Centrifugal Separators/ managment of FO and LO Flashcards
what is water detection function on the multi-monitor for in purifiers
The Water Detector Function (WD) on the Multi-Monitor in fuel oil and lube oil purifiers prevents separated water from leaking into light liquid (purified oil). It is available in two types, i.e., pressure sensor type water detector and electrostatic capacity type water detector.
Explain the Operating Principle of Pressure Sensor Type Water Detector
The Water Detection system provided with a pressure sensor, which is called G-HIDENS system, is controlledon the automatic control panel via the Multi-Monitor of the purifier.The G-HIDENS system constantly monitors separated water being accumulated in the bowl by means of apressure sensor installed in the circulation line and causes separated water to be discharged before it leaksinto light liquid (purified oil).
In the clarifier operation, some of light liquid (purified oil) is returned to the feed liquid inlet via circulation line.The circulation line, which is provided with a back pressure valve, pressure sensor and pressure gauge, ismaintained under a required level of back pressure by means of the back pressure valve, with the shut-offvalve in the heavy liquid outlet line fully closed. The arrangement is shown in the figure above.
Upon arrival of separated water in the bowl at the top disc outside level, the circulation of light liquid is stoppedwith an instantaneous drop in circulation line pressure. Detecting this pressure change, the pressure sensorsends a signal to the control panel via the Multi-Monitor to tell that the predetermined quantity of separatedwater has been accumulated in the bowl and separated water is discharged, normally in the partial dischargemode. In some cases, total charge with sludge takes place, depending on time spent before detection ofpressure drop. By this principle water is detected. Diagram below shows a condition when pressure falls due to arrival of water in the top discperiphery.
Explain the operating principle of the Electrostatic Capacity Type Water Detector
The electrostatic capacity type water detector relies on difference indielectric constant between water and oil to determine the capacitance ofoil, thereby detecting the water content of oil.This detector is installed in the light liquid connection line of the purifierand controlled on the automatic control panel. In the clarifier operation, the detector monitors the water content of lightliquid. When a rise of approximately 0.5% occurs in the water content, thedetector recognizes it as “water in the bowl having arrived atpredetermined level” and issues an output signal to the control panel.Water is discharged as a result.
Briefly explain how a purifier works
Consider gravity separation, as occurs in a settling tank, over a gradual period solids such as sludge, dirt, etc., will settle out at the bottom of the tank. The heavy liquids, such as water, will settle out above the solids and the lighter liquids, such as oil, will be at the top of the tank. The application of heat will speed up the separation process. Separation occurs due to the specific gravities or densities of the liquids and solids. Gravity is responsible for the settling out and this takes quite a while. If the gravitational force is increased, by using centrifugal force, the separation effect is much greater. The centrifugal purifiers or separator consists of a bowl containing a set of discs stacked one on top of the other. The dirty oil flows down the distributor and up through the holes in the discs.
With reference to centrifugal purifiers:
a) State the function of the gravity disc
b) Explain the consequences of fitting the following:
(i) Too large a gravity disc
(ii) Too small a gravity disc.
a.) Gravity Disk in Purifier changes the position of the oil and water interface, which is essentially like a boundary between the oil and water and helps to separate the two liquids at different densities. This oil and water interface can be shifted inwards or outwards with the correct size gravity disk. The gravity disc is located at the top of purifier disc stack, which is attached to the purifier bowl.
b.) the smaller the disc the closer the interface to the disc stack. it also controls the output of the quality of fuel and maintains back pressure. The gravity disc is required to create sufficient back pressure on the water seal to maintain the oil water interface as close to the edge of the bowl as possible without losing the water seal. This results in the oil which has to be purified having a longer dwell time in the bowl in order for centrifugal forces to separate the water which then leaves through the water outlet.
- Too Large
- Water outlet flow will be too large as it will be less restricted
- This will cause the water interface to move outward on the plates away
from the spindle - If the interface moves outward of the plate stack, oil will begin to exit
the bowl via the water outlet - Too Small
- Restriction on the water outlet will be excessive
- Interface will move inward towards the spindle
- This reduction in plate surface area will reduce the efficiency of
separation - Water will begin to mix with the oil in the Clean oil outlet
i.) This makes the oil water interface is displaced too near to the bowl periphery, so it moves outwards and so oil is in the water outlet. Resulting in a collapse of the liquid seal, oil will now pass out the water outlet. Escaping oil via the water outlet could overfill the sludge tank, and cause damage within the machinery spaces. A large gravity disc can also cause oil to flow out of the heavy phase discharge which breaks the seal and causes more contamination.
ii) The oil water interface is too near the bowl centre, not creating an effective water-oil seal and poor solids removal. Water will also pass out of the oil outlet leading to contamination. Water within oil reduces and inhibits its ability to lubricate efficiently, causing machinery damage, or in the case of fuel oil emulsification of the fuel resulting in poor injection and combustion.
a.) State two factors that have an influence on the separating process.
b) Give two reasons for a purifier not attaining full running speed.
a.) 1. Viscosity of the oil in the centrifuge, the higher its value the greater will be the viscous
drag on the particles. Hence the oil should be preheated to as high a temperature as possible according to manufacturer.
