How Taxonomies Lead to Fuel Pathways - The Heavy Gas and Alcohol Pathway

THE HEAVY GAS AND ALCOHOL PATHWAY

This category includes fuels comprised of larger molecules than the light gas group. As such, they have higher C/H ratios — therefore, lower carbon-reduction potential — and lower energy content. Their fuel storage and supply requirements are also less demanding.

LPG, MeOH → Bio-/ElectroFuels → Ammonia

These fuels include LPG, methanol, ethanol and ammonia. The alcohols tend to have lower energy content and the presence of oxygen in the fuel can create issues pertaining to chemical compatibility in fuel-supply systems.

When used as the primary fuel, methanol can reduce CO 2 emissions by around 10 percent 5 . However, methanol has the potential to be a carbon-neutral fuel in the future, if it is produced renewably as biomethanol or electro-methanol.

The lower energy content of some of these fuels (e.g. methanol) limits the amount of fuel energy that can be stored on board a ship; thus, they only may be suited to the types of vessels, trades and routes that allow for frequent refueling.

LPG has higher energy content than the alcohols and may be more conducive to use in modern dual-fuel engines, but it has not been as widely adopted as LNG due to its lower potential to lower emissions, and its different safety challenges.

However, methanol and LPG are currently thought of as mature fuels by engine manufacturers, which have marketed engine platforms able to use them. Therefore, they can be used to meet the carbon-reduction goals of 2030 and can pave the way to carbon-neutral propulsion, if they are produced renewably in the future.

At the end of the heavy gas or alcohol spectrum, lies ammonia, which can be a zero-carbon fuel if produced renewably. Despite its toxicity and more stringent handling requirements, ammonia engines are in the design process.

Recently, designs for ammonia-fueled feeder ships also have been unveiled by consortia that variously include designers, class and shipyards. However, for ammonia to become a commercially viable long-term fuel option, comprehensive supply-side infrastructure would need to be built and new, stringent safety regulations designed and implemented.