Manual Alfa Laval

DNVPS / Alfa Laval

Fuel Oil TreatmentPrintedBook No.

Mar 2010EPS002-E-1 V 3

right to make changes at any time without

g possible errors and omissions or ment of this publication would be

n can be ordered from your local

a Laval Tumba AB mpetance Development - 147 80 Tumba eden

Tumba AB 2010.Alfa Laval reserves the prior notice.

Any comments regardinsuggestions for improvegratefully appreciated.

Copies of this publicatioAlfa Laval company.

Published by: AlfCoSESw

Copyright Alfa Laval

Original instructions

Contents

1 Installation ....................................................................... .51.1 Settling Tanks ............................................................ 51.1.1 Settling tank design......................................................... 61.1.2 Recommendations .......................................................... 7

1.2 Pumping system. ....................................................... 81.2.1 Built-on feed pumps. ....................................................... 91.2.2 Separate feed pumps...................................................... 91.2.3 Lubricity and viscosity................................................... 10

1.2.4 Strainer .......................................................................... 111.2.5 Recommendations ........................................................ 111.3 Flow control .............................................................. 121.3.1 The flow control system................................................. 13

1.4 Heating System ....................................................... 151.4.1 Electric heaters.............................................................. 171.4.2 HEATPAC system .......................................................... 181.4.3 Steam installation .......................................................... 19

1.5 Service Tanks........................................................... 201.5.1 Service tank design....................................................... 211.6 Separation system .................................................. 231.6.1 Double fuel tanks........................................................... 24

1.6.2 ULSMDO/GO................................................................. 251.6.3 Primary steps................................................................. 271.6.4 Further steps ................................................................. 281.6.5 Conclusions................................................................... 29

2 Separation ..................................................................... .312.1 Introduction .............................................................. 312.1.1 Separation by gravity .................................................... 31

2.2 Continuous separation .......................................... 322.2.1 How a disc stack centrifuge works ............................... 352.2.2 Disc stack centrifuge sections. ..................................... 362.3 Fuel and lubricating oils ....................................... 402.4 Running the separator........................................... 452.4.1 Conventional separators, Purifier/Clarifier. .................... 452.4.2 Separation results with purifiers .................................... 462.4.3 Cleaning intervals.......................................................... 49

2.5 Basic operation........................................................ 512.5.1 Purifier/ Clarifier limitations ............................................ 532.5.2 How to find the right Gravity disc .................................. 552.6 Operation on off-spec fuel. .................................. 56

2.6.1 Normal operation........................................................... 562.6.2 High density oil .............................................................. 572.6.3 High catfines oil ............................................................. 582.7 Alcap technology .................................................... 59

2.7.1 ALCAP separators ......................................................... 592.7.2 Operating principle........................................................ 602.7.3 Application..................................................................... 61

2.7.4 Design ........................................................................... 612.7.5 Working Principle........................................................... 622.7.6 Transducer WT 200 operating principle in EPC 400 ..... 632.7.7 Transducer MT 50 operating principle in EPC 50 ......... 73

2.7.8 Self adapting system. .................................................... 78

3 Booster system .......................................................... .793.1 Purpose of the system ........................................... 793.2 Applications .............................................................. 793.3 Atmospheric and pressurized ............................. 803.3.1 Introduction.................................................................... 803.4 An atmospheric system ........................................ 813.5 A pressurized booster system ............................ 863.5.1 A standard booster module : ......................................... 903.6 Viscosity of heavy fuel oil .................................... 933.6.1 Viscosity and its effects on diesel engines.................... 94

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 1 INSTALLATION

Suction to separator

n from separator

from service tank

el alarm switch

l alarm switch

eating with P type controller

rain

op transfer pump

From bunker tanks

I00

10

07

21 Installation

1.1 Settling Tanks

Fig 1.1 Settling tank

Oil retur

Overflow

High Lev

Low leve

Steam h

D

Venting from tank

Start/ St

Transfer pump5

1 INSTALLATION DNVPS / ALFA LAVAL FUEL OIL TREATMENT1.1.1 Settling tank design

The main purpose of the settling tank is:

To act as buffer tank

To provide a constant temperature to the separator plant

To settle and drain high-level water and solids contamination

Heavy fuel oil heating is usually provided by steam, hot water or oil, or by electric coils running through the tanks.The heavy fuel oil temperature must be regulated by a temperature controller to minimize temperature fluctuations in the settling tank. This is important in order to maintain a constant separation temperature in the settling tank. The temperature should not be below 40-50C, otherwise, the oil may not be pumpable. However, it must not be higher than 10 C below the flash point, which is normally around 60 C for HFO. Too high a temperature may lead to ageing (thickening during long term storage), carbon deposition on the heating surfaces, and excessive energy consumption.

The settling tank should have a sloping bottom for the collection of water and heavy sludge.

The fuel should be in a still condition and therefore the effect of turbulence in the supply and return pipes should be minimized by directing them against the upper part of the tank wall. Thermal insulation of the settling tanks is useful to avoid thermal losses and will contribute to the stillness by eliminating convection currents.

A sensor may be fitted to give a signal when high water level is reached to secure proper draining of the settling tank.

The separator suction duct should be located close to the bottom of the tank. However, when the ship starts to roll and sludge is stirred up from the bottom of the tank, the separator and the strainer installed in front of the pump can be overloaded. If the tank is well drained, there is less risk of overloading the separator and strainer.6

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 1 INSTALLATIONOften the separator is connected to the fuel suction pipe for the main engine just adjacent to the tank. This pipe has two suction levels, a high and a low. The fuel feed pipe to the main engine from the settling tank is not used except in an emergency. The low suction valve should, however, be open so that the separator can keep the tank bottom clean.

1.1.2 Recommendations

Install level switches in the settling tank connected to bunker feed pump to avoid extensive temperature fluctuations.

Install a P and I temperature controller to minimize temperature fluctuations in the settling tank.

Install a sensor which gives an alarm when high water level is reached in the settling tank.

Clean the settling tank at least once a year. There is continuous separation in the settling tank and the heavy particles, such as cat-fines fall to the bottom. In bad weather these particles can be suspended in the oil again and overload the separator.

Have a sloping bottom in the tank. If there is no sloping bottom heavy particles can accumulate in the tank bottom furthest away from the drain and get mixed into the oil in bad weather.

If there has been an incident with high cat-fines on board we recommend cleaning the tank as soon as possible after the incident.7

1 INSTALLATION DNVPS / ALFA LAVAL FUEL OIL TREATMENT

PI

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01

01

2A1.2 Pumping system.

A strainer should be incorporated in the suction line of the feed pump to remove coarse particles (0.5 to 0.8 mm mesh size). The drawing above has a separate positive displacement feed pump operating at a constant flow rate. The pumps should be installed close to the settling tanks. This is to avoid long suction pipes, which are often the cause of fluctuating flow. An important factor influencing the cleaning efficiency of a centrifugal separator is the feed pump arrangement which, in turn, is directly related to the need for a correct interface position in the purifier.

The interface position in a conventional purifier is dependent on the following external factors:

constant flow rate constant temperature correct gravity disc.The pump arrangement has a direct influence on the first requirement - a constant flow rate.

Fig 1.2 Pumping system

PI8

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 1 INSTALLATION1.2.1 Built-on feed pumps.

In some of the older fuel cleaning systems, the feed pump is mounted on the separator. The separator and its pump are often located far away from the settling tank with the obvious risk of pump cavitation and flow rate fluctuations. A common fault is the built-on pumps usually have far too high capacity. The nominal size may in some cases be three times greater than the flow rate actually needed.The capacity of the pump should not significantly exceed the required flow rate of the cleaning plant. The pump capacity can normally be reduced by changing pump wheels. In some cases the pump itself must be changed. Built-on inlet pumps are always gear type.

