impact of epa air intake filtration on gas turbines operating in middle east offshore applications...

The Future of Gas Turbine Technology8th International Gas Turbine Conference

12th -13th of October 2016, Brussels,Belgium

Paper ID Number – 45-IGTC16

Impact of EPA Air Intake Filtration on Gas TurbinesOperating in Middle East Offshore Applications and

Fueled with Sour Gas.Dominique Orhon

TOTAL S.A.Centre Scientifique et Technique Jean Feger

Avenue Larribau64018 Pau Cedex, France

+33 628 504 [email protected]

Jeroen Van Der KaagTOTAL AL BUKHOOSH

Abu Dhabi Mall, East Tower, 12th floorP.O. Box 4058

Abu Dhabi, UAE+971 2 6986473

[email protected]

Scott TaylorAAF Ltd (American Air Filter)

Bassington Industrial EstateCramlington,

England+44 7968 855 180

[email protected]

Abstract

Gas turbines, running both power generation andmechanical drive applications are essential toproduce remote offshore assets in the oil & gassector. Gas turbines offer the benefit of a highpower density necessary for platforms. In the 10 to30 MW range, the three different gas turbinetechnologies – aero derivative, light industrial andheavy duty have been operated in the Middle Eastfor decades. Reliability and availability are of primeimportance to ensure production efficiency andrevenue yield.

The availability of high efficiency particulatearrestance (EPA) air filter technology means thatoffshore operations can be considered through anew paradigm. This paradigm consists inmaintaining gas turbine performances with bettercompressor cleanliness, increasing availability byreducing the number of gas turbine water washingand pushing forward planned maintenanceoperations by improving long term part integrity.As an additional benefit, EPA filtration influencesthe gas turbine behaviour against hot corrosionmechanism resulting from the combustion of sourfuel gas, rich in hydrogen sulphide (H2S).

The offshore complex of ABK (Abu Al Bukhoosh)is equipped with three gas turbine technologiesissued by three different manufacturers. ABK runsthree General Electric heavy duty PGT10 2-shaft(12 MW) and one Dresser Rand aero-derivativeRB211 24G56 (26 MW) as turbo-compressors andthree Siemens light industrial SGT 400 (13 MW) asturbo-generators. For decades, these gas turbineswere equipped with high velocity low grade filters.In 2010, the operator of the different platforms thatmake up this production complex started an

extensive retrofit of the air filter housings on theseseven gas turbines. It was decided to install a lowvelocity EPA filtration system. The retrofit wascompleted in 2012. This offshore complex, afteroperating for three years offers a good overview ofhow EPA filters can influence the gas turbineoperation and maintenance activity.

The principal purpose of this paper is to discuss thefour topics that a large unique offshore asset, likeABK, can offer. The first is to provide a betterunderstanding of gas turbine applications burningfuel gas, rich in H2S. Secondly it is to share detailsof the offshore retrofit operation. The third is toidentify the different characteristics of a highvelocity low grade filtration and a low velocity EPAfiltration for different sizes of turbine and fordifferent technologies. Last but not least it is toshare the outcomes of the EPA air filter technologyon these three models of gas turbines throughvarious aspects. A quantitative analysis of theavailability and reliability for the three technologiesis provided and discussed. Changes in water washstrategy will be addressed. The qualitative influenceof EPA filtration on the hot gas path is reviewed inthe light of part integrity and hot corrosiondevelopment. The impact on operation andmaintenance activities is shared.

The coming challenges combining offshore andsour service applications are developed from anoperator viewpoint.

Key Words: EPA filtration, offshore, hot corrosion,hydrogen sulphide, planned maintenance,availability, reliability, part integrity, aero-derivative, light industrial, heavy duty, carbon footprint, energy efficiency.




1. DESCRIPTION OF ABK OFFSHOREASSET

SiteAbu Al Bukhoosh (ABK) is an offshore fieldlocated in the Arabian Gulf at the northern edge ofthe territorial waters of the Emirate of Abu Dhabi.The field is located 180 kilometres away from AbuDhabi. It was discovered in 1969 with anexploration well. Subsequent delineation wasconducted in 1973 and 1974 with an initial oilproduction taking place in 1974. This field,producing oil and gas, is an asset made up ofvarious platforms, NKPP, GLP, KPP and PPSP.

Figure 1 – Platform complex of ABK -

EquipmentThe gas turbines installed at ABK use threedifferent technologies and come from threedifferent original equipment manufacturers(OEMs). The platforms are equipped with one aero-derivative gas turbine RB211 24G56 from DresserRand (26 MW Iso) on KPP, three light industrialgas turbines SGT400 from Siemens (12,9 MW Iso)on NKPP and PPSP and three heavy duty gasturbines PGT10 2-shaft from General Electric (11,9MW Iso) on GLP.

