Rajan Wilcox
Ocean super freighters are massive cargo ships that can carry thousands of containers. These ships are powered by massive marine diesel engines that can consume fuel not by the gallons but by tons per hour. These engines are extremely powerful and can take huge amounts of fuel per stroke. While the exact amount of diesel fuel burned by an ocean super freighter is unclear, it is evident that these ships are major contributors to air pollution. Research has shown that in a year, a single large container ship can emit pollutants equivalent to that of 50 million cars.
| Characteristics | Values |
|---|---|
| Amount of diesel fuel burned by ocean super freighters per year | 370 million tons |
| Amount of sulphur oxide emitted by ocean super freighters per year | 20 million tons |
| Number of cars that emit the same amount of sulphur oxide as ocean super freighters per year | 760 million |
| Number of premature deaths caused by emissions from ocean-going ship engines per year | 60,000 |
| Amount of sulphur in bunker fuel compared to diesel fuel | Up to 2000 times more |
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What You'll Learn
Marine diesel engines and their fuel efficiency
Marine diesel engines are a type of internal combustion engine that relies on the ignition of diesel fuel due to the elevated temperature of the air in the cylinder caused by mechanical compression. They are commonly used in ships and other applications where the overall weight of the engine is less important. Marine diesel engines come in varying speeds and types, including low-speed, medium-speed, and high-speed engines, as well as two-stroke and four-stroke variants.
The fuel efficiency of marine diesel engines depends on several factors, including engine speed, engine load, and engine type. The specific fuel consumption (SFC) of marine engines typically ranges between 155 and 225 g/kWh on optimal load settings, which are usually around 85% of the Maximum Continuous Load (MCR). SFC increases significantly at low power (30% Pmax) and dramatically when the engine is idling (7% Pmax), with a potential doubling of fuel consumption. Idling engines also face issues such as stalling, clogging, and increased maintenance requirements.
To improve fuel efficiency and reduce emissions, various strategies have been explored. One approach is to use a trigeneration system that employs the waste heat of the marine diesel engine for hydrogen extraction, electricity generation, and cooling. Another method involves the addition of fusel oil to diesel fuel, which reduces NOX and CO2 emissions but increases particulate matter, CO, and HC emissions. Optimising engine load based on the second law of thermodynamics can also balance environmental concerns and engine efficiency.
The type of engine used also impacts fuel efficiency. Low-speed two-stroke diesel engines, commonly used in large ships, can achieve efficiencies of up to 55%. Medium-speed four-stroke diesel engines, on the other hand, are suitable for military use and medium-sized boats, offering power outputs in the single-digit Megawatt range. These engines can be started with compressed air acting directly on the pistons or through pneumatic starting motors.
While marine diesel engines have higher thermal efficiency than other combustion engines, they contribute significantly to air pollution. The global fleet of 90,000 cargo ships burning approximately 370 million tons of fuel per year emits 20 million tons of Sulphur Oxides (SOx), equivalent to 260 times the SOx emissions from the world's cars. To address this issue, organisations like the IMO have implemented regulations to reduce sulphur content in marine fuel and enforce fuel reduction targets.
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Sulphur emissions and pollution
In 2020, the International Maritime Organization (IMO) imposed strict limits on the sulphur content of marine fuels to reduce air pollution from shipping. The new rules lowered the maximum percentage of sulphur in marine fuels from 3.5% to 0.5% for all ships operating worldwide. This regulation has had some success in improving public health, with global emissions of sulphur dioxide (SO2) – a health-damaging air pollutant – dropping by about 10% as a result.
However, the shift to low-sulphur shipping fuel has had unintended consequences. Sulphur particles in ships' exhaust fumes have been counteracting some of the warming effects of greenhouse gases. Lowering the sulphur content of marine fuel has weakened this masking effect, effectively contributing to warming. Studies estimate that the 2020 regulations to cut air pollution from shipping may increase global temperatures by around 0.05°C by 2050, equivalent to approximately two additional years of emissions.
The reduction in sulphur content in ship fuel has also led to the increased use of scrubbers, which are exhaust gas cleaning systems that treat pollution before dumping it into the sea. While this reduces atmospheric sulphur oxide emissions, it diverts sulphur emissions from the air to the ocean, causing water pollution. Researchers have found that the guidelines for assessing the environmental risk of scrubber discharge are inadequate, resulting in the release of water containing multiple pollutants that endanger marine life.
The complex interplay between sulphur emissions and pollution has sparked debates about the nuanced approaches needed to address the issue. Some argue that stricter sulphur regulations should be imposed near shore, where the health impacts of emissions are more significant. At the same time, ships could be allowed to burn cheaper sulphur-containing fuel in the middle of the ocean to maintain a cooling effect and prevent sudden temperature increases.
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Bunker fuel and its effects
Bunker fuel, also known as bunker crude, is any type of fuel oil used aboard water vessels. The name originates from the age of steam ships, when the coal used to fuel vessels was stored in coal bunkers onboard. Bunker fuel is the main fuel for marine vessels, and powers the world's shipping fleet, helping convey 90% of traded goods across the world's oceans.
