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Department of Marine Engineering, Rivers State University of Science and Technology,Port Harcourt, Nigeria
K. T. Johnson
Department of Marine Engineering, Rivers State University of Science and Technology,Port Harcourt, Nigeria
H. U. Ugwu
Department of Mechanical Engineering, Michael Okpara University of Agriculture,Umudike-Umuahia, Nigeria
C. A. N. Johnson
Department of Marine Engineering, Niger Delta University, Wilberforce Island,Bayelsa State, Nigeria
Barugu Peter Forsman
Department of Welding, Oil and Gas Engineering, Petroleum Training Institute Effurun, Delta State, Nigeria
*Address all correspondence to:
1. Introduction
The ability to model the behavior of gas turbines (GTs) is critical in all aspects of energy and power generation engineering. A computerized approach giving the possibility for a more detailed gas path component fault diagnosis and prognosis using the MVR is presented. A diagnostic engine performance model is the main tool that points to the faulty engine component. The diagnostic component model was also used to come up with the software code-named Thermodynamics and Performance Condition Monitoring( THAPCOM) written in C++ programming language to effectively identify the fault on the engine. Several scheduled visits were thus made to AFAM IV, GT 18, TYPE 13D power plant located near Port Harcourt, in Rivers State of Nigeria. Continuous and periodic monitoring of the thermodynamics/performance parameters such as temperature, pressure, air pumping capability, rotational speed, air, fuel and gas flow were carried out. This exercise lasted for a period of three months on hourly basis to predict the health of the engine. When these data were analyzed by the software, the following results were obtained ΔANAN=1.4598e-0.008,Δncnc=1.6630e-0.007,ΔTcTc=1.1626e-0.008andΔT3cT3c=7.5508e-0.007, which correspond to average overall efficiency of 27.3% and active load of 48MW. These were indications that the test engine had suffered from fouling, degraded compressor performance and seal leakage. THAPCOM gives an alarm signal when a set limit is exceeded so that maintenance could be scheduled.
Nomenclature and Abbreviation:
A=Actual value
AL=Active load (MW)
AN=Area of nozzle (m2)
Δ=Difference between actual and reference value
ητ=Isentropic efficiency of turbine (IET)
MVR=Multi-variable response
nc=Isentropic efficiency of compressor (ICE)
N=Shaft speed (RPM)
ηo=Overall cycle efficiency
D=Percentage deviation a1, a2...a16are values of the coefficients
P1=Compressor inlet pressure (bar)
P2=Compressor exit pressure (bar)
R=Reference value
T1=Compressor inlet temperature (k)
T2=Compressor exit temperature (k)
T’2= Isentrropic compressor exit temperature (k)
T3=Turbine inlet temperature (k)
T4=Turbine exhaust temperature (k)
T’4=Turbine is isentropic exhaust temperature (k)
Γc=Air pumping capability of compressor, APC (m3/s)
The use of performance engine models in diagnostics has been initiated since the early 70’s. The first approaches were based on linearized models (Aretakis, et al, 2010) while Stamatis, et al., (1991), introduced the concept of using directly non-linear models in diagnostics. Also, methodological steps of simulation and modeling used by Maria (1997), Erbes, et al., (1993), Erbes and Palmer (1994) and Ogbonnaya (2004a) proved that modeling and simulation are handy tools for condition monitoring.
The gas path analysis technique gives the possibility to identify the amount of deterioration of individual components and assess its effect on overall performance providing information, which is valuable for improving cost effectiveness of maintenance actions. An analytical tool that can be used for this purpose was presented in Doel (1994). Performance diagnostic methods for identifying deterioration has also been presented by Urban and Volponi (1992) and Volponi (1994). These approaches show which component is malfunctioning and depending on the established experience, can offer an evaluation of the nature of malfunction. The compressor and turbine deterioration are the main cause of the overall performance deterioration. The introduction of measured gas path variables such as pressure, temperature, rotational speed, fuel flow, air flow, gas flow etc is hereby consolidated through this project.
