(Fuel Oil Handling (Supply & Storage) & Treatment)

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some definitions

Viscosity: It is a measurement of the resistance to flow of a liquid, at a reference temperature.        Kinematic Viscosity in cSt [1 Centistokes = 1 mm2/s]

Viscosity of the Fuel Oil is Reduced by heating

  • (i) To get good Atomisation
  • (ii) To improve separation of sludge and water (purifier)
  • (iii) To ensure ease of pumping

 

Density Mass       kg/m3     {Density at 150C is called standard Density}

Volume

Density of HFO = 920 kg/m3   to   1010 kg/m3 at 150C

Relative Density = Specific Gravity (it is a ratio; so has no units)

RD /SG of HFO= 0.92 -1.01 (no unit)

 

Purifiers/Separators – remove water & sludge (solid contaminants) from the oil  by centrifugal force

 

Conventional purifiers  remove water & sludge from fuel oil up to a max density of 991 kg/m3 at 150C (For removing water- Fuel oil density should be less than water – or else only sludge/Solids can be removed)

Modern Purifiers remove water & sludge from fuel oil up to a max density of 1010 kg/m3 at 150C  (Water can be removed even if Fuel Oil density is more than water)

 

Flash Point It is the lowest temp at which sufficient vapour is given to produce a flash on application of a flame under specified test conditions

[min 600C – due to fire risk during normal storage and handling]

 

Pour Point: It is the lowest temp at which fuel oil can be handled/pumpable (free flow) [Below this temp fuel will form wax/gel preventing flow]

Fuel in the Tank must be 50C above the pour point to prevent solidification

If Fuel gets Solidified, it is impossible to re-liquefy in the tank due to Low heat transfer Coefficient of the Fuels

 

CCAI –Calculated Carbon Aromaticity Index  for Residual Fuel Oils

 

CII – Calculated Ignition Index for Residual Fuel Oils

 

These are reference indices which gives the ignition quality of residual fuel oil

They are used to estimate how long the residual fuel will take from injection to ignition

 

Calculated Cetane Index: Reference index for Distillate Fuel Oils

 

Compatibility of residual fuel allows it to be blended with other fuels to give a stable mix. If two incompatible fuels are mixed they become unstable and causes precipitation of heavy sludge which blocks the fuel system

 

Micro Carbon Residue (MCR)/Asphaltenes: Also called Conradson Carbon Residue (CCR)

It is a measure of tendency of a fuel to form soot and carbon deposits (coke) during combustion/high temp [max limit is 22% m/m].

 

Water content – Fuel contaminated with sea water contains sodium.

Sodium burns to form with vanadium an ash which is very harmful to engine exhaust valves

 

Ash: It is the amount of inorganic material in the fuel. It is the incombustible material which remains after combustion

Ash is formed due to  like Sodium, Vanadium, Sulphur, Catalytic fines (Silicon / Aluminum)

Ash causes Corrosion, Abrasive Wear, Fouling, Overheating of metal surfaces etc

Sulphur burns to sulphur dioxide and forms sulphuric acid  which is corrosive

 

Calorific Value: It is the heat energy given out during combustion [calorimeter]

HFO has  CV of 38.9 to 41.2 MJ/litre

Fuel Oil Handling (Supply & Storage) & Treatment

Supplying of Fuel oil from Shore Terminals / Barge to Ship Storage (Bunker) Tanks is called Bunkering

Fuel oil in Storage tank temp is maintained at 400C [50C above the pour point temp to avoid solidification [wax/gel formation]

Fuel oil is transferred via positive displacement pumps [through suction strainer & shell/tube heaters] to settling tanks through duplex  fine mesh magnetic filters (ferrous metals are removed)

Settling tank Temp is maintained at 900C.  Sludge [solid contaminants / sediments] and water are separated  by gravity (diff in densities) & drained off

[large quantities of water or sludge can be drained effectively than separation by a centrifuge]

Fuel oil is passed  through the centrifugal separators (purifiers separates Sludge & Water from fuel oil]

Sodium (dissolved in water) is removed along with water by Purifier

Vanadium is dissolved in Fuel Oil

Sticking of sodium and vanadium salts on exhaust valves is reduced by keeping the exhaust temp below 5300C

Silicon and aluminum (catalytic fines) are removed in a purifier or clarifier

(slow through put is essential – self driven purifier delivery pump is replaced  with independently driven pumps )

Sulphuric acid is neutralized by alkali additives in cylinder L.O.

Also the Condensation of Sulphuric acid is reduced by keeping liner temp high

Fuel after passing through the purifier reaches the Service tank / Day tank  Service Tank Temp is maintained at 900C

Supply pump pumps the oil from service tank to engine through heaters [1200C] and through very fine mesh strainers.

Temp and viscosity are maintained by automatic controllers fitted to the heaters.

Jerk type fuel pump (1 pump per cylinder) is fitted on the engine

It pumps fuel to the Injectors (1 or 2 per cylinder)