PURIFIERS

Some useful links for purifier construction and working:

http://www.marineinsight.com/marine/marine-news/headline/10-things-must-check-starting-fo-purifier/

http://www.marineinsight.com/tech/auxiliary-machinery/high-speed-centrifuge-on-ship-construction-and-w/

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

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

To understand just follow the below diagram

Actual on board purifier working diagram

Purifier

•        Remove water & suspended Solids particles from oils
•        Two outlets - water , clean oil
•        Gravity disc on top
•        Blind disc on the top of disc stack
•        Sealing water required

Clarifier 

•  Remove finer and lighter solid particles from oil  
•  one outlet for clean oil
•  No gravity disc .only sealing ring
•  Blind disc at bottom.
•  Sealing water not required

To run a  purifier as clarifier

• 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

(Pure D.O purifier cannot change to H.O, it has no heater.Pure clarifier cannot change to purifier, it has no water outlet)

Changing over purifier from H.O to D.O 

•          Replace the gravity disc, which is smaller than the heavy oil                                           
•          Open heater by pass vale.
•          Closed the F. O heater steam in/out valves.
•          Open heater drains v/v.

Why Multi-disc provided in purifier: 

•         To separate the liquid into thin layer. 
•         Thereby create shallow settling distance between discs.                          
•         Improving separation of oil from heaver liquids & solids particle

Need of  sealing water in purifier :

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

 Gravity disc: 

       The gravity disc is important part of purifier, which set the location of the oil and water interface.

                       http://www.marinesite.info/2014/04/what-is-gravity-disc-of-purifier.html

Selection of gravity disc 

1 . Separation temperature 

2. density of oil at this temperature 

3. desired through put of oil and by using of nomogram .

If the gravity disc is too large and/or the outlet line back pressure is too high, the interface will be too close to the periphery of the bowl and fuel will be carried over into the water outlet. 

                                                                                                                                                  Conversely, if the gravity disc is too small and/or back pressure is too low, the interface will be too close to the centre of the bowl and purification will be inefficient, with water being carried over in the purified fuel.

Paring disc

It is a stationary impeller mounted in a chamber at the neck of the bow.

It function is convert the rotating energy into a pressure head.

PURIFIER STARTING PROCEDURE:

Before starting purifier or any other machinery, first check and observe the machinery for lub oil level, is there any job going on with that machinery, brake is free, no obstruction nearby, check for leaks around the machinery etc.

 If you are starting the purifier first and fore most ,

1.       Check the valve line up on your own.
2.       Check the operating water tank level if fitted/open water line valve
3.       Check sludge valve is open.
4.       Ensure before purifier filter is cleaned and purged properly.

Starting the Purifier

• 1. Ensure valves are open, the lines are set from settling tank to service tank.

  2. Start the purifier feed pump with the 3-way re-circulation valve in a position leading to settling tank.

  3. Open the steam to the heater slightly ensuring the drains are open so that the condensate drains. close the drains once steam appears. If steam controller is working fine, do not throttle the inlet/outlet valve of steam line. open fully. By throttling the steam valve slowly the valve seat will erode causing steam to leak always.) 

  4. Start the Purifier motor.

  5. Check for vibrations, check the gear case for noise and abnormal heating.

  6. Note the current (amps) during starting. It goes high during starting and then when the purifier bowl picks-up speed and when it reaches the rated speed, the current drawn drops to normal value.

  7. Ensure the feed inlet temperature has reached optimum temperature for separation as stated in the Bunker Analysis report and nomogram ( bunker delivery note gives the density of the fuel and using this we can get the separation temperature and gravity disc size from the nomogram)

  8. Now check whether the bowl has reached the rated speed by looking at the revolution counter, if provided. The revolution counter gives the scaled down speed of the bowl. The ratio for calculation can be obtained from the manual.

  9. Now, after the bowl reaching the rated RPM, check for the current attaining its normal value.
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• De-sludge Procedure

  10. Open the bowl closing water/operating water, which closes the bowl. (Ensure sufficient water is present in the operating water tank or water line valve is open).close after 30 secs.

  11. Now after 10 seconds, open the sealing water to the bowl.

  12. The sealing water should be kept open till the water comes out of the waste water outlet.

  13. Once the water overflows through the waste water outlet, stop the sealing water.

  14. Now open the de-sludge water/bowl opening water. (This is done to ensure the bowl has closed properly). During de-sludge we can hear a characteristic sound at the opening of the bowl. then close.approx.3 seconds.

