Posted on May 23, 2022
Driven by an ambitious IMO decarbonization strategy and calls from the European Parliament and European Commission to reduce global emissions from shipping, the maritime industry is facing the prospect of transitioning from a century-old fuel source between now and 2050.
The path from heavy fuel oil (HFO) to a zero-emissions future is likely to have several stops along the way, starting with LNG through a more environmentally friendly alternative in bio-LNG and synthetic LNG to untried but promising alternatives in hydrogen, methanol and ammonia.
In a recent report, “LNG as a Marine Fuel,” engineering and consultancy firm Ocean Dynamex explained that LNG is a prominent alternative until a more viable option is discovered. LNG transportation infrastructure and relevant facilities have been operating for decades, and there’s an established expertise. In recent years, major shipping hubs such as Singapore, Shanghai, Rotterdam and Houston (among others) have established LNG bunkering facilities to meet the accelerating demand.
“I value the practicality and technical soundness of LNG solutions,” says Okan Duru, Director of Research at Ocean Dynamex. “Marine engines are huge, and an enormous amount of energy is needed. The energy source must be capable of supplying such power. This requires that the energy source must have well-to-tank superiority. Production of an alternative fuel must not cause an additional environmental footprint.”
Duru is clear, however, that LNG is a bridging solution although it’s the only viable mid-fuel in terms of engineering, technique and economy. There are more than 100,000 cargo ships in the world, most of which are above 10,000 dwt and need significant kW power. “LNG is not a perfect solution,” he adds. “It does not promise ‘net’ zero emission yet. The recycling of natural sources of methane may reduce the environmental footprint, but it will take time.”
LNG is predominantly methane (CH4), which is the simplest possible combination of carbon and hydrogen. With only one carbon atom per molecule, methane’s combustion in air produces the lowest emissions of greenhouse gas (GHG) and carbon dioxide (CO2) of any hydrocarbon fuel. In addition, the combustion of LNG produces very low emissions of particulate matter (PM) and virtually no sulfur oxides (SOx). Commercially available LNG is sulfur-free.
At the same time, lean-burn combustion technology is already widely used in large gas engines employing the Otto combustion process. It has the valuable benefits of enabling fuel-efficient combustion combined with low emissions of nitrogen oxides (NOx), in compliance with strict international limits, without exhaust gas aftertreatment. Additionally, LNG used to power gas and dual-fuel engines has the potential to lower CO2 emissions by up to 25 per cent compared to oil-fueled engines.
“These properties of methane are already allowing gas-burning Otto engines to meet the most important international limits on polluting emissions in both marine and land-based applications,” notes Gunnar Stiesch, Head of Engineering at MAN Energy Solutions. “Fueling engines with methane also offers immediate potential as a starting point for meeting ambitious targets for reductions in GHG emissions.”
This scenario has kick-started growth in demand for the large two- and four-stroke dual-fuel engines designed and built by MAN Energy Solutions. Significantly, in this shift to gas-burning engines, MAN and others see the opportunity for global shipping to undergo a “maritime energy transition.”
“Following conversion from liquid fossil fuels to gaseous fuels,” Stiesch explains, “a road-map for marine engines envisages the mixing of LNG with increasing proportions of synthetic gaseous fuels on the way to 100 per cent synthetic fuels and, hence, carbon-neutrality. Powering ships and providing on-board electrical power is a major application for MAN’s engines, and LNG is becoming increasingly popular as their fuel.”
However, the use of LNG does not come without its challenges. Typically, from 85 to 95 percent of natural gas and LNG is CH4, a GHG several times more potent than CO2. Without countermeasures, there are several routes by which methane can escape unburnt into the atmosphere from both two- and four-stroke gas-burning engines.
“This methane that evades combustion and is emitted via the engine exhaust as well as the crankcase ventilation is referred to as ‘methane slip,’” Stiesch continues. “With legislators’ eyes now firmly on GHG, this aspect of gas engine operation has moved into focus and, if not properly addressed, could severely limit the expansion of LNG as fuel for large engines.”
The phenomenon is most prevalent on gas-burning engines operating according to the Otto combustion process where gas fuel and air are mixed homogenously prior to ignition and combustion. It affects engines in which the premixed fuel and air are ignited by a spark-plug – so called spark-ignited (SI) gas engines − as well as dual-fuel (DF) engines where a liquid fuel pilot initiates ignition of the air-gas mixture.
“In our two-stroke engine program, we’re already offering a very effective solution to minimize methane slip,” Stiesch explains. “ME-GI two-stroke DF engines are achieving extremely low levels of unburnt methane emission due to operation on the diesel combustion principle.”
On the four-stroke side, MAN has been addressing methane slip ever since it introduced DF engines in the mid-2000s and can already point to considerable success. For example, since the launch of the four-stroke MAN 51/60 DF engine, countermeasures have more than halved methane slip, giving this engine type a five to 15 per cent advantage over liquid fuel engines in terms of GHG emissions.
