EFFECTS OF PERFORMANCE DETERIORATION ON GAS PATH .

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VOL. 11, NO. 24, DECEMBER 2016ISSN 1819-6608ARPN Journal of Engineering and Applied Sciences 2006-2016 Asian Research Publishing Network (ARPN). All rights reserved.www.arpnjournals.comEFFECTS OF PERFORMANCE DETERIORATION ON GAS PATHMEASUREMENTS IN AN INDUSTRIAL GAS TURBINEAmare D. F., Aklilu T. B. and Gilani S. I.Department of Mechanical Engineering, Universiti Teknologi Petronas, Tronoh, Perak, MalaysiaE-Mail: dadorthot@gmail.comABSTRACTStudying gas turbine degradation causes and their consequences helps to obtain profound comprehension in howperformance deterioration affects the dependent parameters and to explore relevant information about the nature of thefault signatures for fault diagnostics purpose. In this paper, the effects of compressor fouling, gas generator turbine erosion,and power turbine erosion on the engine dependent parameters were considered separately and together. In this regard,firstly, performance prediction model was developed to LM2500 engine using gas turbine simulation program. It was thenused to simulate the deterioration effects by means of artificially implanted fault case patterns. Comparison of the cleanand deteriorated measurement gives the deviation due to performance degradation. Accordingly, sensitivity order of the gaspath parameters to the corresponding performance deterioration was assessed. This helps to select the key parameters,which are crucial in the process of fault detection and isolation. The results showed that, in most of the cases, air mass flowrate, compressor delivery pressure and temperature, gas generator rotational speed, power turbine inlet pressure, andexhaust gas temperature showed significant deviations. Particularly, the compressor delivery pressure and exhaust gastemperature were the parameters highly influenced by all the fault cases. Moreover, faults that have similar impacts areidentified, in order to show the difficulty of gas turbine health assessment through direct observation to the measurementdeviations.Keywords: gas turbine, component degradation, performance deterioration, measurement deviation.INTRODUCTIONGas turbines have several applications includingpower generation and driving different compressors in oiland gas industries. As time goes on, faults such as fouling,erosion, corrosion, blade tip clearance, object damage andthermal distortion can cause performance degradation.This may result high energy consumption, high operationand maintenance costs, major damage to gas pathcomponents, and environmental pollution. Degradationsare manifested by gas path measurement variations. Thechallenge on engine health assessment based on thehistory of measurement discrepancies is that theperformance can be changed due to ambient condition,load and fuel delivery changes and/or due to componentperformance degradation(s). Regardless of the othereffects, the investigation on the impacts of enginecomponent performance degradation on measurementdeviations provides relevant information about the natureof the fault signatures in fault diagnostics.Over the years, gas turbine performancedegradation has been studied by several scholars. Forinstance some authors in [1-3] and others in [4-5] focusedon the assessment of compressor and turbine degradationeffects, separately. Kurz et al. [6], Morini et al. [7],Lakshminarasimha et al. [8], and recently Campora et al.[9] evaluated the effects of compressor and gas generatorturbine degradations separately and together on singleshaft gas turbine overall performance. In these papers, theresults obtained from the combined effects were the sumof the results of the individual effects. Moreover, Zwebekand Pilidis [10] also investigated the impacts of gasturbine degradation on combined cycle gas turbine(CCGT) power plant performance. In this work, on the gasturbine side, compressor and turbine fouling, compressorand turbine erosion and their combination wereconsidered. In nowadays more attention is given to furtherstudies on compressor fouling causes, their effects onperformance deterioration, and cleaning techniques witheconomic analysis (see, [11-13]). Recently, Mohamedi[14] studied the influence of compressor, compressorturbine and power turbine performance deteriorations,assumed to be happened separately, on gas path parameterdeviations at full load and part load conditions usingcomputer simulation.In the field of engine diagnosis, an optimalparameter selection is very important. Concerning this,many researchers including Ogaji et al. [15], Ganguli et al.