Gas Turbine Engineering Handbook 2 Episode 15 doc

G:/GTE/FINAL (26-10-01)/CHAPTER 19.3D ± 685 ± [634±691/58] 1.11.2001 2:38PM 4. Bearing failure. The symptoms of bearing problems for a turbine are the same as for a compressor. 5. Cooling air failure. Problems associated with the blade cooling system may be detected by an increase in the pressure drop in the cooling line. 6. Turbine maintenance. This should be based on ``equivalent engine time,'' which is the function of temperature, type of fuel used, and number of starts. Figure 19-21 shows the correction that can be applied to running hours for intermittent-duty units with high- start/stop operation. Turbine Efficiency 1. With the current high cost of fuel, very significant savings can be achieved by monitoring equipment operating efficiencies and correct- ing for operational inefficiencies. Some of these operational inefficien- cies may be very simple to correct, such as washing or cleaning of the compressor on a gas turbine unit. In other cases, it may be necessary to develop a load-distribution program that achieves maximum over- all efficiency of the plant equipment for a given load demand. Figure 19-21. Equivalent engine time in the turbine section. Control Systems and Instrumentation 685 G:/GTE/FINAL (26-10-01)/CHAPTER 19.3D ± 686 ± [634±691/58] 1.11.2001 2:38PM 2. Figure 19-22 shows the significant dollar cost penalties that occur when operating a turbine at a very small percentage efficiency degrada- tion. 3. Table 19-8 shows a load-distribution program for an 87.5-MW power station of steam turbines and gas turbines. The selection of equipment and their loading for the most efficient operation can be programmed when the efficiency of individual units are monitored. The program Figure 19-22. Savings versus efficiency. 686 Gas Turbine Engineering Handbook G:/GTE/FINAL (26-10-01)/CHAPTER 19.3D ± 687 ± [634±691/58] 1.11.2001 2:38PM selects the units that should be operated to provide the powerload demand at the maximum overall efficiency of the combination of units. Mechanical Problem Diagnostics The advent of new, more reliable, and sensitive vibration instrumentation such as the eddy-current sensor and the accelerometer coupled with modern Table 19-8 Load Sharing Program Description of Utility Plant Units Unit # Design MW Turbine Type Efficiency at Design Output Point 1 2.5 Steam 22 2 2.5 Steam 22 3 5.0 Steam 24 4 5.0 Steam 24 5 5.0 Steam 24 6 7.5 Steam 25 7 15.0 Steam 30 8 15.0 Steam 23 9 15.0 Gas 21 10 15.0 Gas 21 Combination of Units of Yield Efficient Power Load Distribution for Different Demand Loads Total Demand = 30.00 MW Total Demand = 50.00 MW Total Output Supplied = 30.00 MW Total Output Supplied = 50.00 MW Units not working  1490 Units not working  1400 Unit 1  0.00 0.00 Unit 1  0.00 0.00 Unit 2  0.00 0.00 Unit 2  2.50 22.01 Unit 3  2.50 21.00 Unit 3  5.00 24.50 Unit 4  0.00 0.00 Unit 4  0.00 0.00 Unit 5  5.00 24.50 Unit 5  5.00 24.50 Unit 6  7.50 25.19 Unit 6  7.50 25.19 Unit 7  15.00 29.91 Unit 7  15.00 29.81 Unit 8  0.00 0.00 Unit 8  0.00 0.00 Unit 9  0.00 0.00 Unit 9  0.00 0.00 Unit 10  0.00 0.00 Unit 10  15.00 21.00 Maximum Overall Efficiency  27:04 Maximum Overall Efficiency  25:02 Power Demands  MW (Maximum demand  87:5) Control Systems and Instrumentation 687 G:/GTE/FINAL (26-10-01)/CHAPTER 19.3D ± 688 ± [634±691/58] 1.11.2001 2:38PM technology analysis equipment (the real-time vibration spectrum analyzer and low-cost computers) gives the mechanical engineer very powerful aids in achieving machinery diagnostics. A chart for vibration diagnosis is presented in Table 19-9. While this is a general criterion or rough guideline for diagnosis of mechanical problems, it can be developed into a very powerful diagnostic system when specific problems and their associated frequency domain vibration spectra are Table 19-9 Vibration Diagnosis Usual Predominant Frequency* Cause of Vibration Running frequency at 0  ±40% Loose assembly of bearing liner, bearing casing, or casing and support Loose rotor shrink fits Friction-induced whirl Thrust bearing damage Running frequency at 40  ±50% Bearing-support excitation Loose assembly of bearing liner, bearing case, or casing and support Oil whirl Resonant whirl Clearance induced vibration Running frequency Initial unbalance Rotor bow Lost rotor parts Casing distortion Foundation distortion Misalignment Piping forces Journal & bearing eccentricity Bearing damage Rotor-bearing system critical Coupling critical Structural resonances Thrust-bearing damage Odd frequency Loose casing and support Pressure pulsations Vibration transmission Gear inaccuracy Valve vibration Very high frequency Dry whirl Blade passage *Occurs in most cases predominantly at this frequency; harmonics may or may not exist. 