An international regulatory body is set to finalize decarbonization guidelines for about 50,000 commercial vessels across the world later this month, but liquefied natural gas (LNG) ship owners are not waiting to upgrade their fleets.

LNG carrier owners are already searching for ways to comply with the coming International Maritime Organization (IMO) decarbonization rules, which take effect in 2023. The IMO’s decarbonization strategy requires a 40% reduction over 2008 levels in carbon dioxide (CO2) emissions from the shipping industry by 2030 and a 70% reduction in 2050. 

Finnish technology group Wärtsillä Corp., a major supplier of equipment for LNG carriers, has seen an “exponential increase” in customer inquiries about compliance with the rules, said the company’s Stefano Mori, general manager of marine power.

IMO’s rules being finalized would establish two indexes. The Energy Efficiency Existing Ship Index (EEXI) and the Carbon Intensity Index (CII) would provide shipowners with a baseline to reduce their emissions levels.

“The first issue and concern is compliance,” Mori said. “Since IMO targets can be reached in many different ways, we are often consulted to run tailor-made specific analyses to identify the most optimal and cost effective solution.”

In particular, Wärtsillä’s greenhouse gas (GHG) emissions reductions package, which includes  software upgrading and engine tuning, has gained “major market traction” for retrofits and newbuilds since its introduction last year. Wärtsillä said the package can cut GHG emissions from individual vessels by 20%.

“We really get a lot of inquiries for that,” Mori said. “So it’s really valuable in that sense.”

Making Headway

Though ship owners are scrambling for options to drive down their fleet emissions, LNG carriers have made a fair amount of headway to reduce their carbon footprints, according to DNV Maritime’s Johan Petter Tutturen, business director of gas carriers. 

“This segment has done, in fact, significant improvement when it comes to energy efficiency and the reduction of emissions into the air or atmosphere,” Tutturen said.

The global shipping fleet, which numbers around 65,000 vessels, is responsible for only about 2.6% of GHG emissions, said Flex LNG CEO Øystein Kalleklev. Of those, around 550 are LNG carriers. 

“But what I think we can contribute with is the fact that the new ships are 50% or more efficient than the older ships,” he told NGI. “So if you really want to contribute, it’s kind of making sure that the rules are stringent enough that we are not putting in a lot of loopholes, so that you get this attrition of the older steamships in particular, but also maybe some of these…diesel-powered ships.”

Flex has one of the newest LNG carrier fleets, with the oldest ships built in 2018.

Advancements in propulsion technology have driven down emissions, with more efficient ship engines reducing fuel consumption needs. LNG carriers built today can carry more cargo while using less fuel, making them more efficient.

“Cargo space is up 30%, and fuel consumption is down close to 50%,” Kalleklev said. “So you typically have a CO2 footprint which is 55-60% less on the modern ship.”

Other innovations have helped drive emissions on carriers down. For example, reliquefaction systems, which reliquefy boil-off gas and return it to the cargo tank, are virtually standard issue on new LNG carriers, Tutturen said. Boil-off is LNG that evaporates during transport.

“Today, to order a gas carrier without a reliquefaction system is unheard of,” Tutturen said. 

Seven of Flex’s 13 carriers have partial or full reliquefaction units, Kalleklev said. The ships with full reliquefaction capabilities can bring the boil-off rate to 0.035%, while partial reliquefaction units can bring it to 0.075%. The six ships that don’t have reliquefaction capabilities have newer cargo containment systems with a boil-off rate of around .085%, he noted.

For comparison, steam-driven vessels without reliquefaction systems can have boil-off rates of around .15%, according to Tutturen and Mori.

For its part, Wärtsillä  has developed a line of “compact” reliquefaction units of varying sizes. Boil-off rates differ depending on what type of containment system is used and how much boil-off is needed for fuel.

“We are able to reliquefy .85 tons/hour; we can do 1.5 tons/hour. We can do 1.7, 2.2,” Mori said. “So, we can actually have quite a range of different capacity sizes depending on the boil-off rate, because the boil-off rate depends on the shipyard.”

The sector has also developed energy-saving technologies to help ships move at high speeds with less power. 

Wärtsillä has partnered with SilverStream Technologies to develop an air lubrication system, which pushes air through release units at the bottom of the vessel to reduce friction.

“Basically what happens is, you are creating a sort of a carpet of air bubbles,” Mori said. “And then the ship will need much less propulsion power to reach the same speed.

