Monthly Archives: December 2016

Liquified Natural Gas (LNG) as Fuel for The Shipping Industry

It was a century ago when shipping had transformed from “coal fuelled”to “oil fuelled”. A another hundred years later, transformation to a newer fuel source is making waves, only this time, it is to “gas”.

Driven by tougher international and environmental standards, (Liquified Natural Gas) LNG is being termed as the fuel of the future. Accordig to experts, large scale shipping is believed to be sourced by LNG in the near future. According to DNV, being “LNG Ready” could be the best option for many ships.

Reasons for Transformation

Higher marine fuel oil prices have made way to development of newer technologies based on cost and environment efficient fuels such as natural gas. Natural gas is a potential winner in terms of being environment friendly, safe, reliable and cost effective. When compared to oil, natural gas has become an important commodity with a key global energy impact. Due to the influential properties possessed by natural gas, it is the only alternative fuel which is believed to drive the future. Studies have shown that usage of natural gas or (Liquified Natural Gas) LNG as fuel has cut down the poisonous sulphur emissions or SOx significantly with a substantial reduction in carbon dioxide (CO2) and nitrox or NOx gases.

Boat-Diesel-Black-Exhaust-SmokeLNG or Liquefied Natural Gas is super chilled and in liquid state when transported. Since it is already seen as a supplement fuel for a variety of segments, it can create an even bigger impact when used as ship fuel. Climate changes, current and future international shipping regulations, etc. are anticipated as costly laws which need to be complied at various stages and (Liquified Natural Gas) LNG fuel is expected to support in the process.

LNG fuelled ships are able to emit almost zero sulphur oxide emissions, which is appropriate when the regulatory 2015 ECA’s or Emission Control Areas come in action. Due to lesser carbon content in LNG, release of the harmful carbon dioxide gas is reduce by nearly 25 percent. With the present market value of LNG in commercially viable regions such as the US and Europe, LNG could be offered at  a competitive price when compared to heavy fuel oil or HFO and even more attractive when compared to the low-sulphur gas oil, as fuel on ships.

How is the transformation taking place? 

Major container liner companies such as CMA-CGM are working towards developing future ships which are (Liquified Natural Gas) LNG fueled  along with implementing other technologies to reduce harmful ship emissions. This technology can only be developed when a solution to LNG refueling has been concretely developed. Wartsila, a major ship engine maker has developed and completed conversion from oil-run engines to LNG powered. Such duel fuel engines have now been implemented in several cargo ships.

M/V Bit Viking is considered the largest of the vessels afloat and in service with approx. 25, 000 dwt powered by LNG. Similarly, M/S Viking Grace is the largest passenger vessel to use LNG fuel. After almost a decade in development of LNG technology, presently, approximately 30 floating vessels are (Liquified Natural Gas) LNG fuelled and servicing the European waters. Tugboats and high speed ferries are next in line for the conversion to LNG.

bit-viking

Some companies are building hybrid ships ( Read hybrid ferry and hybrid car carrier) that are able to run on both oil and gas as fuel. The technology will see ships to be powered by natural gas for upto half way through the voyage and still be capable to switch over to bunker fuel for the remainder of the journey. Idea will be to use natural gas as the primary source of power and bunker fuel as a secondary / emergency one.

Disadvantages of Using LNG as Fuel 

A potential disadvantage to using LNG is space. Since gas weighs more, volume-wise it requires more space as compared to bunker oil. The farther the journey, the equally larger amount of storage space is required. So far, tanks are designed to be built in the cargo spaces of the ships for using gas as fuel. This is a major setback for the ship operators in terms of freight earned by the cargo. Engineers and architects are working towards developing systems that would make room for storing (Liquified Natural Gas) LNG. This could be anywhere on the vessel, above-deck, in the superstructures, beneath the cargo containers, astern of the vessel, etc. and this would also call for extra insulation, piping and steelwork as far as construction of the vessels is concerned. Moreover, Hyundai has now developed dedicated LNG storage tank.

Strict pollution regulations mean ship operators will be also installing more expensive units to cut emissions such as scrubbers.  Another drawback before introduction of (Liquified Natural Gas) LNG is the availability of the fuelling stations, as these may have to be set up at major ports or at regular bunkering points, feasibility studies and reports may have to be attained.

