LNG
Harvey Gulf Marine International was the first US owner to order LNG-fuelled vessels
LNG engines attracting growing market share
he session on LNG was designed to address issues such as current industry thinking, different methods of designing and operating LNG ships from the perspectives of designers, owners and engine builders, and what LNG means for the future of emissions compliance. The special session also looked at issues such as safety and operating costs, and aspects of LNG systems required for the safe/reliable operation of LNG fuel ships. Presentations were given by Terje Nordtun, team leader system engineering, OSVs and special vessels at Wärtsilä, and John Shock, offshore segment manager at Caterpillar. As has been highlighted in OSJ on a number of occasions, more and more shipowners have chosen to adopt LNG-fuelled engines. Until recently, all of them were based in northwest Europe and in Norway in particular, but more recently Harvey Gulf International Marine in the Gulf of Mexico has also ordered LNG- fuelled vessels.
T
Wärtsilä has been working on gas and dual-fuel engines for a number of years, and launched a dual-fuel (DF) engine in 1995, an engine that combined fuel flexibility and efficiency with environmental performance.
The last afternoon of the 2013 Annual Offshore Support Journal Conference included a special session on liquefied natural gas (LNG) as a fuel for offshore support vessels, reflecting the growing interest in adopting LNG in the sector
The company’s pure gas-ignition and dual-fuel engine types run on the Otto cycle while the gas-diesel engine operates on the diesel cycle. Only pure gas and DF engines are able to meet the IMO Tier III NOx emission limits without exhaust gas after-treatment.
DF technology enables the engine to be operated on natural gas, light fuel oil or heavy fuel oil, with switching between fuels executed seamlessly during operation without loss of power or speed. The same power output is realised regardless of the fuel used, and DF engines can also be started and stopped in gas mode and idle for up to eight hours on gas. As Mr Nordtun noted, DF engines are particularly attractive for vessels deployed in emission control areas (ECAs) where they can
18 I Annual Offshore Support Journal Conference and Awards 2013
burn clean natural gas, and outside ECAs, where a switch to traditional fuel oils can be made. No special measures, such as exhaust gas after- treatment, have to be adopted to meet the IMO Tier III NOx emission limits. Wärtsilä’s medium speed
DF engine
programme has grown to embrace 200mm, 340mm and 500mm-bore designs, these 20DF, 34DF and 50DF series covering an output band from 1,000 kilowatts (kW) to 17.55 megawatts (MW). Operational flexibility is cited by Wärtsilä as a key factor in promoting DF engines over pure gas engines for propulsion. Taking a typical gas-fuelled installation for an OSV, incorporating two 34DF and one 20DF engine-based gensets, all the engines are arranged for both marine diesel oil (MDO) and LNG supplies; and in normal operation all will run on LNG from a single gas source (such as Wärtsilä’s LNGPac system).
In the event of a gas system failure affecting
one engine, that engine can be switched to MDO operation; likewise, all the DF engines can be switched to MDO if a problem is encountered with the main gas supply. Such full redundancy from a pure gas installation calls for a greater investment on the gas handling side, says Wärtsilä.
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