Understanding Fuel Oils

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

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

FRACTIONS FROM 3 DIFFERENT CRUDES Viscosity,20°C % asphaltenes Gasoline (C5-80°) Heavy gasoline (80-160°) Kerosene (160-250°) Middle distillate (250-300°) Heavy distillate (300-400°) Residue (400 +) 35.8 5.8 4.09 9.05 12.58 14.12 7.51 50.42 10.2 0.93 5.56 12.02 15.5 17.19 8.72 38.71 ARABIAN HEAVY LIGHT NIGERIAN BONNY 11.2 0.08 5.06 15.0 9.32 25.2 44.6

CHARACTERISTICS OF SOME CRUDE OILS Viscosity,20 °C,cSt Sulfur,% Vanadium, ppm Nickel, ppm Asphaltenes, % Conradson carbon,% Arabian light 9.2 1.8 15 5 0.7 5.1 heavy 40 2.8 30 10 2.7 Ekofisk 0.12 < 1 1.4 0.88 Nigeria 6.7 0.11 2 6 0.08 0.86 Basrah 57 3.58 54 22 8.3 Boscan 250000 5.2 1200 100 10.8 16.4 Ural 12.5 65 20

Refinery Process

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.

Atmospheric distillation Crude oil is a product with a very wide boiling range. In an atmospheric distillation column the fractions boiling below 360°C 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 360°C, because otherwise coking would start to occur, and this is not desirable at this stage of crude oil refining.

Vacuum distillation In order to distill off a heavier cut, without exceeding the 360°C 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

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.

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.

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.

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

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 150°C).

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.

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-desulphurization. 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.

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.

Modern Refinery Atmospheric Distillation Vaccum Distillation Reforming Vaccum Distillation Catalytic cracking Hydrocracking Visbreaking Deasphalting

Atmospheric distillation

Vaccum distillation

Vaccum distillation + FCCU

Vaccum distillation + FCCU + VB

REFINERY SCHEMES Gas Reforming Visbreak. Hydrocr. Coking FCC Naphta AD VD Reforming Visbreak. Hydrocr. Coking FCC DA Naphta Gasolines Kerosene Diesel oils Heavy fuels SR 1 2 3 Kero,Diesel Heavy fuels H2, no Heavy Fuels 4 Asphalts

About Fuel oil

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 10–15% residual fuel can be added. Straight run IFO 380 mm2/s (at 50°C) This grade is made starting from the atmospheric residue fraction (typical viscosity of about 800 mm2/s at 50°C) 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 50°C) using a gasoil type cutterstock or with marine diesel.

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.

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.

Complex Refineries Blended marine diesel (MDO/DMC) IFO-380 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.

Complex Refineries HCO (typical viscosity at 50°C: 130 mm2/s) contains approximately 60% aromatics, and is a high-density fraction: the density at 15°C 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 50°C: 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 15°C, 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.

RESIDUE OR HEAVY FUEL OIL CHEMICAL COMPOSITION RESIDUE OR HEAVY FUEL OIL MALTENES ASPHALTENES "OIL" "RESINS" SATURATED AROMATIC

Components OIL RESIN ASPHALTENES Molecular weight < 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

Conclusions-Macro level Fuel oil yield drop More of fluxing Less of lighter components More complications due to types of crudes

Conclusions-Micro level Increased density Increased Viscosity Increased carbon residue Increased asphaltenes Increased sulphur Reducing heating value ???? Increasing trace metals ???? Instability Incompatibility

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

Key Quality Indicators Ash Content Inorganic & non combustible matter CCAI Ignition quality Conradson carbon residue(CCR) Residual matter

HFO CHARACTERISTICS

Effects of quality parameters on engine performance

Viscosity Injection Characteristics Injector pump wear 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

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

Ignition Characteristics(CCAI) Shell proposed Calculated Carbon Aromaticity Index D-140.7LOG LOG (V+.85)-80.6 D:Specific Gravity @ 15deg C V:Viscosity @ 50 deg C Nomographic method most suitable Max acceptable around 900 BP's CCI also used Diesel Index (API gravity*aniline point deg F)/100

Sulphur SOx + water ----> Sulphuric acid Temp drops below dew point Corrosion Cold corrosion Control of temperatures Lubricant

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

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

Calorific Value heat energy contained Emperical formulae FUEL OILS HSD GCV(btu)=1.8(12400-2100d*d) d-Spec gravity @ 60 deg F FUEL OILS GCV=80.84*C +289.2H+22.24S C,H,S % OF carbon,hydrogen & Sulphur

Calorific Value Specific Energy (Gross) MJ/kg Qg = (52.190 - 8.802 p2 10-6) [1 - 0.01 (x+y+s)] + 9.420 (0.01s) Specific Energy (Net) MJ/kg Qn = (46.704 - 8.802p210-6 + 3.167p10-3) [1-0.01(x+y+s)] + 0.01 (9.420s - 2.449x) p = the density at 15 °C, kg/m³ x = the water content, % (m/m) y = the ash content, % (m/m) s = the sulphur content, % m/m

Typical % of C,H,S

Storage & Handling

MODEL OF ASPHALTENE MOLECULE CH2 CH3 CH CH CH2 CH3 N CH2 CH3 CH3 O CH2 CH2 CH3 CH3 CH2 S CH2 CH3 CH2 CH CH2 S CH2 CH3 CH3 CH3

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

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

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

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"

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"

Pre-Preparation Settling Purification Clarification Homogenisation Additives Costly Uncertain efficiency Filteration

UNBURNT PARTICLES PROBLEM ORIGIN SOLUTION 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

ISO 8217 FUEL STANDARD FOR MARINE DISTILLATE FUELS

ISO 8217 FUEL STANDARD FOR MARINE DISTILLATE FUELS

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

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)

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

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