ger 3481c liquid fuel treatment systems

8/19/2019 Ger 3481c Liquid Fuel Treatment Systems

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GE Pow er Generation

Liquid Fuel Treatment Systems

Howard J . Kaplan Technical Leader, Fluid Systems Engineering

Kenneth E. MajchrzakPrincipal Engineer, Power Plant Engineering

GE Power SystemsGE CompanySchenectady, NY

GER-348


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GER-348

GE Pow er Generation

Liquid Fuel Treatment Systems

Howard J . Kaplan Technical Leader, Fluid Systems Engineering

Kenneth E. MajchrzakPrincipal Engineer, Power Plant Engineering

GE Power SystemsGE Company

Schenectady, NY


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Howard J. Kaplan

Howard Kaplan is Technical Leader of Gas Turbine Power PlantFluid Systems. He has over 25 years’ experience in design and develop-ment of gas turbine auxiliary systems, serving three years as principalengineer fo r fuels-related systems. Current responsibilities include fueloil, fuel gas, fuel purge, Dry Low NOx, atomizing air, water injection andlube oil.

Kenneth E. Majchrzak

Kenneth E. Majchrzak is a Principal Mechanical Engineer in the

Power Plant Engineering Department. He is Technical Leader for thedepartment on fuel systems, power plant pumps, and provides primarysupport for HRSGs. Ken joined GE in 1982 as Manager – CompressorApplication Engineering in Fitchburg, Massachusetts. He has nearly 25years’ experience with rotating equipment in the areas of applicationand systems design for a ircraft gas turbines, process centrifugal compres-sors, rad ial inflow steam turbines and pumps.

A l ists of figures and tables appears at the end of this paper


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INTRODUCTIONGE heavy-duty gas turbines are capable of bur n-

ing a variety of liquid fuels, from petroleum naph -thas to residuals. These fuels vary substantially inhydrocarbon composition, physical properties,and levels of contaminants. Operation with ash-forming fuels such as crude and residual oilsrequires special measures to prevent high -temper-ature corrosion and contend with ash fouling inthe turbine section. More than three decades ago,GE initiated a major program to develop a totallyintegrated system for economically utilizing ash-

forming fuels. This paper will highlight the resultsof that effort by describing liquid fuel characteris-tics, methods of treatment, system design consid-erations, and G E experience.

LIQUID FUEL PROPERTIESLiquid petroleum fuels fall into two basic classi-

fications; true distillates and ash-forming oils.True distillate oils are most frequently the lighteroils such as naphtha, kerosene, and No. 2 distillateoil. This class of fuel is clean burning and behavesin a manner similar to natural gas in the internal

portions of the gas turbine.Ash-forming oils are n ormally the heavier oils,

such as blends, crude, and residual oils. Since theyusually contain trace metal contaminants, fueltreatment is required to remove or modify theeffects of harmful constituents prior to combus-tion in the ga s turbine.

The degree of the fuel treatment equipmentsophistication, plant equipment investment, andoperating costs required for this equipment aretied directly to key physical and chemical proper-ties of the fuel. Physically, the parameters of inter-est include specific gravity, viscosity, flash point,pour point, and wax content. Chemically, theprime interests are the amounts of corrosive tracemetals present, the overall fuel washability, andthe compatibility of one fuel with another. The lat-ter is particularly significant for users who obtainfuel from multiple sources.

Trace Metals

Trace metal contaminants of concern includesodium, potassium, calcium, lead, vanadium, andmagnesium. At elevated temperatures, vanadium,sodium, potassium, and lead are corrosive to theturbine buckets, particularly when present inamounts above specification limits. All of thesemateria ls , p lus ca lc ium, can a lso form harddeposits which are difficult to remove with a nor-mal turbine wash system. These deposits can causeplugging and reduced output.

Table 1 lists the trace metals of interest, their

effect on the turbine, and the means of treatmentto reduce harmful effects, along with GE’s typicalpermissible limits. Dealing with these metal con-taminants will be discussed in the Fuel Treatmentsection of th is paper.

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LIQUID FUEL TREATMENT SYSTEMSH. J. Kaplan and K. E. Majchrzak

GE Power SystemsSchenectady, NY

Table 1TRACE METAL EFFECTS

Trace Metal Limits in Effect on Turbine Type of Treatment Limits in FuelRaw Fuel to Turbine

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Sodium plusPotassium 150 ppm H igh temperature corrosion Fuel Washing 1 ppm

Calcium 10 ppm Fouling deposits Fuel Washing to a 10 ppmlimited exten t

Lead 1 ppm High temperature corrosion None (controlled by fuel spec) 1 ppm

Vanadium ** High temperature corrosion Inhibited by magnesium 0.5 ppm

Magnesium None Inhibits vanadium/forms U sed to inhibit vanadium nonedeposits

** Maximum vana dium levels may be d ictated by local codes regard ing stack particulateemissions and the user's acceptable costs to inhibit.


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Specific Gravity

The specific gravity of a fuel oil is the ratio ofthe weight of a given volume of the material at16 C (60 F) to the weight of an equal volume ofdistilled water at the same temperature. The clos-er the specific gravity of the fuel is to that of water,the more difficult it is to trea t it.