[16] and recently Chen et al. [17] proposed differenttechniques. In these studies, compressor dischargepressure (CDP), compressor discharge temperature (CDT),gas generator shaft speed (NGG), power turbine (PT) inletpressure, fuel flow rate (Wf) and exhaust gas temperature(EGT) for twin shaft gas turbines, low pressurecompressor discharge temperature, high pressurecompressor discharge pressure and temperature, highpressure and low pressure compressors’ shaft speeds, Wf,and EGT on double spool gas turbines and air mass flowrate (Ma), fan delivery temperature, high pressurecompressor discharge pressure and temperature, highpressure turbine outlet pressure and temperature, highpressure compressor rotational speed, and Wf on doublespool turbofan engines are suggested as crucial faultdiagnosis parameters, respectively.Although the issue how and in what extent thegas turbine cycle performance affected by the compressorand GG turbine degradations have been addressed, theimpact of PT degradation and concurrent componentdegradations are not considered. Recently, the PT14202

VOL. 11, NO. 24, DECEMBER 2016ISSN 1819-6608ARPN Journal of Engineering and Applied Sciences 2006-2016 Asian Research Publishing Network (ARPN). All rights reserved.www.arpnjournals.comdegradation effect has been addressed by Mohamedi et al.[14]. They evaluated the effects of compressor fouling(CF), gas generator turbine erosion (GGTE), and powerturbine erosion (PTE) taking in to account only one faultat a time. Hence, there is a room to evaluate the degree ofsensitivity of measurement variations and cycleperformance changes to multiple component faults.Thus the fundamental motivation behind thiswork was to give a better comprehension in how a gasturbine engine multiple component degradation affects themeasurement variations. Specifically: to assess theresponse of the measurements to component(s)degradation; to identify key parameters which are highlyinfluenced by engine degradation; to show the level of thechallenge to detect and isolate engine component faults bysimply looking in to measurement deviations.For this purpose, LM2500 engine is consideredand the effects of single, double, and triple componentfaults on the measurements investigated.GAS TURBINE PERFORMANCE SIMULATIONIn this study a double shaft industrial gas turbine engine,LM2500, in oil and gas exploration and productionservices of Petronas Resak Development Project (PRDP)was considered. It consists of 16-stage axial compressor,2-stage gas generator turbine and 6-stage power turbine.Figure-1 illustrates the schematic of the basic enginecomponents with the measurement parameters. The designpoint specifications have also been presented in Table-1.First, the design and off-design performance analysis isperformed using a gas turbine modelling scheme, ‘Gasturbine Simulation Program’ (GSP). For this purpose,generic component maps have been used scaled to thedesign point data of the engine at ISO conditions.Following that the gas turbine performance deteriorationsimulation at full load condition is executed to investigatethe corresponding effects on the engine measurableparameters.Table-1. LM2500 design point specifications.Figure-1. Two-shaft gas turbine engine gas-pathmeasurements.EFFECT OF COMPONENT DEGRADATION ONTHE ENGINE MEASUREMENTS AT FULL LOADGas turbine performance can be degradedtemporarily or permanently. The former can be partiallyrecovered during operation and/or engine overhaul whilethe latter requires replacement [18]. Fouling, erosion,corrosion and blade tip clearance are among temporarydegradation causes. Whereas, airfoil untwist and platformdistortions lead to permanent deterioration. Climateconditions, engine operating conditions, and maintenancepractice are considered as usual sources of these faults.Some studies stated that more than 80% of the enginedegradation is subjected to compressor fouling and turbineerosion [8,19]. The exposure of the power turbine in favorof its location and physical design is lower than thecompressor and gas generator turbine [15]. In this paper,based on Zwebek and Pilidis [10], equal severity rangeshave been considered (see Table-2). Accordingly, for eachfault type listed in Table-3, ten fault patterns rasimha [20], to simulate compressor fouling,for each 0.5% flow capacity loss, its isentropic efficiencyis assumed to be reduced by 0.25%. Likewise, as per [10],to simulate turbine erosion, for each 0.5% flow capacityincrease, isentropic efficiency is assumed to be decreasedby 0.25%. This has been done for the progressivedegradation with steps of 0.5% starting from the healthycondition to the maximum deterioration. Then, themeasurement deviation has been determined usingEquation. (1).(1)Where Zc and Zd are the measurement values atclean and deteriorated conditions, respectively.Table-2. Assumed fault severity ranges.14203

VOL. 11, NO. 24, DECEMBER 2016ISSN 1819-6608ARPN Journal of Engineering and Applied Sciences 2006-2016 Asian Research Publishing Network (ARPN). All rights reserved.www.arpnjournals.comTable-3. Implanted fault cases.Measurement Variation (%)20-2-4MaT3P3NGGWfT4P4T5-6-8-100RESULTS AND DISCUSSIONMeasurement Severity (%)10-1MaT3P3NGGWfT4P4T5-3-4-502040406080100Fault Severity (%)6080Figure-3. Engine measurement variations vs GGTEseverity (%).8MaT3P3NGGWfT4P4T56Measurement Variation (%)Case 1: Single component degradationThis section presents the effects of single gasturbine engine component faults on dependent parameterdeviations. This helps to realize the nature of themeasurement variations associated with single componentfaults. As shown in Figures-(2-4), it has been clear tounderstand that whenever fault severity increases, in allthe cases, measurement variation increases. Themeasurements variation trends obtained from thesimulation agreed with the literature [10,14]. As far ascompressor fouling is considered, at 100% severity EGT,(CDP, PT inlet pressures, Ma, and Wf) and NGG showed5%, 4% and 1.3% delta, respectively. Whereas, the impacton CDT and PT inlet temperature is negligible. When theGGTE is introduced to the engine NGG, CDP, CDT &Ma, PT inlet pressure and temperature, and PT outlettemperature changed by 10%, 9%, 4.6%, 3% and 2.7%,respectively. The maximum variations for all themeasurements, except for NGG, due to PT degradationranges are under 4%. In general, in this work, accordingto their sensitivity to single component degradation, theengine measurements can be categorized as NGG, CDP,Ma and EGT as first class key parameters and CDT, P4and T4 as second class key parameters to identify faults.-220420-2020406080100Fault Severity (%)Figure-4. Engine measurement variations vs PTE severity(%).Case 2: Double components degradationIn this case, the impacts of two component faultsimplanted at the same time has been evaluated. For thispurpose, concurrent fault patterns, i.e., CF and GGTE, CFand PTE, and GGTE and PTE are considered. Figure-(5-7)show the impacts of these faults on measurements’variations. In the case of CF GGTE all the parametersexcept P3 and Ma changes significantly. On the otherhand, the effect of CF PTE on NGG and Ma is negligible.When GGT PTE exists all the measurements changesignificantly. In general, the influence of dual faults onmeasurements is not similar.100Fault Severity (%)Figure-2. Engine measurement variations vs CF (%).14204

