Liquefied Natural Gas as Marine Bunkering Fuel

Global maritime transport has traditionally relied on marine and heavy fuel oils (HFO) for propulsion. Whilst these fuels are cost-effective and bunkering is widely available worldwide, they produce harmful emissions. In response, stricter regulations and laws are being implemented to limit ship emissions, leading to the growing adoption of liquefied natural gas (LNG) as a cleaner alternative for marine bunkering fuel.

1. Overview: LNG as Marine Bunkering Fuel

In light of new regulations aimed at reducing the environmental impact of shipping, fleet owners are looking for alternative solutions. LNG has emerged as a viable, cost-effective alternative, offering significant emissions reductions compared to traditional fuels.

This form of propulsion has been used on LNG carriers for decades (using the boil-off gas from LNG onboard tanks), with about 400-500 in operation today (2017). However, it was only in 2000 that a non-LNG carrier first used LNG as bunkering fuel.

Since then, this market has grown rapidly, with over 100 LNG-fuelled vessels (that are non-LNG carriers) in operation and an equal number on order (2017).

2. LNG as Marine Bunkering Fuel: Emissions Regulations

The International Maritime Organisation (IMO) developed the MARPOL Convention (International Convention for the Prevention of Pollution from Ships) to protect the marine environment. The latest annexe, which came into force in May 2005, aims to regulate air pollution emitted by ships, including Nitrogen oxides (NOx), Sulphur Oxides (SOx) and other volatile organic compounds. It also requires the establishment of Emission Control Areas (ECAs), areas in which stricter controls are in place to minimise airborne emissions.

The established ECAs are:
1. Baltic Sea area
2. North Sea area
3. North American area
4. The United States Caribbean Sea area (around Puerto Rico and the United States Virgin Islands)

In October 2016, the IMO established that a global 0.5% (mass by mass) sulphur limit will apply to fuel oil used by ships from 1 January 2020. Within the ECAs, a sulphur limit of 0.10% m/m has been applied since 1 January 2015.

The limits for SOx are:

Outside an ECA		Inside an ECA
Prior to 1 January 2012:	4.50% m/m	Prior to 1 July 2010:	1.50 % m/m
From 1 January 2012:	3.50% m/m	From 1  July 2010:	1.00 % m/m
From 1 January 2020:	0.50% m/m	From 1  January 2015:	0.10 % m/m

This implies that vessels must either use a compliant fuel or switch from any high sulphur-content fuel to a compliant marine fuel before entering an ECA.

Strict enforcement and inspections will be implemented, especially in European ports. Fines are expected to be levied to offset the economic advantages that may result from disregarding these limits.

Current and Future Sulphur Regulations

3. Advantages of LNG as Marine Bunkering Fuel

LNG primarily consists of methane (CH₄), which reduces carbon dioxide (CO₂) emissions by up to 30% when used as a fuel. Less nitrogen is present in the combustion process due to the compression rations and methane combustion temperatures, reducing the production of nitrogen oxides (NOx) by up to 85%. Additionally, LNG contains no sulfur, leading to a 100% reduction in sulfur oxide (SOx) emissions. In its liquid form, LNG is non-corrosive, non-toxic, and non-flammable. It is also comparable in cost to traditional marine fuels. However, this depends on the availability of LNG bunkering infrastructure for the vessel, and it also offers the advantage of reduced operating costs.

Increasing stringent regulations will require additional investments to reduce SOx and NOx emissions. Although LNG has a high investment cost, the associated operational savings can be substantial, depending on fuel prices. Alternatives, such as exhaust gas treatment systems, significantly increase the overall cost of the vessel. These systems also require additional space and can increase fuel consumption by 2-3%. Therefore, the use of LNG, which is sulfur-free, presents a viable solution for meeting emission limits.

4. LNG as Marine Bunkering Fuel: Infrastructure required

LNG is widely available, with 20 countries exporting the fuel and 35 importing it. However, existing port infrastructure is focused on these import and export activities, which do not cater to small-scale vessel refuelling. Facilities that provide for the refuelling of ships at ports are termed bunkering and are increasingly being provided worldwide. LNG bunkering infrastructure is currently concentrated heavily in Europe.