Viscosity

The viscosity of a fluid is a measure of its resis-tance to flow and is expressed in various units.The most common viscosity units are SayboltUniversal Seconds (SSU), Saybolt Furol Seconds(SSF), and Kinematic Viscosity Centistokes (cSt).

GE experience has shown that viscosities of 380cSt at 50 C (4200 SSU at 100 F or 160 SSU at 210F) can easily be processed. Greater viscosities canbe han dled, but they are evaluated on an ind ividu-al basis.

Flash Point

The flash point is the lowest temperature atwhich application of a flame causes the vaporabove the sample to ignite. This value indicatesthe potential fire hazard associated with handlingthe fuel. Consideration should be given to explo-sion proofing if the flash point of any fuel whichmay be used in the system is below 60 C (140 F).Crude oils typically have flash point temperatureslower than distillate oils, resulting in the use ofexplosion-proo f separa tors.

Pour Point

The pour point is the lowest temperature atwhich the oil will flow under standard test condi-tions. High pour points are characteristic of paraf-fin-base oils and dictate th e need for in creasedstorag e tempera tures, highe r-capa city suctionheaters, heat tracing of lines, as well as certainequipment and recirculation circuits to estab-lish/mainta in operating temperatures.

Wax ContentWax can be present in f uel oil, particular ly

crude oil and heavy distillates. The percentage ofwax and its melting point must be determined,and suitable heating and heat tracing must beprovided to ensure that the wax in the fuel is dis-solved at all times. These steps will help preventsystem clogging.

FUEL TREATMENTIn the case of a true light distillate oil, treat-

ment is required primarily to capture dirt andsh ipment con t a minan t s tha t h ave not beenremoved by the storage tank sett ling systemarrangement. U ndetected an d untreated, a singleshipment o f contaminated fuel can cause substan-

tial damage to th e gas turbine. Filters are the mostcommon ly used device, although centrifuges mayalso be required to remove sodium if present as aresult of seawater contamina tion.

Treatment and conditioning systems for ash-forming fuels are more complex because of theprocessing steps required to remove or controltheir characteristic trace metal contaminants.Particular attention must be paid to sodium andvanadium. Complete fuel treatment includesthree basic steps:

1. Fuel/Water Separation• Wash ing:

Washing in volves add ition o f water to th efuel and subsequent removal of the contam-inan t laden water . Washing is don e toremove the water soluable trace metals -such as sodium, potassium and certain calci-um compon ents - and much of the organ icand inorganic particulate material that isnor mally forwarded to th e filtering systems.

• Purifica tion:Under special circumstances, it is possible toobtain adequate contaminant removal with-out the addition of any water to the fuel.This process is called purification, and it is

frequen tly applied to lighter crudes and dis-tillates.

2. Filtering th e fuel to remove solid oxides, sili-cates, and related compounds that are notadequately removed prior to forwarding tothe gas turbine. These particles can clog fuelpumps, flow dividers, and fuel nozzles.

3. Inhibiting the vanad ium in the fuel withmagnesium compounds in a ratio of threeparts of magnesium, by weight, to each parto f vanad ium. This form of t rea tmentinhibits the corrosive characteristics of vana-dium by forming high melting-temperatureash composed of magnesium sulfate, mag-nesium oxide, and magnesium vanad ates.

It should be noted that lead is also cor rosive toturbine components and should be avoided. Sincethere is no known economical technique forremoving lead or providing inhibition, it is neces-sary to restrict purchases to fuel with extremelylow amounts of lead (less than 1 ppm).

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Fuel Treatment System Equipment

Figure 1 presents a schematic arran gement of ahea vy-du ty gas turb ine fu el system which wasdeveloped af ter years of experience with ash-form-ing fuels. The system is configured to provide sim-plified plant operation. It has the flexibility toincorporate future improvements, and can pro-

vid e a m e a n s f o r p e r f o r m in g p l a n n e d a n dunplanned maintenance without interruption tothe gas turbine operation.

Typical fuel-wash eq uipm en t includ es heatexchangers, heat economizers, mixers, and oil-water separation devices. The fuel is pumpedfrom the storage tank through a strainer whereforeign materials are removed. After straining, thefuel go es throu gh a pressure-red ucing valve,where the demulsification agent is injected. Thefuel then flows through an economizing heatexchanger where heat is removed from the hotfuel leaving later stages of the wash system. Theraw fuel flows to another heat exchanger wherethe fuel is brought to its process temperaturethrough either steam or electric heating. At thisstage, the demulsification agent is thoroughlymixed into the fuel. A short distance upstreamfrom the mixer, water is injected at a rate of up to10 percent of the fuel flow rate. The water, whichis normally condensate, comes from a water skidwhich contains a heat exchanger in order to raisethe water temperature to within 10 or 20 degreesof th e fuel temperature. The washing operation isperformed one or two times. After washing is

complete, the fuel flows through th e economizingheat exchanger, the water-in-oil monitor, and theninto the washed fuel storage tanks.

