Gas Turbine Performance Optimization Using Compressor Online Water Washing Technique

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1 Engineering, 2011, 3, doi: /eng Published Online May 2011 (htt:// Gas urbine Performane Otimization Using Comressor Online Water Washing ehnique Abstrat Ezenwa Alfred Ogbonnaya Deartment of Marine Engineering Rivers State University of Siene and ehnology, Nkolu, Port Harourt, Nigeria Reeived February 10, 2011; revised Marh 22, 2011; aeted Aril 6, 2011 he ability to redit the behaviour of a gas turbine engine and otimize its erformane is ritial in eonomi, thermal and ondition monitoring studies. Having identified fouling as one of the major soures of omressor and therefore gas turbine deterioration, a omuter-based engine model was develoed to otimize the erformane of gas turbines. he aer thus resents an analysis of omressor hand leaning, on and offline omressor washing to atualize the tehnique using a omuter rogram in Visual Basi rogramming language with data olleted over a eriod of fifteen weeks for 2 gas turbine lants G1 and G2. he results of the data olleted, when ollated, shows that after washing, the overall oerational effiieny hanged from 39.2% to 46.25%. o otimize the erformane of gas turbine engines, it is therefore reommended that oerators should erform a ombination of omressor hand leaning, offline and online washing simultaneously. Keywords: Gas urbine, urbomahinery Comonents, Fouling, Performane Otimization, Oerational Praties, Comressor Water Washing 1. Introdution Gas urbines (Gs) have wide range of industrial aliations. Proer maintenane and oerating raties an signifiantly affet the level of erformane degradation and thus time between reairs or overhauls of a G [1-5]. he orret onstrution and oeration of the omonents of G lants are also neessary for roer understanding and monitoring. Furthermore, the funtion of a G is the result of the fine-tuned ooeration of many different omonents of the lant. [6-9]. he emhasis of this work is on the turbomahinery or aerodynami omonents of the G. Hene the seial ontribution of this work to G oeration and maintenane is that it hels to rolong the life of the turbomahinery omonents of the engine. From the oint of view of aliation, the G s omressor is affeted by the environmental onditions of the site [10-12]. With inreasing oerating time, degradation of the omressor manifest in the form of redued erformane. he major ause of redution in omressor effiieny and inlet air mass flow is fouling. Others are abrasion, orrosion and erosion of the blade surfaes. he degradations of the G omressor has diret influene on the G ower lant effiieny, ressure ratio and ower. With a view to revent degradation, otimize erformane and inrease availability, Gs are equied with sohistiated air filter systems. hese air filter systems signifiantly redue the amount of ontaminants that Gs are subjeted to but annot filter out the ontaminant omletely [11]. his resent work alied online water washing to otimize the erformane of a G lant on industrial duty for eletriity generation in Saele, Delta State of Nigeria. It further looked into the lus and minus of other Gs maintenane tehniques. Oeration of a G at steady oututs an lead to deosition from the ombustion gas on the blades. Deosits ause outut and effiieny to dro by reduing the effiieny of energy transfer and eventually restriting the flow of the ombustion gases [5,13]. here are quite a number of wear out roblems assoiated with G. he blades may break off or orrode, while bearings may wear out due to frition and vibration. Common faults on the rotor inlude rubbing, temorary unbalane, eentriity raking or/and misalignment [10]. he omressor may exeriene air leakage roblems while

