1. Descri Describe be a simp simple le gas turbin turbine. e. Answer: A simple gas turbine has a compressor, combustion combustion chamber, and turbine. The turbine and the compressor are on the same shaft. The compressor raises the pressure of atmospheric air and sends this air to the co mbustion chamber. chamber. Here, a fuel (oil, gas, or pulverized coal burns, burns, raising the temperature temperature and increasing the heat energ! energ!.. The hot gas in the turbine e"pands to develop mechanical energ!, as e"panding steam does in a steam turbine. This simple unit has a thermal efficienc! of about #$ percent. An open%c!cle gas turbine also ta&es air from the atmosphere and discharges e"haust to the atmosphere. 'pen%c!cle hoo&ups differ in man! wa!s, but the compressor inlet is atmospheric and there is a relativel! narrow range of best pressure ratios. This puts a limit on the top%c!cle pressure. These units can have a regenerator, intercooler, and other refinements and can still be open%c!cle gas turbines. #. How How does does stea steam m inec inectio tion n lower lower the )' " discharged to the atmosphere b! a gas turbine* Answer: Adding steam in the combustion zone of the turbine lowers both the flame and gas temperature, preventing up to +$ percent of uncontrolled )' " for mation. -. How How does does the gas gas turbin turbinee use therm thermal al energ! energ!** Answer: To &now &now how gas turbines behave, we must understand the basic steps in the simple c!cle. Heat energ! of tile fuel is converted into mechanical energ!. energ!. The compressor and the combustion chamber produce a high%energ! wor&ing fluid that can be e"panded in the turbine. This develops mechanical energ! similar similar to e"panding steam in a steam turbine. The volume of the wor&ing fluid is smallest at the compressor outlet, though its temperature is higher than at the compressor inlet. High e"cess air ratio in the combustor &eeps air and gas temperatures below a ma"imum limit. At the turbine outlet, gas volume is at ma"imum. The main elements of the gas%turbine plant must be proportional to handle the flow of wor&ing fluid with minimum pressure loss through the s!stem. . How is is the efficien efficienc! c! of a modern modern gas gas turbin turbinee increased increased** Answers: /onverting more heat energ! to mechanical energ! increases gas%turbine efficienc!. efficienc!. 'ne wa! to do this is to raise the turbine inlet gas temperature, which, in turn, raises thermal efficienc!. efficienc!. At higher temperatures, the best efficienc! occurs at the higher%pressure ratios. 0ncreasing the temperature of the gas also betters both the air rate and the wor& ratio.
The ne"t step is to add a regenerator to transfer heat from the e"haust to compressed air. The hotter air temperature recovered from waste heat cuts the fuel needed to bring the air up to the turbine inlet temperature. )e"t, add an intercooler. Divide the compression. The ne"t step is to split the turbine in two and to place a combustor before each turbine. The first combustor discharges high%temperature gas into the high%pressure turbine. As the gas does wor& on the turbine rotor, both its pressure and temperature drop partl! e"panded. . 2&etch a single%stage%heated closed%c!cle gas turbine and give the temperatures and pressures it needs for full%load operation: Answer: Hot gases of 3+45/ and #$$ &6a go into the high%pressure turbine from the combustor, and e"haust goes from the low%pressure turbine at -5/ and 34$ &6a. Air enters the low% pressure compressor at 1357 and 3 &6a and leaves at +5/ and #-$ &6a. 3. To avoid condensation, what precautions are necessar! for natural gas fuel that supplies a gas turbine* Answer: 8ost gas turbines for industrial use is hoo&ed up to pipeline %9ualit! natural gas with li9uid fuel, usuall! no.#, as bac&up. The natural gas should go through water &noc&out vessels before entering the gas turbine room. These vessels normall! contain coalescing and filtering elements. To avoid condensation, the natural gas temperature should be maintained at least 1$5/ above its dew point. 6oc&ets must be avoided in pipe runs so that condensate will not collect in low spots. 6iping is usuall! stainless steel. 4. hat are some conditions that re9uire a gas turbine train trip* Answer: 1. Trips are re9uired for overspeed. #. ;ow lube oil pressure. -. High turbine e"haust temperature. . <"cess vibration. . 7lame failure in combustor. 3. 0nlet air filter having high differential pressure. 4. An! initiation of fire protection around the unit. +. hat are some of the factors that ma! determine the service life of gas turbine components* Answer: The manufacturers e"press this as used%up service life based on their methods of calculating remaining life.
7actors to consider include: 1. #. -. . . 3. 4. +. =.
