industry, the dual-fuel MT30 would apply fuel system hardware derived from the industrial Trent engine. Some 24 dual-passage injectors (one for diesel oil, the other for gas) would supply both fuels to the combustion chamber. Using a dual-passage injector allows both fuels to be burned simultaneously in the chamber, enabling the turbine to maintain power output while changing fuels or burning a mixture of gas and liquid fuels. The engine’s electronic controller governs the fuel admitted via metering valves, underwriting safe operation in all fuelling modes. A number of MT30
gas turbine-based
propulsion systems were proposed for LNGCs of between 145,000m3 and 250,000m3 capacity. The power density offered the potential
to
reduce engineroom length by approximately 19m compared with a steam turbine plant of equivalent output. The machinery space saving on a typical LNGC thus enabled the cargo- carrying capacity to be increased by up to 12 per cent, Rolls-Royce reported.
An electric drive further helped to optimise both the cargo area layout and the machinery system design. Additionally, the very lightweight power generating plant could be located aft on the quarterdeck behind the superstructure, leaving only electrical distribution equipment and propulsion motors enclosed in the hull below. Proposals included a combined gas turbine and steam turbine electric (COGES) propulsion system featuring a dual-fuel MT30 set arranged primarily to burn cargo boil-off gas delivered at a pressure of around 40 bar. A waste heat recovery steam generator incorporated in the exhaust stack of the gas turbine supplies a steam turbo- alternator set which supplements the electrical output of the main genset. System efficiencies in excess of 50 per cent were claimed. Both COGES and simple-cycle gas turbine
electric propulsion concepts were highly flexible in terms of machinery layout, ease of access for maintenance and simplified installation, Rolls- Royce asserted. Furthermore, the low noise and vibration characteristics of the gas turbine allowed the machinery to be located next to the superstructure and accommodation. US rival GE Marine also promoted the merits
of a number of dual-fuel gas turbine-based systems in either electric or mechanical drive arrangements for LNGC propulsion, including combined-cycle configurations with waste heat recovery steam turbines. Long experience with aero-derived gas turbines serving warships as well as cruise vessels and fast ferries supported GE Marine’s confidence in solutions based on its successful LM2500 and LM2500+ series. Similar benefits in plant layout flexibility and enhanced cargo capacity to the Rolls-Royce solutions were advanced by GE Marine. Further operational benefits – higher manoeuvrability and propulsion efficiency – were also promised
www.mpropulsion.com
GE Marine’s LM2500 series gas turbines have a long pedigree in naval and commercial ship propulsion
by adopting an electric podded propulsor instead of a conventional propeller system and optimising the aftbody of the hull.
Despite extensive and sustained promotional campaigns, however, neither GE Marine nor Rolls-Royce succeeded in breaking into the market. The US group last year revived its challenge with an LNGC design jointly developed with Dalian Shipbuilding Industry Co and Lloyd’s Register. “We are excited to team up with one of China’s largest shipyards and a leading maritime classification agency on this conceptual design,” said GE Marine’s vice president of marine operations Brien Bolsinger. “By employing GE gas turbines, this LNGC design will address increasingly stringent worldwide environmental regulations, while providing operators with reduced life-cycle costs.”
The initial design envisages a COGES system incorporating a 25MW gas turbine, a steam turbine-generator set and two dual-fuel diesel gensets for low power operations and back-up. Flexibility in prime mover configurations is facilitated, however, allowing a total installed power of 50MW if required.
The gas turbines can be equipped with a GE Dry Low Emissions (DLE) or single annular combustion system, both of which can meet IMO Tier III and US EPA Tier 4 NOx requirements with no exhaust treatment and no methane slip. Lloyd’s Register last year completed a preliminary hazard identification study – the first in a planned series – on the COGES- powered LNG carrier. The study examined the carrier’s hazardous areas, structural integrity, safe separation, pipe routeing and ventilation.
“The studies will help mature the design and minimise risk for the carrier system,” explained Lloyd’s Register’s director of business development and innovation, Nicholas Brown. The classification society will contribute a
series of risk assessment studies during design development, leading to a safety case document that it said will meet or exceed the most onerous bidding qualification requirements of oil majors for new technologies for shipping for LNG projects. Among the benefits of its gas turbine-based propulsion system for LNGCs, GE Marine cites: • NOx emissions are inherently low compared with traditional diesel engines; by last December, GE had manufactured 835 of its DLE systems for its aero-derived gas turbines with an aggregate operating time of almost 18 million hours;
• Fuel flexibility is increasingly appreciated by operators valuing dual-fuel capabilities for service in emission control areas; GE gas turbines can operate on a range of fuels, including marine gas oil, biodiesel, bio-synthetic paraffinic kerosene blends and natural gas; • Lower maintenance costs: even with turbines operating at full power all the time, combustor and hot section repair intervals can stretch to 25,000 hours when burning natural gas; • High availability is fostered by easy maintenance and scheduled inspections. When engine overhaul is required, the gas turbine can be changed-out in 24 hours and replaced with a spare unit; • Maximum reliability and component life in the marine gas turbines are promoted by incorporating the latest aircraft engine design technologies, quality requirements and corrosion-resistant materials. MP
Marine Propulsion I April/May 2014 I 31
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