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TURBO MACHINES Steam and Gas Turbines

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TURBO MACHINES Steam and Gas Turbines Powered By Docstoc
					  TURBO MACHINES
Steam and Gas Turbines

          Eng. R. L. Nkumbwa MSc, REng.
          Copperbelt University, ST
          ©August, 2010
    Intended Contents

       Gas Turbine
        –   The Power Cycle for a Jet Engine
                Joule (UK) or Brayton (US) Cycle
       Steam Turbine
        –   Rankine or Vapor Cycle
       Combined Cycles
       Gas Turbine Engine Pressure Ratio


2
     “Classical Thermodynamics is the only
    physical theory of universal content which
       …. within the framework of its basic
         notions, will never be toppled.”

               Albert Einstein

3
    Global Energy Crisis!!

       Do we have an Energy, Enthalpy or an Entropy Crisis?
       Freeman Dyson explains Entropy as a "measure
        of disorder in a physical system".
       Another useful thermodynamic quantity in the
        context of energy conversion is Enthalpy, which
        is used to quantify the thermal energy content of
        hot steam.
       The energy available from a thermal power
        system depends on the temperature and
        pressure of the hot steam entering the turbine.
4
    Gas Turbines

       So, what are Gas Turbines?
       Popularly called the ―GT‖
       Copperbelt Energy Corporation (CEC) has
        Rolls-Royce Gas Turbines at Luano Station
        along Chingola Road.




5
    Gas Turbine Principle

       A gas turbine is a rotary machine, similar in
        principle to a steam turbine.
       In an open cycle gas turbine working on Joule
        cycle, the air is compressed in a rotary
        compressor and passed into a combustion
        chamber where fuel is burnt, the products of
        combustion are then made to impinge over rings
        of turbine blades with high velocity and work is
        produced.
6
7
       Sadi Carnot, Reflection On The Motive Power of Heat And On
        Machines Fitted To Develop That Power, 1824.



    “Nature, in providing us with combustibles on all
    sides, has given us the power to produce, at all times
    and in all places, heat and the impelling power which
    is the result of it.

    To develop this power, to appropriate it to our uses,
    is the objective of heat engines. The study of these
    engines is of greatest interest, their importance is
    enormous, their use is continually increasing, and
    they seem destined to produce a great revolution in
    the civilized world.”
8
    Nicolas Léonard Sadi Carnot
     (1796-1832) “French Army”




9
        Carnot Animation

        http://www.cs.sbcc.net/~physics/flash/heaten
         gines/Carnot%20cycle.html




10
        Carnot Animation

        http://www.cs.sbcc.net/~physics/flash/heaten
         gines/Carnot%20cycle.html




11
     Carnot Animation


        http://www.cs.sbcc.net/~physics/flash/heaten
         gines/Carnot%20cycle.html




12
     So, What is a Heat Engine?




13
     Real Engines

        Heat Engines in the real world are constrained
         by various factors.
        In commercial power plants the work needed to
         turn the generator is supplied by a device called
         turbine, which has curved blades at the
         circumference and the working fluid is air and
         water at ambient temperature (in case of
         hydroelectric plants) or high temperature
        (in steam cycle plants).
14
     Real Engines

        Most commercial power plants use steam or hot
         gas supplied by combustion of fuels to propel the
         turbine.
        Efficiencies of steam cycle plants are low, but the
         quantity of working fluid is less.
        There are different types of cycles that can be
         employed for extracted work from steam and
         other working fluids.
15
     What is Work?

        Efficiency depends on the heat input and work
         output.
        The Work Output can mean different things to
         different folks…
        Work to turn a shaft …. electric generator, ship
         propulsion, helicopter rotor,
        Turboprop engine, Abrams A1A tank, Automotive
         propulsion, …
16      Thrust efficiency @ NASA, etc
     What Drives this AV-8B Harrier Attack
                 Fighter Jet?