Fuel Washing

Since ash-forming fuel oils are a lmost universal-ly contaminated with salts and salt water, they nor-mally require water washing to remove the water-soluble salts of sodium and potassium. Fuelwashing involves mixing heated fuel with 5 to 10percent of potable water a long with a small

amo unt (0.02 percent) of a n emulsion-breakingfluid to aid in separation. The washing process is aon e- or two-stage extraction pro cedure with th eextraction water flowing counter-current t o th efuel. Each stage has a mixer to initiate contact ofthe wash water with the fuel, followed by a mecha-nism to separate the salt-laden water from theextracted fuel. Either centrifuges or electrostaticdesalters are used for this separation process. GEhas found that centrifuges remove fuel contami-nan ts more reliably and completely than the elec-trostatic desalters. Currently GE is only using cen-trifuges in its fuel treatment systems.

The number of extract ion stages requireddepends on the salt level in the fuel to be pro-cessed and on certain properties of the fuel, suchas specific gravity and viscosity. Since the success-ful opera tion o f the fuel-washing system depend son a working difference between the specific grav-ities of the fuel and that of the water, fuels withspecific gravities above 0.98 may not be washableunless they are first blended with a compatible liq-uid which has a lower specific gravity, such as dis-tillate fuel.

Chemicals referred to a s demulsifiers are add ed

to the fuel to assist in breaking up difficult oil-water emulsions. Water is add ed to the o il andsubjected to controlled mixing in order to dis-tribute the sodium-seeking water throughout theraw oil. The mixture then goes to a separator.Here, the oil and water are separated, and theclean oil flows into one pipe, and the wash waterwith a high concentration o f salts flows out an oth-er.

To comply with loca l codes, the effluent watermay requ ire a t rea tment sys tem to removeentrained oil. For example, a customer specifica-tion of “no visible sheen” is equivalent to a surface

thickness of 3 x 10-6 in. (7.62 x 10-6cm), orapproximately 15 ppm of free oil content in thewater. Reduction of oil content below these valuesmay require complicated systems that include bac-teria d igestion.

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GT24348A

Figure 1. Heavy fuel gas turbine system


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Separation by Electrostatic Systems

Figure 2 gives a schematic arrang ement of atypical two-stage electrostatic system, while Figure3 shows an actual installation.

The principle behind any electrostatic system isthat the oil/water separation process is inducedthrough the application of an electric field. The

electric field causes finely dispersed water d ropletsto coa lesce, thereby increasing the droplet diame-ter. This pheno mena increases set t ling ratesaccording to Stokes Law, which states that “thevelocity of a water droplet falling through oil isproportional to the square of the diameter of thedroplet.”

There are two types of electrical separatorspresently used: d irect-curren t and a lternating-cur-rent . Direct-current electrostatic systems are ver yefficient devices when employed with light refined

fuels of low con ductivity. Alterna ting-curren t elec-trostatic separators are applicable for heavier fuelshaving greater conductivity. Electrostatic separa-tors are appealing because there are no high-speed rota t ing parts with in the vessel .Maintena nce inter vals can be lon g, but on -lineoperation can be complicated with changes infuel properties or fuels having high sediment con-

tent.Sludge removal is accomplished by the trans-

port of solids in the effluent water from the vessel.This can be accelerated by a hydraulic systemwithin th e vessel tha t recirculates the water.

Electrostatic units generally perform reason-ably well, and generous sizing can be incorporat-ed with minimal increase in cost. The key parame-ter in sizing such a system is the selection of thenumber of stages. Generally, one can expect 85 to90 percent sodium removal per stage. Three-stagesystems are usually considered for initial sodiumplus potassium inputs up to 150 ppm and two-stage systems are considered for initial sodiumplus potassium inputs of up to 100 ppm. Althoughsystem start-up times using electrostat ic precipita-tors are somewhat long, usually taking three orfour hours per stage, the operator is capable ofdetecting small changes in operating effectivenessof the system and can take corrective action withthe system on line.

Electrostatic systems are pressure vessels; thusthe oil temperatures can be raised as high as149° C (300° F), without concern for bo iling th ewater. This in turn can permit significant reduc-

tions of fuel viscosity, but the high temperaturesmay lead to fuel degrada tion.

Separation by Centrifugal Force

The mechanical process of washing fuel isshown schematically in Figure 4. This arrange-men t represents a typical two-stage centr ifuga lseparation system. Figure 5 is an actual installa-tion. The principle behind this centrifugal processis that th e oil and water are separated as a result ofthe high centrifugal forces developed in the cen-trifuge. In contrast to electrostatic precipitators,

which rely on increased particle diameters in ahigh voltage gradient field and a 1G gravity field,the centrifuge employs only a high gravity field ofmany thousands of Gs to accomplish the oil andwater separation. A variety of centrifuge modelsare currently available, having capacity rangesfrom 5 to 660 U.S. gpm (1.1 to 150 cubicmeters/hour).

Centrifugal fuel washing systems have been suc-cessfully applied on GE gas turbine systems since

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GT24346

Figure 2. Heavy fuel treatment system –electrostatic

GT2041

Figure 3. Heavy fuel treatment system –electrostatic


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the early 1970's using fuels with specific gravitiesup to 0.995 before blending.

With correct systems parameters, a typical two-stage system can reduce sodium from 150 ppm toless than 1 ppm for ash-forming oils. Centrifugesare also effective in removing inorganic particlesand dirt which are forced out with the effluent

wash water. This added benefit minimizes the loa don the downstream fuel filtration system.

