ADDITIVES FOR HEAVY FUEL OILS

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UnderstandingFuel Oils
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Topics

• Introduction
• Refining Processes
• Fuel oil composition
• Fuel Oil production
• A Modern refinery
• Refining trends with example
• Conclusions
• Key quality indicators
• Quality trends Vs Technology
• Effect of Fuel oil quality on engine performance
• Storage handling-A Recall

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Introduction

• Fuel oil is Cheap but has fair CV
• Residual Fuel
• Diesel Cycle
• Low Cetane value
• Hence for Low/Medium speed
• Natural source
• Not much can be done on quality
• Engines built to suit this fuel

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FRACTIONS FROM 3 DIFFERENT CRUDES
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CHARACTERISTICS OF SOME CRUDE OILS
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Refinery Process
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Crude oil desalting

• Water and inorganic salts are removed in an
  electrostatic field.
• The main purpose of crude oil desalting is to
  protect the refining process units against
  corrosion.

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Atmospheric distillation

• Crude oil is a product with a very wide boiling
  range.
• In an atmospheric distillation column the
  fractions
• boiling below 360C are distilled off under
  reflux, and,
• according to boiling range, recovered as naphtha,
• kero, and gasoil type stocks. Atmospheric
  distillation is
• limited to a maximum temperature of 360C,
  because
• otherwise coking would start to occur, and this
  is not
• desirable at this stage of crude oil refining.

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Vacuum distillation

• In order to distill off a heavier cut, without
  exceeding
• the 360C temperature limit, a second
  distillation is
• done under reduced pressure the vacuum
  distillation.
• The distillate fraction of the vacuum
  distillation unit is
• the feedstock for a catalytic cracking unit

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Catalytic cracking

• The main feedstock for a catalytic cracker is
  vacuum gasoil. The cracking operation breaks
  large molecules into smaller, lighter molecules.
  The process runs at high temperatures, and in the
  presence of the appropriate catalyst (crystalline
  aluminum silicate).
• Atmospheric residue, with a low metal and MCR
  content, can also be used as catalytic cracker
  feed, necessitating an adjustment of the catalyst
  type.
• The main purpose of a catalytic cracker is to
  produce light hydrocarbon fractions, which will
  increase the refinery gasoline yield.
• Additional streams coming from the catalytic
  cracker are light cycle oil (increases the gasoil
  pool) and heavy cycle oil (base stock for carbon
  black manufacturing). Both streams are also used
  in heavy fuel oil blending.

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Catalytic hydrocracking

• Some refineries have catalytic hydrocracking as a
  supplementary operation to catalytic cracking.
• Catalytic hydrocracking further upgrades heavy
• aromatic stocks to gasoline, jet fuel and
  gasoil type material. The heaviest aromatic
  fractions of a cat cracker are the normal
  feedstock for a hydrocracker.
• Hydrocracking requires a very high investment ,
  but
• makes the refinery yield pattern nearly
  independent
• from the crude oil feed.

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Visbreaking

• The feedstock of a visbreaker is the bottom
  product
• of the vacuum unit, which has an extremely high
• viscosity. In order to reduce that viscosity and
  to
• produce a marketable product, a relatively mild
• thermal cracking operation is performed. The
• amount of cracking is limited by the overruling
• requirement to safeguard the heavy fuel
  stability.
• The light product yield of the visbreaker (around
• 20) increases the blendstock pool for gasoil.

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Coking (delayed coking, fluid coking, flexicoking)

• Coking is a very severe thermal cracking process,
  and
• completely destroys the residual fuel fraction.
  The
• yield of a coker unit is lighter-range boiling
  material,
• which ultimately goes to the blending pool for
  the
• lighter products, and coke, which is essentially
  solid
• carbon with varying amounts of impurities. The
• heavier distillate fraction of a coker can be
  used as
• feedstock for a hydrocracker

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Catalytic reforming and Isomerization

• Both processes are in fact catalytic reforming,
  and are intended to upgrade low octane naphta
  fractions of the crude distillation unit into
  high octane components for gasoline production.
  The type of catalyst and the operating conditions
  determine if the reforming is mainly to
  iso-paraffins, or to aromatics. The terminology
  reforming is generally used for the change to
  aromatics, while the change to iso-paraffins is
  referred to as isomerization. Isomerization is
  normally done on a lighter fraction(C5/C6), while
  reforming is done on the heavy naphtha fraction
  (C7 and heavier, up to 150C).

