Fuel oil (bunker) blending An overview - Fuel Oil (bunker...The blending of Heavy Fuel Oil (HFO)...

Fuel oil (bunker) blending An overview - Fuel Oil (bunker...The blending of Heavy Fuel Oil (HFO) with Gas Oil or Marine Diesel Oil (MDO) to produce a range of intermediate fuel oils
Fuel oil (bunker) blending An overview - Fuel Oil (bunker...The blending of Heavy Fuel Oil (HFO) with Gas Oil or Marine Diesel Oil (MDO) to produce a range of intermediate fuel oils
Fuel oil (bunker) blending An overview - Fuel Oil (bunker...The blending of Heavy Fuel Oil (HFO) with Gas Oil or Marine Diesel Oil (MDO) to produce a range of intermediate fuel oils
Fuel oil (bunker) blending An overview - Fuel Oil (bunker...The blending of Heavy Fuel Oil (HFO) with Gas Oil or Marine Diesel Oil (MDO) to produce a range of intermediate fuel oils
download Fuel oil (bunker) blending An overview - Fuel Oil (bunker...The blending of Heavy Fuel Oil (HFO) with Gas Oil or Marine Diesel Oil (MDO) to produce a range of intermediate fuel oils

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Transcript of Fuel oil (bunker) blending An overview - Fuel Oil (bunker...The blending of Heavy Fuel Oil (HFO)...

  • The blending of Heavy Fuel Oil (HFO) with Gas Oil orMarine Diesel Oil (MDO) to produce a range ofintermediate fuel oils of specified viscosity for marinebunkers is one of the major skills of the bunkersupplier. The ability to accurately blend to a pre-determined viscosity and deliver precise meteredvolumes can provide an operator with a competitiveedge in this very commercial market.

    Blending is not new to the bunker industry; indeedbatch blending in one form or another has beenpractised for several decades. There are twofundamental forms of blending; batch/sparge and in-line.

    Batch Blending

    This takes one of two main forms. In both cases thetwo base components HFO and MDO are addedtogether sequentially into a tank that is thenmechanically mixed to provide a homogenousproduct. The difference in sparge blending is that the

    blend in the tank is recycled. The oil re-enters thetank via a sloping tube with holes cut in it toenhance the dispersion effect. This method improvestotal homogenisation of the fuel and allowsrepresentative samples to be taken from the recyclepipework for analysis.

    The drawback with both these methods is the timedelay to fully mix the components. On occasions thiscan sometimes take as long as 1 hour. After this asample frequently has to be extracted and taken foranalysis which incurs a further delay. In additionbatch blending is only really practical as a shorebased system. The bunkering barge therefore canonly carry pre-blended grades of fuel; althoughsparge mixing can be performed on the bunkeringbarge. The accuracy of the blend is totally reliant onthe accuracy to specification of both base oils, andthe equipment performing the sequential metering.In some cases the volumes to be added arecalculated by tank level of the base oils. Batchblending however is still a viable method wheremarket demand is small and /or intermittent.

    In-line blending

    By definition, in-line blending is "the continuousproportioning of two or more components in orderto produce a final product of closely defined quality".

    In the early days this was performed using amechanical blender to ratio two streams. Its basicoperation was very simple and utilised two valves(one for each component), sharing a commondiaphragm actuator.

    J ISKOOT QUALITY SYSTEMS

    M E A S U R E M E N T S Y S T E M S

    TECHNICAL PAPER TB009-1204-4

    Fuel oil (bunker) blendingAn overview

    Jiskoot Limited

    Typical batch blending system

    Component tank farm

    Blendtank

    Mixingloop Blended product

  • One valve was opened the second valve wasproportionally closed, thus achieving the ratiobetween the components. Adjustment of the ratiowas by means of a handwheel on the metering valve.

    However because of the competitiveness of thebunkering market and the need for tighterspecification, there are strong indications that thetrend is now moving towards in-line blenderscontrolled by microprocessor based blend controllers.

    The basic principle of operation of these blenders isthat the flow in each component line is measured bymeans of a flowmeter, and controlled (regulated) bymeans of either a control valve, or by varying theoutput from a positive displacement pump. Themeter may be a positive displacement type fittedwith a pulse transmitter, vortex or "coriolis" massmeter. The control system generates the demandflowrate for each component stream. This is fed tothe PID algorithm of each stream as a set point andcompared to the measured flow from the streamflowmeter. Any deviation between the set point andthe measured flowrate is stored in memory and anappropriate adjustment is made automatically to thecontrol valve in that stream. Thus opening or closingthe valve to increase or decrease the component flowto bring this back to the required stream flowrate.

