PURIFICATION OF OIL : Purifier/Clarifier/Separator/Homogenizing/Blending (Questions & Answers) Part-1

### Types purification of lubricating oil:

There are two types of purification system such as-

i) Batch purification system.
ii) Continuous by pass system.(Tank→ Purifier →Tank.)

### What is meant by batch purification ?

1. Firstly take the immobilization permit from the port authority.
2. The entire oil charge should be pumped by the purifier or by main circulation p/p into settling tank.
3. It should be allowed to settle for at least for 24 hours with heating about 60° C .
4. Water and sludge should be drained out periodically.
5. Cleaned the interior of the sump tank and carefully examined.
6. The oil should be passed through the purifier at its optimum efficiency and than pump back into the sump tank.
7. When sump tank empty, its interior should be cleaned and examined.

### When do periodic batch purification make ?

1. If the oil is suspected from containing strong acids
2. High insoluble contents due to poor combustion or water due to leak cooling system.
3. It is also made at least once a year when cleaned and examined for sump tank.
4. Suspecting biological contamination.

### How to maintain lube oil on board ships?

1. L.O on board test is carried out regularly.
2. Regular cleaned L.O line filter.
3. L.O purifier should be run during ship is in sea
4. Maintain L.O purifier performance
5. Periodic batch purification must be carried out & cleaned L.O sump tank once a year
6. Maintain L.O temperature within limit
7. Maintain good L.O cooler efficiency
8. Keep good fuel combustion system

### Principle of Working (Purifier)

The separation principle of high speed centrifuge depends on the difference in the specific gravity of two different liquids. To understand, let’s take a settling tank where fuel is stored and because of the difference in the gravity of water and fuel (water is heavier) the water gets collected at the bottom part of the due to the effect of gravity. Mathematically this process can be represented by:

Fs = ∏/6x D3 (ρw-ρo) g

Where Fs is the separating force, ρw is density of water, ρo is density of oil and “g” is gravitational force.

Now if we convert the tank into a conical rotating object, then the gravitational factor g will be replaced by the centrifugal force ω2 r, where ω2 is angular velocity of rotation and r is effective radius.

Fs = ∏/6x D3 (ρw-ρo) ω2 r.

Now the separating force will be much higher in centrifuge as compare to settling tank.

### Necessity to purify L.O & F.O:

L.O :- All lub oil contains some unexpected impurities like sludge, water rust etc. which is harmful for the normal operation of the machinery. The problem may arise for low quality non purified lub oil is piston ring. Blow past wear of sliding surface water /oil leakage, malfunction of bearing etc. That’s why L.O purification in necessary.

F.O:- Normally F.O is mixed with small solids particles & water. These are removed by purification and ensure good combustion. Purification of F.O prevent the wear & corrosion of fuel P/P injector, linear, piston etc. it also prevent to block the small hole. The proper working of the injector depends upon the fuel oil used.

### What is water washing? 

Water washing is a widely used technique to remove acids, salt and other impurities from the oil.
That oil must be straight mineral oil or without dispersant additive oils.
Water should be injected into the oil before purifying at a rate of between 3 to 5% of oil flow that is also continuously renews the water seal in the purifier bowl.
The oil temperature should be around 75 c and water temperature about 5c higher than oil.
It can be done continuously or intermittently.

### Difference Between Purifier & Calarifier:

PURIFIER	CLARIFIER
A. Remove water and suspended solids particle from oil.	A. Remove finer and lighter particles from oil.
B. Two outlets water and clean oil.	B. One outlet for cleans oil.
C. Gravity disc on top	C. No gravity disc (only sealing ring)
D. Blind disc on top of discs stack	D. Blind disc at bottom
E. Sealing water required	E. Sealing water not required

### Explain how the feed rate, separation temp & gravity disc of centrifuge is selected for optimum purification.

Feed rate:
For lub oil purifier the throughput should be about 1/3 of the maximum capacity
For fuel oil purifier the throughput should be about 15 – 20% of SFOC
This will ensure sufficient dwell time is present to effectively remove water and unwanted in-solubles.

Temperature:
Temp should not exceed 98’C as this may cause the sealing water to boil & loose bowl seal
Higher temp assist in the separation process

Gravity disc :
Reference should be made to the nomogram with information on the measured density & temp.
The diameter of gravity disc determines the location of the interface. Smaller diameter brings interface inwards and larger diameter brings it outward.
Interface should be maintained between top disc & disc stack.

### How to choose correct size of gravity disc?

It can be chosen by,

1. Separation temperature 
2. Density of oil at this temperature. 
3. Desired through put of oil by using of nomogram.

Interface :

It is the boundary layer between the heavy phase & light phase in the separator bowl.

### How to monitor the performance of a purifier?

During in operation interface must be in correct position for proper purification

1. Check abnormal vibration 
2. Check motor ampere 
3. Check lub oil level in gear case & lub oil cooler 
4. Back pressure 
5. Throughput pressure 
6. F.O/L.O inlet pressure/temp 
7. Operating water temp & level in the header tank 
8. Check the sludge discharge side from peep hole 
9. Check the sight glass of drain line, some water should be leaking

### Change purifier to clarifier:

1. Open up the purifier and set blind disc at bottom of the disc stack. 
2. A seal on the gravity disc blocks the water outlet. 
3. Blank of the sealing water inlet line. 

### Change purifier from HO to DO:

1. Replace the gravity disc, which is smaller than HO 
2. Open heater by pass valve. 
3. Close the HO heater steam in and out valves. 
4. Open heater drain valve. 

• Pure DO purifier cannot be changed to HO, it has no heater. 
• Pure clarifier cannot be changed to purifier it has no water outlet.

### What is paring disc?

1. It is a stationary impeller mounted in a chamber at the neck of bowl. 
2. Its function is converted the rotating energy into a pressure head.