ApplicationsThe RB211 24G56 gas turbine drives through agear increaser, a compressor for gas export whereasthe PGT 10’s are coupled to two gas-liftcompressors and one gas injection compressor.Each gas lift compressor train consists of a speedincreaser gear box driving 2 compressor casingscontaining the LP/MP sections in one casing andone HP section in the other (Figure 2). The gasinjection train consists of one gas turbine, one gearand one compressor casing (Figure 3). Thecompressor trains are not equipped with a back up.

This means a train shut-down generates animmediate lack of production.

Figure 2 – PGT10 2-Shaft Gas Turbines Used as 2x 50% Gas-lift and 1 x 100% Gas Injection Turbo-

compressors -

Figure 3 – RB211 24G56 Gas Turbine Used as 1 x100% Export Turbo-compressor -

In parallel, three SGT 400 gas turbines are allocatedto the production of electricity. These gas turbinesrun generators (Figure 4). The function ensuring theproduction of electricity is equipped with a back upshaft line ready to start up in case of a shut down. 2out of 3 are necessary to meet the demand forelectricity.

Figure 4 – SGT400 Gas Turbines Used as 3 x 50%Turbo-generators -

Fuel GasThe NKPP fuel gas is a sour gas rich in hydrogensulphide (H2S) (Table 1). The 2% H2S molarcontent is very high for gas turbines runningoffshore. As a matter of comparison, years ofoperating experience show that it is recommendedto operate gas turbines with a level of hydrogen




sulphide below 10 ppm when the installation isoffshore.

Component Molar Composition (%)Nitrogen 3,63

Carbon Dioxide 3,00Hydrogen Sulphide 2,05

Methane 84,06Ethane 4,29

Propane 1,45iso – Butane 0,33n – Butane 0,51

iso – Pentane 0,21n – Pentane 0,18

Hexane 0,18Heptane 0,11

Table 1 – Typical Fuel Gas Composition

Hot CorrosionThe ABK gas turbines are subject to hot corrosionattacks because its fuel gas contains H2S and thelocation of the field is offshore where salts areavailable in large quantities in the marineatmosphere. The ABK gas turbines are sensitive tohot corrosion in the hot gas path. On ABK, this hotcorrosion chemical reaction takes place betweensulfur and the alkali (sodium, potassium, calcium,etc…) to create sulfuric acid as shown in thefollowing equations.

H2S + O2 => SO2 + H2

2NaCl + SO2 + O2 => Na2SO4 + Cl2

Operation RequirementsThe objective is to run the different gas turbines24/7. Each gas turbine stop related to waterwashing, inspection, maintenance or failure isdetrimental to production. The best rates ofavailability and reliability are expected in order tomaximize the use of the asset.The gas-lift production arrangement is 2 x 50%,nevertheless the gas injection compressor train maysustain the gas-lift function to some extent. The gasinjection production arrangement and the gas exportproduction arrangement are both 1 x 100%.Commonly, the compressor train expectedavailability is 97.5% with gas turbines fuelled bymild fuel gas. Achieving this level of availability isparticularly difficult.The electricity production arrangement is 3 x 50%.The expected availability of the entire electricityfunction is 99.99% meaning availability per train of66.7% on average. This requirement does notdepend on the fuel gas acidity. This value is much

easier to attain for teams in operation butnecessitates additional investment.

Water WashingThe online water wash requires a substantialquantity of demineralised water on a daily basis. OnABK platforms, it is not possible to store this largequantity of demineralised water. This is why on linewater washing is not the practice on this asset.The remaining option to wash the axial compressoris to use an off-line water wash. This washsequence consists of a soak period for the axialcompressor with a detergent and then a rinse orclean sequence to remove the soaked dirt depositsfrom the machine. Although off line engine washesrestore compressor performance, they generatecostly servicing and even costlier downtime, alongwith a great quantity of dirty washing agent todispose of. On a regular basis, the off-line waterwash sequence duration can last up to twelve hours.The different steps are as follows: A gas turbine cool-down of 8 hours. A gas turbine water-wash preparation of 2

hours. A soak for the axial compressor with detergent

of 1 hour. A rinse with clean water of 1 hour.How long the soak and rinse steps last depends onthe axial compressor level of fouling because therinsing drains must be cleaned.

Boroscope InspectionOn an aero-derivative gas turbine, a 4-hourboroscope inspection is carried out after the waterwash operation.

Compressor EfficiencyThe axial compressor efficiency of the gas turbinesis monitored by the ABK site operation team.Technical support from shore recommends washingwhen necessary.