- Throughput which is the quantity of oil pumped into the purifier. If this is low the size of particles will be small and the oil discharged will be cleaner. If throughput is great size of particles will be larger. if the oil is contaminated by water this creates high throughput.
Good maintenance of purifiers is important for smooth and accurate operation of the units. Some factors that influence a good working purifier are temperature, feed rate, the type of gravity disc and oil density. To maintain optimal efficiency of the equipment, filters and heaters should be regularly cleaned and opened as per the vessel’s planned maintenance system or manufactures’ recommendations.
The diameter of holes in the dam rings also plays an important role in the creation of interface and purification process. If the diameter of the holes is more, the interface is formed towards the periphery and oil globules are found with water and sludge. If the diameter is less the oil-water interface moves inwards and water is released with the clean oil discharged.This prevents the impurities and water to remain inside the bowl unless they are discharged automatically or manually by opening the cleansing bowl. Also, the conical discs in a clarifier usually don’t have feed holes in them but if they do, then a disc without any holes is fitted at the bottom of the stack.
b.) Oil in purifier gear case is low. Check the level and fill up if required. If oil is below adequate level this causes insufficient lubrication and damages gears and other rotating parts (shaft bearings).
Emergency breaks lever is in stop position. This is located at the bottom of the purifier and must be in released position for purifier to increase speed. If purifier is started with lever in closed position motor current will increase and there will be damage and wear down of brakes.
- The brake pads and brake block: when the brake pads are not in the normal position, it will get in contact with the brake damper. This will cause the motor to continue pushing to increase the rpm and may cause the motor to damage. Moreover, in such case, the purifier may work, but during desludging, due to water weight, it may result in malfunctioning.
- Bearing wear: If the above-mentioned subject has been checked, all okay and problem continue, then you need to check the bearings.
- Bowel not in the proper position: if the bowel is inclined or touching on the water distributor. This also can cause reductions on the rpm. After checking the above, try to inspect the water distributor and bowel seat surface for any contacts.
- Excessive sludge in bowl
- Bearing failure
- Motor running at overload
- power failure
- Sump oil level too high
- Vertical shaft and horizontal shaft out of alignment
- Improper bowl assembly
With reference to the treatment of lubricating or fuel oil:
a) State function of a purifier,
b) State function of a clarifier,
c) State TWO constructional differences found in the bowls of purifiers and
clarifiers.
a.) Purifiers’ purpose is to separate water and other contaminants in the oil mixture using the principle of density difference and gravity separation, which is aided by centrifugal force. Heavier particles will be forced outward, and lighter particles will remain near to the centre. Purifiers remove water, sludge, and solid particles from oil. Purifiers clean fuels and lubricants and onboard vessels they are mainly part of fuel and lube oil treatment system.
b.) Clarifiers clean oil by removing solids. A clarifier centrifuge is a simplified version of a purifier. The clarifier will separate the liquids from solids in order to remove any solid foreign material that is not removed from the oil. separate finer solid impurities from the oil.
c.) The main difference between a clarifier and a purifier is the presence of a gravity disc. In a purifier, the interface or the line of separation between the oil and water is changed using a gravity disc (dam ring). However, clarifiers do not have a gravity disc but have a sealing ring which seals the water outlet this is because they cannot really separate water and so to prevent it flowing to service tanks they have a sealing ring.
purifiers supply oil to the disc stack through the discs themselves using feed holes, designing the oil/water interface to be located at the point the holes pass through. Clarifier discs do not have these holes, and oil is fed from outside the disc stack.
