Man L23/30DF, Project Manual

Page: 166 / 392

Separator unit installation
With multi-engine plants, one separator unit per engine in operation is rec-
ommended (
see figure 3), but if only one separator unit is in operation, the
following layout can be used:
▪
A common separator unit (
see figure 4) can be installed, with one in
reserve, if possible, for operation of all engines through a pipe system,
which can be carried out in various ways. The aim is to ensure that the
separator unit is only connected to one engine at a time. Thus there will
be no suction and discharging from one engine to another.
It is recommended that inlet and outlet valves are connected so that they can
only be changed over simultaneously.
With only one engine in operation there are no problems with separating, but
if several engines are in operation for some time it is recommended to split
up the separation time in turns on all operating engines.
With 2 out of 3 engines in operation the 23.5 hours separating time must be
split up in around 4-6 hours intervals between changeover.
Stokes' law
The operating principles of centrifugal separation are based on Stokes’ Law.
V = settling velocity [m/sec]
r
ω
2
= acceleration in centrifugal field [m/sec
2
]
d = diameter of particle [m]
ρ
p
= density of particle [kg/m
3
]
ρ
l
= density of medium [kg/m 3 ]
µ = viscosity of medium [kg/m, sec.]
The rate of settling (V) for a given capacity is determined by Stokes’ Law.
This expression takes into account the particle size, the difference between
density of the particles and the lubricating oil, and the viscosity of the lubri-
cating oil.
Density and viscosity are important parameters for efficient separation. The
greater the difference in density between the particle and the lubricating oil,
the higher the separation efficiency. The settling velocity increases in inverse
proportion to viscosity. However, since both density and viscosity vary with
temperature, separation temperature is the critical operating parameter.
Particle size is another important factor. The settling velocity increases rapidly
with particle size. This means that the smaller the particle, the more challeng-
ing the separation task. In a centrifuge, the term (r
ω
2
) represents the centrifu-
gal force which is several thousand times greater than the acceleration due
to gravitational force. Centrifugal force enables the efficient separation of par-
ticles which are only a few microns in size.
The separation efficiency is a function of:
2016-02-26 - en
Description
Treatment and maintenance of lubricating oil
1643494-3.11
MAN Diesel & Turbo
B 12 15 0
L28/32S; L27/38S; L23/30S; L21/31S; L16/24S; L23/30DF; V28/32S-DF;
L28/32DF; V28/32H; V28/32S; L16/24; L21/31; L23/30H; L27/38;
L28/32H EN
7 (11)