688 Gas Turbine Engineering Handbook G:/GTE/FINAL (26-10-01)/CHAPTER 19.3D ± 689 ± [634±691/58] 1.11.2001 2:38PM logged and correlated in a computerized system. With the extensive memory capability of the computer system, case histories can be recalled and efficient diagnostics achieved. Data Retrieval In addition to being valuable as a diagnostic and analysis tool, a data retrieval program also provides an extremely flexible method of data storage and recovery. By careful design of a health monitoring system, an engineer or technician can compare the present operation of a unit with the operation of the same machine, or of another machine, under similar conditions in the past. This can be done by selecting one or several limit- ing parameters and defining the other parameters that are to be displayed when the limiting parameters are met. This eliminates the necessity of sifting through large amounts of data. A few examples of how this system is used are: 1. Retrieval by time. In this mode, the computer retrieves data taken during a specified time period, thus enabling the user to evaluate the period of interest. 2. Retrieval by ambient temperature. The failure of a gas turbine may occur during an unusually hot or cold period, and the operator may wish to determine how his unit functioned at this temperature in the past. 3. Retrieval by turbine exhaust temperature. The exhaust temperature can be an important parameter in failure investigations. An analysis of this parameter in failure investigations. An analysis of this parameter can verify the existence of a problem with either the combustor or turbine. 4. Retrieval by vibration levels. Inspection of data provided by this mode can be useful in determining compressor fouling, compressor or tur- bine blade failure, nozzle bowing, uneven combustion, and bearing problems. 5. Retrieval by output power. In this mode, the user should input the output power range of interest and thus obtain only data applying to that particular power setting. In this manner, he has only to consider the pertinent data to pinpoint the problem areas. 6. Retrieval by two or more limiting parameters. By retrieving data with limits on several parameters, the data can be evaluated and will be even further reduced. Diagnostic criteria can then be developed. Control Systems and Instrumentation 689 G:/GTE/FINAL (26-10-01)/CHAPTER 19.3D ± 690 ± [634±691/58] 1.11.2001 2:38PM Summary 1. The monitoring of turbomachinery mechanical characteristics, such as vibrations, has been applied extensively over the past decade. The advent of the accelerometer and the real-time vibration spectrum analyzer has required a computer to match and utilize the extensive analysis and diagnostic capability of these instruments. 2. The high cost for machinery replacements and downtime makes machinery operational reliability very important; however, with the current and projected increases in fuel costs, aerothermal monitoring has become very important. Aerothermal monitoring can provide not merely increased operational efficiency for turbomachinery but, when combined with mechanical monitoring, it provides an overall, more effective system than one that monitors only the mechanical functions or aerothermal functions. 3. While there had been concern about the reliability of computer sys- tems, they are currently receiving wide acceptance and are fast repla- cing analog systems. 