Properties And Working System Of Marine Fuel Oil

Properties Of Marine Fuel

Density:

• This Is Described As The Weight Of A Unit Volume Of A Liquid.
• The Unit Is Kg/ M3.
• The Density Is Measured At A Standard Temp., Of 150c As It Varies With The Temp.
• If Density Is Taken At Different Temp., A Correction Factor Is Applied To Ascertain Correct Density At That Temp.
• Reciprocal Of Density Is Specific Volume.
• This Is Important Property For Estimation Of Bunker Capacity.

Viscosity:

• This Is Defined As The Resistance Of Fluids To Change Shape, Which Is Due To The Friction Between The Molecules Of A Fluid Producing A Frictional Drag.
• Absolute Dynamic Viscosity: This Is Defined As The Force Required To Shear A Plane Fluid Surface From Other Plane Surface, Over An Area Of 1sq. M. At The Rate Of 1m/Sec., When The Distance Between The Two Surfaces Is 1m. Absolute Viscosity Is Difficult To Ascertain And Therefore , Kinematic Viscosity Is Generally Used To Measure.
• Kinematic Viscosity: This Is The Ratio Of Absolute Viscosity To Density Of The Fluid At A Particular Tyemp. This Is Measured By Flow Of A Set Of Volume Of A Fluid At A Particular Temp., And Through A Specifically Calibrated Instrument. It Is Measured On The Basis I.E., Number Of Seconds For A Calibrated Instrument Like Redwood No.1, At 380c.
• Centistoke: This Is The Unit Used By International Standard And Measured At 500c. Higher Temperature At The Time Measurement Can Be Used For Viscous Fluids And Appropriate Corrections Can Be Made Later.
• Temperature Affects The Viscosity , Which Decreases With The Temperature Of The Liquid.
• Viscosity And Temp., Play A Vital Role While Selecting Oil For A Particular Service.
• For Best Results During Automisation Of Fuels Of High Viscosity, It Is Necessary To Heat The Fuel To Bring Down The Viscosity To About 30 Centistokes Or Still Lower At The Injector Point.
• Viscosity Of Diesel Oil Is 7centistoke At 380c.
• Viscosity Is Always Quoted At A Certain Temp., Without Which, It Has No Meaning.

Flash Point:

• This Is The Minimum Temperature At Which The Oil Begins To Give Out Flamable Vapours, Which Would Cause Momentary Ignition On Application Of Heat / Flame In A Specified Apparatus.
• The Test May Be Specified As ‘OPEN’ Or ‘CLOSED’ Depending On The Type Of Apparatus.

Fire Point:

• It Is The Minimum Temperature At Which The Vapours Given Out By The Heated Oil Are Sufficient To Ignite And Give Out More Vapours By The Heat So Produced, So That They Burn Continuosly.
• This Temp., Is Different From Flash Point And Is Higher By Anything Up To 400c.

Acidity (ALKALINITY):

• It Is Indicated By Neutralisation Number.
• The Number Is The Mass In Miligram Of An Alkali  Required For Neutralising The Acid Present In 1gm Of The Sample.Neutralsation Number Can Also Be Expressed As Parts Per Million Per Ml Of Sample Of Oil.
• Total Base Number (TBN) Is Often Used For Alkalinity Indication Of Lubricating Oils.

Ash:

• This Is Expressed As Percentage By Mass Of The Original Sample Of Oil, Which Is Evaporated And Ignited Until All The Traces Of Carbon Have Disappeared
• The Ash Left After Above Process Contains Hard And Abrasive Minerals Such As Quartz, Silicates, Iron, Aluminium Oxides, Sand Etc.

Preparation Of Heavy Fuel Oil:

• Present Days Modern Marine Diesel Engines Are Run Continuosly On Heavy Fuel Oil Only
• The Main Purpose / Object Of Preparing The Heavy Fuel Oil For Use In Two Stroke Diesel And Four Stroke  Engine Is To Remove The Impurities Like Water, Sludge, Catfines. Also To Heat The Fuel To  Get The Correct Injection Viscosity As Recommended By Engine Manufacturer.

Preparation:

• After Receipt On Board Fuel Oil Is Stored In Bunker Tanks. In These Storage Tanks Fuel Is Heated To Just The Required temp To Keep It Pumpable.
• The Fuel Is Transferred From The Storage Tanks To The Settling Tank By Using A Transfer Pump. The Settling Tanks Are Normally Two In Number Having Capacity Of  24 Hours Use.
• In The Settling Tank Fuel Is Further Heated And Retained For As Long As Possible. In The Settling Tank Some Of The Heavier Solid Impurities And Water Get Separated By Gravity And Collect At The Bottom Of Tank. These Have To Drained Out Regularly.
• Heavy Fuel Oil Is Then Purified Further By Centrifuges. Centrifuges I.E., Purifiers And Clarifier Are Connected In Series. In Centrifuges The Impurities Such As Solid, Liquid And Sludge Are Removed Completely.
• In case Of Alfa Laval Purifiers Then By Using Alcap System  The Oil Is Clarified And At Same Time Separated Water Is Removed From Bowl.
• Purified Oil Is Then Pumped To The Daily Service Tanks. From Daily Service Tank Oil Flows Through A Three Way Valve To A Mixing Tank. 
• A Flow Meter Is Fitted In The System To Indicate The Fuel Consumption.
• A Mixing Tank Installed In Fuel Oil System Of Engine, Is Designed To Operate On Heavy Fuel Oil. The Purpose Is To Produce A Gradual Variation Of Fuel Quantity During Transition Period From Diesel Oil To Heavy Oil Or Vice Versa. The Supply Oil Changes In Viscosity And Temp., Progressively With This System. Mixing Tanks Has Proved To Be Useful For De gasification And Entrainment Of Air From The System. Mixing Tank Can Also Be Used As A Metering Tank. This Is Used To Collect Recirculated Oil And Also Acts As A Buffer Tank As It Will Supply Fuel Oil When Daily Service Tank Is Empty.
• Booster Pump Draw Fuel From Mixing Tank, Raises It’s Pressure And Passes Through The Heater. Oil Is Heated Up With Curresponding Reduction In Viscosity In Accordance With The Temperature – Viscosity Relationship.
• Controled Temperature By Viscosity Regulator Ensures Fuel Have A Viscosity Of Combustion Quality.
• A Pressure Control Valve Provides Constant Supply To Engine Driven Fuel Pump Ensuring High-Pressure Injection Supply Pressure.
• Pre-Warming Bypass Valve / Line Is Used To Heat Up The Fuel Before Starting The Engine.
• Service Tank Diesel Oil Are Connected To System Through A Three-Way Valve. The Engine Can Be Started And Manevier On Diesel Oil Or Even A Mixture Of Diesel Oil And Heavy Oil.
• Further The Sestem Include Various Safety Devices Viz., Low Level Alarms And Remotely Operated Tank Outlet Valves Viz., Quick Closing Valves, Which Can Be Closed From Outside The Engine Room In The Event Of Fire.

