MARINE PURIFIER

Group 3 – BSMT 3B3Delos Santos, Jay V.

De Villa, Paul EugeneDasco, Marben

Del Mundo, Mark LorenzCorre, Jaymar

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Separation Separation as a means of removing impurities from a fuel

can be undertaken by means of gravity in a settling tank or by means of centrifuging the fuel. Both methods work on the same principles that by subjecting the fuel to a constant force, the denser components of the fuel i.e  water and dirt will be separated from the lighter components i.e. the fuel itself.

Gravity acting on the fuel as it passes slowly through the tank will separate the denser components from the fuel where they will accumulate at the bottom of the tank. The contaminants can then be remove by separation of sludge from the tank.

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Principle of separation If an oily water mix is placed into a tank then separation

of the two parts will begin with the lighter element rising to the top. The rate the separation occurs is governed by several factors including the difference in specific gravities and the force of gravity acting upon it. 

For mixes placed into a settling tank there is little that can be done about the gravity but the difference in the specific gravities can be increased by heating. This because water density changes at a much reduced rate when compared to oil.

A wide shallow tank will increase the rate of

clarification over a tall thin tank

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Principles of SeparationWhen a volume of light oil is placed into a

tank contain a weir and a quantity of water the fluids will tend to arrange themselves as shown above. The height of the water in the weir rises to a point governed by the volume (and thereby relative height) and specific gravity of the light oil.

Knowing this it is possible to form a rudimentary purification system.

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Principle of separation As a oil/water mix is fed into the tank separation

begins with heavy particulates falling to the base of the tank along with water which joins the other water excess overflowing the heavy phase weir. Hopefully clear oil passes over the light phase weir. The problem arises that to ensure their is suffcient time to allow for full (separation of the oily mix the flow would have to be very small relative to the size of the tank.

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CentrifugingCentrifuging is the process by which the effects of

gravity can be amplified by the use of centrifugal force to the extent that the separation process becomes rapid and continuous. Centrifuges work by rapidly spinning a bowl containing the liquid, thus producing the required centrifugal force to produce separation.

The principle of operation of the centrifuge is simple. When a bowl containing impure fuel is rotated, centrifugal forces will throw any item with density greater than the fuel oil density (solids and free water) to the periphery of the bowl.

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CentrifugingCentrifugal separators used for the separation of two liquids of different densities (fuel and water) are known as purifiers and those used for separating solid impurities are known as clarifiers. Purifiers will also remove some solids and clarifiers will also remove small quantities of water.

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Principle of seperation in centrifuge containing angled plate stack

04/19/2023 Mohammud Hanif Dewan, Senior Engg. Lecturer, International Maritime Academy, Bangladesh

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Fluid moving between two plates has a velocity greatest at mid point and minimum approaching the plates.a particle entering into the plates will tend to be pushed upwards by the fluid flow. All the time centrifugal force tends to retard the horizontal component of the movement causing the partical to approach the underside of the top disc. As it approaches the fluid flow velocity reduces.

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The centrifugal force eventually overcomes the force acting on the particle due to fluid movement and the particle starts to move towards the outer rim. The centrifugal force acting on a particle is proportional to its mass therefore a small particle will tend to move further under the influence of fluid flow. Indeed a particle small enough will be carried through the plates and out with the discharge. In this way it can be seen that reducing the flow rate to a purifier will tend to increase the quality of the output.

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Types of Centrifuge: 

There are normally two types based on the application:

1) Clarifier &

2) Purifier

1) Clarifier:

When a centrifugal is arranged to remove only impurities and small amount of water, it is called as clarifier. Since it is used mainly for that fluid where mostly solid impurities are to be removed, gravity disc is not used in clarifier; instead a sealing ring is used to keep the impurities intact unless desludged.

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Clarifier

The particle is pushed upwards with the oil stream towards the centre while the centrifugal force directs it to the periphery. The residual force on denser particles (impurities) will drive them towards the periphery, while the less dense particles (oil) will be directed towards the centre of the bowl and raise to the outlet connection.

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Clarifier

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2) Purifier: When a centrifuge is arranged for separating two liquids of different densities, for e.g. water from oil, it is known as a purifier. The main component of purifier is correct size gravity disc or dam ring which is responsible to create interface between the oil and water.

The basic operations of clarifier and purifier are: - It contains stack of disk numbering up to 150 and are separated from each other by very small gap. A series of holes are aligned in each disk near the outside edge which permits the entry of dirty oil.

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- Due to difference in gravity and centrifugal force, the heavier impure liquid (water) and particles moves outside and lighter clean oil flows inwards and get separated. - The collected sludge and impurity can be discharged continuously or at a time intervals, depending upon the construction, automation and system incorporated.

