Gas Turbine Engineering Handbook 2 Episode 4 pot

G:/GTE/FINAL (26-10-01)/CHAPTER 3.3D ± 135 ± [112±140/29] 1.11.2001 3:58PM be when the turbine's automatic controls took over. These controls are actuated by the exhaust temperature. Figure 3-16 shows the effect of efficiency as a function of the load for both the compressor and turbine. Part-load turbine efficiencies are affected more than compressor efficiencies. The discrepancy results from the compressor operating at a relatively constant inlet temperature, pressure, and pressure ratio, while the turbine inlet temperature is greatly varied (Figure 3-17). Figure 3-16. Compressor and turbine efficiency as a function of load. 1650°F 894°C 1350°F 732°C 1050°F 566°C 7,500 Computed Inlet Turbine Temperature load in kWh 3,750 11,250 15,000 0 Figure 3-17. Turbine inlet temperature as a function of turbine load. Compressor and Turbine Performance Characteristics 135 G:/GTE/FINAL (26-10-01)/CHAPTER 3.3D ± 136 ± [112±140/29] 1.11.2001 3:58PM The turbine pressure ratio, however, remains relatively constant. The back- pressure on the turbine was measured at a relatively constant value of 30.25 inches Hg abs (1.02 Bar). This value creates about a 9-inch H 2 O (228 mm H 2 O) back-pressure on the turbine. The efficiency of the compres- sor is based on the following equation:  c  T t1 P t2 P t1  À1  À1 45 ÁT act 3-43 where: T t1  inlet temperature P t2  pressure at compressor outlet P t1  pressure at compressor inlet ÁT act  actual temperature rise in the compressor   specific heat ratio; average value between inlet and outlet temperature was used The turbine efficiency calculation is more complex. The first part is the calculation of the turbine inlet temperature. The calculation is based on the following equation: T t3   m a c P2 T t2  n b  m f LHV natural gas c P3 c P3   m f   m a  3-44 where: T t2  temperature at the outlet of the compressor c P  specific heat at constant pressure  m f  mass flow rate for the fuel  m a  mass flow rate of the air  b  combustion efficiency LHVlower heating value of the natural gas supplied (950 Btu=cu ft [(35,426 kJ=cu m)] and specific gravity 0:557) 136 Gas Turbine Engineering Handbook G:/GTE/FINAL (26-10-01)/CHAPTER 3.3D ± 137 ± [112±140/29] 1.11.2001 3:58PM The mass flow value of the air was obtained by measuring the flow at the inlet of the gas turbine using an ion-gun velocimeter. Figure 3-18 shows the values obtained across the inlet. These values give an average flow rate of 720,868 lbs/hr (327,667 kg/hr). This flow rate is within experimental accu- racy. The temperature drop in the turbine is based on an energy balance and is given by the following equation: ÁT tact  W load  gen m f   m a c P avg   m a   m f   m a  c P cavg c P tavg ÁT cact 3-45 where: W load  generator output in kilowatts  gen  generator efficiency c P tavg  turbine average specific heat c P cavg  compressor average specific heat ÁT tact  temperature drop in turbine 64 in. (1630 mm) 49 68 42 43 37 48 67 68 68 68 71 39 49 52 61 121 in. (3070 mm) Average Velocity = 55.3 ft/sec, 16.9 m/sec Assumed Blockage = 2.8 Inlet Area = 53.8 ft , 16.9 m Average Density = 0.71 lb/ft , 1.14 kg/m Mass Flow Rate = 720,868 lb/hr, 327,667 kg/hr Percent Deviation = +0.1% 22 3 3 Figure 3-18. Typical inlet velocity profile for an industrial gas turbine. Compressor and Turbine Performance Characteristics 137 G:/GTE/FINAL (26-10-01)/CHAPTER 3.3D ± 138 ± [112±140/29] 1.11.2001 3:58PM The temperature drop calculated in this manner was compared to the drop calculated by subtracting the measured average exhaust temperature reading from the inlet temperature as obtained by the previous equation. The differ- ence between these two methods was about 20  at the high-temperature exit. The second method gives a smaller drop, indicating that the temperature recorded is lower than the actual temperature. This result is expected, since the thermocouples are placed a distance downstream from the turbine blades and are not measuring the actual gas exhaust temperature. This comment is not a criticism of the control package, since that operates on a base exhaust temperature. The turbine efficiency can now be calculated with the use of the following relationship:  t  ÁT tact T t3 1 À 1 P t3 P t4  À1  P T T T T R Q U U U U S V b b b b ` b b b b X W b b b b a b b b b Y 3-46 where the value of  was an average value in the turbine. The gas turbine is coupled with a steam recovery boiler. The exhaust gas from the turbine is used to supplement fire the boiler. The thermal efficiency of the gas turbine alone