1.2.2 Separate feed pumps

In modern systems, the built-on pumps are replaced by separate positive displacement type pumps operating at a constant flow rate. Modern separate screw and gear pumps treat the oil gently, max pump speed 1800 rpm. The feed pump, which must always be placed as close to the oil tank as possible, should be fitted with a built-on relief valve, set for an opening pressure of 600 kPa (6 bar). The recommended flow to a separator varies with viscosity and temperature. As a rule, the flow should be as small as possible to allow the oil being treated to stay as long as possible in the separator bowl, so that maximum cleaning effect is achieved. Controlling the oil flow by throttling the valve before or after the pump is a poor technical solution. This method is unfortunately very common and results in a partly emulsified oil entering the separator and also cavitation problems in the pump. 9


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0A1.2.3 Lubricity and viscosity

If we look at the built on pump it has a minimum viscosity limit of 3 cSt when new. Old worn pumps will have a higher viscosity, which means problems handling the new ULS oil. Another big issue is the lubricity. All the pressure in the pump is taken up by the sleeve bearings. The total bearing surface is small and the low lubricity issue will increase the veer on the sleeve bearings resulting in siezing and non functioning pump. The solution for this is to increase the number of services and change the sleeve bearings more often, or replace the built-on gear pump with a stand alone screw pump, thus rebuilding the separator system.

This will not apply to smaller separators with double gear pumps, pumping in to the separator and out from the separator, for example the MAB separator.

The screw pump does not have the same problems with viscosity. The min. viscosity for the IMO pump is 1.4 cSt, which is well under the average viscosity of ULSMDO/GO oil.

The lubricity issue will of course have an effect on the IMO screw pumps. IMO say that there can be some heightened veer in the pump and especially at the shaft seal that can result in leaking. This is of course not a situation we wish for with the circulation pumps in the booster system.

One solution is to increase the frequency and change the shaft seal more often. Another solution is to change to the new OptiLine, magnetically coupled pumps. These operate without shaft seals and thus do not leak. 10

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 1 INSTALLATION1.2.4 Strainer

To protect the pump from coarse particles, there must be a strainer in front of the pump. The diameter of the holes in the screen should be 0.5-0.8 mm. The strainer free-flow area must be at least 35% of the total filter area. It is a good idea to check that a screen is actually installed.

1.2.5 Recommendations

Fit a correctly-sized pump. Built-on pumps should be replaced by

separate feed pumps installed close to the settling tank, if possible below the suction connection on the tank.

Use a positive displacement type for the separate feed pump. If there is a problem in keeping a constant level in the service tank, suspect leakage in the three-way valve in front of the separator instead of malfunction of the pump.

All the pumps should be able to deliver to all the separators in the system and a flow control system should be installed. in all fuel oil systems, see chapter 1.3 for more info.

NOTE

The return pipe from the three-way valve in front of the separator should lead back to the settling tank, and not to the suction side of the pump. The latter case will lead to operational problems.11


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0C1.3 Flow control

Conventional separators;

For optimum separation results, it is very important that the feed flow to the separator is kept constant. Controlling the flow is very important when treating bad fuel with lots of contamination such as cat-fines. To maintain the highest possible separation efficiency, the flow through the separator then has to be reduced and we also have to make sure the separator bowl is clean. The interface between separated oil and water in the bowl must be kept in the correct position. It should be well outside the disc stack, but inside the edge of the top disc to preserve the water seal and prevent oil escaping through the water outlet. The correct interface position is obtained by fitting the correct size gravity disc matching the density, viscosity and flow rate of the oil under treatment. Pump capacity varies constantly depending on temperature, viscosity and pump net suction height. Maintaining a constant flow rate is the key to consistent optimum separation efficiency and the prevention of oil losses.

Fig 1.3 Constant flow system

PI PI12

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 1 INSTALLATIONALCAP separators;

The same principle applies for the ALCAP separators as for the conventional separators i.e. the more time the oil has in the separator, the higher the separation efficiency. With HFO containing high cat fines, or unstable oil, the recommendation is to lower the flow to increase the efficiency.

1.3.1 The flow control system

Alfa Laval has developed the constant flow regulation system as a complement to the feed pump to ensure a constant feed to mineral oil separators. This equipment ensures the desired constant flow rate by maintaining a constant pressure in the oil feed line. The desired flow rate is set manually by means of a flow regulating valve. Besides helping to maintain the correct interface position, the constant flow regulation system also enables the feed pump capacity to be matched to the desired separator throughput

In principle, there are four ways to control the flow:

Adjustment of the built-in safety valve on the pump. This method is NOT recommended since the built-on valve is nothing but a safety valve. The opening pressure is often too high and its characteristic far from linear. In addition, circulation in the pump may result in oil emulsions and cavitation in the pump.

In our S separator systems we have developed a flow control with a regulating valve and a spring loaded valve set at 2 bars. When the regulating valve is throttled and the pressure overcomes 2 bar the valve opens and oil is then sent back to the settling tank. This is a very cheap and easy way to make a good flow control system.13


Fig 1.4 Heating system

PI PI

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69 A flow control valve arrangement on the pressure side of the pump, such as the Alfa Laval MCFR system. In an alarm condition, the oil should be recirculated back to the settling tank and not fed directly back to the suction side of the pump.

Speed control of the motor with a frequency converter. This is a relatively cheap solution today and can be a good alternative for flow control.

1.4 Heating System

A large proportion of the smaller tonnage does however use electric heaters. It is essential to keep the incoming oil temperature to the separator steady with only a small variation in temperature allowed (maximum 2 C). The position of the interface between oil and water in the separator bowl is a result of the density and the viscosity of the oil which in turn depends on the temperature.

A control circuit including a temperature transmitter, and a PI-type controller with accuracy of 2 C should be installed. The heating system could preferably be controlled from the EPC. One of the most common sources of problems with fuel or lube oil cleaning systems is undersized heaters or heaters that have very poor temperature control. If steam heated, a correctly-sized steam valve should be fitted with the right KvS value. The steam trap should be a mechanical float type. The most common heaters on board are steam heaters. This is due to the fact that steam in most cases is available at low cost. Most ships are equipped with an exhaust boiler utilizing the exhaust gases to generate steam. 14

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 1 INSTALLATIONWhen the optimum gravity disc has been selected corresponding to a given oil, temperature, and flow, any change in the flow and temperature parameters will move the interface. A temperature increase will move the interface into the disc stack resulting in a very poor cleaning efficiency.

The bowl discs will be contaminated and clogged and will have to be cleaned very often. On the other hand, a decrease in temperature will cause a broken water seal. The latter is most common, and to avoid broken water seals the operator often changes to a gravity disc that is too small.

This affects the cleaning efficiency of the separator and it will act more as a pump than a separator. There are several reasons why the temperature does not remain steady after being set correctly:

With the 3-way valve between the heater and separator circulating the oil back to the pump suction side instead of back to the tank, the temperature will fluctuate often more than 10 degrees, thus requiring a smaller gravity disc than the optimum choice. This will happen at each discharge (except separators with feed on during discharge). At each start-up, however, the problem will remain.

A temperature controller with only (P) proportional function cannot cope with temperature changes in the incoming oil. Changes can occur when filling up the settling tank with oil which has a lower temperature or stopping a diesel engine in port.

An undersized or dirty heater is also a problem as the temperature cannot be maintained under all conditions thus requiring frequent changes of gravity discs.

The following requirements must be considered for all types of heaters and are especially important for heaters with high surface loads such as electric heaters. 15

1 INSTALLATION DNVPS / ALFA LAVAL FUEL OIL TREATMENT A turbulent oil flow is required for optimum thermal efficiency and to avoid coking.

No dead zones present where hot spots can occur.

The heater should be designed to prevent short circuiting of the oil flow.

Short retention time in the heater. To prevent blockages caused by coking, the

heater must always be started after the feed pump, and switched off prior to the pump being stopped.

The heating media which can be used in the different basic types of heaters are: Electric power; HEATPAC EHM Steam; HEATPAC SHM, CBM Hot water; Thermal oil; CBM16

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 1 INSTALLATION1.4.1 Electric heaters

Conventional electric heaters for separator preheating are mostly of the same basic design:

a tube stack of heating elements in a pressure vessel together with

an electro-mechanical stepwise on-off regulation, often with manual control.