17
     Harrier Fighter Jet

        Harrier Vertical Takeoff
        Gulf War / Iraq / Afghanistan
        US Marines / UK Royal Air Force / Italy –
         Spain




18
     Harrier Fighter Jet

        Power Plant:
         –   One Rolls-Royce Pegasus 105 vectored-thrust
             turbofan.
        Thrust = 21,750 lb
        Max payload for vertical take off ~9,000 lb
        Max payload for short take off ~17,000 lb
        Max speed ~ Mach 0.98

19
     What is the Motive Power?




20
     Gas Turbine




21
     Gas Turbine Characteristics

        Relatively Small
        Light Weight
        Balanced Operation
        No Oil
        More Reliable




22
     Gas Turbines Timeline…
        1791 John Barber patent but nothing more
        1872 -04 Stolze, no result
        1882 -03 Aegidius Elling 11-44 hp
        1901 -06 Charles Lemale patent, Rateau design
        1906-08 Hans Holzwarth Brown Boveri
        1936 Noack (Stodola ) at Brown Boveri
        1939 Escher -Wyss, closed cycle with He
        1939 Ganz-Jendrassik
        1930 -39 Frank Whittle patented with Han von Ohain
23      1936 -39 Hans von Ohain First Flight
     Steam Turbine Timeline…

        1848 Francis first turbine
        1849 James Francis improved Howdturbine
        1874 Francis turbine with variable guide vanes
        1880s Modern pumps by Massachusetts pump in
         USA
        1880 Peltons free jet turbine
        1905 Föttingers torque converter
        1913 Victor Kaplans propeller turbine
24
     Gas Turbine Heat Source

        Liquid petrol
        Gas
        Coal
        Residuals
        Gasified coal
        Nuclear
        Bio, renewable
        All other
25
     Problems Associated with Turbines

        Turbine erosion
        Turbine corrosion
        Fuel oxidizer
        Stochiometric temperature




26
     Turbine Elementary Components

        Compressor
        Turbine
        Combustor
        Heat exchanger
        Gear
        Flow divider
        Flow unifier
        Nozzle
27
     Gas Turbine Layouts

        Single shaft
        Free load turbine
        Two spool
        Three spool
        Separate units
        Variable geometry
        Several combustors and heat exchangers

28
     Gas Turbine vs. Steam Turbines

        Direct heating          Liquid compression
        Higher max temp         Closed system
        Cooling possible
        Liquid compression
        Closed system



29
     Turbine Cycle Improvements

        Reduce compression work
        Increase expansion work
        Reduce outlet heat loss
        Improve thermodynamics
        Inter-cooling
        Reheat
        Heat exchanger

30
     Gas Turbine Applications

        Jet Engines
         –   Straight jet
         –   Turbofan
         –   Turboprop
         –   Helicopter
        Pump units
        Compressor units
        Naval or Marine Engines
31
     Gas Turbine Applications

        Power Generation
         –   Peak load
         –   Auxiliary Power Unit (APU)
         –   Base load CC, CHP
        Not for Land transportation
         –   Trucks
         –   Trains


32
     Gas Turbine Operation

        Military jets 500-5000 h

        Civil jets 5000-20000 h

        Stationary GT >100000 h




33
     Gas Turbine Sizes


        0.5 - 10 MW vehicle       40% Simple cycle

        20 - 100 MW mobile unit   60%Combined cycle




34
     Brayton Cycle

        The Brayton cycle models power systems
         based on Gas Turbines.
        When hot gas is used to drive turbine to
         generate work, the energy conversion process is
         much simpler because the working fluid (gas) is
         directly heated without need for a large boiler as
         in case of steam cycle plants.


35
36
     Brayton Cycle




37
     Brayton Closed Cycle Operation




38
     Brayton Open Cycle Operation




39
     Components and States in a Brayton
       Combustion Gas Turbine cycle.




40
     Brayton Combustion Gas Turbine cycle




41
     Brayton Combustion Gas Turbine cycle

        The Brayton cycle (or Joule cycle) represents the
         operation of a gas turbine engine.
        The cycle consists of four processes, as shown
         in Figure above of an engine:
         –   a - b Adiabatic, quasi-static (or reversible)
             compression in the inlet and compressor;
         –   b - c Constant pressure fuel combustion (idealized as
             constant pressure heat addition);

42
     Brayton Combustion Gas Turbine cycle

       –   c - d Adiabatic, quasi-static (or reversible) expansion
           in the turbine and exhaust nozzle, with which we take
           some work out of the air and use it to drive the
           compressor, and take the remaining work out and use
           it to accelerate fluid for jet propulsion, or to turn a
           generator for electrical power generation;
       –   d - a Cool the air at constant pressure back to its initial
           condition.