4. The systematized application of modern technology (instrumentation, both mechanical and aerothermal and low-cost computers) and turbo-machinery engineering experience will result in the development and application of cost-effective systems. Bibliography ASME, Gas Turbine Control and Protection Systems, B133.4 Published: 1978 (Reaffirmed year: 1997). Boyce, M.P., Gabriles, G.A., Meher-Homji, C.B., Lakshminarasimha, A.N., and Meher-Homji, F.J., ``Case Studies in Turbomachinery Operation and Maintenance Using Condition Monitoring,'' Proceeding of the 22nd Turbo- machinery Symposium, Dallas, Texas. September 14  ±16, 1993, pp. 101  ±12. Boyce, M.P., and Herrera, G., ``Health Evaluation of Turbine Engines Under- going Automated FAA Type Cyclic Testing,'' Presented at the SAE Inter- national Ameritech '93, Costa Mesa, California, September 27  ±30, 1993, SAE Paper No. 932633. Boyce, M.P., Gabriles, G.A., and Meher-Homji, C.B., ``Enhancing System Availability and Performance in Combined Cycle Power Plants by the Use of Condition Monitoring,'' European Conference and Exhibition Cogenera- tion of Heat and Power, Athens, Greece, November 3  ±5, 1993. 690 Gas Turbine Engineering Handbook G:/GTE/FINAL (26-10-01)/CHAPTER 19.3D ± 691 ± [634±691/58] 1.11.2001 2:38PM Boyce, M.P., ``Control and Monitoring an Integrated Approach,'' Middle East Electricity, December 1994, pp. 17  ±20. Boyce, M.P., ``Improving Performance with Condition Monitoring''ÐPower Plant Technology Economics and Maintenance, March/April 1996, pp. 52  ±55. Boyce, M.P., and Venema, J., ``Condition Monitoring and Control Center'', Power Gen Europe in Madrid, Spain, June 1997. Boyce, M.P., and Cox, W.M., ``Condition Monitoring Management-Strategy'', The Intelligent Software Systems in Inspection and Life Management of Power and Process Plants in Paris, France, August 1997. Boyce, M.P., ``How to Identify and Correct Efficiency Losses Through Modeling Plant Thermodynamics,'' Proceedings of the CCGT Generation Power Con- ference, London, United Kingdom, March, 1999. Boyce, M.P., ``Condition Monitoring of Combined Cycle Power Plants,'' Asian Electricity July/August 1999, pp. 35  ±36. Meher-Homji, C.B., Boyce, M.P., Lakshminarasimha, A.N., Whitten, J.A., and Meher-Homji, F.J., ``Condition Monitoring and Diagnostic Approaches for Advanced Gas Turbines,'' Proceedings of ASME Cogen Turbo Power 1993, 7th Congress and Exposition on Gas Turbines in Cogeneration and Utility, Sponsored by ASME in participation of BEAMA, IGTI-Vol. 8 Bournemouth, United Kingdom, September 21  ±23, 1993, pp. 347  ±55. Control Systems and Instrumentation 691 //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 20.3D ± 692 ± [692±721/30] 29.10.2001 4:07PM 20 Gas Turbine Performance Test Introduction The performance analysis of the new generation of gas turbines are complex and presents new problems, which have to be addressed. The new units operate at very high turbine firing temperatures. Thus, variation in this firing temperature significantly affects the performance and life of the com- ponents in the hot section of the turbine. The compressor pressure ratio is high which leads to a very narrow operation margin, thus making the tur- bine very susceptible to compressor fouling. The turbines are also very sensi- tive to backpressure exerted on them when used in combined cycle or cogeneration duty. The pressure drop through the air filter also results in major deterioration of the performance of the turbine. If a life cycle analysis were conducted the new costs of a plant are about 7  ±10% of the life cycle costs. Maintenance costs are approximately 15  ±20% of the life cycle costs. Operating costs, which essentially consist of energy costs, make up the remainder, between 70  ±80% of the life cycle costs, of any major power plant. Thus, performance evaluation of the turbine is one of the most important parameter in the operation of a plant. Total performance monitoring on or off line is important for the plant engineers to achieve their goals of: 1. Maintaining high availability of their machinery. 2. Minimize degradation and maintain operation near design efficiencies. 3. Diagnose problems, and avoid operating in regions, which could lead to serious malfunctions. 692 //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 20.3D ± 693 ± [692±721/30] 29.10.2001 4:07PM 4. Extend time between inspections and overhauls. 