VOC to be used to power North Sea tanker

Dec 16, 1997 01:00 AM

Equipment for adapting one of an existing tanker's two main engines to burn oil cargo vapour, or volatile organic compounds (VOC), is to be produced in Denmark next year.
Following combustion tests with various VOC compositions on MAN B&W's research engine in Copenhagen, the company is to supply the means for converting machinery on a North Sea shuttle tanker to operate on VOC.
Powered by two 6L55GUCA diesels, the subject vessel serves the Statfjord oilfield, which yields relatively large amounts of VOC.
Norwegian energy group Statoil, MAN B&W's partner in the VOC utilisation initiative, is to provide the complete gas collection, storage and supply system.
Statoil and MAN B&W had earlier indicated that one of the 127,000 dwt shuttle tankers on order for the Norwegian group in Spain would provide an in-service reference for a vapour recovery and mechatronic VOC fuel injection system.
A subsequent position paper from MAN B&W, though, focuses on plans to modify one of the present mainstays of the Statfjord traffic.
The conversion is expected to be completed in early 1999, leading to an 18 month evaluation programme to confirm the efficiency and reliability of all aspects of the system and engine performance.
The results will have an important bearing on Statoil's decision as to whether or not to apply VOC fuel technology throughout the fleet operated by its associated shipping company Navion.
Although only one engine in the Statfjord tanker is to be prepared for VOC combustion, the system installation will be undertaken in such a way as to facilitate extension of the arrangements to the other engine.
The fact that both units drive shaft generators offers added potential economic benefits.
Statoil has been monitoring VOC emissions from shuttle tankers since 1986 and has implemented measures such as modified tank design, new loading procedures, lower crude oil vapour pressures and lower temperatures at loading, as well as absorption of the VOC back into the crude, in an ongoing bid to cut vapour production and loss.
But the magnitude of the release, much of which occurs during loading, and the ensuing energy loss, spurred it into considering ways of using the flash-off as fuel, and developing the requisite process systems.
Besides offering savings in propulsion machinery fuel costs, the virtue of the concept lies in its promise of reduced environmental impact.
The quantities of VOC typically produced with oil cargoes are dependent on a number of key factors, including crude oil type and source and cargo tank configuration.
Statoil, however, is in no doubt that the volumes produced by its intensive North shuttle tanker activity are very substantial.
Back in 1994, it estimated that the equivalent of 850,000 barrels of crude, equal to the typical capacity of a newbuilding shuttle carrier, was being lost annually through evaporation during shipping operations from the Statfjord field alone.
MAN B&W suggests that a staggering 90% of a shuttle tanker's heavy fuel oil consumption might potentially be substituted with VOC, depending on the composition and volume of VOC generated and the ship-s operating profile.
It has also been estimated that VOC given off has a global climatic impact 20 times greater than carbon dioxide, one of the main gases implicated in the greenhouse effect.
The Norwegian authorities have already committed themselves to reducing VOC emissions in the environment to a sustainable level.
The VOC utilisation arrangements will be available to other shipowners, as Statoil is prepared to license its technology, while the engine concept is available to MAN B&W's licensees.
Since the extra cost of preparing a two-stroke diesel for VOC operation is only 1% to 1.5% of the engine cost, according to MAN B&W, it warrants consideration by companies contracting for new crude carriers, and particularly shuttle tankers.
The company reports that a number of engines have already been ordered with "prepared for VOC" written intothe specification.
The engine designer and licenser said the system would become commercially available for newbuildings after the successful completion of the sea demonstration test programme.
But it may be of interest to owners to have the engines in shuttle tankers and other crude oil carriers prepared for this technology before then, suggested MAN B&W's Danish arm.

Source: not available
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