43
     Brayton Components




44
     Temperature Entropy Diagram of Ideal
               Brayton Cycle




45
     Brayton Cycle

        Air is first compressed in a compressor and then
         heated in a combustion chamber fired by cleaner
         fuel like natural gas.
        The working fluid in this case would be a mixture
         of air and the combustion products (carbon
         dioxide, water vapor and nitrous oxide).
        Dirtier fuels like coal cannot be used in this
         cycle. As in the case of steam cycle, the hot gas
         is directed through a nozzle to drive the gas
         turbine blades that turns a generator to produce
46       work or electricity.
     Brayton Cycle

        At the turbine exit, the gas has to be cooled to a
         temperature of around 550 degree Celsius,
         which is still hot but not sufficient to efficiently
         extract additional work in the turbine.
        At most gas turbine plants the exhaust gas is
         directly vented into the atmosphere.
        Simple gas plants and airplane engines are
         common examples of Brayton cycle in an open
         cycle arrangement.
47
     Brayton Thermodynamic Efficiency

        The thermodynamic efficiency of a Brayton cycle
         can be defined using enthalpy changes
         between various points inside a gas plant as:




48
     Brayton Thermodynamic Efficiency

        Alternatively, the efficiency of a Brayton cycle
         can also be expressed in terms of pressure
         ratios and the thermodynamic properties of
         air and combustion products.
        Brayton efficiency equations says that for a
         high cycle efficiency, the pressure ratio of
         the cycle should be increased.
        See figure below the effects of increased
         pressure
49
     Methods to Improve Efficiency

        The efficiency of a Brayton engine can be
         improved in the following manners:
        Intercooling, wherein the working fluid passes through a first stage
         of compressors, then a cooler, then a second stage of compressors before
         entering the combustion chamber. While this requires an increase in the fuel
         consumption of the combustion chamber, this allows for a reduction in the
         specific volume of the fluid entering the second stage of compressors, with
         an attendant decrease in the amount of work needed for the compression
         stage overall. There is also an increase in the maximum feasible pressure
         ratio due to reduced compressor discharge temperature for a given amount
         of compression, improving overall efficiency.


50
     Methods to Improve Efficiency

        Regeneration, wherein the still-warm post-
         turbine fluid is passed through a heat exchanger
         to pre-heat the fluid just entering the combustion
         chamber. This directly offsets fuel consumption
         for the same operating conditions improving
         efficiency; it also results in less power lost as
         waste heat.


51
     Methods to Improve Efficiency

        A Brayton engine also forms half of the
         combined cycle system, which combines with
         a Rankine engine to further increase overall
         efficiency.
        Cogeneration systems make use of the waste
         heat from Brayton engines, typically for hot
         water production or space heating.


52
     Methods to Increase Power

        The power output of a Brayton engine can be
         improved in the following manners:
        Reheat, wherein the working fluid—in most cases air—expands
         through a series of turbines, then is passed through a second
         combustion chamber before expanding to ambient pressure
         through a final set of turbines. This has the advantage of increasing
         the power output possible for a given compression ratio without
         exceeding any metallurgical constraints (typically about 1000°C).
         The use of an afterburner for jet aircraft engines can also be
         referred to as reheat, it is a different process in that the reheated air
         is expanded through a thrust nozzle rather than a turbine.
53
     Methods to Increase Power

        The metallurgical constraints are somewhat alleviated enabling
         much higher reheat temperatures (about 2000°C).
        The use of reheat is most often used to improve the specific
         power (per throughput of air) and is usually associated with a
         reduction in efficiency, this is most pronounced with the use of
         afterburners due to the extreme amounts of extra fuel used.




54
     Trend of Brayton cycle thermal efficiency
         with compressor pressure ratio




55
     Basic Gas Generator




56
     Basic Gas Generator

        Shaft could provide power take off for electric
         generator, ship propulsion, etc.
        Compressor and turbine could be axial or
         radial.




57
     Altitude Vs. Mach Number




58
     Turbojet Systems




59
     Turbojet Systems

        Output of gas turbine passed through exhaust
         nozzle and used entirely for thrust.
        High subsonic and supersonic.
        Developed by the British - Wiggins Co., Rolls
         Royce, Parsons, Bristol Engines, ABB,
         SIEMENS



60
     Turbojet Systems

        And the Germans - Junkers, BMW,
         Messerschmidt in 1930’s and 1940’s.

        General Electric (GE) started US production in
         1942 in Massachusetts, today with a production
         facilities in Angola and Egypt
        Original designs from Frank Whittle who had a
         centrifugal compressor.
61
     So, who is Sir Frank Whittle?