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PurifierWhen a centrifuge is set up as a purifier, a

second outlet pipe is used for discharging water as shown. In the fuel oil purifier, the untreated fuel contains a mixture of oil, solids and water, which the centrifuge separates into three layers. While in operation, a quantity of oil remains in the bowl to form a complete seal around the underside of the top disc and, because of the density difference, confines the oil within the outside diameter of the top disc.

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PurifierAs marine fuel oil normally contains a small

quantity of water, it is necessary to prime the bowl each time that it is run, otherwise all the oil will pass over the water outlet side to waste. The water outlet is at greater radius than that of the fuel. Within the water outlet there is a gravity disc, which controls the radial position of the fuel water interface

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Purifier

A set of gravity discs is supplied with each machine and the optimum size to be fitted depends on the density of the untreated oil. When the fuel centrifuge is operating, particulate matter will accumulate on the walls of the bowl. If the centrifuge is set as a clarifier, the particulate matter will be a combination of water and solid material.

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PurifierIf it is set as a purifier, the free water is

continuously discharged, therefore, the particulate matter will consist of solid material. In older machines it is necessary to stop the centrifuge to manually clean the bowl and disc stack, however, the majority of machines today can discharge the bowl contents while the centrifuge is running.

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Purifier

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Purifier Operation

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The following factors are of importance when understanding the function of the purifier

Increasing the sg of the oil will tend to push the interface outlet and cause overflow from the heavy phase outlet untill the equilibrium is restored. Should the interface be moved so far as to breach the dam oil will be issued from the heavy phase outlet and an alarm will sound.The ideal position for the interface is to lie over the distribution holes

Reducing the sg of the oil will tend to bring the interface towards the axis, this reduces the force of separation on the oil mix and reduces the efficiency of the unit possibly leading to contaminants and water carryover with the light phase outlet

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- The "gravity" disc are changeable on virtually all purifers. Their centre bore is governed by the sg of the oil being centrifuged. The largest bore should be used without risking overflow.

- The flow rate of a purifer should be set to optimise removal of whole system impurities. The lower the oil feed the greater the time for impurity removal and the more efficient the purification. The higher the rate the greater the amount of system oil is treated per unit of time.

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Choosing Gravity Disc

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The graph shown above is one typical of one found in a purifier instruction book for selecting appropriate gravity disc size. Shown on the diagram is an example of an oil of sg 0.93 at 0'C. The sg at 15'C for use with this graph is found by projecting along a horizontal line to 15'C. This step would be omitted if the sg at 15'C was already known. A line is then drawn parallel to the pre-drawn sloping lines. Where the drawn sloping line cuts the appropriate oil supply temperature isothermal then This becomes the selection point for the disc. This is found simply by ascertaining which size band the point lies in.

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PARTS OF A PURIFIER

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Basic components of the centrifuge are as follows:

Exterior framework:

The exterior frame work is normally made up of caste iron which supports the internal bowl and disk parts and carries water line, feed line and outlet line connections.

Bowl and disk:

There are bowls inside the frame, which can be a solid assembly operating non continuous and have space enough to retain the separated sludge. There can also be an arrangement in which the upper and lower parts are separate for discharging the accumulated sludge by a continuous operation. These parts are normally made up of high tension stainless steel.

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Vertical shaft:The Vertical shaft is used to transform the electrical motor output into rotational motion for rotating the bowl in high speed through spur gear and horizontal shaft or belt. material used for vertical shaft construction is an alloy of steel.

Horizontal shaft or belt drive: The electrical motor drives the horizontal shaft through clutch pads and is used for transmitting the rotational motion to bowl assembly. A special belt having elastic character is used in some models in place of horizontal shaft, thus removing the use of the gear assembly. The horizontal shaft material is a special alloy of steel.

Attached Gear pump: A general construction of centrifuge consists of a horizontal shaft driven attached supply or discharge gear pump. In some system an external supply pump may be installed in place of the attached pump.

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Spur gear: A spur gear is placed between the horizontal and vertical shafts for the transfer of rotational motion. These gears are manufactured by special aluminum bronze material. Clutch or friction pads: An electric motor will get overloaded if it is connected directly to the bowl assembly for the rotation of the same as the complete assembly is very heavier. To avoid this, clutch or friction pads and drum assembly are installed on the horizontal shaft. Normally the number of pads varies from 2 to 4 depending upon the frequency supply to the motor.As the motor starts, the pads inside the drum moves out gradually due to centrifugal force and cause friction in the internal wall of the drum resulting in rotation of the shaft and the bowl gradually without overloading and damaging the motor and gears.

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Thank you!

Group 3 – BSMT 3B3Delos Santos, Jay V.

De Villa, Paul EugeneDasco, Marben

Del Mundo, Mark LorenzCorre, Jaymar