Bunker fuel is part of a broader family of fuels known as fuel oils. Fuel oils are various fractions obtained from the distillation of petroleum (crude oil). Fuel oils can be divided into distillates (lighter fractions) and residues (heavier fractions). Distillate fuel oils are produced by conventional distillation only and are cleaner-burning. Residual fuel oils are denser, with a density approaching that of seawater.
Bunker fuel is refined and blended to a set specification, which is currently ISO 8217:2017. This standard sets out the requirements for both marine distillate and marine residual fuels, stipulating the tests that should be carried out to determine whether a sample meets those requirements. Tests for residual fuel include kinematic viscosity, density, sulphur content, flash point, carbon residue, pour point, water, ash, and Total Sediment Potential (TSP).
The use of bunker fuel has been linked to harmful environmental and health impacts. Bunker fuel is a major contributor to shipping emissions, which have been linked to sickness and premature deaths in coastal residents near busy shipping lanes. Shipping emissions contain high levels of sulfur and sulfur oxides, which cause asthma and cancer. Bunker fuel is also implicated in oil spills, which can have devastating effects on marine ecosystems, including the total collapse of existing benthic communities. Oil spills are often the result of human error or technological failure, but they can also be caused by neglect or the intentional violation of international conventions.
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LNG power and its dangers
Ocean super freighters, along with the world's 90,000 cargo ships, burn approximately 370 million tons of low-grade bunker fuel annually. This fuel contains up to 2,000 times more sulfur than diesel fuel used in automobiles, emitting pollutants that cause cancer and asthma. The pollution emitted by 15 of the largest ships is equivalent to that produced by the world's 760 million cars.
Liquefied Natural Gas (LNG) is being considered as an alternative power source in the shipping industry. LNG is natural gas, typically methane, that has been cooled to -259 degrees Fahrenheit, turning it into a liquid. LNG is used as a vehicle fuel for some heavy-duty trucks, buses, and ships. It is also used as a backup fuel in power plants.
However, LNG has its dangers. LNG is highly energy-intensive to produce, transport, and regasify, resulting in a larger carbon footprint than ordinary gas. LNG is also a methane-based fuel, and leaks during production and transportation can release significant amounts of methane, a potent greenhouse gas.
Despite these concerns, LNG is seen as a step towards cleaner energy. It is argued that LNG can serve as a transition fuel on the path to a sustainable future. LNG infrastructure can be adapted for zero-carbon fuels, and LNG can be blended with renewable gases. Additionally, LNG projects are attractive to investors, with well-structured projects drawing interest from commercial banks, development finance institutions, and export credit agencies.
In summary, while LNG may offer some benefits over traditional bunker fuels, it is not without its dangers. The high energy intensity and potential for methane leaks contribute to climate change. However, with proper regulations and infrastructure, LNG could play a role in the transition to a greener energy mix.
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Shipping emissions and regulation
The shipping industry is a major source of carbon emissions, accounting for about 3% of global carbon emissions. The burning of fossil fuels by the world's 90,000 cargo ships emits approximately 20 million tons of Sulphur Oxides (SOx) annually. This is equivalent to 260 times more SOx emitted by ships than by the world's entire car fleet. In addition, up to 60,000 premature deaths per year are attributed to particulate matter emissions from ship engines.
To address these environmental concerns, the International Maritime Organization (IMO) has been working to reduce greenhouse gas emissions from the maritime transportation business. In 2018, the IMO agreed to reduce GHG emissions by at least 50% by 2050 compared to 2008 levels, with carbon intensity reduction targets for 2030 and 2050. The IMO has also implemented Operational GHG standards, which mandate that ships reduce their operational carbon intensity. These standards allow for a flexible compliance strategy while gradually tightening GHG reduction requirements.
In addition to the IMO, the European Commission has also taken steps to reduce emissions from the shipping sector. For example, the EU MRV Regulation requires all ship operators of vessels over 5,000 GT calling at EU ports to conduct independent carbon emissions verification. This regulation includes analyzing the ship operator's emission data collection, comparing it with ship-tracking satellite data, and reporting the results. The European Commission has also published several implementing acts and regulations, such as the Commission Implementing Regulation (EU) 2023/2449, which lays down rules for monitoring plans, emissions reports, and compliance documents.
Furthermore, industry players across the shipping sector have initiated their own initiatives to promote shipping decarbonization strategies. For instance, Cargo Owners for Zero Emission Vessels (CoZEV) brings together several international companies, including Amazon, with the goal of using only zero-carbon ocean freight transport by 2040.
While these regulations and initiatives are a step in the right direction, the high cost of low- and zero-emission fuels compared to fossil fuels remains a challenge. However, market-based measures such as carbon taxes or emission permits can help incentivize investment in alternative fuel supply chains and vessels.
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Frequently asked questions
Ocean superfreighters burn approximately 370 million tons of fuel per year.
One large ship can generate approximately 5,200 tonnes of sulphur oxide pollution in a year.
An ocean superfreighter can burn 500,000 gallons of fuel per trip.