Importance Of Viscocity In Fuel Oil:

• Steady Values Of Viscosity Is To Be Maintained For Proper Atomization. Atomization Is Breaking Down Of Fuel Oil To Fine Droplets So That A Large Surface Of Oil Is Exposed To Heat And Oxidation.
• Low Viscosity Cause Too Fine Atomization And Thus Droplets Will Not Penetrate Deep Enough. This Will Cause Burning Close To Nozzle Tip. Because Of This Poor Combustion Nozzle Operation May Be Troublesome.
• On The Other Hand High Viscosity Cause Too Large Droplets Of Oil And Have Enough Energy To Strike Metallic Surface. This Will Lead To Overheating. This Also Create Problems In Functioning Of Centrifuges

Settling Tank

• The Fuel Is Transferred From Bunker Storage Tanks To The Settling Tanks Prior To Centrifuging, For Use In Diesel Engines And Also For Burning In Boilers.
• The Fuel Is Heated In Settling Tank And Retained There For As Long As Possible. The Settling Period Should Not Be Less Than 24 Hours For Optimum Separation Of Impurities.
• While The Fuel Is In Settling Tank Some Of The Solids, Sludge And Water Separates Out And Settle Down At The Bottom Of The Tank From Where They Can Be Drained Off Through The Drain Connections Which Must Be Of Self Closing Type.
• For Use In Diesel Engines, Only Purification By Settling Is Not Enough As Subsequent Centrifuging Is Carried Out To Separate The Impurities. Still Draining Of The Settling Tank Regularly Once In A Watch Is Recommended.
• High And Low Level Alarms Are Fitted On The Tanks.
• Fuel Oil Is Heated In The Settling Tank For Faster Separation Of Impurities, For This Reason Settling Tanks Are Provided With Heating Arrangement.
• The Rate Of Separation Of Impurities In Settling Tank Depends On Following Factors.
• Higher The Density Difference Between Oil And Other Impurities, Greater Will Be The Rate Of Separation.
• Bigger The Size Of The Impurity Particle Better Will Be The Rate Of Separation.
• Lower The Viscosity Of Oil, Better Will Be The Rate Of Separation.
• As Heating Results In Better Separation, The Fuel Is Generally Heated To A Minimum Temp., Of 500c Or To A Temp., About 700c.
• One Of The Solid Contaminats In The Fuel Oil Is A Cat (CATALYTIC) Fine, Having Density Of 2600 To 2800 Kg/M3 And Having Particle Size Of 10 To 50 Microns. These Compound Take Long Time To Settle Even When The Fuel Temp., Is Raised To 700c.
• An Ideal Settling Tank Should Have Inclined Bottom To Facilitate The Separation And Draining.

Safety Devices Fitted  On Settling Tank;

Fuel Outlet Valve: This Is Remotely Operated Quick Closing Valve Fitted On The Settling Tank.  It Is Arranged To Operate From Outside The Engine Room In Case Of Emergency.
Air Pipe: This Pipe Is Led To Above The Upper Deck Level And External To The Deck House. The Outlet Of This Pipe Is Fitted With Metallic Wire Gauge Screen Called Flame Trap To Prevent Fire Hazards.
Thermometer:This Is Used For Measuring The Temp., Of Oil
Sludge Valve / Cock: This Is Used For Draining Water And Sludge  Collected At The Bottom Of The Tank. This Valve Must Be Self-Closing Type.
Over Flow Pipe: It Is Fitted At The Top Of The Tank And Led To An Over Tank In The Double Bottom. An Alarm Activated By An Over Flow Condition Is Sometime Fitted To The Tank.
Alarms: These Are Fitted To Warn High Fuel Temp., And Low Fuel Level.
Dumping Valve: This Valve Is Used In The Event Of Fire, To Dump The Oil To The Double Bottom Tank.
Quick Closing Valve: In Case Of Emergency To Stop The Engine, This Valve Cuts The Supply Of Oil To The Engine. The Arrangement Provided Outside The Engine Room  To Close This Valve.
Sounding Valve: This Pipe Is Provided To Take Sounding Of The Tank For Checking Fuel Level.

---

Author Amit                                                                 

---

Read more

Basic concept on Ship stability and free surface area

Stability Of Ships

Two Principal Forces Which Act On A Ship Floating Freely Are – Weight  &  Buoyancy.

For The Ship To Float, It Must Displace It’s Own Weight Of Water.

Then To Be In Equilibrium Condition, The Centre Of Weight & The Centre Of Buoyancy Must Be Vertically In Line.

External Or Internal Forces Can Move The Ship In Either Transverse Direction Or Longitudinal Direction. But It’s Ability To Return To It’s Original Stable Position I.E., Equilibrium Condition Is Related To The Stability.

Upright Position Of Ship :  A Vessel Is Said To Upright If It Is Rolling Slightly About The Upright Position.
Statical Stability : This Is The Measure Of The Tendency Of A Ship To Return To The Upright Position If Inclined By An External Force.
Upright Position Of Ship : In The Upright Position, Weight Of The Ship Acts Vertically Down Through The Centre Of Gravity ‘G’. While The Upthrust Acts Through The Centre Of Buoyancy ‘B’.
Equilibrium Condition Of Ship : When Weight Of The Ship Is Equal To The Upthrust And The Centre Of Gravity And The Centre Of Buoyancy Are In The Same Vertical Line, The Ship Is Said To Be In Equilibrium Condition.

