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Comprehensive solution for clean propulsion

Comprehensive solution for clean propulsion…
a case for dual-fuel technology


Rick McArthur presents Wärtsilä’s case for dual-fuel propulsion with gas combustion technology as the
low-emission, economical alternative to conventional fuels.

Dual-fuel propulsion with gas combustion technology offers the most comprehensive solution for operating vessels without smoke or particulate emissions, and with the lowest possible levels of carbon dioxide and sulphur oxide.

Three approaches can be employed to reduce the emissions generated by vessels powered by fossil fuels: 

(1) Using conventional liquid fuel and adding emission-reduction solutions to the engines; 

(2) Using liquefied natural gas (LNG) as the only on-board fuel; 

(3) Dual-fuel technology, which allows the most economical option – marine diesel oil (MDO) or LNG – to be used in all circumstances.

The strength of dual-fuel technology is its ‘fuel flexibility’: dual-fuel solutions make it possible to use MDO in transfers and LNG when operating in port, close to shore or in an emissions control area (ECA). Using LNG as fuel can also reduce a vessel’s operating costs because owners and operators are free to opt for the most suitable fuel. These features have, for example, persuaded a number of offshore service companies to employ the latest dual-fuel technology to power their ships.

Simple and effective

Using LNG with combustion technology means that no exhaust gas treatment is required in order to comply with nitrogen oxide (NOx) emission requirements, as the emission levels fall well within the parameters. Another benefit is that the space needed for equipment installation and the storage of consumables is reduced. Sulphur oxide (SOx) levels are practically zero, no particulates (soot) are generated, and carbon dioxide (CO2) emissions are also significantly reduced.

More than 100 vessels in merchant, offshore and ferry applications are already operating on gas and many of them are regularly sailing the Caribbean. 

Natural gas consists primarily of methane, a potent greenhouse gas (GHG).

“In overall terms, dual-fuel propulsion solutions, applying lean-burn technology, produce approximately 10 per cent less GHG emissions than a diesel engine of equivalent output running on MDO,” said Tomas Aminoff, director of product management at Wärtsilä Ship Power.

From a design viewpoint, the biggest challenge when using LNG is providing the on-board space required for fuel storage. Specific bunkering arrangements also have to be provided. In dual-fuel configurations, as LNG will only be used in port and when operating in ECAs, the storage tank can be smaller than if it was the only on-board fuel.

Maximising comfort and convenience

The design already exists for an LNG-powered super yacht. In a joint project, Fincantieri Yachts, Wärtsilä and Stefano Pastrovich of Pastrovich Studio developed a new concept in which dual-fuel technology is fully integrated into a world first – the 99 metre, dual-fuel, IMO Tier III-compliant XVintage motor yacht. The XVintage power and propulsion system is based on Wärtsilä 20DF dual-fuel engines, compact units. Fully compliant with upcoming IMO Tier III regulations when operating in gas mode, they can be switched between fuels without any loss in speed or power output.

The dual-fuel gensets in XVintage are equipped with alternators mounted on a common bedframe and utilise double-mounting arrangements, meeting the most stringent standards for levels of noise and vibration.

Wärtsilä’s pioneering of dual-fuel engine technology has paid particular dividends in the LNG carrier and offshore service vessel markets. Many vessels of this type operating in Caribbean waters are powered by Wärtsilä dual-fuel engines, thereby furthering the environmental sustainability of the region.

Bunkering and fuel storage 

All fuels require safe handling arrangements and LNG is no exception. Pumped from one location to another through pipelines in gaseous form, or transported by sea in liquid form, the transformation phase from gas to liquid requires cryogenic temperatures.

LNG carriers move natural gas from liquefaction terminals to regasification terminals all over the world. And LNG is available at all of these shore-based facilities. Marine LNG import and export terminals are located almost everywhere. LNG is available anywhere in the world. Several new terminals are scheduled to come on stream.

What is missing at this time is the infrastructure to transfer LNG from these terminals to the vessels that require it. The availability of LNG bunkering for vessels using LNG as marine fuel is also spreading widely – mainly in environmentally sensitive regions or in locations where price makes this propulsion alternative particularly appealing.