  15. Repeat the steps 10, 11 ,12 & 13.

  16. Open the 3-way re-circulation valve such that the dirty oil feed is fed into the purifier. observe the 3 way valve cylinder position

  17. Wait for the back pressure to build up.

  18. Check for overflowing of dirty-oil through waste water outlet & sludge port.

  19. Now adjust the throughput to a value specified in the manual. Correspondingly adjust the back pressure, too.

  20. Now the purifier is put into operation. Change over the clean-oil filling valve to service tank.

  
  

  Checks after starting the purifier during regular watches:

• 
  
• 1. Adjust the throughput, back pressure, temperature of feed inlet if necessary

  2. gear case oil level, motor amps, general leakages, vibration have to be monitored

  3. De-sludge every 2 hours for heavy oil purifiers & every 4 hours for lubricating oil purifiers.                                                                                                                                                                                                                                                                                             

  Stopping of Purifiers:                                                                                                                      

  1. De-sludge the purifier after stopping the feed inlet.

  2. Shut down the steam inlet to the oil.

  3. Stop the purifier after filling up the bowl with water.

  4. Apply brakes and bring up the purifier to complete rest.

  5. If any emergency, the purifiers has emergency stops, on pressing it, will stop the purifiers immediately shutting off the feed.

  Thus we have seen in detail how to start the purifier after carrying out all safety checks and we have also seen how to stop it.
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Purifier overflow reasons:

1. Incorrect  gravity disc size (if this is the reason it will happen only on bunker change)
2. Excessive sludge deposit inside the bowl (purifier will vibrate, also motor Amps will increase slightly)
3. Sealing water low (if you are in doubt with this point, manually increase the sealing water amount/duration. this may be due to clogged filter in water line. usually water line used to have a filter before solenoid ,to avoid solenoid valve being affected by debris in water. clean the filter)
4. Excessive back pressure or service tank valve closed
5. Feed oil temperature high or low(with the large deviation of temperature in purifier inlet oil this may happen.)
6. Orifice plat installed wrongly in the inlet side( this is a human error, it will happen after overhaul or bowl routines).
7. Excessive feed rate (Always set the feed rate with normal operating temperature, around 98 deg.c)
8. Main Sealing ring leakage, between bowl and hood.
9. Low rpm or wrong direction(low rpm mainly by friction pad worn out)
10. Leaking three way valve

In case of overflow of purifier, as a junior engineer you just close the feed valve.
if you know the de sludge operation carry on. otherwise inform senior engineers.

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BASIC MARINE DIESEL ENGINES

                                                

BASIC MARINE DIESEL ENGINES

IC (INTERNAL COMBUSTION)  ENGINES:

         Internal combustion engine : Combustion of fuel takes place inside the cylinder of the engine. e.g. - PETROL ENGINE - DIESEL ENGINE

External combustion Engine :  Combustion of fuel takes place outside the cylinder of the engine.   e.g. STEAM ENGINE.

DIESEL ENGINES or COMPRESSION IGNITION ENGINES:

                           The diesel engine was first patented in 1892 by Rudolph Diesel

As  the name implies,the engine using diesel oil as the fuel, to produce power by combustion process.

The fuel is burnt inside the combustion chamber by means of compressing atmospheric air(compression ignition engine).

The combustion of fuel taking place inside the combustion chamber by increasing the temperature of air.At the point of auto ignition temperature(self ignition temperature) of  fuel reaches,the fuel catches fire without any external sources of heat such as spark plug.

it can be either 2 stroke diesel engine or four stroke diesel engine or etc.but concept is same.only stroke is the difference.

PETROL ENGINES or SPARK IGNITION ENGINE:

The burning of fuel (petrol) occurs by the spark generated by the spark plug located in the cylinder head. 

Auto ignition temperature        

                  The auto ignition temperature or self ignition temperature of a substance is the lowest temperature at which it will spontaneously ignite in a normal atmosphere without an external source of ignition, such as a flame or spark .                                                                                                                                                                                                                                                                                Diesel oil auto ignition temperature- 256 °C (493 °F) varies upto 300°C depending upon grade.


2 STROKE DIESEL ENGINES:

1. The crankshaft is revolving clockwise and the piston is moving up the cylinder, compressing the charge of air from pressure 2 bar and the temperature 40°C  .Because energy is being transferred into the air, its pressure and temperature increase. By the time the piston is approaching the top of the cylinder (known as Top Dead Center or TDC) the pressure is over 100 bar and the temperature over 500°C

2. Just before TDC fuel is injected into the cylinder by the fuel injector. The  fuel is "atomised" into tiny droplets. Because they are very small these droplets heat up very quickly and start to burn as the piston passes over TDC. The expanding gas from the fuel burning in the oxygen forces the piston down the cylinder, turning the crankshaft. It is during this stroke that work energy is being put into the engine; during the upward stroke of the piston, the engine is having to do the work.

