This is certainly a consideration with superyachts where space is at a premium. Requiring more volume for fuel, ancillary equipment, and associated safety systems, will either compromise the interior, significantly reduce the range, or both.
Apart from bio-diesel such as 2nd generation Hydrotreated Vegetable Oils (HVO) the most promising fuel may be Methanol.
What is Methanol
Methanol (CH3OH) is one of the four basic chemicals used to produce all other chemical products such as formaldehyde, acetic acid, and plastics.
It is a colourless water-soluble and biodegradable liquid at atmospheric conditions with a mild alcoholic odour. Energy density is approx. 14MJ/l compared to diesel which is 34MJ/l. It boils at 64.6 C and has a Flashpoint of 11 so requires additional precautions for use, storage and handling but, these are well understood.
It burns cleanly with no particulates, does not contain sulphur and the combustion of Methanol emits a very small amount of NOx. Engines using Methanol can be Tier III compliant without exhaust gas after treatment.
Methanol is mainly produced from natural gas or coal and, according to the International Renewable Energy Agency (IRENA), annual production is around 98Mt and accounts for about 10% of the CO2 emissions from the chemical and petrochemical industries.
With all alternative fuels it is important to understand the GHG emissions along the whole value chain, including production, storage, transportation, and final use. Methanol does emit CO2 when combusted and in the reforming process for Hydrogen but, importantly, it can be carbon-neutral depending on the energy and feedstocks used in the production of the fuel.
Production methods include: –
• Bio-Methanol from bio-mass such as agricultural waste, bio-gas, sewage, municipal solid waste and black liquor from the pulp and paper industry.
• E-Methanol from Green Hydrogen and, either CO2 from direct air capture (DAC), or carbon capture and storage (CCS).
Currently only about 0.2Mt of Green Methanol is produced. Studies suggest this is forecast to grow to 2Mt by the end of this decade. It is one of the easier fuels to scale as the technology is well understood and much of the infrastructure, such as storage and distribution, is already in place.
Like all alternative fuels this is a challenge, and much will depend on demand and the scaling up of production and bunkering infrastructure.
Shipping companies such as Stena and Maersk are already driving maritime demand, and the chemical industry will require Green Methanol to reduce their CO2 emissions. This increasing demand will provide the producers the confidence to invest in production and improving availability – it’s likely there will be more demand than supply in the early days.
In the meantime, Grey and Blue Methanol that use natural gas, carbon capture and renewable feedstocks, could be a suitable pathway until such time Green Methanol is more widely available.
According to the DNV Alternative Fuel Insight, Methanol is already available in 117 port terminals around the World, including Algeciras, Tarragona, Genoa, Livorno and Trieste. It can also easily transported by truck.
A major benefit is Methanol, unlike Hydrogen and Ammonia, can be carried in structural tanks – the same as diesel. It does require additional barriers, double walled piping, ventilation, and inert gas, but there is wide experience in its transport and use. The IMO have produced guidelines for its use as a marine fuel under the IGF Code – Interim Guidelines For The Safety Of Ships Using Methyl/Ethyl Alcohol As Fuel (MSC.1/Circ.1621).
It can also be used in diesel engines and reformed to produce Hydrogen for Fuel Cells.
Diesel engines are a mature technology with some engines around 45% energy efficiency at optimum power. Overall efficiency can be further improved by using hybrid systems, waste heat recovery and power management to optimise engine performance and electricity generation. In addition, they are well suited to running on alternative liquid and gaseous fuels.
In a recent White Paper titled “The Future of Internal Combustion Engines” Rolls Royce maintain combustion engines will continue to play an important role but, with a steady transition away from fossil fuels to sustainable fuels. And, as well as new engines optimised to run such fuels, they also see the need to offer conversion kits for existing engines.
As an example the Stena Germanica, operating in an Emissions Control Area (ECA) between Germany and Sweden, was successfully converted in 2015 to burn Methanol in its engines.
AP Molller Maersk believe in the fuel for shipping and have signed a contract for 8 x 18,000 TEU container ships to be delivered in 2024 with engines running Green Methanol.
ScandiNAOS has produced a diesel engine with power outputs from 150 – 450kW that runs on Methanol for propulsion and genset applications. Approved by Lloyds and DNV.