Shipping is more than 80% of global trade volume, and with that, more than 3% of global greenhouse gas emissions. Emissions from shipping can create air pollution near coasts and ports, all leading to an examination of alternative fuels that could reduce the negative impact of trade. The Paris Agreement has also put some pressure on the shipping industry to reduce SOx (sulfur oxide), NOx (nitrogen oxide), and PM (particulate matter). The reductions possible depend on the type of fuel being used and the entire chain around creating, transporting, and burning each fuel. According to DNV, “On a technical level, the introduction of alternative fuels will be accompanied by additional complexity, in the areas of fuel supply infrastructure, rules for safe use of fuels on board, and operation of new systems.” The ease of creation and availability of these fuels means a global standard may not emerge and different low emissions and renewable fuels may be used in different areas of the world.
LNG powered Bit Viking. Image from Marine Insight.
Why do we need alternative fuels?
The global merchant fleet uses a lot of fuel, about 330 million tons each year. With 80%+ of this fuel being high sulfur content; new regulations seek to lower this number to reduce greenhouse gas emissions (GHG). Alternative fuels started in the 1920s when a process was created to convert solid fuel sources like coal, biomass, or natural gas into liquid fuels. It was then used heavily during World War II and during the oil embargo in South Africa in the 1970s and 1980s. In the 80s and 90s concern started to grow regarding the emissions of automobiles, reigniting interest in alternative fuels.
The list of alternative fuels for shipping is fairly long, including:
Methanol
Liquified Petroleum Gas (LPG)
Ethanol
Dimethyl Ether (DME)
Biogas
These fuels easily comply with sulfur regulations as they are mostly sulfur-free. Some of them can even be used in conjunction with oil-based marine fuels, especially in dual-fuel engines. The impact on total emissions is highly dependent on the mix of fuels used. It’s easy to measure emissions at the ship, but a more complete measure is the lifecycle of the fuel from creation to use. This is where fuels like biofuel need to be examined in the amount of land and water they use, as well as the energy used in transporting and burning them. According to DNV, this is done via a Life Cycle Assessment (LCA) that gives a comparison of the energy value chain and the total impact compared to conventional fuels. In the context of marine fuels, the lifecycle assessment is the Well-To-Propeller Analysis.
What are the alternative fuels?
LNG eliminates SOx, reduces NOx and particulate matter greatly, and lowers GHG. It is the cleanest fossil fuel and a proven solution and is already in use on many new vessels. Methane slip is almost eliminated with newer 2-stroke engines, with 4-stroke engines performing even better. Shale gas has added more possibilities for LNG as well, and it is being used by more and more ships. Potential downsides: It does not reduce the level of CO2 emissions required to address climate change and the bunkering grid also needs to develop further to make this fuel source more widely available. LNG is a fast-growing solution to lower emissions with conventionally built vessels. The PERFECt - Piston Engine Room Free Efficient Containership - concept is one of the designs for a new mega box ship, powered by LNG.
PERFECt containership concept. Image from Safety4Sea.
Electrification has many benefits in vessels such as reduced noise, less vibration, and power redundancy. Many new vessels are moving to a hybrid format where they use conventional fuels supplemented with a hybrid system. These systems save fuel and can provide complete battery power for short durations such as in ports and sometimes even for stationkeeping during offshore activities. If renewables and nuclear are used to produce the electricity, this method is very low emissions. The main issue with this tech is energy storage regarding safety and amount of power stored. Batteries don’t have enough storage capacity for long journeys, and there have been some incidents with battery failures and fires. Small vessels such as ferries and tugs are already going fully electric, since they can recharge frequently. Technologies like thermal energy storage, supercapacitors, and flywheels could provide a good storage solution for larger vessels
According to DNV: “Biofuels can be derived from three primary sources: edible crops, non-edible crops (waste, or crops harvested on marginal land) and algae, which can grow on water and does not compete with food production.” Biofuels made from organic materials biodegrade quickly, which makes them safer if released into the environment through a spill. They can be easily mixed with other fuels in standard combustion engines and biogas from waste can replace LNG. They also provide a big reduction in GHG emissions. Some of the challenges with biofuels is the space required to produce the volume of fuel needed. Algae may be the most efficient biofuel base, since it consumes large amounts of CO2 during growth, but more research into the specific strains are needed. Problems with corrosion of current storage methods needs to be examined as well for long-term use.