Pressure vessels are normally quite bulky resulting in a large oil volume in the vessel. A large volume in combination with stepwise regulation of heating power results in either too much or too little power. Outlet oil temperature variations of up to 10 C are not unusual. Another factor that limits the suitability of conventional electric heaters is the uncontrolled laminar flow distribution of oil inside the heater. This results in dead pockets and the consequent obvious risk of fouling and coking of oil on the elements. The above mentioned temperature fluctuation of 10 C means that operators may have to decrease the temperature setpoint to approximately 90 C in order to avoid the boiling of water in the untreated oil before separation. As the optimum separation temperature is 98 C (2 C), this lower setpoint has a direct negative effect on separation efficiency. It was to overcome and eliminate these weak points that Alfa Laval developed the HEATPAC heating system.17


Fig 1.6 EHM electric heater oil flow

A

INFO

OP

ENTER

HEATER

SEPARATION

STOP

DISCHARGE

OP ACTIVE

ALARM

EPC-50

TT

16

MT PT

PT

PT

15 101.4.2 HEATPAC system

.

The HEATPAC EHS 62 system is developed to work with Alfa Laval separation systems. The HEATPAC EHS 62 system consists of a heater vessel, and a heater cabinet controlled by the EPC control system. The heater regulation is stepless working with Triacks controlling two of the three phases in the system. This secures a very exact temperature control and is perfect for separation systems.

The HEATPC system offers the following advantages:

Compact and robust heater with minimal hold-up volume, with few and reliable seals

Specially designed heating elements and shell for high heat transfer

Infinitely variable electronic temperature control

Temperature accuracy 1C Fully automatic operation Easy to retrofit in existing systems Resistance to pressure pulsation

The HEATPAC electric heater comprises a heating element bundle inserted in a pressure vessel. Mineral oil is fed continuously to the heater. A baffle plate inside the vessel divides the flow into two passes. 18


P0

01

15

0B

INFO

OP

ENTER

HEATER

SEPARATION

STOP

DISCHARGE

OP ACTIVE

ALARM

EPC-50

TT

16

MT PT

PT

PT

15 10

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H1.4.3 Steam installation

The steam installation plays a large part in securing trouble-free operation of the steam heater. Operation of the steam heater can be very difficult if the installation is wrong.

Steam trap

Installation

One of the most important parts of the steam installation is the steam trap. We recommend a mechanical steam trap due to the fact that this opens when there is condensate present. Other solutions such as thermo-dynamic steam traps react to temperature and are not suitable for marine installation.

The steam trap should be mounted underneath the heater to make sure there is no condensate accumulation in the heater. Another important aspect is the height from the steam trap to the collecting tank. If this height is over 10m, it can have an effect on the transportation of the condensate. After the heater the pressure on the condensate can be as low as 0,1 bar and if the lifting height is too high, the heater can be filled with condensate.This can result in thermal cracking and internal leakage in the area inside the heater where there is condensate and hot steam.The solution is to mount a condensate pump in the system after the last steam trap.19


settling tank

larm switch

l alarm switch

controller with P type controller

Suction for Booster pumpsSuction for Boliler

in I001

00

711.5 Service Tanks

Fig 1.8 Service tank

Oil from separator

Overflow to

High Level a

Low leve

Steam

Dra

Venting from tank20

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 1 INSTALLATION1.5.1 Service tank design

An overflow pipe should be installed from the service tank to the settling tank. The overflow pipe should be connected to the lower part of the service tank to recirculate any water that may find its way into the oil after the separators, due to condensation, coil leakage, etc. It will also remove any heavy particles collecting in the lower part of the tank. If the overflow is mounted in the top of the tank, all the benevolent lighter fractions in the oil, will return to the settling tank and not the heavy fractions that might need more separation.This feature also helps fulfil the design requirement to have constant flow through the cleaning system at all times. It is not necessary to reduce the flow because of high level in the clean oil tank.

Heating of heavy fuel is usually provided by steam, hot water or thermal oil running through the tanks. The heavy fuel oil temperature must be regulated by a temperature controller to minimize temperature fluctuations in the day tank. Too high a temperature may lead to ageing (thickening during long term storage), carbon deposits on the heating surfaces, and excessive energy consumption.

The fuel should be in a static condition in the service tank and therefore the effect of the supply pipe should be minimized by directing the flow against the upper part of the tank wall. Thermal insulation of the day tank is useful to avoid thermal losses and can contribute to a static condition by eliminating convection currents.The day tank should have a sloping bottom to collect the water and sludge. A sensor should be installed to give a signal when a high water level is reached, to secure proper drainage of the day tank. It is recommended that the clean oil day tank should also be equipped with a draining arrangement at the lowest point.

In a modern ship, regular manual draining of the day tank is considered to be a burden. It is also difficult to judge how much to drain off. 21

1 INSTALLATION DNVPS / ALFA LAVAL FUEL OIL TREATMENTSome operators use a system where the oil in the service tank is separated when the ship is at birth, to make sure the service tank is clean. This is not what Alfa Laval recommends as this will only clean the service tank. For all installations with settling and service tanks this can be solved by the overflow pipe to the settling tank leading from the bottom of the service tank. This makes sure that the most contaminated products are sent back to the settling tank and once more through the separator. A system like this secures that the oil is cleaner in the service tank and in the settling tank, increasing the efficiency of the whole separation system.

NOTE

Our recommendation is to clean the service tank at least once a year, or every time the ship docks. It is also important to clean the tanks if they have contained oil with a high cat fines content.22


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A1.6 Separation system

The low grade of todays HFO makes it necessary to have a pre-treatment system and a separation system in good working in order to obtain an optimum separation result. It also sets high demands on the operators of the separation system. They have to know how to set up the separators according to the fuel quality. The complexity of a system with multiple fuel grades increases the possibility of contamination of high grade fuel with low grade fuel. Strict guidelines for how to handle the different grades of fuel must be made. Mixing a high sulphur fuel with low sulphur fuel can have devastating consequences.

This is a schematic drawing of a common separation system, one settling tank, the separators with the ancillaries and two service tanks. A straightforward system that is fairly easy to operate and in which not much can go wrong. 23


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E1.6.1 Double fuel tanks

This is a schematic drawing of a more complex separation system mainly used for operating on multiple fuel grades.There are two settling tanks, the separator with the ancillarys and two service tanks. When operating on fuels with different sulphur content, it is imperative that the fuels are not mixed. Low sulphur fuel mixed into the high sulphur fuel results in higher cost since the low sulphur fuel is more expensive. High sulphur oil mixed into low sulphur oil is more serious. Very little high sulphur oil is needed to contaminate low sulphur oil since the low sulphur oil is already on the limit from the supplier and the oil is then off spec. Off spec. oil can have severe consequences for the operators, with different penalties in the different ports. Some involve jail for the Chief engineer and captain, others involve high fines (millions of euro). Some even involve both. Make sure to give strict and rigorous instructions on the operation of the system and make sure the operators are educated and able to understand the system and instructions. 24


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E1.6.2 ULSMDO/GO

We now have to handle another type of fuel, ULSMDO/GO and the low sulphur cap and implications if the fuel becomes off spec. demands this is done carefully. Since this type of fuel has to be used for the main engine entering California and at birth in ECA, to date, the small separators usually handling the MGO and MDO fuel are too small and we have to use separators with higher capacities.

We can use one of the existing HFO separators for cleaning the ULSMDO. This creates some handling problems! When changing from HFO, even LSHFO the piping, pumps and heaters are filled with the higher sulphur fuel. Getting this higher sulphur fuel into the ULSMDO, even in small quantities can make the fuel off spec. and cause a lot of problems. This means we have to clean the system by running the ULSMDO into the HFO tank until the system is clean of any higher sulphur oil. The ULSMDO is more unstable and can create compability problems in the HFO! We also introduce more valves and consequently have a more complex system, increasing the possibility for all kinds of handling problems.25


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HIf we going to use an existing separator for ULSMDO separation we recommend to use the standby separator for this purpose. This separator must then be dedicated to the ULSMDO treatment only so as not to cause any problems with the ULSMDO spec.

Make sure to give strict and rigorous instructions on the operation of the system and make sure the operators are educated and able to understand the system and instructions.

Recommendation

Invest in a higher capacity separator to handle the ULSMDO. This will remove all the problems associated with using one of the HFO separators for cleaning. There will be no danger of mixing fuels and ending up with an off spec. fuel. The separator used for MDO/MGO can be a purifier type separator since the density is more stable and we do not need to change the gravity disc that often. 26

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 1 INSTALLATION1.6.3 Primary steps

Settling tank:

Install level switches. Install temperature control. Install a sensor for high water level

Pumps:

Install a suitable flow control device (see chapter 1.2.5).