Fuel Purification – SimplifiedWashing

The purification process is shown schematicallyin Figure 6, and an actual installation is shown inFigure 7.

Fuel purification is a one-stage extraction pro-cedure to treat light distillates and crude oils with-

out adding water to the fuel. This process relies

on the fact that the salts are already dissolved inthe entrained water; thus by removing the waterthe salts are removed.

Purification is practical with distillate and crudeoils having a minimum 0.5 percent water in thefuel, and a salt concentration not exceeding 20ppm of sodium plus potassium. Since the purifica-tion process eliminates the need for added waterand demulsifiers, it also simplifies the overallwaste disposal process.

Direct-Feed Approach

Another purification technique employing cen-trifuges is the direct feed approach. This is differ-ent from the other systems discussed because itforwards the fuel directly to the gas turbine with-out going through an intermediate fuel storagetank or a fuel forwarding skid. The centrifugegenerates the proper pressure required by the tur-bine ma in fuel pump. H owever, some of th e func-tions from the fuel forwarding skid need to beretained in the delivery system upstream of thegas turbine to ensure that the fuel being d elivered

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GT24347

Figure 4. Heavy fuel treatment system –centrifugal

GT2040

Figure 5. Heavy fuel treatment system –centrifugal

GT03729B

Figure 6. Fuel purification

GT10248

Figure 7. Qaisumah purification system


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to the gas turbine has been handled and treated

properly. These functions include the flow meterand solenoid operated stop valve.

The basic flow diagram of this type of purifica-tion system, illustrated in Figure 8, applies eitherto turbines starting and stopping on crude, or tounits that start on distillate and then transfer tocrude. The flow path of fuel is as follows:

• The raw fuel (crude or distillate) is pumpedfrom a raw-fuel storag e tank into the cen-trifuge(s), where it is purified. The purifiedfuel is then pumped directly to the turbineby the centrifuge. Any excess fuel the tur-bine cannot use (or all of the fuel if the tur-bine is not operating) is sent to a cleanreserve tank, where i t is s tored . I f thereserve tank is full, the clean fuel overflowsinto the raw-fuel storage tank. The vana di-um inhibitor is injected downstream of anyrecirculation loop or return lines. Thus, allof the inh ibited fuel is burned.

• I f the processed fue l does not meet thevalue for water conten t set on th e water-in-oil monitor (WOM), the fuel is automatical-ly diverted back to the raw storage tank forprocessing.

• If the centrifuges are not operating or thefuel is being d iverted back to the raw-fueltank because it does not meet the specifica-tion, the reserve fuel pump will pump fuelf rom the reserve t ank to the turb inesthrough a set of d uplex filters.

• If the raw fuel does not require purificationdue to low particulate and/or low sodiumlevels, the fuel can be bypassed around thecentrifuges through the duplex filters, usingthe raw-fuel pump.

While this system uses the direct-feed as the pri-mary approach, it also functions in an indirectfuel mode, i.e., pumping from the reserve fueltank. If the user desires it, the system can bedesigned for normal operation in either direct orindirect mode, permitting the user to elect theoperational mode for normal use. The size of thecentrifug e system, reserve fuel tan k, and in-line

heaters are a direct function of the planned oper-ating modes of the gas turbines, expected directvs. indirect operation of the system, and the type,quality, and availability of the raw fuel.

GE concludes that the purification processdescribed can be used on most distillates and onlight crude oils with sodium plus potassium levelsof up to 20 ppm. Greater levels can be permitteddepending upon the fuel. In some cases involvinghigher sodium, it may be necessary to allow thefuel to settle to 20 ppm and to drain the waterfrom the fuel prior to processing.

Filtration

Solids, oxides, silicates, and related compoundsthat are not adequately removed by the fuel treat-ment systems must be removed by the fuel systemfilters prior to entering the fuel pump and flow divider. The particles that are not removed mayclog the flow divider and fuel nozzles.

Incorporatin g a motor-driven, self-cleaning fil-ter minimizes the load on the downstream high-efficiency filters. The use of a duplex filtration sys-tem for the high efficiency filters permits filtermaintenance without turbine shutdown.

Inhibition

Crude oils and heavy residual fuels usually con-tain organic vanadium which is extremely corro-sive to the hot gas path parts of the turbine. Thisvanadium is not present in liquid fuels in a waterso lub le form, hence i t c annot be removedthrough the washing process. Instead, its effectsare inhibited by the addition of magnesium to thefuel in the ratio of three parts of magnesium byweight to each part of vanadium. At this level ofinhibition, the cor rosive vanadium pentoxide thatis formed during combustion reacts to form mag-nesium orthovanadate. This has a melting pointsufficiently high to allow its passage downstreamthrough the turbine with deposition that is easilyremoved, an d without resultant cor rosion.

