carbon due to high temperatures and can result in the blocking of oil ways. The
tendency of an oil to break down and produce coke may be exacerbated by tur-
bine operating procedures commonly encountered in fast ferry service, such as
rapid acceleration and sudden shutdowns, resulting in the oil being subjected
to excessive temperature rises.
Swell is caused by synthetic seals coming into contact with synthetic oils
and absorbing the oil. Some swelling is desirable to ensure good sealing but
too much can damage the seal and result in leakage. In addition to swell char-
acteristics, the oil and the elastomers which come into contact must be compat-
ible in all other respects so that degradation is avoided.
BP Marine’s Enersyn MGT synthetic lubricant for marine gas turbines, a
corrosion inhibiting product, is claimed to offer the desirable properties out-
lined above, along with good thermal, oxidative and hydrolytic stability, and
corrosion resistance. It also conforms to the commonly required viscosity of
most synthetic oils for gas turbines, nominally 5 cSt at 100°C.
A 5 cSt synthetic lube oil from Castrol Marine, Castrol 5000, is also
approved for use in a range of aero-derived marine turbines, promising excel-
lent high-temperature and oxidation stability as well as superior load-carrying
capabilities. Another synthetic lubricant, Castrol 778, is claimed to exhibit excel-
lent anti-wear and rust-protection properties supported by superior oxidation
stability. The turbine is protected during extreme cold weather starting and dur-
ing extended high-temperature operation, and deposit or sludge formation is pre-
vented over prolonged drain interval periods.
air filTraTion
The use of air filtration systems tailored to the individual application can sig-
nificantly enhance the reliability and efficiency of a marine gas turbine instal-
lation. A typical filtration system comprises three stages:
l Vane separator: a static mechanical device that exploits inertia to
remove liquid droplets from an airflow passing through it. The intended
purpose of this first stage is to remove the bulk of any large quantities
of water and coarse spray that may otherwise overload the remaining
components of the filtration system. This type of device can remove
droplets down to around 12 microns in size, beyond which inertia has
little effect. Unfortunately, the damaging salt aerosol experienced within
this environment is predominantly below this size and so will pass to the
next filtration stage.
l Coalescer: this filter-type device—usually of the one-inch depth pleated
variety—is specifically designed to coalesce small water (and particu-
larly salt aerosol) droplets; in other words, to capture small liquid drop-
lets and make them form larger droplets. This comparatively easy task
for a filter can be achieved with a relatively open filter material which,
although a good coalescer, only has a very limited efficiency against
dust particulate.
air ltration 839