Check that the return pipe from the three-way valve is led back to the settling tank and is not in front of the pump. If it is in the front of the pump, change it.

Remove the built-on feed pump and install separate feed pump(s).

Never use the internal safety valve on the pump for flow control - it will create lots of problems.

Steam heating system:

Install a P/I temperature control for the steam heater. Preferably use the built in P/I controller in the Alfa Laval EPC control equipment in the separator system.

Check that the steam valve is neither over dimensioned or under dimensioned.

Check that a mechanical float-type steam trap is fitted and in the right position.

Set the temperature set point at 98 C and check that this temperature is reached and remains constant.

Electric heating system:

Install a stepless electronic temperature control system, Preferably the Alfa Laval EPC system.

Establish the temperature set point at 98 C and check that this temperature is reached. Separator inlet temperature should not deviate by more than 2 C.27

1 INSTALLATION DNVPS / ALFA LAVAL FUEL OIL TREATMENTSeparators

Use self-cleaning type separators only. Use the stand-by separator for parallel

operation. Install a separate small separator for DO.

Preferably use ALCAP separators in parallel for best results and lower maintenance time.

Operating water system:

Check the operating water system. If it does not meet the recommendations for the separator, it is strongly suggested that action be taken to meet these recommendations. This is one of the major causes of malfunction of self-cleaning separators. Be aware of growth in old pipes. After a number of years all water pipes have mineral growth inside reducing the pipe diameter and thereby the flow of water. Always check the piping during upgrading to new equipment.

1.6.4 Further steps

Replace the regular electric or steam heater with a complete HEATPAC System.

Set the discharge frequency according to the recommendations and fuel quality.

Check that sludge pipes are vertical, or max. 30 from the vertical without sharp bends, etc.

Check that the sludge tank ventilation is correctly dimensioned and installed, see installation instructions in the service manual for the specific separator.

Be aware that the proper equipment, wrongly installed, not will do the required job!28

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 1 INSTALLATION1.6.5 Conclusions

Experience and future trends indicate that there is an increasing need for efficient and reliable fuel and lube oil treatment on board ships - whether existing operational ships or projected new buildings.

There are numerous factors that must be considered and various actions that can be taken to upgrade existing installations or designs.

Our basic recommendations can be summarized as follows:

Install the best equipment to ensure reliable, efficient operation.

Consider life-cycle costs when specifying new equipment and modifications.

Apply a systems approach to the selection and installation of the equipment. Alfa Laval Separation, with its worldwide marketing and service organization, is at the customers disposal to assist with any level of upgrading of an existing separator installation.29

1 INSTALLATION DNVPS / ALFA LAVAL FUEL OIL TREATMENT30

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATION2 Separation

2.1 IntroductionThe purpose of separation can be:

To free a liquid from solid particles, e.g. sludge in lube oil.

To separate two mutually insoluble liquids with different densities while removing any solids present at the same time, e.g. bunker oil.

To separate and concentrate solid particles from a liquid, e.g. the content in a sludge tank.

In Marine installations, water and solids are removed from fuel oil and lube oil.

In fuel oil, the percentage of water and solids can vary from batch to batch. Whenever you change to another bunker tank, the physical character of the oil may differ. It may be necessary to make some changes to reach optimum separation depending on the separator installation.

2.1.1 Separation by gravity

A liquid mixture in a stationary tank will clear slowly as the heavy particles in the liquid mixture sink to the bottom under the influence of gravity, 1 g.

A lighter liquid (e.g. oil) rises while a heavier liquid (e.g. water) sinks.

Continuous separation of sludge can be achieved in a settling tank with outlets arranged according to the difference in density of the liquids.

Heavier particles in the liquid mixture will settle and form a layer on the tank bottom.To increase the efficiency in the tank we add buffer plates to reduce the distance for the particles to travel and thereby increasing the efficiency.31

2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENT

ig 2.1 Tank with oil, water and solids

ig 2.2 Tank with buffer plates

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06

8B2.2 Continuous separation

Accelerating the process

Virtually all branches of industry need to separate different liquids and solids at some point in their manufacturing processes.

Alfa Laval has well over a century of experience in meeting these requirements using different kinds of centrifuge technology.

The basic centrifuge idea is based on what happens in a settling tank, in which particles, sediment and solids gradually fall to the bottom, and the liquid phases of different density separate due to the force of gravity. However, such clarification is an extremely slow process and is unable to meet industry's needs for rapid, controllable results. The general idea behind centrifuges is therefore to ensure that the mechanical separation of different liquid phases and solids can be carried out on a rapid, continuous basis in order to meet the demands associated with modern industrial processes.

F

In essence, a centrifuge is a settling tank whose base is wrapped around a centre line. Rotating this entire unit rapidly means that the effect of gravity is replaced by a controllable centrifugal force that can have an effect up to 10,000 times greater. This force is then used to separate liquids from other liquids and solids efficiently and with great accuracy, and in a manner that is easy to control

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DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATION

ig 2.3 Rotating bowl

06

8CCentrifugal separation

In fuel oil, the percentage of water and solids can vary from batch to batch. Whenever you change to another bunker tank the physical character of the oil may differ. It may be necessary to make some changes to reach optimum separation depending on the separator installation. See chapter 2.4 Running the separator.

The discs must be kept clean. If the small distances between the discs are reduced due to dirt, the flow speed between the discs will increase and the separation effect will be reduced.

Types of centrifuge

There are several different basic types of centrifuge normally used in industrial separation. Disc stack centrifuges are ideal for a wide range of separation tasks that involve lower concentrations of solids and smaller particle and droplet sizes. This applies to both liquid-liquid and liquid-solid separation. The most difficult separation tasks can often involve three phases, where there is hardly any difference in the densities of the separate liquid phases and where the particles to be separated are very small in size. In such applications, no other technology can compete with disc stack centrifuge technology.

In a rapidly rotating bowl, the force of gravity is replaced by centrifugal force, which can be thousands of times greater. Separation of sludge is continuous and fast. The centrifugal force in the separator bowl can in a few seconds achieve what takes many hours in a tank under the influence of gravity. In the new S-type separators with up to 13000 rpm, the G-force in the bowl can reach up to 7000 G.

In the marine installations water and solids are removed from fuel oil and lube oil.

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2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENTTypical marine separators are;

MAPX; Older type of conventional separator with an MRC (Maximum rated capacity) varying from 900 to 7300 l/h depending on the installation and application. Water outlet is open. Can be used for both lube oil and fuel oil.

MOPX; same as the MAPX with an MRC from 6900 to 21500 l/h.

WHPX: Same as the two earlier mentioned with an MRC from 4700 to 29400 l/h. The WHPX separator can also be rebuilt to an ALCAP machine with a conversion kit.

MMPX; Conventional separator with an MRC varying from 1700 to 2900 l/h depending on the installation and application. Water outlet is open.

FOPX and MFPX ALCAP HFO separators with the water outlet closed. The capacity varies from 850 to 15200 l/h. These separators are only for fuel oil and cannot be used in a lube oil system.

LOPX: ALCAP separators with no water outlet. This means that the water handling capacity is very low and can thereby only be utilised in lube oil systems. The capacity varies from 1800 to 9600 l/h.

MAB; small size separator ideal for diesel oil and smaller fishing vessels

S separators, the newest ALCAP separators in Alfa Laval portfolio. Ideal for HFO, Lube oil and diesel oil cleaning. Applicable for all flow requirements.34

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATION2.2.1 How a disc stack centrifuge works

A disc stack centrifuge separates solids and one or two liquid phases from each other in one single continuous process, using extremely high centrifugal forces. When the denser solids are subjected to such forces, they are forced outwards against the rotating bowl wall, while the less dense liquid phases form concentric inner layers.

The area where these two different liquid phases meet is called the interface position. This can be easily varied in order to ensure that the separation takes place with maximum efficiency.

