The Rising Tide: Carriage of Liquified Carbon Dioxide.

High tide for Liquified Carbon Dioxide (LCO2) transportation.

Transportation of carbon dioxide via gas carriers is not a recent phenomenon. However, it is reaching its breakout point. So why was carbon dioxide being transported earlier and what triggered a sudden rise in the carriage demand of carbon dioxide? Let us explore in this blog and understand a few carriage aspects of carbon dioxide.

Carbon dioxide today is being transported mainly for below reasons –

1. For the food and beverages industry, where it is used for carbonation in soft drinks, beer, and sparkling water.
2. It is also used in industrial processes such as chemical production, fire suppression systems, and as a solvent in certain applications.

The reason that triggered the up move.

In recent times, a strong need to reduce greenhouse gas (GHG) emissions and mitigate climate change has triggered a high need for transporting captured carbon to its storage units. Gas carriers are the preferred mode for transportation of carbon dioxide in its liquified state (LCO2). Gas carriers are specifically designed and equipped to safely transport CO2 from emission sources to storage sites. Another reason why ships are considered apt is because they can carry large amounts over long distances to suitable storage sites, which are usually underground deep ocean reservoirs.

Properties of carbon dioxide.

Carbon dioxide (CO2) is a colourless, odourless gas with several important properties: 

1. Toxicity: CO2 is not flammable but a toxic product, however, the toxicity is much lower than other toxic cargoes listed in IGC code chapter 19.

2. Density: CO2 is denser than air, which means it can settle into low-lying areas undetected. 

3. Triple Point: CO2 has a triple point, which is the temperature and pressure at which the solid, liquid, and vapor phases of a substance can coexist in equilibrium. 

 4. Impurities: CO2 may contain impurities, such as water, sulfur oxides, nitrous oxides, and hydrogen sulfide, which can affect its physical properties and require consideration in the design and operation of transportation systems.

5. Pressurization: When CO2 is introduced into a pipeline or tank, it has to be pressurized with vapor to the correct pressure to prevent reaching the minimum design temperature or dry ice formation. 

The responsibility for analyzing the physical and chemical properties of CO2 cargo lies with the shipper, as the ship does not have the equipment or expertise for this task.

Some key terms:

1.Solid CO2: Also known as dry ice, is the solid form of carbon dioxide. It has a greater density than liquid CO2 and if it forms in a tank, it tends to accumulate at the bottom of the tank. The formation of solid CO2 can occur if there is a loss of pressure in the piping or cargo tank. 

Precautions for handling solid CO2 include: 

a. Pressure management: It is important to manage the pressure in the CO2 piping and cargo tanks to prevent the formation of solid CO2.

b. Clear procedures: There should be clear step-by-step information on what steps to take in the event of solid CO2 formation in tanks and piping. This critical information should also form part of regular drills and training for the ship crew.

c. Mitigation measures: If solid CO2 forms, caution should be exercised when attempting to pressurize or heat the tank to mitigate this issue, as the combination of low temperature and higher pressure may exceed the design limits of the cargo tank. 

2. Triple Point: The triple point is the temperature and pressure at which a substance can coexist in the solid, liquid, and vapor phases in equilibrium. 

image: Phase diagram of CO2

The triple point for CO2 is -56.6 C at pressure 517 Kpa. This implies that CO2 can only exist as a solid or vapor at atmospheric pressure. Further, if LCO2 is released at a pressure lower than 517 Kpa it will become a mixture of solid and vapour. The possible temperature conditions for LCO2 transportation are between its tripe point (-56C) and critical point (31.1C).

What are the precautions seafarers should consider for carriage of LCO2?

When transporting liquified carbon dioxide (LCO2) cargo on gas carriers, several key safety considerations must be taken into account to ensure the safe and reliable operation of the vessels. Some of these considerations include:

The International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code) provides requirements for the design, construction, and operation of gas carriers carrying liquefied gases, including CO2.

1. Design Philosophy: The design should minimize the probability of significant events, such as uncontrolled depressurization resulting in the formation of dry ice in tanks and pipelines. Care should be taken to understand the effect of impurities that may be present in CO2 cargoes.

2. Material Selection: Material selection for CO2 carriage should consider possible corrosion due to impurities such as water, sulfur oxides, nitrous oxides, and hydrogen sulfide. 

3. Carriage Temperature and Pressure: The selection of carriage temperature and pressure should prevent the solidification of CO2, and all credible scenarios that can arise due to crew error or equipment malfunction. 

4. Operational Considerations: Critical information on the physical and chemical properties of the CO2 cargo should be provided to all relevant stakeholders, including the ship, terminals, and receivers. 

Training considerations for seafarers.

The training requirements for carrying carbon dioxide (CO2) as a cargo include the following considerations: 

1. Structured classroom training: Crew members should undergo structured classroom training to educate them on the specific hazards of CO2 operations. This training should cover safety, contingency planning, routine operations, dry ice formation, and management, and concerns regarding impurities and mitigation measures. 

2. Equipment-specific training: Due to the novel design and equipment used for CO2 operations, consideration should be given to providing equipment-specific training to the crew.

3. Simulator training: Simulator training for cargo operations should be carried out to ensure that the crew is well-prepared to handle CO2 cargo operations effectively and safely. 

These training requirements are essential for ensuring that the crew members are adequately prepared to handle the unique hazards and operational aspects associated with carrying CO2 as cargo on gas carriers.

Conclusions

The recent surge in CO2 carriage demand, propelled by CCS initiatives clearly demands education and training initiatives for seafarers as well. Collaborative efforts between industry stakeholders, along with guidelines provided by SIGTTO, IGC code, etc are essential in upholding safety standards. By embracing these challenges and opportunities, the maritime sector can play a vital role in mitigating climate change and fostering a greener, more resilient planet for generations to come.