LNG is imported in large LNG tankers, with common storage capacities ranging between 80,000 and 260,000 cubic metres.  These vessels are substantial in size and cannot be used to deliver LNG to smaller terminals. Instead, smaller LNG feeder vessels, typically ranging from 7,500 to 20,000 cubic meters, supply these smaller terminals in ports. Integrating transfer facilities with existing port infrastructure can be challenging; consequently, bunker vessels are often employed to transfer LNG to ships.

Bunkering requires storage and transfer facilities. LNG can be transferred to vessels from a stationary shore-based tank by pipeline or from mobile units in the form of vessels (ship-to-ship transfer) and trucks (truck-to-ship). The mobile units require their own LNG supply source in the form of strategically placed terminals. The ship-to-ship transfer is the transfer of LNG from a vessel or barge, with LNG as cargo, to another vessel to use as fuel. It can be done at sea or at a port, allowing large volumes to be transferred. The development costs can, however, be high and require space to accommodate the vessels in a port. The truck-to-ship transfer is flexible and costs less, but the quantity of fuel that can be transferred is smaller, and the loading is lower. The ship-to-shore transfer is desirable for large volumes and has a faster turnaround time. However, it requires a large investment to build the facilities in ports. LNG can also be supplied in standardised containers and loaded directly onto the ship.

LNG bunkering is currently available at over 60 locations, with an additional 70 facilities in the planning stages. By the end of 2017, six LNG bunker vessels are expected to be in operation, enabling ship-to-ship bunkering in Northwest Europe and the USA.

5. LNG as Marine Bunkering Fuel: Vessel considerations

5.1 Storage of LNG

The design of LNG storage tanks has to adhere to the various codes. The type, size and tank locations are important considerations. LNG requires approximately four times the storage space required for conventional fuels, so an optimum layout is important. The location of tanks is important from a safety perspective, with their position being restricted by IMO guidelines. The tanks have to be well insulated, and a surrounding safe area is required in case of accidental spillage.

5.2 Handling boil-off gas

The boil-off gas increases the pressure in the storage tanks. The tanks are, therefore, designed to handle higher pressures and are fitted with pressure relief valves to allow the venting of gas to the atmosphere if the pressures become excessive.  Venting gas is only allowed in emergencies and is not a method for pressure control. Venting of the gas is also undesirable from an economic and environmental perspective. The more volatile components of LNG (nitrogen and methane) boil off first, changing the composition and quality of LNG over time. This is known as ageing.

Some methods to manage the boil-off gas are:

• Reliquefaction of the gas to LNG. This can be done by a direct system, where the gas is compressed and condensed before being returned to the tank. An indirect system condenses or cools the gas with an external refrigerant without being compressed.
• Burning off the excess gas in a thermal oxidiser. On an LNG-fuelled vessel, this is primarily done by feeding the excess gas to the engines. If the boil-off gas exceeds the rate at which it can be used, it can be fed to a gas combustion unit, which burns the gas in a controlled manner. No useful energy can be recovered from burning the gas using this method.
• Allowing the pressure to accumulate
• Cooling the LNG
• Using the boil-off gas as energy for ship operation. The gas can also be used to produce steam or hot water in boilers.

5.3 Engines

The first LNG-fueled vessels that were not LNG carriers used gas-only engines. Dual-fuel (DF) engines can operate on either gas or diesel fuel and can also run on a combination of both, with approximately 70% of energy derived from gas and 30% from diesel. This option is suited to refits of engines that cannot be converted to dual fuel. The most prominent engine manufacturers are currently Wärtsilä, MAN, Caterpillar, HiMSEN, Siemens, Mitsubishi and Rolls Royce.

LNG-ready vessels allow the vessels to be converted to LNG-fuelled vessels in the future. Measures can include structural reinforcements and the correct choice of material to support future LNG tanks, preparations for future gas fuel systems and installation of machinery which can be converted to gas fuel (or is already capable of burning gas fuel). This simplifies a later conversion. An LNG-ready ship is suitable where the current market conditions and/or LNG availability do not make current commercial sense. The additional investment can then be made when the commercial situation is favourable. Being LNG-ready, therefore, increases the flexibility of the vessel, extends its lifetime and can increase its second-hand value.

Converting existing diesel engines for LNG operation is relatively straightforward. This process typically involves changes to the cylinder heads and liners, pistons and rings, connecting rods and turbochargers. Gas rails and admission valves, together with a pilot fuel system and the fitment of storage tanks, were also required.