Inserting special plates (the "disc stack") provides additional surface settling area, which contributes to speeding up the separation process dramatically. It is the particular configuration, shape and design of these plates that make it possible for a disc stack centrifuge to undertake the continuous separation of a wide range of different solids from either one or two liquids. The concentrated solids phase formed by the particles can be removed continuously, intermittently or manually, depending on centrifuge type and the amount of solids involved in the specific application.

The clarified liquid phases overflow close to the rotating axis, in the outlet area on top of the bowl. The liquids then flow into separate chambers. Each separated liquid phase then leaves the bowl due to the force of gravity or by means of a paring disc, which is a special pumping device. The chambers can be sealed off from each other to prevent any risk of cross-contamination.35

2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENT2.2.2 Disc stack centrifuge sections.

Inlet zone

The inlet zone accelerates the process liquid up to the speed of the rotating bowl. A properly designed inlet zone makes sure that the feed solids and liquids are not degraded or affected in any other way. Good inlet design also prevents foaming, reduces the sheer forces in the product, minimizes temperature increases and avoids disturbance of the separation processes taking place in the bowl. A number of different inlet configurations are available for Alfa Laval disc stack centrifuges, each designed to ensure maximum performance in conjunction with a specific process.

Disc stack area

The key to good separation performance lies in the efficiency of the disc stack, which is the heart of the centrifuge. The design of the disc is therefore crucial. Alfa Laval has the expertise needed to match the demands associated with specific industrial processes by providing particular disc stack configurations that ensure a flow evenly spread among the discs, along with an optimized flow pattern in the disc stack itself. The layout and design of the distribution holes also have a crucial influence on good performance. These ensure that the process flow is evenly spread among all the discs, for the most efficient results.

Inside the disc stack.

Inside the disc stack there is two forces working on the particle, flow and G force. The flow is decided by the size of the pump. In a HFO system there can also be a constant flow system; see chapter 1.3. The other force working is G force. The G force inside the bowl is decided by the bowl size and RPM and can reach forces up to 7000 G.36


ig 2.4 Flow between discs

ig 2.5 Particle movement

0,5 - 0,8 mm

I00

10

59

I00

10

67.

It is important that all separator installations are designed for to the oil type used. An installation running on IF 60 needs a different installation than an installation on HFO 380.

If we look inside the disc stack, between the discs, there is a distance of between 0.5 and 0.8 mm, and it is here forces come into play.In this area between the discs we have a flow that creates a parabolic velocity profile i.e. the forces of the flow are higher in the middle between the discs than on the disc surface.If we compare this with a river, you often see the rapid flow in the middle whereas near the banks the water is almost standing still. We utilize this in the separation process. We try to move the particles we need to remove into the area where the flow is at its lowest in the shortest distance possible.

F

This means that the faster we can move the particles up underneath the disc the easier it is to remove them.

When a particle is moved underneath the disc, the G-force vector is higher than the flow vector and the particle will move outwards to the periphery of the bowl (see drawing), collecting in the sludge area.

If you have ever cleaned a disc stack, you will have noticed that there is more dirt under the discs than on top of the discs. This is the reason. If the flow is too high, however, the particles will travel further inside the disc stack and possibly through the disc stack. The oil is then not cleaned properly

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2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENTLiquid discharge section

Once separated, the liquid must often be conveyed out of the centrifuge as delicately as possible. In some applications, it is important that oxygen pick-up is kept to a minimum, and that temperature increases in the liquid must be avoided in order to prevent problems later in the process. Alfa Laval has designed solutions to these and many other detailed requirements, in order to provide our customers with the best possible process conditions for their operations. The most straightforward way of discharging the liquid phases is the use of open outlets. In most applications, however, a positive pressure is needed. This is created by a stationary paring disc with specially designed channels. This disc decelerates the rotating liquid and transforms the kinetic energy into pressure, thus pushing the liquid out of the centrifuge via the channels in the disc. The pressure needed for the particular process is normally regulated by a valve on the outlet.

Solids discharge section

There are three basic ways of removing the solids from disc stack centrifuges

continuous solids discharge, in which solids and liquids exit via nozzles in the periphery

intermittent solids discharge, in which a carefully designed system opens ports in the bowl periphery at controlled intervals in order to remove the collected solids

manual removal, in which the machine is stopped and the bowl is opened so that the collected solids can be removed manually.

The solution most appropriate for a particular application depends on a combination of factors. The most important of these are the amount of solids in the liquid, the nature of the particular application, and the consistency of the solids once they have been separated.38

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATIONSeparator system

Naturally, the overall efficiency of a disc stack centrifuge as part of a production set-up is heavily dependent on many other ancillary systems and equipment.

Unparalleled experience means that Alfa Laval has a unique capability for providing all the necessary equipment to achieve maximum efficiency in the continuous separation of different liquid phases and solids in countless industrial processes.

This can be done on the basis of highly efficient, standardised equipment packages and fully tested modular units, or specially customized disc stack centrifuge installations to meet individual liquid-liquid and liquid-solid separation requirements.39

2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENT2.3 Fuel and lubricating oils

To understand the challenges of cleaning fuel and lubricating oil, one must put into context the different types of oil, their characteristics and contaminants that must be separated from the oils to ensure high performance and long service intervals of marine and diesel engines.

The quality of the fuel and lubricating oils varies widely, depending on the grade and processing of fuel and lubricating oils. Some may contain higher levels of contaminants, such as water and abrasive solids, while others contain lower levels.

Efficient cleaning of all fuel and lubricating oils is essential to achieve reliable and economical operation of diesel engines and other equipment.

Fuel oil

Diesel engines generally burn residual, or heavy fuel oils. For marine installations, fuel is purchased in different locations as the ship sails from port to port. Mixing heavy fuels with highly diverse compositions can lead to incompatibility problems, causing instability.

Such instability problems are particularly severe for heavy fuel oil because of the diverse refining processes used to produce it.

Heavy fuel oil is essentially a refinery by-product. After the most valuable fractions of crude oil have been extracted, the remains are processed further to recover what is known as heavy fuel oil, a cheap source of energy - and one that is not manufactured according to specifications.

The ISO 8217 2005 Fuel Standard specifies a number of physical and chemical limitations for marine fuels, but does not define several critical characteristics that are essential for separation.

Density, or more specifically the difference in density between the water and oil to be separated, is a critical parameter for effective cleaning of fuel oil.40

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATIONBecause it is a residue, heavy fuel oil typically is a high density fraction that contains the heaviest components. In the heaviest types of residual oil, the difference in density is so great that it is impossible to clean the oil using a gravity disc type purifier. This was one of the driving forces behind the development of the ALCAP system.

Catalytic fines;

Catalytic fines are the most harmful of all substances in heavy fuel oil. These are fragments of a catalyst added to the oil to optimize the refining process. Composed of solid particles of aluminium and silicon compounds, catalytic fines are almost as hard as diamonds and vary in size from sub-micron to approximately 50 . If allowed to enter the engine, catalytic fines wear down engine components - sometimes causing considerable damage within a few hours. For more information about catalytic fines and how to separate them from fuel oil, ask your Alfa Laval representative for a copy of "Marine diesel engines, catalytic fines and a new standard to ensure safe operation," (Ref. No. EMD00078EN) written by Alfa Laval, BP Marine and MAN B&W Diesel. There is also a copy of this in the thumb drive presented on this course.

Low sulphur fuel

Environmental considerations have led to the increased use of fuels with low sulphur content. In certain regions known as sulphur emission control areas or SECA the maximum allowable content of sulphur in the fuel is 1.5 percent in HFO. Few heavy fuel oils satisfy this stringent limit without further mixing or processing to remove sulphur, which causes the oil characteristics to change. This processing of oil increases the risk of making the heavy fuel oil incompatible with the heavy fuel oil that has not been de-sulphurize and, for economical reasons, may be burned outside SECA. In addition, low sulphur fuel tends to contain more catalytic fines than ordinary heavy fuel oil, even though low sulphur fuel may have a lower viscosity. See DNVPS presentation for more information41

2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENTDistillate and marine diesel oil

Distillate and marine diesel oils generally are more uniform in nature than heavy fuel oil. The main differences can be attributed to the origin of the oils. Refining processes have less of an impact on the characteristics of marine diesel oil and distillates than on those of heavy fuel oils.