Hot Section WearingThis hot section wearing leads the engineexchanges and impacts the operations at sitedirectly. This is mainly due to the capability of theengine to endure under the hot corrosiondevelopment.

Offshore Atmospheric ImpuritiesGenerally with offshore fixed platform and FPSOenvironments in the Middle East, air intake




filtration systems must address the efficientremoval of rain, fogs/mists, sea spray aerosols,hydrocarbons, salt particles, seasonal ‘Harmattan’dusts and local sources of offshore asset generatedpollution, in order to protect gas turbine compressorsections from erosion, corrosion and fouling.

The seasonal ‘Harmattan’ dusts is an industry-wideterm used to describe the phenomena of land-produced dust like contamination, that becomesuspended in the air and are carried hundreds ofmiles out to sea, which, when ingested, interferewith aerospace, ocean going vessels and gas turbineengine performance.

However, it must be acknowledged for informationand paper correctness, that the actual occurrence of‘Harmattan’ is defined as warm, dry and dustywinds, that blow from the Sahara desert over thesubcontinent of West Africa and out to sea, and aremost prevalent between the months of November toMarch.

With regards to specific atmospheric impurities atABK, several ‘snap shot’ air samples were taken atthe platform, which, when averaged, providedairborne particle size and correspondingconcentration data (particle count).

This average air sample data is shown below infigure 5, with the data range from 0.3 to 10.0microns:

Figure 5 – ABK Average Air Sample ParticleSize vs Concentration

From this average air sample data, it can be seenthat 96.77% of the particles collected were 0.3μm,and it can be calculated that 99.828% of the

airborne particles at ABK are in the 0.3μm to1.0μm range as shown below in table 2.

Size(microns) 0.3 0.5 1.0 3.0 5.0 10.0

Percentage(%) 96.77 2.455 0.703 0.045 0.022 0.005

Table 2 – ABK Average Air Sample Particle Size(microns) versus Percentage (%)

2. ABK AIR INTAKE FILTRATIONSYSTEMS BEFORE RETROFIT

EquipmentThe air intake filtration systems installed on ABKprior to retrofit were multi stage high velocity,typically comprising upstream vane separators, pre-filter bags inserted into medium efficiency filterbags and a downstream vane separator, as shown infigure 6.

Figure 6 – Typical Multi Stage High VelocityFiltration System (1 - Upstream Vane Separator, 2 -Pre-filter Bags, 3 – High Efficiency Filter Bags, 4 -

Downstream Vane Separator).

High Velocity Filtration System OperatingPrinciplesThe multi stage high velocity filtration principles ofoperation are:

The upstream vane separator removes themajority of large airborne water droplets, suchas sea sprays, fogs, mists and large aerosols.

The pre-filter bags (G3 classification inaccordance with EN779:2012) and mediumefficiency bags (M5 classification inaccordance with EN779:2012) remove airborneparticulates and also coalesce small aerosolsthat have passed through the upstream vane




separator, whereby the small aerosols coalesceinto larger droplets which can be captured bythe downstream vane separator.

The downstream vane separator captures thelarge coalesced droplets which pass through thepre-filter and medium efficiency filter bags,which are then removed from the air intakefiltration system via a sealed manometric drain.

3. FILTRATION EFFICIENCYCLASSIFICATIONS ACCORDING TOEN779:2012 AND EN1822:2009.

In Europe air filtration products are tested inaccordance with ISO standards EN779:2012 andEN1822:2009.

EN779:2012 distinguishes three filtrationcategories: coarse (C), medium (M) and fine (F).The classifications are based on the minimumefficiency (ME) of a filter. For testing andclassification a single filter element is challengedwith DEHS aerosol, an aerosol for measurement offiltration efficiency as a function of particle size,and a standardised test dust is used to comparefilters for test dust capacity. Additionally for coarsefilters, filtration efficiency with regards to loadingdust arrestance is measured when filtrationefficiency is not high enough to give a reliableresult. This standard was tailored to HVAC filters,to provide a method of standardisation throughoutthe air filtration industry, and is applicable to airfilters having efficiency lower than that required fortesting in accordance with EN1822:2009.

EN1822:2009 likewise distinguishes three filtrationcategories: efficiency particulate air filters (EPA),high efficiency particulate air filters (HEPA) andultralow penetration air filters (ULPA). For testingand classification, a single filter element ischallenged with aerosols and at the MPPS (MostPenetrating Particle Size) both the local and overallefficiency are determined.

However, it should be noted, that testing to theseISO standards occurs in laboratory conditions, withrelatively dry ambient air and new and clean filterelements, and thus does not take into considerationreal world offshore conditions and the atmosphericimpurities described above.