5.4 LNG as Marine Bunkering Fuel: Fuel supply

IMO regulations require a fully redundant fuel supply system. Where gas-only is used, the LNG has to be stored in two or more tanks of approximately equal size. Dual fuel engines are allowed to have a single LNG storage tank, with liquid fuel as a backup.

5.5 LNG as Marine Bunkering Fuel: NG safety

LNG brings some unique safety considerations when compared with heavy fuel oils. LNG is non-flammable due to a lack of oxygen in the liquid. However, when LNG vapourises, the resulting natural gas becomes flammable when mixed with air in concentrations ranging from 5% to 15% (by volume). Natural gas is both odourless and colourless, and LNG cannot be odorized, making detection without specialized equipment difficult.

LNG’s low temperature (-162 degrees Celsius) can result in severe injuries from direct body contact. It can also render normal ship steel very brittle and fracture it when exposed to LNG.

Due to the large energy content contained in the LNG storage tank, it must be protected. This entails protecting it from possible ship collision and grounding, mechanical impacts, external fires, and BLEVE (boiling liquid expanding vapour explosion).

Despite the associated risks, LNG has proven to be a safe fuel choice for marine transport. The guidelines set by the IMO and the IGF Code ensure that the design and operation of ships adhere to best practices, thereby minimizing potential risks.

6. LNG as Marine Bunkering Fuel: Market

The first LNG-fuelled vessel that was not an LNG carrier was the Norwegian ferry Glutra, which came into service in 2000. Within three years, two oil and gas platform supply vessels (PSV) also began operation in Norway.  Since then, there has been an increasing rate of new LNG-fueled vessels coming into service.  Norway’s tax on NOx, introduced in 2007, and the availability of LNG in the region helped spur the introduction of LNG-fuelled vessels there. Until 2013, all 37 LNG-fuelled vessels (bar one) were based in Norway. The formation of ECA’s in Europe and North America and a steep increase in the price of heavy fuel oils led to more consideration for LNG as a marine fuel. As of May 2017, there are 106 vessels in operation, with an additional 115 on order.

There has also been a diversification in the type of LNG-fuelled vessels, and the areas of operation are expanding.

The gas market has experienced a recent boom, driven partly by the surge in non-traditional (shale) gas production, which utilizes the hydraulic fracturing (fracking) process.

7. LNG as Marine Bunkering Fuel: Organisations

The European Union is actively promoting the use of LNG and funding projects to improve its supply. Current EU policy requires at least one LNG bunkering port in each member state.

The Society for Gas as a Marine Fuel (SGMF) was established in 2014 following a decision by the Society of International Gas Tankers and Terminal Operators (SIGTTO). SGMF is an NGO that aims to promote the safe and responsible operation of LNG-fuelled vessels and develop guidelines for best practices amongst its members. Multi-sector industry organisations, such as SEA/LNG (founded in 2016), are also being formed to create coalitions to promote LNG as a marine fuel. SEA/LNG unites key stakeholders, including shipping companies, LNG suppliers, bunkering companies, ports, and engine manufacturers, to create coalitions that advocate for the use of LNG in marine transport.

8. References

• DNV-GL. (2014). LNG as ship fuel (No. 01 2014).
• DNV-GL. (2015). In focus – LNG as ship fuel (No. 01 2015).
• Dobrota, D., Lalić, B., & Komar, I. (2013). Problem of boil-off in the LNG supply chain. Transactions on Maritime Science, 2(1), 1-8. https://doi.org/10.7225/toms.v02.n01.a01
• International Maritime Organization. (2016). Studies on the feasibility and use of LNG as a fuel for shipping.
• Royal Academy of Engineering. (2013). Future ship powering options: Exploring alternative methods of ship propulsion.
• Rutkowski, J. (2016). Study of new generation LNG dual fuel marine propulsion green technologies. The International Journal on Marine Navigation and Safety of Sea Transportation, 10(1), 49-54.

9. Further Reading

EPCM LNG Archive

International Maritime Organisation

International Maritime Organisation – 2020 Global Sulphur Limit

IMO Studies On The Feasibility and Use of LNG as a Fuel for Shipping 

IMO – MARPOL International Conventional for The Prevention of Pollution from Ships

SEA\LNG is a multi-sector industry coalition created to accelerate the widespread adoption of LNG as a marine fuel. Our vision is to establish a competitive global LNG value chain for cleaner maritime shipping by 2020.