3. As the piston moves down the cylinder, the useful energy from the burning fuel is expended. At about 110° after TDC the exhaust valve opens and the hot exhaust gas at 600°C,pressure 4 bar   (consisting mostly of nitrogen, carbon dioxide, water vapour and unused oxygen)  begin to leave the cylinder.

4. At about 140º after TDC the piston uncovers a set of ports known as scavenge ports. Pressurised air enters the cylinder via these ports and pushes the remaining exhaust gas from the cylinder in a process known as "scavenging". The piston now goes past Bottom Dead Centre and starts moving up the cylinder, closing off the scavenge ports. The exhaust valve then closes and compression begins

2 STROKE VALVE TIMING DIAGRAM:

1 -2 Compression 2 - 3 Fuel Injection 3 - 4 Power 4 - 5 Exhaust Blowdown 5 - 6 Scavenging 6 - 1 Post Scavenging

1. approx 110º BTDC 2. approx 10º BTDC 3. approx 12º ATDC 4. approx 110º ATDC 5. approx 140º ATDC 6. approx 140º BTDC

4 STROKE DIESEL ENGINES:

1. INDUCTION: The crankshaft is rotating clockwise and the piston is moving down the cylinder. The inlet valve is open and a fresh charge of air is being drawn or pushed into the cylinder by the turbocharger

2. COMPRESSION: The inlet valve has closed and the charge of air is being compressed by the piston as it moves up the cylinder. Because energy is being transferred into the air, its pressure and temperature increase. By the time the piston is approaching the top of the cylinder (known as Top Dead Centre or TDC) the pressure is over 100 bar and the temperature over 500°C

3. POWER: Just before TDC fuel is injected into the cylinder by the fuel injector. The  fuel is "atomised" into tiny droplets. Because they are very small these droplets heat up very quickly and start to burn as the piston passes over TDC. The expanding gas from the fuel burning in the oxygen forces the piston down the cylinder, turning the crankshaft. It is during this stroke that work energy is being put into the engine; during the other 3 strokes of the piston, the engine is having to do the work.

4. EXHAUST: As the piston approaches the bottom of the cylinder (known as Bottom Dead Centre or BDC) the exhaust valve starts to open. As the piston now moves up the cylinder, the hot gases (consisting mostly of nitrogen, carbon dioxide, water vapour and unused oxygen)  are expelled  from the cylinder. As the Piston approaches TDC again the inlet valve starts to open and the cycle repeats itself.

4 STROKE ENGINE VALVE TIMING DIAGRAM

                                                                                              

Marine Motor Engineering Knowledge

           soon will update all the materials guys.preparing the notes and need to justify some answers before posting on blog.kindly share your materials and knowledge.       please wait few days......       thank you.                       

              Ramkumar Krishnan

   (mail id: rammarsea@gmail.com)

   

    MARINE DIESEL ENGINES:  

      MAN B&w:

                       

       MAN – Germany – Maschinenfabrik Augsburg Nurnberg

        B&W – Denmark – Burmeister &Wain

              

         

The merger of above two Giants is now known as MAN B&W.

         

      DETAILED TIMELINE OF MAN IS 

           http://www.corporate.man.eu/en/company/history/man-timeline/MAN-Timeline.html

      sulzer and man b&w engines series:

