Gas Turbine Engineering Handbook 2 Episode 12 ppt

//INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 14.3D ± 535 ± [521±538/18] 29.10.2001 4:05PM submarine gears, where the ultimate in quietness is essential, the hallmarks are moderate tooth loading, fine pitch, high-helix angle, and low-pressure angleÐall diametrically opposite from the usual and necessary practice for single-helical, hardened and ground gearing, which have low-helix angle (for minimum thrust), very coarse pitch teeth (to get adequate strength), and high loading (because of the carburized hardening). Some factors causing gear noise can be attributed to, but not limited to, the following: 1. Tooth spacing or involute error 2. Contact ratio 3. Surface finish 4. Wear on tooth flanks or pitting 5. Excessive or too little backlash 6. Gear, shaft, or housing resonance 7. Tooth deflections 8. Pitch-line runout 9. Load intensity on gearing 10. Clutches and couplings 11. Lube oil pump and piping 12. Transmitted noise from driven or driving machinery Installation and Initial Operation The mounting of a gearbox into trains is a precision job and should be done carefully. Gear unit installation is one of the most important factors to be considered for long, trouble-free operation. No matter how accurately the gear unit is manufactured, it can be destroyed in a few hours of operation when improperly installed. The same care should be taken when installing a gearbox as with any high-speed machinery. The mounting surface should be a flat, level, single-plane surface of finished steel at a height that will permit the shimming necessary to align the gear unit properly to connecting shafts. The shims should be of a size at least equal to the width of the unit foot pad. Then the gear unit should be placed on the foundation in the approximate required position. Uneven supports can distort the gearbox and adversely affect the gear tooth contact. Shaft alignment is very important for long gear life. Poor alignment can cause unequal distribution of tooth loads and distortion of the gear elements from overhung moments. A 2.0-mil shaft vibration level on the gear unit produced by misalignment is equivalent to a gear pitch-line runout of 2.0 mils. Gears 535 //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 14.3D ± 536 ± [521±538/18] 29.10.2001 4:05PM The gear housing must be properly supported to maintain proper internal gear alignment. When a gear unit is installed, the support pads must be maintained in the same plane as used by the manufacturer during assembly when gear face contact was obtained in the plant. Before startup, gear face contact should be checked using high-spot bluing, and rotating or rocking the pinion or lighter element back and forth sharply within the confines of the backlash. Inspection of this blued area should show approximately 90% face contact. If this contact is not obtained, the gear housing can be shimmed under the proper corner until an acceptable face contact is achieved. Many large, high-hardness or wide-face width gears are manufactured with helix angle modifications to account for torsional and bending deflec- tion. When the helix angle has been modified, good face contact will not be obtained under light load. In this case, the gear supplier should furnish data on percent of face contact versus load to be used as a guide during installa- tion and startup. Also, many gears have a short area of ease-off on each end of the teeth to prevent end-loading, and this area usually will not show contact under light load. The larger the gear unit, the more important this check becomes, since large housings tend to be more flexible. Also, the use of baseplates furnished by the original equipment manufacturer does not eliminate face contact problems, and these inspection procedures should be carried out. After the gear checks have been made, the foundation bolts should be uniformly tightened and the alignment rechecked. It may be necessary to repeat the shimming and tightening of foundation bolts to obtain final, correct cold alignment. Alignment of high-speed gear units should always be hot-checked and adjustments made as necessary. Temperatures vary so greatly throughout the housing and shafting that it is impossible to calculate a thermal growth accurately and, therefore, an alignment check must be made in the hot condition. When the alignment is complete, the baseplate or bed should be grouted in as close to the gear housing as possible. Journal bearings are used on the gear shafts and proper oil flow must be maintained. The oil system should there- fore be checked thoroughly prior to startup. The gear lube system is nor- mally flushed prior to any operations. The usual procedure is to seal off the gearbox components to which acid would be harmful, acid flush the system, and follow with a neutralizing flush before filling with the lube oil. Gear mesh spray nozzles should be checked to be sure dirt was not pumped through the system by observing the sprays or by introducing high-pressure air into the spray nozzle manifold. 