Woodyard D. (ed.) Pounders Marine diesel engines and Gas Turbines

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108 Fuels and Lubes: Chemistry and Treatment

FiguRe 4.4 hFo treatment plant layout approved by wärtsilä for its low-speed engines

From HFO transfer pump To MDO storage tank

From MDO storage tanks

1. Heavy fuel oil settling tank

2. Heavy fuel oil daily tank

3. Marine diesel oil tank

4. Heavy fuel oil supply pump

5. Heavy fuel oil/marine diesel

oil supply pump

6. Marine diesel oil supply pump

7. Heavy fuel oil preheater

8. Marine diesel oil preheater. Marine

diesel oil is to be heated above the

wax point ≈ 30˚C depending on

origin of the fuel and ambient

temperature

9. Self-cleaning heavy fuel oil

purifier/clarifier

10.Self-cleaning heavy fuel oil clarifie

11. Self-cleaning marine diesel oil

purifier

12.Pressure regulating valve

13.Automatic filter

HFO pipes heated and insulated

MDO pipes insulated

HFO pipes insulated

Note:

The air vent and drain pipes must

have a continuous slope of 5 per cent

minimum.

To separators sludge tank

109

Drain

The function of the settling tank is to separate the sludge and water con-

tained in the fuel oil, to act as a buffer tank and to provide a suitable constant

fuel temperature of 50–70°C. This can be improved by installing two settling

tanks for alternate daily use.

Wärtsilä also advises the use of ‘new generation’ separators without grav-

ity disc to treat heavy fuels of up to 700 cSt/50°C viscosity and facilitate

continuous and unattended operation. When using conventional gravity disc

separators, two such sets working in series (puriﬁer–clariﬁer) are dictated. The

clariﬁer enhances the separation result and acts as a safety measure in case the

puriﬁer is not properly adjusted.

The effective separator throughput should accord with the maximum con-

sumption of the diesel engine plus a margin of about 18 per cent to ensure that

separated fuel oil ﬂows back from the daily tank to the settling tank. The sepa-

rators should be in continuous operation from port to port. To maintain a con-

stant ﬂow through the separators, individual positive displacement-type pumps

operating at constant capacity should be installed. The separation temperature

is to be controlled within 2°C by a pre-heater.

The fuel-treatment system can be improved further by an automatic ﬁltra-

tion unit installed to act as a monitoring/safety device in the event of separator

malfunction. Such a ﬁltration unit is particularly recommended when conven-

tional separators with gravity discs are deployed. Separators can also be sup-

ported by homogenizers (see p. 111) in cases where possible asphaltene sludge

precipitation due to unstable or incompatible fuels is anticipated or where the

size of abrasive particles has to be reduced.

The fuel oil heater may be of the shell and tube or plate heat exchanger

type, with electricity, steam or thermal oil as the heating medium. The required

heating temperature for different oil viscosities is derived from a fuel oil heat-

ing chart (Figure 4.8), based on the information from oil suppliers with respect

to typical marine fuels with a viscosity index (VI) of 70–80. Since the viscos-

ity after the heater is the controlled parameter, the heating temperature may

vary, depending on the viscosity and viscosity index of the fuel. The viscosity

meter setting, reﬂecting the desired fuel-injection viscosity recommended for

an engine by the enginebuilder, is typically 10–15 cSt.

To maintain a correct and constant viscosity of the fuel oil at the inlet to the

main engine, the heater steam supply should be automatically controlled, usu-

ally based on a pneumatic or electronic control system.

Alfa Laval believes that two-stage pressurized systems are preferable for

fuel conditioning (feeder and booster) systems, suggesting that single-stage

systems can be difﬁcult to control and suffer from cavitation and gasiﬁcation

problems associated with high fuel temperatures (120–150°C). Its own two-

stage system features a 4-bar low-pressure section, while the HP side ranges

between 6 bar and 16 bar, depending on the requirements of the enginebuilder.