Going forward, MAN’s technical department sees three promising routes to lower methane slip.
First, ongoing improvements to internal engine design and electronic controls will further increase combustion efficiency and thus fuel efficiency. Second, newly developed aftertreatment solutions, namely oxidation catalysts, have the potential to reduce methane slip by up to 70 percent. And third, MAN engineers are evaluating ways to apply the technology of direct gas injection, as used on MAN’s two-stroke DF engine, to its four-stroke DF engines. This will potentially reduce methane slip by greater than 90 percent.
“With these countermeasures,” Stiesch concludes, “MAN is confident that methane slip will not become a barrier to either the expansion of the market for gas-burning engines or the progression of the maritime energy transition.”
If LNG is to be utilized across existing fleets, it’s crucial that the cost of retrofitting be reduced substantially. Given that the average life of a cargo ship is around 30 years, this is a problem that needs urgent attention if emission targets are to be met.
Marine Service GmbH and Newport Shipping believe they have developed an approach that will be simpler for the refit, requiring less time and cost while being easier to operate. The companies report they have identified up to 900 in-service container ships with a capacity of 4,000 TEUs and above that would be best suited for the conversion.
Their concept consists of LNG cylinders containerized in open frames the same size as existing 40-foot containers. Since LNG containers are portable, the exact number of containers can be easily optimized according to the owner’s requirements. Simple and easy to install on board when a ship is in port, the empty containers can be taken out and replaced by new, filled ones.
“When both time and scale are put into perspective,” says Ingmar Loges, Managing Director of Newport Shipping, “LNG is the most practical choice of fuel for the current generation of fleet to meet the IMO decarbonization target. The main reason for this is it’s been used for decades as a fuel and the supply chain and infrastructure are well established.”
In the retrofit, the LNG containers would be stacked on deck like current container stacks, handled in the same process and loaded and unloaded with container cranes. LNG piping and venting systems along with firefighting systems would be integrated into the container cell guides’ structure. The gas-handling room would be arranged adjacent to the container storage and separated from the containers by a cofferdam and fire protection, allowing it to feed low-pressure and high-pressure fuel gas systems suited to the current 4-stroke and 2-stroke dual-fuel engines.
“We can provide a comprehensive solution with Class-approved design, technical execution and financing support,” Loges adds. “The total turnaround time is around 14 months. The vessel can continue normal trading during the planning and design stage before entering the yard for finishing the retrofit. Our solution is more cost-competitive and time-efficient when compared to a traditional retrofit solution.”
Ammonia to the Rescue?
At the recent Asia Pacific Maritime conference held at Marina Bay Sands, Singapore, the final day’s program included a panel on decarbonization. There was much talk about the role LNG would play and whether it is in fact the fuel of choice to meet the industry’s decarbonization goal of eliminating half of all GHG emissions by 2050 compared to 2008 levels.
Dr. Sanjay Kuttan, Chief Technology Officer at the Global Centre for Maritime Decarbonization (GCMD) in Singapore, detailed how the Singapore Centre will coordinate regional and global decarbonization efforts strategically in the world’s largest maritime fueling hub and second-largest container port. In January, GCMD began its 13-month ammonia bunkering safety study to pave the way for ammonia bunkering trials in Singapore.
Kuttan believes LNG should be phased out over the next 20 years as there is a faster need to transition to a low or zero-carbon fuel such as ammonia. “Chemically, ammonia consists of three hydrogen atoms and one nitrogen atom (NH3), so there is no carbon molecule,” he says. “Therefore, unlike fossil fuels, there are no CO2 emissions when combusted. However, lifecycle analysis is still needed to compare practical against environmental needs.”
However, as Ocean Dynamex’s Duru points out, ammonia is a poisonous matter: “You first convert LNG to hydrogen, then hydrogen to ammonia. Transport and storage of ammonia and hydrogen are much more complicated and technically sophisticated than LNG. In shipowners’ shoes, you would not want to keep these fuels on board your ships until a better, safer, easier and economically viable method is developed.”
Dr. Shahrin Osman, Director of the Maritime Decarbonization & Autonomy Centre at DNV, understands that interchangeability of fuels such as LNG, NH3, H2 and other green biofuels are going to bridge the gap from HFO to LNG to zero-carbon. “It’s all based on a supply and demand equation,” he states. “Addressing demand, engine manufacturers such as MAN plan to burn ammonia by 2024/26.”
DNV’s role in the bunkering study addresses supply. To support IMO’s stated goals, Osman believes that decarbonization, digitalization and the democratization or free distribution of information is required. “Industry must also focus on reducing consumption of fuels,” he concludes. “The importance of data extraction and automation supports that.”
London-based Mark Venables is a freelance technical writer making his first appearance in the magazine.