- A clarifier has a dirty oil inlet and a clean oil outlet
- A purifier has a dirty oil inlet, a clean oil outlet and a water outlet
Another difference between a clarifier and purifier is that a purifier needs to be filled completely with water for the generation of a seal that prevents the oil to leave from the water outlet. Whereas a clarifier doesn’t needs to be filled up with water. Purifiers are used for filtering lubricating oil whereas clarifiers are not used for the same unless the oil is completely devoid of water.
a.) Outline the separation process that occurs within centrifugal oil purifiers
b) Describe the change required to the purifier if it is to be used for an oil of
lower density
a.) Start purifier from local control panel so that purifier can generate required rpm, motor then starts to produce current, monitor the current rating at the control panel when it shoots up and then settles this mean purifier bowl has has reached required rpm so that later centrifugal force can be generated. Then fuel supply pump starts, and fuel receives external heating from steam heater and steam line to reach required temperature. A Solenoid valve then opens to prime the purifier bowl with water and prevent oil carrying over into water discharge by creating a water seal. Once oil set temperature is reached the three way valve opens to supply oil to purifier. When oil enters purifier it displaces the water inside and an oil and water interface is created due to centrifugal force created by having bowl spin at required rpm. The centrifugal force created enhances gravitational force meaning the smaller particles are slung out of the oil to form sludge on the outer part of the bowl. Additionally, when oil is fed inside the bowl the high-speed rotation causes the dense particles such as water and solid containments to be forced to outside of the bowl leaving the much clean oil near the centre. There is a fixed type centrifugal pump that creates suction and provides sufficient flow velocity to purifier so that the clean oil is then sent to the service tank. Separation is also aided by the addition of a disk stack which enlarges the bowls surface area. Within the oil outlet there is a gravity disc which controls the oil water interface during operation to prevent cross contamination. Periodically the purifier will automatically de-sludge to discharge any solids and contaminants and particles that are collected and these are direct to sludge tank.
b.) For fuel of a lower density, a smaller gravity disc will be needed in order to maintain the oil water interface. If the gravity disc wasn’t changed oil would be lost in the water outlet, which could drain a sump, fill the bilge sludge tank or even cause damage to a machine. to choose size of gravity disc you use the nomogram from the purifier manual, this is responsible for setting the location of oil and water interface line variable as per maker’s design and the machinery need.
With reference to a centrifugal fuel oil separator:
State the TWO factors that determine the size of “Gravity Disc” to be used. (4)
b.) The gravity disc size depends on separation temperature, the density of oil at the temperature and desired throughput of oil and by using of nomogram from the purifier manual; is responsible for setting the location of oil and water interface line as per maker’s design and the machinery need.
How would u choose the correct size of gravity disc ?
Correct size is selected using:
Separation temperature
Density of oil at this temperature
Desired throughput of oil and by using of nomogram from the purifier manual.
What is paring disc ?
It is a stationary impeller mounted in a chamber at the neck of the bow.
Its function is to convert the rotating energy of the liquid into a pressure head.
What is water washing ?
Water washing is widely used techniques to remove acids, salts, and other impurities from the oil.
The oil must be straight mineral oils or without dispersant additive oils.
Water should be injected into the oil before purifying at a rate of between 3 to 5% of the oil flow that is continuously renews the water seal in the purifier bowl.
The oil temperature should be around 75 °C and water temperature about 5 °C higher than oil. It can be done continuously or intermittently.
What is steam jetting ?
Steam Jetting is a technique in which steam is blown into the engine lube oil which pairs to the purification by removing carbon more effectively through coagulation of colloidal carbon.
differences between purifier and clarifier ?
Purifier
Remove water and suspended solids particles from oils
Two outlets water and clean oil
Gravity disc on top
Blind disc on the top of disc stack
Sealing water required
Clarifier
Remove finer and lighter particles from oil
One outlet for clean oil
No gravity disc only sealing ring
Blind disc at bottom.
Sealing water not required
what is a blind disc?
A blind disc (without holes) is assembled at the bottom of the disc stack in clarifier. This closure prevents the fluid from entering the disc stack through the bottom holes or fluid passage mentioned above. The incoming liquid enters the disc stack from the outside.
what are Operational Differences Between Purifier and Clarifier Centrifuges?
A clarifier is a simplified version of a purifier centrifuge. This difference between the centrifuge configurations reflects in the operation of either design.
Firstly, a clarifier does not require sealing liquid due to the absence of the gravity ring. Since the heavy phase outlet is closed out by the sealing ring, the incoming process liquid fills the bowl and can only exit the bowl through the light phase outlet.
In a purifier, sealing liquid is needed before feeding the process fluid to the bowl. This liquid is also known as the priming fluid and typically consists of the fluid’s heavy phase.
The priming liquid prevents the incoming process fluid from escaping the bowl through the heavy phase outlet.
Secondly, back-pressure on the light phase outlet is essential for the operation of a purifier. The back pressure stabilizes the liquid column within the bowl and helps keep the paring disc pump immersed in the light phase. Backpressure is not essential to the operation of a clarifier centrifuge.
Thirdly, selecting the correct gravity ring is crucial for effectively separating the two phases in a purifier centrifuge. A clarifier does not have a gravity ring, so problems associated with an incorrect gravity disc do not apply to clarifiers.
