PURIFIERS QUESTIONS WITH ANSWER

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

1. Refer to the nomogram given in the figure above. Click on the figure to enlarge.

2. 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℃.

3. Connect between the right end of line ② and the point of 3000 L/h on the treating capacity scale using straight line ③.

4. Read within which section of gravity disc inside diameter scale the intersection made by line ③ falls.

5. 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

1. Refer to the nomogram given in the figure above. Click on the figure to enlarge.

2. 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℃.

3. 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.

4. 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.

Water Detection in Mitsubishi Purifiers on Ships

Types of Water Detectors

The Water Detector Function (WD) of the Multi-Monitor in Mitsubishi fuel oil and lube oil purifiers is a device to prevent 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.

Operating Principle of Pressure Sensor Type Water Detector

The Water Detection system provided with a pressure sensor, which is called G-HIDENS system, is controlled on 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 a pressure sensor installed in the circulation line and causes separated water to be discharged before it leaks into 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, is maintained under a required level of back pressure by means of the back pressure valve, with the shut-off valve 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 stopped with an instantaneous drop in circulation line pressure. Detecting this pressure change, the pressure sensor sends a signal to the control panel via the Multi-Monitor to tell that the predetermined quantity of separated water has been accumulated in the bowl and separated water is discharged, normally in the partial discharge mode. In some cases, total charge with sludge takes place, depending on time spent before detection of pressure drop. By this principle water is detected. Diagram below shows a condition when pressure falls due to arrival of water in the top disc periphery.

Electrostatic Capacity Type Water Detector

The electrostatic capacity type water detector relies on difference in dielectric constant between water and oil to determine the capacitance of oil, thereby detecting the water content of oil. This detector is installed in the light liquid connection line of the purifier and controlled on the automatic control panel. Figure below shows a capacitance type water detector connected to the purified oil outlet in a purifier.

In the clarifier operation, the detector monitors the water content of light liquid. When a rise of approximately 0.5% occurs in the water content, the detector recognizes it as “water in the bowl having arrived at predetermined level” and issues an output signal to the control panel. Water is discharged as a result.

Centrifugal Purifiers Basic Principle and Working on Ships

Gravity Separation

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.

Centrifugal Purifiers

In the above case it is gravity that 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. This is shown in figure below by imagining settling tank on its side and rotated, which is the basic principle of centrifugal purifiers.

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.

What is gravity disc ?

• The gravity disc is important part of purifier, which set the location of the oil, and water interface line, which is variable according to the maker’s design.

How to 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 about 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 ?

• By blowing steam into the engine lube oil just pair to its purification.

• Coagulation of colloidal carbon will occur.

• Purifier will remove this carbon more effectively.

Compare purifier and clarifier ?

Purifier

1. Remove water and suspended solids particles from oils

2. Two outlets water and clean oil

3. Gravity disc on top

4. Blind disc on the top of disc stack

5. Sealing water required

Clarifier

1. Remove finer and lighter particles from oil

2. One outlet for clean oil

3. No gravity disc only sealing ring

4. Blind disc at bottom.

5. Sealing water not required

How do you change purifier to clarifier ?

1. Open up the purifier and set the blind disc at the bottom of the disc stack.

2. The water outlet is blocked by a seal on the gravity disc.

3. Blank off the sealing water inlet line.

What is purifier, clarifier ?

• Purifier is a centrifuge, which is arranged to separate water and solid impurities from oil.

• Clarifier is a centrifuge, which is arranged to separate finer solid impurities from the oil.

How to change purifier from HFO to DO ?

1. Replace the gravity disc, which is smaller than the heavy oil

2. Open heater by pass vale.

3. Close the FO heater steam in/out valves.

4. Open heater drains v/v.

5. Pure DO purifier cannot change to HFO, it has no heater.

6. Pure clarifier cannot change to purifier, it has no water outlet.

Why multidisc provided inside purifier ?

1. To separate the liquid into thin layer & create shallow settling distance between discs.

2. Improving separation of oil from heaver liquids & solids particle

Cause of excessive vibration on purifier ?

1. Sludge too much inside the bowl

2. Foundation damper & spring failure

3. Bearing failure

4. Worn gear

5. Uneven wear of frictional clutch

6. Motor speed too high or too low

What are reaseons for purifier over flow ?

1. Incorrect purifier disc size (inside diameter too large)

2. Too low fuel oil temperature

3. Too much rate of throughput

4. Too much sludge inside the bowl

5. Low speed (rpm) of bowl rotation

6. Sealing water failure

7. Operating water failure

8. Worn out main sealing ring

Why purifier is not building up speed while running ?

1. Improper touching with friction clutch (worn out frictional clutch)

2. Touching with break

3. Excessive sludge in the bowl

4. Bearing failure

5. Motor running at overload

6. One phase power failure (Single phasing)

7. Sump oil level too high

8. Vertical shaft and horizontal shaft are out of alignment

How to adjust purifier bowl height ?

• By shim by bowl body

Effect of reduced purifier bowl height ?

• Oil goes through the water outlet.

Why need sealing water ?

• To seal the water outlet & to prevent the overflow of oil from the water outlet.