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Chapter 4..., , Gas Turbine Power Plants, , , , , , Weightage of Marks = 07 Teaching Hours = 05, , 4.1 Open and Close Cycle with Constant Pressure Gas Turbine Power Plant, 4.2 Components of Gas Turbine Power Plant, , 4.3 Meth cl ji, oe Improve the Thermal Efficiency of a Simple Open Cycle Constant Pressure Gas Turbine, , 44 Advantages of Gas Turbine Power Plant over others., 4.5 Maintenance Procedure of Major Components of Gas Turbine Power Plants., , About This Chapter, After reading this chapter, the students will able to,, e Identify the given component(s) of gas power plant., e Explain preventive maintenance of the given major component of given turbine power plants., , e Explain predictive maintenance of the given major component of given turbine power plants., , , , , , , , , , , , , , , , , , , , lain components of open cycle gas turbine power plant are:, i) Compressor, h, , i) Combustion chamber, and, , Turbine., , e working of open cycle gas turbine follows constant pressure process., , starting motor is required to run the compressor initially., , tmospheric air is compressed in the compressor., , his compressed air is supplied to the combustion chamber. Fuel supplied in the combustion chamber is, ignited with the help of oxygen present in the compressed air to produce hot gases., , creased internal energy of hot gases during combustion is converted into kinetic energy with the help, nozzles, These high velocity jets of hot gases are made to strike over the blades of turbine rotor, thus, , naking the rotor to rotate., hus, kinetic energy is converted into mechanical energy or work, which is now made available at, J, , ine's output shaft. : 5 ,, soon as the turbine starts to produce the mechanical work, the starting motor is made shut-off., , ior portion of this mechanical work made available at turbine shaft is supplied to run the compressor., aining quantity of power (i.e. mechanical work) produced by turbine is used to generate electric, , er. : i in, r this purpose, a generator is coupled to turbine, which converts mechanical energy (work) into useful, , ectrical energy., , [4.1] \

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Fuel supply, Heal, , vi Vey, Combustion chamber, , , , , , , , , , , , , , H.P. Hot Shaft coupling, gases Turbine's, output shaft, , , , , , , , Generator, producing, electricity, , , , , , , 2, , , , , , , , , , , , , , , , , , Compressor Turbine ., (Compressing (Expanding [7 ’, atmospheric air) gases), , | Mechanical, work, , , , , , , , , 4, , a Exhaust gases, Atmospheric air released to, sucked in atmosphere, , Fig. 4.1: Open cycle gas turbine, , , , , , , , , , , In case of open cycle gas turbine,, corrode the turbine blades., This difficulty is overcomed using clos, , direct contact with the compressed air., Construction:, , ¢ Basic components of closed cycle gas turbine power, (iv) Pre-cooler and (v) Heat exchanger., Working:, , the combustible gases are expanded in the gas turbine, which, , ed cycle gas turbine power plant, where fuel does not come i, , plant are: (i) Compressor, (ii) Air heater, (iii) Ti, , The air compressed in the compressor is passed throu, heater. The compressed air is preheated in the heat e, leaving the air heater, this high pressurized hot air stri, expanded continuously,, , Thus, the pressure energy associated with i inetic energy, which makes th, turbine rotor to rotate producing mechanical work, 7, This mechanical work obtained is the Output of gas turbine,, combustion is carried out in combustion chamber,, c- ‘85 an external combustion engine., , ot air leaving the turbine is, of heat to the com, , which is available at its Output shaft. §, ie, outside the turbine, therefore gas turb, , , , , Passed through the heat exchanger (see 5-6),, pressed air (see 2-3) entering into the air heate:, g the heat exchanger and enterin, , i g the air heater gets preheated. Due to, F amount of fuel is consumed in the air heater to heat the air upto desi, , So that, it can give awa, r., , , , , , the air entering the compressor still contains some heat,, , €-cooler and then supplied back to the inlet of compressor,, consumption to compress the air as well as re-circulation of sai, , In and again, this gas turbine Power plant is called as “Closed, @O REDMINOTE8 PRO, CO Al QUAD CAMERA

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Power Plant Engineering, , , , a aS, Shaft Coupling, Starting, Motor outa, shaft, , , , , , Gas Turbine Power Plants, EE rine Power Plants, , , , Shaft coupling, Mechanical, , , , Generator, , , , Producing, electricity, , __ oe work, , Turbine i, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Recirculated and High pr, an Compressed a Dreseute sat 4 ii, re-h ii i, pre-heated air in air out Rot alr (~ aac, Hot water Fuel injection 8 Air after its expansion, out externally B} heater producing turbine, work, Cold water, in 3 5, Preheated air, Precooler, , , , , , , , , 5, Heat exchanger, , Fig. 4.2: Closed cycle gas turbine, , led to turbine, then the mechanical work produced at the Output of, electric power in the generator (G). *, , Out at constant pressure, therefore it is called as “constant pressure, , If an electric generator is coup, turbine can be converted into, The complete cycle is carried, closed cycle gas turbine., , In the air heater, fuel may be added and burnt to heat the compressed air flowing through pipe., Please note that, compressed air does not come in direct contact with the fuel., , In this case, air heater can also be called as combustion chamber., , A starting motor is required to run the compressor initially. As soon as, the turbine starts developing, power and supplying part of it to run the compressor, starting motor is made shut-off., , , , , , It works on Closed cycle. The working, fluid (air) is recirculated again and, again. Therefore, it is said to be clean, cycle., , Heat is transferred indirectly through, surface contact in the air heater, It, means that, combusted fuel does not, come in direct contact with air., , Compressed air is heated in air, , heater., No mixing of air and burning fuel., , Air leaving the turbine is passed into, the precooler and then to compressor, for re-circulation., , , , , , It works on Open cycle. The fresh, working fluid (air) is supplied in every, cycle and after combustion and, expansion, it is exhausted to, atmosphere in the form of pollutant, exhaust gases. Therefore, it leads to, pollution., , Direct heat supply., , Heat is generated in the combustion, chamber itself., , , , , , , , , , , , , , , heated, , , , Compressed air is, combustion chamber., , Mixing of burning fuel directly or, compressed air., , Gas leaving the turbine is exhausted, , into the atmosphere, and fresh, , atmospheric air is required and, , sucked in each cycle., contd. ,..