Two pumps (one standby), an auto-ﬁlter with back-up manual bypass ﬁlter and

a ﬂow transmitter are on the low-pressure (LP) side. There is also a mixing

tank, where fresh fuel is mixed with hot fuel returning from the engine. Oil

Fuel oil treatment 109

110 Fuels and Lubes: Chemistry and Treatment

from the day tanks is fed to the system under pressure via LP supply pumps to

eliminate any gasiﬁcation and cavitation problems.

From the mixing tank, the fuel enters the HP section, where the ﬂow rate

is maintained at a multiple of the actual fuel consumption rate so as to prevent

fuel starvation at the injectors. The HP section incorporates circulation pumps,

heaters and a viscosity transducer. The transducer compares viscosity against

a value set by the enginebuilder and sends a signal to the controller allowing

it to alter the fuel temperature by adjusting the ﬂow of heating medium (steam

or thermal oil) to the heater. ‘Self-cure’ functions include pump changeover to

standby in the event of failure or too low pressure, and change from viscosity

to temperature control (or vice versa).

separator Developments

The main aim of centrifugal separators is to remove fuel contaminants—notably

water, catalyst ﬁnes, abrasive grit and sodium from sea water—that can cause

excessive wear when burned in the engine. Continuing development pursues even

higher separation efﬁciencies to maximize engine protection, and more efﬁcient

discharge systems that reduce overall discharge volumes, decrease the amount of

water used and hence cut the amount of material collected in the sludge tank.

When partial discharge-type separators replaced total discharge designs,

the actual oil consumed at each discharge fell dramatically. In the partial dis-

charge process, however, larger volumes of water are needed for displacing the

oil interface and for the operating system. This quantity of water is a major

FiguRe 4.5 an alfa Laval centrifugal separator module

contributor to the overall sludge volume, as it too must be processed. Alfa

Laval’s separation (Figure 4.5) unit exploits a discharge process called

CentriShoot, which combines several design improvements to help reduce the

sludge consumption volumes associated with separators: by at least 30 per cent

and up to 50 per cent compared with previous models.

First, the bowl volume and therefore its contents are much lower than equiv-

alent separators, which means that at each discharge the contents discharged

will be signiﬁcantly less. Second, the frequency of discharge has been extended

by around four times compared with partial discharging separators. A new

design of discharge slide replaces the traditional sliding bowl bottom; the new

component is a form of ﬂexible plate that is secured at the centre, the slide outer

edge ﬂexing approximately 1–2 mm at each discharge to allow the sludge to be

evacuated through the sludge ports.

Installed as standard in the separation unit is a REMIND software pack-

age which allows the operator to install the program discs on a laptop compu-

ter. Connected to the control cabinet, the system can then review and store the

alarm history and processing parameters in the computer. The data can be used

later to check processing conditions for trouble shooting.

GEA Westfalia Separator’s C-generation family of separators exploits

Hydrostop and Softstream systems. Hydrostop features special discharge ports

and a separator bowl architecture allowing more efﬁcient sludge ejections

at full operating speed; this, in turn, extends desludging intervals and reduces main-

tenance costs. Softstream allows liquids to enter the bowl in a ‘super calm’ state,

thus improving separator efﬁciency, increasing ﬂow rates and reducing component

wear. Typically, says GEA Westfalia, a C-generation separator will reduce sludge

volumes by up to 50 per cent during fuel and lube oil puriﬁcation. The separators

can also be speciﬁed with Unitrol, a self-thinking system for automatically hand-

ling fuel and lube oils of varying quality and density in an unmanned engineroom.

Reﬁnements introduced by Mitsubishi Kakoki Kaisha (MKK) in recent years

have sought improved overall performance and capacity, easier operation and

reduced maintenance from the Japanese designer’s Selfjector Future (SJ-F) series

of separators. More compact and lighter units have also been targeted (Figure 4.6).

