Gas is coming of age in the shipping world

Wärtsilä article, 30 November 2011

Produced by Mirja-Maija Santala, Media Manager, Wärtsilä Corporation

An article based on the text was originally published in Motorship magazine July/August 2011 issue

Text: Patrick Baan, Director, Concept & Solutions, Ship Power Technology, Wärtsilä Italia

Gas is both competitively priced and environmentally sound, making it a viable and sustainable fuel alternative for shipping in the foreseeable future. Gas engines are being installed not only in newbuild vessels, but also as conversion packages for ships already in operation.

For most vessel types, fuel costs are the most dominant item in the overall cost of ownership. Whilst diesel engines need after treatment to abate nitrogen oxide (NOx) emissions, and costly lower sulphur fuels or, alternatively, scrubbing systems to meet SOX requirements, Wärtsilä’s dual fuel engines can operate with no added systems or costs. In gas mode they already comply with upcoming emissions legislation. The more time a ship spends in emission sensitive areas, the more attractive the gaseous fuel alternative is from a total cost of ownership perspective.

Wärtsilä has been involved in a number of feasibility studies to evaluate the total cost of ownership using gas as a fuel alternative. The key question in these discussions has been the price one has to pay to get the fuel on board. It is of note that even with fairly moderate assumptions regarding the difference in cost between bunker liquefied natural gas (LNG) and traditional fuels, LNG has consistently been shown to be an attractive alternative to marine diesel oil (MDO) and low sulphur fuel oils.

Combating emissions

Lean burn gas engines have lower peak temperatures, which in turn results in less NOx formation from the combustion. In fact, the NOx emission requirements for NECAs, scheduled to come into force in 2016, can be met by these engines without secondary means. When liquefying natural gas, the sulphur (S) is removed, thereby eliminating sulphur oxide (SOx) emissions. The cleanliness of the combustion is also reflected in the low particulate matter (PM) and carbon dioxide (CO2) emissions. PM is reduced to about 1% of the value of that from a diesel engine, while CO2 is reduced by some 20% - thanks to the lower carbon content of natural gas compared to heavier hydro carbons, and to the higher efficiency of the Otto cycle. When calculating a ship’s Energy Efficiency Design Index (EEDI), the lower levels of CO2 are of significance since ships using dual fuel engines have a lower EEDI value.

LNGPac enables safe and convenient onboard storage and supply

LNG carriers have, for a long time, used boil-off gas to generate power for their propulsion. In 2006, the introduction of dual fuel engines created a revolution in LNG carrier propulsion, improving total efficiency by more than 10 percent (comparing steam turbines with dual fuel gensets + electric propulsion).
To facilitate the expansion of dual fuel technology use beyond LNG carriers, Wärtsilä has developed a range of standardised onboard LNG storage and supply systems. These consist of a type-C tank and pressure build up unit, without any moving parts. The Wärtsilä LNGPac comprises a complete gaseous fuel feed system, including bunkering lines, storage tank, safety systems, documentation for installation, operation and maintenance, and training for the ship’s crew. The alarm and control system of the Wärtsilä LNG Pac is based on the same proven UNIC technology as used to control the engines. The LNGPac can be delivered as turnkey solution, both for newbuilds as well as for existing ships.

Cost efficient alternative

Utilities and industry in general are more and more selecting gas as a means of reducing their carbon footprint. This is promoted heavily by governments striving to meet their commitment to cut CO2 emissions. At the same time, the availability of new technologies is propelling a move towards a gas based energy supply system. Abundant shale gas reserves in North America are likely to result in future gas prices being established by competition and coal displacement, rather than by oil product pricing thus making gas a cost efficient alternative. The USA may change from being a net LNG importer to a LNG exporter by the year 2020.

Flexibly switching between gas and diesel

For a land-based power plant, available fuels are easy to identify and engines can be optimised exclusively for the fuel of choice (mono fuel engine). Should the situation change at a later time, an upgrade to another mono fuel configuration may be an easy option.

Shipping is a different business though. When deploying a vessel worldwide, the bunkering of LNG may be a problem in some parts of the world. Traditional shipping fuels could, in that case, seem the better solution. Alternatively, one could compromise the space needed for onboard LNG storage capacity by using LNG for fuel only when sailing in emission sensitive areas (meeting IMO Tier III requirements for NOx and SOx), and then switching to heavy fuel oil (HFO) on the open sea.

Wärtsilä dual fuel engines offer all the benefits of a gas engine, whilst maintaining the ability to be operated as a conventional diesel engine when required. This provides maximum fuel flexibility without operational limitations. . Furthermore, the capacity of the gas storage system can be designed to have the optimal balance between the space required for gas storage and the space deployment for vessel mission specific needs.

    

 

Even for ships where gas is available most of the time, dual fuel technology with its built-in liquid fuel back-up mode, allows the ship to be safely and continuously operated should the gas supply be interrupted. In the case that the onboard gas feed system is interrupted, dual fuel engines automatically trip to diesel without loss of the delivered power. For this reason, dual fuel engines have the highest operational availability and reliability.

Wärtsilä dual fuel engines are based on the company’s well proven diesel engines. This means that the mechanical system of the engine is based on sound and well proven design. It also offers significant benefits where the vessel’s power plant comprises a combination of gas and diesel engines, so that common spares can be used for non-combustion specific items.

Even though the emission and cost benefits of gaseous fuels are widely recognised, some owners are reluctant to adopt dual fuel technology because of questions concerning the availability of gas. In such cases, “DF ready” can be the solution. In this case one gets initially a “pure” diesel engine, but with the essential retrofit measures already taken so that a future conversion to dual fuel technology is relatively easy as and when LNG becomes available.

Also for passenger vessels

Passenger vessels usually have high installed power and are often deployed in coastal areas with stringent emission requirements. After carefully exploring the alternatives Viking Lines, the Finland-based ferry operator, selected Wärtsilä duel fuel technology for their new passenger liner that will operate between Stockholm, Sweden and Turku, Finland. The ship will be built at the STX Turku shipyard in Finland, and is scheduled to enter service in 2013. LNG offers the most economically and environmentally sound solution for the future.

An active interest in gas conversion

Although the question as to whether or not to opt for gas may get much attention when discussing newbuilds, the first conversion of a merchant vessel to gas fuel is already close to completion at the time of writing. In 2010, the Tarbit Shipping AB company decided to upgrade its 25.000dwt chemical tanker, the ‘Bit Viking’, to natural gas fuel via a dual fuel solution. The ‘Bit Viking’ is operated in Norway, where support from the Norwegian NOx fund could be accessed to help finance the conversion. The conversion involves upgrading the two existing Wärtsilä 46 main engines to Wärtsilä 50DF engines, and installing two Wärtsilä LNG storage tanks of 500m3 each on deck. Several other conversion projects are under discussion and appear likely to materialize soon.

    

New developments for shipping

The expansion of dual fuel technology from LNG carriers to other vessel types and sizes, requires new features to be developed in order to meet customer expectations. Utilizing dual fuel technology for smaller vessels, for example, resulted in the introduction of the Wärtsilä 20DF engine. The use of this technology for direct driven applications with 4-stroke engines driving controllable pitch propellers, is yet another example, as is the development of multi fuel capability for slow-speed engines. Other new applications for the use of gaseous fuels in shipping may result in other specific requirements, for which new technologies need to be implemented.

As the marine industry’s leading solutions provider, Wärtsilä has taken the lead in promoting natural-gas-based power. The market can expect the development of a product portfolio that matches the needs of both today and tomorrow.