4. CONTRAST BETWEEN CURRENTDAY OEM FILTRATIONCLASSIFICATION SPECIFICATIONS,THE ABK INSTALLED HIGHVELOCITY FILTRATIONCLASSIFICATION AND EPAFILTRATION CLASSIFICATIONS

Today, gas turbine OEMs typically specify that airintake filtration systems are to meet therequirements of either F8 or F9 classification, inaccordance with EN779:2012. Whereas in starkcontrast, high velocity filtration systems of ABKmeet the requirements of M5 classification, inaccordance with EN779:2012

Therefore, in order to understand the differences inthe air cleanliness quality and thus thecontamination that enters the gas turbinecompressor section, direct performancecomparisons can be made at particle size filtrationefficiencies.

For example, if we consider the ABK average airsample, where 96.77% of the particles were 0.3μm:

A filtration product that is certified inaccordance with EN779:2012 classification M5will have a particle removal efficiency ofapproximately 30% at 0.3μm

A filtration product that is certified inaccordance with EN779:2012 classification F9will have a particle removal efficiency ofapproximately 60% at 0.3μm.

A filtration product that is certified inaccordance with EN1822:2009 classificationEPA E10 will have a particle removalefficiency approximately 97% at 0.3μm.

A filtration product that is certified inaccordance with EN1822:2009 classificationEPA E12 will have a particle removalefficiency of approximately 99.993 at 0.3μm(AAF HydroCel EPA E12 efficiency).

Therefore, it is possible to calculate the quantity of0.3μm particles that would pass through thedifferent air filtration classifications into the cleanair stream, from which a ratio may be derived on aircleanliness quality delivered to the gas turbinecompressor:




From the average air sample data at the ABKplatform, whereby there was an average of 421,829particles collected at 0.3μm:

421,829 x (1 - 0.3) = 295,280 particles wouldpenetrate a M5 classification filter element.

421,829 x (1 - 0.6) = 168,732 particles wouldpenetrate a F9 classification filter element.

421,829 x (1 - 0.97) = 12,655 particles wouldpenetrate an E10 classification filter element.

421,829 x (1 - 0.9993) = 295 particles wouldpenetrate an E12 classification filter element.

Therefore, filtration to classification F9 is 2 timesmore efficient than M5. Filtration to classificationEPA E10 is 23 times more efficient than filtrationto classification M5, and EPA E12 is 1,000 timesmore efficient than filtration to classification M5.

5. RELATING FILTRATIONCLASSIFICATION AND FILTRATIONDIFFERENTIAL PRESSURE OVERTIME TO GAS TURBINE OUTPUTLOSSES

As a result of close cooperation and collaborationwith end users, who employ 100s of small tomedium and large gas turbines, of both aero andindustrial derivatives, in offshore, coastal andinland applications, AAF has built a thoroughunderstanding of engine losses and its directcorrelations with air cleanliness quality and filterdifferential pressure (p) over time.

These correlations are common to both aero andindustrial derivatives, the phenomena of which arecommon to offshore, coastal and inlandapplications, and are illustrated for filtrationefficiency classifications F9, E10 and E12 as shownbelow in figures 7, 8 and 9:

Figure 7 – Gas Turbine Losses (Filter p, Foulingand Total) Post Crank Wash F9 Classification -

Figure 8 – Gas Turbine Losses (Filter p, Foulingand Total) Post Crank Wash E10 Classification -

Figure 9 – Gas Turbine Losses (Filter p, Foulingand Total) Post Crank Wash E12 Classification -

Therefore, a comparison can be made of total gasturbine output losses post crank wash, resultingfrom both compressor fouling and filter differentialpressure (p) over time, with regards to filtrationefficiency class, as shown below in figure 10:




Figure 10 – Total Losses (Filter p, Fouling) PostCrank Wash F9, E10 and E12 Classification -

These losses post compressor crank wash attributedto compressor fouling and filter differentialpressure (p) over time relative to filtrationclassification are summarised below, in table 3:

FilterClassification Losses (Filter p) Losses

(Fouling)*TOTAL Loss

(6 Months)F9 0.15% 2.78% 2.93%

E10 0.18% 1.34% 1.96%E12 0.21% 0.69% 1.5%

*TOTAL losses include p penalty for higher filtration classification i.e.E10 or E12 in lieu of F9.

Table 3 – Total Gas Turbine Losses (Filter p,Fouling) Post Crank Wash F9, E10 and E12

Classification –

Therefore, it can be seen that increasing filtrationefficiency classification significantly reducesengine losses due to fouling, and the resultingincreased losses due to higher filter differentialpressure, which historically has been viewed by endusers and operators as highly undesirable, is in factmore than acceptable, when considering the overallimproved engine performance.

