Everything About Fuels Chevron

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Everything You Need to

Know About Marine Fuels


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Everything You Need toKnow About Marine Fuels

Published by Chevron Global Marine ProductsJuly 2007

Prepared by Monique B. Vermeire

Ghent, Belgium

This publication was prepared for Chevron GlobalMarine Products by Monique B. Vermeire of the MarineLubricants and Fuels Technical Department, located atChevron Technology Ghent in Belgium. Monique doesexclusive work for Chevron Global Marine Products inthe area of fuel technology, with related eld support

for matters concerning fuel quality issues. The MarineLubricants and Fuels Technical Department activelysupports Chevron Global Marine Products withinternational fuel projects and at industry seminars.


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I. Introduction 1

II. Crude oil 3

1. How is a crude oil eld formed? 3

2. Composition and classication of crude oil 3

3. Crude oil rening and stocks for marine fuel blending 3

III. Fuel oil 7

1. Fuel oil applications 7

2. Fuel specications 7

2a. Signicance of the marine fuel properties listed in ISO 8217:2005 10

2b. Correspondence of specications and test methods 12

3. Test specications and precision 13

4. Onboard fuel oil treatment 13

4a. Conventional cleaning with puriers/clariers 14

4b. Advanced computer-driven fuel cleaning system 15

5. Fuel oil stability and compatibility 16

6. Commingling of fuels 17

7. Microbiological contamination 17

8. Fuel contamination in lubricants 18Attachments 21

Attachment I: Crude oil rening 21

Attachment II: Reproducibility (R) of marine fuel test methods 22

Attachment III: Gas turbine fuel requirements 24

References 25

Everything You Need toKnow About Marine Fuels

Reference in this brochure to any specic commercial product, process or service, or the use of any

trade, rm, or corporation name is for the information and convenience of the reader, and does not

constitute endorsement, recommendation, or favoring by Chevron Global Marine Products.

Contents


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From the early 19th century until the third quarter ofthe 20th century, steamships crossed the seven seas,gradually eliminating sailing ships from commercialshipping.

In the second half of the 20th century, the motor shipstarted to dominate. The history of the diesel enginebegan in 1892 with Rudolf Diesel and twenty years later,the rst four-stroke marine diesel engine ships wereoperational.

Around 1930, two-stroke designs took a strong lead asships became larger and faster.

Between World War I and World War II, the share ofmarine engine-driven ships increased to approximately25 percent of the overall ocean-going eet tonnage.

A series of innovations of the diesel engine followed,which made it possible to use heavy fuel oil in medium-speed trunk piston engines, pioneered by the MV ThePrincess of Vancouver. In the mid-1950s, high alkalinitycylinder lubricants became available to neutralize theacids generated by the combustion of high sulphurresidual fuels, and wear rates became comparable tothose found when using distillate diesel fuel.

Diesel ships using residual fuel oil gained in popularityand in the second half of the 1960s, motor shipsovertook steamships, both in terms of numbers, and ingross tonnage. By the start of the 21st century, motorships accounted for 98 percent of the world eet.

Marine engines have also found their way into thepower industry.

I. Introduction

Through thermal plants, marine engines and gas turbines, the energy

obtained from fuel oil combustion is made available to fulll our needs,

be it for transport purposes or for electrical power applications.

Liquid fuelcombustion...mechanical energy

propulsion energy and electricity


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1. How is a crude oil eld formed?

The generally accepted theory is that crude oil wasformed over millions of years from the remains of plants

and animals that lived in the seas. As they died, theysank to the seabed, were buried with sand and mud,and became an organic-rich layer. Steadily, these layerspiled up, tens of meters thick. The sand and mud becamesedimentary rock, and the organic remains becamedroplets of oil and gas. Oil and gas passed throughthe porous rock and were eventually trapped by animpervious layer of rock, collecting at the highest point.

The formation of an oil/gas eld requires the presenceof four geological features:

Source rock:contains suitable organic matter, which,under the conditions of heat and pressure, produceshydrocarbons

Reservoir rock:a porous layer of rock in which thehydrocarbons are retained

Cap rock: a rock or clay, which prevents the hydrocar-bons from escaping

Trap: a rock formation bent into a dome or broken bya fault which blocks the escape of the hydrocarbonseither upward or sideways

Most importantly, these four factors have to occur atthe right time, place and in the right order for oil andgas to be formed and trapped. Currently, successfulpetroleum exploration relies on modern techniques

such as seismic surveying. The fundamental principleof seismic surveying is to initiate a seismic pulse at ornear the earths surface and to record the amplitudesand travel times of waves returning to the surface afterbeing reected or refracted from the interface(s) onone or more layers of rock. Once seismic data has beenacquired, it must be processed into a format suitablefor geological interpretation and petroleum reservoirdetection.

2. Composition and classication of crude oil

Crude oil is a mixture of many different hydrocarbonsand small amounts of impurities. The composition of

crude oil can vary signicantly depending on its source.Crude oils from the same geographical area can be verydifferent due to different petroleum formation strata.Different classications of crude oil are based on:

1. Hydrocarbons:

Parafnic crudes

Naphtenic crudes

Asphaltenic (aromatic) crudes

Each crude oil contains the three different types ofhydrocarbons, but the relative percentage may varywidely. For example, there is parafnic crude in Saudi

Arabia, naphtenic crude in some Nigerian formationsand asphaltenic crude in Venezuela.

2. American Petroleum Institute (API) gravity: The lowerthe density of the crude oil, the higher its API gravity.A higher API gravity means that the crude containsmore valuable lower boiling fractions.

3. Sulphur content: The ever-growing concern forthe environment and the impact on rening costcalculations are the basis for this classication.

Low sulphur crude

High sulphur crude

3. Crude oil rening and stocks for marinefuel blending

Petroleum reneries are a complex system ofmultiple operations. The processes used at a givenrenery depend upon the desired product slate andcharacteristics of the crude oil mix. Today, complexrening has a denite impact on the characteristics ofmarine diesel and intermediate fuel oil (IFO) bunker fuel.

II. Crude Oil


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Typical rening schemes and the inuenceon marine fuels

Straight run refinery

Atmospheric crude distillation and further rening ofdistillates:

* Diesel refers here to specic atmospheric distillation cuts,and is not related to an engine application.

Straight run stocks for marine fuel blending

Light diesel, heavy diesel, and straight run residue

Straight run marine gasoil and distillate marine

diesel (MDO)

Marine gasoil and distillate marine diesel oil (MDO)are manufactured from kero, light, and heavy gasoilfractions. For DMC distillate marine diesel up to 1015%,residual fuel can be added.

Straight run IFO 380 mm2/s (at 50C)

This grade is obtained by blending the atmosphericresidue fraction (typical viscosity of about 800 mm2/s at50C) with a gasoil fraction.

Straight run lower viscosity grade IFOs

Blending to lower grade IFOs is done from the IFO 380mm2/s (at 50C) using a gasoil cutter stock or with

marine diesel.All IFOs have good ignition characteristics, due to thehigh percentage of parafnic material still present inthe atmospheric residue, and the parafnic nature of

the cutterstocks used. The high amount of parafnichydrocarbons in the straight run marine fuels leads torelatively low densities for these products, ensuring easy

and efcient onboard fuel purication.The product slate of a straight run renery, with itsheavy fuel production of approximately 50% of thecrude feed, does not correspond to the product demandin industrialized countries where the ever-growingdemand for light products (jet fuel, gasoline, and gasoil)coincides with a strong reduction in the demand forheavy fuel (10 to 15% of the crude oil). This results in theneed to convert the residue fraction into lighter, hence,more valuable, fractions and to the construction ofcomplex reneries.