Biofuels image from DNV.
One of the biggest benefits of hydrogen is that renewable electricity can be used to produce it, then it can be used to power fuel cells. Hydrogen molecules are small and light, giving them a great energy-to-weight ratio for storage. Energy density is low however, and it requires 6-7 times more space than heavy fuel oil. Liquid hydrogen requires temperatures below -253 degrees Celsius, creating its own problems of efficiency in insulation and keeping temperatures low. Fuel cells are most commonly used for hydrogen, but investment costs can be high, storage requirements are an issue, and safety has to be maintained. Land-based fuel cells are doing well, and costs will likely fall as hydrogen becomes more widely used.
Other liquid or gas fuels
With dual-fuel engines, other fuels can be used such as Liquefied Petroleum Gas (LPG), methanol, ethanol, or di-methyl ether (DME). These fuels are sulfur-free and have significant reductions in other emissions. Limited availability of these fuels is the only hold-up, although they could be used locally where available. Right now they are not common for shipping.
Nuclear power is already used for large Navy vessels like aircraft carriers and submarines, as well as large Russian ice breakers operating in the Arctic. Nuclear material can be uranium, plutonium, or thorium. After the creation and transportation of the fuel to the vessel, there are no greenhouse gases emitted. Thorium can also provide advantages over uranium and plutonium, the conventional nuclear fuels. Thorium is more readily available, has better efficiency, and reduced waste. According to DNV: “Thorium oxide can be mixed with 10% plutonium oxide, which also offers a way to recycle plutonium.” The main impediments to nuclear adoption are public perception and cost. Nuclear accidents are few and far between, but have a large negative impact on how nuclear power is viewed. Costs of running nuclear reactors can also be quite high, although recent efforts seek to bring those costs down. Nuclear could be a big win for shipping, as a container ship could install a nuclear power plant and never need to refuel. Small nuclear reactors are starting to be considered for commercial shipping vessels.
“The nuclear-powered aircraft carrier USS Enterprise. REUTERS/U.S. Navy/Mass Communication Specialist Seaman Harry Andrew D. Gordon/Handout”. Image from Business Insider.
Well to Propeller
As mentioned earlier, DNV’s research went beyond the emissions from using fuels to the entire energy chain. In the chart below, the green bars are the tank-to-propeller emissions, meaning the emissions produced from using the fuel for transport. The blue bars are the well-to-tank, meaning the emissions and energy used to get the fuel to the vessel. You can see from the results below that current infrastructure and fuel creation can heavily impact the total emissions of a fuel. The absolute lowest emissions fuel is renewable liquified hydrogen, which comes with its own challenges of safety and storage. Nuclear power is also very low, but public perception and safety are top concerns. This mix will continue to change with advances in technology and changes in infrastructure that may support different fuels.
Image from DNV.
Future
The adoption of a new energy source takes time as technology develops and infrastructure is built to support it. Fuel usage will grow at different rates depending on location and availability. Alternatives like LNG and hybrid battery technologies are already being implemented in new ships and in retrofits. New technologies for energy storage are also emerging and could have a drastic effect on the fuels used above. Wind is being added to new and existing vessels, but in many cases isn’t enough to fully power large ships. We will likely see a mixture of these fuels, including a slow adoption of small scale nuclear in shipping in the near future as the world reduces emissions.
With this reduction in fuel emissions, it is important to mention the cost of building new ships. Retrofitting and upgrading current vessels is a great way to get more life out of the steel and energy that has been put into building vessels. When deciding whether to scrap an old ship to build a new one or retrofit a new power plant into an existing vessel, the energy use of creating the materials as well as the time and energy that goes into the build has to be calculated. Most models don’t take into the account the energy it takes to build a new vessel, when retrofitting an old one could save a lot of steelmaking and building costs. We look forward to continuing to see new fuel technology develop in the maritime industry. We’ll be here to test those systems for safety and efficiency!
Happy Friday!
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