The development comes as a way of bridging the gaps present in international regulations for such fuels, with the exception of LNG, the classification society said.
“Except for liquefied natural gas, currently, all gases and low-flashpoint fuels are subject to the ‘alternative design approach’, which means that they may be used if their safety, reliability and dependability of the systems can be shown to be equivalent to those achieved by new and comparable conventionally fuelled main and auxiliary machinery,” DNV GL explains.
“This can be a time-consuming and costly process and may impede the uptake and expansion of lower emission alternative fuels.”
The rules and notation are based on DNV GL’s rules for ships using LNG as fuel but account for the differences in properties and phases between LPG and LNG.
The class notation covers internal combustion engines, boilers and gas turbines for both gas-only and dual-fuel operations. It also includes requirements for the ship’s fuel supply, considering all aspects of the installation from the bunkering connection up to and including the LPG consumers (main and auxiliary engines, boilers, etc.).
“With the new rules and class notation, we want to offer owners interested in LPG a straightforward path towards compliance with the alternative design approach mandated by the IGF Code,” said Geir Dugstad, Director of Ship Classification & Technical Director at DNV GL – Maritime.
“As the fuel environment within the maritime industry becomes more diverse, it is essential that we continue to broaden the enabling rules and regulation to support these new choices.”
LPG as a fuel can lower a vessel’s emissions to air, both in terms of greenhouse gases and other pollutants. It virtually eliminates sulphur emissions and reduces GHG output by approximately 17 per cent compared to burning HFO or MGO, DNV GL explained.
LPG could also act as a bridging fuel to ammonia, as the materials used for LPG tanks and systems is, in most cases, suitable for ammonia. With advanced planning, the adjustments needed for a switch to ammonia from LPG could also be minimized, the classification society adds.
In August 2019, BW LPG announced plans to retrofit four ships with LPG-propelled dual-fuel engines. The move has been described by the company as a pioneering step in the development of next-generation, high-tech green ships with dual-fuel propulsion.
With LPG propulsion, BW LPG plans to reduce its sulphur oxide emissions by up to 97 percent, allowing for full compliance with all current and future sulphur emissions requirements.
This means the retrofitted ships, when operating on LPG, will go beyond IMO’s global 0.5% sulphur emissions cap to also be in full compliance with Emission Control Areas (ECA) and Sulphur Emission Control Areas’ (SECA) 0.1% sulphur cap.
Dorian LPG is also interested in the viability of LPG as an attractive and cost-effective alternative fuel that is widely available and inherently compliant with the IMO mandate.
In 2018, the company teamed up with Hyundai Global Service to study the retrofitting of engines onboard ten of its very large gas carriers to use LPG as fuel.
The initiative follows the conclusion of a study announced in September 2017 by Dorian LPG and the American Bureau of Shipping to evaluate the use of LPG as a marine fuel in advance of the sulphur cap.
Global engine makers such as MAN Energy Solution also support the switch to natural gases as the fuels of choice in global shipping as one of the best ways of decarbonizing the industry.