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Alkylation

• Process intended to increase the yield of
  valuable gasoline blend components. Alkylation is
  a catalyst steered combination reaction of low
  molecular weight olefins with an iso-paraffin to
  form higher molecular weight iso-paraffins. The
  feed to the alkylation unit is C3 and C4s from
  the catalytic cracker unit, and iso-butane.

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Hydrotreating

• A hydrotreating process is, as the name
  indicates, a process, which uses hydrogen to
  remove impurities from product streams, and
  replaces them with hydrogen. Hydrotreating is
  generally used to remove sulphur (very low
  sulphur limits in the specifications of gasoline
  and gasoil) and is then called hydro-desulphurizat
  ion. It is a catalytic process. The process is
  generally used on kerosene and gasoil fractions.
  Residual hydro-desulphurization is an existing
  process, and is in theory feasible, but the
  economics are not favorable.

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Merox

• A merox unit is used on naphtha and kerosene
  streams. It is a catalytic process which is not
  intended to remove the sulphur from the stream,
  but to convert mercaptan sulphur type molecules
  (corrosive, and with a very obnoxious smell) into
  disulphide type molecules.

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Modern Refinery

• Atmospheric Distillation
• Reforming
• Vaccum Distillation
• Catalytic cracking
• Hydrocracking
• Visbreaking
• Deasphalting

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Atmospheric distillation
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Vaccum distillation
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Vaccum distillation FCCU
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Vaccum distillation FCCU VB
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REFINERY SCHEMES
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About Fuel oil
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Straight run marine gasoil and distillate

• Marine diesel
• type MDO are manufactured from kero, light, and
  heavy gasoil fractions.
• For DMC type gasoil, up to 1015 residual fuel
  can be added.
• Straight run IFO 380 mm2/s (at 50C)
• This grade is made starting from the atmospheric
  residue fraction (typical viscosity of about 800
  mm2/s at 50C) by blending with a gasoil
  fraction.
• Straight run lower viscosity grade IFOs
• Blending to lower grade IFOs is done from the IFO
  380 mm2/s (at 50C) using a gasoil type
  cutterstock or with marine diesel.

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Complex Refineries

• The main marine fuel blending components from a
  Fluidized Bed Catalytic Cracking (FCC) type
  refinery with visbreaker are the same distillates
  as those from a straight run refinery (light and
  heavy diesel) as well as light cycle (gas) oil
  (LC(G)O) and heavy cycle oil (HCO) from the
  catcracker and visbroken residue from the
  visbreaker.
• Atmospheric residue is used as feedstock for the
  vacuum unit and will only seldom be available for
  fuel blending.

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Complex Refineries

• Marine gasoil (MGO/DMA)
• A new blend component has appeared LC(G)O
  (light cycle (gas) oil) which contains about
  60 aromatics. Due to the high aromatic nature of
  LC(G)O, the density of a marine gasoil blended
  with LC(G)O will be higher than when using gasoil
  of an atmospheric distillation type refinery. No
  performance or handling differences with
  atmospheric type gasoil
• Distillate marine diesel (MDO/DMB)
• Distillate marine diesel typically has a lower
  cetane number than marine gasoil, and a higher
  density. With the production slate of a catalytic
  cracking refinery, distillate marine diesel
  therefore contain a higher percentage of LC(G)O
  than marine gasoil.

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Complex Refineries

• Blended marine diesel (MDO/DMC)
• With atmospheric type refining, blended marine
  diesel (MDO/DMC) can contain up to 10 IFO with
  either marine gasoil (MGO/DMA) or distillate
  marine diesel (MD)/DMB). With complex refining,
  blended marine diesel (MDO/DMC) no longer
  corresponds to a specific composition and extreme
  care needs be used when blending this grade to
  prevent stability and/or combustion problems.
• IFO-380
• This grade is usually manufactured at the
  refinery and contains visbroken residue, HCO and
  LC(G)O These three components influence the
  characteristics of the visbroken IF-380 Vacuum
  distillation reduces the residue yield to about
  20 of the crude feed, unavoidably leading to a
  concentration of the heaviest molecules in this
  fraction. Visbreaking converts about 25 of its
  vacuum residue feed into distillate fractions.
  This means that about 15 of the original crude
  remains as visbroken residue. The asphaltene1,
  sulphur and metal content in visbroken residue
  are 3 to 3.5 times higher than in atmospheric
  residue. Visbreaking affects the molecular
  structure molecules are broken thermally and
  this can deteriorate the stability of the
  asphaltenes.