A variety of m agn esium-con tainin g inh ibitionagents are available, and their choice is deter-mined largely by the economics of the system andthe overall amount of vanadium present in thefuel. Three additives frequently employed are

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GT10247A

Figure 8. On-line inhibition Schematic


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magnesium sulfonate, which is oil soluble and deliv-ered ready for use, magnesium oxide, which is an oil-based slurr y, an d magn esium sulfate, comm onlyknown as Epsom salts, which must be mixed withwater on the site. On-line inhibition systems are thepreferred method of applying the magnesium agent.The inhibitor is injected into the fuel immediatelyahead of its introduction to the gas turbine (Figure

9). The system consists of a small in-line meteringpump and a flow switch which provides an alarm sig-nal in the event flow of inhibitor stops. Either con-stant flow systems or systems that provide a flow vary-ing with the actual fuel use rate are available.

SYSTEM CONSIDERATIONS

There is no one fuel-treatment system suitablefor all applications. A design must be tailored tothe specific needs and requirements of each cus-tomer. The optimum approach results from anevaluation of operational requirements for the gasturbine, the expected fuel characteristics, thedesired maintenance philosophy, the choice ofequ ipment , the cho ice o f add i t ive , and thedesired system flexibility. Generally, there is a ten-dency to request “worst case” design without giv-ing due thought to the many constraints that mayexist. This may result in an overdesigned andexpensive installation.

Fuel Selection

Residual fuels display a wide range of proper-ties including vanadium content, specific gravity,and viscosity. Depending largely on economictrade-offs, the user may or may not decide to burnall of the fuels available at his location. The maxi-mum allowable vanadium content may be con-trolled by local regulations governing total stackparticulate emissions. Lower vanadium level fuels,

where available, can substantially reduce fueltreatment additive costs.

Users requiring a capability for washing fuelswith a specific gravity and/or viscosity higher th anspecified for the fuel-washing system can a ccom-modate these fuels by blending them with a com-patible distillate fuel before washing.

Fuel Handling and Storage

Ash-forming fuels do not gen erally have consis-tent chemical and physical properties; purchasedsupplies can vary in composition by wide margins.Observation of the following precautions for stor-age and handling of fuel prior to use can enhancefuel washing and assure greater consistency in thefuel delivered to the gas turbine.

1. The use of three tan ks sized to provide a 24-hour settling time needed for electrostaticsystems will permit one tank to be in usewhile the second tank is being filled and thethird is settling after being filled.

2. Tanks should be covered an d pro vide foreasy drainage of water and sediment fromthe bottom, which should be d one d aily.

3. Fuel should n ot be pumped d irectly fromthe bottom o f the tank.

4. All fuel del ivered should be f i l tered toremove any large par t ic les, an d pipingshould be arranged to minimize agitation ofsediment at the bo ttom of the tank.

5. Storage tanks for high viscosity fuels such asresiduals should be heated to keep the vis-

cosity low enough so that the fuel can bepumped.6. Oil storage temperature should be as low as

possible, consistent with the operat ion.Washed o il must be delivered t o th e da ytank below the flash point.

7. Cadmium, zinc, and copper catalyze thedecomposition of hydrocarbons. These ele-ments and their alloys, therefore, should n otbe used in the construction of storage tanksand related items.

Fuel-Wash Capacity

The fuel-use prof ile is significant in establishingthe size of the fuel-washing equipment and treat-ed fuel storage tan k.

Fuel demand is a function of the site ambienttemperature and number of hours each turbine ison line. Demand determines the required fueltreatment capacity to support the site operation.Final sizing depends on the margin d esired by thecustomer and the maintenance philosophy adopt-ed to keep the washing eq uipment on line.

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GT05462B

Figure 9. Purifying and burning fuel


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Selection of Fuel-Washing EquipmentType

The selection of either centrifuges or electro-static precipitators to reduce the soluble trace

metals to acceptable limits is usually dictated bythe application. For example, where space is at apremium or for higher salt levels, the naturalchoice is centrifuges. Where space is not a majorconstraint, where the customer has large storagetanks, and the raw fuel has low salt levels, electro-static desalters may be a choice to consider. Table2 gives a functional comparison of both types ofsystems.

Fuel-Washing Equipment Design

Fuel wash ing suppor t equ ipment , wh ichincludes mixers, demulsifier injection pumps,heat exchangers, economizers, etc., must be com-patible with overall system objectives. The perfor-

mance of the support equipment can determinethe performance of the entire fuel treatment sys-tem. On -line redundancy of critical components,such as heat exchangers, economizers, pumps andmotors, is necessary for continuously running sys-tems. This redundancy also permits the fuel wash-ing equipment size to be minimized, which helpsto reduce initial cost. Peaking systems require lit-t le redundancy, as maintenance may be per-formed during scheduled outages.

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Table 2COMPARISION OF CENTRIFUGE AND ELECTROSTATIC FEATURES


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Turbine Cleaning

Both compressor fouling and ash build-up onthe hot gas path parts contribute to turbine per-formance deterioration. Fouling occurs whencontaminants injested into the inlet deposit onthe compressor blades.

The ash deposits result primarily from crude

and heavy residual oils containing vanadium andmagnesium for inhibition. Effective fuel washingand treatment can reduce the frequency of clean-ing required.

Fuel Analysis and System Controls

A mod ern , ash-forming fuel gas turbine instal-lation requires controls for the fuel treatmentequipment as part of the total system control.Actual control philosophy is dictated by customerpreference. Generally, each functional compo-nent is equipped with its own control system and

has manual set points. Once the set points arepreselected, the system can be in itiated on-site orat a remote location, after which the entire pro-cess is self-regulat ing. Monitoring of critical func-tions can be incorpora ted if desired.