Consider A Ship Inclined By External Force To An Angle ‘Ǿ’.
               In This Case Centre Of Gravity Remains In The Same Position, But The Centre Of Buoyancy Moves From ‘B’ To ‘B1’.
    Therefore Buoyancy Acts Through ‘B1’  And The Weight Still Acts Through ‘G’, This Creates
    The Righting Moment = Δg X Gz -------------------(1)
    This Moment Tends To Turn The Ship To It’s Upright Position.
    Righting Lever = Gz = Gm Sinǿ
    Now

The Vertical Through New Centre Of Buoyancy -‘B1’ Intersects The Centreline At ‘M’ Which Is Called The Metacentre. The Height  Of ‘M’ From The Centre Of Gravity Is Called The Metacentric Height- ‘GM’

Stable Ship : ‘GM’ Is Said To Be Positive When ‘G’ Lies Below ‘M’. In Such Case Ship Will Roll Back To Original Upright Position When Disturbed By External Or Internal Force.

Tender Ship : A Stable Ship With Small Metacentric Height Will Have Small Righting Lever At Any Angle And Roll Easily. In Such Case Ship Is Said To Be Tender Ship.

Stiff Ship : A Stable Ship With Large Metacentric Height Will Have A Large Righting Lever At Any Angle And Will Have Considerable Resistance To Rolling. In Such Case It Is Called The Stiff Ship.

Unstable Ship : When Metacentre ‘M’ Lies Below The Centre Of Gravity ‘G’, Then ‘GM’ Is Said To Negetive, Which Increases The Angle Of Heel. In Such Case The Vessel Is Said To Be Unstable And Will Not Return To Upright Positon.

Neutral Equilibrium : When Centre Of Gravity And The Transverdse Metacentre ‘M’ Coinside, The Righting Lever Is Zero And There Is No Righting Moment Acting On The Ship. In Such Case Ship Will Remain In Inclined Position With An Angle ‘Ǿ’, And The Ship Is Said To Be In Neutral Equilibrium Condition.

Stability At Small Angle Of Heel
Transverse Metacentre :
The Height Of Transverse Metacentre Above The Keel ‘KM’ May Be Found Out, By Considering The Small Inclination Of The Ship About It’s Centre Line.
For Small Angle Of Heel
Upright And Inclined Water Line Intersects.
Volumes Of The Emerged And The Immersed Wedges Are Equal For Constant Displacement.
    Now
    The Distance Of The Transverse Metacentre Above The Keel Is Given By
    Km = Kb + Bm -------------------------------------------(1)
    Note : ‘KB’ Is The Distance Of The Centre Of Buoyancy Above The Keel. This Can Be Found Out From The Hydrostatic Curve.

‘BM’ Can Be Found Out As Follows.
        Let Us Consider A Ship As Shown In Figure, Whose Volume Of Displacement Is ‘▼’, Lying Upright At Water Line ‘WL’. The Centre Of Buoyancy ‘B’ Being On The Centre Line Of The Ship.
        If The Ship Is Now Inclined By An Angle ‘Ǿ’, It Will Lie At The Water Line W1l1, Which Intersects The Original Water Line ‘WL’ At ‘S’. Since ‘Ǿ’ Is Small It May Be Assumed That ‘S’ Is Lying On The Centre Line.
        A Triangular Wedge Of Buoyancy ‘W1SW’ Has Been Moved Across The Ship To ‘L1SL’ Causing The Centre Of Buoyanmcy To Move From ‘B’ To ‘B1’
    Now
    Moment Of Shift Of Ship’s Buoyany From B To B1
    = Moment Due To Shift Of Buoyancy Wedge
Therefore
    ▼ X Bb1  =  V X Gg1
                                         V X Gg1                                        
                Bb1  =   ---------
                              ▼
                                   V X Gg1
             Bm Tanǿ = ---------- -----------------( As Bb1 = Bm Tanǿ )
                                      ▼
                     V X Gg1
        Bm = --------------  ----------------------------------(2)
                        ▼ X Tan∆

    Now To Determine The Value Of (v X Gg1) , Ship’s Length Is Devided In To Thin Strips Of Length
    Δx. The Half Width Of Original Water Line Is ‘Y’
    Therefore
    Immersed C/S Area Of Wedge = ½ Y X Y Tanǿ X Δx
                                                                   = ½ Y2tanǿ X Δx
    Volume Of Immersed Wedge  = Σ ½ Y2tanǿ X Δx

The Volume Of This Wedge Is Effectively Moved From One Side To The Other By A Distance Of (4Y/3)
    Therefore
    Total  Moment Of Shift Of Wedge
                        = Σ ½ Y2tanǿ X Δx  X (4Y/3)
                                                        = Tanǿ (2/3) Σ Y3 Δx
    We Know That,  (2/3) Σ Y3 Δx = Ixx
    (IXX = Second Moment Of Area Of Water Plane         About The Centre Line Of The Ship )
    Therefore
    Total  Moment Of Shift Of Wedge = Ixx X Tanǿ --(3)
    From Equation (2) And (3)
                                                                                     Ixx
    Height Of Metacentre From ‘B’  =  ------ ------------(4)
                                                                                      ▼
Metacentric Diagram
In This Diagram Kb (HEIGHT Of Centre Of Buoyancyfrom Keel ) & Bm ( Height Of Metacentre Above The Centre Of Buoyancy )  Are Plotted Against The Ship’s Draught As Shown In Figure.
As The Position Of Buoyancy-B & The Position Of Metacentre-M Depends Only Upon The Geometry Of The Ship & Draught Of The Ship At Which It Is Floating, Position Of ‘B’ & ‘M’ (HEIGHT Of Metacentre) Can Be Found Out Without The Knowledge Of Loading Of The Ship At Any Intermediate  Draught.

Stability At Large Angle Of Heel
Stability Discussed So Far Is For Small Angle Of Heel With Certain Assumptions ( Two Water Planes Intersect At The Centreline,Wedges Formed Are Right Angled Tringles) The Metacentric Height ‘GM’ Was Taken As The Measure Of Stabilty.
When Ship Heels To An Angle Greater Than 100, Above Assumptions Cannot Be Made & The Principle On Which Initial Stability Were Based Are No Longer True. Insteadthe Righting Lever ‘GZ’, Which Is The Peprendicular Distance Between Vertical Lines Through The Centre Of Gravity & The Inclined Centre Of Buoyancy, Is Used As Measure Of Stability.