6. ABK RETROFIT AIR INTAKEFILTRATION SYSTEMS AFTERRETROFIT.

EquipmentThe high velocity air intake filtration systemsinstalled on ABK were retrofitted with AAF multistage, low velocity EPA system technology, whichhas been extensively proven offshore since itsintroduction in early 2003. The systems comprisingupstream vane separators, temporary sacrificialextended surface DriPak GT60 filter bags,AmerKleen M80 pre-filter coalescing pads close

coupled with HydroCel EPA E12 high efficiencyfilter panels, as shown in figure 11 :

Figure 11 – Typical AAF Multi Stage Low VelocityEPA Filtration System (1 - Upstream Vane

Separator, 2 - Temporary Sacrificial ExtendedSurface DriPak GT60 Filter Bags, 3 - AmerKleenM80 Pre-filter Coalescing Pads, 4 - HydroCel E12

EPA High Efficiency Filter Panels)

The AAF multi stage low velocity EPA filtrationprincipals of operation are:

The upstream vane separator removes themajority of large airborne water droplets, suchas sea sprays, fogs, mists and large aerosols.

The sacrificial extended surface Dripak GT60filter bags (being a hybrid filtration stageaddition for Middle East applications,temporarily installed during annual high dustconcentration periods), remove sand and dustparticulate that are carried from the MiddleEastern deserts out to sea by Harmattan likewinds, and prevent the AmerKleen M80 pre-filter coalescer pads and AAF HydroCel EPAE12 high efficiency panel filters reaching anundesirable premature terminal resistanceduring these cyclical high dust load conditions.

The AmerKleen M80 pre-filter pads removeairborne particulates and also coalesce smallaerosols that have passed through the upstreamvane separator, whereby the aerosols coalesceinto larger droplets and due to gravity drainfreely from the pad fibre structure.

The HydroCel EPA E12 panel filters removesmall and sub-micron airborne particulates andalso capture any sub-micron aerosols that may




have passed through the upstream pre-filtercoalescing pads.

The HydroCel EPA E12 has many intricateinnovative drainage design features, that incombination with highly hydrophobic andoleophobic media (in both clean and dirtymedia conditions) and full polyurethane pottingof the media pack, ensures the aerosols cannotpass further into the clean air stream and drainfreely from the filter elements.

Additionally the AmerKleen M80 coalescingpre-filters and HydroCel EPA E12 panel filtersare close coupled together and retained in aninclined filter matrix to effectively drain anycaptured aerosols and droplets into multi-levelhorizontal drain channels, thus furthermoreensuring effective removal of aerosols from theair intake system.

Note: as ISO EN779:2012 and EN1822:2009 teststandards do not take into consideration real worldoffshore conditions, AAF take this shortfall in mindand perform additional testing of offshore filterelements and filtration systems, using a purposelydeveloped offshore simulation rig, whereby theproducts under test are simultaneously challengedwith hydrocarbon rich dusts, hydrocarbon aerosolsand sea water aerosol sprays.

Materials of ConstructionThe retrofit multistage low velocity EPA filtrationsystems are constructed from industry recognisedand widely specified materials, namely stainlesssteel 316L housings, filter bank matrices and vaneseparators.

Additionally, the filtration media materialscomprise state of the art synthetics, progressivedensity glass fibres and EPA glass fibres, withvarying degrees of advanced hydrophobic andoleophobic media treatments.

Filtration Efficiency ClassesThe individual filtration efficiency classifications ofthe products employed for the ABK retrofit areshown below in table 4.

Filter Element EN779 Class EN1822Class

DriPak GT60 F6 -AmerKleen M80 G4 -HydroCel E12 - E12

Table 4 – ABK Retrofit Low VelocityFiltration Efficiency Classes -

The final filtration stage HydroCel EPA filter istested to EN1822:2009, with a classification ofE12 and a minimum efficiency of 99.806% at theMPPS of 0.134μm, as shown below in figure 12,thus the filtration efficiency classification beinghighly suited and matched to the atmosphericimpurities at ABK.

Figure 12 – HydroCel MPPS Performance Curve-

7. COMPARISON BETWEEN ORIGINALFILTERS AND NEW FILTERS.

Comparison of Filtration Differential PressuresOriginal High Velocity Air Intake Filtration VersusAAF Low Velocity EPA E12 Air Intake FiltrationThe individual differential pressures of both theoriginal high velocity and retrofitted low velocityair intake filtration stages utilised at ABK, areshown below in table 5. The overall differentialpressures are similar between the low velocity highefficiency EPA filter and the high velocity mediumefficiency filter:




High Velocity Low VelocityVane Separator 70 23*TemporarySacrificial Filter

N/A 55

Pre-filter 100 96High EfficiencyFilter

310 N/A

EPA Filter N/A 370Vane Separator 70 N/ATOTAL (Pa) 550 544* Temporarily installed during Harmattan periods.