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Complex Refineries

• HCO (typical viscosity at 50C 130 mm2/s)
  contains approximately 60 aromatics, and is a
  high-density fraction the density at 15C is
  above 1 kg/l (typically 1.02). It is the bottom
  fraction of the FCC unit. The catalytic process
  of this unit is based on an aluminum silicate.
  Some mechanical deterioration of the catalyst
  occurs in the FCC process, and the resulting cat
  fines are removed from the HCO in the refinery.
  This removal however, is not 100 efficient, and
  a certain amount (ppm level) of cat fines remains
  in the HCO, and from there end up in heavy fuel
  blended with HCO. The aromaticity of HCO assists
  in ensuring optimum stability for the visbroken
  fuel blend.
• LC(G)O (typical viscosity at 50C 2.5 mm2/s) has
  the same aromaticity as HCO, but is a distillate
  fraction of the FCC unit, with a distillation
  range comparable to that of gasoil. With a
  typical density of 0.94 kg/l at 15C, it is used
  to fine-tune the marine heavy fuel oil blending
  where generally a density maximum limit of 0.9910
  kg/l has to be observed.

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CHEMICAL COMPOSITION

ASPHALTENES
"RESINS"
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Components

• OIL
• Molecular weight lt 800
• Mixture of paraffins,naphthenes aromatic
• RESIN
• Molecular weight 1000
• condensed aromatics with aliphatic ring chains
• ASPHALTENES
• Molecular weight between 1000 2000
• Highly condensed aromatics

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Conclusions-Macro level

• Fuel oil yield drop
• More of fluxing
• Less of lighter components
• More complications due to types of crudes

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Conclusions-Micro level

• Increased density
• Increased Viscosity
• Increased carbon residue
• Increased asphaltenes
• Increased sulphur
• Reducing heating value ????
• Increasing trace metals ????
• Instability
• Incompatibility

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Key Quality Indicators

• Specific gravity
• Weight per unit volume
• Flash point
• Safe operating temperature
• Viscosity(Kinematic)
• Resistance to flow
• Pour Point
• Lowest Flowable temperature
• Sulphur content
• wt of Sulphur in Fuel oil
• Calorific value
• Heat per unit weight

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Key Quality Indicators

• Ash Content
• Inorganic non combustible matter
• CCAI
• Ignition quality
• Conradson carbon residue(CCR)
• Residual matter

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HFO CHARACTERISTICS
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Effects of quality parameters on engine
performance
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Viscosity

• Injection Characteristics
• Droplet size of 10-100 microns
• 10-15 Cst at nozzle tip
• Injector pump wear
• Fuel flow properties
• Preheating to correct viscosity at nozzle tip
• Certain cases upto 150 deg C

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• FUEL INJ VISC INJ VISC
• 13 CST 17 CST
• 120 100
  91
• 160 112 104
• 170 115 107
• 180 119 109
• 200 121 111
• 220 123 113

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Ignition Characteristics(CCAI)

• Shell proposed
• Calculated Carbon Aromaticity Index
• D-140.7LOG LOG (V.85)-80.6
• DSpecific Gravity _at_ 15deg C
• VViscosity _at_ 50 deg C
• Nomographic method most suitable
• Max acceptable around 900
• BP's CCI also used
• Diesel Index
• (API gravityaniline point deg F)/100

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Sulphur

• SOx water ----gt Sulphuric acid
• Temp drops below dew point
• Corrosion
• Cold corrosion
• Control of temperatures
• Lubricant

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Conradson Carbon residue

• Formation carbon deposits
• "Trumpets"
• Injection characreristics are altered
• lower the speed more the tolerance for CCR
• Indicative of apshaltene content
• CCR 2 asphaltenes