Let Us Consider
A Ship Which Is Inclined To Some Angle ‘Ǿ’ From The Vertical.
‘WL’ Is The Initial Water Line And W1li New Water Line When Inclined.
The Volume Of Displacement In Each Case Is Same.
If The Side Of The Ship Were Vertical Along It’s Length, Then The Two Water Line Would Intersect At The Centreline At Point ‘P’
    Further,
Volume Wpw1 Which Has Emerged Will Be Equal To The Volume Which Has Been Immersed. Let This Volume Be ‘v’
The Centroid Of These Two Wedges ‘g’ And “g1’ Be Located At A Distance Of ‘d’

Now
    Moment Of Shift Of Ship’s Buoyancy
    = Moment Due To Shift Of Buoyancy Wedge
    Bc X ▼ = D X V
                       D X V
            Bc = -------  ------------------------------------------------(1)
                         ▼
    &   Gz = Bc – Bg Sinǿ
                       D X V
                 =  -------- - Bg Sinǿ          
                        ▼
                                                   D X V
     Righting Lever ‘GZ’ = -------- - Bg Sinǿ -------------(2)
                                                      ▼
    Note ;  This Is Called Atwood’s Formula. From This Formula If ‘v’ And ‘d’ Are Evaluated For A Range Of Angles Of Inclination ‘Ǿ’ , The Graph Of Righting Lever ‘GZ’ Verses The Angle Of Inclination ‘Ǿ’ Can Be Drawn. The Curve So Drawn Is Called ‘CURVE Of Statical Stability’

Curve Of Statical Stability

In This Curve Righting Lever Can Be Seen, Rising To A Maximum Value And Then Slowly Fall To Zero.
A Ship Inclined Beyond The Point Of Zero ‘GZ’ Will Be Unstable.
Angle Up To Zero ‘GZ’ Point Is The Range Of Ship Stability At That Particular Load Condition.
Ship Operator Should Know This For Safe Operation Of The Ship.

Free Surface Effect

If The Tank On A Ship Containing Liquid Is Not Fully Filled, The Liquid Moved Through The Tank In The Direction Same As The Heel. For This Reason, The Focus Of The Vessels Central Gravity Shifts Away From The Centre Reducing The Righting Lever "GZ" And Height Metacenter Which Results In Increase In Heel Angle. This Effect Is Known As The Effect Of The Free Surface.
We Consider A Full Tank Water In Ship Of Displacement "Δ" With Inclination To Any Angle Ǿ.
The Focus Of Vessel Moves From "G" To "G1", As Wedge Of Liquid Moves Through The Tank

Tank Divisions Use In Tankers:

Largest Ship With Free Surface Effect Must Be Left Space Of Oil Tank For Expansion.
Tanker Was Built Initially With Centeline Bulkhead And Expansion Tanks. Twin Length, Bulkhead Were Introduced Without Expansion Tanks And Successfully Proved Because It Deals With The Loss Of Metacentric Height Of Design Due To The Free Surface Effect.
It Is Not Possible To Design A Dry Cargo Ship In Same Way As C.G Position Varry With The Nature Of Deposition Of Cargo. Effect Of The Free Surface Is Dangerous For A Ship With Small Metacentric Height And Can Make The Ship Unstable.
In These Ship Tanks Required To Be Pressed Up. If The Ship Is Initially Unstable And Helling To Port, Then Any Attempt To Fill The Water Ballast Results In Reduction Of Stability.

# Various books, study material and other online sources has been refereed prior to writing this article but no part is copied or produced  from any of the source but explained same thing in better detailed way.

---

Author Arpit Singh and Amit                                                                 Article requested by: Deepak Kumar

---

Read more

Overhaul and Repair of a Marine Turbocharger

Introduction
The turbocharger is a very sensitive device; It must be treated with caution. It is very important to know the detailed step by step, to disassemble and in this article we will discuss some safety measures that must be taken before and during the dismantling process.
A turbocharger has a turbine on one side and a compressor on the other. The disassembly should always keep the compressor side beginning to measure the critical clearance between the mounting of the cover on the compressor side and the compressor side tree. This is a very important area that needs to be met and must be supported as he left.

THE MAKER’S MANUAL MUST BE READ AND UNDERSTOOD BEFORE ANY WORK IS UNDERTAKEN ON ANY MACHINERY.

Safety while Dismantling the Turbocharger

Inform the operating personnel accordingly before starting any maintenance work on turbocharger.
As a precaution, place a receptacle for leaking oil under the turbocharger.
Before starting work, secure the rotor against turning.
Ensure that absorbent material is available to soak up any spilled oil.
Ensure that operation and process materials are drained, collected, and disposed of in a safe manner.
Ensure that all spares and tools are available for dismantling and assembling.
Dismantled safety devices must be reassembled and subjected to a functional test immediately after conclusion of maintenance and repair.

Turbocharger Overhauling

Tools Required for Dismantling

Open and ring spanner
Box spanner
Claw spanner
Tommy spanner
Bearing pushing tool
Bearing pulling tool
Pump disc locking plate
Pump removing tool set (provided by manufacturer)
Impeller removing tool set (provided by manufacturer )
Shaft pushing tool
Clearance measuring instruments
Screw driver

Preliminaries before Dismantling:

Before dismantling, exhaust gas from the turbine should be bypassed and a blanking plate should be fitted in turbine inlet casing.
Drain the lube oil from the built-in sump.
Remove the turbine side cooling water connection and drain all water

Turbocharger Sectional View

Image credit:www.auto-innovations.com

Turbine and Impeller

Image credit: www.romaga.com

Turbocharger Dismantling Procedure

Compressor Side Removal:
Dismantling should always be started from the compressor side.
1) First remove the filter silencer assembly or compressor inlet casing from position.
2) Remove the compressor end cover and drain plug on the compressor side.
3) Remove the suction cover and measure the critical clearance .It is the distance between the compressor end cover mounting face and shaft end .Mark it as K.
4) Pull the rotor shaft towards the compressor side until the impeller comes in contact with the insert and determine K2.
1. Impeller clearance L = K - K2
5) Thrust the rotor shaft towards the turbine side until the turbine disc and nozzle ring comes in contact with each other and measure K1
2. Disc clearance M = K1 - K
6) The above measured clearance is very important as this will determine the proper functioning of the labyrinth seal between the impeller and exhaust shield and also the alignment of the shaft.
7) Remove the lube oil pump assembly after removing the pump locking plate.
8) Remove the bearing nut and bearing nut washer.
9) Fix the bearing pulling tool in position and slowly tighten it. This will pull the ball bearing assembly out. Care should be taken while removing bearing to avoid any damage to the bearing and rotor shaft end threads.
10) Mark the position of the bearing in position to put it back as it is while assembling.
11) The ball bearing assembly should not be disturbed in any case. If it is damaged, the whole assembly should be replaced with the manufacturer's new part.
12) Now remove the compressor outlet casing with diffuser.
13) Remove the impeller nut and impeller washer.
14) Remove the impeller and inducer from position.

