding.
6. Conclusion
Onboard carbon capture systems (OCCS) are emerging as a promising technology to address the maritime industry's significant contribution to greenhouse gas emissions. However, successful implementation requires overcoming unique challenges associated with the marine environment and complex shipboard operations.
Benefits:
Reduced CO2 Emissions: OCCS directly captures CO2 from ship exhaust, mitigating climate change impact.
Enhanced Environmental Performance: By lowering a ship's carbon footprint and potentially improving its CII rating, OCCS contributes to a cleaner maritime environment.
Reduced Emission-Related Costs: Effective OCCS performance can minimize costs associated with emission regulations like EU ETS, FuelEU, and future IMO GHG pricing mechanisms.
Compliance with Regulations: OCCS equips ships to comply with increasingly stringent emission regulations set by IMO on the path to 2050 targets.
Challenges:
Technical Challenges: Limited space, safety concerns, material degradation from constant exposure to seawater, vibrations, and ship motion necessitate specialized technologies and robust system design.
Integration Challenges: Integrating OCCS with existing ship systems can impact performance and operations, requiring careful engineering and operational adjustments.
Selection Challenges: Choosing the optimal OCCS technology involves a comprehensive analysis of factors like space availability, weight limitations, desired capture rate, economic feasibility, and technological maturity.
Operational Challenges: Additional energy consumption, potential fuel consumption increase due to system operation, and the need for additional wastewater treatment systems (if applicable) necessitate careful operational considerations.
Infrastructure Challenges: The widespread adoption of OCCS hinges on the availability of port infrastructure for CO2 storage or utilization within the carbon value chain.
The Role of OCCS in Achieving Maritime Sustainability
OCCS plays a critical role in the maritime industry's transition towards a sustainable future. By capturing CO2 emissions, OCCS directly reduces the industry's environmental footprint and mitigates climate change and can help ships comply with stricter emission related regulations.
Studies have highlighted the significant challenges associated with OCCS implementation, including high capital and operational expenditures, increased fuel consumption, and space constraints for system integration and CO2 storage.
However, research into innovative technologies and optimized system designs is ongoing. Collaboration between stakeholders, including shipbuilders, technology developers, and regulatory bodies, is critical to address these challenges. Strategic investments in port infrastructure for CO2 storage or utilization are also essential to create a supportive ecosystem for OCCS adoption.
OCCS can stand as a viable technology contributing to a more sustainable future for the maritime industry by reducing its historical contribution to CO2 emissions if difficulties and challenges can be solved.
Disclaimer: The opinions and views expressed in this article are solely those of the author and do not necessarily reflect the official position or policies of ABS. This article is not endorsed by ABS and should not be construed as an official communication from the company. While the author is an employee of ABS, this article is written in a personal capacity and does not represent ABS in any official manner. The content provided herein is for informational purposes only and should not be interpreted as professional or legal advice from ABS.
Marine Engineer | 10+ Years of Marine Engineering Experience | Specialist in Vessel Operations, Maintenance, Dry-Docking | 2nd Engineer of Tankers & Chemical Carriers | Cost Optimisation | Regulatory Compliance
6 个月Thanks Muammer for sharing this insightful article.
Senior Manager Fleet Performance , Incharge of Retrofits and Upgrades
6 个月Insightful Article covering all aspects of CCUS. Clear utilization pathway and firmed up regulations would unleash true potential of OCCS in maritime decarbonization. IMO WG and CG are working in this direction to drafting regulatory frameworks for OCCS following MEPC 81 outcomes. In addition, power optimization, a large footprint with the use of SOx scrubbers, amine slip, and crew safety are a few of the technical challenges to a retrofit solution.
Marine & Industrial Services (ELECTROTECHN?CAL AND ELECTROMECHAN?CAL)
6 个月Hello Their information is like a light for us. Well, while IMO is looking for a solution to the maritime traffic and passage priority problem, do you think the issue of carbon emissions will provide an additional advantage? I wonder if there are any studies on this subject?
KOTC- Team Leader fleet engineering - CEng. ?????? ?????
6 个月Insightful! Content-- well done ... ??. With current CII rating criteria and challenges that ship owners are facingi. I Believe its time that for IMO to step forward and revise CII calculation method ... and not to consider idle time --- long anchorage and long port stays ... as these factors beyond ship owners control and regardless how much you do .. you wont be able to plan or how much fuel vessel should use/consume !!
C.Eng Marine/ M.Eng Naval Architecture and Marine Engineering/ B.Eng Mechanical
6 个月Thanks for sharing. Great insight.