was calculated by using the following relationship:  ad  W load  K LHVÂQ 3-47 where: K  3,412 BtU=kW-Hr (3,600 KJ=kW-hr) LHV  heating value; Btu=ft 3 (kJ=cu m) Q ft  volume flow rate of fuel to turbine, ft 3 =hr (cu m=hr) The overall system efficiency is based on the following equation:  sad  W load K LHVÂQ À  m sb h s À h fw LHVQ fb 3-48 138 Gas Turbine Engineering Handbook G:/GTE/FINAL (26-10-01)/CHAPTER 3.3D ± 139 ± [112±140/29] 1.11.2001 3:58PM Figure 3-19. Combined cycle and simple cycle efficiency as a function of gas turbine load. 0 25 50 75 100 (%) load 234,000 scfh 50 60 70 80 90 100 (%) fuel rate 6627 s cu.m.h Figure 3-20. Fuel consumption as a function of gas turbine load. Compressor and Turbine Performance Characteristics 139 G:/GTE/FINAL (26-10-01)/CHAPTER 3.3D ± 140 ± [112±140/29] 1.11.2001 3:58PM where:  m sb  mass flow of steam from recovery boiler h s  enthalpy of the superheated steam h fw  enthalpy of the feedwater Q fb  volume flow rate of fuel to boiler Figure 3-19 shows the thermal efficiency of the gas turbine and the Brayton-Rankin cycle (gas turbine exhaust being used in the boiler) based on the LHV of the gas. This figure shows that below 50% of the rated load, the combination cycle is not effective. At full load, it is obvious the benefits one can reap from a combination cycle. Figure 3-20 shows the fuel con- sumption as a function of the load, and Figure 3-21 shows the amount of steam generated by the recovery boiler. Bibliography Balje, O.I., ``A Study of Reynolds Number Effects in Turbomachinery,'' Journal of Engineering for Power, ASME Trans., Vol. 86, Series A, 1964, p. 227. Figure 3-21. Steam generated by exhaust gases of gas turbine as a function of gas turbine load. 140 Gas Turbine Engineering Handbook //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 4.3D ± 141 ± [141±177/37] 29.10.2001 3:56PM 4 Performance and Mechanical Standards The gas turbine is a complex machine, and its performance and reliability are governed by many standards. The American Society of Mechanical Engineers (ASME) performance test codes have been written to ensure that test, are conducted in a manner that guarantees that all turbines are tested under the same set of rules and conditions to ensure that the test results can be compared in a judicious manner. The reliability of the turbines depend on the mechanical codes that govern the design of many gas turbines. The mechanical standards and codes have been written by both ASME and the American Petroleum Institute (API). Major Variables for a Gas Turbine Application The major variables that affect the gas turbines are the following factors: 1. Type of application 2. Plant location and site configuration 3. Plant size and efficiency 4. Type of fuel 5. Enclosures 6. Plant operation mode; base or peaking 7. Start-up techniques Each of the above points are discussed in the following sections. 141 //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 4.3D ± 142 ± [141±177/37] 29.10.2001 3:56PM Type of Application The gas turbine is used in many applications, and the application determines in most parts the type of gas turbine best suited. The three major types of applications are aircraft propulsion, power generation, and mechanical drives. Aircraft Propulsion. The aircraft propulsion gas turbines can be sub- divided into two major categories, the jet propulsion and turboprop engines. The jet engine consists of a gasifier section and a propulsive thrust section as shown in Figure 4-1. The gasifier section is the section of the turbine, which produces high pressure and temperature gas for the power turbine. This comprises of a compressor section and a turbine section. the sole job of the gasifier turbine section is to drive the gas turbine compressor. This section has one or two shafts. The two-shaft gasifier section usually exists in the new high pressure type gas turbine where the compressor produces a very high pressure ratio, and has two different sections. Each section is comprised many stages. The two different compressor sections consist of the low pressure compressor section, followed by a high-pressure section. Each section may have between 10 to 15, stages. The jet engine has a nozzle following the gasifier turbine, which produces the thrust for the Figure 4-1. A schematic of a fan jet engine with a by-pass fan. 142 Gas Turbine Engineering Handbook //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 4.3D ± 143 ± [141±177/37] 29.10.2001 3:56PM engine. In the newer jet turbines the compressor also has a fan section ahead of the turbine