2 E. A. OGBONNAYA E AL. 501 deosits on the blades an reate blade washing effets [14]. Performane analysis an be alied to both rotating and stationary arts of the G. It is one ondition monitoring tehnique whih allows the otimum time for restorative maintenane to be alulated, where the deterioration may result in inreased fuel onsumtion or in redued outut or both [15-21]. he tyes of omressor leaning methods with their merits and demerits are detailed as follows: 1.1. Comressor Abrasive Cleaning he aliation of abrasive materials for leaning of omressors suh as the injetion of rive or walnut shell into the omressor for its learing is beoming outdated [11,22,23]. his is beause the erosion imat is more followed by the danger that these non-liquid materials are aable of logging the assages of the seonddary air system. Furthermore, these non-liquid artiles may ause damage to the omressor blade oating. Saele, Delta State of Nigeria. Both Gs were ommissioned on the same day. After a eriod of three month G1 and G2 were shutdown for maintenane. he online washing method was done on weekly intervals for a eriod of fifteen weeks. Deminerialized water was injeted through a onfiguration of small nozzles in the air flow before the first omressor stage. At the end of the exerise, the data gathered from both lants on daily basis were samled and the mean used in this researh. hese arameters enabled the alulation of the omressor effiieny and other relevant oerational arameters. In this work, it was assumed that the omressor inlet onditions orresond to the ambient onditions. he analyses were erformed with the equations below, while the exerimental setu is shown in Figure 1. Figure 2 also shows the enthalhy versus entroy ma of a omressor. It is between 2 and 2' that water washing takes lae. herefore H 2 is the enthaly after water washing Comressor Hand Cleaning his entails leaning the inlet guide vanes (IGV) and the blades of the first omressor row with brushes and a detergent [24]. Although this method is effetive for removing artiles stiking to the blade surfae, its shortoming is that it is time onsuming and requires the Gs to be shutdown. Hene this method should be suorted by offline washing Comressor Offline Washing In this method, the G has to be shutdown and ooled, followed by flushing the omressor with demineralized water [24]. his aroah enables omressor fouling to be removed virtually omletely. With a view to avoid Gs non-availability, this method should be used during normal insetion interval. Figure 1. Exerimental setu for Gs 1 and Comressor Online Washing his tehnique is normally done during Gs base-load oeration with the IGVs in the fully oen ondition. It is ahieved by installing an online washing system at the air inlet of the Gs [25,11]. Although this method is known to diminish omressor fouling, it an not omletely eliminate it. 2. Methodology he test engines are Gs 1 and 2 of the same aaity (45 MW) on industrial duty for eletriity generation in Figure 2. Enthaly versus entrohy ma of omression [11].

3 502 E. A. OGBONNAYA E AL. he omressor omonent is modeled as: P P ' Similarly, the turbine omonent is exressed as: P 3 3 ' 4 P4 1 (1) (2) Furthermore, the isentroi effiieny of the omressor is exressed as; Isentroi enthalhy dro Atual enthaly dro h h ' 2 2 h1 h 1 (3) Also, the isentroi effiieny of the turbine is given by: Atual enthalhy dro Isentroi enthaly dro (4) he omressor work is modeled as: W h h (5) 2 1 Sine, dh = Cdt, W C (6) 2 1 he turbine work is modeled as: 4 3 W h h (7) W C (8) 4 3 he heat inut is exressed as: Q h h (9) in in Q C (10) Similarly, the heat outut is given by: Q h h (11) out out Q C (12) he Network outut and heat inut is exressed resetively as: W W W (13) Q Qin Qout (14) he overall effiieny of the test engine is modeled as: Net work th (15) NetHeatSulied W W th (16) Qin By aroriate substitutions, Noting that is alled the ressure ratio and is exressed as: 3. Results 1 th 1 1 (17) P P 2 3 P 1 P (18) 4 he results of the analyses arried out on G 1, and G2 are shown in ables 1 and 2. able 2 shows the data taken before water washing. able 3 shows the monitored data for G2 during the ombination of the 3 water washing methods onsidered in this work while able 4 shows the values of erentage derivations in outlet arameter. he values in these tables were used to lot the various grahs shown from Figures 5 to 9. hese grahs are further used to exlain the imat of this work to engineering ratise. Figure 3 shows a rogramme flowhart to determine the erformane of the Gs. he flowhart was onstruted from Equations 6, 8 and Disussion of Results he trajetories of the Gs when the omressor outlet ressure is lotted against date in weeks are shown in Figure 4. It shows that before the washing exerise, the lants were oerating at 7.00 bar, as deited in trend for G1. he omressor outlet ressure is an indiation of fouling, as this menae auses a redution of the ressure. Following the aliation of water washing to G1, it was observed that the ressure inreased to 7.88 bar. hese ressures were maintained by the regular weekly online washing. Furthermore, the aliation of omressor hand leaning, online and offline washing during shutdown resulted to a ressure of 8.8 bar against the design value of 9.4 bar. It is reasonable to say that although online water washing yielded a meaningful result but a ombination of omressor hand leaning during shutdown, online and offline washing resulted to a better erformane.

4 E. A. OGBONNAYA E AL. 503 Figure 4. Grah of omressor outlet ressure against date in weeks. Figure 5. Grah of turbine inlet temerature against date in weeks. Figure 3. Flow hart for erformane trending drawn from Equations (6), (8) and (17). he ath of the Gs when the turbine inlet temerature is lotted against date in weeks is shown in Figure 5. he trend shows that the use of online water washing imroved the firing temerature of G1 but a ombination of online and offline water washing resulted in an inrease in the firing temerature of 1900k for G2. he grahs of the Gs when the Network outut is lotted against date in weeks are shown in Figure 6. It shows that G1 had initial high network outut whih later dereased due to redeosition of foulants in the later stages of the omressor. Furthermore, Figure 6 shows that with a ombination of omressor hand leaning, offline and online water washing, the network outut of Figure 6. Grah of network against date in weeks.