Fail-safe an d permissive fea tures are provided aspart of the control system. When a malfunctionoccurs in the fuel wash equipment, the fuel isautomatically diverted back to the raw fuel storagetank until the malfunction is cleared.

Additionally, the fuel quality must be moni-tored at various steps of the process: sodium andvanadium level after washing, and total sodium,vanad ium, and magn esium after inhibition.

For light fuels not req uiring inhibition (vanadi-um less than 0.5 ppm), only the sodium level ismon itored . This is most readily accomplished witha flame photometer, which is available as a manu-al instrument for spot checks.

Fuels requiring both washing and vanadiuminhibition by a magnesium additive should bemon itored with a direct-read ing, rota ting diskelectrode (RDE) (Figure 10). While this is a com-plex instrument, its operation is very simple andsuitable to use by on-site labor. The operator col-

lects samples, inserts them sequent ially in th e exci-tation chamber, presses a button, and one minutelater reads the analysis printed from a printer.About once every two weeks the instrument cali-bration is checked.

EXPERIENCEGE has accumulated extensive experience in

fuel purification and washing ( Table 3). The fo l-lowing section describes some important exam-

ples which have contributed significantly to the

state of the a rt of fuel treatment.

Purification

The effect of purification had been studied onGuatemalan and Middle Eastern Crude. SeeTable 4 for typical analyses of these crud e oils.

Guatemala

At times, the raw crude fuel contained high lev-els of con tamination that the two stage electrostat-ic fuel treatment system could n ot hand le without

recycling of the fuel back through the system. Acentrifuge was add ed to the o riginal treatment sys-tem between the day tank and the turbine mani-fold (Figure 11), to improve the removal of waterand solids from the fuel. It was found that the cen-trifuge greatly reduced asphaltic and inorganicparticulates, reduced moisture to very low levels,and provided the needed support to the electro-

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Figure 10. Fuel analysis spectrometer

GT07653B

Figure 11. Final modification, February 1981


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Table 3

GE’S EXPERIENCE WITH HEAVY FUEL TREATMENT SYSTEMS

FEBRUARY 1994

C = Crude CDS-P = Centri fuge Puri fication

R = Residual CDS-W = Centri fuge Washing

B = Blend EDS-W = Electrostatic Washing

Fuel Treatment Customer Frame Size Number Gas TurbineSystem Type Fired Hours

C EDS-W APS, Arizona 7 4 3,600

C CDS-W ARAMCO, Saudi Arabia 3 9

C CDS-W Caltex, Sumatra 5 9 200,000

C CDS-W Caltex, Indonesia 5 1 16,000

C CDS-W China National, China 5 1

C CDS-W Electrico, Saudia Arabia 5 6 39,000

C CDS/EDS-W Empressa, G uatemala 5 2 22,000

C EDS-W FPC, Bartow, Florida 7 4 12,000

C CDS-W MEW (Dona, Al Wajbah) Quatar 9 4 150,000

C CDS-W Phillips, North Sea 3 6 45,000

C CDS-P SCECO-C Al Juba Saudi Arabia 6 7 104,000

C CDS-P SCECO-C Leyla Saudia Arabia 5 6 81,000

C EDS-W SCECO-C Riyadh Saudi Arbia 5 2 48,000

C EDS-W SCECO-C Riyadh Saudi Arabia 7 14 919,000

C CDS-P SCECO-E Al Quisumah Saudi Arabia 5 4 60,000

C CDS-P SCECO-E Al Quisumah Saudi Arabia 6 2 90,000

C CDS-P SCECO-S Al Duba Saudi Arabia 5 2 20,000

C CDS-P SCECO-S G izan Saudi Arabia 6 2 10,000

C CDS-P SCECO-S G izan Saudi Arabia 7 1

C CDS-P SCECO-S Asir Saudi Arabia 7 4

C CDS-P SCECO-S Tihama Saudi Arabia 7 5 53,000

C EDS/CDS-P SCECO-W Jeddah Saudi Arabia 7 7 693,000

C CDS-W SEDC Shantou China 6 6 8,100

C CDS-W SMPPC Shenzmeh China 6 2 40,000

C CDS-W SOE Mosul Iraq 5 10C CDS-P Sonatrach Djamha Algeria 3 2 250,000

C CDS-P Sonatrach Elnamra & Dishra Algeria 3 2 12,000

C CDS-P Sonatrach Elnamra II Argeria 3 1 180,000

C CDS-P SOPEG Algeria 3 2 120,000

C CDS-W WED Al Ain VAE 5 2 10,000

C CDS-W ZDC Zhuhhai China 6 2 6,400

NOTE: The " G as Turbine Fired H ours" reported in this table are n ot curr ent in all cases.


