A new environmental concept for tanker shipping

06 Dec 2010
Artist’s impression of DNV’s Triality VLCC concept

Artist’s impression of DNV’s Triality VLCC concept

Class Society DNV has unveiled a new design concept for a VLCC that offers drastic savings in exhaust emissions, and in which the need for ballast water is eliminated and VOC emissions are cut to virtually zero.

The new crude oil concept vessel, named Triality, has been developed through a Det Norske Veritas innovation project. The name indicates its three main aims: it is environmentally superior to a conventional crude oil tanker, its new solutions are feasible and based on well known technology, and it is financially attractive compared to conventional crude oil tankers operating on heavy fuel oil (HFO). These goals, says DNV, can be achieved through operating on LNG rather than HFO as main fuel, redesigning the hull form to cut the need for ballast water, and recovering cargo vapour gases for use onboard.

DNV CEO Henrik O. Madsen, who presented the new concept in its VLCC version in London, says: “I am convinced that gas will become the dominant fuel for merchant ships. By 2020, the majority of owners will order ships that can operate on liquefied natural gas (LNG). As a leading class society, DNV has an important role to play in finding more environmentally friendly solutions for the shipping industry, and I’m proud of what has been achieved for the crude oil tanker segment through this innovation project that we are presenting today.”

The Triality concept VLCC has the same operational range as a conventional VLCC and can operate in the same ordinary spot market. DNV claims that compared with a conventional VLCC, the Triality will:

  • emit 34% less CO2
  • eliminate entirely the need for ballast water
  • eliminate entirely the venting of cargo vapours (volatile organic compounds - VOCs)
  • use 25% less energy

Less harm will be caused to the health of people living close to busy shipping routes and ports as NOx emissions will be reduced by more than 80% while emissions of SOx and particulate matter will fall by as much as 95%.

Two IMO type C pressure tanks capable of holding 13,500 m3 of LNG - enough for 25,000 nautical miles of operation - are located on the deck in front of the superstructure. The generators are dual fuel (LNG and MGO - marine gas oil) while the auxiliary boilers operate on recovered cargo vapours (VOCs).

According to DNV, a traditional tanker in unloaded transit needs ballast water to obtain full propeller immersion and sufficient forward draught to avoid bottom slamming. The V-shaped hull form and cargo tank arrangements are said to completely eliminate the need for ballast water in the VLCC version. The same principles can be applied to other tanker types, such as Suezmax, Aframax and smaller ships. The new hull shape results in a reduced wetted surface on a round trip and has a lower block coefficient and thus a more energy efficient hull.

A VLCC in unloaded transit will normally carry between 80 000 and 100 000 tons of sea water containing organisms that can cause damage when released into foreign ecosystems. In addition, transporting ballast water involves consumption of fuel, and hence higher exhaust emissions, conmpared with a totally empty ship. Finally, DNV says that the elimination of ballast tanks will also eliminate a major concern for most shipowners – i.e. the initial coating and later maintenance of ballast tanks during operations.

The concept tanker design is powered by two high pressure dual fuel low speed main engines fuelled by LNG, with MGO as pilot fuel. Because the absence of ballast water means that the ship runs at much reduced draught when empty (6m-8m is estimated) two smaller-diameter propellers are needed to transmit the propulsion power. DNV says that the next phase of the Triality concept development will review the use of dual fuel medium speed engines and pure gas engines.

DNV has calculated that the Triality VLCC can collect and liquefy more than 500 tons of cargo vapours during one single round trip. These liquefied petroleum gases can then be stored in deck tanks and up to half will be used as fuel for boilers powering steam-driven cargo discharge pumps, while the rest can be returned to the cargo tanks or delivered to shore during oil cargo discharge. The low storage temperature of the LNG fuel can be used in the vapour liquefaction process; this can also help lower the engine intake temperature, improving engine efficiency and hence fuel economy.

DNV president Tor E. Svenson told The Motorship that he was excited about the concept. He pointed out that the technology was well-proven, but this is the first time it had all been brought together in one ship design. DNV had been speaking to owners and yards, as well as suppliers: e.g. MAN Diesel and Turbo for the ME-GI main engines, and Hamworthy for the gas systems. Everything should work well together, he said – for example the V-shaped hull offered benefits in propulsion efficiency as well as doing away with ballast. The nest stage is for a shipyard to produce a detailed design in which DNV’s concept can be translated into reality.

When it comes to the additional cost of building a vessel like Triality and the reduced cost of operating it, Madsen says the conclusion is clear: “It is possible to develop an environmentally superior ship and be profitable at the same time. Our best estimate is an additional capital expenditure of 10%-15% for a Triality VLCC newbuilding compared to a traditional VLCC. Even with this extra cost included, we estimate a reduced life cycle cost equal to 25% of the newbuilding cost for a traditional VLCC.

“Triality is a concept vessel and a ship builder will need to prepare a detailed design before the first Triality crude oil tanker can be constructed. The Triality concept is based on well known and proven components and systems, so in principle a Triality crude oil tanker introducing all or some of the innovative elements in the concept can be designed today. I am convinced that the Triality concept will create great interest among ship builders and crude oil tanker operators, so that the first Triality crude oil tanker will leave a shipyard before the end of 2014,” concludes Madsen.

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