5 504 E. A. OGBONNAYA E AL. able 1. Monitored Data for G2 before water-washing (G o ). Date (wks) 1 (k) 2 (k) P 1 (bar) P 2 (bar) 3 (k) 4 (k) W net (kj/kg) able 2. Monitored data for G1 with online water-washing. Date (wks) 1 (k) 2 (k) P 1 (bar) P 2 (bar) 3 (k) 4 (k) W net (kj/kg) able 3. Monitored data for G2 during a ombination of omressor hand leaning, online and offline water-washing. Date (wks) 1 (k) 2 (k) P 1 (bar) P 2 (bar) 3 (k) 4 (k) W net (kj/kg)

6 E. A. OGBONNAYA E AL. 505 able 4. s of erentage derivation in omressor outlet ressure under various oerational raties. Date P2 (bar) G1 P2 (bar) G2 P2 (bar) G3 (wks) Design Oerational %D Design Oerational %D Design Oerational %D G2 inreased to 480.0kJ/kg. he grah of omressor effiieny is shown in Figure 7. From the grah, G2 has the highest omressor effiieny of 85%. his is as a result of a ombination of omressor hand leaning and offline/online water washing. Also, G1 yielded omressor effiieny of 82% as a result of alying online water washing only. It also imlies that the air uming aaity of the G2 omressor has inreased. he grah of overall Gs oerational effiieny is shown in Figure 8. It is observed that a small hange of the omressor effiieny have a signifiant effet on theoverall G erformane and effiieny. G1 has om- Figure 8. Grah of overall oerational effiieny against date in weeks. Figure 7. Grah of isotroi omressor outlet effiieny against date in weeks Figure 9. Perentage deviation in omressor outlet against date in weeks.