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——, , Power Plant Engineering _ 44, , | Working medium (air) is replaced, , Working | Working medium (air) is circulated |, medium ‘| continuously, ie. same air is re, Gas Turbine Power Plants, , continuously, i.e. fresh atmospheric air, , , , , , , , | Rye ‘ circulated again and again for | is required and sucked for each new, , | ie multiple number of cycles. cycle., 7. | Type of fuel As the heat is supplied | Since combustion chamber is an, used } externally through surface contact, integral part of system, it requires, , therefore fuels either solid, liquid,, gaseous or a combination of fuels can, be used for heat generation., , high quality liquid or gaseous fuel for, burning., , , , , , , , , , , , , , , , , , 8. High thermal efficiency for given | Low thermal efficiency for same, | temperature limits. temperature limits., 9. Better. Comparatively less., |, 10. As air does not come in direct contact | As air gets mixed up with the, with fuel, the turbine blades do not | combustible fuel producing hot gases,, wear or corrode. So blade life is more. | the turbine blades may get corroded |, ' leading to wear. So blade life is less., il. Better control is possible on power | Poor control on power generation., generation. 5, 12. Heat can be supplied from sources | It requires high grade heat energy for 4, , , , like waste heat recovered during a, process, nuclear heat or solar heat for, generation of power in gas turbine., , generation of power in a gas turbine., , its, , , , _ Costlier due to complex construction, of plant., , Less costly due to simple construction, of plant., , , , High maintenance cost., , Low maintenance cost., , , , Since air coming from turbine is, cooled by circulating water in, precooler, it is suited for stationary, installations as well as marine uses., , , , Since the exhaust pollutant gas from, turbine is discharged into}, atmosphere, it is best suited for|, moving vehicles, air-crafts etc., , , , Other than air, the gases like Helium, or Helium-CO2 mixture can be used,, leading to high thermal efficiency., , , , Only air is used, but it leads to low, thermal efficiency., , , , , , 1€ various components of gas turbine power plants are,, Compressor,, , _ 3. Intercoolers and Heat exchangers,, , 5. Fuel injection system etc., , e, , , , , , , , , , , 4.4.1 Compressors, , , , 2. Combustion chamber,, 4. Regenerators,, , tary compressors are used in case of gas turbine power plants due to high flow rates of turbines and, , _ moderate pressure ratios., , , , Centrifugal Compressor, orking Princinles, , , , » Thecommonly used rotary compressors are centrifugal and axial flow compressors., , The centrifugal compressor increases the pressure of low pressure air by first creating a very high velocity, and then converting a part of this kinetic energy of moving air into high static pressure by centrifugal force., , 4

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=, , Power Plant Engineering Fnn, , Construction and Working:, , ¢ Asingle stage centrifu ., fitted symmetrically, Tee of an impeller, < which, a number of curved vanes are, , e The impeller rotates j ir-ti ‘ aa, air romane atinoseheley, air-tight volute casing with inlet and outlet points and draws in low pressure, , a5 Gas Turbine Power Plants, , ° oe we impeller rotates, it pushes the air from the centre of ei, a ee er to its periphery by centrifugal force,, , e The high speed of impeller leaves the air with high velocity at, vane tips of the impeller,, , e The kinetic energy thus attained at the impeller outlet is, converted into pressure energy, when the high velocity air, passes over the diffuser,, , . The diffuser iS normally a vaneless pipe, as it permits more, efficient part load Operation., , e The volute casing collects the air from the diffuser and it, further converts kinetic energy into pressure energy before it, leaves the compressed air to outlet, Impeller, , Fig. 4.3: Centrifugal compressor, Er Axial Flow Compressor, , ¢ In axial flow compressor, the air enters and leaves in the axial direction., , Construction:, , e Axial flow compressor consists of several moving blade rings attached to a common rotating, shaft., The moving blade rings are separated by rings of fixed blades attached to casing., , The main parts include a stationary (stator) part and a moving (rotor) part., , The drum rotates inside an air tight casing, to which, fixed stator blades are attached., , The blades are made of aerofoil section to reduce the loss caused by turbulence and boundary, separation. ;, , The air flow through the axial flow compressor is constrained to flow in a direction parallel to its, axis., , Working:, , * The mechanical energy is provided to the rotating shaft, which rotates the drum., , e, , oe, , ae, , , , The air enters from the left side of the compressor., , As the drum rotates, the air flows through the alternately arranged stator and rotor., , Here, the rotor increases the absolute velocity of the fluid and the stator converts this increase, in velocity into pressure rise. ;, , In short, the diffusing action in stator converts absolute kinetic head of the fluid into rise in, pressure. Thus, successive compression of the air, in all sets of stator and rotor, delivers the, high-pressure air at the outlet., , In other words, when the atmospheric air flows from one set of stator and rotor to another set,, it is compressed in successive manner till last set, which delivers the compressed air at high, , pressure and temperature., , , , Fixed blades, , , , Fig. 4.4: Axial flow compressor