In addition, marine diesel oils and distillates typically do not contain any emulsifying compounds, which can make the separation of heavy fuel oil difficult. Thanks to lower and more consistent densities, distillate and marine diesel oils are considered to be far easier to clean using centrifugal separation than heavy fuel oils.

Lubricating oil

Lubricating oils for diesel engines in ships and power plants are essential for operation. Keeping lubricating oil clean by means of separation helps prevent the accumulation of substances that increase viscosity as well as any solid particles that can cause engine wear and pose the risk of very expensive replacement costs.

In general, there are two basic types of diesel engines that require lubricating oil: the trunk engine and the cross-head engine.

Trunk engines

There are two types of trunk engines, which are also called four-stroke engines:

1. The medium speed engine that runs at between roughly 300 and 600 rpm.

2. The high speed engine that operates at between 600 and 2000 rpm or higher.

The lubricating oil used in trunk engines is prone to contamination from blow-by, which is a leaking gas stream from the combustion chamber to the oil sump that contains remainders of burned fuel and lubricating oil.42

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATIONContaminants that result from blow-by, such as particles of soot and other partly burned hydrocarbons, must therefore be removed from lubricating oil. In addition, calcium sulphate or gypsum forms as a result of the reaction between sulphur in the fuel and the neutralizing calcium-based base number (BN) additives in the lubricating oil, and comprises a major portion of the resulting sludge. The BN additives are important for preventing the formation of sulphuric acid and thus protect against acidic, or cold corrosion.

Cross-head engines

Called long-stroke or two-stroke engines, crosshead engines operate at lower speeds than trunk engines, generally between 90 and 200 rpm. Larger than trunk engines, crosshead engines burn more fuel per stroke, and are capable of producing more power.

System oils in crosshead engines are, however, less susceptible to contamination than those in trunk engines due to the crosshead engine's stuffing box. The stuffing box is a seal that surrounds the piston rod and protects the oil sump from contamination due to leaks from the combustion chamber.

Contaminants in the lubricating oil of crosshead engines are therefore less advanced in composition than those found in the lubricating oil of trunk engines.

Box oil is highly contaminated oil, which is emptied through the drain in the stuffing box. This ensures that box oil does not mix with system oil. Highly alkaline lubricants used between the cylinders and cylinder liners, called cylinder oil, are added separately.

Any leaking oil together with remainders of oil burned during the combustion process is drained as box oil. Water is another contaminant found in engine lubricants.

Water may result from condensate that forms when the engine is not in operation or originate from accidental leaks.43

2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENTBecause lubricating oil contains dispersants and detergents, it easily emulsifies water. More importantly, some BN additives may deteriorate in the presence of water. It is therefore important to keep the water content in the lubricating oil system at the lowest possible level.

An essential application

Separating lubricating oil is a relatively straightforward but essential application, thanks to defined oil density and constant system conditions. Separation is recommended during engine operation. It is also recommended for short periods while the engine is not in operation in order to prevent condensate build-up and the formation of water, which can compromise operation when the engine is put into service.44

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATION2.4 Running the separator.

2.4.1 Conventional separators, Purifier/Clarifier.

Conventional cleaning plants are based on purifier/clarifier type separators. Practical operation has confirmed that the maximum density limit for fuel oil is 991 kg/m3 at 15 C. If this limit is exceeded at bunkering, operational difficulties with the cleaning plant will arise along with the obvious risks for unreliable engine operation or excessive engine wear.

Consequently, the density of available fuel oils can restrict the use of purifier type separators. However, for lighter marine diesel oils and lubricating oils, conventional purifiers are suitable.

The use of conventional purifiers is limited using the gravity disc:

It restricts the use of diesel engine fuels to those with a maximum density of 991 kg/m3 at 15 C.

Optimum separation depends on selecting the correct gravity disc, which corresponds to the prevailing density, viscosity, feed flow rate and temperature.

To ensure satisfactory cleaning a second separator may be required in series. This means a separation system consisting of a purifier followed by a clarifier.45


ig 2.6 Interface in normal position

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63

A2.4.2 Separation results with purifiers

To achieve optimum separation results using conventional purifiers/clarifiers, the interface between the oil and water in the bowl must be located outside the disc stack but inside the top disc. The position of the interface is adjusted by means of a gravity disc. To get the correct interface position the purifier must be fitted with a correctly sized gravity disc.

With higher fuel densities, maintaining optimum separation results by means of gravity discs becomes increasingly difficult. Factors that affect the interface position are - changes in oil density, viscosity, feed flow rate, and temperature. With increasing fuel density, the interface position becomes progressively more sensitive to these factors. This easily leads to a situation where the interface is not in the correct position:

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ig 2.7 Interface outside the top disc

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10

63

CIf the interface moves too far away from the centre, the result is a broken water seal. This means that oil escapes via the water outlet and is lost. This scenario gives a low pressure in oil outlet alarm.

This is caused by one or several of the following:

Gravity disc is too large Density of the oil increases Viscosity of the oil increases Flow rate increases Temperature of the oil decreases Dirty disc stackThis scenario is not dangerous since there is an alarm indication that something is wrong in the bowl. The only way to avoid this is to always have the right gravity disc in the bowl. This means a lot of work for the operator, and that he must have good knowledge of the separator system.

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ig 2.8 Interface into the disc stack

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10

63

BIf the oil density is changed and there are no alarms, or if there are no alarms at all, this is a certain indication that something is wrong.

If you suspect that there is something wrong, carry out the test in chapter 2.5 Basic operation. This is not accurate, but will give an indication. We strongly recommend that the disc size is checked to make sure you have the right gravity disc, follow the description in chapter 2.5.2 How to find the right gravity disc.

If the interface moves too close to the centre, water blocks the upper part of the disc stack, and the lower part of the disc stack become overloaded. This results in poor separation efficiency.

This is caused by one or several of the following:

Gravity disc is too small Density of the oil decreases Viscosity of the oil decreases Flow rate decreases Temperature of the oil increaseThis scenario is the most dangerous since there is no alarm to indicate that something is wrong in the bowl. The separator will keep on going but the oil will not be cleaned.

The only way to avoid this is to always have the right gravity disc in the bowl. This means a lot of work for the operator, and that he must have good knowledge of the separator system.

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DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATION2.4.3 Cleaning intervals

Cleaning the separator at certain intervals is imperative for the high efficiency of the separator. Cleaning intervals are NOT the same as service intervals. Cleaning intervals in the separator depend on the oil passing through the separator. If separating light HFO or gas/diesel oil less cleaning is needed than for HFO.

Determining the right cleaning interval is done by experience; know the system and the contamination in the oil you are separating. We recommend using the CIP unit for the cleaning. This will reduce the veer on the bowl parts and seal rings. It will also reduce the down time on the separator and work force needed so that they can do other work. See the manual for correct procedure to find right cleaning intervals.49

2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENTLimitations common to conventional clarifiers.

Oil losses and limited water handling capability are the basic problems encountered when treating fuel oil of any density in a clarifier. Clarifiers are not to be installed for single stage operation but should always be preceded by a purifier.

Oil losses

When operating a separator in clarifier mode, no displacement water is added prior to sludge discharge. Therefore, not only sludge and separated water are discharged, but a certain volume of oil is also discharged.

Limited water handling capability

For optimum separation efficiency, separated water must not enter the disc stack. The separated water can only be discharged with the sludge through the sludge ports at the bowl periphery since the water outlet is closed in a conventional clarifier. 50

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATION2.5 Basic operation

The conventional purifier is much more labour intense than an ALCAP separator. It is important that the gravity disc on a purifier is the right size all the time. When bunker tanks are changed, the gravity disc has to be controlled. The gravity disc decides the interface between water and oil and has to be in a certain position, see chapter 2.4.2 for more information.

One of the most common mistakes made is to fit the clarifier disc in the separator because then there are no alarms for broken water seal. This will only change the separator into a pump with no separation effect on the oil, and the operator will have no control over the process.

To check if the interface is in the right position on a purifier, slowly close the counter pressure valve until water and eventually oil come out of the water outlet. If the oil is coming out very fast in the water outlet the interface is most likely in the right position. If the oil comes after a high pressure increase or not at all, the gravity disc is most likely too small. This is not an exact test method. The only way to be sure if the gravity disc is correct is to increase the size until the water seal breaks, and then reduce size by one, see chapter 2.5.2 for more information.