A complex renery processing scheme can be separatedinto two parts:

1. Crude oil distillation (atmospheric and vacuumdistillation)

2. Streams from the vacuum distillation unit areconverted through catalytic and thermal crackingprocesses.

GASNAPHTHAKEROLIGHT DIESEL*HEAVY DIESEL*

Distillates

Atmospheric

distillation

unit

RESIDUAL FUEL OIL

Crude Oil


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Complex reneries have been favored since the early1980s and are intended to boost gasoline production.All further information herein is based on a complexrenery. The main marine fuel blending componentsfrom a uidized bed catalytic cracking (FCC) renerywith visbreaker are the same distillates as those from astraight run renery (light and heavy diesel) as well aslight cycle (gas) oil (LC(G)O) and heavy cycle oil (HCO)from the catcracker and visbroken residue from thevisbreaker.

Atmospheric residue is used as feedstock for the vacuumunit and will seldom be available for fuel blending.

More detailed information on complex rening is

provided in Attachment I.Marine fuels resulting from a catalytic cracking/visbreaking renery have a composition that is markedlydifferent from that of an atmospheric renery.

Marine gasoil (MGO/DMA)

A new blend component has appeared light cycle (gas)oil that contains about 60% aromatics. Due to the higharomatic nature of LC(G)O, the density of a marine gasoilblended with LC(G)O will be higher than when usinggasoil from an atmospheric distillation renery. Thedensity will typically be close to 860 kg/m3(at 15C). Noperformance or handling differences with atmosphericgasoil are to be expected.

Note:Marine gasoil S max. legislation usually follows thatof gasoil for inland use. This is the case in the EuropeanUnion (EU) where the max. S level of marine gasoil foruse in territorial waters is currently 0.20 m/m % max.

and subject to decrease to 0.10 m/m % max in 2008. Thishas an effect on the acidity of the combustion gases, andthe alkalinity (BN) and dispersancy of the lubricant mayhave to be adjusted accordingly.

Distillates

Residue

Atmosphericdistillation

unit

Vacuumdistillationunit

FCC*

LCO*

HCO*

Visbreaker

Residue

Crude Oil

* FCC: Fluidized Bed Catalytic Cracking

* LCO: Light Cycle Oil

* HCO: Heavy Cycle Oil

Example: Complex renery with (uid) catalytic cracking and visbreaking


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Due to logistics, it is possible that in some areas marinegasoil is, in fact, automotive diesel (with added markerand dye and without the excise duty applicable to

automotive fuel). Currently in the EU a max. S level is0.0050 m/m % max., and subject to decrease to 0.0010m/m % max. in 2009. Again, the alkalinity (BN) anddispersancy of the lubricant may have to be adjustedaccordingly.

Distillate marine diesel (MDO/DMB)

Distillate marine diesel (commercial denomination)typically has a lower cetane index than marine gasoil,and has a higher density. With the production slate of acatalytic cracking renery, distillate marine diesel cantherefore contain a higher percentage of LC(G)O thanmarine gasoil.

Note:Worldwide, marine diesel has a sulphur contentbetween approx. 0.3 and 2.0 m/m %. Due to recent EUlegislation (Directive 2005/33/EC amending Directive1999/32/EC), the sale of marine diesel oil with a sulphurcontent above 1.5 m/m % within the EU is prohibited as of

August 11, 2006.

Blended marine diesel (MDO/DMC)

With atmospheric rening, blended marine diesel (MDO/DMC) can contain up to 10% IFO with either marinegasoil (MGO/DMA) or distillate marine diesel (MD)/DMB).With complex rening, MDO/DMC no longer correspondsto a specic composition and extreme care must be usedwhen blending this grade to prevent stability and/or

combustion problems.

IFO-380

This grade is usually manufactured at the renery andcontains visbroken residue, HCO and LC(G)O. Thesethree components inuence the characteristics of thevisbroken IF-380.

Vacuum distillation reduces the residue yield to about20% of the crude feed, unavoidably leading to aconcentration of the heaviest molecules in this fraction.Visbreaking converts about 25% of its vacuum residuefeed into distillate fractions. This means that about 15%of the original crude remains as visbroken residue. The

asphaltenes1, sulphur and metal content in visbrokenresidue are 3 to 3.5 times higher than in atmospheric

1 Asphaltenes: residual fuel components that are insoluble in heptanebut soluble in toluene

residue. Visbreaking affects the molecular structure:Molecules are broken thermally, and this can deterioratethe stability of the asphaltenes.

HCO (typical viscosity at 50C: 130 mm2/s) containsapproximately 60% aromatics, and is a high-densityfraction: the density at 15C is above 1 kg/l (typically1.02). It is the bottom fraction of the FCC unit. Thecatalytic process of this unit is based on an aluminumsilicate. Some mechanical deterioration of the catalystoccurs in the FCC process, and the resulting cat nesare removed from the HCO in the renery. This removal,however, is not 100% efcient and a certain amount(ppm level) of cat nes remains in the HCO. From therethey end up in heavy fuel blended with HCO. (See alsoChapters III-2)

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 thesame aromaticity as HCO, but is a distillate fraction ofthe FCC unit, with a distillation range comparable to thatof gasoil. With a typical density of 0.94 kg/l at 15C, itis used to ne-tune the marine heavy fuel oil blendingwhere generally a density maximum limit of 0.9910 kg/lhas to be observed.

IFOs


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1. Fuel oil applications

All fuel oil applications create energy by burning fuel oil.Fuel oil combustion (oxidation reaction) releases a large

amount of heat, which can be used for steam generation,for example, in steam turbines. The high volume(pressure) of the combustion gases can be used to drivean engine, or (less frequent for HFO, but widespread forgasoil) a gas turbine.

When fuel oil is burned, an amount of heat is released,which is dened by the specic energy (internationalunit MJ/kg) of the fuel.

Thermal plants use this heat to generate steam, whichthen drives steam turbines, thus providing mechanicalenergy that can be used for propulsion or to beconverted into electrical energy.

For marine engines and gas turbines, mechanical energyprovided by the combustion gases is used either directlyfor propulsion or converted into electrical energy forpower plants. For larger installations, cost efciencyoptimization and environmental constraints led to theintroduction of co-generation. In co-generation, some ofthe electrical energy lost is used to generate low-pressuresteam, suitable for a wide range of heating applications.

2. Fuel specications

Different types of fuel oil applications and environmentalconsiderations have led to different types of fuel oilspecications. These are much more demanding than

the original fuel oil n 6 or Bunker C requirements whenall heavy fuel was used for thermal plants and steamturbines. Emission standards for thermal plants can varywidely, depending on the geographical area. Since allemitted SO2originates from sulphur in the fuel, emissionstandards on SO2automatically limit the sulphur contentof the fuel, except for large combustion plants, wherethe standard can be economically met by ue gasdesulphurization.

In the late 1960s, marine diesel engines were theprimary means of ship propulsion. Through the late1970s, marine engine heavy fuel oil grades remainedidentied solely by their maximum viscosity. This worked

well with heavy fuel originating from atmosphericreneries. Fuel-related operational problems arosewith the generalized upgrading of renery operations

in the second half of the 1970s from straight run tocomplex rening.

1982 saw the publication of marine fuel specication

requirements by the British Standard Organization(BS MA 100), and by CIMAC (Conseil International deMachines Combustion).

An international ISO standard has existed since 1987:ISO 8217. The stated purpose of ISO 8217 is to denethe requirements for petroleum fuels for use in marinediesel engines and boilers, for the guidance of interestedparties such as marine equipment designers, suppliersand purchasers of marine fuels. These specications areregularly revised to accommodate changes in marinediesel engine technology, crude oil rening processesand environmental developments. The ISO 8217:2005specications for marine fuels will be discussed in detail

in Chapter III-2a (see pages 8 & 9, Tables 1 & 2).

The most important specications to ensure reliableengine operation with fuel originating from complexrening are:

Maximum density limit: Important for classical purieroperation and to ensure satisfactory ignition qualityfor low viscosity fuel grades

Maximum Al+Si limit: In a complex renery, HCOis used as a blending component. Mechanicallydamaged aluminum silicate catalyst particles ofthe catalytic cracker are not completely removedfrom the HCO stream, and are found back in mg/kg

amounts in heavy fuel blended with HCO. In order toavoid abrasive damage in the fuel system onboardthe vessel, it is necessary to limit the amount of Al+Sito a level, which can be adequately removed by theships fuel cleaning system.

