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Ocean Yield ASA, the Oslo-based shipowner, has placed orders for three LEGCs (Liquefied Ethylene Gas Carriers) of 36,000 cubic metre (cbm) capacity, to be built at Sinopacific Offshore & Engineering, China. Each will be powered by a single MAN B&W ME-GI low-speed, dual-fuel engine [pictured]. The engines will run on ethane, which ethylene carriers are also equipped to transport, and represent the first time ethane will be used as fuel to propel an ocean-going vessel, engine manufacturer MAN Diesel & Turbo says.

Hartmann Schiffahrt, part of Hartmann AG, the German ship-owning and management group, has acted as technical leader on the LEGC project, while Gaschem Service, another Hartmann division, is commercially responsible for the employment of the vessel. The vessels are scheduled for delivery in August, October and December 2016 respectively.

MAN Diesel & Turbo reports that ethane was chosen as fuel, in preference to heavy fuel oil (HFO), due to its more competitive pricing and because bunkering is "significantly shorter". As a fuel, its emissions profile is also superior to HFO – in which respect it is similar to methane – and compared to HFO contains negligible sulphur, 15-20% lower carbon dioxide (CO2) and emits significantly fewer particles under combustion. MAN Diesel & Turbo also states that the ME-GI engines will be set up so that they can easily be converted to run on methane as an alternative, as per the owner’s wish.

Diesel vs. Otto

The ME-GI is a diesel engine in contrast to the other dual- or triple-fuel engines on the market, which are Otto engines. Simply put, engines that operate according to the diesel principle have a higher efficiency and power concentration than those following the Otto principle.

MAN Diesel & Turbo reports that its ME-GI technology uses the diesel cycle to maintain high efficiency and robust combustion with no need for any derating. The company also states that the engine – by virtue of its diesel operating principle – will have negligible methane/fuel slip, one of many low-emission characteristics, and dispenses with the need for restrictive load ramps or other knock-preventing measures.

The ME-GI engine

The ME-GI engine gives shipowners and operators the option of utilising fuel or gas depending on relative price and availability, as well as environmental considerations.

MAN Diesel & Turbo says it sees significant opportunities arising for gas-fuelled tonnage as fuel prices rise and modern exhaust-emission limits tighten. Research indicates that the ME-GI engine delivers significant reductions in CO2, nitrous oxide (NOx) and sulphur oxide (SOx) emissions, the company points out.

Furthermore, MAN Diesel & Turbo says the ME-GI engine’s negligible fuel slip makes it "the most environmentally friendly technology available", adding that the ME-GI engine represents a "highly efficient, flexible, propulsion-plant solution".

An ME-LGI counterpart that uses LPG, methanol and other liquid gasses is also available, and has already been ordered.

LEGCs

Ethylene carriers are generally considered the most sophisticated of all gas tankers and are capable of carrying most liquefied gas cargoes, but also ethylene at its atmospheric boiling point of W22;104 °C. These vessels have insulated, 5% nickel-steel cargo tanks and can accommodate most liquefied gas cargoes up to a maximum specific gravity of 1.8 at temperatures ranging from W22;104°C to +80 °C at a maximum tank pressure of 4 bar.

Ethane

While ME-GI engines have been designed for use by several, different fuel types to date, ethane is a new departure. Ethane is one of the natural-gas liquids (NGLs) that are naturally occurring elements found in natural gas (and frequently separated removed and sold as a separate product), and include propane and butane, among others.

Hartmann Schiffahrt

Hartmann Schiffahrt is a ship-management company based in the northern German city of Leer. Founded in 1981, it manages the technical and economical aspects of its own and other fleets with a focus on the gas and container segments and is a world leader within the gas tanker segment. The company is part of Hartmann AG, which has diverse interests in the maritime transport and logistics sector such as dry bulk, product tankers, multi-purpose-vessels and offshore support vessel (OSVs).

Image: MAN B&W ME-GI low-speed, dual-fuel engine.