536 Gas Turbine Engineering Handbook //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 14.3D ± 537 ± [521±538/18] 29.10.2001 4:05PM When possible, gears should be run-in on initial startup. Speeds and loads should be increased in percentage increments. Lube oil temperature, and pressure and bearing temperatures should be observed and adjust- ments made to the lube system as required. The number of adjustments made will depend on the complexity of the system. Oil pressure is of primary importance. When an auxiliary pump has been provided, oil should be circulated before the actual start. If not, the pump should be primed, and the journals wetted with oil. Primer holes are sometimes provided or alternate journals can be oiled through the holes provided for bearing temperature detectors. It is recommended that warning devices be provided to eliminate as much human error as possible, and the set points should be checked carefully. As with any startup, vibrations should be monitored and recorded. The vibra- tion monitoring system should include at least one accelerometer to detect any vibrations generated at gearmesh frequency. The recorded data should be saved to provide baseline vibration data for future reference. Shutdowns, as well as startups, require care and attention. Shutdown of a unit, which has been operating in a humid atmosphere, can result in con- siderable condensation and subsequent rusting of the gears, shaft journals, and housing in a very short time. When water contacts clean steel, it begins to etch the steel immediately. When shutdowns in such conditions are necessary, provisions to prevent condensation must be furnished. Under normal operating conditions, the oil should be changed every 2,500 operating hours or every six months, whichever occurs first. Where oper- ating conditions warrant, this period may be extended; conversely, severe operating conditions may make it necessary to change oil at more frequent intervals. Such conditions may occur with the rapid rise and fall in tempera- ture, which produces condensation, when operating in moist or dusty atmo- spheres, or in the presence of chemical fumes. In any case, the lubrication supplier should be consulted when determining a lubricant maintenance program. It may be necessary to analyze the oil periodically until a reason- able program can be established. Bibliography AGMA 211.02, ``Surface Durability (Pitting) of Helical and Herringbone Gear Teeth,'' Washington, D.C., 1969. AGMA 390.03, ``Gear Classification, Materials, and Measuring Methods of Unassernbled Gears,'' Gear Handbook, Vol. 1, Washington, D.C., 1973. Gears 537 //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 14.3D ± 538 ± [521±538/18] 29.10.2001 4:05PM API 613, Special Purpose Gear Units for Refinery Services, 2nd edition, Washing- ton, D.C., 1977. API 617, Centrifugal Compressors for General Refinery Services, Washington, D.C., 1979. Partridge, J.R., ``High-Speed Gears-Design and Application,'' Proceedings of the 6th Turbomachinery Symposium, Texas A&M University, December 1977, pp. 133  ±142. Phinney, J.M., ``Selection and Application of High-Speed Gear Drives,'' Proceedings of the 1st Turbomachinery Symposium, Texas A&M University, October 1972, pp. 62  ±66. 538 Gas Turbine Engineering Handbook //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 15.3D ± 539 ± [539±557/19] 29.10.2001 4:05PM Part V Installation, Operation, and Maintenance //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 15.3D ± 540 ± [539±557/19] 29.10.2001 4:05PM //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 15.3D ± 541 ± [539±557/19] 29.10.2001 4:05PM 15 Lubrication For reliable turbomachine performance, it is vital to have a properly designed, installed, operated, and maintained lubrication system. The lubri- cation system of a turbomachine is the ``lifeblood'' for this complex and finely tuned piece of machinery. The oil must be pumped in continuous circulation, conditioned, drained, and returned to be pumped again. In some units there are independent and dedicated turbine lube oil, compressor lube oil, and turbine control oil systems. There are combined systems with turbine lube oil and control oil from one system and compressor lube oil from another, or with turbine and compressor lube oil from one system and turbine control oil from another. In most cases, one system will supply all lube and control oil. This chapter deals with the principles involved in the operation and main- tenance of a lubrication system, and it describes the main components of such a system, including the lubricant itself. The following topics are discussed: 1. Basic oil system 2. Lubricant selection 3. Oil sampling and testing 4. Oil contamination 5. Filter selection 6. Cleaning and flushing 7. Coupling lubrication Basic Oil System API Standard 614 covers in detail the minimum requirements for lubrica- tion systems, oil-type shaft-sealing systems, and control-oil supply systems for special-purpose applications. 