Maximum total potential sediment limit: The stabilityof asphaltenes is deteriorated by the visbreakingprocess, and instability problems can cause fuelpurication and lter-blocking problems, hence theneed for a specication to ensure adequate fuelstability.

A less widespread application of heavy fuel is found inheavy-duty gas turbines: Here the fuel specication

requirements before the injection are very severe,and can only be obtained by an extremely thoroughprecleaning of the fuel.

III. Fuel Oil

continued on page 10


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Table 1: Requirements for marine distillate fuels

Characteristic Unit LimitCategory ISO-F

Test method

DMX DMA DMB DMCa reference

Density at 15C kg/m3 max. 890.0 900.0 920.0 ISO 3675 or ISO 12185

(see also 7.1)

Viscosity at 40C mm2/sb min. 1.40 1.50 ISO 3104

max 5.50 6.00 11.0 14.0 ISO 3104

Flash point C min. 60 60 60 ISO 2719

min. 43 (see also 7.2)

Pour point (upper)c

winter quality C max. 6 0 0 ISO 3016

summer quality max. 0 6 6 ISO 3016

Cloud point C max. 16 ISO 3015

Sulfurc % (m/m) max. 1.00 1.50 2.00e 2.00e ISO 8754 or

ISO 14596

(see also 7.3)

Cetane index min. 45 40 35 ISO 4264

Carbon residue on

10% (V/V) distillation

bottoms % (m/m) max. 0.30 0.30 ISO 10370

Carbon residue % (m/m) max. 0.30 2.50 ISO 10370

Ash % (m/m) % (m/m) max. 0.01 0.01 0.01 0.05 ISO 6245

Appearancef Clear and bright f See 7.4 and 7.5

Total sediment,

existent % (m/m) max. 0.10f 0.10 ISO 10307-1 (see 7.5)

Water % (V/V) max. 0.3f 0.3 ISO 3733

Vanadium mg/kg max. 100 ISO 14597 or IP 501 orIP 470 (see 7.8)

Aluminium plus silicon mg/kg max. 25 ISO 10478 or IP 501

or IP 470 (see 7.9)

Used lubricating oil (ULO) The fuel shall

Zinc mg/kg max. be free of IP 501 or IP 470

Phosphorus mg/kg max. ULOg15 IP 501 or IP 500

Calcium mg/kg max. 15 IP 501 or IP 470

30 (see 7.7)

a Note that although predominantly consisting of distillate fuel, the residual oil proportion can be significant.

b 1 mm2/s = 1 cSt

c Purchasers should ensure that this pour point is suitable for the equipment on board, especially if the vessel operates in both the northern and southernhemispheres.

d This fuel is suitable for use without heating at ambient temperatures down to 16C.e A sulfur limit of 1.5 % (m/m) will apply in SOx emission control areas designated by the International Maritime Organization, when its relevant protocol

enters into force. There may be local variations, for example the EU requires that sulphur content of certain distillate grades be limited to 0.2 % (m/m)in certain applications.

f If the sample is clear and with no visible sediment or water, the total sediment existent and water tests shall not be required.

g A fuel shall be considered to be free of used lubricating oils (ULOs) if one or more of the elements zinc, phosphorus and calciumare below or at the specifiedlimits. All three elements shall exceed the same limits before a fuel shall be deemed to contain ULOs.


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Category ISO-F

TestCharacteristic Unit Limit

RMA RMB RMD RME RMF RMG RMH RMK RMH RMK method

30 30 80 180 180 380 380 380 700 700 reference

ISO 3675

Density at 15C kg/m3 max. 960.0 975.0 980.0 991.0 991.0 1010.0 991.0 1010.0 or ISO 12185

(see also 7.1)

Kinematic

viscosity at 50C mm2/sa max. 30.0 80.0 180.0 380.0 700.0 ISO 3104

Flash point C min. 60 60 60 60 60 ISO 2719 (see also 7.2)

Pour point (upper)b

winter quality C max. 0 24 30 30 30 30 ISO 3016

summer quality C max. 6 24 30 30 30 30 ISO 3016

Carbon residue % (m/m) max. 10 14 15 20 18 22 22 ISO 10370

Ash % (m/m) max. 0.10 0.10 0.10 0.15 0.15 0.15 ISO 6245

Water % (V/V) max. 0.5 0.5 0.5 0.5 0.5 ISO 3733

Sulfur c % (m/m) max. 3.50 4.00 4.50 4.50 4.50 ISO 8754 or ISO 14596 (see also 7.3)

ISO 14597 or

Vanadium mg/kg max. 150 350 200 500 300 600 600 IP 501 or

IP 470 (see 7.8)

Total sediment

potential % (m/m) max. 0.10 0.10 0.10 0.10 0.10 ISO 10307-2 (see 7.6)

Aluminium plus ISO 10478 or IP 501 or

silicon mg/kg max. 80 80 80 80 80 IP 470 (see 7.9)

Used lubricating

oil (ULO) The fuel shall be free of ULOd

Zinc mg/kg max. 15 IP 501 or IP 470 (see 7.7)

Phosphorus max. 15 IP 501 or IP 500 (see 7.7) Calcium max. 30 IP 501 or IP 470 (see 7.7)

a Annex C gives a brief viscosit y/temperature table, for information purposes only. 1 mm2/s = 1 cSt

b Purchasers should ensure that this pour point is suitable for the equipment on board, especially if the vessel operates in both the northern andsouthern hemispheres.

c A sulfur limit of 1.5 % (m/m) will apply in SOx emission control areas designated by the International Maritime Organization, when its relevantprotocol comes into force. There may be local variations.

d A fuel shal l be considered to be free of ULO if one or more of the elements zinc, phosphorus and calcium are below or at the specified limits.All three elements shall exceed the same limits before a fuel shall be deemed to contain ULO.

Table 2: Requirements for marine residual fuels


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The fuel treatment consists of the removal of thealkalimetals by fuel precleaning and inhibition ofvanadium-induced corrosion by injecting magnesium-

containing additives that react with the vanadium toform non-corrosive compounds. The heavy-duty gas-turbine application of heavy fuel is further discussed inAttachment II.

2a. Signicance of the marine fuelproperties listed in ISO 8217:2005

Kinematic viscosity:

Kinematic viscosity is a measure for the uidity of theproduct at a certain temperature. The viscosity of a fueldecreases with increasing temperature. The viscosityat the moment the fuel leaves the injectors must bewithin the limits prescribed by the engine manufacturerto obtain an optimal spray pattern. Viscosity outsidemanufacturers specications at the injectors will leadto poor combustion, deposit formation and energyloss. The viscosity of the fuel must be such that therequired injection viscosity can be reached by the shipspreheating system.

Density:

The ofcial unit is kg/m3at 15C, while kg/l at 15C is themost commonly used unit. Density is used to calculatethe quantity of fuel delivered. The density gives anindication of the ignition quality of the fuel within acertain product class. This is particularly the case for

the low-viscosity IFOs. The product density is importantfor the onboard purication of the fuel; the higher thedensity, the more critical it becomes (see Chapter III-4on fuel oil treatment).

Cetane index:

Cetane index is only applicable for gasoil and distillatefuels. It is a measure for the ignition quality of the fuelin a diesel engine. The higher the rpm of the engine, thehigher the required cetane index. The cetane index isan approximate calculated value of the cetane number,based on the density and the distillation of the fuel. Thecetane index is not applicable when cetane-improvingadditives have been used.

Carbon residue:

Carbon residue is determined by a laboratory testperformed under specied reduced air supply. It does

not represent combustion conditions in an engine.It gives an indication of the amount of hydrocarbons inthe fuel which have difcult combustion characteristics,

but there is no conclusive correlation between carbonresidue gures and actual eld experience. The microcarbon residue method is specied by ISO 8217.

Ash:

The ash content is a measure of the metalspresent in the fuel, either as inherent to the fuelor as contamination.

Flash point:

Flash point is the temperature at which the vapors of afuel ignite (under specied test conditions), when a testame is applied. The ash point for all fuels to be usedin bulk onboard vessels is set at PM, CC, 60C minimum

(SOLAS agreement). DMX, a special low cloud pointgasoil, may only be stored onboard in drums because ofits < 60C ash point.