and a large amount of the air from the fan section by-passes the rest of the compressor and produces thrust. The thrust from the fan amounts to more than the thrust from the exhaust. The jet engine has lead the field of gas turbines in firing temperatures. Pressure ratio of 40:1 with firing temperatures reaching 2500  F (1371  C), is now the mode of operation of these engines. The turboprop engine has a power turbine instead of the nozzle as seen in Figure 4-2. The power turbine drives the propeller. The unit shown schematically is a two-shaft unit, this enables the speed of the propeller to be better controlled, as the gasifier turbine can then operate at a nearly constant speed. Similar engines are used in helicopter drive applications and many have axial flow compressors with a last stage as a centrifugal compressor as shown in Figure 1-14. Mechanical Drives. Mechanical drive gas turbines are widely used to drive pumps and compressors. Their application is widely used by offshore and petrochemical industrial complexes. These turbines must be operated at various speeds and thus usually have a gasifier section and a power section. These units in most cases are aero-derivative turbines, turbines, which were originally designed for aircraft application. There are some smaller frame type units, which have been converted to mechanical drive units with a gasifier and power turbine. Power Generation. The power generation turbines can be further divided into three categories: 1. Small standby power turbines less than 2-MW. The smaller size of these turbines in many cases have centrifugal compressors driven by radial inflow turbines, the larger units in this range are usually axial Figure 4-2. Schematic of a turboprop engine. Performance and Mechanical Standards 143 //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 4.3D ± 144 ± [141±177/37] 29.10.2001 3:56PM flow compressors sometimes combined with a centrifugal compressor as the last stage, operated by axial turbines. 2. Medium-sized gas turbines between 5  ±50 MW are a combination of aero-derivative and frame type turbines. These gas turbines have axial flow compressors and axial flow turbines. 3. Large power turbines over 50  ±480 MW, these are frame-type turbines, the new large turbines are operating at very high firing temperatures about 2400  F (1315  C) with cooling provided by steam, at pressure ratios approaching 35:1. Plant Location and Site Configuration The location of the plant is the principal determination of the type of plant best configured to meet its needs. Aero-derivatives are used on offshore platforms. Industrial turbines are mostly used in petrochemical applications, and the frame type units are used for large power production. Other important parameters that govern the selection and location of the plant are distance from transmission lines, location from fuel port or pipe lines, and type of fuel availability. Site configuration is generally not a constraint. Periodically, sites are encountered where one plant configuration or another is best suited. Plant Type. The determination to have an aero-derivative type gas turbine or a frame-type gas turbine is the plant location. In most cases if the plant is located off-shore on a platform then an aero-derivative plant is required. On most on-shore applications, if the size of the plant exceeds 100 MW then the frame type is best suited for the gas turbine. In smaller plants between 2  ±20 MW, the industrial type small turbines best suit the application, and in plants between 20  ±100 MW, both aero-derivative or frame types can apply. Aero-derivatives have lower maintenance and have high heat-recovery capabilities. In many cases, the type of fuel and service facilities may be the determination. Natural gas or diesel no. 2 would be suited for aero-derivative gas turbines, but heavy fuels would require a frame type gas turbine. Gas Turbine Size and Efficiency Gas turbine size is important in the cost of the plant. The larger the gas turbine the less the initial cost per kW. The aero-derivative turbines have traditionally been higher in efficiency however, the new frame type tur- bines have been closing the gap in efficiency. Figure 4-3 shows typical gas 144 Gas Turbine Engineering Handbook [...]