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Ash

• Na,V,Si,Fe compounds
• Hot Corrosion
• At melting points they form deposits
• Hard At hot spots
• Cooler valve seats etc

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Calorific Value

• heat energy contained
• Emperical formulae
• HSD
• GCV(btu)1.8(12400-2100dd)
• d-Spec gravity _at_ 60 deg F
• FUEL OILS
• GCV80.84C 289.2H22.24S
• C,H,S OF carbon,hydrogen Sulphur

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Calorific Value

• Specific Energy (Gross) MJ/kg
• Qg (52.190 - 8.802 p2 10-6) 1 - 0.01 (xys)
  9.420 (0.01s)
• Specific Energy (Net) MJ/kg
• Qn (46.704 - 8.802p210-6 3.167p10-3)
  1-0.01(xys)
• 0.01 (9.420s - 2.449x)
• p the density at 15 C, kg/m³x the water
  content, (m/m)y the ash content, (m/m)s
  the sulphur content, m/m

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Typical of C,H,S
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Storage Handling
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MODEL OF ASPHALTENE MOLECULE

CH3
O
CH2
CH3
CH3
CH2
S
CH3
CH2
CH3
CH3
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ASPHALTENES CHARACTERISTICS

• Polycondensed aromatic structures with few alkyl
  chains
• Contains hetero-atoms S, N, O
• Contains metals V, Ni, Na
• Not soluble in oil
• Size of the micellar unit 8 - 20 A
• Cannot boil even under reduced pressure
• Molecular structure depends on crude oil origin

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RESINS CHARACTERISTICS

• Chemical structure close to asphaltenes structure
  but
• LONGER ALKYL CHAINS
• LESS CONDENSED RINGS
• MORE SOLUBLE IN OIL
• Molecular structure depends on crude oil origin
• Presence necessary to provide a good stability to
  the fuel

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HEAVY FUEL OILS
Resins ensure seperation of heavy asphaltene
molecules. Flocculated Asphaltene molecules tend
to form sludge and settle at the bottom of the
tank.
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Instability

• Asphaltenes "peptized" by resins
• Instability occurs when this peptization breaks
• Apshaltenes "flocculate"
• Precipitation occurs
• Filter clogging,Overloading of Centrifuge,deposits
  in tanks
• "No more a major problem"

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Incompatibilty

• When 2 different source FO's mix
• Effects will be similar to Instability
• ASTM D 4740 "spot test"
• "Avoid mixing FO's from different refineries"

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Pre-Preparation

• Settling
• Purification
• Clarification
• Homogenisation
• Additives
• Costly
• Uncertain efficiency
• Filteration

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UNBURNT PARTICLES

• PROBLEM
• EMISSIONS OF UNBURNT PARTICLES
• HEATING SURFACES FOULING
• FREQUENT BOILER CLEANING
• COST OF EMISSION LIMITATIONS
• ORIGIN
• NEED OF COMBUSTION IMPROVER
• VERY LOW METAL CONTENT
• SOLUTION
• ADDITIVE B

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ISO 8217 FUEL STANDARD FOR MARINE DISTILLATE
FUELS
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ISO 8217 FUEL STANDARD FOR MARINE DISTILLATE
FUELS
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ISO FUEL STANDARD 8217, 1ST REVISION 1996, FOR
MARINE RESIDUAL FUELS
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Revision of ISO 8217

• Release end 2005, early 2006 ?
• Main changes
• Fuel grades basis viscosity at 50 C instead of
  100 C
• RMC 10 no longer exists
• RMA 30 , RMB 30 and RMD 80 lower max. density
• Water content max. 0.5 v/v for all grades
• Ash content
• Fuel grades with a max ash of 0.10 m/m no
  changes
• Fuel grades with a max ash of 0.20 m/m new
  max limit 0.15 m/m
• Sulphur content as of RME 180 4.5 m/m max.
• Limits for used lubricating oils (ULO) A fuel
  shall be considered to be free of ULO if one or
  more of the elements Zn, P and Ca are below or at
  the specified limits (resp. 30/15/15 mg/kg)

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• FUEL VISC
• Temp cSt
• 40 720
• 100 33
• 110 24
• 115 20
• 120 18
• 125 15
• 130 13

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THANK YOU