Table 5 – High Velocity and Low VelocityFiltration System Initial Differential Pressures p

(Pa) -

Equipment Weight and Dimensional EnvelopeComparison of Multistage High Velocity Air IntakeFiltration Systems vs Retrofit Multistage LowVelocity Air Intake Filtration Systems.The table 6 below illustrates the delta in equipmentestimated weights for the multistage high velocityair intake filtration systems versus retrofitmultistage low velocity air intake filtration systems.

Air Filtration SGT400(Kg)

RB211(Kg)

PGT10(Kg)

HighVelocity 1800 10650 2030

LowVelocity 5940 14500 4450

Variation inWeight % +330% +136% +219%

Table 6 – Equipment Estimated Weights -

The images below illustrate the differences inequipment envelope dimensions for the multistagehigh velocity air intake filtration systems vs retrofitmultistage low velocity air intake filtration systems,including the associated intake duct systems, for theSGT400s (Figure 13), PGT10s (Figure 14), andRB211 (Figure 15):

Figure 13 – SGT400s Filter Arrangement(Side View and Top View) -

Figure 14 – PGT10s Filter Arrangement(Side View and Top View)-




Figure 15 – RB211 Filter Arrangement (SideView and Top View)

A summary of equipment envelope dimensions isshown below in table 7-1 and table 7-2:

Engine AirFiltration

A(mm)

B(mm)

C(mm)

D(mm)

E(mm)

SGT400

HighVelocity 2,280 6,680 2,949 2,702 6680

LowVelocity 4,240 9,750 4,959 5,380 9750

RB211

HighVelocity 5,600 8,362 10,126 5,800 NA

LowVelocity 7,739 7,162 12,165 5,800 NA

PGT10

HighVelocity 2425 5476 2755 3938 NA

LowVelocity 4190 3920 3138 4570 NA

Table 7-1 – Summary Equipment EnvelopeDimensions –

Air Filtration SGT400 RB211 PGT10High VelocityFootprint (m2) 18.0 48.5 21.6

Low VelocityFootprint (m2) 52.5 41.5 17.9

Variation inFootprint % 292% -14% -17%

Table 7-2 – Summary Footprint –

8. CHALLENGES OF PERFORMING AIRINTAKE FILTRATION SYSTEMSRETROFIT OFFSHORE

Due to the various air intake filtration systemequipment locations on the ABK platform and theirassociated access limitations, retrofitting of the airintake filtration systems warranted severalchallenges to be overcome by both TOTAL andAAF:

RB211 24G56 on KPP and SGT400 on PPSP,the platform crane at full radius was short ofthe required centre-line lifting for the air intakefiltration modules, requiring the design andmanufacture of a bespoke overhangingplatform and specialised lifting frame, whichwas used in conjunction with machine skates,to pull the equipment into the requiredposition.

SGT400s on NKPP were not accessible withthe platform crane, but required the provisionof a crane barge, to perform the heavy destructand installation lifts.

PGT10s on GLP due to space restrictionsbetween adjacent units, required a modularretrofit concept and build sequence.

Additionally the retrofits were performed inextreme heat of up to 50 degrees C, requiringthe workforce to rest frequently on an hourlybasis and follow a continuous hydrationregime.

9. PERFORMANCE IMPROVEMENTAFTER AIR INTAKE RETROFIT

Pollution Arrested at ABKIn the case of ABK, filter elements from each stagewere removed after 8,000 hours operation andexamined using Scanning Electron Microscopy(SEM) and localised chemical information (EDX)analysis. The results of these tests showed that thefiltration system had arrested inorganic materials ofaluminium silicates, and calcium and sulphur richparticles that were most likely calcium sulphate.

Also present were other silicates (sand), sodium andsulphur rich particles (most likely sodium sulphate),salt (NaCl), iron oxide based corrosion residues,




insect parts and what appeared to be turquoisecoloured polymeric debris.

The size of the particulate residues arrested by theair intake filtration system varied considerably fromlarge shards of wood, insects and feathers, to themajor inorganic components. The inorganic debriswas in general bound in agglomerates comprised ofindividual particles, with varying micron and sub-micron particle size, as shown below in figure 16.