The most important issue is to keep the bowl clean at all times, especially the disc stack. The intervals between cleaning can vary from fuel batch to fuel batch. There is great variation in the oil and some fuels can be almost impossible to treat. See DNVPS documentation for further information.

In a purifier system the temperature of the oil is very important. If the temperature changes the interface will also change, and if the interface is moved too much, the water seal will break or be moved into the disc stack. The temperature is also important for the efficiency, so securing a stable temperature is one of the most important parameters in the separation process. Make sure that the heater system is in perfect operating order and use a P/ I control type, preferably the EPC controller in the separator system, to prevent alarms from temperature variations. 51

2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENTIf the separator is in clarifier mode, operated in series with a purifier, the same rules for cleanliness apply. However there is no water seal and temperature is not that important since there is no interface to consider. It is still important that conditioning water is added after a discharge to keep the sludge in a liquid state.52

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATION2.5.1 Purifier/ Clarifier limitations

All conventional separators after 1985 have a density limit at 991 kg/m.

In lubricating oil cleaning systems a clarifier type separator may not be used for the following reason:

Calcium sulphate is a product of neutralizing sulphuric acid when it forms in the engine. The acid, of course, arises through the burning of fuel that contains sulphur. Some of the sulphur is converted to sulphuric acid. Most marine engine lubricants are over-based, meaning that they contain calcium carbonate, which is a base. The reaction of calcium carbonate with sulphuric acid results in calcium sulphate, water and carbon dioxide. Gypsum is a hydrated form of calcium sulphate, CaSO4*2H2O, and there is usually a fair amount of water in the oil.

This gypsum will dry out due to the lack of water in a clarifier (no water seal, therefore no water is added into the bowl at start-up) and will subsequently create a risk of only partial removal of sludge during a sludge discharge sequence.

If only a part of the sludge cake is discharged, the remainder of the sludge in the bowl may be distributed unevenly and the result will be a severe unbalance of the bowl - a heavy side unbalance.

This can lead to severe damage to the separator and to injury of personnel operating the separator.

As for the LOPX or S type separators, which are basically clarifiers, this risk is eliminated by the introduction of conditioning water into the bowl.

NOTE

Separators from before 1985 have a density limit at 985 kg/m. This is important to know when you order fuel as otherwise the separator might not be able to handle the oil.53

2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENTConditioning water is fed into the bowl prior to the opening of the oil feed valves. This water will create a thin layer in the bowl periphery and all the sludge removed from the oil will have to pass through this water layer, where it will absorb a little water and thus obtain a soft consistency. It will not dry out and there will be no risk of gypsum formation and heavy side unbalance. 54


3 4 5 6

Max.45,8

48,747,3

50,151,553,3

55,5

58,2

61,6

65,8

70,9

77

Q m3/h

O (mm)I0

01

06

52.5.2 How to find the right Gravity disc

As an aid, use the nomogram to find the correct gravity disc. It can be used when the density of the oil at a temperature of 15 C is known. However, note that the nomogram is purely theoretical. In practical operation, practice the following general rule:

Fit a gravity disc one size larger than the recommended in the nomogram.

Run the separator. Observe if oil flows through the water outlet. If Yes, stop the separator and fit the gravity

disc next size down.

If No, stop the separator and fit the gravity disc next size up.

Repeat steps above until you find the gravity disc with the largest hole diameter without breaking the water seal. Now you have the right gravity disc for this oil.

Fig 2.9 Nomogram

0,75

0,80

0,85

0,90

0,95

1,00

0 1 2

60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 212

CooF

800

850

900

950

991

1000

I

II

kg/m3

20 30 40 50 60 70 80 90 100

T

D55

2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENT2.6 Operation on off-spec fuel.

2.6.1 Normal operation

The illustration shows the normal way to run conventional separators.

If we follow the oil flow in this system (in blue) we can see that the oil first enters the purifier, then the clarifier, then is led to the service tank. Operating in this way means the same oil is going through two separators before going to the service tank. Both separators are discharging meaning we have higher sludge production per litre oil cleaned through separators working in series than working in parallel.

We will also consume more electricity and thereby more fuel via aux engines hence more expensive operation. It also means more labour and more down time on the system, since you cannot run one of the separators and stop the other.56


CLARIFIERLARIFIER2.6.2 High density oil

If we have to treat oil with higher density than the separator limit, we can use the separators as clarifiers in parallel. This means changing the gravity disc to clarifier disc and splitting the flow through two separators.

This can only be done if the water level in the oil is very low, since the clarifier has low water handling capacity and only removes water through discharge. The discharge time has to be set to 10 min to make sure that any water in the bowl is removed.

C57


PURIFIERPURIFIER2.6.3 High catfines oil

If we have HFO with high contamination of cat fines we can set up the separators to maximise the efficiency of the separation. We split the flow through two separators to reduce the flow and increase the time for the oil in the separators. We should reduce the flow to consumption and if the oil is heavily contaminated maybe less. The first thing we should do is to make sure that the separator bowl is clean so that the separating conditions are as good as possible. Make sure that the gravity disc installed is the correct one for the oil so that the interface is as far away from the disc stack as possible.58

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATION2.7 Alcap technology

2.7.1 ALCAP separators

The ALCAP separator is much less labour intense than the conventional separators. There is no gravity disc and thereby no water seal to consider. This makes the separator much less dependent on oil and temperature changes. There is no need to check the separator after changing bunker tanks in regards to oil density. The temperature is still important due to the impact on the separation efficiency.

In an ALCAP system one of the benefits is the continuous monitoring of the cleaned oil. This means that changes in the oil/water content are detected in the system, and when the alarm is given there is most likely something wrong in the system. We have found many times that the alarms are reset without any action from the operator and the same alarm repeats itself. When there is an alarm, make sure to check what the alarm means and act accordingly. It is important that the operators are educated to a level where they are familiar with the separator and system functions and limitations.

The most important issue is still to keep the bowl clean at all times, especially the disc stack. The intervals between cleaning can vary from fuel batch to fuel batch and will vary from installation to installation, see recommendations in the service manual. There is great variation in the oil and some fuels can be almost impossible to treat, see DNVPS documentation.

On the LOPX and FOPX separators we have what is known as partial discharge. We only discharge a small part of the bowl content - the sludge area, with the flow on. On the S-type separators we discharge the whole bowl content with the flow off, after replacing the oil with water. This keeps the disc stack cleaner.

There are many advantages with the ALCAP system and our recommendation is to upgrade to the ALCAP system to secure the best possible oil quality and the lowest possible labour. 59

2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENT2.7.2 Operating principle

In 1983, Alfa Laval introduced the ALCAP technology in response to the need for a reliable method to separate impurities from the heaviest fuel oils with densities above the maximum density limit for fuel oil handled by conventional purifiers.

Conventional purifiers handle fuel oil densities of up to 991 kg/m3 at 15 C and require manual adjustment of the gravity disc to achieve optimum separation results.

Computer-driven Alcap separators handle fuel oil densities of up to 1010 kg/m3 at 15 C, automatically adjusting operation to the nature of the oil. This section describes the fuel and lubricating oil cleaning process using ALCAP separators.

Dirty, pre-heated oil is continuously fed to the ALCAP separator, which essentially operates as a clarifier, with the ability to remove water. Clean oil is continuously discharged from the clean oil outlet. Separated sludge and water accumulate at the periphery of the bowl. When separated water approaches the disc stack, traces of water start to escape with the cleaned oil. This minor increase in water content of the cleaned oil is detected by the transducer WT 200, which is installed in the clean oil outlet. Increased water content in the cleaned oil is a sign of reduced separation efficiency not only of water, but of solid particles too. The transducer continuously measures changes in water content. No absolute values of water content or volume are involved. The transducer measures the deviation from a non-calibrated reference value and transmits a signal to the EPC process controller for interpretation. Measurements that fall within the permissible deviation values are known as the trigger range. The EPC process controller stores a new reference value after the transducer stabilizing time that follows every sludge discharge sequence has elapsed.60


ig 2.10 Water transducer

Test circuit boardTransducer housingInsulatorsElectrode

I00

10

50

D

14

33

2During the reference time the best possible separation result is obtained. This gives the separator time to establish the interface between oil and water. At the trigger point, which is when the water content in cleaned oil reaches its maximum allowable deviation of approximately 0.2 percent in water content, the EPC process controller initiates an automatic discharge of the water that has accumulated in the separator bowl. Depending on the amount of water in the oil, water is discharged either through the water drain valve, or with the sludge through the sludge ports at the periphery of the bowl.