MKK’s Hidens system is offered for treating oils with densities of up to 1.01 g/

at 15°C, the installation comprising the separator, an automatic control panel,

water detector, water detector controller and discharge detector. The water content

of the oil is continuously monitored and when a pre-set maximum level is reached,

a total discharge function is automatically actuated. Among the options that can

be speciﬁed is a sludge discharge control system that automatically sets the

most suitable discharge interval based on feedback from an oil inlet sensor con-

tinually measuring sludge concentration in the dirty oil; differences in bunker

quality can also be detected at the ﬁrst stage. A monitoring and diagnostic system

can supervise the operating conditions of up to six separators simultaneously.

A homogenizer may be installed to support the separators and ﬁlters of a

fuel-treatment system. The shearing action breaks down particles in the fuel oil

to sub-micron sizes and ﬁnely distributes any water present as small droplets.

Fuel oil treatment 111

112 Fuels and Lubes: Chemistry and Treatment

A considerable reduction in sludge amounts and improved combustion are

claimed. Some homogenizer systems are designed to produce a stable fuel/

water emulsion with water amounts up to 50 per cent and higher, contributing

to a reduction of NOx emissions in the exhaust gas.

There is some disagreement, however, over the positioning of a homoge-

nizer in the fuel-treatment system (before or after the separator). Alfa Laval

argues that installing such a unit prior to the separator reduces the ability of

the treatment system to remove those particles that can cause damage to the

fuel-injection system and the main engine, and should therefore be avoided.

The role of ﬁltration systems has been strengthened by higher fuel-injection

pressures and the wider use of common rail fuel systems. Solids remaining after

previous treatment stages are removed from the fuel circuit by manual cleaning in

a simplex ﬁlter or by an automatic back-ﬂushing ﬁlter. Common rail fuel systems

call for stricter ﬁltration regimes, typically dictating 5-m ﬁltration to protect

injection components from extensive wear. Such ﬁne ﬁlter elements translate to

either a shorter lifetime or larger ﬁlter sizes, and this must be compensated by

centrifugal separator equipment, which is not dimensioned at the maximum ﬂow

rate to reach its best possible solid removal performance.

gooD bunKeRing pRaCTiCe

Marine fuel oil is the residue after the crude oil has been processed at the reﬁn-

ery to produce diverse high value products such as gasoline, jet fuels, diesel

and petrochemical feedstocks.

FiguRe 4.6 mitsubishi selector sJ-Fh design centrifugal separator

1386

Reﬁneries traditionally created these products by a relatively simple dis-

tillation process. But to satisfy increased demand, additional processes—for

example, thermal and catalytic cracking—were introduced to use residues and

heavier distillates as feedstocks. The volume of the ﬁnal residue available for

bunker fuel was thus reduced, concentrating the impurities remaining.

Between the reﬁnery and the delivery of the bunkers onboard, via any inter-

mediary storage that might be required, are many opportunities for the fuel

to become contaminated: sometimes so badly that it may damage the ship’s

machinery and associated systems. Especially threatening is the presence in the

fuel of catﬁnes resulting from the catalytic cracking stage at the reﬁnery in which

the oil is heated over aluminium silicate catalyst, a substance harder than metal.

Immediate and longer term risks to ship and machinery are associated with

poor fuel quality, including ﬁre and explosion, loss of main engine power and/

or auxiliary power black-out and difﬁculty in fulﬁlling charter party clauses

with regard to ship speed, engine power and speciﬁc fuel consumption.

Little legislation exists to govern bunker fuel, but the parameters of the interna-

tional standard ISO 8217 have been widened in recent years. Since most risk asso-

ciated with bunkers impacts on the ship and owner (even though the fuel is bought

by and belongs to any charterer), the best protection is for all parties to know

exactly what fuel is needed for the vessel, and then to test that the delivered bunkers

meet these requirements. Most problems and disputes can be traced back to either

the ordering or the sampling of the fuel. The traditional way of ordering bunkers

has been by quoting IFO grades, which refer only to viscosity at 50°C, but this can

be technically inaccurate. It is more important in the ﬁrst instance to make sure that

the fuel is suitable for the machinery and fuel system in which it will be used.

The best starting point is the fuel speciﬁcation provided by the enginebuilder.