However, air lubrication systems also pose a problem, since they require electric compressors to work. Mori said they can be powered by shaft generators, which produce electricity from a vessel’s main engine shaft.

Tutturen said most carriers have considered using air lubrication systems, which may yield a 2-4% reduction in fuel consumption.

In addition, Wärtsillä  has developed digital efficiency tools, including a ship-to-shore communication system that can enable a ”just in time” arrival.

“You don’t need to speed up to 20 knots and then wait at anchor,” Mori said. “We can also have this kind of tuning in the approach to the terminals, taking into account weather forecasts and safety.”

Jarring Impact

Transitioning vessels to create “cleaner” seas could have a jarring impact on the global LNG carrier fleet, however. About 42% of the LNG carrier fleet is still made up of older, higher-emission steam-powered vessels, Kalleklev said. 

“I think the ambition here of reducing carbon intensity by 40% by 2030 will mean that the attrition of older steam ships will go much quicker,” he added.

Retrofitting old ships with new equipment comes at higher costs, which could be a major impediment, Tutturen said. Installing a reliquefaction system or upgrading insulation on a 15-year-old vessel may not be economic in the long run, he added.

“To retrofit old gas carriers with brand new energy efficient equipment, or to look at a proven insulation material will, unfortunately, cost too much money,” which is why carrier owners will “most probably not do it.”

Kalleklev said it makes sense to install air lubrication systems onto older, “fuel-thirsty” ships, “But again, the question remains: Will you continue investing in legacy assets or not?”

There are some options for older vessels that may be phased out because they are unable to comply with the new rules. Tutturen sees the potential for older vessels to be converted to floating storage and regasification units (FSRU), or as floating storage units for existing FSRUs or terminals.

Carbon-Neutral LNG?

While the sector has made strides in lowering its carbon footprint, more will be needed to ensure compliance with the IMO’s guidelines.

While boil-off rates have come down sharply over the past 15 years, eliminating them completely isn’t really feasible, Kalleklev said. That’s because crews rely on some of that boil-off for fuel. 

“Getting the boil-off down to 0.00 doesn’t really make sense, because then you will have to burn diesel, which is typically more expensive,” he said.

This is where new fuels, such as biogas and synthetic gas, can play a role, said DNV Maritime’s Christos Chryssakis, business development manager.

“They have this cargo that has to be used, otherwise it’s wasted,” he told NGI. “So I think the only option for businesses then is to start using some kind of carbon-neutral LNG, or low carbon LNG, and that could be biogas, or it could be synthetic gas in the future. Biogas is already available in some volumes.”

Norwegian cruise line Hurtigruten has tested powering some of its vessels with liquid biogas culled from dead fish, while French container ship owner CMA CGM said recently it was purchasing biomethane to power some of its ships.  

“I think we’ll see a bit more of that moving forward,” Chryssakis said.

Meanwhile, Mori sees a number of factors that could lead to the adoption of different fuels. In particular, he noted a push to lower speeds to optimize ship operations. “Traditional propulsion systems are not efficient when deviating from a fixed design speed, and currently ships speeds are getting lower, main engines are operated at lower loads and therefore inefficiently,” he said.

That trend, combined with the new regulations, could promote the use of electric drive propulsion systems, which can reduce overall energy consumption at any given speed.

Mori said Wärtsillä engines offer “easy adoption” to blend multiple fuels as they become available, such as hydrogen, synthetic methane and bio-LNG.

“I’m not saying that our engines are going 100% on hydrogen as of now,” he said. “They can run 25% hydrogen as a blend, so you can put 75% of the energy you need as LNG and the remaining 25% hydrogen. So then you start reducing your emissions considerably and that is a way to reach IMO targets.”

As boil-off rates decline and reliquefaction technology improves, he also sees the potential for hydrogen, synthetic gas and biogas to be stored in dedicated tanks to work as fuels “independent” of the LNG cargo.

“So the cargo will remain untouched from the export to the import terminal,” he said. 

Kalleklev is more skeptical about the potential for alternative fuels. Hydrogen is notably expensive to develop and tricky to contain. Ammonia, which is being explored as an alternative fuel, is toxic and therefore a safety hazard. Biogas development could eat into local food supplies. And synthetic fuels, though a proven technology, are expensive to make.

“I think there are lots of smart people  putting investments into biofuels, synthetic fuels, ammonia, hydrogen,” he said, “but today, they’re not really viable as fuel.”