VOL. 11, NO. 24, DECEMBER 2016ISSN 1819-6608ARPN Journal of Engineering and Applied Sciences 2006-2016 Asian Research Publishing Network (ARPN). All rights urement Severity (%)86420-2-4-6-8020406080100Faulty Severity (%)Figure-5. Engine measurement variations vs CF andGGTE exist simultaneously (%).degradation effects on NGG and PT inlet pressure showednegligible deviation.0Measurement Variations (%)10-2-4MaT3P3NGGWfT4P4T5-6-8-1002Measurement Variation (%)406080100Fault Severity (%)Figure-8. Engine measurement variations vs CF, GGTE,and PTE exist simultaneously (%).10-1MaT3P3NGGWfT4P4T5-2-3-4-5020406080100Fault Severity (%)Figure-6. Engine measurement variations vs CF and PTEexist simultaneously (%).20Measurement Severity 0Comparison between the effects of component faults onmeasurementsThis section aims to compare the responses ofengine measurements on component degradations, whichexist(s) one at a time or concurrently. For this purpose, theengine model is simulated at maximum severity of all faulttypes considered in this work. Figure-9 illustrates themeasurement responses to each fault types. Themeasurement variations due to double and triplecomponent faults are the sum of the deltas due to the faultswhen they exist separately. For example, Ma decreased by4.14% and 4.5% owing to CF and GGTE, respectively,and increased by 3.44% due to PTE. Consequently, whendouble faults such as CF & GGTE and CF & PTE occur atthe same time, the Ma reduced by 8.54% and increased by0.7%, respectively. In the same manner, when all the threefaults occur simultaneously, the Ma decreased by about4.5%. This works for all of the measurement variations.Thus, it can be concluded that, as also proved by Zwebek[10], the combined effects are additive. Moreover, duringcompressor fouling Ma, CDP, Wf, PT inlet pressure andEGT showed similar variation (about 4%) whereas CDTand PT inlet temperature changed insignificantly.The percentage change in P3 and NGG due toGGTE reached 10% and 9%, respectively, which is twotimes of Ma and T3 changes. P4, T4, and EGT changed by3%. On the other hand, the GGTE has the least effect onFault Severity (%)Figure-7. Engine measurement variations vs GGTE andPTE exist simultaneously (%).Case 3: Three components degradationIn this case, the effects of simultaneous triplecomponent faults namely CF, GGTE and PTE on theengine measurement have been evaluated (see Figure-8). Itis found that EGT, CDP, and PT inlet pressure are the firstthree key parameters in triple fault diagnosis. On the otherhand, the gas turbine simulation for three components14205

VOL. 11, NO. 24, DECEMBER 2016ISSN 1819-6608ARPN Journal of Engineering and Applied Sciences 2006-2016 Asian Research Publishing Network (ARPN). All rights reserved.www.arpnjournals.comWf. Likewise, the highest effect has been shownon NGG (i.e. 7%). Air mass flow rate and CDP changedby 3.5%, CDT, PT inlet presser shows similar variationmore than 2%. The remaining two parameters, fuel massflow rate and PT inlet temperature changes by 1%.For more clarity, the comparative evaluation ofthe parameters’ sensitivity order is given in Table-4. Forthe most part, the EGT and P3 responds were similar. P3showed an insignificant change only under the CF & PTE.Moreover, NGG was very sensitive to single and doublefaults than triple faults. Under all the fault cases T4slightly changed at high severity. Furthermore, thesensitivity of Wf was good in multiple faults than singlefaults. In general, NGG, CDP, EGT, mass flow rate andP4 are the key parameters for all fault types.Figure-9. Gas turbine measurement variations vs singledouble and triple component faults at 100% severity.Table-4. Order of sensitivity of measurement variations to performance deterioration.CONCLUSIONSIn this paper, a gas turbine simulation program(GSP) is utilized to model and simulate a two-shaftstationary gas turbine engine (LM2500) in order toevaluate the effect of performance deterioration on gaspath measurements. The effects of the most common gasturbine faults namely, compressor fouling and turbineerosion on engine measurements such as Ma, CDP, CDT,NGG, Wf, PT inlet pressure and temperature and EGT areinvestigated. For this purpose, CF, GGTE and PTE as asingle component faults, CF & GGTE, CF & PTE andGGTE & PTE as double