Page 171 - Introduction to Marine Engineering

Fuel oils, lubricating oils and their treatment 157

down the bowl, using only the special tools provided and noting that
some left-hand threads are used. The centrifuge is a perfectly balanced
piece of equipment, rotating at high speeds: all parts should therefore
be handled and treated with care.

Heavy fuel oil separation
Changes in refinery techniques are resulting in heavy fuel oils with
increased density and usually contaminated with catalytic fines. These
are small particles of the catalysts used in the refining process. They are
extremely abrasive and must be removed from the fuel before it enters
the engine. The generally accepted maximum density limit for purifier
3
operation is 991 kg/m at 15*C.
In the ALCAP separation system the separator has no gravity disc and
operates, to some extent, as a clarifier. Clean oil is discharged from the
oil outlet and separated sludge and water collect at the periphery of the
bowl. When the separated water reaches the disc stack, some water will
escape with the cleaned oil. The increase in water content is sensed by a
water-detecting transducer in the outlet (Figure 8.4). The water

Sludge
and water
Figure 8.4 Fuel oil separation control

transducer signal is fed to the MARST 1 microprocessor which will
discharge the water when a predetermined level is reached. The water
will be discharged from sludge ports in the bowl or, if the amount is
large, from a water drain valve.
The ALCAP system has also proved effective in the removal of
catalytic fines from fuel oil.