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Table 3 (Continued)

GE’S EXPERIENCE WITH HEAVY FUEL TREATMENT SYSTEMS

FEBRUARY 1994

C = Crude CDS-P = Centrifuge Purification

R = Residual CDS-W = Centrifuge Washing

B = Blend EDS-W = Electrostatic Washing

Fuel Treatment Customer Frame Size Number of Gas TurbineSystem Type Units Fired Hours

R CDS-W Alcoa, Suriname 7 1 26,000

R CDS-W Alto Ferrara Italy 5 2 54,000

R CDS-W Central Vermont Power, Vermont 5 1 700

R CDS-W EDF, France 9 5 13,000

R CDS-W EECI, Ivory Coast 5 4 70,000

R CDS-W EMSA, Argentina 5 2 60,000

R CDS-W ENDESA, Chile 5 2 50,000

R CDS-W ENDESA, Chile 6 1 9,000

R CDS-W EPC, Burma 5 1

B EDS-W FPC, Debary, Florida 7 6 45,000

R CDS/EDS-W G E Lynn 5 2 50,000

B CDS-W G eneral Petro, Syria 5 6 101,000

B EDS-W G olden Valley, Alaska 7 2 47,500

R CDS-W G reen Mountain Power, Vermont 5 1 600

R CDS-W Hess, St. Croix 5 1

R CDS-W IPCL, India 5 3 200

R CDS-W IPCL, India 6 2 120,000

R EDS-W O.N.E. Morocco 5 6 192,000

R CDS-W O.N.E. Mohammedia Morocco 6 3 19,000

R CDS-W O.N.E. (Tan-Tan), Morocco 6 3 15,400

R CDS-W Pee, Syria 5 3 15,000

B CDS-W PLN, Indonesia 5 2 40,000

B CDS-W PLN, Indonesia 7 4 30,000

R CDS-W Progil, France 5 8 1,080,000

R EDS-W Puerto Rico 7 8

R CDS-W Reksten, Norway 5 1 9,100

R CDS-W SEDC Nanshan, China 5 3 400

R CDS-W SENELEC Dakar Senegal 5 1 24,000

B CDS-W Shell, Curacao 5 1 17,000

R CDS-W Slough Estates, England 5 1 2,000

R CDS-W Taunton, Mass 5 1 10,000

R CDS-W TPC Tunghsaio, China 7 6 117,000

R EDS/CDS-W WAPDA Kot Addu, Pakistan 9 4 63,000

NOTE: The " G as Turbine Fired H ours" reported in this table are n ot curr ent in all cases.


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Table 4TYPICAL CRUDE ANALYSIS

Table 5DATA FROM CENTRIFUGAL PLANT OPERATIONS

ON GUATEMALAN CRUDE WITHOUT WATER WASHING


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static system to eliminate any need for fuel recy-cling to meet the required fuel specification. Inadd ition, considerable data was taken on the oper-ation of the centrifuge at this site. It showed thatthis crude could be desalted from initial levels ofabout 20 ppm of sodium to less than 1 ppm by sin-gle stage centrifugal purification without wateraddition (see Table 5).

Anoth er problem experienced was gumming ofgas turbine and system parts by the vanadiuminhib itor bein g used (oil-soluable mag nesiumnapthenate). While it was injected into the crudein very sma ll quan tities - on the o rder of 0.015percent by volume - the napthena te had the prop-erties of detergents, and a gummy mass would beformed in the presence of trace moisture. Thegumming had a deterimental effect on the life of"on-base" equipment such as filters, flow dividers,high pressure pumps, and combustion nozzles.Even though this chemical has good oil soluabili-ty, it did not go into solution well. The chemicalwas being injected ah ead o f the storage tan ks andit was found that sedimentation and loss of mag-nesium content resulted. Moving the injectionpoint further downstream cured the sedimentionproblem. A change to an additive less sensitive tomoisture further helped the problem. The addi-tion o f the centrifuge to the treatmen t process eli-mated the problem because it reduced the mois-ture to a level where the additive created nofurther gumming.

Qaisumah

The Qaisumah power stat ion is located innorth central Saudi Arabia. Crude, with the typi-cal analysis shown in Table 4, was delivered bypipeline. Sodium levels in “ as-received” fuel runfrom 4 to 10 ppm, only rarely exceeding 10 ppm.The fuel purification system consists of electricheaters followed by four centrifuges operating inpara llel (see Figure 7). The capacity of the systemis 200 U.S. gpm (45.4 cubic meters/hour) .Operation was without water addition or demulsi-fier injection.

The only operational difficulty observed was as

fuel temperatures dropped below 55° C (131°F),which appeared to be the a pproximate “waxpoint”, waxes began to precipitate from solution.Furthermore, it is interesting that there were nofailures of flow d ividers, high -pressure pumps, fuelnozzle coking, etc. Due to a duty cycle of freq uentstartups and shutdowns, the magnesium baseddeposits were spalled-off the turbine buckets.This allowed the turbine water wash cycle to beextend ed to 2500 hours.

Washing Residual Fuel

The effect of fuel washing on residual fuel hasbeen studied at both GE’s Lynn, Massachusettssite and Paranam, Surinam.

GE Lynn

GE Lynn had been operating boilers using No.6 oil for more than 30 years. This installation pro-vided the opportunity to evaluate the perfor-mance of a modern gas turbine burning veryheavy oils and, at the same time, provided themeans to conduct exhaustive tests on various new elements of ash-forming fuels treating an d han -dling. Figure 12 illustrates the overall plantarrangement. It should be noted that the arrange-

ment incorporated two fuel-wash systems: a two-stage electrostatic unit and a two-stage centrifugeunit.