Fourthly, liquid seal breaking is a common occurrence in purifier centrifuges. When the heavy phase or sealing liquid is not present in the bowl or escapes the bowl during operation, the light phase exits the bowl through the heavy phase outlet.
This issue is known as a “liquid seal break” condition. Since there is no sealing liquid in a clarifier, this problem does not occur in clarifiers.
briefly outline how a conversion from purifier to clarifier can be made
two essential components are required to convert a purifier to a clarifier centrifuge. The first and most crucial part is a clarifier disc or a sealing ring.
A standard purifier has a gravity disc installed in it, which regulates the bowl’s oil-water interface location. A seal ring, which is a gravity disc with the smallest opening, replaces the gravity disc.
The second component that needs to be replaced is the bottom bowl disc in the disc stack. A blind disc replaces the bottom disc. This replacement closes out the rising fluid pathway through the disc stack.
It is important to note that though it is possible to convert all purifiers to a clarifier, switching a clarifier to a purifier centrifuge is not always possible.
This inability to modify is because some centrifuges designed as clarifiers do not have a water chamber. They may also lack the water-paring disc pump and not have a provision to install a gravity disc.
to convert
Open up the purifier and set the blind disc at the bottom of the disc stack.
The water outlet is blocked by a seal on the gravity disc.
Blank off the sealing water inlet line.
How to change purifier from HFO to DO ?
Replace the gravity disc, which is smaller than the heavy oil
Open heater by pass vale.
Close the FO heater steam in/out valves.
Open heater drains v/v.
Pure DO purifier cannot change to HFO, it has no heater.
Pure clarifier cannot change to purifier, it has no water outlet.
Why is a multidisc provided inside purifier ?
To separate the liquid into thin layer & create shallow settling distance between discs.
Improving separation of oil from heaver liquids & solids particle
what can cause excessive vibration of purifier ?
too much sludge inside the bowl
Foundation damper & spring failure
Bearing failure
Worn gear
Uneven wear of frictional clutch
Motor speed too high or too low
What are reasons for purifier over flow ?
Incorrect purifier disc size (inside diameter too large)
Too low fuel oil temperature
Too much rate of throughput
Too much sludge inside the bowl
Low speed (rpm) of bowl rotation
Sealing water failure
Operating water failure
Worn out main sealing ring
Why purifier is not building up speed while running ?
Improper touching with friction clutch (worn out frictional clutch)
Touching with break
Excessive sludge in the bowl
Bearing failure
Motor running at overload
One phase power failure (Single phasing)
Sump oil level too high
Vertical shaft and horizontal shaft are out of alignment
Why need sealing water ?
To seal the water outlet & to prevent the overflow of oil from the water outlet.
Effect of reduced purifier bowl height ?
Oil goes through the water outlet.
Explain the working principle of a clarifier
A clarifier centrifuge separates a liquid phase from the solids in the fluid. In other words, it is a liquid-solid separation device. Therefore a clarifier continuously separates the solids from liquid-carrying solids. The process fluid enters the bowl through the distributor to the underside of the distributor. A blind disc (without holes) is assembled at the bottom of the disc stack.
This closure prevents the fluid from entering the disc stack through the bottom holes or fluid passage.
The incoming liquid enters the disc stack from the outside. As the fluid passes through the disc stack, the heavier solids move outward due to the centrifugal force. Also, in a clarifier centrifuge, the gravity disc is replaced by a sealing ring (clarifier disc), closing the passage of water to the water chamber in the bowl top. This closure of the heavy phase pathway essentially blocks one fluid passage from the bowl.
All the processed fluid moves towards the only exit in the bowl. The liquid passes through the disc stack into the fluid passage between the distributor’s ribs. The fluid then enters the light-phase chamber inside the top disc.
The centripetal pump (paring disc) converts the liquid’s rotational energy into pressure, and the pressurized fluid exits the bowl through the light phase pathway.
what are the steps involved in Operation of marine oil purifier’s bowl
The operation of marine oil purifier bowl steps:
The oil to be purified is heated to a suitable temperature and fed into the purifier bowl through a feed pipe.
The purifier bowl rotates at a high speed (up to 10,000 rpm) and creates a centrifugal force that separates the oil from the water and solids based on their density difference.
The purified oil flows to the center of the bowl and is discharged through a paring disc, which is a conical device that skims off the oil from the surface.
The water and solids accumulate in the sludge space of the bowl and are periodically discharged through an automatic or manual valve.
The purifier bowl is equipped with a gravity disc or a clarifier disc, depending on whether it is used as a purifier or a clarifier. A purifier separates both water and solids from the oil, while a clarifier only separates solids from the oil. A gravity disc has two holes: one for water and one for oil. A clarifier disc has only one hole for oil.