### Check in purifier:

1. Sump level in gear box 
2. Visual inspection (over flow, vibration) 
3. All valves are in order. 
4. Feed condition (through put) 
5. Discharge pressure or rate. 
6. Back pressure. 
7. Fuel oil temperature. 
8. Motors ampere (LOAD) 
9. Sealing water level. 
10. Any leakage

### Sealing water/ liquid seal :

A liquid seal is required to operator a purifier because if forms a separation line or interface between two liquids. If there is no liquid seal, there will be over flow.

### Reasons (Purifier is not taking suction): 

1. Tank empty.
2. Suction v/v shut.
3. Filter chocked.
4. Suction line jammed by foreign material.
5. p/p rotational speed not appropriate.
6. Backlash clearance increased.
7. Wear down of gear teeth.
8. Feed bypass v/v fully open.
9. Incorrect fuel temperature.
10. High viscosity fuel.

### Selection of Gravity Disc for Purifiers on Ships:

For efficient purifier operation, use of appropriate size gravity discs according to the density of the medium to be treated and throughput is necessary. The selection of gravity disc is carried out using nomograms given in the purifier manual. Nomograms are different for different types of purifier models from the same manufacturer. This article explains the procedure of selection of gravity disc
size depending on the density and throughput of the oil to be purified on ships.

Example 1
The specific gravity of treated oil at 15℃ is known.

Treating condition
Specific gravity of treated oil: 0.925 at 15℃
Treating temperature: 70℃
Feed rate: 3000 L/h

Selection method
Refer to the nomogram given in the figure above. Click on the figure to enlarge.
From an intersection between falling curve ① of specific gravity of 0.925 and the vertical line of 70℃, draw horizontal line ② to reach the vertical line of 100℃.
Connect between the right end of line ② and the point of 3000 L/h on the treating capacity scale using straight line ③.
Read within which section of gravity disc inside diameter scale the intersection made by line ③ falls.
For this [Example 1] select a gravity disc having an Inside diameter of φ79.

Example 2
The specific gravity of treated oil at a certain temperature is known.

Treating condition
Specific gravity of treated oil: 0.944 at 50℃
Treating temperature: 98℃
Feed rate: 1250 L/h

Selection method
Refer to the nomogram given in the figure above. Click on the figure to enlarge.
From an intersection between rising curve ④ of specific gravity of 0.944 and the vertical line of 50℃ (being converted to a specific gravity at 15℃), draw curve ⑤ along the falling curve to reach the vertical line of 98℃, then draw a horizontal line to reach the vertical line of 100℃.
Connect between the right end of the horizontal line and the point of 1250 L/h on the treating capacity scale using straight line ⑥.
Read within which section of gravity disc inside diameter scale the intersection made by line ⑥ falls. For this [Example 2] select a gravity disc having an Inside diameter of φ71.5.

### What is steam jetting?

1. By blowing steam into the engine LO just prior to its purification. 
2. Coagulation of colloidal carbon will occur. 
3. Purifier can remove the carbon more effectively.

### The causes of purifier over flow:

1. Too large gravity disc. 
2. High fuel viscosity. 
3. Low separation temp. 
4. High back pressure. 
5. Large or small level ring. 
6. Bowl speed too low. 
7. Bowl incorrect assembled. 
8. Bowl disc set clogged. 
9. ‘O’ ring of clean oil outlet side of paring disc in broken. 
10. Shifting of interface line outward. 
11. Through put too high. 
12. Bowl does not seal properly.

### De-sludge procedure of a Purifier:

1. Stop the purifier heater. 
2. By pass the feed or recirculate the feed. 
3. Open the replacement water & overflow the bowl chamber. Then close the replacement water. 
4. Close the operating water. 
5. Open the de-sludge water. 
6. After de-sludge close de-sludge water. 
7. Open operation water & observe for few seconds that bowl is closed or not. If bowl is closed. Then open sealing water & overflow it then close the sealing water. 
8. Open the feed. 
9. Open steam heating of heater

### Why liquid seal is required to operate a purifier?

A liquid seal is required to operator a purifier because if forms a separation line or interface between two liquids. If there is no liquid seal, there will be over flow.

### Why lub oil needs to be continuous purification?

The same lub oil is used for long time in main engine. The lub oil used in engine contaminated by wear particles combustion products & water which is harmful for engine. Operation as lub oil is very costly. The same used L.O is taken from the Engine Sump, Purified then again used for lubrication of different parts. As the same oil is being used continuously, the continuous purification is necessary.

### Homogenizer System

With fuel oil often accounting for more than 40% of a vessels operation costs, efficient combustion is of crucial importance. Furthermore, fuel oil quality can have serious long term implications for engine wear and it’s associated costs.

The Homogenizer has been specifically designed to solve the uniformity problems ship owners and operators face when running on heavy fuel oil. There is no better chemical-free approach for best treatment of heavy fuel oil, water-in-fuel-emulsion and sludge.

The equipment incorporates a hermetically sealed magnetic coupling drive and special hard material combination, suitable for very high pressure and temperature applications.

Operational Principle:
The Homogenizer operates on the principles of mechanical shearing and ultrasonic forces. It utilises a special conical shaped milling gear, to generate high hydrodynamic power consisting of shearing, friction and acceleration forces with pressure waves of high frequency. The high molecular asphaltenes, the existing cat-fines, remaining water etc. are homogenized into heavy fuel oil with maximum particle size of 5 µm.

Main Features:

1. Reduction of fuel oil sludge
2. Increased burnable fuel amount with improved fuel efficiency
3. Improved combustion quality and reduced exhaust emissions
4. Reduced wear on engine components and reduced operational costs

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References: 

marineengineeringonline.com

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