The gas path components, such as compressors, turbines and combustion chamber can be affected by foreign object damage, fouling, tip rubs, seal wear and erosion. The ability to identify the faulty component and simultaneously diagnose the defect with its consequences is another purpose of this chapter. It also allows the operator to take necessary maintenance measures to rectify the fault and provide an assessment of the GTs life cycle and valuable data for prognostics and condition based maintenance scheduling. To achieve these, a detailed component diagnostic modeling needs to be applied. Therefore, the technology of prognosis is recommended in this work because it involves diagnosis, condition and failure model. Prevention of catastrophic and unexpected downtime was thoroughly considered to come up with the software called “THAPCOM” written in C++ programming language to diagnose and prognose the health of the GT. Trend monitoring technique was applied using multiple variable mathematical models (MCMV) in matrix form (Bently et al., 2002). The introduction of “THAPCOM” into GT diagnosis and prognosis conforms to the use of thermodynamics / performance parameters (dependent and independent parameters) as it is the driving force of the GT. “THAPCOM” stands for THermodynamics And Performance COndition Monitoring. As stated in Uhumnwangho, et al., (2003), Brun and Kurz (2007) and Ogbonnaya (2009), the deviation of GT thermodynamics and performance parametric values from their reference values stated in the manufacturer’s manual is an indication of impending failure. This is because condition monitoring is the process of ascertaining the state of a parameter in an equipment such that any adverse significant deviation/change is an indication of impending failure.
1.1. Approaches to monitoring and data collection
Recently, continuous and periodic monitoring are used for GT data collections. Although, the presence of continuous monitoring does not eliminate the need for periodic monitoring (Guy, 1995), the continuous monitoring system warns the operator about imminent problems. Periodic monitoring along with the collection of external data provides a means for analysis and projection of potential long-term problem with respect to maintenance and operation (Ogbonnaya and Theophilus-Johnson, 2010). The collection of GT model data is capable of acquiring the necessary information to monitor and trend the engine health. This present work also utilized periodic monitoring to achieve its aim.
THAPCOM is a viable diagnostic tool because it is capable of providing early warning to progressively indicate imminent fault during engine operation. It analyses conditions to prevent unplanned down time. THAPCOM is an inexpensive diagnostic tool that gives accurate maintenance decision information which is understandable to both low and semi-skilled personnel. Therefore, it also eliminates the short-comings of both performance and trend monitoring. Their similarity is that they all measure pressure, flow temperature and rotational speed simultaneously. The plus of THAPCOM is that it relates deterioration to consequences. THAPCOM uses model-based fault detection and diagnostic techniques (Ogbonnaya and Theophilus-Johnson (2011). This relates the deterioration which the engine has undergone to consequences along the gas path of a GT engine. When THAPCOM is interfaced with a GT, it first studies the system for a period of time through acquiring and processing the real-time data from the engine. The data is processed using system identification algorithms for both the actual (operational) behavior to the reference (design) behavior of the engine.
THAPCOM stores the processed data in its internal data base and also serves as the reference (design) values. These reference values are usually mean values of the performance parameters during factory test. During the monitoring session, THAPCOM processes the acquired engine data and compares the results with the data stored in its internal database. If the results obtained from the acquired data are significantly different from the reference values, THAPCOM indicates a faulty level through a series of alarm signal. The level is determined by the magnitude of their percentage deviation when compared. THAPCOM monitors, compares 15 thermodynamics and performance parameters and uses 4 of the parameters to obtain the coefficients. THAPCOM is similar to MCM, ANNs used in Ogbonnaya (2004a and 2009) in their mode of operation but their difference is that MCM measures only current and voltage while THAPCOM measures thermodynamics and performance parameters. ANNs was used to diagnose and prognose GT rotor shaft faults. THAPCOM displays the most sensitive performance parameters of the engine such as those which are used for diagnostics and prognostics. It is an advancement of the component model-based condition monitoring for a GT engine (Ogbonnaya et al, 2010).