starts and stops load and temperature swings running hours whether components have protective coatings material creep strength endurance limit for fatigue strength evaluation method of blade cooling effect of steam inection erosion wear noted during inspections
This also includes hot gas metal o"idation. The trend is to convert man! of these items to e9ual a certain amount of actual running hours, adding them to the running hours, and then comparing them to the manufacturer>s predicted life. 0n this wa!, a decision is made for a planned replacement before a failure can he e"pected. 0t is important for operators to become familiar with the manufacturer>s method of assigning remaining life because operating practices influences man! of these. =. hat are the basic components of a simple gas%turbine s!stem* Answer: The basic components for a simple gas%turbine s!stem include a compressor, combustor, and the turbine. A rotating compressor draws in air from the atmosphere, pressurizes it, and forces it into the combustor (the furnace in a stead! flow. 7uel forced into the air burns, raising the temperature of the mi"ture of air and combustion products. This high% energ! mi"ture then flows through the turbine, dropping in pressure and temperature as it does wor& on the moving blades. The spent gases then leave at atmospheric pressure but at high temperature. The turbine drives the compressor rotor through a shaft and also an e"ternal load through the load coupling. 1$. hat are the main components of a gas turbine* Answer: 1. air compressor #. combuster -. flue gas e"pander turbine 11. hat gas is used in the 2/? method of controlling )'"* Answer: Air%diluted ammonia vapor is inected into the flue gas stream before it enters the catal!st units consisting of hone!comb%shaped ceramic material. These cells, with the ammonia vapor, convert nitrogen o"ides to nitrogen and water vapor for discharge into the atmosphere. 1#. hat is a booster compressor*
Answer: A booster machine compresses air or gas from a pressure above atmospheric to a still higher pressure. @ooster machines have man! uses, especiall! in oil and gas fields and related industries. /ompression ma! be either single or multistage, depending upon the ratio of compressions, horsepower, and gas anal!sis 1-. hat is combined%c!cle cogeneration* Answer: A combined c!cle using a gas turbine or diesel, usuall! driving a generator in which the e"haust gases are directed to a waste heat%recover! boiler or heat%recover! steam generator (H?2. The steam from the H?2 is then directed to a steam turbo%generator for additional electric power production. The use of the e"haust heat from a gas turbine improves the overall thermal efficienc!. 0n cogeneration, electric power is produced, but part of the steam from the H?2 or from e"traction from the steam turbine is used for process heat, hence the term cogeneration%the simultaneous production of electric power and process heat steam. 1. hat is compression efficienc!* Answer: /ompression efficienc! is the ratio of the wor& needed for ideal adiabatic compression through a given pressure range to the wor& actuall! needed b! the compressor. 1. hat is engine efficienc!*
Answer: This is the basic gas turbine c!cle of adiabatic compression of air in a compressor, constant pressure burning in a combustor, followed b! adiabatic e"pansion of the wor&ing fluid in a turbine to produce mechanical power. 1=. hat is the effect of ambient temperature on gas turbine performance* Answer: 8ost designs are based on an air temperature of 135/ entering the air compressor. 0n general, unless preheating is used, the thermal efficienc! will decrease about one percentage point for each 45/ rise in air inlet temperature. #$. hat is the effect of creep on high%allo! material used in gas turbines* Answer: The high%allo! materials ma! show a loss of ductilit! at high temperature over a period and thus becomes brittle and prone to crac&ing. The higher the temperature, the more rapidl! the material loses its strength and ductilit!. #1. hat is thermal efficienc!* Answer: Thermal efficienc! is the percentage of the total fuel energ! input that appears as the net wor& output of the c!cle. ##. hat is wor& ratio* Answer: 0t is the ratio of the uct wor& output of the c!cle to the total wor& developed in the turbine or turbines. #-. hat provisions in the la!out of a combined%c!cle should be considered* Answer: 0t is important to consider the use of a b!pass stac& that will permit operating the gas turbo%generator in case of a forced outage on the H?2 or steam turbo%generator. However, in certain states, such as /alifornia, also to be considered are )' limits that re9uire steam inection and loading to limit the e"haust temperature coming out of the simple%c!cle gas turbine so that the! do not e"ceed urisdictional limits. #. here ma! !ou e"pect to find thermal stress crac&s in a gas turbine when sna&ing internal inspections*
Answer: Thermal stress crac&s appear in those components, which are subected to high temperatures, such as combustors, entrance nozzle segments, and first stage blades, and which have abrupt changes in stiffness or configuration that produce stress concentration. #. h! are fuel considerations important in gas turbines* Answer: The products of combustion come in direct contact with turbine blading. This dictates using fuels those produce combustion products that do not cause high%temperature corrosion or o"idation, erosion, and deposition of ash on blades. 6referred are natural gas, properl! prepared s!ngas, and distillate oils. 8ost other li9uid fuels re9uire e"ternal treatment to remove harmful vanadium and sodium. Banadium pento"ide and sodium sulfate are the principal ash components formed at higher temperatures. This ash adheres to blades and causes corrosion on the blades
1. A combined gas%vapor power c!cle includes onl! the combination of a gas turbine with a steam turbine. a. true b. false #. enerator speed is controlled b!: a. number of windings and size of electromagnet b. e"citer circuit and field rheostat c. steam turbine speed and the turbine governor C d. e"pansion indicator and vibration sensors e. pairs of poles and core material -. A condenser is alwa!s under a negative (vacuum pressure. a. true b. false . A condensing turbine re9uires a vacuum brea&er. The vacuum brea&er initiates one of the following, should the vacuum start to fail on the condenser: a. it will lower the cooling water flow to the condenser b. it will increase the cooling water flow to the condenser c. it will trip the turbine at a preset vacuum pressure d. it will unload the electrical load in proportion to the vacuum change e. it will increase the load on the condenser . A condensing turbine: 1. has a higher efficienc! than a non%condensing turbine #. has a lower efficienc! than a non%condensing turbine -. operates at less than atmospheric pressure . are mostl! used in process plants . are mostl! used in power generating stations
3. ma! be single or multi%stage machines a. b. c. d.
1, , 3 1, -, C #, -, #, , 3