It makes commercial sense for ship operators to follow a recognized speciﬁca-

tion such as ISO 8217. This will help to secure a charter party and should help to

secure economically priced bunkers worldwide. The charter party clause should

clearly state what fuel is required and may also include other aspects such as seg-

regation, testing and the services of a surveyor for quantity determination. The

charter party clause should also be kept as simple as possible, Lloyd’s Register

recommending the following wording as an example: “Charterer to provide all

fuel oil and diesel required, in accordance with ISO 8217:1987, Grades RM …

and DM …, as updated from time to time”. Ship operators are encouraged to

stipulate that the bunker supplied is ‘ﬁt for its intended use’ on the delivery note.

Among the key parameters of a fuel speciﬁcation are the following:

l A maximum viscosity: this is required to be within the enginebuilder’s

speciﬁed limit; it is also a guide to the storage and handling properties

of the fuel.

l A maximum density or speciﬁc gravity: dictated by the ship’s fuel-

treatment plant.

l A minimum ﬂash point: dictated by safety regulations for the storage of

fuel at sea.

good bunkering practice 113

114 Fuels and Lubes: Chemistry and Treatment

l A maximum pour point: this limits the amount of heating required to

store and handle the fuel.

l A maximum water content.

l A maximum sulphur content: this may be necessary to satisfy regional

environmental regulations but is also desirable to limit the corrosive

products of combustion and to ensure that the lubricants used in the

engine can cope with these products.

Bunker fuel short delivery and quality disputes can be extremely conten-

tious. In the event of a dispute, the conduct of measurement and sampling tech-

niques will usually come under close scrutiny, and it will be necessary for the

ship’s interests to demonstrate that proper procedures were carried out during

the bunkering.

Diligent participation of both ship and supplier during measurement and

sampling is very important in preventing or resolving disputes, and the impor-

tance of maintaining proper records and documentation before, during and

after bunkering cannot be overstated.

It is essential that prior to bunkering, the chief engineer and any attending

surveyor should ﬁrst check the bunker receipt to ensure that the fuel on the

barge complies with that ordered. The tanks of the receiving ship and the bun-

ker barge should then be carefully measured to ascertain the exact quantities on

both vessels. If no surveyor is in attendance, the task should be performed by

either the chief or ﬁrst engineer assisted by an engineroom rating. The engineer

should preferably use his or her own sounding tape, thermometers, hydrom-

eters and temperature/volume correction tables. Water-ﬁnding paste should be

used on the measuring tape or sounding rod to check for free water. If found,

the quantity of free water should be deducted from the volume of ﬂuids in the

tank to arrive at the correct oil volume.

On the receiving vessel, when sufﬁcient empty tanks are available, many

chief engineers prefer to segregate fuels from different stemmings: both to ease

the calculation of the quantity loaded and to eliminate as far as possible any prob-

lems with incompatibilities of fuels produced from different crude feedstocks.

Once the measuring has taken place, the quantity onboard the barge should

be calculated using its calibration tables. As the supply of fuel is often under

customs control, bunker tankers have ofﬁcially approved calibration tables

adorned with various stamps verifying their authenticity. The receiving ship’s

representatives must therefore ensure that the tables offered to them are suita-

bly approved and declined if they are at all suspected. Poor quality, unapproved

tables may be encountered and even cases when no tables are available. If no

tables can be provided, measures should be taken to obtain them. If no tables

can be found, the fuel on the barge should be rejected, even if there is a deliv-

ery meter onboard. The veracity of fuel meters should be regarded as suspect

even when meter correction factors and calibration certiﬁcates are present.

Transfer can commence provided that the quantity in the barge tanks is the

same as that on the bunker delivery receipt. Agreement must be reached on

the rate of delivery and signals for the starting, stopping and slowing down of

delivery. In Japanese ports an interpreter is often provided to liaise between the

supplier and the receiver.