The approach used in this research is trend monitoring as MVR in matrix form. Data were obtained both statistically and analytically and constitute the most sensitive thermodynamics and performance parameters at the various components of the engine. Data were collected on hourly basis, for a period of three months from an operational GT plant used for electric power generation. The data were sampled and the mean taken for weekly basis. The GT is a 75 MW plant. This technique is in accordance with the methods stated in subsection (1.2). For instance, the method of model-based computer program yielded accurate results than the manual method. The method of model-based computer programming is faster in diagnosing faults. This use of computer program approach, signals the limit of operation through instrumentation in the form of alarm (Baker, 1991; Bergman, et al, 1993; Stamatis et al, 2001; Alexious and Mathioudakis, 2006; Ogbonnaya et al, 2010). This present work would contribute solution to the unexpected failure/down time of GTs by giving timely alarm signals. The deviations of the thermodynamics and performance parameters when the actual values were compared to their reference values will be used to analyze the MVMMs to diagnose and prognosis the health of the GT. The data collected from the test engine was obtained using the following model thermodynamics equations. It was assumed that P1 = P4 and P2 = P3.
Isentropic compression of the compressor was obtained as follows:
T'2T1=P2P1Υ-1ΥE2
Similarly, isentropic expansion of the turbine was obtained as follows:
T3T'4=P3P4Υ-1ΥE3
Isentropic efficiency of compressor =IsentropicEnthalpyDropActualEnthalpyDrop
ηc=τ21-τ1τ2-τ1E4
Isentropic efficiency of turbine=ActualEnthalpyDropIsentropicEnthalpyDrop
ητ=T3-T4T2-T'4E5
While the following model deviation equations were applied
ΔT3T3=T3A-T3RT3RE6
ΔNN=NA-NRNRE7
Δηcηc=ηcA-ηcRηcRE8
ΔΓCΓC=ΓCA-ΓCRaCRE9
The parameters in Equations (5) to (8) are the independent variables in the MVMMs. These equations were used to generate the coefficients a1 to a16 in the MVMMs. a1 to a16 are expressed as functions of:
The significance of this approach is based on the interface between the components of air and gas path. This approach considered the analysis in terms of the measurable dependent data and the independent performance parameters calculated by a mathematical model based on engine thermodynamics.
The independent and dependent parameters represent the variables in various engine components thermodynamics relationship such as the compressor, combustor and turbine units (Bently, et al., 2002). The differential and manipulation of these equations allow the derivation of a general relationship between each change in a dependent parameter and its resulting effects on each independent parameter in turn with all other variables held constant. A matrix was formed using these coefficient relationships by superposition of the independent variable on each independent parameter. The independent parameters are T3, N, ηC, andΓC, while the dependent parameters are P2, T2 WF and An. A combination of the MVMMs constitute a 4 x 4 matrix in which the variables are related by the constant coefficients a1 to a16. This matrix was evaluated as a 4 x 3 matrix holding the speed constant in turn to generate each independent parameter change (Bentley, et al., 2002). This is shown in equation (11).
By substituting equation (12) into (14), ΔANANcan be obtained. Equations (5) to (8) and (14) were used for the simulation of THAPCOM in C++ programming language to proactively monitor the health of the GT. The flowchart drawn from these equations is presented in figure 1. It is from this flowchart that a computer program in C++ used to actualise the work is written. The most salient feature of THAPCOM flowchart and program is that it has two subroutines for ease of manipulation.
The input subroutine in the flowchart helped to store values of T1, T2, P1, P2, T3, N, T4, ΓC, WF and L. These values were later returned in subsequent parts of the program where they were needed and used to computeyΔT3T3, ΔηCηCandΔΓCΓC. This was done after individual values ofηT, ηC,η0.... were computed.
With a view to actualize MVMMs, the data shown in tables 1(a) and (b) were collected from the operational GT plant. Figures 2 and 3 are the graphs of percentage deviation in P2 and T2 against date in weeks while a combined graph of percentage deviation in P2, T2, ΓCand T3 are shown in figure 4.