Sulphur:

The sulphur content of a marine fuel depends on thecrude oil origin and the rening process. When a fuelburns, sulphur is converted into sulphur oxides. Theseoxides reach the lubricating oil via the blow-by gas.These oxides are corrosive to engine piston liners andmust be neutralized by the cylinder lubricant. Marineengine lubricants are developed to cope with this acidity(high BN). If the correct lubricant is used, the sulphur

content of a marine fuel is technically not important butmay have environmental implications.

Therefore, Annex VI to Marpol 73/78 currently requiresthe sulphur content of any fuel oil used onboard shipsnot to exceed 4.5 m/m % max. In 2006, both Annex VIand the EU directive 2005/33/EC have restricted theSOxemissions of ships sailing in the Baltic Sea SECA(Sulphur oxides Emission Control Area) to 6 g/kWh whichcorresponds to a fuel oil sulphur content of maximum1.5 m/m %. In addition, the EU directive extended the1.5 m/m % S limit to ferries operating to and from anyEU port. In 2007, the North Sea and English channel willbecome a SECA area where the 1.5 m/m % S limit willalso apply.

The EU directive also has set a limit of 0.1 m/m% max onthe sulphur content of marine fuels used by shipsat berth (and by inland waterways), effectiveJanuary 1, 2010.


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The process to review already enacted environmentallegislation in order to further reduce emissions hasalready started. Therefore, the limits and requirements

stated above are subject to change.Water content:

Water in fuel is a contamination and does not yieldany energy. The percentage of water in the fuel canbe translated into a corresponding energy loss for thecustomer. Water is removed onboard the vessel bycentrifugal purication. If after purication, the watercontent remains too high, water vapor lock can occurand pumps can cut out. If water-contaminated fuelreaches the injectors, combustion can be erratic. Waterin fuel that remains standing in lines for a longer periodcan cause corrosion.

Pour point:Pour point is the lowest temperature at which a fuelwill continue to ow when it is cooled under speciedstandard conditions. Contrary to straight run heavyfuels (pour point typically in the +w20C range), bunkerfuels from a complex renery generally have pourpoints below 0C (range 10 to 20C). This is becausebunker fuel tanks are usually not completely heated only before the fuel transfer pump. This can thenlead to problems if a vessel receives high pour straightrun bunker fuel. For distillate marine diesel, the coldtemperature behavior is controlled in ISO 8217 by a pourpoint maximum. With marine diesels with a high contentof heavier n-parafns, vigilance is required if strongtemperature changes are expected. (Wax settling canoccur, even when the pour point specication is met.)

Elements:

Vanadium and nickel are elements found in certainheavy fuel oil molecules (asphaltenes). Uponcombustion, vanadiumoxides are formed, and some havecritical melting temperatures. The most critical are thedouble oxides/sulphates with sodium. Some countrieshave implemented maximum Ni concentrations for inlanduse of heavy fuel.

Total sediment potential:

Inorganic material naturally occurring in crude oil isremoved in the reneries prior to the atmosphericdistillation. Some minor contamination (for example,ironoxides) of a nished heavy fuel can not be excluded.

The biggest risk for sediment formation in heavy fuel isdue to potential coagulation of organic material inherentto the fuel itself. Visbroken asphaltenes, if insufciently

stable, can form sediment (coagulation is inuencedby time and temperature). A decrease in aromaticity ofthe fuel matrix by blending with parafnic cutterstockscan also deteriorate the stability of the asphaltenes.In cases of heavy fuel instability, only a relative smallfraction of the asphaltenes forms sediment, but thisorganic sediment includes in its mass some of the fuelitself, and water (onboard purifying problems), and theamount of generated sludge can become quite high. Thetotal potential sediment is the total amount of sedimentthat can be formed under normal storage conditions,excluding external inuences. If the total potentialsediment of the heavy fuel oil markedly exceeds thespecication value (0.10% m/m max) for all grades of

IFOs and HFOs), problems with the fuel cleaning systemcan occur, fuel lters can get plugged and combustioncan become erratic.

Catalytic fines:

Heavy cycle oil is used worldwide in complex reningas a blending component for heavy fuel. Mechanicallydamaged catalyst particles (aluminum silicate) cannotbe removed completely in a cost-effective way, and arefound in blended heavy fuel. Fuel precleaning onboardships has a removal efciency of approximately 80% forcatalytic nes. In order to avoid abrasive wear of fuelpumps, injectors and cylinder liners the maximum limitfor Al+Si dened in ISO 8217 is 80 mg/kg.

Used lubricating oil (ULO):

The use of used lubricants (predominantly used motorvehicle crankcase oils) in marine fuels rst surfaced as apotential problem in the mid-1980s. Both CIMAC and ISO8217 working groups have discussed the technical andcommercial considerations at length. Calcium, zinc andphosphorous are considered ngerprint elements ofULOs, and limits for these elements have been set in ISO8217:2005. A fuel oil is considered to contain ULO onlywhen all three elements simultaneously exceed theselimits. This, however, does not necessarily imply thatthe fuel oil is not suitable for use. Generally, 10 mg/kg

Zn corresponds to approximately 1% used oil in the fuel.This is only an approximation; the zincdithiophosphatecontent of lubricants can vary considerably.


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Calculated carbon aromaticity index (CCAI):

CCAI is an indicator of the ignition delay of an IFO. CCAIis calculated from the density and the viscosity of the

fuel oil. Although it is not an ofcial specication, it hasfound its way into many users bunker fuel specicationrequirements. Some manufacturers specify CCAIlimits for their engines, depending on engine type andapplication.

2b. Correspondence of specications andtest methods

ISO 8217:2005 lists test requirements and methodsfor testing. While these methods should be usedworldwide for testing marine fuels, experience hasshown that they are not. In some areas, precursors ofthe presently dened ISO methods are still being used.

The correspondence (discrepancy) between such testmethods/results and the test methods/data of ISO 8217are described hereafter.

Density:

The mass (weight in vacuum) of the liquid per unitvolume at 15C. Ofcial unit: kg/m3. Often used variant:kg/l. The density limits in ISO 8217 are expressed inkg/m3. Specic gravity 60/60F: Specic gravity is theratio of the mass of a given volume of liquid at 60F tothe mass of an equal volume of pure water at the sametemperature. No unit.

API gravity:

A function of the specic gravity 60/60F. API gravity isexpressed as degrees API.

API gravity, deg =(141.5 / spec. gr. 60/60F) 131.5

Micro Carbon Residue (MCR):

MCR is the carbon residue test prescribed by ISO8217:2005. Formerly, the carbon residue test wasConradson Carbon Residue. MCR is quicker and moreprecise than CCR.

Al+Si:

The ISO 8217 prescribed test methods are ISO 10478

or IP 501 or IP 470. Only these methods and fullyequivalent methods from national standardizationorganizations should be used. A former industry-widelimit for catalyst nes in heavy fuel was dened on Alalone (30 mg/kg max.). The ratio between Al and Si can,

however, vary considerably between different types andmanufacturers of aluminum silicate catalyst. This is whythe test measures the sum of Al and Si. In practice, the

two ways of limiting the catalytic nes content in heavyfuel give the same degree of protection.

Total sediment existent and total sediment potential:

Differentiation can be made between tests for inorganicsediment and organic sediment, existent sediment andpotential sediment.

According to ISO 8217:2005, the former limit oninorganic sediment (rust, sand) applicable to DMBmarine diesel has been replaced by the requirement tomeasure the total sediment existent (ISO 10307-1) on allDMB category products that fail the visual inspectionrequirement to be free from visible sediment and water.

