ECAs (Emission-Controlled Areas) were established a few years ago in the North Sea and Baltic shipping areas, the English Channel and the U.S. and Canadian coastal regions. Ships that operate in these waters must reduce their sulfur emissions to 0.1 percent m/m. While heavy fuel oil (HFO) is used as a fuel outside these ECAs, ships switch to light fuel oil (MDO – Marine Diesel Oil) with its lower sulfur content within the environmental zones and in harbors.
These fuel changeovers are particularly frequent on cruise liners, which often go to new destinations every day. This puts considerable strain on machines and components, including the booster pumps that transport the fuel from the bunker to the ship’s engines under pressure—and consequently the mechanical seals in these pumps, which are designed for stable operating conditions and continuous lubrication of the seal faces.
PROBLEM MEDIA AND SPECIAL CONDITIONS
The seals applied to seal the pump shafts are exposed to extreme stresses due to the lack of lubrication of the seal faces and the constantly changing pressure and temperature conditions. In addition to the changes between HFO and MDO, the quality of the heavy fuel oil also has a negative effect on the lubrication required for the seal faces, and thus on how reliably the seals function. In HFO operation, water vapor can be mixed in with the fuel to reduce the amount of soot in the exhaust gas.
Furthermore, HFO can contain up to 30 percent of substances that cannot be defined more precisely according to current standards, and thus can potentially impair the seal. In addition, temperature jumps of around 126 degrees Fahrenheit (70 degrees Celsius) occur at the booster pumps and their seals during fuel changes.
As the vertical screw pumps used have mechanical seals installed at the top, gas building up in the seal compartment can also cause a lack of lubrication. Furthermore, the temperature limits for the FKM (fluoroelastomer) secondary seals applied as standard are regularly exceeded. The operating conditions immediately suggest the application of double mechanical seals, but this is often impossible due to the limited installation space and is undesirable on cost grounds. Conventional mechanical seals used to achieve a limited service life of 50 to 500 operating hours before unacceptable leakages occurred. This contrasts sharply with the operators’ demand for a MTBF of 8,000 hours.
Early wear of the mechanical seals thus caused massive problems for shipyards and cruise ship owners. Time and time again, the unavoidable replacement of seals resulted in a lot of time and money being spent on maintenance.
SOLUTION IN SIGHT: DIAMONDFACE
EagleBurgmann DiamondFace is the key to solving such sealing problems. The positive experiences gained from other applications, such as high tolerance to dry running and significantly longer service life, are impressively demonstrated yet again in these applications.
The four booster pumps in each of five cruise liners operated by one of the world’s largest ship owners have been equipped with type DF-M7S91 single mechanical seals coated with DiamondFace since 2011. While the pumps in the first two ships were retrofitted, the DF-M7S91 seals were installed in the other three ships while they were under construction in Papenburg, Germany.
These twenty seals with the high-tech coating have been working perfectly and without a hitch since commissioning. The massive leakages that used to occur have been eliminated and reduced to a minimum. Running times of up to 10,000 hours are now achieved by the M7S91, promoted by its extraordinary tolerance to dry running and the extreme chemical resistance of DiamondFace. This is combined with never before achieved MTBF values, much to the operator’s satisfaction. ◆
EagleBurgmann is one of the worldwide leading providers of industrial sealing technology. Mechanical seals, seal supply systems, magnetic couplings, carbon floating ring seals, expansion joints, gaskets and packings as well as comprehensive services are used wherever reliability and safety are needed. For more information, visit www.eagleburgmann.us.