The coefficients of each performance parameters are depicted in equation (9) in relation to equations (5) to (8), when the actual value is compared to the reference value. When these coefficients are used with the MVMMs, to diagnose and prognose the GT faults, its state of health was made known. If, while trending its health using equations (12) and (14), and all the Δs = 0, with no performance change, then the GT is said to be healthy.
When ΔANAN = 0, ΔηcηCand ΔΓcΓC are downward and ΔT3T3 is upward, it implies degraded compressor. This is an indication of built up dirt, foreign object damage, blade erosion, missing blade, warped blade or seal leakage. The results of the simulation show that ΔANAN = 1.4598e-0.008, Δncnc=1.6630e-0.007, ΔΓcΓc= 1.1626e-0.008 and ΔT3cT3cy= 7.5508e-0.007 for the first four weeks, since THAPCOM analyses data on cumulative basis. This showed that the GT had suffered from fouling, degraded compressor performance and seal leakage. Furthermore, figures 2 and 3 show the graphs of percentage deviation in compressor outlet pressure and temperature against date in weeks respectively. The table of values shows that the trajectories depict a sinusoidal trend. This is as a result of fouling, which is known for the reduction in compressor exit pressure from its design value. Figure 4 is a combined plot of P2, T2, T3, N, ΓC, ηCand AL against date in weeks. It shows that, AL suffered the highest deviation. Moreover figures 5, 6 and 7 show the path of percentage deviation in ICE, AL and APC against date in weeks. The sinusoidal trend also means that compressor instabilities were setting in.
Figure 2.
Percentage Deviation in P2 against Date (in Weeks)
Figure 3.
Percentage deviation in T2 against date (in weeks)
Table 1.
(a) Values of the thermodynamics and performance parameters taken from AFAM IV, GT18, TYPE 13D
Weeks
ΔT3T3
ΔNN
Δηcηc
ΔΓcΓc
1. 2. 3. 4.
a1 a5 a9 a13
-0.075 -0.075 -0.075 -0.078
a2 a6 a10 a14
0.021 0.020 0.019 0.019
a3 a7 a11 a15
0.0012 0.0012 -0.0059 0.0107
a4 a8 a12 a16
-0.044 -0.017 -0.051 0.000
Table 1.
(b) Values of the ccoefficients
Figure 4.
Percentage deviation in P2, T2, T3, N, APC, ICE and AL against date (in weeks)
Figure 5.
Percentage deviation of ICE against date (in weeks)
Figure 6.
Percentage deviation in AL against date (in weeks)
Figure 7.
Percentage deviation in APC against date (in weeks)
In this work, the MVMMs of a test engine was generated by taking advantage of the gas path analysis. The models were applied to develop the software “THAPCOM”. This software thus enabled diagnosis and prognosis to be carried out on the equipment through the comparison between the actual and reference values of the engine. Advantage was brought to bear using previous works done on adaptive modelling of various aspects of GT health monitoring. The software when installed in a system interface of the GT enabled the proactive monitoring of the engine’s health. The software gives an alarm signal whenever a set limit is near the dependent or independent parameters. This alarm signal allows the operator to carry out maintenance before the equipment fails.
The authors are highly grateful for the contributions of the staff of Afam Thermal Station where the data and experimentations were conducted. They are Engrs. D. U. Obiagazie, L. Ofurum, M. U. Ukpai, K. Kalio.