Organic type sediment can occur in DMB and DMCmarine diesel and in intermediate fuel oils. The causeof the formation of organic sediment resides in thethermal cracking of the heaviest molecules of crude,generally in visbreaking operations. Asphaltenes, theheaviest molecules of crude, can become unstable bythermal cracking, and must be carefully monitored bythe reneries. Once visbroken, the asphaltenes are moreor less sensitive to changes in the aromaticity of thetotal fuel matrix. This must be taken into account forfuel blending when using visbroken heavy fuel and gasoil(parafnic) blending stocks. The asphaltene sedimentformation is a function of time and temperature(excluding external inuences), and an unstable fuel willonly reach its nal sediment formation after a certainstorage time. The sediment present in a sample of heavyfuel at a certain moment is given by the total existentsediment test, but there is no certainty that this gurecorresponds to the condition of the bulk of the fuelat that same time. The total potential sediment testshows the total amount of sediment that can be formedunder normal storage conditions, excluding externalinuences. The prescribed test method is ISO 10307-2(IP 390+375 is equivalent).

The test method originally used in the industry fordetermining the total sediment was the Shell HotFiltration Test. The test results can be existing sediment

or potential sediment, depending on the ageingprocedure. The results of this test are not equivalent t0those of ISO 10307-2, due to a difference in the solventused for the test. The Shell Hot Filtration Test withageing generally gives slightly higher results.


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Viscosity:

Kinematic viscosity is the only accepted method,expressed in mm2/s at a certain temperature. ISO

8217:2005 lists the maximum kinematic viscosities at50C (note: 1 mm2/s =1cSt). SSU, SSF and RW1 (SayboltSeconds Universal, Saybolt Seconds Furol and RedwoodNo. 1) are obsolete units.

3. Test specications and precision

ISO 8217:2005 not only species the requirements formarine distillate and residual fuels and the test methodreferences, it also lists ISO 4259:1992, Petroleumproducts determination and application of precisiondata in relation to methods of test.

The application of precision data in relation to methods

of test automatically assumes that acquiring the samplewas performed to the best industry standard possible,and that the sample is representative for the supply.Experience shows that the sample itself is often theweakest point in the chain. Chevron recognizes only thebunker fuel retain samples taken by its representative(for example, bunker barge attendant) at the moment ofbunkering as valid.

Should a dispute arise due to a difference between testdata obtained on valid retain samples by two differentlaboratories (one acting on behalf of the supplier, theother on behalf of the customer), ISO 4259 shouldbe used to evaluate the validity of the results. If the

reproducibility of the test method is met, both valuesare considered acceptable, and the average of the twois taken as the true value. If the reproducibility is notmet, both results have to be rejected, and the guidelinesset forth in ISO 4259 should be followed to solve theproblem. This can be very time-consuming, and is veryseldom done in practice. Both parties generally agree tothe use of a third laboratory, the result of which will thenbe binding for both parties.

Let it be noted that reproducibility limits are onlyapplicable between two analysis gures on the samesample (or samples considered as being the same). Thereproducibility of a test method may not be invoked toexplain a deviation against a specication limit.

The testing margin, however, has an effect on a singleresult; for example, the analysis result on a certainspecication test obtained by the end user. If the enduser has no other information on the true value of thecharacteristic than a (single) test result, the product fails

when the result exceeds the specication limit by morethan 0.59R upper limit (where R is reproducibility of thetest method), and more than 0.59R lower limit.

The signicance of reproducibility should not beunderestimated. It is the basis for all quality controlagainst specications. Without reproducibility data, testresults would lose a major part of their signicance,since there would be no way to dene how close a testresult approaches the true value.

Attachment II lists the methods for marine fuel testinglisted in ISO 8217:2005, together with reproducibility.Whenever national standardization methods oftesting are used, the full correspondence with the ISOprescribed method has to be checked. There can also besome differences in the precision data.

4. Onboard fuel oil treatment

In the late 1970s, the increasing market demand fordistillate fuels (gasoline, diesel) and the resultingchanges in renery processes to cope with this demand,resulted in a deterioration of heavy fuel quality. Efcientcleaning of heavy fuel oil is mandatory to achievereliable and economical operation of diesel enginesburning heavy fuel.

Examples:

Water is a common contaminant in fuel oil. Except forwater content in the fuel oil due to transport, therecan be a further contamination in the storage tank

due to water condensation as a result of temperaturechanges.

Catalyst nes from aluminum silicate catalyst usedin the catalytic cracking process may end up in theheavy fuel and need to be removed to avoidabrasive wear of various engine parts.

Fuel from the storage tank is pumped to the settling tankand contaminants (water, solids) sink to the bottom ofthe tank under inuence of the gravity force (g). The rateof separation by gravity, Vg is dened by Stokes law:

Vg=[d2(D2-D1) / 18 ] g

d: particle diameterD2: particle densityD1: density of the fuel oil: viscosity of the fuel oilg: gravitational acceleration


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Complete separation in a reasonable period of time canonly be achieved by mechanically generated centrifugalforce. Fuel from the settling tank is fed to a centrifugal

system or purier and water and solids are separatedout of the fuel. The rate of separation in a centrifugaleld (V) is dened as:

V =Vg Z

Where Z equals r 2/g (r =distance of the particle fromthe axis of rotation, is the angular velocity). Thefactor Z species how much greater the sedimentationrate is in the centrifugal eld compared to thegravitational eld.

4a. Conventional cleaning withpuriers/clariers

The increasing difference in density between waterand fuel oil with increasing temperature is the base forcentrifugal cleaning (purication).

In a purier separator, cleaned oil and separated waterare continuously discharged during operation. Aninterface is formed in the bowl between the water andthe oil (see Figure 1). This interface position is affectedby several factors, such as density and viscosityof the fuel oil, temperature and ow rate. Figure 2illustrates that the position of the interface becomesprogressively more sensitive with increasing fuel density.The generally accepted maximum density limit for aconventional purier is 991 kg/m3(at 15C).

In order to achieve optimum separation results withpuriers, the interface between oil and water in the bowlmust be outside the disc stack but at the inside of theouter edge of the top disc (detailed view in Figure 1). Theposition of the interface is affected mainly by the densityand the viscosity of the fuel oil and is adjusted by meansof gravity discs. The correct gravity disc is dened asthe largest disc that does not cause a broken water seal.With the correct interface position, the oil feed can enterthe narrow channels of the disc stack along its entireheight. This is important since separation takes place inthese channels.

For fuel oils with a viscosity above 180 mm2/s at 50C, it

is recommended that the highest possible temperature(98C) be maintained. The fuel oil has to remain in thecentrifuge bowl for as long as possible by adjusting theow rates through the centrifuge so that it correspondsto the amount of fuel required by the engine.

If the interface is in an incorrect position (see Figure 3),the oil to be cleaned will pass through only the lowerpart of the disc stack, since the upper part is blocked

with water. Thus, separation is inefcient because onlypart of the disc stack is being used.

(Source: Alfa Laval)

Figure 1: Correct interface position Oil distributed to allchannels in the disc stack


Figure 2: Interface position sensitivity


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To ensure optimal cleaning of a fuel oil, a secondseparator can be used in series operation, for example,a purier followed by a clarier. The density limit of

991 kg/m

3

is not applicable to clarier operation, butthe combined system of purier and clarier in seriesremains restricted to a maximum density of 991 kg/m3at 15C. Heavy movements of the vessel can stir up dirt,water and sludge that have accumulated over time onthe bottom of the bunker and settling tanks. Efcientpurication is not always possible when separators havebeen put in a parallel purifying function.

In a conventional clarier (see Figure 4), the wateroutlet is closed off and the separated water can onlybe discharged with the sludge through the sludgeports at the bowl periphery. A sludge discharge causesturbulence in the bowl and leads to less efcientseparation. Consequently, the water handling capabilityof a conventional clarier is insufcient for the cleaningof fuel oil if the fuel oil has a signicant amount of water.(The prior use of a purier with its continuous waterremoval is mandatory.)

4b. Advanced computer driven fuelcleaning systems

Example: ALCAP

Fuel oils with densities above 991 kg/m3at 15C areavailable on the market and can be puried, for example,with the ALCAP system, which allows fuel oil densities upto 1010 kg/m3at 15C. Fuel oil is continuously fed to the

separator. The oil ow is not interrupted when sludge isdischarged.