Turbocharger turbine side dismantling procedure for overhauling,for repairing damaged turbine blades, for cleaning cooling water spaces is detailed in the second page of the article "Overhaul and Repair of a Marine Turbocharger."
Turbine Side Removal
1) Remove the turbine end cover with sight glass on the turbine side.
2) Measure the clearance between the turbine end cover mounting face and shaft end.
3) Check the axial deflection of the pump disc cover. The permissible axial deflection of the pump cover is 0.05 mm.
4) Check the rotor shaft by turning by hand.
5) Remove the pump disc locking plate.
6) Loosen the lube oil disc cover and pump washer on the lube oil pump disc by removing the bolt.
7) Remove the outer shaft end nut and tab washer and then remove inner shaft end nut.
8) Remove the lube oil disc from position.
9) Loosen the bearing nut and bearing nut washer and remove from place.
10) Fix the bearing pulling tool on a resilient mounting and slowly tighten it, and this will pull the roller bearing on turbine side slowly out.
11) Care should be taken while removing the bearing to avoid damage to the shaft outer end threads and bearing.
12) Do not disturb the bearing assembly as improper bearing position may misalign the rotor shaft.
13) Before removing, put punch mark on the bearing in position so that it can be put back as it is.
14) Remove the turbine inlet casing from the turbine outlet casing.
15) Now the whole rotor shaft can be pulled out from the compressor side. While pulling out the shaft, care must be taken to avoid damage to the turbine blades and labyrinth sealing arrangements on the shaft.
16) Remove tab washer and remove seal plate to the turbine outlet casing.
17) Remove shroud ring and shaft seal from the turbine outlet casing.
18) Remove nozzle ring assembly from the turbine inlet casing.
Finally remove the air seal adjusting screw, anti-corrosion zinc assembly, sand cover, and other various accessories in position

# Various books, study material and other online sources has been refereed prior to writing this article but no part is copied or produced  from any of the source but explained same thing in better detailed way.

---

Author Amit                                                                     

---

If you have any problem with the content contact us! we will act ASAP

Read more

What is marine boiler and Boiler system on oil tankers.

A boiler is a closed pressure vessel, in which water vapor is produced from distilled water / feed water. All boilers have a furnace or a combustion chamber in which fuel is combusted to release energy. Air is provided in the boiler furnace for assisting the combustion of the fuel. A large clearance between the combustion chamber and the water allows the transfer of combustion energy to the water, as heat. The boilers are equipped with a steam drum and a water drum, which ensure steam and water respectively, can be separated. It should also provide a variety of accessories and to ensure that the fuel, the supply of air and water is to meet the steam requirements.

VARIOUS USES OF STEAM ON SHIPS

For main engine propulsion/turbines (in case of steam ships)
For power generation (to run steam turbo generators)
For running auxiliaries (in case of steam ships)
For soot blowing and for the steam atomized burners.
For fresh water generation (Evaporators)
For fire major fighting (steam drenching)
For heating duties (ME fuel oil heater, Galley supply, Purifier, Calorifier, Galley, Accommodation heating, Sea chests tracer lines for pipeline heating)
For cargo heating
For fuel tank heating
For deck machineries
For running Cargo pump turbines
For operating bilge, stripping and other steam driven pumps.
For tank washing in tanker ships and general cleaning.
For using as a steam ejector media for ejector pumps and vacuum devices
For Driving steam driven deck machineries like winches etc.

Pressures used:
The working pressure used in marine boilers will vary from boiler to boiler as required.For Tanker Vessels Medium pressure 17-30 bar(normally 16bar).

Boiler system in oil tankers:

Due to the high demand in the oil-Tankers, high capacity composite boilers or Dual pressure boilers are used. The main reason for the introduction of double pressure boiler is the use of modern boiler water pipes of high yield, without fear of load damage or contamination of Fuel oils. The basic construction is made of a D-Type boiler design upon which is mounted a Steam/Steam generator drum. Steam heating by the main boiler warms the water in the steam generator which full fill all the requirements for a propulsion pump, the heating load and fuel tanks and all other tasks of turbines.

The drum is initially filled with the primary quality of feed water and is well balanced. Make-up is limited to small amounts due to leaks and the fuel pump can be simple. An example of this could be an alternative pump driven by steam or air. The chemical treatment/dozing is simple and requires only minimal for the addition or rinsing. The above design shows super heater in the system but this is usually installed where the generated steam is required for the turbine alternators.

Secondary drum.

The U-shaped heating elements welded through the door of the shaft and at the end covered with the drum head. The tubes are well supported. In the lower part of the housing a manhole can be installed to allow access to the heating elements. The secondary drum also acts as a receiver for the exhaust gases of the steam boiler. Typical pressures above 63 bar (278degC) for the primary and 23.5deg (219degC) for the secondary. Primary pressure of 35bar (242degC) and closer to 15bar high pressure (198degC) proved to be sufficient to drive turbines for cargo oil pumps on tankers.

On another hand Composite boilers are a combination of oil boilers and exhaust gas economiser. When the diesel engine is at full load, the fuel burner starts only when the steam demand is higher than the production of steam from the exhaust gas of diesel engines. Composite boilers are so arranged that these can generate steam on Main engine exhaust gases or by burning oil in the furnace. In most cases the gas flows are kept separate each having its own uptake this permits the oil firing to be used in conjunction with the engine exhaust gases. By this means the output of steam can be maintained independent of the engine power.