Figure 16 – AAF HydroCel SEM Image-

Water WashingThe data analyses from 2004 up to 2016 are veryinteresting regarding water wash practices withEPA filtration. With low grade filtration, theaverage number of water washes per year wasrepeatedly ten per year for turbo-compressors (aero-derivative and heavy duty technologies), whereas itwas five for turbo-generators (light industrialtechnology). After the installation of the EPAfiltration in 2012, the number of water washes wasdrastically reduced to 1 per year on average forboth applications and all technologies (refer toFigure 17). Theoretically, passing from 10 to 1, thesuppression of the water washes allows 1.2% ofavailability to be recovered per gas turbine. If weconsider a gas turbine that is available 90% of thetime, this represents 12% of the necessary effortand becomes a huge improvement.

Figure 17 – Cumulative Numberof Water Washes along Years –

Compressor efficiencyThe effect of the E12 high grade filtration is quiteimpressive in maintaining compressor cleanliness.For the ABK turbo-generators and for operationalreasons, we had the possibility to compare tworotors showing a similar number of running hoursand equipped with two different filter grades (M5and E12) shown figure 18 and figure 19. TheSGT400 gas turbine exhibits a rotor that looksbrand new with the E12 high filtration grade. Therotor equipped with the M5 low grade filtrationdisplays salt deposits on both sides of the rotorblades.

Figure 18 - ABK SGT400 Compressor Foulingafter 4000 Running Hours with the initial M5

Filtration Grade -




Figure 19 - ABK SGT400 Compressor Cleanlinessafter 5300 Running Hours with the Retrofitted E12

Filtration Grade -

In the example given, the E12 grade efficiencyagainst salt ingress seems to be quite satisfactory.

Unlike the SGT400s, the RB211 engine is installedin a different part of the prevailing winds carryingthe exhaust fumes from the PGT10 2-shaft andSGT400 gas turbines. The RB211 VIGV (VariableInlet Guide Vane) shows varying degrees ofcontamination and oil staining over the concave andconvex aerofoil surfaces with minor erosion,coating loss and corrosion. The IP (IntermediatePressure) compressor blades exhibit airbornecontamination and carbon built up even with theE12 high grade filtration (Figure 20). The size ofthe carbon fumes particle is less than 1 micron andfor most of them it is around 0.1 micron. Despitethe EPA E12 high grade filtration, quantities ofsoot, oil mist and carbon particles close to MPPSvalue (Most Penetrating Particle Size) are passingthrough the air filters potentially. The propersealing of the filter is also questionable.

Figure 20 - IP Compressor Blades DisplayingCarbon Deposit and Airborne Contamination after

7650 Running Hours. Rotor Equipped with E12Filtration -

From a quantitative viewpoint, the impact of theEPA filtration on compressor efficiency is quitespectacular. With a low grade filtration system thecompressor efficiency of a PGT10 2-shaft over8000 running hours is 83% on average (Figure 21)whereas the performance of the axial compressor isconstantly maintained at 85% with the EPAfiltration system (Figure 22). Fuel gas consumptionis therefore improved by 2.5% and contributes to anincrease in production.

Figure 21 - PGT10 2-shaft Axial CompressorEfficiency over 8000 Running Hours and 9 Water

Washes -




Figure 22 - PGT10 2-shaft Axial CompressorEfficiency over 8000 Running Hours and 2 Water

Washes -

Engine Part Integrity - Hot section wearingThe new EPA filtration system makes it possible todelay the effect of hot corrosion. This is particularlynoticeable on the heavy duty combustor liners ofthe PGT10 2-shaft. With the low grade filtration,the combustor liners were able to last 2,600 runninghours on average. Figure 23 shows excessivedamage on the combustion liners after 8,000 hourswith a low grade filtration. With the E12 filtrationgrade, the liners are able to last 8,000 running hourson average in reasonable condition for an expectedlife, without being replaced, of 16,000 runninghours.

Figure 23 – ABK PGT10 2-Shaft Combustion LinerSubject to Hot Corrosion after 8,000 Running

Hours with Low Grade Air Filtration –

For aero-derivative gas turbines, a hot gas pathexchange with mild fuel gas is normally anticipatedat 25,000 hours. A sour fuel gas application is verydemanding because a hot gas path is a matter of hotcorrosion (Figure 24). The engine integrity isclearly impacted by running EPA filters. BeforeEPA implementation the gas generator life spanvaried from 1,000 to 4,000 hours and the generatorgenerally had to be replaced after a majorbreakdown creating an unplanned event and aproduction shortfall.

Figure 24 - ABK RB 211 Front Combustion Linernot Re-Usable after 6,800 Running Hours and Low

Grade F7 Filtration –

Since 2013, the gas generator replacement for theRB211 engines initially engaged after 3,800running hours has been pushed forward to 7,650running hours (Figure 25).

Figure 25 - ABK RB 211 Front Combustion LinerRe-Usable after 7650 Running Hours and E12 High

Grade Filtration -




The table below (Table 8) shows the replacement ofthe gas generators in recent years.