The ALCAP basically operates as a clarier. Clean oilis continuously discharged from the clean oil outlet.Separated sludge and water accumulate at the peripheryof the bowl. Sludge (and water) is discharged after a pre-set time. If separated water approaches the disc stack(before the pre-set time interval between two sludgedischarges is reached), some droplets of water start toescape with the cleaned oil. A water transducer, installedin the clean oil outlet, immediately senses the smallincrease of the water content in the clean oil. A signalfrom the water transducer is transmitted to a control

unit and changes in water content are measured.


Figure 3: Incorrect interface position


Figure 4: Conventional clarier


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Increased water content in the cleaned oil is the sign ofreduced separation efciency for not only water, but forthe removal of solid particles, as well. When the water

content in the cleaned oil reaches the pre-set triggerpoint, the control unit will initiate an automatic dischargeof the water that has accumulated in the bowl throughthe water drain valve.

In summary, water is discharged either with the sludgeat the periphery of the bowl (Figure 6a): separated

water does not reach the disc stack in the pre-set timebetween sludge discharges, or through the water drainvalve (Figure 6b): separated water reaches the disc stackbefore the pre-set time between sludge discharges.

5. Fuel oil stability and compatibility

Total potential sediment is an important specication forheavy fuels. Currently, nearly all heavy fuel is marketed

with the stability guarantee of total potential sediment(ISO 10307-2) 0.10 m/m % max. Stratication in heavyfuel oil tanks is minimal when this specication is met.

The reason for the specication requirement is thepresence of asphaltenes in the heavy fuel. Asphaltenesare present in crude oil, and are dened as the fractioninsoluble in n-heptane, but soluble in toluene. Theirconcentration in the crude oil is dependent on the crudeoil origin itself. Asphaltenes are the highest molecularweight molecules in the crude, and contain all of theorganically bound vanadium and most of the nickelfound in the crude. They also contain a relatively highpercentage of sulphur and nitrogen. Their hydrogen

content (and hence, combustion characteristics) can bequite different from one crude to another. Asphalteneshave a predominantly aromatic structure and the Cand H atoms are combined in ring structures asillustrated below.

Asphaltenes are polar molecules, kept in colloidalsuspension2by their outer molecular structure.Thermally cracked asphaltene molecules have lost partof their outer structure (depending on the severity of thethermal cracking process), and even visbreaking, whichis a relatively soft thermal cracking process, affectsthis outer molecular structure. If too much is removed,part of the asphaltenes can start clogging together, and

will no longer be kept in suspension in the fuel matrix,sludge will be formed. Avoiding the formation of thissludge during the manufacturing of visbroken fuel isthe responsibility of the renery. A change in the fuelmatrix composition by blending a stable visbroken fuelto a lower viscosity can also affect the stability of theasphaltenes. This means that viscosity reduction of avisbroken fuel with a parafnic-type cutterstock canmake the fuel unstable. When this happens, the two fuelsare said to be incompatible. When two fuels that aremixed together do not cause any asphaltene coagulation,they are compatible with each other. Test methods existto predict the nal stability of a fuel mixture, and hence,the compatibility of the two components. In practice, one

chooses a cutterstock with a high enough aromaticity to

2 Colloidal suspension: a suspension in which gravitational forces arenegligible

Figure 6a: Discharge ofseparated water throughsludge outlet

Figure 6b: Discharge ofseparated water throughwater drain valve

(Source: Alfa Laval)(Source: Alfa Laval)


Figure 5: ALCAP separator


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keep the asphaltenes dispersed (for example, by addingheavy and/or light cycle oil) and to provide an adequatestability reserve.

Two heavy fuels with diverse compositions (for example,one an atmospheric heavy fuel from parafnic crude,and the other from a relatively severe visbreakeroperation) can also be incompatible with each other.When storing fuel, the potential of compatibilityproblems between two different heavy fuels should bekept in mind.

6. Commingling of fuels

Indiscriminate commingling of fuels can lead to stabilityproblems of the nal fuel due to incompatibility of thefuels used as blend components. Eventual problems/damages arising from the commingling of fuels are the

responsibility of the individual who made the decisionto commingle the fuels. Fuel suppliers guarantee thestability of the fuel they deliver, but can not be heldresponsible for compatibility problems with another fuel.

Rules, in descending order of safety:

Do not commingle fuels.

If commingling is unavoidable, check the compatibilityof the fuels in advance, and make a nal decisionbased on the test result.

If a compatibility check is not possible (onecomponent unavailable at the moment the decision

has to be made), reduce the amount of one fuel to aminimum before adding the second fuel.

Note:Generally fuels of the same viscosity grade withsimilar densities will be compatible.

7. Microbiological contamination

Plugging of lters on gasoil and marine distillatefuel feed lines can be caused by microbiologicalcontamination (bacteria, fungi and yeast).

Microbiological contamination can always occur,especially if temperature conditions are favorable(between 15 and 40C, for the most common types), and

if non-dissolved water is present in the fuel.NO WATER =NO MICROBIOLOGICAL CONTAMINATION

Microbiological contamination ideally occurs in tropicaland sub-tropical regions: high air humidity combinedwith a high ambient temperature.

To avoid contamination, VOS, the Dutch organizationthat supervises the quality of gasoil delivered in theNetherlands, offers these points:

Good water-housekeeping is essential.

No water =no bacterial contamination

Fuel-producing companies, dealers, and end-users have a common responsibility: Bacterialcontamination can occur in each link of the chain.

Consequences of bacterial contamination: lthy fuelsystem, plugged fuel lters and erratic engineoperation

Bacterial contamination can be found in slime, sludge,and as possible corrosion in lters, tanks, lines

What the end-user can do:

Make sure no water enters the gasoil

Check lters

Check bunker and day tank for water

Whenever necessary, drain tanks. Securepermanent connection devices at the fuelreceiving site

Have de-aerating openings which can be closed(to prevent waves entering the bunkertank)

On-site macroscopic (visual) examination offersa rst screening between the contaminated andnon-contaminated tanks. Possible microbiological

contamination indicators are: Gasoil is hazy and/or contains suspended uffy

material

Emulsion or a slimy interface layer between waterand gasoil

A turbid, badly smelling water bottom, with sludge-like deposits

Bacteria and fungi are the most important agents ofmicrobiological contamination (yeast normally onlyoccur as co-contaminant). All are living cells, whichmultiply through cell division.


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The prime contamination of fuel is almost alwaysby aerobic bacteria and/or by fungi. Both use then. parafn fraction of the fuel as nutrient. Aerobic

bacteria need oxygen for their metabolism and evolveat the interface between the water and the gasoil;fungi (aerobic) also attach themselves to the tank wall.When oxygen is no longer present, anaerobic bacteriastart to develop. The anaerobic metabolism processgenerates hydrogen sulphide. Besides being a verydangerous toxin, hydrogen sulphide can also causesevere corrosion.

Anaerobic microbiological contamination should beavoided at all costs. Keep close control on the presenceof microbiological contaminants in the complete fuelsystem, from manufacturing to end use. In regions withmoderate climatic conditions, efcient water drainingis often sufcient to avoid exponential growth; insub-tropical and tropical climates, the continuous useof a biocide is often the only way to avoid problems.Biocides are also used worldwide to combat importedmicrobiological problems. Commercially availablebiocides have been developed to eliminate the totalmicrobiological contamination (bacteria, fungi andyeast). There are two different types of biocides: watersoluble and oil soluble. To eliminate microbiologicalcontamination in fuel tanks, water soluble biocidesare generally the most cost-effective. The treat ratecan differ according to the type and severity of thecontamination (and the amount of non-removablewater). Water drained from tanks after a biocide

treatment cannot be sent directly to a biologicalwater purication system; the biocide has to bedeactivated rst.

8. Fuel contamination in lubricants

In the 1990s, the demands on marine lubricants changedconsiderably for medium-speed engines. Operating theengines at higher thermal and mechanical loads madeit more difcult for the lubricant to cope with the issuesof borderline lubrication. At the same time, enginedesign changes, such as the introduction of the anti-borepolishing ring, decreased oil consumption in medium-speed engines considerably from 11.5 g/kWh or more to

0.40.7 g/kWh or lower in modern engines.