Most of the tank type auxiliary boilers can be modified for composite firing, the modification consists of an additional tube nest added to basic oil fired design, the engine exhaust gases are circulated thru this tube nest so providing heat for generation of steam. In port stays boiler pressure is controlled by start/stop of burner at required pressure, and during sailing the pressure control is by excess steam dump valve.

But on which principle D-type water tube boiler work?

This boiler has 2 drums, an integral furnace with wall mounted burners and is often referred to as ‘D’ type boiler because of its shape. The furnace is at the side of the 2 drums and is surrounded on all sides by water tube walls. These water wall tubes are connected either to upper and lower headers or a lower header and the steam drum. The larger steam drum is placed above a smaller water drum , The two drums are connected to a large number of pipes of small diameter, which carry feed water. These small diameter pipes are known as the generating tubes that provide the main heat transfer surfaces for the generation of steam. The water circulates between the two drums with the aid of large diameter downcomers. The superheater is located through several rows of screen tubes covered between the drums. The fireproof material is used in the manufacture of the furnace, the burner wall and behind the water walls. The fire-resistant material acts as an insulator, which prevents heat loss. The boiler is also provided with a jacket for the combustion air, around the air control registers, which are surrounded by the burner.

# Various books, study material and other online sources has been refereed prior to writing this article but no part is copied or produced  from any of the source but explained same thing in better detailed way.

---

Author Arpit Singh                                                                             Article requested by: bilal ahmad

---

Read more

General arrangement of IG Plant, Production and Deck Distribution System

The 3 elements necessary for combustion are : 1. Fuel(hydrocarbon vapour),  2.Heat(Source of Ignition),  3.Air(Oxygen); Oil tanker is basically meant for carriage of petroleum products/crude oil, thus fuel is available in plenty on board. Heat includes various sources of Ignition; these are also plenty on board from boilers, generators, hot work, galley, smoking etc. Air is present all around us, thus all 3 sides of the fire triangle exist on board a tanker, and therefore the flammability hazard is always present.

Why IG is required?

To maintain a safe atmosphere within ship’s cargo tanks a fixed inert gas system is used. Hydrocarbon gas normally encountered in petroleum tankers cannot burn in an atmosphere containing less than approximately 11% oxygen by volume. Accordingly, one way to provide protection against fire or explosion in the vapour space of cargo tanks is to keep the oxygen level below that figure. This is usually achieved by using a fixed piping arrangement to blow inert gas into each cargo tank in order to reduce the air content, and hence the oxygen content, and render the tank atmosphere non-flammable. As inert gas is added to the hydrocarbon gas/air mixture, the flammable range decreases until a point, is reached where the LFL and UFL coincide. This point corresponds to an oxygen content of approximately 11%. No hydrocarbon gas/air mixture can burn at this oxygen level. For practical purposes and to allow a safety margin, 8% is taken as the level of oxygen at which no hydrocarbon gas/air mixture can burn under any circumstances. To prevent fire or explosion in a tank containing a hydrocarbon gas/air mixture, it is therefore necessary to produce and supply inert gas having an oxygen content not normally exceeding 5% and to displace the existing air in the tank until the resultant oxygen level throughout the tank does not exceed 8% by volume.

Inert gas systems should be capable of delivering inert gas with an oxygen content in the inert gas main of not more than 5% by volume at any required rate of flow; and of maintaining a positive pressure in the cargo tanks at all times with an atmosphere having an oxygen content of not more than 8% by volume except when it is necessary for the tank to be gas free. 

Lower flammable limit (LFL): It is the concentration of a hydrocarbon gas in air below which there is insufficient hydrocarbon gas to support combustion. It is also referred to as Lower explosive limit (LEL). Mixture below this limit is also called as lean mixture.

Upper flammable limit (UFL): It is the concentration of hydrocarbon gas in air above which there is insufficient amount of air to support and propagate combustion. It is also referred to as Upper explosive limit (UEL). Mixture above this limit is called as rich mixture

Sources of inert gas; Possible sources of inert gas on tankers are:

1. Uptake gas from the ships main and auxiliary boilers.
2. An independent inert gas generator.
3. A gas turbine plant when equipped with an afterburner.
When an independent inert gas generator or a gas turbine plant with afterburner is fitted, the oxygen content can be automatically controlled within finer limits, usually within the range 1.5% to 2.5% by volume, and not normally exceeding 5%.

In certain ports, the maximum oxygen content of inert gas in the cargo tanks may be set at 5% to meet particular safety requirements, such as the operation of a vapour emission control system. Where such a limitation is in place, the vessel is usually advised of the requirements in the pre-arrival information exchange.

The Inert gas, besides not supporting combustion, should also fulfill certain other requirements, such as –
1. It should be non-reactive with cargo (e.g. in case of chemical gas)
2. It should not taint cargo (e.g. product)
3. It should not react with tank material (e.g. not causing corrosion)
4. It should have negligible or no toxic constituents.
5. It should be easily available at reasonable cost.

Other advantages of using IG are:

1. Positive pressure is maintained in the tank. This keeps out other gases that could cause combustion.
2. The positive pressure helps a faster discharge rate.
3. It prevents cargo loss due to evaporation.
Oil tankers may be fitted with an IG system, which utilizes the flue gases from engine room boilers as a means of reducing the oxygen content in cargo tanks. Some vessels may be fitted with IG Generators which are self contained units burning diesel oil to produce inert gas.

Usually, the inert gas composition is:

Oxygen (02) % by volume:  2 to 4%
Carbon dioxide (CO2) % by volume :  12 to 14%
Nitrogen (N2) : Balance
Sulphur dioxide (SO2) : Traces
Carbon monoxide (CO) : Trace
Nitrogen Oxide (NOX) : Trace
Water vapour H2O : Trace (high if not dried)
Ash and soot (C) : Traces

GENERAL ARRANGEMENT OF THE INERT GAS SYSTEM.

Flue gas generated from the boiler flows through the Boiler Up-take Valve and into the Scrubber. There, the gas is cooled down and washed by sea water supplied by the Scrubber Water Pump. Before leaving the Scrubber the gas passes through the Demister where water droplets are removed before entering the Blower suction. On the discharge side of the Blower, oxygen content and temperature of the flue gas are monitored. High oxygen content and high temperature activate alarms.

