Heavy lift vessel MV Eagle, owners Offshore Heavy Transport AS. One of two ships fitted with the new Fuglesangs marine gas oil booster unit incorporating the seal-less Hydra-Cell pump
The MV Eagle and the MV Falcon, two heavy lift ships working in northern waters, could be carrying the answer to potentially serious fuel pumping problems facing marine engineers in respect of ships berthing in EU ports or operating in SECA (Sulphur Emission Control Area) zones Baltic and North Sea. Both vessels have been fitted with marine gas oil booster units designed around the Wanner Hydra-Cell G35 – a pump of seal-less design that won DNV certification in January 2010. It can handle ultra-thin non-lubricating liquids – including light fuel oils satisfying all current and planned regulations on maximum sulphur content.
MARPOL pollution control regulations and EU Council Directives already in force for EU ports and SECA zones have been further tightened in 2010. Their practical effect is to oblige many ships to switch from viscous high-sulphur Heavy Fuel Oil to thin distillate fuels such as Marine Gas Oil (MGO).
But there is a technical difficulty. The 3-screw type of pump traditionally used for handling heavier oils has been able to rely on a full film of oil to prevent metallic contact and consequent wear as the rotors turn. Thin distillates are very poor lubricants - so there is potential for premature wear, high repair costs and even failure of pumps obliged to work close to the borderline of low fuel lubricity. Measures adopted by pump manufacturers to combat lubricity problems include the use of more wear-resistant materials and (for shaft seals) special cooling arrangements.
This is not a problem confined to screw pumps. Gear pumps and other types of pump reliant on seals or requiring a lubricating film between close-tolerance moving surfaces are potentially vulnerable when handling non-lubricating liquids.
In the Hydra-Cell design there are no dynamic seals. Smooth, low-pulse pumping action is achieved through the sequential flexing of multiple hydraulically balanced diaphgragms. Built into a single compact head, the diaphragms (5 in the G35 model) also isolate liquid media from the drive end of the pump, allowing it to handle many different liquids, hot or cold, viscous or thin, clean or dirty, including acids, caustics, slurries and abrasives.
Industrially Hydra-Cell pumps have successfully replaced seal-reliant types in pumping non-lubricating liquids in applications ranging from recycled solvents to raw turpentine and benzine, even Jet A-1 aviation fuel at high pressure. System pressures have varied, but the pumps can operate at any level from 1 bar (14.5 psi) to 70 bar (1014 psi) or higher. Flow is controlled by varying pump speed and remains constant irrespective of pressure.
Alexander Fuglesang, divisional director at Oslo-based pump specialists Fuglesangs AS, believes seal-less design is the factor that can make a critical difference in achieving a high reliability fuel line booster system.
“Unlike more conventional marine pumps,” he says, “this pump will not be operating close to the borderline because it does not depend on the pumped fluid for lubrication. With no seals to leak, there can be no question of internal or external fuel leakage. In a ship’s engine room that is a real benefit.”
New unit, with seal-less pump, installed in engine room of MV Eagle
The Eagle and the Falcon are the first vessels to be fitted with Hydra-Cell pumps since DNV certification was granted. Both ships are operated by the Norwegian oil service company Offshore Heavy Transport AS, second largest owner of heavy lift vessels in the world. For each ship Fuglesangs designed and built a complete system. With pump, motor, valving and controls mounted on a single skid, each system was supplied ready for use as a low maintenance ‘plug and pump’unit, handling liquids whose very low viscosities do not affect the performance or reliability of the pump.