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A wide range of alternative fuels for ships are currently under discussion. The main aspects to compare a fuel to the existing benchmark of crude-oil-based ship fuels are the environmental impact, the fuel price, the available/needed infrastructure and availability, the regulatory framework, the required technology, the CAPEX and the part of the OPEX related to the use of the fuel, for instance exhaust gas cleaning.

The fuels presented here are in our view the most promising alternatives to conventional ship fuel.

LNG

Liquefied natural gas (LNG) has more or less the same composition as natural gas used for households and power generation and in the industry. Its main component is methane (CH4), the hydrocarbon fuel with the lowest carbon content. It should be noted that it is possible to produce methane from hydrogen (H2) and carbon dioxide (CO2) (see comparison below under “Hydrogen and PtF”). If liquefied, the physical properties are nearly equivalent to those of LNG. LNG is a cryogenic liquid with a boiling temperature of approximately –160°C at atmospheric pressure.

Molecuele_LNG

LPG

Liquefied petroleum gas (LPG) is by definition any mixture of propane and butane in liquid form. For instance, in the USA, the term LPG is generally associated with propane. Mixing butane and propane enables specific saturation pressure and temperature characteristics. LPG can be handled in pressure tanks at ambient temperature. As an example, the saturation pressure of propane at 45°C is approximately 16 bar g.

Molecuele_Propan

Methanol

With its chemical structure CH3OH, methanol is the simplest alcohol with the lowest carbon content and highest hydrogen content of any liquid fuel. Methanol is a basic building block for hundreds of essential chemical commodities and is also used as a fuel for transport. It can be produced from a number of different feedstock resources like natural gas or coal, or from renewable resources such as biomass or CO2 and hydrogen.

Molecuele_Methanol

Bio Fuel

Biofuels are derived from primary biomass or biomass residues that are converted into liquid or gaseous fuels. A large variety of processes exist for the production of conventional (first-generation) and advanced (second and third-generation) biofuels, involving a variety of feedstocks and conversions. The most promising biofuels for ships are biodiesel (e.g. HVO – hydrotreated vegetable oil, BTL – biomass-to-liquids, FAME – fatty acid methyl ester) and LBG (liquid biogas, which primarily consists of methane). Biodiesel is most suitable for replacing MDO/MGO, LBG for replacing fossil LNG, and SVO (straight vegetable oil) for replacing HFO.

Molecuele Butan

Hydrogen and PtF

Hydrogen (H2) can be produced in several different ways. Today, nearly all hydrogen is produced by reforming natural gas. The production of hydrogen through water electrolysis could be combined with the growing renewable energy sector, which delivers, by nature, intermittent electrical power only. Conversion to hydrogen could facilitate storage and transport of this renewable energy. Hydrogen from electrolysis and renewable energy (wind, solar, water) is the basic building block for a range of fuels. Hydrogen can be used directly as compressed or liquefied gas. In combination with carbon dioxide, it can be converted to methane gas (i.e. power-to-gas [PtG]). Methane can be liquefied and used in the same way as LNG. Hydrogen and carbon dioxide also can be converted to liquid “diesel-like” fuels (i.e. power-to-liquid [PtL]). The PtG and PtL processes can be summarized as power-to-fuel (PtF).

Molecuele_Hydrogen

Batteries

Batteries provide the ability to directly store electrical energy for propulsion, opening up many other opportunities to optimize the power system. Recent advancements in battery technology and falling costs thanks to the growing worldwide demand for batteries make this technology attractive to the shipping industry.

revolt-batteries

Fuel cell systems

Fuel cells convert the chemical energy contained in a fuel directly into electrical and thermal energy through electrochemical oxidation. This direct conversion process enables electrical efficiencies of up to 60%, depending on the type of fuel cell and fuel used. It also minimizes vibration and noise emissions, a major setback of combustion engines.

AFC

Wind-assisted propulsion

For thousands of years, wind was the primary energy source used to propel ships, apart from manpower. Today, wind-assisted propulsion is understood to be a potential method of reducing the fossil-fuel-based energy consumption of ships. Wind is an inexhaustible source of energy.

skysail