It is now mandatory for vessels to have clearly laid down procedures for

bunkering. This is an extension of US Coastguard directives which required

all tonnage visiting US ports to display diagrams of their fuel loading, transfer

and storage systems. For bunkering, these rules required that a senior engineer

ofﬁcer be nominated as ‘in charge’ and the ranks of his or her assistants to

be given. Before bunkering, a detailed plan was to be prepared showing how

much of each type of oil was to be loaded or transferred, which tanks were to

be used and the anticipated ﬁnishing ullages. A deck ofﬁcer was to be nomi-

nated to maintain the ship’s mooring and other arrangements during bunkering.

All deck scuppers were to be sealed and sawdust or other absorbent material

provided. Receptacles for spilled oil and oil-contaminated sawdust were to be

at hand. Fire extinguishers and hoses were to be deployed nearby and the ﬁre

main was to be pressurized. The method of communication between the vari-

ous participants was to be given, with a back-up mode provided.

After all necessary pollution prevention precautions have been taken, the

valves of the receiving ship’s bunkering lines can be set and delivery started.

When the integrity of the delivery hose and its connection to the ship’s system

has been proven, the rate of delivery can be slowly increased to the agreed level.

If possible, during the delivery, a set of three samples of the fuel should

be taken using a small bore valve ﬁtted to the ship’s loading connection and

retained for any necessary future analysis. Proprietary sampling devices which

can be bolted to the loading ﬂange are available. The best of these has a small

bore pipe directed against the ﬂow, which leads outside to three branches, each

ﬁtted with a valve. It is therefore possible to obtain three continuous drip sam-

ples during loading to give an ‘average’ of the fuel quality.

The bunker barge normally provides samples of the fuel delivered, and the

ofﬁcer in charge of the operation should always attend to observe the samples

being taken and sealed. It is customary for the ship’s representative to sign the

labels for the sample cans. Both barge and receiving vessel then retain samples.

The ship’s samples should be retained for at least 6 months.

When the transfer has been completed and the hose blown through and

disconnected, the tanks of both vessels should be re-measured to enable the

quantity transferred to be calculated. Any discrepancy between the ship and

barge ﬁgures then becomes a matter for negotiation or protest, depending on

the magnitude involved.

Vigilance on the part of personnel at the time of stemming fuel, and during

its subsequent correct storage and centrifuge treatment, is essential in prevent-

ing or mitigating future problems.

On a motor ship, at least two centrifugal separators are usually installed

for removing water and other impurities from fuel. Under normal conditions

only one of these units operates as a separator on a continuous basis. When

it is known, however, that the fuel to be treated contains excessive particulate

good bunkering practice 115

116 Fuels and Lubes: Chemistry and Treatment

matter, two centrifuges can be operated in series. The ﬁrst acts as a separator

to remove water and particulate matter, and the second as a clariﬁer to remove

only particulate matter. In all cases, the throughput of the centrifuges should

be as low as possible to achieve the greatest dwell time in the bowl and hence

maximum separation efﬁciency.

bunker Quality Testing

Onboard test kits are available to allow ship’s staff to carry out a range of tests

during or after bunkering or during storage (if fuel stratiﬁcation is suspected),

for checking puriﬁer or clariﬁer efﬁciency, for determining the cause of exces-

sive sludging at the separators, if water ingress into the fuel is suspected, or

when transferring bunkers to a new tank. The most comprehensive kits can

detect catalytic ﬁnes and the presence of microbes, and test comparative vis-

cosity, compatibility/stability, density, content of insolubles, pour point, salt

water, sludge or wax and water content.

Fuel testing services—such as those offered worldwide by specialist divisions

of Lloyd’s Register, Det Norske Veritas and the American Bureau of Shipping—

offer swift analysis and advice on the handling and use of bunkers based on the

samples supplied. Under ISO 8217, even if a fuel meets all the usual speciﬁca-

tion criteria, it should still not contain harmful chemicals or chemical wastes that

would cause machinery damage or pose a health hazard to personnel.