Changes to engine construction and the deteriorationof heavy fuel quality, which began in the late 1970s,spawned signicant challenges to marine lubricants.

Liner lacquering, undercrown deposits, increased oilconsumption, base number depletion, hot corrosion ofthe piston crown, oil scraper ring clogging and increasedpiston deposits occurred. As a result, formulationsneeded to be adapted.

Medium-speed engine blackening due to HFOcontamination of the lubricant, piston head corrosionand undercrown deposits were typical consequences ofincreased fuel pump pressure and the switch-over fromatmospheric heavy fuel to visbroken heavy fuel.

Its possible for HFO to enter the lubricant directlyas a result of leaking fuel pumps, or unburned HFOthat remains on the cylinder walls can be washed

down into the sump. HFO contamination can now beassessed by measuring the concentration of unburnedasphaltenes in the lubricant. Chevron Global MarineProducts, in cooperation with MAN Diesel in Augsburg,developed a test method which accurately measuresthis concentration (in %wt) and also qualies the originof the asphaltene ingress. The typical contaminationlevel of medium-speed engine oil with asphaltenes, asmeasured by Chevron Technology Ghent during the lastten years, has been between 0.25 and 0.30%wt.

Common issues encountered with conventionallubricant due to HFO contamination:

1. Engine blackening

The increase of the fuel pump pressure up to 1600 barin medium-speed diesel engines results in a higher fuelpump leakage, meaning increased fuel contamination.Most HFOs originate from visbreaking installations. Theasphaltenes dont dissolve in the parafnic lubricant,instead they coagulate and form oating asphaltparticles of 2 to 5 microns in the lubricant. Theseparticles are very sticky and form black deposits on allmetal surfaces of the engine. This then results in blackdeposits in the cambox and in the crankcase. Thesedeposits cause oil scraper ring clogging, sometimesresulting in high oil consumption. They may form

deposits in the hot areas of the piston grooves and onthe piston lands and in the cooling spaces of the piston.


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If an oil barrier is used to seal the fuel pump, asphaltenecoagulation can occur on the surface of the fuel pumpplunger, at times resulting in fuel pump blockages.

These deposits can obstruct the fuel pump drain. Thisresults in excessive fuel ingress into the lubricant,aggravating the deposit problems and causing seriousviscosity increases due to fuel admixture. Theseproblems can be minimized by effectively removingthe asphalt particles from the lubricant.

2. Undercrown deposits and piston head corrosion

The tendency to increase the piston undercrowntemperature can result in carbon deposits on the

piston undercrown due to thermal carbonization of thelubricant. Also, asphalt particles originating from HFOcan adhere to the piston undercrown when conventionallubricants are used.

Undercrown deposits combined with high loadoperations can lead to piston head corrosion.Undercrown deposits cause a reduction in the coolingeffect, resulting in about 100C increase in pistontemperatures. Above 450C, some Na/V oxides (whenpresent) can melt with the piston crown material causinghot corrosion on the top of the piston.

Figure 7: Conventional lubricant

Figure 8: Conventional lubricant showing heavyfuel contamination

Figure 9: Conventional lubricant typical piston deposits ina medium-speed engine with heavy fuel contamination

Figure 10: Conventional lubricant typical oil scraperdeposits in a medium-speed engine with heavy fuelcontamination


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To respond to the HFO challenges, Chevron GlobalMarine Products developed a lubricant series withhigh asphaltene dispersancy, to optimize lubrication

of medium-speed engines and to avoid the issuesresulting from asphaltene contamination. TARO DP/XL(available as a 20, 30, 40, 50 or 60 BN) were developedspecically to cope with increasing mechanical andthermal stresses and the changes in fuel quality. Sinceits introduction in the mid-1990s, the Taro DP/XL serieshas demonstrated excellent performance in a wide rangeof medium-speed engine types. Taro DP/XL is currentlyrecognized as a top-tier product technology for medium-speed engine lubrication.

Figure 11 illustrates the cambox cleanliness obtained withTARO DP technology, compared with the blackening ofthe cambox using a conventional lubricant, as illustratedin Figure 8.

Figure 11: Taro DP technology cambox cleanliness despite4% heavy fuel contamination


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Attachment I: Crude oil rening

The purpose of crude oil rening is to convert crude andother feedstocks into saleable products. The desired

products are mainly gasoline, kerosene, jet fuel, gasoiland diesel.

In order to obtain these products, crude oil is rstseparated into fractions by distillation, then the differentfractions are further processed in order to obtain thedesired characteristics and optimum yield.

The different processes used in a modern renery are:

1. Crude oil desalting

Water and inorganic salts are removed in an electrostaticeld. The main purpose of crude oil desalting is toprotect the rening process units against corrosion.

2. Atmospheric distillation

Crude oil is a product with a very wide boiling range.In an atmospheric distillation column the fractionsboiling below 360C are distilled off under reux, and,according to boiling range, recovered as naphtha, kero,and gasoil type stocks. Atmospheric distillation is limitedto a maximum temperature of 360C, because otherwisecoking would start to occur, which is not desirable at thisstage of crude oil rening.

3. Vacuum distillation

In order to distill off a heavier cut without exceeding the360C temperature limit, a second distillation is doneunder reduced pressure: the vacuum distillation. Thedistillate fraction of the vacuum distillation unit is thefeedstock for a catalytic cracking unit (see item 4).

4. Catalytic cracking (for example, fluidized bed

catalytic cracking)

The main feedstock for a catalytic cracker is vacuumgasoil. The cracking operation breaks large moleculesinto smaller, lighter molecules. The process runs at hightemperatures, and in the presence of the appropriatecatalyst (crystalline aluminum silicate).

Atmospheric residue, with a low metal and MCR content,can also be used as catalytic cracker feed, necessitatingan adjustment of the catalyst type.

The main purpose of a catalytic cracker is to producelight hydrocarbon fractions, which will increase therenery gasoline yield.

Additional streams coming from the catalytic cracker arelight cycle oil (increases the gasoil pool) and heavy cycleoil (base stock for carbon black manufacturing). Both

streams are also used in heavy fuel oil blending.5. Catalytic hydrocracking

Some reneries use catalytic hydrocracking as asupplementary operation to catalytic cracking. Catalytichydrocracking further upgrades heavy aromatic stocksto gasoline, jet fuel and gasoil material. The heaviestaromatic fractions of a cat cracker are the normalfeedstock for a hydrocracker. Hydrocracking requiresa very high investment, but makes the renery yieldpattern nearly independent from the crude oil feed.

6. 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 amarketable product, a relatively mild thermal crackingoperation is performed. The amount of cracking islimited by the overruling requirement to safeguardthe heavy fuel stability. The light product yield of thevisbreaker (around 20%) increases the blendstock poolfor gasoil.

7. Coking (delayed coking, fluid coking, flexicoking)

Coking is a very severe thermal cracking process, andcompletely destroys the residual fuel fraction. The yieldof a coker unit is lighter-range boiling material, which

ultimately goes to the blending pool for the lighterproducts, and coke, which is essentially solid carbon withvarying amounts of impurities. The heavier distillatefraction of a coker can be used as feedstock for ahydrocracker (see item 5).

More processes are required before the end productsleave a renery. Most processes are designed to meetthe technical requirements of the end products, othersare needed to meet environmental limits (mainly sulphurreduction, both in the end products and in the reneryemissions).

8. Catalytic reforming and isomerization

Both processes are catalytic reforming, and are intendedto upgrade low-octane naphta fractions of the crudedistillation unit into high octane components for gasolineproduction. The type of catalyst and the operatingconditions determine if the reforming is mainly to

Attachments


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iso-parafns or to aromatics. The terminologyreforming is generally used for the change toaromatics, while the change to iso-parafns is referred

to as isomerization. Isomerization is normally done ona lighter fraction (C5/C6), while reforming is done on theheavy naphtha fraction (C7 and heavier, up to 150C).