Research has been progressive regarding extraction of natural gas trapped in rock formations around the globe. Future for low sulphur fuel oil looks bright and at the same time demanding with refineries falling short of delivering upto standard requirements. Ship operators are definitely going to spend from their nose with the implementation of stricter global laws and safety standards. Due to this, use of low-Sulphur fuel oil or marine diesel oils will raise the shipping companies’ operating costs by four folds. This is slowly making the owners realise the value of natural gas as a prime fuel for ships engaged in long voyages. The dynamics of the ever-increasing global trade and transportation industry are working in favour of investing in natural gas for fuel on ships.

Before taking a call for the change-over decision, ship operators need to identify the scope of transition with introduction to dual fuel system, price comparison of the commodities and the areas where their ships would ply. This means ships that frequently pass through the ECA and SECA’s or the emission control areas would be depending on the rise in (Liquified Natural Gas) LNG fuelling technology.

LNG fuel surely holds a promising future in the shipping industry. However, only time can tell as to how well it becomes an integral part of the shipping industry in the days to come.

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World’s First Dual-Fuel, Low-Speed ME-GI Engine Delivered

 Doosan Engine has confirmed delivery of the world’s first dual-fuel, low-speed ME-GI engine to the American National Steel and Shipbuilding Company (NASSCO) shipyard in San Diego, USA. The new engine is capable of operation on LNG and/or bunker C oil and will power the first of two 3,100-teu container ships ordered by TOTE, the American marine transportation company.

The Korean engine maker originally won the order to build the ME-GI engines in 2013, since which time the first ME-GI unit has successfully passed through design, manufacture, and test-run stages. On 3 June 2014, Doosan Engine successfully completed the engine’s official trial run in the presence of the shipowner, shipyard, and classification society representatives.

Doosan Engine also tested the ME-GI’s Fuel Gas Supply System (FGSS), which has 300 bar of operating pressure, at its Changwon plant. At the
culmination of two months of extensive testing, the gas system had passed all regulations and restrictions as regulated by the American Bureau of Shipping (ABS) and United States Coast Guard (USCG).

TOTE-ship_highres-XL

The TOTE ME-GI engine will primarily operate on LNG, which is currently more competitively priced than bunker-C oil. The ME-GI is a next-generation, eco-friendly engine, which reduces polluted material such as carbon dioxide, nitrogenous compound, and sulphur compounds compared to existing diesel engines.

The Contract

The TOTE contract provides for the construction of two newbuilding, state-of-the-art containerships – with an option for three more vessels – for primarily domestic services. The vessels will each be powered by a single 8L70ME-GI dual-fuel gas-powered engine.

The two 3100 TEU vessels will be the most environmentally friendly containerships in the world, powered primarily by LNG, and will operate between Florida and Puerto Rico. The ship design will allow the transport of conceivable products.

The ME-GI Engine

The ME-GI engine represents the culmination of many years’ work. Depending on relative price and availability, as well as environmental
considerations, the ME-GI engine gives shipowners and operators the option of using either HFO or gas – predominantly natural gas. An ME-LGI
counterpart is also being developed that uses LPG and methanol.

Doosans-Changwon-works_highres-L

MAN Diesel & Turbo sees significant opportunities arising for gas-fuelled tonnage as fuel prices rise and modern exhaust-emission limits tighten.
Indeed, research indicates that the ME-GI engine delivers significant reductions in CO2, NOx and SOx emissions. Furthermore, the ME-GI engine
has no methane slip and is therefore the most environmentally friendly technology available. As such, the ME-GI engine represents a highly efficient, flexible, propulsion-plant solution.

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Selection of stainless steels for cryogenic applications_toughness

Selection of stainless steels

Affect of steel structure on toughness

The toughness of the austenitics relies on their fcc atomic structure. The presence of either ferrite or martensite can limit the cryogenic usefulness of the austenitic stainless steels.
The small levels of ferrite usually present in wrought austenitics is not usually detrimental.