       
                          Sulzer engine series: RD, RND , RTA, RT -flex

                        MAN B&w  : KEF , KGF , MC,ME

      
                                COMPARISON BETWEEN SULZER AND MAN

Technology/ System	Wartsila SULZER	MAN Diesel Turbo	Who gets the EDGE?
Intelligent Engine	RT Flex- A complete electronically controlled engine with common rail system	ME Engine- Complete electronically controlled engine integrated with hydraulic control.	Wartsila- For installing an Intelligent engine technology in 2001. Prior to MAN (2003).
Fuel Injection System	Common rail Electronic control with Delta Injection System	Hydraulic actuated Electronic Control Injection system	Wartsila- For integrating Delta control with 3 injectors controlled independently for different load.
Exhaust Valve Control	Electronically controlled variable exhaust valve timing	Camshaft operated Exhaust valve for reliable operation	MAN- For integrating a smart mechanical exhaust valve operation in Intelligent engine for reliable operation.
Fuel Injectors	Conventional fuel injectors	Zero Sac Volume type fuel injectors with slide valve	MAN- Slide type fuel injector reduces after burning and hence NOx emission
Fuel Pump	Spill, suction valve controlled pump with VIT	Jerk type plunger barrel controlled pump with Super VIT	MAN- Super VIT with independent injection timing control w.r.t fuel index.
Starting Air system	Starting air valve opened by 30 bar air and a closing supply for positive shut along with spring. A relief valve in air manifold to avoid overpressure during starting airline explosion.	Starting air valve open by 30 bar air and shut by spring. Bursting disc provided to avoid overpressure during explosion	Wartsila- Additional safety provided in positive closing and relief valve for reliability during manoeuvring.
Piston and Rings	Convex shaped piston with Jet Shaker cooling. Chromium coated Piston ring.	OROS type Piston for better combustion area and reduction in piston temperature. Controlled Pressure Relief type top piston ring.	MAN-With OROS piston, the Maximum piston temperature reduces by 90°C. With CPR ring, better pressure distribution on liner and lower ring.
Cylinder Liner	Fine honed and bore cooled Liner with mid layer insulation.	Bore cooled liner.	Wartsila- Better cooling and insulation increases Cylinder liner Life
Main Bearing	White metal bearing lined on thin back.	Tri metal bearing with high load carrying capacity.	MAN-Tri metal bearing with long life and better embed ability.
Crosshead	12-15 bar pressure from separate pump supplied to bigger size plain bearing.	Small size bearing with oil wedges to retain oil which is supplied by normal system pressure.	Wartsila-Elevated pressure ensures better lubrication at high load. A back up line is provided in case of failure of crosshead pump.
Cylinder Lubrication	Electronically controlled Pulse Lubrication System with metered quantity injection	Alpha Adaptive Cylinder Lubrication control system allowing blending of cylinder oil for different grade of sulphur in fuel	MAN- ACC with different inputs like sulphur content and load index provide better neutralizing features.
Drive	Gear driven with timing gear driving the camshaft	Chain driven with 2 chains driving a camshaft	MAN- Chain drives are cheaper, lighter and easier to maintain and duplication provides backup.
Turbocharging	Prefers Axial turbocharger with constant pulse system.	Variable Turbine Angle turbocharger provides better operation at all load range	MAN-VTA allows engine to run without auxiliary blower at low load operation.
Exhaust Valve	Cobentional Valve seat with Nimonic and Stellite coating	W seat for better operation and increased time between overhaul. Dura spindle with better heat resistant property.	MAN- W seat allows cooling of exhaust valve during combustion stroke
Miscellaneous	Tribo pack allows increased time between overhaul of cylinder component up to 3 years. Electronic monitoring system for safe operation	Electronic monitoring system for safe operation.	Wartsila- With Tribo pack which is a package of design measures increases the TBO to 3 years.

       

   Governor is a device which controls the speed of engine automatically in the prescribed

limits.governor does its job by  measuring the speed and control the a amount of fuel supply to the engine.

Types of governors.

a.    Mechanical governor.           b.    Hydraulic governor

c.    Inertia governor [fitted on older slow speed engine]    d.  Electronic governor

Hydraulic governor is widely used because of their   sensitivity,having grater power to move the fuel control mechanism of the engine


 G/E governor is a droop speed governor with over speed trip.

 M/E governor is a constant speed governor with over speed trip



isochronous governor 

It is a constant speed governor .It is able to maintain exactly constant speed without hunting. This type of governor that has proportional and reset is called isochronous governor

speed droop governor is used at G/E - It is fitted to get load sharing ability isochronous governor gives constant speed, thus can not sharing the load.

AVR is fitted at alternator


governor droop -  When considering the engine and governor combination, the difference between the no load speed and full load speed is called governor droop.

Small droop causes rapid swing

Large drop causes slower response to change in speed

The use of temporary speed droop to prevent over correction of the fuel supply is called

compensation
It required two actions-
	Droop application	- as the fuel supply is changed
	Droop removal	- as the engine response to the fuel change and returns to original
	speed .

Why Inertia type Governor is not used nowadays 

1)        Although very simple type, it requires an engine speed increase of 5% or more to make it operate

2)        In some cases, increase of engine speed will bring into or near to critical speed that can cause severe vibration.

Governor Maintenance

Periodically check oil level,Change the governor oil,Grease the linkage and joint