9. Alkylation

This is another process intended to increase the yieldof valuable gasoline blend components. Alkylation is acatalyst-steered combination reaction of low molecularweight olens with an iso-parafn to form highermolecular weight iso-parafns. The feed to the alkylationunit is C3 and C4s from the catalytic cracker unit andiso-butane.

10. Hydrotreating

Hydrotreating process is a process that uses hydrogen toremove impurities from product streams, while replacingthese impurities by hydrogen. When hydrotreating isused to remove sulphur (very low sulphur limits in thespecications of gasoline and gasoil), it is called hydro-desulphurization. It is a catalytic process. The processis generally used on kerosene and gasoil fractions.Residual hydro-desulphurization is also a process, and isfeasible, but not economical.

11. 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 mercaptansulphur molecules (corrosive, and obnoxious smelling)into disulphide type molecules.

12. Sulphur recovery

As a result of the removal of sulphur from the renerystreams by hydrotreating, and the generation ofhydrogen sulphide during cracking and coking, renerygases contain a very high concentration of hydrogensulphide. The simple solution to eliminate the highlytoxic hydrogen sulphide is to burn it, but this thengenerates SO2, which contributes to acidicationproblems. In order to safeguard the environment, thehydrogen sulphide is converted in reneries to elemental

sulphur. This is typically accomplished by extracting thehydrogen sulphide from the renery gas by a chemicalsolvent, for example, an aqueous amine solution. Therich solution is then preheated and stripped by steam.

The Claus process consists of the partial combustion ofthe hydrogen sulphide rich gas stream (sufcient air isintroduced to combust 1/3 of the H2S to SO2). This SO2

then reacts (under inuence of a catalyst) with H2S inthe order of one SO2for two H2S, and thus provideselemental sulphur. The tail gas of the Claus unit is stillrich in SO2, and environmental legislation can requirethe further clean-up of this tail gas.

Attachment II: Reproducibility (R) of marine fueltest methods

Density at 15C, kg/m3

1. ISO 3675

For transparent, non viscous products:R =1.2 kg/m3or 0.0012 kg/lFor opaque products: R =1.5 kg/m3or

0.0015 kg/l

2. ISO 12185

For transparent middle distillates:R =0.5 kg/m3or 0.0005 kg/lFor crude oils and other petroleum products:R =1.5 kg/m3or 0.0015 kg/l

Kinematic viscosity, mm2/sISO 3104

Heavy fuels: at 50C : R =0.074xWhere x is the average of the results beingcompared

Flash point, P.M., closed testerISO 2719

Procedure A (distillate fuels) : 0.071xWhere x is the average of the results (C)being comparedProcedure B (residual fuel oils) : 6C

Pour Point, CISO 3016

R =6.59C

Cloud Point, CISO 3015

For distillate fractions: R =4C


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Sulphur, % (m/m)1. ISO 8754

R =0.00812(x + 0.15)

Where x is the mean sulphur content2. ISO 14596

For sulphur content in the range 0.100.99 m/m% : R =0.02For sulphur content in the range 1.002.50 m/m% : R =0.04

Cetane index (4 variable equation)ISO 4264

Precision depends on the precision of the originaldensity and distillation recovery temperaturecalculations.

Micro carbon residue, % (m/m)

ISO 10370R =X2/30.2451Where X is the average of the results beingcompared

Ash, % (m/m)ISO 6245

For ash content between 0.001 and 0.079 wt %:R =0.005For ash content between 0.080 and 0.180 wt %:R =0.024

Total existent sediment, % (m/m)ISO 10307-1

Heavy fuels: R =0.294 xDistillate fuels containing heavy components:R =0.174 xWhere x is the average of the test resultsin % (m/m)

Total potential sediment, ageing, % (m/m)ISO 10307-2

Heavy fuels: R =0.294 xDistillate fuels containing heavy components:R =0.174 xWhere x is the average of the test results in% (m/m)

Water, % (v/v)ISO 3733

Water collected between 0.0 and 1.0 ml:R =0.2 mlWater collected between 1.1 and 25 ml: R =0.2 mlor 10% of mean, whichever is greater

Vanadium, mg/kg1. ISO 14597

The method is applicable to products having V

content in the range of 5 to 1000 mg/kg, althoughreproducibility data have only been determined upto 100 mg/kg for VFor V content between 530 mg/kg: R =5 mg/kgFor V content between 31100 mg/kg:R =10 mg/kg

2. IP 501

R =1.6799 x0.6Where x is the average of the results (mg/kg)being compared

3. IP 470

R =3.26 x0.5

Where x is the average of the results (mg/kg)being compared

Cat fines Al+Si, mg/kg1. ISO 10478, IP 501

ICP detection:Al: R =0.337xSi: R =0.332xWhere x is the average of the results (mg/kg)being compared

2. IP 470

AAS detection:Al: R =0.789 x0.67Si: R =1.388 x0.67


Ca, Zn, P, mg/kg1. Ca

IP 501 (ICP) R =0.6440 x0.65IP 470 (AAS) R =1.139 x0.8

2. Zn

IP 501 (ICP) R =0.5082 x0.7IP 470 (AAS) R =0.580 x0.75

3. P

IP 501 (ICP) R =1.2765 x0.55

IP 500 (UV) R =1.2103 x0.4



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Attachment III: Gas turbine fuel requirements

Most heavy-duty gas turbines operate on natural gasand distillate fuels. Gas turbines operating on natural

gas require minimum fuel treatment. Distillate fuels,immediately after rening, have no or extremely lowcontamination levels of water, solids and trace metals.Contamination (mainly by water) during transport cannot be excluded, and centrifuging is the best methodfor the removal of water and solids. Sodium saltsare very detrimental for gas turbines, and seawatercontamination must be completely removed.

Gas turbine manufacturers have also developed efcienttechnologies for gas turbine operation with ash formingfuels (for example, heavy fuels), as a cost-effectiveoption instead of gasoil for sites where natural gas willnot be available in the foreseeable future.

The use of heavy fuels requires that attention be paid totwo types of potential hot path corrosion:

Sulphidation corrosion, caused by alkaline sulphates(mainly Na2SO4)

Vanadic corrosion, caused by low melting vanadiumoxides (V2O5)

Sulphidation corrosion is avoided by removing thesodium and potassium from the fuel by stringent waterwashing up to the level Na + K 0.5 mg/kg.The complex oxides between Mg and V which are thenformed, are no longer corrosive (traditionally, a m/mratio Mg/V of three is adhered to).

Heavy-duty gas turbines have been operatingsatisfactorily on ash forming fuels since the mid-1980s.It is clear that the need to use magnesium-basedadditives to combat vanadic corrosion imposes atechnical and economical upper limit on the vanadiumcontent of the fuel.


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References

Alfa Laval, Technical information, ALCAP, Cleaningsystem for fuel oil.

CIMAC, Recommendations regarding fuel quality fordiesel engines, volume 21, 2006.

Dr. Gehring H, Van Geeteruyen C, New test methods forHFO contamination of lube oils

Gary, J. H., Handwerk, G. E., Petroleum rening,Technology and Economics, 2nd edition, Revised andExpanded.

ISO 8217:2005, Petroleum products Fuels (class F) Specications of marine fuels.

Mansoori, G.A., Arterial blockage/fouling in petroleumand natural gas industries (asphaltene/bitumen, resin.),

University Illinois-Chicago/Thermodynamics ResearchLaboratory.

Molire, M., Gazonnet, J.P., Vivicorsi, J.P., EGTExperience with gas turbines burning ash-forming fuels,GEC ALSTHOM Technical Review, 1993, NA1.11.

Selley, R.C., Elements of petroleum geology, 2ndedition.

Verhelst, A., Latest developments in marine lubricationtechnology, Texaco Technology Ghent.

VOS, Publication Stichting VOS

The terms and denitions taken from ISO 8217:2005Petroleum products Fuels (class F) Specicationsof marine fuels, Tables 1 and 2 are reproduced withthe permission of the International Organization forStandardization, ISO. This standard can be obtainedfrom any ISO member and from the Web site atwww.iso.org. Copyright remains with ISO.

References


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