541 //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 15.3D ± 542 ± [539±557/19] 29.10.2001 4:05PM Lubrication Oil System A typical lubrication oil system is shown in Figure 15-1. Oil is stored in a reservoir to feed the pumps and is then cooled, filtered, distributed to the end users, and returned to the reservoir. The reservoir can be heated for startup purposes and is provided with local temperature indication, a high-tempera- ture alarm and high/low level alarm in the control room, a sight glass, and a controlled dry nitrogen purge blanket to minimize moisture intake. Figure 15-1. A typical lube oil system. 542 Gas Turbine Engineering Handbook //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 15.3D ± 543 ± [539±557/19] 29.10.2001 4:05PM The reservoir shown in Figure 15-2 should be separate from the equip- ment base plate and sealed against the entrance of dirt and water. The bottom should be sloped to the low drain point, and the return oil lines should enter the reservoir away from the oil pump suction to avoid disturb- ances of the pump suction. The working capacity should be at least five minutes based on normal flow. Reservoir retention time should be 10 minutes, based on normal flow and total volume below minimum operating level. Heating for the oil should also be provided. If thermostatically con- trolled electrical emersion heating is provided, the maximum watt density should be 15 watts per square inch (2.33 w/cm 2 ). When steam heating is used, the heating element should be external to the reservoir. The rundown level, which is the highest level the oil in the reservoir may reach during system idleness, is computed by considering the oil contained in all components, bearing and seal housings, control elements, and furnished piping that drains back to the reservoir. The rundown capacity should also include a 10% minimum allowance for the interconnecting piping. The capacity between the minimum and the maximum operating levels in an oil system that discharges seal oil from the unit should be enough for a minimum Figure 15-2. Lube oil reservoir. Lubrication 543 //INTEGRA/B&H/GTE/FINAL (26-10-01)/CHAPTER 15.3D ± 544 ± [539±557/19] 29.10.2001 4:05PM operation of three days with no oil being added to the reservoir. The free surface should be a minimum of 0.25 sq ft/gpm (0.023m 2 /gpm)ofnormalflow. The reservoir interior should be smooth to avoid pockets and provide an unbroken finish for any interior protection. Reservoir wall-to-top junctions may be welded from the outside by utilizing full-penetration welds. Each reservoir compartment should be provided with two three-quarter- inch minimum size plugged connections above the rundown oil level. These connections may be used for such services as purge gas, makeup, oil supply, and clarifier return. One connection should be strategically located to ensure an effective sweep of purge gas toward the vents. The oil system should be equipped with a main oil pump, a standby and, for critical machines, an emergency pump. Each pump must have its own driver, and check valves must be installed on each pump discharge to prevent reverse flow through idle pumps. The pump capacity of the main and standby pumps should be 10  ±15% greater than maximum system usage. The pumps should be provided with different prime movers. The main pumps are usually steam turbine driven with an electric motor driven backup pump. A small mechanical-drive turbine is highly reliable as long as it is running, but it is undependable for starting automatically after long idle periods. A motor is thus the preferred backup pump driver. A ``ready-to-run'' status light is usually provided for the motor in the control room to give visible evidence that the electrical circuit is viable. Starting of the backup pump is initiated by multiple and redundant sources. The turbine drivers should be maintained for failure by either low-speed or low-steam chest pressure or both. Low oil pressure switches are provided on the pumps and discharge header ahead of the coolers and filters, sometimes after the cooler and filters, and always at the end of the line where the reduced oil pressure feeds the various users. A signal from any of these should start the motor-driven pump and all alarms should be activated in the control room. The emergency oil pump can be driven with an AC motor but from a power source that is different to the standby pump. When dc power is available, DC electric motors can also be used. Process gas or air-driven turbines and quick-start steam turbines are often used to drive the emergency pumps. The pump capacities for lube and control oil systems should be based upon the particular system's maximum usage (including transients) plus a minimum of 15%. The pump capacity for a seal oil system should be based upon the system's maximum usage plus either 10 gpm or 20%, whichever is greater. Maximum system usage should include allowance for normal wear. Check valves should be provided on each pump discharge to prevent reverse flow through the idle pump. 544 Gas Turbine Engineering Handbook [...]