GE’s purchases of fuel from many sources pro-vided a large sampling of different fuels with vari-ous characteristics, yielding a representative pic-ture of the regionally available No. 6 oils. Figure13 illustrates the wide array of fuel propert iesreceived over a 6-year period . Note th at the sod i-um contents varied from a low of 10 ppm to ahigh of 100 ppm, the API gravity ranged from aslow as 12 to 21 degrees API, (SpGr 0.986 to0.928), and the vanadium from 15 ppm to 220

ppm.Evalua tion s of th e two-stage cen trifug e system

were conducted to examine the effects of temper-ature, water/oil mixing, viscosity, d emulsifiers andthroughput. Figure 14 delineates the progressmade on the system from installation to the finalperformance, and key events are noted. Sodiumremoval to less than 1 ppm was readily achieved.

A similar program to evaluate and improve theperforman ce of the two-stage electrostatic desalterwas a lso carr ied out . Figure 15 presents the

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GT24351

Figure 12. GE Lynn arrangement


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improvement and best performance. The data isgiven in percentage washing efficiency. A 90 per-cent efficient 1 stage system removed 90 ppm ofsodium from an initial 100 ppm input. Additionof a second stage raised the removal efficiency

accordingly.

Surinam

The No. 6 residual oil typically had a specificgravity of 0.955 at 15.5° C (60°F)and a viscosity of330 cSt at 38 C (100.4 F), and contained as muchas 100 ppm vanadium and 250 ppm sodium andpot assium. The fu el trea tmen t was a two-stagefuel-wash system with three automatic desludgingcentrifuges in each stage, and was rated for a max-

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GER-3481C

GT02051/GT02052/GT02053/GT02054/GT02055

Figure 13. Fuel characteristics

GT10253A

Figure 14. Two-stage centrifuge performance

GT10254A

Figure 15. Two-stage electrostatic performance


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imum of 100 gpm (22.7 cubic meters/hour) fuelflow. The system successfully desalted 17,000 bblsof fuel during a 120 hour test run.

The system also processed residual oils with aspecific gravity of 0.966 and reduced sodium andpotassium levels to less than 1.0 ppm from an ini-tial level of sodium plus potassium of 122 ppm(see Table 6).

The a bove operational experiences enabled GEto improve the flexibility of site operation, accu-mulate more experience using ash-form ing fuel,and maximize reliability and availability for burn-ing these fuels.

SUMMARY The work described in this paper represents a

major undertaking by GE to arrive at optimal, well-balanced, reliable fuel systems capable of economi-cally burning ash-forming fuels. The prime objectivehas been to extend our past experience to new appli-cations with even more demanding requirements.

Objective evaluation of electrostatic and cen-t r i fuga l t ypes o f separa t ion equ ipment hasresulted in greater awareness of techniques forfuel washing. Development of the fuel purifica-tion concept for distillates and light crudes hasresulted in simple, low-cost systems with con sid-erable flexibility and reliability. Centrifuge sys-tems have also been refined and developed for

application in newer, simplified fuel systems.Lesson s learn ed in ra w-fuel han dling a nd stor-age have enabled us to improve system opera-tional capa bility and minimize the serious conse-q uences of field pro blems.

In all, GE has evolved new types of fuel treat-ment systems with simplified design, automatedoperat ion, and demonstrated success in realinstallations in many parts of the world.

REFERENCES1. “Liquid Fuel Treatment Systems,” Shlomo S.

Dreyman n an d Ern est H. Gault - GER 3481

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Table 6RAW RESIDUAL FUEL CHARATERISTICS FOR SURINAM ALUMINUM COMPANY

© 1996 G E Compan y


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LIST OF FIGURES

Figure 1. Heavy fuel gas turbine systemFigure 2. Heavy fuel treatment system – electrostaticFigure 3. Heavy fuel treatment system – electrosaticFigure 4. Heavy fuel treatment system – centrifugalFigure 5. Heavy fuel treatment system – centrifugal

Figure 6. Fuel purificat ionFigure 7. Qaisumah purification systemFigure 8. On-line inhibition schematicFigure 9. Purifying and burning fuelFigure 10. Fuel analysis spectrometerFigure 11. Final modification, February 1981Figure 12. GE Lynn arrangementFigure 13. Fuel characteristicsFigure 14. Two-stage centrifuge perfor manceFigure 15. Two-stage electrostatic perfor man ce

LIST OF TABLES

Table 1. Trace Meta l Ef fect sTable 2. Comparision of Centrifuge and Electrostatic FeaturesTable 3. GE Experience with Heavy Fuel Treatment Systems - Februar y 1993Table 4. Typical Crude AnalysisTable 5. Data from Centrifugal Plant Operations on Guatemalan Crude without Water WashingTable 6. Raw Residual Fuel Charateristics for Surinam Aluminum Company

GER-3481C


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For furt her inform ation, cont act your GE Field Sales Representative or w rite t o GE Pow er Systems M arketing

GE Pow er Systems

General Electric Company

Building 2, Room 115B One River Road

Schenectady, NY 12345

ger 3481c liquid fuel treatment systems

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