Any ship operator doubting the need to test bunkers should be reminded

that some 3–5 per cent of stems are critically off-spec. Among the diverse con-

taminants (mixed inadvertently with the fuel) and adulterants (added wilfully)

found over the years have been acids, polypropylene, organic chlorides and

hydrogen sulphite. A number of ships have suffered serious machinery damage

in recent years from contaminated or adulterated fuels, the culprit components

identiﬁed as:

l Petroleum-based solvents, with the potential to destroy lubricant oil

ﬁlm and cause damage to the rubbing parts of fuel pumps and engine

cylinders.

l Organic chlorides, which not only damage machinery but are also haz-

ardous to ship staff.

l Methyl esters, while environmentally safe and friendly, are nevertheless

solvents, which can remove the oil ﬁlm and destroy lubrication between

rubbing parts.

The damage potential is very high. A very high wear rate can be expected

between fuel pump plungers and barrels, and also between piston rings and

cylinder liners. Additionally, the solvents are hazardous to personnel and

exposure, even at low ppm levels, is not recommended. If they are mixed

with bunker fuels there is a real risk of engineroom staff coming into contact

with the solvent fumes, particularly in the puriﬁer room. In the absence of any

method of removing such contaminants from onboard, it is better to ofﬂoad

the bunkers.

Det Norske Veritas cites the case of a fully loaded VLCC which bunkered

3000 tonnes of heavy fuel oil. Shortly after, the tanker suffered main and aux-

iliary engine breakdown and a full black-out in the Malacca Strait, resulting

from sticking fuel pumps and clogged ﬁlters. An investigation revealed: fuel

apparently within the ISO speciﬁcation but quite ‘aggressive’; solvent-like

organic contaminants (detected by sophisticated additional analyses); consider-

able risk potential; and at least 10 other ships affected with severe problems.

The rapid identiﬁcation of the problem prevented major accidents.

In a contaminated marine diesel oil incident, the fuel-injection system

failed due to corrosion, paint was stripped off pumps and engine components,

rubber seals and gaskets dissolved, and crew members suffered skin irritation.

As an example of the potential impact of catalyst ﬁnes on engines, Det

Norske Veritas highlights the case of 2400 tonnes of HFO bunkered in the

Middle East. Catﬁnes in the fuel caused extreme wear on the piston rings, pis-

ton rods and cylinder liners during the subsequent voyage to France. A fuel

analysis showed an Al

Si content of 91 ppm compared with the speciﬁcation

maximum of 80 ppm. The damage to the engine cost US$500 000 to rectify and

the offhire time a similar amount.

The Whole Fuels section includes information from Lloyd’s Register’s

Fuel Oil Bunker Analysis Service (FOBAS), the International Bunker Industry

Association (IBIA), Shell Marine, ExxonMobil Marine Fuels, Tramp Oil,

Salters Maritime Consultants, BP Marine, Alfa Laval, MAN Diesel, DNV

Petroleum Services, Wärtsilä, Chevron and Inﬁneum.

LubRiCaTing oiLs

Signiﬁcantly improved thermal efﬁciency, fuel economy and ability to burn

poor quality bunkers have resulted from the intensive development of low-

speed crosshead and high-/medium-speed trunk piston engine designs in the

past 20 years. Further progress in performance and enhanced lifetimes can be

expected from the exploitation of higher ﬁring pressures and better combustion

characteristics.

Such advances pose a continuing challenge to engine lubricant formula-

tors, however: higher pressures and temperatures make it more difﬁcult to pro-

vide an oil ﬁlm in the critical zones, and longer strokes (another design trend)

lead to spreadability problems. The success of new generations of engines will

therefore continue to depend on the quality of their lubricants.

Lubricants are complex blends of base oils and chemical additives. Base

oils are derived from the reﬁning of speciﬁc crudes, and their properties—such

as stability at high temperature and viscosity—depend on the nature of the

crude and the production process. Additives either improve the basic properties

of oils or underwrite new properties. Marine lubricants exploit many types of

additives:

l Detergent and dispersant additives are used to clean engines. Detergents

are most effective in the hot areas (e.g. pistons) where they destroy

Lubricating oils 117