... maintenance cost would increase from natural gas to the heavy oils 37 36 500 Efficiency 35 40 0 34 300 33 20 0 Cost 32 100 31 30 0 0 20 40 60 80 100 120 140 160 180 20 0 22 0 24 0 GAS TURBINE- FRAME TYPE-RATED POWER (MW) Figure 4- 5 Installed cost and efficiency of frame type turbines Table 4- 1 Typical Gas Turbine Maintenance Cost Based on Type of Fuel Type of Fuel Natural gas No 2 Distillate Oil Typical Crude Oil... (US$) 120 0 5 0 0 0 2 4 6 8 10 12 GAS TURBINE- INDUSTRIAL TYPE-RATED POWER (MW) Figure 4- 3 Installed cost and efficiency of industrial type turbines 39.5 45 0 39 EFFICIENCY 40 0 38.5 350 38 300 25 0 37.5 20 0 37 COST 150 36.5 100 36 50 0 35.5 15 20 25 30 35 40 45 GAS TURBINE- AERODERIVATIVE-RATED POWER (MW) Figure 4- 4 Installed cost and efficiency of aero-derivative type turbines EFFICIENCY SIMPLE CYCLE (%) GAS. .. system, and turbine ASME Gas Turbine Fuels B 133.7M Published: 1985 (Reaffirmed Year: 19 92) Gas turbines may be designed to burn either gaseous or liquid fuels, or both with or without changeover while under load This standard covers both types of fuel //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 4. 3D ± 1 52 ± [ 141 ±177/37] 29 .10 .20 01 3:57PM 1 52 Gas Turbine Engineering Handbook ASME Gas Turbine Control and... aero-derivative type turbines EFFICIENCY SIMPLE CYCLE (%) GAS TURBINE INSTALLED COST PER kW (US$) 500 //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 4. 3D ± 146 ± [ 141 ±177/37] 29 .10 .20 01 3:56PM 146 Gas Turbine Engineering Handbook cost of $40 0/kW and an efficiency of about 40 % Figure 4- 5 is for a frame type turbines These turbines range from about 10 MW to about 25 0 MW with an installed cost for the larger units at... of the hot section components in the gas turbine //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 4. 3D ± 148 ± [ 141 ±177/37] 29 .10 .20 01 3:57PM 148 Gas Turbine Engineering Handbook Start-up Techniques The start-up of a gas turbine is done by the use of electrical motors, diesel motors, and in plants where there is an independent source of steam by a steam turbine New turbines use the generator as a motor... Maintenance Cost Factor 0.35 0 .49 0.77 1 .23 1.0 1 .4 2. 2 3.5 EFFICIENCY SIMPLE CYCLE (%) GAS TURBINEINSTALLED COST PER kW (US$) 600 //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 4. 3D ± 147 ± [ 141 ±177/37] 29 .10 .20 01 3:57PM Performance and Mechanical Standards 147 Aero-derivative gas turbines cannot operate on heavy fuels, thus if heavy fuels was a criteria then the frame type turbines would have to be used... mils (0.051 mm) on rotors  with speeds below 40 00 rpm, 1.5 mils (0. 04 mm) for speeds between 40 00±  ± 12, 000 rpm, and 8000 rpm, 1.0 mil (0. 025 4 mm) for speeds between 8000 0.5 mils (0.0 127 mm) for speeds above 12, 000 rpm These requirements are to //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 4. 3D ± 158 ± [ 141 ±177/37] 29 .10 .20 01 3:57PM 158 Gas Turbine Engineering Handbook be met in any plane and also include... //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 4. 3D ± 1 54 ± [ 141 ±177/37] 29 .10 .20 01 3:57PM 1 54 Gas Turbine Engineering Handbook API Std 618, Reciprocating Compressors for Petroleum, Chemical, and Gas Industry Services, 4th Edition, June 1995 This standard could be adapted to the fuel compressor for the natural gas to be brought up to the injection pressure required for the gas turbine Covers the minimum...//INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 4. 3D ± 145 ± [ 141 ±177/37] 29 .10 .20 01 3:56PM Performance and Mechanical Standards 145 turbine cost and efficiency as a function of gas turbine output for an industrial type turbine Industrial turbines range from micro-turbines of 20 kW at an installed cost of nearly $1000/kW and an efficiency of about 15±18%, to turbines rated at about 10 MW at a... tip diameters should be 0.190±0.195 inches (4. 8± 4. 95 mm) with body diameters of 1 /4 (6.35 mm)  28 UNF À2A threaded, or   0.3±0.3 12 inches (7. 62 7. 92 mm) with a body diameter of 3/8 (9. 52 mm) 24 UNF 24 A threaded The probe length is about 1 inch long Tests   conducted on various manufacturer's probes indicate that the 0.3±0.3 12- inch  (7. 62 7. 92 mm) probe has a better linearity in most cases . oils. 0 100 20 0 300 40 0 500 600 0 20 40 60 80 100 120 140 160 180 20 0 22 0 24 0 GAS TURBINE- FRAME TYPE-RATED POWER (MW) 30 31 32 33 34 35 36 37 Efficiency Cost EFFICIENCY SIMPLE CYCLE (%) GAS TURBINEINSTALLED. in efficiency. Figure 4- 3 shows typical gas 144 Gas Turbine Engineering Handbook //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 4. 3D ± 145 ± [ 141 ±177/37] 29 .10 .20 01 3:56PM turbine cost and efficiency. gas 0.35 1.0 No. 2 Distillate Oil 0 .49 1 .4 Typical Crude Oil 0.77 2. 2 No. 6 Residual Oil 1 .23 3.5 146 Gas Turbine Engineering Handbook //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 4. 3D ± 147