pressure cryogenic pump, pulsation damper, vaporiser and a gas flow/pressure/temperature control system.
The cryogenic centrifugal pump supplies the LNG from the cryogenic storage tank to a suction drum at the inlet of the cryogenic high pressure pump. This pressurises the LNG to the required pressure. The vaporiser is connected to the pump outlet and the LNG is heated to 45°C, vaporising it to form CNG. The ME-GI control system supplies a gas pressure set point to the gas supply system depending on engine load. Highlighting the importance of the research project when it came to the gas supply system, Mr Juliussen said it was important for MAN Diesel & Turbo to be able to take control of it for safety reasons, “as it meant that safety was in our hands at all times. We could control this, so there was no chance of any kind of failure. There was no random development of the system, as we could test it and verify it to be assured that it was working as it must do.”
Another important safety element was the fact that the fuel lines were double walled, in order to prevent gas leakage in the engineroom. The space between the two walls was ventilated so that a sensor placed in that area could detect any gas leaks.
Elsewhere, the inclusion of a gas composition sensor allowed the engine to be optimised to the actual condition of the gas. “The engine can run on any quality of natural gas, as long as the sensor tells the engine the calorific value of the gas at any time,” Mr Juliussen explained. He pointed out the quality of the gas could change quite significantly throughout the voyage of an
LNG tanker so the sensor tells the engine control unit the calorific value of the gas and, based on this, it calculates how much gas to inject in order to have the optimum performance. Once the conversion of the gas engine was completed, it was benchmarked against operation on diesel oil. The conclusions were extremely positive: NOx emission levels of the ME-GI gas engine are about 25 per cent lower than on diesel oil operation given comparable
engine operating conditions, while CO2 emissions have been slashed by 23 per cent. Direct injection of gas also results in low
methane slip. Mr Juliussen commented: “While the sulphur content is the most obvious benefit, a low methane slip is a main contributor to low emission values.”
Since December 2012, 20 ME-GI gas engines have been ordered for gas tankers and container ships, including for the US container lines Matson Navigation and TOTE and the LNG operator Teekay LNG Partners.
Mr Juliussen revealed that 50 more orders would be coming through in the near future. He told conference delegates: “We originally targeted the conversion of LNG tankers, but the first order was for container ships, which was a little bit of a surprise for us. But because of the market conditions, gas is an attractive fuel of the future.” He added: “US operators like TOTE have to operate in Emission Control Areas (ECA) and gas is available in the US at a relatively low cost, so this is the cheapest way to use a fuel with low sulphur.”
TOTE ordered the dual-fuel 8L70ME-GI engine for two 3,100 teu container ships that
San Diego shipyard NASSCO is building. It also has an option for possibly three more vessels. The first ship is expected to be delivered by the fourth quarter of 2015, with the second ship expected by the first quarter of 2016. Matson has placed an order for two MAN
Diesel & Turbo 7S90ME-GI dual-fuel engines, with options for a further three vessels. The engines will be manufactured by MAN Diesel & Turbo's licensee Hyundai Heavy Industries and will be able to use heavy fuel oil, marine diesel oil or LNG as fuel. MAN Diesel & Turbo said that they are the largest dual-fuel engines ever ordered in terms of power output, with each engine capable of 42,700kW. The vessels are being constructed by Aker Philadelphia Shipyard and are slated for delivery in the third and fourth quarters of 2018. Meanwhile, Teekay LNG Partners has placed
an order for two LNG carriers, each powered by a pair of 5G70ME-GI engines, with an option for three further ships. The ships will be constructed by Daewoo Shipbuilding & Marine Engineering and are due to be delivered in the first half of 2016.
The ME-GI engine can also be retrofitted; since the conference, the first such order has been announced, to convert the engine on a Qatari LNG carrier (see page 100). While retrofitting the engine could in many cases be more complex and costly than fitting it on a newbuild, this will not always the case. “If you retrofit an LNG carrier, you have the gas tanks already available on-board, which is an advantage as then you only need to convert the engines to gas,” Mr Juliussen said. While the Helios project has been completed, developments are still being continued. MAN Diesel & Turbo is already working on a design that can be used with Liquid Petroleum Gas (LPG), which is not currently used as a fuel for ships. Mr Juliussen said that the benefits of using it included that the gas has a low sulphur content and could be cheaper to use than low sulphur oil.
Here, the engine’s design is being adapted slightly to suit the different type of gas. While the control system is the same, Mr Juliussen said that because LPG was being used in liquid format (heated to 20°C) rather than the gas format of CNG, a pressure booster system is used to inject it, rather than the common rail system currently used. Mr Juliussen estimated that it is possible that the LPG-operated engine could be in use by the end of 2015. While CNG would be the preferred solution for large vessels, LPG could be a solution for smaller vessels, as well as for tankers that carry LPG. MP
The Helios project involved converting an electronically-controlled 4T50ME-X two-stroke, low speed research engine to gas operation
www.mpropulsion.com
•More details of the Helios project, including presentations from the November conference, are available at
http://helios-fp7.eu/
Marine Propulsion I April/May 2014 I 97
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