References
1.AlexiousA.MathioudakisK.2006 Gas Turbine Engine Performance Model Application Using an Objective Oriented Simulation Tool, ASME Turbo-Expo 2006, Power for Land, Sea and Air, The Barcelona, Spain, 811 . Available at http://www.137.205.176.10/content/engine/sp2-asme-turbo-2006-alexious.pdf
2.AretakisN.RoumelioticI.MathioudakisK.2010Performance Model “Zooming” for In-Depth Component Fault Diagonsis, Proceedings of ASME Turbo-Expo 2010, GT2010-23262, Glasgow-Scotland, UK, 12
3.AretakisN.MathioudakisK.StamatisA.2003 Non- Linear Engine Component Fault Diagnosis From a Limited Number of Measurements Using a Combinational Approach, Journal of Engineering for Gas Turbines and Power, 1253642650
4.BakerW.E1991 Similarity Methods in Engineering Dynamics:Theory and Practice of Scale Modeling(Revised Edition)0-444-88156-5, Elsevier Science Publishers B.V, Amsterdam, The Netherlands, 718
5.BellD. R.2003 The Hidden Cost of Downtime: Strategies for Improving Return on Assets, Smart Signal Co. USA.14
6.BergmanJ. M.BootP.WoudK.1993 Condition Monitoring of Diesel Engines with Component Models, Paper 17 International Conference on Marine Environnmental and Safety (ICMES) 93, Marine Management(Holdings) Limited,, The Netherlands.
8.DoelD.1994 A Gas Path Analysis Toolfor Commercial Jet Engines, Transaction of ASME Journal. of Engineering for Gas Turbines and Power, 1168289
9.DonaldL. S.VolponiA. J.BirdJ.DavisonC.VersonR.E.2008Benchmarking Gas Path Diagnostic Methods: Public Approach, IGTI/ASME Turbo-Expo 2008, GT2008- 51360, Berlin- Germany, 2
10.ErbesM. R.PalmerC. A.1994 Simulation Mehtods used to Analyse the Performance of the GE E6541B Gas Turbine utilizing Low Heating Value Fuels. ASME Cogen Turbo Power, Portland Oregen. 12 .
11.ErbesM. R.PalmerC. A.PechtiP. A.1993 Gas Cycle Performance Analysis of the LM2500 Gas Turbine utilizing Low Heating Values. IGTI- 8 ASME Cogen- Turbo Power. 12 .
12.FastM.AssadiM.PikeA.BreuhausP.2009 Different Conditon Monitoing Models for Gas Turbines by Means of Artifical Neural Networks, IGTI/ASME Turbo-Expo2009, GT2009-59364, Orlando- Florida, USA11
13.GuyK. R.1995 Turbine Generator Monitoring and Analysis, Mini-Course Notes, Proceedings of Vibration Institute. 2www.sandv.com /downloads/0703puse.pdf
14.KamboukasP.MathioudakisK.2005 Comparison of Linear and Non- linear of Gas Turbine Performance Diagnostics, Journal of Engineering for Gas Turbines and Power, 12714956 .
15.LobodaI.2008 Trustworthiness Problem of Gas Turbine Parametric Diagnosing, 5th IEAC Symposium of Technical and Safe Processes, 2003, Washinton DC, USA, 8
16.LobodaI.YepifanovS.2010A mixed Data-Driven and Model-Based Fault Classification For Gas Turbines DiagnosisProceedings of ASME Turbo-Expo 2010, PaperGT2010-23075 , Glasgow- Scotland, UK, 12 .
17.MariaA.1997 Introduction to Modeling and simulation, Proceedings of the 1997 Winter Simulation Conference (ed. S. Androdothi, K. J. Healy, D. H. Withers and B. L. Nelson), 79 .
18.OgbonnayaE. A.2004a Modeling Vibration- Based Faults in Rotor Shaft of a Gas Turbine, Ph.D Thesis, Dept. of Mar. Engrg., RSUST, Nkpolu Port Harcourt, Nigeria. 82160 .
19.OgbonnayaE. A.2004b Thermodynamics of Steam and Gas Turbines, 1st edition, Oru’s Press Ltd, Port Harcourt. 45 .
20.OgbonnayaE. A.KoumakoK. E. E.2006 Basic Automatic Control, 1st edition, King Jovic Int’l. Publisher Port Harcourt.114115 .
21.OgbonnayaE. A.1998 Condition Monitoring of a Diesel Engine for Electricity Generation, M-Tech. Thesis, Dept. of Mar. Engrg. RSUST, Port Harcourt, Nigeria. 4243 .