5. Reduce life cycle costs. To determine the deterioration in component performance and efficiency, the values must be corrected to a reference plane. These corrected measure- ments will be referenced to different reference planes depending upon the point, which is being investigated. Corrected values can further be adjusted to a transposed design value to properly evaluate the deterioration of any given component. Transposed data points are very dependent on the char- acteristics of the components performance curves. To determine the charac- teristics of these curves, raw data points must be corrected and then plotted against representative nondimensional parameters. It is for this reason that we must evaluate the turbine train while its characteristics have not been altered due to component deterioration. If component data were available from the manufacturer, the task would be greatly reduced. Performance Codes Performance analysis is not only extremely important in determining overall performance of the cycle but in also determining life cycle considera- tions of various critical hot section components. In this chapter, a detailed technique with all the major equations govern- ing a Gas Turbine Power Plant are presented based on the various ASME Test Codes. The following five ASME Test Codes govern the test of a Gas Turbine Power Plant: 1. ASME, Performance Test Code on Overall Plant Performance, ASME PTC 46 1996, American Society of Mechanical Engineers 1996 2. ASME, Performance Test Code on Test Uncertainty: Instruments and Apparatus PTC 19.1, 1988 3. ASME, Performance Test Code on Gas Turbines, ASME PTC 22 1997, American Society of Mechanical Engineers 1997 The ASME, Performance Test Code on Overall Plant Performance, ASME PTC 46, was designed to determine the performance of the entire heat cycle as an integrated system. This code provides explicit procedures to determination of power plant thermal performance and electrical output. The ASME, Performance Test Code on Test Uncertainty: Instruments and Apparatus PTC 19.1 specifies procedures for evaluation of uncertainties in individual test measurements, arising form both random errors and Gas Turbine Performance Test 693 //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 20.3D ± 694 ± [692±721/30] 29.10.2001 4:07PM systematic errors, and for the propagation of random and systematic uncer- tainties into the uncertainty of a test results. The various statistical terms involved are defined. The end result of a measurement uncertainty analysis is to provide numerical estimates of systematic uncertainties, random uncer- tainties, and the combination of these into a total uncertainty with an approximate confidence level. This is especially very important when com- puting guarantees in plant output and plant efficiency. The PTC 22 establishes a limit of uncertainty of each measurement required; the overall uncertainty must then be calculated in accordance with the procedures defined in ASME PTC 19.1 Measurement Uncertainty. The code requires that the typical uncertainties be within a 1.1% for the Power Output, and 0.9% in the heat rate calculations. It is very important that the post-test uncertainty analysis should be also performed to assure the parties that the actual test has met the requirement of the code. The instrumentation will be calibrated as per the requirements of the test codes. All the instrumentation must be calibrated before a test and certified that they meet the code requirements. The ASME PTC 19 series outlines the governing requirements of all instrumentation for an ASME Performance Test to be within the governing band of uncertainty. Table 20-1 is a very short abstract of the test measurement requirements for the performance tests; the ASME PTC 19 series should be the final governing document: Flow Straighteners Minimum lengths of straight pipe are required for flow-measuring devices and for certain pressure measurements. Flow straighteners and/or equalizers should be used in the vicinity of throttle valves and elbows, as shown in Figure 20-1. Table 20-1 Instrumentation Accuracy Measurement Bias Uncertainty Temperature below 200  F (93.3  C) 0.5  F (0.27  C) Temperature above 200  F (93.3  C) 1.0  F (0.56  C) Pressure 0.1% Vacuum pressure Absolute pressure transmitters recommended Mass flow of fuel gas 0.8% 694 Gas Turbine Engineering Handbook [...]