Cold working of austenitic stainless steels can also affect their cryogenic toughness.
This is due to the progressive formation of martensite from the ‘meta-stable‘ austenite. In effect this is similar to the presence of ferrite and can be controlled in the same way through compositional changes that stabilise the austenite.
In addition the effects of cold work can be removed by heat treatment. Solution annealing (softening) by heating to around 1050 / 1100 °C and cooling in air, depending on section size, will completely stress relieve the structure and transform the structure back the naturally tough austenitic one.

Welded areas may be at risk of brittle failure at very low temperatures, as ferrite levels in welds are higher than the surrounding wrought steel (to avoid hot cracking on solidification).
Special low ferrite level welding consumables are available for cryogenic applications and should be considered for very low, safety critical, temperature applications.

Castings compositions for austenitic stainless steel also have ferrite levels higher than the corresponding wrought grades BS3100 – Steel Castings for General Engineering Purposes, requires special impact tests at -196°C for the cryogenic application grades such as 304C12LT196. Although there are no major restrictions on composition, this grade is required to meet an additional Charpy impact test requirement of 41 Joules minimum at -196°C

Impact toughness of austenitic stainless steels

When austenitic stainless steels are Charpy tested at -196°C the test piece is usually ductile enough not to fracture (which actually invalidates the test).

Data available however quotes impact energies of over 130J for the 304 (1.4301) type. This is well within the 60-Joule minimum required in BS EN 10028-7 pressure vessel standard for 304 (1.4301) at -196°C.
Any of the austenitic stainless steels should be suitable for applications at these temperatures. The best choices of grades for very low temperatures are those with austenite stabilising additions such as nitrogen e.g. asi n grade 304LN (1.4311). (Higher alloy grades such as 310 (1.4845) or 904L (1.4539) which derive their austenite stability from higher nickel levels could also be considered)

Wrought grades with ferrite stabilising additions such as 321 (1.4541) or 347 (1.4550) may not be suitable at very low temperatures e.g. at the liquid helium boiling point of -269°C.

Impact toughness of other stainless steels

The ferritic, martensitic and duplex stainless steels cannot be considered as cryogenic steels.
Their impact characteristics change at sub-zero temperatures in a similar way to low alloy steels. The transition temperatures will depend on composition and heat treatment.

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Selection of stainless steels for cryogenic applications

stainless steelsIntroduction

  Ferritic, martensitic and duplex stainless steels tend to become brittle as the temperature is reduced, in a similar way to other ferritic / martensitic steels.

  The austenitics stainless steels such as 304 (1.4301) and 316 (1.4401) are however ‘tough’ at cryogenic temperatures and can be classed a cryogenic steels.

They can be considered suitable for sub-zero ‘ambient’ temperatures sometimes mentioned in service specifications sub-arctic and arctic applications and locations (typically down to -40°C).

This is the result of the ‘fcc’ (face centred cube) atomic structure of the austenite, which is the result of the nickel addition to these steels.

  The austenitics do not exhibit an impact ductile / brittle transition, but a progressive reduction in Charpy impact values as the temperature is lowered.

  There is a useful summary of low temperature data for austenitic stainless steels on the Nickel Institute website.

Impact toughness and impact strength measurement

  Impact tests e.g. Charpy, are done to assess the toughness of materials. To assess their suitability for cryogenic applications, the test is done after cooling the test piece.

  The Charpy impact test measures the energy absorbed in Joules when a standard 10mm square test piece (usually with a 2mm deep ‘v’ notch) is fractured by striking it in a pendulum type testing machine.

The more energy absorbed, the tougher the material, and less likely it is to fail ‘catastrophically’ if subject to mechanical shocks or impacts.

The impact toughness of steels varies with temperature.

Ferritic and martensitic steels exhibit what is known as a ‘ductile / brittle transition’ where, over a certain temperature range, there is a pronounced reduction in the impact toughness for a small decrease in test temperature.

  When plotted on a graph, the energy absorbed against temperature produces an ‘S’ curve.

The mid-point on the ‘S’ is known as the ‘transition temperature‘. Here the fracture failure mode changes as the temperature is lowered, from ‘ductile’, where the steel can absorb quite a lot of energy in breaking, to brittle, where only a small of amount of energy is absorbed.

For this reason it is dangerous to use steels in this brittle state in structural applications, as even small shock loads can result in sudden, possiblecatastrophic failures.

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