Alternative Fuel and Energy Sources

DNV have predicted that ammonia will be the most popular of the alternative fuels by 2050.

Like hydrogen, most ammonia is currently made using natural gas. For it to be a viable option, it must in the future be manufactured through low-carbon processes. Ammonia can be burnt in dual-fuel internal combustion engine (MAN B&W report only minor modifications to its LPG fuelled engine are required) or as the energy source for fuel cells.

There is precedence on using ammonia on vessels, but this has been limited to its use as a refrigerant. The concerns on its toxicity are well-known and it requires careful handling.

Biofuels can be blended with traditional crude-derived marine fuel oils or used as a ‘drop-in’ fuel, where they act as a direct substitute.

There are numerous biofuels, all derived from various feedstocks through different processes. Two of the more well-known biofuels whose use may become more widespread include heavy vegetable oil (HVO) and biodiesel (FAME, fatty acid methyl ester). Both are sourced from vegetable oil crops but through different processes.

There are several significant barriers to the widespread adoption of biofuels – the nature of which are environmental, economic and technical. For example, fuels must be sourced from sustainable feedstocks if it is to be a ‘green’ option. Also, there is competition for the oil crop feedstocks from the food, cosmetics and pharmaceutical industries. Furthermore, there are long term storage issues with some biofuels, especially if they come into contact with water.

Hydrogen as a marine fuel

As the maritime industry looks for zero-carbon fuels to replace traditional fossil-fuels, hydrogen has emerged as a serious contender.

Whether it can be a true zero-carbon fuel on a lifecycle (or ‘well-to-wake’) basis depends on how the hydrogen is derived.

While hydrogen has the potential to be a truly zero-carbon fuel, it is not without its hazards and challenges.

Here, we take a closer look at hydrogen and how it can be used as a marine fuel.

Hydrogen Production methods

Below is a schematic showing more information on the hydrogen production methods.

• The above is a basic guide open to interpretation and subject to change
• Pink and purple Hydrogen are different names for the same process.
• Brown and black carbon is effectively the same but the type of coal burnt differs.
• In some cases fossil fuels are used to produce yellow hydrogen

Hydrogen properties 

• Very buoyant and much lighter than air
• It’s non toxic and does not contaminate the environment or threaten humans or wildlife.
• Low energy density – requiring a lot of storage space which may reduce cargo carrying capacity

Hydrogen – dangers

• Highly combustible, explosive gas, invisible and tasteless
• Very wide flammability range – ignited at 4-74% concentration in air by volume
• Bunkering operations – may require specific risk assessments and safety zones

Safety Systems – required

The below is an example of some of the safety systems required. Please consult with your Classification Society for further guidance.

• Emergency shut downs
• Double walled system – ventilation
• Leak strategy sensors
• 3 layer safety system

Safety planning

Guidance by the owner’s Classification Society is required. Below are some points to consider at the planning stage.

DNV strongly predict LNG will be the transition fuel of choice. Comprising mostly of methane (CH4), LNG is already being adopted by an albeit small proportion of the world fleet. It is an attractive option because of its zero-sulphur content (satisfying the IMO 2020 sulphur cap) and its CO₂ emissions are approximately 20% lower than that of distillate fuels (such as MGO) and the new VLSFO products.

However, LNG as a marine fuel is not without its drawbacks. Bunkering, storage and handling takes much more care and presents very different risks to those of traditional marine fuels. Making a vessel LNG-ready requires significant investment – from installing gas (or dual fuel) engines, to additional storage requirements. Also, the global warming potential (GWP) of methane is more than twenty times that of CO₂ , which will be an issue if excessive ‘methane-slip’ is experienced in the engines.

The definition of liquified petroleum gas (LPG) is a mixture of propane and butane in liquid form. A tank of LPG will typically be three times the size of a tank containing oil-based fuel so needs to be factored into the design of the ship.

LPG can be used in dual fuel internal combustion engines (two and four stroke) with pilot ignition. It can also be used with gas turbines.

LPG has a higher density than air which may create a danger if it leaks in lower spaces.  This places extra focus on leak prevention and suitable ventilation. The flashpoint of LPG is also very low, and this means that double walled pipelines are required in the engine room with suitable leak detection equipment. The IGF code mandates a risk-based design approach which can be quite time consuming and expensive.

When considering CO₂ emissions on a well to wake basis LPG is not as low as LNG but lower than oil-based fuels.

In a 2019 DNV article they advised that LPG may act as a suitable bridging fuel to ammonia since LPG installations in a ship may be suitable for ammonia too.

Currently, methanol is produced using natural gas feedstock, and as such it provides only a very modest reduction in CO₂ emissions compared to traditional marine fuels. However, methanol derived from biomass can bring up to a 50% reduction.

Mostly used in the chemical industry, methanol is gaining popularity as an automotive fuel in China.

Methanol is a liquid at ambient pressure and temperature. This makes storage and handling much simpler compared to many of the other alternative fuels.