CONTENTS
PRINCIPLE
VISCOSITY
ALCAP- ALFA LAVAL
OPERATION OF PURIFIER
PURIFIER SEPARATION PROCESS
Liquid flow
Liquid seal in purification
Displacement of oil
Gravity disc
Clarifier disc
Sludge discharge mechanism
Bowl opening & closing
PRINCIPLE OF PURIFIER
The centrifuge includes parts that rotate at high speed. This means that:
•Kinetic energy is high
•Great forces are generated
•Stopping time is long
The Marine high-speed centrifugal separator is specifically designed for cleaning lubricating oils and low viscosity fuel oils from water and solid particles (sludge). The cleaned oil is discharged continuously, while the sludge is discharged at intervals.
VISCOSITY
The separator handles the following types of lubricating oils and low viscosity fuel oils:
•Distillate, viscosity 1,5 - 5,5 cSt/40 °C
•Marine diesel oil, viscosity 13 cSt/40 °C
•Intermediate fuel oil and heavy fuel oil (viscosity 30-380 cSt/50 °C)
•Lubricating oil of R & O type, detergent, or steam turbine.
Items that can be removed via the
purifier
Items that cannot be removed via the purifier
Vanadium, and SulphurALCAP- ALFA LAVAL
The separator can be operated either as a purifier or as a clarifier.
When operated as a purifier the separator discharges the separated water continuously.
When the oil contains only small amounts of water the separator is operated as a clarifier, discharging the water with the solid particles.
The separator has to be installed together with devices to control it.
OPERATION OF PURIFIER
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| purifier sectional view |
The separator Bowl (C) is driven by an electric motor(A) via a flat-belt power transmission (D) and bowl spindle(B). The motor drive is equipped with a friction coupling to prevent overload.
The bowl is of disc type and hydraulically operated at sludge discharges. The hollow bowl spindle (B) features an impeller that pumps closing water from a built-in tank to the operating system for sludge discharge.
The main inlets and outlets are shown with their connection numbers in the illustration.
Outline of function
The separation process takes place in the rotating bowl. Un-separated oil is fed into the bowl through the inlet The oil is cleaned in the bowl and leaves the separator through the outlet via a paring chamber.
Impurities heavier than the oil are collected in the sludge space at the bowl periphery and removed automatically at regular intervals.
PURIFIER SEPARATION PROCESS
Liquid flow
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| purifier Liquid flow |
Separation takes place in the separator bowl to which unseparated oil is fed through the inlet pipe (201). The oil is led by the distributor (T) towards the periphery of the bowl.
When the unseparated oil reaches the slots of the distributor, it will rise through the channels formed by the disc stack (G) where it is evenly distributed into the disc stack.
The oil is continuously separated from water and sludge as it will flow toward the center of the bowl. When the cleaned oil leaves the disc stack it rises upwards and enters the paring chamber. From there it is pumped by the paring disc (F) and leaves the bowl through the outlet (220).
Separated sludge and water move towards the bowl periphery. In purification separated water rises along the outside of the disc stack, passes from the top disc channels over the edge of the gravity disc (K), and leaves the bowl into the common sludge and water outlet (221) of the separator.
Heavier impurities are collected in the sludge space (H) outside the disc stack and are discharged at intervals through the sludge ports (L).
Process Water
Water that enters the purifier or separator through a valve on top of the apparatus and is used for filling the bowl first and thus obtaining a seal and interface for purification of oil.
Operating Water
1)Water which
opens and closes the sliding bowl,
2) It enters the separator through
the paring disc at the bottom of the bowl body,
3) It operates the slide mechanism
also to lower the bowl for desludging purposes
4) It again assists to close the bowl
and keeps it closed continuously during purification.
By applying a high pressure the
interface moves outward and with a low back pressure the opposite results,
therefore a constant pressure control valve is fitted at the clean oil outlet. It
is important to note that when an excessive amount of water is present in the
fuel the temperature for centrifuging must be kept below the boiling point of
water, otherwise foaming and agitation of the fuel takes place making it impossible to control. Under these circumstances, it will be necessary to purify at a
very low rate to realize a reasonable efficiency.
Liquid seal in purification
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| Liquid seal in purification |
Displacement of oil
To avoid oil losses at sludge discharge, displacement water is fed to the bowl.
Prior to a discharge, the oil feed is stopped and displacement water is added through the water inlet (206). This water changes the balance in the bowl and the interface (X) moves inwards to a new position (Y), increasing the water volume in the sludge space. When the sludge discharge takes place sludge and water alone are discharged.
Sludge discharge occurs while the displacement water is still flowing. A new water seal will therefore be established immediately afterward. The oil feed is then turned on again.
Gravity disc
What is the use of a gravity disc?
The main component of the purifier is the correct size gravity disc or dam ring which is responsible for creating an interface between the oil and water. 2) Clarifier: When a centrifugal is arranged to remove only impurities and a small amount of water, it is called the clarifier.
In the purification mode, the position of the interface (X) can be adjusted by replacing the gravity disc (K) with one of a larger or smaller size.
A gravity disc of a larger size will move the interface towards the bowl periphery, whereas a disc of a smaller size will place it closer to the bowl center
Clarifier disc
In the clarification mode, the gravity disc is replaced by a clarifier disc which seals off the water outlet. In this case, no water seal is required and consequently, there is no oil/water interface in the bowl. The clarifier disc is an optional disc with a hole diameter of 40 mm. This disc is not shown in the nomograms.
Sludge discharge function
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Sludge discharge mechanism |
Sludge is discharged through a number of ports (L) in the bowl wall. Between discharges, these ports are covered by the sliding bowl bottom (M), which forms an internal bottom in the separating space of the bowl. The sliding bowl bottom is pressed upwards against a sealing ring (m) by the force of the closing water underneath.
The sliding bowl bottom is operated hydraulically by means of operating water supplied to the discharge mechanism from an external freshwater line. Opening water is supplied directly to the operating system in the bowl while closing water is supplied to the built-in closing water tank, and pumped to the operating system through the bowl spindle.
The opening and closing only take a fraction of a second, therefore the discharge volume is limited to a certain percentage of the bowl volume. This action is achieved by the closing water filling space above the upper distributor ring and pushing the sliding bowl bottom upwards. Simultaneously, the water in the chamber below the operating slide is drained off through the nozzles in the bowl body.
Bowl opening
The key event to starting a sludge discharge is the downward movement of the operating slide. This is accomplished by the supply of opening water (372) to the discharge mechanism. Water is drained off through nozzles (Y) in the bowl body. The sliding bowl bottom is rapidly pressed downwards by the force from the liquid in the bowl, opening the sludge ports.
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| opening closing |
Bowl closing
After the sludge is discharged the sliding bowl bottom is immediately pressed up and the sludge ports in the bowl wall are closed.
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