    If there is starvation of flow in the metering stream,the control valve will open to compensate. Howeverif it reaches a point at which it can no longerproperly control, a cut-back (pacing) signal is sent tothe control system to reduce the master demand rateto equal the maximum flowrate at which the laggingcomponent can maintain correct ratio and accuracy.Most blending systems, particularly those in thepetrochemical industries, operate this way andproduce very good results. This type of system alsolends itself to skid or trailer mounting, enabling it tobe towed around a harbour/terminal or mounted onthe deck of a bunkering barge.

    The use of microprocessor based controllers enablesseveral advanced features and facilities to beprovided. For example a number of predeterminedrecipes can be stored, the operator then only calls upa recipe by name or number and the controller setscorrect ratios. Temperature compensation can beperformed electronically using the signal from aresistance bulb or temperature transmitter to correctmeasured volumes to a base temperature. The blendcontrollers also provide the facility to drive a printerto and communicate with another computer system

    over an RS232 or 422 serial link using Allen Bradleyor Modicon Modbus protocols.

    As the systems are digital and closed-loop, theaccuracy of the electronics should be 1 pulse forthe flow signal, and analogue conversion fortemperature is around 1 part in 8000 for the 4-20mArange. The control system accuracy therefore is asgood as the accuracy of the field equipment. Theaccuracy of the whole system will depend entirely onthe accuracy of the flow meter used.

    This means, therefore, that you can volumetricallyblend components to within 0.5% ofinstantaneous flow rate. Alternatively blending canbe performed on a mass basis. It follows that if oneknows the quality parameters of the basecomponents, one can produce a very good finalproduct within very close quality parameters.

    Analyser feedback and trim

    There are occasions were the quality of the basecomponents of a blend may vary and yet it is stillrequired to produce a final product to close viscosity

    M E A S U R E M E N T S Y S T E M S

    Typical In-line blending system

    Component tank farm

    Blend controller

    Blendedproduct

  • M E A S U R E M E N T S Y S T E M S

    tolerances. The solution is quite simple really, adensity or viscosity analyser can be installed in thefinal blend header and the analyser signal allowed alimited freedom to reset the volumetric ratio setting.It is usual to allow only a small drift in qualityadjustment before raising an alarm, thus preventingthe analyser controls from trying to trim for anincorrect base oil. This practice of "analyserfeedback" is now a regular occurrence in manymulti-stream applications.

    In-line blending has several important advantages,both technical and economic, over the moretraditional batch blending techniques.

    Reduction in production timeNo in tank mixing required

    Reduction in give-away Higher blend accuracy and continuous meteringof all streams provides better quality control andless wastage of expensive components. Savingscan be achieved even with a relatively low annualthroughput.

    Improvement in qualityVolumetric accuracy's of < + 0.5% can be easilyobtained with in-line blenders, and theincorporation of an output analyser trimguarantees that the final product is of a highlyuniform quality.

    Improved production flexibility Changes in schedules and clients' requirementscan be accommodated simply by the selection ofa different recipe from the controller. Thesupplier can provide a wide range of products invarying batch sizes from two base stocks.

    Reduced operating costOnce the blender has been started the process isself supervisory, and can produce the finalproduct and billing, totally unsupervised, onlyinforming an operator if an alarm conditionoccurs.

    Reduced tankage requirementsThere is no need to hold any stocks of blendedproduct. (capital lockup), as the In-line blenderproduces the final product almost simultaneously.

    Typical mobile blenders

  • M E A S U R E M E N T S Y S T E M S

    TB-009-1204-4 Copyright 2011 Cameron International Corp. All Rights Reserved.

    Blending chart

    SEC

    Cst.

    B

    Diesel oilHeavy oil

    Vis

    cosi

    ty(S

    EC R

    edw

    ood

    No.

    1)

    Hea

    vy f

    uel

    B

    Hea

    vy f

    uel

    spe

    cial

    B

    Hea

    vy f

    uel

    C

    Die

    sel f

    uel

    Blending ratio (%)

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