7 506 E. A. OGBONNAYA E AL. ressor effiieny of 82% whih resulted to overall G effiieny of 45.8%. Also, G2 has omressor effiieny of 85% and it resulted to overall oerational effiieny of 46.25%. Also, the grah of erentage derivation in omressor outlet ressure against date in weeks is shown in Figure 9(a). 5. Conlusions A omarative analysis has been arried out on three Gs on industrial duty for eletriity generation. hese Gs were ommissioned at the same time before the researh was arried out on them. Go served as a ontrol while omressor online washing was alied on G1, a ombination of omressor hand leaning and online/offline water washing was alied to G2. he exerise lasted for fifteen weeks. he result of the analysis shows that with the use of omressor online water washing on G1 yielded a omressor effiieny of 82% and overall oerational effiieny of 45.8%. Also, the use of omressor hand leaning, online and offline water washing on G2 yielded a omressor effiieny of 85% and overall oerational effiieny of 46.25% the results are handy to onlude that an aetable balane between these maintenane and oerational raties imroves the Gs erformane and otimize their availability. 6. Referenes [1] I. S. Diakunhak, Performane Degradation in Industrial Gas urbines, ASME Paer 91-G-228, [2] P. C. Frith, he Effet of Comressor Rotor i Cros on urbo- Engine Performane, ASME Paer 92-G-83, [3] S. A. Khalid, A. S. Khalsa, I. I. A. Waitz, S. C. an, E. M. Greitzer, N. A. Cumsty, J. J. Adamzyk and F. E. Marble, Endwal Blokage in Axial Comressor, ASME Paer 98-G-203,1998. [4] R. J. Kind, P. J. Serjak and M. W. P. Abbott, Measurements and Predition of the Effets of Surfae Roughness on Profile Losses and Deviation in a urbine Casade, ASME Paer 96-G-203, [5] R. Kurz and K. Brun, Degradation in Gas urbine Systems, ASME Journal of Engineering for Gas urbines and Power, Vol. 123, No. 1, doi: / [6] R. K. Rajut, A extbook of Power Plant Engineering, Laximi Publiations, New Delhi, [7] D. G. Wilson, he Design of High Effiieny urbomahinery and Gas urbines, MI Press, Mass, [8]. D. Easto and A. MConkey Alied hermodynamis for Engineering ehnologists, 5th Edition, Addison-Wesley Longman, Ltd., UK, [9] P. K. Nag, Power Plant Engineering, 2nd Edition, ata MGraw Hill Publishing Comany Limited, New Delhi, 2001,.764. [10] E. A. Ogbonnaya, Modeling Vibration Based Faults in Rotor Shaft of Gas urbines, Ph.D hesis, Rivers State University of Siene and ehnology, Port Harourt, [11] E. Shneider, Dermiriioglu, S. Fraano and D. herkom, Analysis of Comressor Online Washing to Otimize Gas urbine Power Plant Performane, Proeedings of ASME urbo Exo 2009, Orlando, 8-12 June 2009, [12] E. A. Ogbonnaya and K. heohilus Johnson, Use of Multile Variable Mathematial Method for Effetive Condition Monitoring of Gas urbine, Proeedings of ASME urbo-exo, Glasgow, June 2010, [13] R. J. Boyle, Predition of Surfae Roughness and Inidene Effets on urbine Performane, Journal of urbomahinery, Vol. 116, No. 4, 1994, doi: / [14] E. A. Ogbonnaya, H. U. Ugwu and C. N. Johnson, Comuter-Aided Solution to the Vibrational Effet of Instabilities in Gas urbine Comressors, Engineering, Vol. 2, No. 8, 2010, doi: /eng [15] R. Beebe, Condition Monitoring by Performane Analysis to Otimize ime for Overhaul of Centrifugal Pums, 52nd Annual Meeting for Mahinery Failure Prevention Soiety, Virginia Beah, 3 August 2009, [16] C. B. Meher-Homji, M. Chaka and A. E. Brouley, he Fouling of Axial Flow Comressor-Causes,Effets, Susetibility and Sensitivity, Proeedings of ASME urbo Exo Orlando, Florida, 8-12 June 2009, [17] M. Venturini, Influene of Blade Determination on Comressor and urbine Performane ASME Paer G , [18] R. E. Duudas, he Use of Performane Monitoring to Prevent Comressor and urbine Failures, ASME Intentional Gas urine and Aeroengine Congress, Paer No. 82-G-66, [19] E. D. Bently, C.. Hath and B. Grissom Fundamental of Rotating Mahine Diagnositi, Bently Pressurized Bearing Press, Minden, [20] E. A. Ogbonnaya, Diagnosing and Prognosing Gas urbine Rotor Shaft Faults Using the MICE, Proeedings of ASME urbo Exo G , Orlando, 8-12 June 2009, [21] H. C. Pussey, urbo-mahinery Condition Monitoring and Failure Prognosis, Shok and Vibration Information Analysis, entre/h1-est Laboratories, Proeedings of Institute of Vibration, Virginia, 8 November 2007, [22] M. P. Boye and F. Gonzales, A Study of Online and Offline urbine Washing to Otimize the Oeration of a

8 E. A. OGBONNAYA E AL. 507 Gas urbine, Journal of Engineering for Gas urbine and Power, Vol. 129, No. 1, 2007, doi: / [23] J. P. Stalder, Gas urbine Comressor Washing State of the Art: Field Exerienes, Journal of Engineering for Gas urbine and Power, Vol. 123, No. 2, 2001, doi: / [24] S. Demirioglu, Detail Analysis of Comressor Online Wash Imat in the Gas urbine Performane, Diloma hesis, F. H. Offenbury, [25] K. R. Brun and H. Simmons, Aerodynami Instability and Life Limiting Effets of Inlet and Interstage Water Injetion into Gas urbines, ASME Paer G , Nomenlature C = Seifi heat aaity at onstant ressure (kj/kg) D= Perentage derivation ΣQ= Network outut (kj/kg) ΣW= Network outut (kj/kg) G= Gas turbine Go= Monitored data before water washing of Gs. h 1 = Seifi enthaly at omressor inlet (kj/kg) h 2 = Seifi enthaly at omressor outlet (kj/kg) h 3 = Seifi enthaly at turbine inlet (kj/kg) h 4 = Seifi enthaly at turbine outlet (kj/kg) n = Isentroi effiieny of omressor η τ = Isentroi effiieny of turbine η th = Overall thermal effiieny P 1 = Comressor inlet ressure (bar) P 2 = Comressor exit ressure (bar) P 3 = urbine inlet ressure (bar) P 4 = Q in = Q out = = 1 = 2 = 2 1= 3 = 4 = 4 1= W= W = urbine outlet ressure (bar) Heat inut (kj/kg) Heat outut (kj/kg) Pressure ratio Comressor inlet temerature (k) Comressor outlet temerature (k) Comressor isentroi outlet temerature (k) urbine inlet temerature (k) urbine outlet temerature (k) urbine isentroi outlet temerature (k) Comressor work (kj/kg) urbine work (kj/kg)