... provided with an inert -gas purge To assist in degassing the oil, the drum will be heated by electricity or steam //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 15.3D ± 548 ± [539±557/19] 29 .10 .20 01 4:05PM 548 Gas Turbine Engineering Handbook Figure 15-4 Seal oil system Figure 15-5 Typical degassing drum arrangement //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 15.3D ± 549 ± [539±557/19] 29 .10 .20 01 4:05PM Lubrication... … 2 i=N†…nk† Fk e 2 K Kˆ0 …16-17† If we further define Fk ˆ T " Fk 2 K …16-18† and W ˆ e 2 i=N we have Gn ˆ K À1 ˆ F nk …16-19† kˆ0 or in matrix form ‰Gn Š ˆ ‰W …nk† Š‰Fk Š n ˆ 0; 1; 2; F F F ; N À 1 k ˆ 0; 1; 2; F F F ; K À 1 …16 -20 † //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 16.3D ± 564 ± [558±583 /26 ] 29 .10 .20 01 4:05PM 564 Gas Turbine Engineering Handbook The matrices [G] and [F ] are column matrices with... reasons By using Euler identities, Equations (16-6) and (16-7) can be written G…!n †real ˆ nÀ1 ˆ nˆ0 F…tk † cos…!n tk † …16-9† //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 16.3D ± 5 62 ± [558±583 /26 ] 29 .10 .20 01 4:05PM 5 62 Gas Turbine Engineering Handbook Figure 16 -2 Discrete Fourier transform representation G…!n †imaginary ˆ F…tk † ˆ Á! nÀ1 ˆ nˆ0 nÀ1 ˆ F…tk † sin…!n tk † …16-10† nˆ0 …G…!n †real cos…!n tk † ‡... bearing (by mounting them within the bearing itself) or to measure thrust //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 16.3D ± 566 ± [558±583 /26 ] 29 .10 .20 01 4:05PM 566 Gas Turbine Engineering Handbook motions They are generally indifferent to hostile environments, including temperatures up to 25 0  F ( 121  C) and are not expensive One drawback is that shaft surface conditions and electrical runout can... University, 19 72 //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 15.3D ± 557 ± [539±557/19] 29 .10 .20 01 4:05PM Lubrication 557 Fuller, D.D., Theory & Practice of Lubrication for Engineers, Wiley Interscience, 1956 O'Connor, J.J., and Boyd, J., eds., Standard Handbook of Lubrication Engineering, McGraw-Hill Book Co., 1968 //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 16.3D ± 558 ± [558±583 /26 ] 29 .10 .20 01 4:05PM... //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 16.3D ± 563 ± [558±583 /26 ] 29 .10 .20 01 4:05PM Spectrum Analysis 563 The equations may be rewritten in a simpler form by making the following definitions: " Fk ˆ F…tk † …16- 12 Gn ˆ G…!n † …16-13† !n ˆ nÁ! ˆ 2 nK NT …16-14† tK ˆ KÁt …16-15† so that Equations (16-6) and (16-7) become " Fk ˆ Á! nÀ1 ˆ Gn e 2 i=N†…nk† …16-16† nˆ0 Gn ˆ ˆ T K À1 " … 2 i=N†…nk† Fk e 2 K Kˆ0 …16-17†... problems in the compressor The very high pressure in most of the advanced gas turbines cause these compressors to have a very narrow operating range between surge and choke Thus, these units are very susceptible to dirt and //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 16.3D ± 568 ± [558±583 /26 ] 29 .10 .20 01 4:05PM 568 Gas Turbine Engineering Handbook blade vane angles Dynamic pressure transducers are used to... and resin degradation For gas turbines, especially the more advanced high-temperature gas turbines, the oil of choice should be synthetic oil, since synthetic oils have a high flash point Gas turbine lubrication systems should be run for about 20 minutes after shutdown since maximum temperatures are reached after 10 minutes of shutdown especially in the bearing area Most gas turbines are also on turning... main sources of contamination are atmospheric condensation, steam leaks, and faulty oil coolers, preventive measures should be taken //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 15.3D ± 5 52 ± [539±557/19] 29 .10 .20 01 4:05PM 5 52 Gas Turbine Engineering Handbook Condensation will occur in the atmospheric vented oil system whenever the temperature in the vapor space areas drops below the dew point This effect... consecutive inspections Observe the pressure drop across the filters during the consecutive operation Do not allow the pressure drop to exceed 20 psig (1.4 Bar) //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 15.3D ± 554 ± [539±557/19] 29 .10 .20 01 4:05PM 554 Gas Turbine Engineering Handbook When the system is considered clean, empty the oil reservoir, and clean out all debris by washing with a detergent solution . lube oil system. 5 42 Gas Turbine Engineering Handbook //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 15.3D ± 543 ± [539±557/19] 29 .10 .20 01 4:05PM The reservoir shown in Figure 15 -2 should be separate. high-pressure air into the spray nozzle manifold. 536 Gas Turbine Engineering Handbook //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 14.3D ± 537 ± [ 521 ±538/18] 29 .10 .20 01 4:05PM When possible, gears should. system. Figure 15-5. Typical degassing drum arrangement. 548 Gas Turbine Engineering Handbook //INTEGRA/B&H/GTE/FINAL (26 -10-01)/CHAPTER 15.3D ± 549 ± [539±557/19] 29 .10 .20 01 4:05PM Lubricant Selection A