component faults, and CF, GGTEand PTE as triple component faults are considered. Ingeneral, in most of the cases, Ma, CDP, CDT, NGG, PTinlet pressure, and EGT showed significant deviation.Particularly, the EGT and CDP are highly influenced byall the fault cases.On the other hand, Wf and NGG showed lesssensitivity to single faults and triple faults, respectively.P3 showed an insignificant change only under the CF &PTE. Moreover, when two or more components degradetogether, some of the measurements change insignificantlydue to the additive nature of the faults’ effects.ACKNOWLEDGEMENTSThe authors would like to thank UniversitiTeknologi Petronas (UTP) for supporting this workfinancially.REFERENCES[1] Aker, G.F. and H.I.H. Saravanamuttoo, Predicting gasturbine performance degradation due to compressorfouling using computer simulation techniques. Journalof Engineering for Gas Turbines and Power, 1989.111(2): p. 343-350.[2] Tabakoff, W., A.N. Lakshminarasimha, and M. Pasin,Simulation of compressor performance deteriorationdue to erosion. Journal of Turbomachinery, 1990.112(1): p. 78-83.[3] Saravanamuttoo, I.H. and A.N. Lakshminarasimha,Preliminary assessment of compressor fouling.Turbomachinery International, 1985. 26(7): p. 14-18.[4] Naeem, M., Implications of Turbine Erosion for anAero-Engine’s High-Pressure-Turbine Blade’s LowCycle-FatigueLife-Consumption.Journalof14206

VOL. 11, NO. 24, DECEMBER 2016ISSN 1819-6608ARPN Journal of Engineering and Applied Sciences 2006-2016 Asian Research Publishing Network (ARPN). All rights reserved.www.arpnjournals.comEngineering for Gas Turbines and Power, 2009.131(5): p. 052501-052501.[5] Hamed, A.A., Tabakoff W., Rivir R.B., Das K., AroraP., Turbine Blade Surface Deterioration by Erosion.Journal of Turbomachinery, 2004. 127(3): p. 445-452.[6] Kurz, R., Brun K., and Wollie M., DegradationEffects on Industrial Gas Turbines. Journal ofEngineering for Gas Turbines and Power, 2009.131(6): p. 062401-062401.[7] Morini, M., Pinelli M., Spina P.R., Venturini M.,Influence of Blade Deterioration on Compressor andTurbine Performance. Journal of Engineering for GasTurbines and Power, 2009. 132(3): p. 032401032401.[8] Lakshminarasimha, A.N., Boyce M.P., and MeherHomji C.B., Modelling and analysis of gas turbineperformance deterioration. in ASME 1992International Gas Turbine and Aeroengine Congressand Exposition, GT 1992. 1992.[9] Campora, U., M. Carretta, and C. Cravero. Simulationof a gas turbine engine with performance degradationmodeling. in ASME 2011 International MechanicalEngineering Congress and Exposition, IMECE 2011.2011.[15] Ogaji, S.O.T., Sampath S., Singh R., Probert S.D.,Parameter selection for diagnosing a gas-turbine'sperformance-deterioration. Applied Energy, 2002.73(1): p. 25-46.[16] Ganguli, R., Fuzzy logic intelligent system for gasturbine module and system fault isolation. Journal ofPropulsion and Power, 2002. 18(2): p. 440-447.[17] Chen, M., L. Quan Hu, and H. Tang, an Approach forOptimal Measurements Selection on Gas TurbineEngine Fault Diagnosis. Journal of Engineering forGas Turbines and Power, 2015. 137(7).[18] Meher-Homji, C.B., Chaker, M.A., Motivwala, H.M.,2001, Gas turbine performance deterioration. In: Proc.Thirtieth Turbomachinery Symposium, Texas,pp.139- 175.[19] Diakunchak, I.S. (1992). Performance deterioration inindustrial gas turbines. Journal of Engineering for GasTurbines and Power, 1992. 114(2): p. 161-168.[20] Saravanamuttoo H. I. H., and Lakshminarasimha,1985, A preliminary assessment of compressorfouling, ASME paper No. 85-GT-153.[10] Zwebek, A.I. and P. Pilidis, Degradation Effects onCombined Cycl

In this study a double shaft industrial gas turbine engine, LM2500, in oil and gas exploration and production services of Petronas Resak Development Project (PRDP) was considered. It consists of 16-stage axial compressor, 2-stage gas generator turbine and 6-stage power turbine. Figure-1 illustrates the schematic of the basic engine components with the measurement parameters. The design point .

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