Dec 15, 2020 | Clean shipping articles and long reads

Natural gas has been regarded as the marine “fuel of the future”, but growing concerns over the impact of methane emissions on climate change means that some owners remain sceptical. CSI spoke to Christos Chryssakis business development manager at DNV GL – Maritime for the class society’s view.

A decade ago, analysts predicted that there would be about 1,000 LNG-fuelled vessels by 2020. At the time, high oil prices and pending IMO regulations on sulphur emissions seemed to justify these rosy forecasts.

After all, LNG is readily available, relatively affordable and because it had negligible NOx, particulate matter (PM) and zero SOx emissions, it would help owners comply with pending International Maritime Organization (IMO) emissions regulations. While more expensive to install, gas-fuelled propulsion systems already had a proven track record and work to develop a reliable network of LNG bunkering stations was underway.

Since then, the price of oil dropped and LNG bunkering infrastructure did not develop as quickly as predicted, leading many owners to pass on investing in gas-fuelled vessels in favour of exhaust gas cleaning systems (EGCS), which (at least) help to meet the IMO’s recent ban on fuels with a sulphur content above 0.5%. The result? Today, there are only about 170 LNG-fuelled ships in service. And while there are more than 180 LNG- fuelled ships on order, LNG as marine fuel has not developed as predicted. 

What happened?

According to Christos Chryssakis, owners are facing some tough choices – and a lot of conflicting information – about how to think about LNG. “A growing sense of urgency about climate change has resulted in intense pressure on the industry to act to limit greenhouses gasses,” he says. “At the same time, questions have been raised about the viability of LNG as an alternative to high sulphur fuel oil to help owners stay in compliance with pending regulations.”

Indeed, the IMO has pledged to reduce the total annual greenhouse gas (GHG) emissions by at least 50% by 2050 compared to 2008, while simultaneously pursuing efforts towards phasing them out entirely.

While analysts agree that burning natural gas generates about 20% less CO2 emissions than high sulphur fuel oil (HSFO), it is mostly made up of methane, which has been identified as a major contributor to global warming. According to US Environmental Protection Agency, “Pound for pound, the comparative impact of methane is more than 25 times greater than carbon dioxide over a 100-year period.”

One key concern for owners and regulators alike is the issue of methane slip. Methane slip can occur during the gas exchange phase of the cycle when unused fuel can get trapped in the combustion chamber and top piston area, allowing some unburned methane gas to escape from the exhaust into the atmosphere. For owners, methane slip not only results in less efficiency (higher fuel costs), it may add to the GHG impacts of burning LNG.

To calculate gas related GHG impacts more accurately, researchers have measured emissions throughout the value chain, from “well to tank” and “tank to wake.” For example, the process of producing natural gas can result in methane leaks from wells, pipelines or processing equipment. Risk of methane leaks related to the storage, handling and loading at LNG terminals are also a factor. Regulatory requirements to report emissions provides researchers with fairly robust data sets, making calculations relatively straight-forward.

Once on board, “tank to wake” calculations on methane emissions are subject to a number of variables, including vessel operational parameters (e.g. how often engines operate at low loads), engine design (e.g. high-pressure diesel process as opposed to low-pressure Otto process) and engine type (two stroke or four stroke).

Well to wake

Taken together, “well to wake” emissions calculations, combined with the high cost of installing specialised fuel tanks and storage systems for gas engines and variable fuel prices have created a lot of uncertainty, helping to explain why owners have been slow to embrace LNG as a fuel. After all, without the confidence that transitioning to LNG will achieve long-term regulatory compliance or save on fuel costs, it’s hard to justify the CAPEX for gas engines. And when you consider that EGCSs (or scrubbers) are far cheaper and offer a return-on-investment up to three times faster than gas engines, it is not hard to see why, for now, scrubbers are the more attractive option for many owners.

Chryssakis acknowledges that there is a good business case for scrubbers – at least in the short term.  But he notes that new gas engine designs have largely solved the methane slip issue. “Over the past decade, methane slip has been drastically reduced in modern engines –and further reductions are expected in the future,” he says. “The next generation of two and four stroke gas engines will be more efficient, not only saving on fuel costs but also capable of making significant reductions of greenhouse gas emissions.”

