Uzmar pilot Mustafa Sokukcu reviews the options for tug owners to reduce emissions using alternative fuels and energy storage solutions.
Concerns for shipping industry
Lowering fuel consumption and greenhouse gas (GHG) emissions from the shipping industry has emerged as one of the most dominant concerns of the maritime sector, driving interest in developing alternative fuels and green propulsion technologies, which have pros and cons compared to diesel fuels.
The main alternative fuels include methanol, ammonia, hydrogen, LNG and biofuels, and technologies like electric energy, batteries, fuel cells and hybrid/dual-fuel systems. Although the alternatives are cleaner and promise lower emissions than diesel (MGO) fuels, there are many uncertainties when using them in tugboats, including suitability, availability, useability and cost.
Methanol
Methanol is a significant alternative since it may be supplied and stored on a tugboat, and its energy density is similar to diesel fuels. But its flash point is low, so even a small amount of flammable material can cause a fire.
Ammonia
Ammonia is an alternative in terms of compliance with emissions, but it has disadvantages such as a lack of infrastructure, not being easily accessible, and not being tested at sufficient levels.
Hydrogen
Hydrogen is difficult and risky to store on a tugboat for safety reasons. Its flammability and explosivity are high and it requires very large volumes of storage. Other disadvantages are the lack of trials with this fuel and undeveloped production technologies.
Supplying hydrogen to the tugboat is a difficult, lengthy operation. It must be cooled in its liquid form to -253˚C, or highly pressurised, increasing maintenance costs on fuel pipes and equipment in the medium and long term. It is not currently considered possible to use due to the high volumes requiring storage on the tugboat and the complex cooling system requirements to keep it in liquid form.
LNG
Liquefied natural gas (LNG) is a fossil fuel with no sulphur, low NOx emissions and less CO2 than MGO. It is already used on tugs, and engine technology and infrastructure is available for newbuilds and retrofits.
HVO
Hydrotreated vegetable oil (HVO) biofuel is one of the most important alternatives to diesel fuels, especially for tugboats. It has 99.9% biofuel content and promises zero emissions in terms of well-tank-wake emissions.
These fuels can be combusted in engines or generators, or could be used with fuel cells, which have attracted great attention recently with their advantages, such as having a higher energy density compared to batteries and taking up less space on the tugboat. Engine manufacturers are conducting research on fuel cells that can operate with different fuels, and among these, hydrogen appears to be the most important option.
There are projects based on the principle of obtaining hydrogen by processing methanol or ammonia and producing hydrogen from seawater through electrolysis using electricity from renewable resources.
Fuel cells are not being fully assimilated yet and standards are limited. Storing hydrogen on the tugboat is challenging and the cost of installing fuel cells is high compared to other alternative fuels.
Batteries
Batteries are one of the most important alternatives for zero emissions and are increasingly used in tugboats. The necessary infrastructure and technology requirements have also been determined.
Factors such as charging the batteries too many times and how low the charge level is before charging can play a role in extending the life of the batteries. Another important point is whether the battery modules have safe management systems.
Furthermore, when replacing a battery, it is critical to consider if the appropriate battery is readily available or compatible with other battery types. The safety precautions and storage conditions required by batteries on the tugboat are other negative aspects.
Batteries pose a fire risk, and battery fires take a long time to extinguish. Sparks and fire may occur due to seawater leaking into the battery compartment, so they must be insulated and watertight.
There should be no leaks from the condensation circuits of the cooling system onto the batteries and no seawater ingress through the ventilation gaps, while their high voltage poses a danger to the crew. Other disadvantages are charging infrastructure in ports is insufficient and electricity is still not green.
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Source : Riviera
Looking forward to your next post. Keep up the good work!