22.OgbonnayaE. A.2009 Diagnosing and Prognosing Gas Turbine Rotor Shaft Faults Using “The MICE”, Proceedings of ASME Turbo Expo, GT 2009-59450, Orlando, Florida, USA. 16 .
23.OgbonnayaE.ATheophilus-JohnsonK.2010 Use of Multiple Variable Mathmatical Method for Effective Condition Monitoring of Gas Turbines, Proceedings of ASME Turbo- Expo GT 2010-22568 ,Glasgow, Scotland
24.OgbonnayaE.A.Theophilus-JohnsonK.UgwuH.U and OrjiC.U2010 Component Model-Based Condition Monitoring of a Gas Turbine, ARPN Journal of Engineering and Applied Sciences, 53Available at: www.arpnjournal.com.
25.Ogbonnaya E.ATheophilus-JohnsonK.2011 Optimizing Gas Turbine Rotor Shaft fault Detection, Identification and Analysis for Effective Condition Monitoring, Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS)211117 Copright Scholarlink Research Instite Journals (2141-7016). Available at:. http://www.jeteas.scholarlinkresearch.org and http://www.scholarlinkresearch.org.
26.PusseyH. C.2007 Turbo machinery Condition Monitoring and Failure Prognosis, Shock and Vibration Information Analysis Centre/Hi-Test Laboratories, Proceedings of Institute of Vibration, Winchester, Virginia.. 210 .
27.RiegerN.F.McCoskyT.HDavey R.P1990 The High Cost of Failure of Rotating Equipment, Proceedings of 44th Conference of Machinery Failure Prevention Group (MFPG), Vibration Institute, 23 .
28.RoemerM. J.KacprzynskiG.J.2000Advanced Diagnosyic and Prognostic for Gas Turbine Risk Assessment, Proceedings of ASME Turbo Expo GT2000, gt2000-30, Germany. 10
29.RomesisC.MathioudakisK.2003 Setting up of a Probabilistic Neural Network for Senor Fault Detection Including Operation with Component Fault, Journal Of Engineering for Gas Turbines and Power, 125, 634641 .
30.SchneiderE..DemirciogluS.FrancoS.TherkornD.2009Analysis of Compressor On-Line Washing to Optimize Gas Turbine Power Plant Performance, Proceedings of ASME Turbo Expo 2009, GT 2009-59356, Orlando, Florida, USA. 14 .
31.StamatisA.MathioudakisK.BeriosG.PapailiouK.1991 Jet Engine Fault Detection with Discrete Operating Points Using Gas Path Analysis, Journal of Propulsion and Power, 7623 .
32.StamatisA.MathioudakisK.RuisJ.CurnockB.2001Real-Time Engine Model Implementation for Adaptive Control and Performance Monitoring of Large Turbo-fans, ASME2001 -GT-362. Available at: http://www.ase.aec.nasa.gov/projects/ishem/paper/vdponi_ac_prop.doc.
33.UhumnwanghoR.OfoduJ. C.EmiriU. V.2003 Performance Evaluation of a Gas Turbine Engine, Univ. of Port Harcourt, Nigeria. Nigerian Journal of Engineering Research and Development, 21920 .
34.UrbanL.AVolponiA.J1992 Mathematical Methods Of Relative Engine Performance Diagnostics, SAE Transactions, Journal of Aerospace10192204845 .
36.VolponiA. J.DepoldH.AndGanguli. R.2003The Use of Kalman Filter and Neural Network Methodologies in Gas Turbine Performance Diagnostics: A Comparative StudyJournal of Engineering for Gas Turbines and Power, 1254917924 .
37.BrunK.KurzR.2007 Gas Turbine Tutorial- Maintenance and Operating Practice Effects on Degradation and life, Proceedings of the Thirty-sixth Turbo Machinery Symposium, 12www.igu.org/html/wgc2009/papers/docs/ wgcFinal00076.pdf
Written By
E. A. Ogbonnaya, K. T. Johnson, H. U. Ugwu, C. A. N. Johnson and Barugu Peter Forsman
Submitted: 09 November 2010Published: 13 January 2012