... accounting for the steam turbine producing more work at low part loads The work produced by the gasifier turbine (Wgt) is equal to the gas turbine compressor work (Wc): Powgt ˆ Powc mc 20 -29 † 100 90 Turbine efficiency (%) 80 70 60 50 40 30 20 10 0 20 00 (1094 °C) 20 50 21 00 (1149 °C) 21 50 22 00 22 50 ( 120 4 °C) Turbine Firing Temperature 23 00 ( 126 0 °C) 23 50 ( 128 8 °C) Figure 20 - 12 Gas turbine efficiency as... temperature 24 00 //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 20 .3D ± 716 ± [6 92 721 /30] 29 .10 .20 01 4:08PM 716 Gas Turbine Engineering Handbook 150 0 1300 Temperature (C) 1100 Turbine Firing Temperature 900 Gas Turbine Exhaust Temperature 700 500 300 0.00 20 .00 40.00 60.00 80.00 100.00 120 .00 Plant load (%) Figure 20 -13 Effect of the plant load on turbine firing temperature and the turbine exhaust The gasifier turbine. .. high pressure gas at elevated temperature uses a very large part of the turbine power produced by the gas Gasifier Power as Percent of Total Power (%) 56 55.5 55 54.5 54 53.5 0 20 40 60 80 Total Gas Turbine Power (%) 100 Figure 20 -10 Gasifier power as a function of total gas turbine power 120 //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 20 .3D ± 713 ± [6 92 721 /30] 29 .10 .20 01 4:08PM Gas Turbine Performance... state P R ˆZ T  MW 20 -4† //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 20 .3D ± 708 ± [6 92 721 /30] 29 .10 .20 01 4:08PM 708 Gas Turbine Engineering Handbook 1. 025 1.1 1.08 1. 02 1.06 Plant Power (%) 1. 02 1.01 1 Plant Heat Plate 1. 015 1.04 Plant Power(%) Plant Heat Rate(%) 1.005 0.98 0.96 1 0.94 0. 92 –10 –5 0 5 10 15 Ambient Temperature (C) 20 25 0.995 30 Figure 20 -8 Plant conditions as a function of inlet ambient... code: 1 2 3 Gas turbine overall computation Gas turbine output Inlet air flow Figure 20 -6 Gas turbine suggested measurement points //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 20 .3D ± 703 ± [6 92 721 /30] 29 .10 .20 01 4:08PM Gas Turbine Performance Test 4 5 6 7 8 9 10 703 First stage nozzle cooling flow rate Total cooling flow rate Heat rate Expander efficiency Gas turbine efficiency Exhaust flue gas flow... Pdgt 20 -31† where Pdgt is the pressure at the gasifier turbine exit Thus, the ideal enthalpy at the gasifier turbine exit is given by Htit Hpiti ˆ cp  À Á tit Pgrt À1 cppit 20 - 32 //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 20 .3D ± 717 ± [6 92 721 /30] 29 .10 .20 01 4:08PM Gas Turbine Performance Test 717 where is based on an average temperature across the gasifier turbine based on equation (20 -24 ) The... 2 0.9 //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 20 .3D ± 720 ± [6 92 721 /30] 29 .10 .20 01 4:08PM 720 Gas Turbine Engineering Handbook Table 20 -4 Effect of Controllable Losses on the Output and Heat Rate Parameters Compressor fouling Pressure drop in filter Increase in gas turbine back pressure Lower heating value Power factor 4 Parameter Change Power Output (%) Heat Rate Change (%) 2% À1.5 1 in H2O (25 ... V2 2cp 20 - 12 where Ts ˆ static temperature, and V ˆ gas stream velocity and P ˆ Ps ‡  V2 2gc 20 -13† //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 20 .3D ± 710 ± [6 92 721 /30] 29 .10 .20 01 4:08PM 710 Gas Turbine Engineering Handbook where Ps ˆ static pressure and the acoustic velocity in a gas is given by the following relationship   @P a ˆ @ sˆc 2 20 -14† for an adiabatic process (s ˆ entropy ˆ constant)... //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 20 .3D ± 7 02 ± [6 92 721 /30] 29 .10 .20 01 4:08PM 7 02 Gas Turbine Engineering Handbook the power The following are the parameters that need to be computed to fully understand the macro picture of the plant 1 2 Overall plant system Gross unit heat rate a Net unit heat rate b Gross output c Net output d Auxiliary power Gas Turbine The ASME, Performance Test Code on Gas Turbines,... ac ˆ Isentropic work …H2TI À HIT † ˆ Actual work …H2a À H1T † 20 -20 † where H2TI ˆ total enthalpy of the gas at isentropic exit conditions, and H2a ˆ total enthalpy of the gas at actual exit conditions, and H1 ˆ total enthalpy of the gas at inlet conditions for a caloricaly perfect gas the equation can be written as: 4  À1 5 P2 … † À1 P1 ! ac ˆ T2a À1 T1 20 -21 † The gas turbine compressor which . Design MW Turbine Type Efficiency at Design Output Point 1 2. 5 Steam 22 2 2.5 Steam 22 3 5.0 Steam 24 4 5.0 Steam 24 5 5.0 Steam 24 6 7.5 Steam 25 7 15. 0 Steam 30 8 15. 0 Steam 23 9 15. 0 Gas 21 10 15. 0. the formula P v  V av  2  2g c  144  V av  2  926 6:1 20 -1 696 Gas Turbine Engineering Handbook //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 20 .3D ± 697 ± [6 92 721 /30] 29 .10 .20 01 4:07PM where. based on the code: 1. Gas turbine overall computation 2. Gas turbine output 3. Inlet air flow Figure 20 -6. Gas turbine suggested measurement points. 7 02 Gas Turbine Engineering Handbook //INTEGRA/B&H/GTE/FINAL