62
     Sir Frank Whittle

        Air Commodore, OM, KBE, CB, FRS, Hon FRAeS
        Born in Earlsdon, CoventryNRL, United Kingdom
         on 1st June 1907 – Died 9th August 1996
        Was a British Royal Air Force (RAF) Officer.
        Sharing credit with Germany's Dr. Hans von
         Ohain for independently Inventing the Jet
         Engine,
        He is hailed as a Father of Jet Propulsion.
63
     Whittle W2/700 Turbojet Engine - 1943




64
     Whittle’s Contributions…

        Frank Whittle, Royal Air Force, patented a jet
         engine in 1930.
        Axial PLUS centrifugal compression, 2-stage
         turbine.
        Free vortex turbine blade design.
        Host of mechanical and thermal challenges, not
         too reliable.
        Whittle considered high temperature ceramic
65       blades.
     Real Engineers! See Real Engines!

        Eng. Nkumbwa visits Sir Frank Whittle birth
         place and invention centre in Rugby,
         Coventry – UK.
        See Living evidence below…




66
     Sir Frank Whittle

        MIT Video Lecture on Sir Frank Whittle Jet
         Engine Invention in Coventry, England
        Engineer Nkumbwa visits Sir Frank Whittle
         birth place in Rugby – Coventry, England
         2006.




67
     Turbojet Operation

        Output of gas turbine passed through exhaust
         nozzle and used entirely for thrust.
        High subsonic and supersonic.
        Developed by the British (Wiggins Co., Rolls
         Royce, Parsons, Bristol Engines)
        And the Germans (Junkers, BMW,
         Messerschmidt) in 1930’s and 1940’s.
        GE started US production in 1942 in
68       Massachusetts.
     T-s Block Diagram for a TBJET




69
     Turbofan

        Exhaust passes through additional turbine stage
         to power a ducted fan that accelerates
        A large stream of air passing around the core.
        Typically flow through the outer part of the fan is
         5-6 times that flowing through the engine core
         (compressor).
        Thrust from both hot gases leaving the nozzle
         and from the cold by-pass flow.
        Bypass ratio = flow through fan / Flow through
70       engine Type values: 0 -10
71
72
     Turbofan Operation




73
     Turbofan Operation




74
75
     T-s Diagram for a Turbofan




76
     Turboprop Operation




77
     Turboprop Operation

        Actually developed prior to the turbofan.
        Rate of airflow through the prop may be 25-30
         times that through the engine.
        Gear box necessary for both lower prop speed
         and higher turbine speed.
        At higher speeds, tip losses considerable.
        Also called a Turbo shaft engine to power
         helicopter or marine.
78
79
     Ramjet Engine




80
     Ramjet Engines

        Air-breathing engine similar to a turbojet but
         without the mechanical compressor or turbine.
        Compression is accomplished entirely by ram air
         and it is thus sensitive to vehicle forward speed.
         No thrust at rest.
        Subsonic combustion, interior air slowed to
         subsonic speed for combustion.
        Mach number: 3~6
81
     Scramjet Engines




82
     Scramjet Engines

        Supersonic combustion ramjet. The flow
         through the combustor is still supersonic.
        ―Strange and tricky‖ combustion dynamics.
         Typically hydrogen fuels.
        Mach number >5+




83
     Combined Ramjet and Scramjet Engine




84
     Rocket Engine




85
     Internal forces to Create Thrust




86
     Thrust Force Analysis

        The thrust from a jet engine is not as easy to
         assess as a rocket.
        Thrust and drag forces occur throughout the
         engine.
        Del-P across compressor stages helps push
         engine forward.



87
     Internal Pressure & Thrust Distribution

        Single Shaft Turbo Engine




88
89
     Power to Weight Ratio

        Look at the following Case Study for the
         ―Proflight Zambia Airlines‖ which operates
         between Lusaka and Copperbelt




90
91
     Gas Turbines Engine Manufacturers

        General Electric (GE) - Ecomagination
        Rolls-Royce
        Platt & Whitney (PW)
        ABB
        SIEMENS




92
     Gas Turbine Engine Pressure Ratios

        See the next slide




93
94
     Gas Turbines Advantages

        They operate at high temperatures.
        They can and are capable of meeting peak
         load demands.
        They are compact and easy to operate, and
         take advantage of aerospace propulsion
         applications.
        They operate at relatively low pressures.

95
     Gas Turbines Advantages…

        Many installations burn natural gas, or in dual
         fuel mode burning NG and/or oil.
        They do not handle wet gases, and are not as
         vulnerable to corrosion as steam turbines.
        Combustion Gas Turbines do not require heat
         transfer equipment on the low-temperature side,
         and no coolant either


96
     Gas Turbines Limitations…

        They have relatively low efficiency since their
         maximum temperature is limited by material.
        Their efficiency is low because of the high
         compressor work, and low efficiency of
         compressors.