2.7.3 Application

The WT 200/MT 50 water transducer is used to monitor the water content in the processed oil leaving a separator. The signal from the water transducer is processed in the EPC program unit, and appropriate action is initiated, depending on the status in the separation system.

2.7.4 Design

The water transducer consists of a housing (2), a concentric electrode (4), and an electrical connection box fitted to the housing. The box contains a test circuit board (1) and connections. The electrode is insulated (3) from the housing and forms a circular capacitor. The transducer is mounted in the oil pipe by flanges on the outer pipe, and the full oil flow passes through the capacitor.

F

123461

2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENT2.7.5 Working Principle

The EPC supplies direct current (DC) to the transducer. The oscillator converts the DC to a high frequency alternating current (AC) which is fed to the capacitor. Changes of capacitance are detected and continuously transmitted to and interpreted by the EPC.

The capacitance varies with the dielectric constant of the liquid flowing through it. As the water content in the oil increases, so does the dielectric constant, and consequently its capacitance.

There is a large difference between the dielectric constant of water and oil. Hence fluctuations in dielectric constant is a very sensitive measure of changes in water content. Both free and emulsified water contamination are measured.

Dielectric constant

(Approximate values)

Mineral oil: 2 6

Water: 90 9562

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATION2.7.6 Transducer WT 200 operating principle in EPC 400

Fuel oil system.

Dirty oil is continuously fed to the FOPX/MFPX separator. The flow of oil is not interrupted when sludge and/or water is discharged.

The FOPX/MFPX separator basically operates as a clarifier. Clean oil is continuously discharged from the clean oil outlet. Separated sludge and water accumulate at the periphery of the bowl.

When separated water approaches the disc stack, some droplets of water start to escape with the cleaned oil. The small increase of the water content in the cleaned oil is then immediately sensed by the water transducer, installed in the clean oil outlet. Increased water content in the cleaned oil is the significant sign of reduced separation efficiency of not only water but solid particles too.

The signal from the water transducer is continuously transmitted to and interpreted by the EPC-400 control unit. Note that only changes in water content are measured, no absolute values of water content are involved. It is the deviation of the water transducer signal from a non-calibrated reference value that is measured. The allowed deviation range is the trigger range.

A new reference value is stored by the EPC-400 control unit during the reference time that follows every sludge discharge sequence, see Fig. 2.11.63


Ref. time

Dis

char

ge s

eque

nce.

Fee

d O

n

0,2% increace in dialectic value

Min

Sep

arat

ion

perio

d.

Separation period

I00

10

61During the reference time the best possible separation result is obtained. The trigger point is reached when the water transducer signal has reached its maximum allowable deviation. This is when the water content deviation equals about 0.2%.

When the water content in the cleaned oil reaches the trigger point, 100% on the Trigger range, the EPC-400 unit will initiate an automatic discharge of the water that has accumulated in the FOPX/MFPX bowl. The water is discharged in one of two ways:

with the sludge through the sludge ports at the periphery of the bowl

or through the water drain valve

When the separated water approaches the disc stack within a preset minimum time between sludge discharges set to 10 minutes, the water transducer signal triggers the EPC-400 unit to open the water drain valve, V5, to drain accumulated water from the FOPX/MFPX bowl, see Fig.2.12.

Fig 2.11 EPC 400 trigger range

100%

Separation periodRef. Time

Transducer value

Trigger rangeM

in S

epar

atio

n pe

riod.64


n period

d

P0

01

06

0A

d

I00

10

60

BThis may occur several times within the minimum time between sludge discharges, see Fig. 2.3

When the separated water reaches the disc stack after this minimum time has elapsed, the water transducer signal triggers the EPC-400 unit to initiate a sludge discharge sequence, thus discharging the accumulated water together with the sludge and solid particles. See Fig. 2.14.

Fig 2.12 Trigger during pre-set separation period

Fig 2.13 Several triggering during pre-set separatio

V5 closing

100%

Ref. time Separation perioMin Sep. period

Stored reference

Trigger pointV5 opening

V5 closing

100%

Ref. time Separation perioMin Sep. period

Trigger pointV5 opening

Stored reference 65


ge

P0

01

06

0CIf the water content of the dirty oil is extremely low, the separated water will not reach the disc stack within the preset maximum time between sludge discharges. A sludge discharge sequence will therefore be initiated by a timer in the EPC-400 unit to prevent excessive sludge build-up in the FOPX/MFPX bowl, see Fig. 2.11.

In the case of very low free water content in the dirty oil, water addition to the FOPX/MFPX bowl takes place automatically. Bunkered oils normally contain sufficient free water to displace the oil prior to sludge discharge. Water addition is therefore only necessary when treating dry oils to minimize oil losses and benefit sludge condition.

The EPC-400 software decides whether or not the oil feed contains sufficient separable water to fill the sludge space in the separator bowl. When insufficient separable water is present, water addition is performed.

In the case of Fig. 2.11, the trigger point is never reached within the preset maximum time between sludge discharges. This tells the EPC-400 that the oil does not contain any separable water.

Fig 2.14 Trigger in adjustable period

100%

Ref. time

Trigger point

Separation periodMin Separation

Sludgedischar66

DNVPS / ALFA LAVAL FUEL OIL TREATMENT 2 SEPARATIONAt the time when the sludge discharge sequence starts, some displacement water is therefore added to bring the transducer value up to the trigger point, thus triggering a sludge discharge. Conditioning water is then added to condition the sludge that will accumulate.

With oils containing more water, as in Figs. 2.12 and 2.13, the fact that the water drain valve has operated at least once within the minimum time between sludge discharges is stored in the EPC-400 memory. Therefore no conditioning water need be added after the next sludge discharge as there is enough water in the oil for the purpose. Also, when a sludge discharge occurs initiated by the water transducer value reaching the trigger point, no displacement water is needed.

The dielectric constant of oil contaminated with water increases when the water content of the oil increases and vice versa. Thus, change in dielectric constant of the cleaned oil is a very sensitive and convenient measure of change in water content of the oil.67

2 SEPARATION DNVPS / ALFA LAVAL FUEL OIL TREATMENTLube oil system.

Dirty oil is continuously fed to the LOPX separator. The flow of oil is not interrupted when sludge and/or water is discharged. Clean oil is continuously discharged from the clean oil outlet. Separated sludge and water accumulate at the periphery of the bowl. When the separated water approaches the disc stack, some droplets of water start to escape with the cleaned oil. This small increase of water content in the cleaned oil is immediately sensed by the water transducer, installed in the clean oil outlet.

Increased water content in the cleaned oil is the most significant sign of reduced separation efficiency and that insufficiently cleaned oil leaves the separator.

The signal from the water transducer is continuously transmitted to the EPC-400 control unit and interpreted as an amount of water in the lube oil sludge. A reference value from this signal is stored in the EPC-400 after each discharge.

Normal condition, low water content in the oil

A new reference value is stored by the EPC-400 control unit during the reference time that follows every sludge discharge sequence, see fig. 2.11. During this time the best possible separation result is obtained, because the interface is correctly placed outside the disc stack. The signal condition from the water transducer illustrated below reflects a normal condition, i.e. no water contamination is present in the oil. The max. time between sludge discharges is set in the EPC-400 control unit as a timer function. 68


10

Ref. time Min separation period

0,2% increace in dialectic

Discharge30% increace in trigger range

I00

10

64

AOnce conditioning water is added to the separator bowl the reference value is stored. Conditioning/ displacement water is added in a number of pulses. There will always be water in the bowl to soften the sludge in order to accomplish a good discharge. When the max. time between sludge discharges has elapsed, displacement water is added to the separator bowl prior to the sludge discharge. Initially, water is continuously admitted. Then, a number of short pulses add a minor amount of water, to eliminate the

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