In response to demand, engine manufacturers have been competing to deliver the most fuel-efficient gas engines for multiple applications. In 2015, the German engine manufacturer MAN ES launched the ME-GI two stroke dual fuel engine, and recently announced it is working on a second-generation of the engine design. That same year, the Finnish engine manufacturer Wärtsilä introduced the four-stroke 31GS, which reaches efficiencies surpassing 50%. And recently, the Swiss engine manufacturer WinGD announced a series of next-generation engines which will reduce methane slip by 40-50%, scheduled to be available in 2021.

“Given the fact that there are solutions for methane slip available now and technology is likely to improve over the next few years, the decision comes down to cost, not technology,” says Chryssakis.

Independent studies, released amongst others by SINTEF Ocean in 2018, shows that developments in lean burn spark ignition (LBSI) and low-pressure dual fuel (LPDF) four stroke engines have halved emissions related methane slip from 2010 to 2017. Also, new combustion chamber designs, efforts to optimise combustion processes and optimised after-treatment can yield overall GHG savings of 14 to 21% for two stroke gas engines and 6 to 15% for four stroke gas engines. “Technology for methane slip reduction has been continuously improving over the last 10-20 years,” says Chryssakis. “We anticipate that further reductions are likely in the near future.”

First-generation gas engines were most often found on LNG carriers and later were installed on PSVs or ferries operating on fixed short sea routes. However, as technology for high pressure two-stroke engines has improved, LNG has become a more viable option for owners operating larger vessels seeking to cut fuel costs and corresponding emissions on longer trades. In fact, the recent spike in newbuilding orders for LNG dual-fuelled vessels applies to multiple shipping segments, from cruise lines (Carnival, AIDA) to containership lines (CMA CGM, Hapag-Lloyd), oil and chemical tankers (Rosneft, Thun Tankers) to ro-ro operators (UECC, TOTE, etc), among others.

While it is too early to declare that LNG as a fuel has reached a tipping point, momentum seems to be building: more dual fuel vessels will create more demand for LNG bunkering options and with more ports offering LNG bunkering, the more owners will be more likely to commit to LNG.

Today, LNG bunkering options are mostly found in major ports in Europe (e.g. Rotterdam, Stockholm and Zeebrugge) and North America (e.g. Jacksonville, Florida, Fourchon, Louisiana), with more hubs in the planning stages. At the same time, Asian ports serving deep-sea shipping routes (e.g. Incheon, South Korea, Singapore and the world largest cargo port, Ningbo-Zhoushan in China) are in the process of establishing LNG bunkering facilities.

In addition, efforts are underway to equip existing LNG bunkering stations with methane leak abatement technologies. For example, members of NGVA Europe (the Natural & bio-Gas Vehicle Association), have committed to a “Zero Venting Target” policy for all new CNG and LNG bunkering stations. To meet this commitment, bunkering stations will be designed in such way that methane emissions from venting operations are minimised during operation. For example, bunker operators have committed to installing improved leak detection systems and compressors to allow the re-injection of the boil-off gas instead of flaring it.

While LNG is gaining more acceptance, a lot of work is being done in parallel to develop new technologies and alternative fuels that have an even lower emissions profile. While alternative fuels now being developed hold significant promise, Chryssakis argues that hoping a “perfect” solution appears in 2030-2035 may be risky. Likewise, while he applauds the industry’s embrace of new battery technologies, fuel cells and propulsion assist technologies to reduce emissions, he notes that not all are suitable for every trade or purpose.   

“There is a lot of exciting work being done to develop new technologies and alternative fuels, such as hydrogen, ammonia, biofuels, LPG and synthetic gas, but these technologies are still expensive and each one has different safety and/or environmental challenges,” says Chryssakis. “We view LNG as a transition fuel: It is not perfect, but perfect should not be the enemy of good.”

Natural gas may not the be the “fuel of the future” for long, but it is an important, transitional step in the right direction for at least one to two vessel generations. And with more LNG bunkering options planned, pending GHG regulations and new technologies developed to address “well to wake” methane emissions, the case for LNG will only get stronger.

Sceptics are right to point out that LNG alone cannot cut GHG to the extent required by UN COP targets, but the fact is that natural gas remains the best commercially available and proven technology to reduce CO2 emissions for most ship types and trades. So, until something better comes along, LNG is industry’s best chance to fight climate change.

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