97
     Gas Turbines Limitations

        Open cycle turbines are limited by the high
         exhaust temperature, which limits the turbine
         work.
        They cannot be used with ―dirty‖ fuels, such
         as coal, since sulfur oxides can damage their
         blades.



98
     Steam or Rankine Cycle

        Steam, or Vapor Rankine Cycles overcome some
         of these limitations, and hence have been very
         popular in electric power generation.
        All steam cycle plants are modeled using what is
         known as Rankine cycle.
        Steam cycle can be constructed using closed and
         open cycles.
        Open cycle require dumping exit steam into
         environment and so is restricted to 100 degree
         Celsius.
99
     Rankine Cycle Plants

        Modern steam cycle plants consist of a boiler
         which generates steam using the energy
         provided by coal, oil, gas or nuclear fuels.
        In addition they have a feed water pump that
         pumps the fully condensed steam exiting the
         condenser to the boiler at high pressure.


10
0
     Rankine Efficiency

        Efficiencies are very low in such arrangement.
        Modern steam plants are based on a closed
         cycle arrangement that uses a condenser to cool
         the waste steam, an innovation that was
         originally conceived and designed by James
         Watt.


10
1
     Rankine Efficiency

        Here overall efficiency is the electrical output
         from the turbine generator minus the energy
         needed to operate the feed water pump and
         frictional losses in the turbine generator.
        The steam cycle efficiency in this case is defined
         by the following equation:


10
2
     Rankine Efficiency

        Modern steam plants achieve steam cycle
         efficiencies of 30-45%.
        It is possible to raise efficiencies by maximizing
         the inlet steam enthalpy, but these are limited
         due to engineering constraints.



10
3
     Components of a Rankine Cycle




10
4
     T-s Diagram of Open Rankine Cycle




10
5
     Rankine Power Cycles Operation

        A schematic of the components of a Rankine
         cycle is shown in Figure below.

        The cycle is shown on P-v, T-s, and h-s
         coordinates.



10
6
     Rankine p-v Coordinates




10
7
     Rankine T-s Coordinates




10
8
     Rankine h-s Coordinates




10
9
     Rankine Cycle Process

        The processes in the Rankine cycle are as
         follows:
         –   a b: Heat added at constant temperature T2 (constant
             pressure), with transition of liquid to vapor
         –   c d: Liquid-vapor mixture condensed at temperature
             T1 by extracting heat.
         –   d e: Cold liquid at initial temperatureT1 is pressurized
             reversibly to a high pressure by a pump. In this, the
             volume changes slightly.
         –   e a: Reversible constant pressure heating in a boiler
11           to temperature T2
0
     Rankine Cycle Process

        In the Rankine cycle, the mean temperature
         at which heat is supplied is less than the
         maximum temperature, T2 , so that the
         efficiency is less than that of a Carnot cycle
         working between the same maximum and
         minimum temperatures.


11
1
     Rankine Cycle Process

        The heat absorption takes place at constant
         pressure over eab, but only the part ab is
         isothermal.
        The heat rejected occurs over cd; this is at both
         constant temperature and pressure.



11
2
     Rankine Cycles Advantages…

        Fuel flexible, works well with coal (closed
         cycle).
        High efficiency, low pumping power.
        Lower flow rate (latent enthalpy).
        Run at low T (works with geothermal and
         solar), but high p.


11
3
     Rankine Cycles Advantages

        Works well with nuclear energy:
         –   Pressurized : T = 350 C
         –   Boiling : T = 400-500 C
         –   Gas Cooled R: T = 600-800 C
         –   High Temperature GR T > 800 C




11
4
     Rankine Cycle Disadvantages

        High inertia, good for base load but not for
         load following.
        Require cooling, big condensers, .. Water …
        Find bellow the Efficiency levels of Current
         Power plants



11
5
11
6
11
7
     Combined Cycles

        Recent years have seen a growth of plants
         employing Rankine and Brayton cycles.
        Such plants are called combined cycle plants.
        Rather than venting the hot exhaust gas from the
         Brayton cycle into the atmosphere there are
         plant designs that use this heat for other
         purposes using heat recovery steam generators.
        This has resulted in overall efficiencies
11
         reaching as high as 50 to 55%.
8
     Combined Cycle




11
9
     Combined cycles take advantage of high T gas
     turbine exhaust. Combined cycle efficiency:




12
0
     Wrap up…

        Any more worries…
        God help u…




12
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