The regulation for ships to use liquefied natural gas (LNG) as a fuel is set to include an LNG Bunker Delivery Note with detailed information about the LNG properties and composition.

Sulphur should be among the items to be included, the 95th session of the International Maritime Organization’s (IMO) Maritime Safety Committee (MSC 95) has agreed.

Some objected that the sulphur content was not relevant to the ship’s safety, and hence should not be considered by MSC, but rather by the IMO’s Marine Environment Protection Committee (MEPC). Despite this procedural objection, MSC 95 agreed to include sulphur as there was majority support for it.

The push for adopting LNG as fuel has, in large part, been driven by the fact that it can help operators meet emission regulations in MARPOL Annex VI, including the strictest limits for sulphur oxides (SOx) and nitrogen oxides (NOx) in emission control areas (ECAs).

“We have to establish that LNG does meet the Annex and we think including sulphur content in the BDN would address this quite easily,” commented the Marshall Islands at MSC 95.

The proposed LNG BDN is annexed to the draft International Code of Safety for Ships using Gases or other Low-flashpoint Fuels (IGF Code). A working group at MSC 95 is making the final tweaks to the draft IGF Code and will report back to plenary on Thursday this week, when it is hoped remaining niggles have been ironed out sufficiently to formally adopt the draft.

The sulphur content on the LNG BDN will be expressed as a percentage of mass over mass. This is in line with how sulphur is expressed on BDNs for regular marine fuels, where suppliers are obliged to provide information on the exact sulphur content of the fuel.

The amount of sulphur in LNG is typically very small. According to a guide by the Society for Gas as a Marine Fuel, typical sulphur specifications in LNG are less than 30 parts per million (ppm), which translates to about 0.004% by mass.

Sulphur in LNG is normally not expressed as a percentage of mass over mass (m/m %), but rather as milligrams per cubic metre (mg/Nm3), meaning LNG suppliers may have to do some conversions to provide the exact sulphur content on the BDN.

Typical LNG specifications for the Japanese market limits sulphur to 30 mg/Nm3 maximum and hydrogen sulphide (H2S) to 5 mg/Nm3 maximum.

The proposed LNG BDN for the IGF Code does not ask for H2S to be specified, but has a field listing H2S, hydrogen, ammonia, chlorine, fluoride and water as “negligible<5ppm”.

The ISO 8217:2012 marine fuel standard sets a 2 ppm (mg/kg) limit for H2S in marine residual and distillate fuels.

The group working on the IGF Code has agreed that a BDN should be included in the draft IGF Code “to ensure that information on the LNG composition is made available to the Master by the LNG supplier at every bunkering operation” and that the amount delivered should represent the net total.

Unlike conventional bunker fuels, there is no International Organization for Standardization (ISO) quality standard for LNG as a marine fuel.

The draft IGF Code says LNG properties to be included are methane number, calorific value, Wobbe Indices, density, pressure and temperature.

LNG composition parameters to be included (expressed in m/m%) are methane, ethane, propane, isobutane, N-butane, pentane, hexane, heptane, nitrogen and sulphur.