Inert Gas from the blower flows in to the Deck Seal through Inert Gas Pressure Regulating Valve. Main line pressure is automatically controlled to keep desired pressure constant. Excessive pressure is avoided by the Inert Gas Pressure Regulating Valve working in conjunction with the Recirculation Valve.

The Deck Seal isolates the boiler up-take from the deck line by using sea water and to prevent the backflow of the hydrocarbon gas. Inert Gas from the deck seal flows into the deck supply line through the Non-return Valve and Deck Isolating Valve and then enters each tank through the Inert Gas Supply Valve (some vessels do not have individual valves). The Inert Gas System can also be used for Gas Freeing by opening the Fresh Air Inlet Valve.

The P/V breaker is installed to protect the cargo tanks from excessive pressure or vacuum.

Functions of the Inert Gas System Unit

BOILER UP-TAKE VALVE

Flue Gas generated by the boiler flows into the Scrubber Unit through the Up-Take valve. This valve is opened by remote control on Blower start up and when the Blower stops this valve has to be closed in order to avoid Flue Gas entering the Scrubber Unit.

SCRUBBER UNIT
This is installed to clean and cool the flue gas and to reduce the sulfur dioxide (SO2 ) from the flue gas.
DEMISTER

The demister is provided to remove water droplets contained in the inert gas which have passed through the scrubber. Since the inert gas is cooled and cleaned at the scrubber, the gas at the scrubber outlet inevitably contains water droplets as a result of its direct contact with the sea water used for cleaning it and could thus overload the blower and damage and increase corrosion on the blower impellers.

BLOWER

Total blower capacity is more than 125% of total cargo pumps capacity. And combination of two blowers is;-two blowers together giving 125% (i.e. 62.5% each) of total cargo pump capacity. Thus two blowers must be used during normal cargo discharging one blower having 125% capacity plus one standby/ auxiliary with either 30/ 60/ 125% of total cargo pump capacity

RECIRCULATION LINE
This allows the blower to operate when the pressure regulating valve is being closed. Gas flows back through this line to the Scrubber and thus avoids pressure built up on the discharge side of the blower.
DECK SEAL UNIT

The IGS connects the boiler up-take indirectly with the cargo oil tanks, and while the system is not in operation, the backflow of the oil vapour under pressure from the cargo tanks must be protected against. The Deck Seal is provided for this purpose.

DECK ISOLATING VALVE.
The inert gas coming out of the deck seal unit is distributed to each cargo tank through this valve.
P/V (Pressure Vacuum)
BREAKER

Under normal conditions, the Breather Valve controls the cargo tank pressure/vacuum automatically when the I.G.S. is off. As a back-up safety device, a Pressure/Vacuum Breaker is fitted to the deck main piping and is designed to release pressure from this piping and cargo tanks to atmosphere in the event that the Breather Valve capacity is exceeded while operating the I.G.S.The P/V Breaker does not have any moving parts and is filled to be required level by oil or fresh water containing an antifreeze solution.

Inert Gas system is required under SOLAS Regulation 60 of chapter II-2, for all Petroleum tankers of 20000 dwt and above, keel laid after 1984.
Exhaust from Main Engine is not used for inert gas for 2 reasons:
1. Inert gas is most required during discharge in port, when the main engine is not running.
2. To ensure complete combustion of fuel, extra air is fed into the engine (turbocharged) resulting in greater concentration of oxygen in the exhaust.
3. Air fuel ratio cannot be controlled for getting a certain O2% in exhaust.

# Various books, study material and other online sources has been refereed prior to writing this article but no part is copied or produced  from any of the source but explained same thing in better detailed way.

---

Author: Amit                                                                                      

---

If you have any complain regarding the post please do contact us!

Read more

What are Centrifugal pump? Its Operating principle | Explained

Centrifugal pump is a machine used to convert mechanical energy into pressure energy by utilizing centrifugal forces with radical outward flow. It is the most common type of pump used world wide for various section such as agricultural, sewage, power generation and shipping. It is a subcategory of kinetic pumps and based on the principle of forward vertex flow, which states that when a fluid of certain mass is rotated by external torque, there is a sudden rise in pressure head.

Centrifugal pumps are used world wide to handle liquid of low viscosity. Talking about shipping they comprises for more than 60% of total fluid handle and pumps on ship. Rather its working is too simple. It consists of two main components, the diffuser or volute and the impeller. The impeller is the one which rotate converting driver energy to kinetic energy and the volute remain stationary converting the kinetic energy to pressure energy.

Centrifugal pumps are rather unique as they can pump at very high flow rate and even can be throttled. The answers to these lies to the shaft driven impeller rotating at a speed of 1750 to 3500 rpm inside the casing. The liquid flows to the suction port and then leave out of the discharge port of the volute casing at pressure heat with the same flow rate.

But let get back to the basics;

Q.What is a pump?

Ans- Pump is a device/machine which provides energy to a fluid in a fluid system by converting mechanical energy supplied to hydraulic energy and transfer it to liquid flowing through a pipe. On the basis of the way mechanical energy is converted to hydraulic energy, pumps are classified as:
1)Rotodynamic / Kinetic pump.
2)Positive displacement
They can be further classified into:

Working of centrifugal pump

Like any other pump, centrifugal pump also converts the rotational energy from prime mover to moving fluid during which a portion of energy add up to kinetic energy of the fluid. The fluid enters axially to the eye of the impeller under atmospheric pressure. The centrifugal energy exerted on the fluid by the impeller moves the flow away from the eye of the impeller through impeller vanes to the walls of the volute casing and get out through the discharge port. Fluid is drawn continuously into the pump due to the pressure drop in the pump.The volute is designed and manufactured such that it is wider at the discharge, which leads to increase in viscosity when fluid strikes on them. This specific shape helps liquid/fluid to expand leading to slow flow due to which the kinetic energy get converted to pressure energy. As it is said "Energy can neither be created nor destroyed but only be changed". This generated pressure then forces the liquid out of pump discharge.

Main difference between Kinetic/Rotodynamic pumps and Positive displacement pump 

The main difference between the kinetic and positive displacement pump depends on the method of fluid transfer. Rotodynamic pumps on one hand gives kinetic energy to the fluid and then convert it to pressure energy during discharge through the pump. On other hand a positive displacement pump moves a fixed amount of fluid / liquid within the pump by applying mechanical force to boundaries containing fluid volume.