ExchangeDate

June2013

February2014

November2014

October2015

RunningHours 3,800 4,500 6,300 7,300

Increase 0% +18% +66% +92%Table 8 – RB211 Gas Generator Exchange -

This delay in the gas generator exchange isobtained principally by reducing the impact of thehot corrosion mechanism. EPA filtration helps toretain both the dry particulates of alkali and someof the wet alkali.

Availability, ReliabilityFrom an availability and reliability standpoint, theuse of EPA filtration seems to be beneficial on allthree technologies. It reduces the availabilityvariances and improves the general availabilityaverage as shown in figure 26. The variance spreadis particularly high for heavy duty and lightindustrial.

Figure 26 – Gas Turbine Availability

EPA filtration exhibits the same effects onreliability showing variance containment and theimprovement of the average reliability value asshown in figure 27.

Figure 27 – Gas Turbine Reliability -

Planned and Unplanned DowntimeThe EPA filtration provides a reduction inunplanned downtime for the three gas turbinetechnologies (Figure 28). Variance is contained in alower value at around 500 minutes on average in2015. This represents 8 hours of unplanneddowntime in a year.

Figure 28 – Gas Turbine Unplanned Downtime -

The effect of EPA filtration on gas turbine planneddowntime is not significant (Figure 29).

Figure 29 – Gas Turbine Planned Downtime -MTBF, MTTFConsidering the hot corrosion phenomena in ABKgas turbines, EPA filtration generates a beneficialtrend for the three gas turbine technologies. MTBF




values exhibit a continuous improvement. The mostspectacular consequence is relative to the aero-derivative gas turbine. The aero-derivative MTBFvalue is multiplied increased by 6 and moves from200 hours to 1,300 hours (Figure 30).

Figure 30 – Gas Turbine MTBF -

The incidence of EPA filtration on MTTR isdifficult to identify (Figure 31).

Figure 31 – Gas Turbine MTTR -

Filter ExchangeWith the new configuration, the pre-filter GT 60and M80 coalescer are removed and changed every6 months. For the Hydrocel E12, new filterelements replace the old ones every 12 months.

ProductionThe new EPA filter arrangement provides areduction in production shortfall over time. Thisreduction mainly comes from the reduction in gasturbine axial compressor washing. The productionshortfall improvement is highly dependent on themachinery duty as shown in figure 32.

Figure 32 – Production Shortfall for Turbo-compressors –

10. DISCUSSIONS

Hot Corrosion still ContinuesDespite the installation of high efficiency EPA E12air filtration, hot corrosion continues to progressinside the gas turbine in marine environments. Gasturbines are not able to reach their expected lifespan. Alkali, such as salt, are still passing throughthe air filters even when they are EPA andhydrophobic. Industry standards and codes do notconsider the efficiency of the filter regarding saltand dissolved salt in water in humid environments.The alkali filtration remains a matter of interestknowing hot corrosion eradication is still a strongdriver for future Opex and Capex cuts.

Soot and Oil IngestionAccording to this 3-year ABK experience, gasturbine cleanliness is highly sensitive to theinstallation location. Locations which are moreexposed to oil fumes and soot have an impact onaxial compressor efficiency. The pointing questionis how oleophobic filters are and what the optimumsize would be for the MPPS (Most PenetratingParticle Size) value.

Filter ExchangeComplementary experience is necessary in order tohave a good understanding of filter ageing.Additional data are needed to optimize the air filterexchanges on ABK.




11. CONCLUSION

The EPA E12 air filtration retrofit is a huge task tocarry out offshore but this grade of filtration bringsa real improvement in oil and gas operations.

Quantitatively, for seven gas turbines, EPAfiltration maintains the cleanliness of the axialcompressor and reduces the water washingoperations (7 per year instead of 31) with multipleassociated consequences. Firstly, this is atremendous reduction in demineralised water usagegenerating energy savings and grey water disposalreduction. Secondly, keeping a high compressorefficiency, it generates a reduction in the carbonfoot print of 2.5% per machine. Both of thesereductions are good contributors to improving theoverall ABK energy efficiency. In addition, EPAfiltration delays the effect of the hot corrosion,contains the variance of availability and reliabilityand, depending on the gas turbine application,improves the production.

Qualitatively, such a high grade of filtration helpsto maintain a longer integrity of gas turbine internalparts generating Opex savings in the long term.

12. REFERENCES

EN 779:2012 Particulate Air Filters for GeneralVentilation – Determination of the FiltrationPerformance.

EN 1822-1:2009 High Efficiency Air Filters (EPA,HEPA and UPLA) – Part1: Classification,Performance, Testing and Marking.

impact of epa air intake filtration on gas turbines operating in middle east offshore applications...

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