Difference between centrifugal pump and reciprocating pump:

Source for creating below table: (https://www.slideshare.net/506314/pump-46519851)

Parameter	Centrifugal Pumps	Reciprocating Pumps
Optimum Flow and Pressure Applications	Medium/High Capacity,Low/Medium Pressure	Low Capacity,High Pressure
Maximum Flow Rate	100,000+ GPM	10,000+ GPM
Low Flow Rate Capability	No	Yes
Maximum Pressure	6,000+ PSI	100,000+ PSI
Requires Relief Valve	No	Yes
Smooth or Pulsating Flow	Smooth	Pulsating
Variable or Constant Flow	Variable	Constant
Self-priming	No	Yes
Space Considerations	Requires Less Space	Requires More Space
Costs	Lower Initial Lower Maintenance Higher Power	Higher Initial Higher Maintenance Lower Power
Fluid Handling	Suitable for a wide range including clean, non-abrasive fluids to fluids with abrasive, high-solid content. Not suitable for high viscosity fluids, Lower tolerance for entrained gases	Suitable for clean, clear, non-abrasive fluids., Specially-fitted pumps suitable for abrasive-slurry service. Suitable for high viscosity fluids, Higher tolerance for entrained gases

Q.How is head developed by an Impeller?
Out of the two main components, impeller and diffuser/volute/vortex the impeller takes power from the rotating shaft and accelerate the fluid and the diffuser transform the high velocity kinetic energy into pressure.
True velocity profile of fluid inside an impeller

velocity at the inlet and outlet of impeller.

velocity at one paint on the impeller blade

Based on free body diagram
The mass of the segment:

The centrifugal force acting on this elementary mass would be:

The pressure increase due to action of centrifugal pump:

Integrating the equation between intake and discharge:

In terms of head:

In practice the potential head is not only due to the centrifugal force but also due to the change in relative velocity of the fluid inside the impeller. Hence:

For one stage of an ESP, The total head is due to the sum of potential head and velocity head. Thus theoretical head can be calculated as:


Moment equation:

Total pressure loss along the streamline:
If the fluid is inviscid; No change of velocity in z and  (symmetric velocity) direction; Neglect the pressure drop due to gravity:

Therefore, the total pressure losses along the streamline can be express as:



From the triangle geometric relationship:

Hence:

Simplifying this equation gives



 

Finally, the pressure difference across a streamline is given:

Integrate this equation gives the pressure increase across one stage:

By definition:
 
Hence:

Using the geometrical relationships:

This equation can be expressed as the Euler Equation:

Field unit:

Construction of centrifugal pump

Casing: This part performs the function of converting the kinetic energy into pressure energy. This is of three main types:

Volute casing (For high head): It is a curved funnel with advance in area as it reach the discharge port. This reduces the flow rate and so increases the pressure of the fluid.

Circular casing (For low head and high capacity):These have stationary diffusion vanes surrounding the impeller periphery such that they convert kinetic energy to pressure energy . Conventionally they are used in multi-stage pump.

Vortex casing:A circular chamber is introduced between casing and impeller-increasing the efficiency of the pump.

Impeller: It is the main rotating part that provides the centrifugal acceleration to the fluid. There are mainly three types of impeller used in the centrifugal pump:
1)Open Impeller: Vanes are cast-free on both sides.
2)Semi-Open Impeller: Vanes are free cast on one side and enclosed on other.
3)Enclosed Impeller: Vanes are located between the two discs in one single casing.

Shaft:It acts as a transmitter of torque during start and operation of pump. It also support Impeller and other rotating parts of pump.

Net positive suction head(NPSH)

In a hydraulic fluid pump system, NPSH is the minimum head required to avoid cavitation due to flashing of fluid as low presure at suction side leads to cavitation. During operation of pump if the presure at the suction drops below the vapour presure of fluid, fluid start to boil forming bubble at high presure and brust when they reach low presure leading to severe cavitation damage to the impeller blade and sudden impulsive shocks. This fact puts a limit to the maximum suction head a pump can had.

NPSH can be defined as:

Where, Pv is the vapour pressure and V is speed of water at suction side.

Classification of centrifugal pump

Centrifugal pumps may be classified according to:

1)Working Head: Centrifugal pumps are classified into low(15m), medium(15-45m), High speed pump(more than 45m).

2)Specific Speed
3)Types of casing: Centrifugal pumps can be divided into following type based on casing; Volute, Vortex and diffuser.

Image credit: www.educationdiscussion.com

4)Direction of flow of water: Centrifugal pumps can also be classified according to the type of flow as under:

• Radial flow: It is a type of flow in which the flow in the impeller is radial direction. They are generally used when requirements are high at low discharge.
• Mixed flow: It is a type of flow in which the flow is mixture of radial and axial increasing the area of flow. Then they are used where discharge and head requirement are medium.
• Axial flow:These pumps find their use where discharge is high at low head such as in the case of irrigation.

5)Number of entrance to impeller: Centrifugal pumps can have either single or double entrance according to the discharge needed.
6)Number of stages: A centrifugal pump can have a single stage with a impeller key to the shaft or it can be a multi stage pump. A multi stage pump has a no of impellers mounted on the same shaft and enclosed in the same casing.

Advantages and disadvantages of centrifugal pump

Advantage:
1)Very high flow rate
2)Low maintenance
3)Continuous flow
4) cost of installation and size does not affect the performance at any cost.

Disadvantage:
1)Pressure generated by pump is less compared to positive displacement pump.
2)Need priming before start.

Centrifugal pump Characteristic Curves

Pump performance:

Brake horse power and capacity:

 NPSH and capacity: The curves show the relationship between the capacity by which the pump will deliver and the NPSH, which is required for proper operation of pump at that capacity. Lack of NPSH will lead the pump to run improperly and cause cavitation.

#Cover Image Credit: www.pumpsandsystems.com

# Too many books, study material,ppt notes and other online sources has been refereed prior to writing this article but no part is copied or produced  from any of the source except for the one little part which is clearly mentioned with site/source link, but explained same thing in better detailed way.

---

Author: Amit                                                                                      Article Requested by: Deepak Kumar

---

If you have any complain regarding the post please do contact us!
  

Read more