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Steam Cycle TheoryDr. K.C. Yadav, AVP & Head,Noida Technical Training Centre
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Learning Agenda H2O availability status Energy potential Power generation applications Thermodynamic
Properties, Processes & Cycles
Steam temperature and pressure management
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H2O Energy Potential Potential Energy Kinetic Energy Pressure Energy Flow Energy
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ThermodynamicProperties
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Thermodynamic Processes Non Flow Processes
P=C, W=mp(v2-v1), Q=H2-H1, U=mCvdT V=C W=0 Q=U2-U1, U=mCvdTT=C W=mpV1ln(v2/v1), Q=W, U=0Poly W=m(p1v1-p2v2)/(n-1), Q=(r-n)W/n-1 U=mCvdTIsent W=m(p1v1-p2v2)/(r-1), Q=0 U=mCvdTH=C Free Expansion & Throttling (W, Q & U = 0)
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Thermodynamic Processes Flow Processes
P=C, Ws=0 Q=H2-H1 U=mCvdT V=C W=-vdP Q=U2-U1 U=mCvdTT=C W=RTln(p2/p1) Q=W U=0Poly W=nm(p1v1-p2v2)/(n-1) Q=(r-n)W/n-1 U=mCvdTIsent W=rm(p1v1-p2v2)/(r-1) Q=0 U=mCvdT
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Steady Flow Energy Equation
q+hi+ci**2/2+gzi = w+he+ce**2/2+gze
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Applications of Steady Flow Energy Equation
Nozzles; C2 = sq root of [2(h1-h2)+C1**2] Diffuser; C2 = sq root of [2(h1-h2)+C1**2] Centri. Pump; p2v2 - p1v1 + (C2**2 – C1**2)/2 + g(z2-z1) Turbine; W = h2-h1 : Compressor; W = h2-h1 Condenser; q = h2-h1 : Boiler; h2-h1 Throttling; h2 – h1 = 0 : Free Expansion; h2 – h1 = 0
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Uniform State Uniform Flow Process
Qcv + Sum[mi(hi + Ci**2/2 + gzi)] = Wcv + Sum[me(he + Ce**2/2 + gze)]
+ [m2(u2+C2**2/2+gzi)-m1(u1+C1**2/2+gzi)]
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H2O Phase Cycles Ice – Water – Ice Cycle Water – Steam – Water Cycle Steam – Ice – Steam Cycle Water – Steam – Ice – Water Cycle
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Two Phase Cycles
Ice Water
Steam
IceSteam
Water
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Steam Cycle (Natural)Three Phase Cycles
Water
Steam
Ice
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Water/Steam Cycles
Natural Cycle
Carnot Cycle
Rankine Cycle (Thermal Cycle)
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Carnot Cycle Hypothetical Carnot Equipments
IsentropicPressure Reducing
Device
Isothermal Heat
AdditionDevice
IsentropicPressure RaisingDevice
Isothermal Heat
RejectionDevice
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Carnot Cycle Temperature V/S Entropy
Entropy
Temp
1
2 3
4
η = 1 – T1/T2 = 1- TR/TA
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Carnot Difficulties & Rankine Solution T-S diagram of Possible Processes
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Rankine Cycle Four Equipment Rankine Cycle
Boiler FeedPump
Boiler
Condenser
Turbine
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Why Rankine Cycle for a Coal Fired Thermal Power Plant?
Does not it related to:
Coal combustion problems at a desired high pressure?
High erosion rate of the prime mover due to highly erosive
impurities in the products of coal combustion?
Metallurgical impossibility?
Techno-economic feasibility?
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Rankine Cycle (Thermal Cycle)
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Rankine Cycle (Thermal Cycle) T-S diagram of simple Rankine Cycle
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Rankine Efficiency Comparison
Work done – work consumed
Heat addedThermal Cycle Efficiency =
= He – Hf – Wp
He – hb =
He – Hf – Wp
He-ha –(hb-ha)=
He – Hf – Wp
He – ha – Wp
=He – Hf
He – ha =
fun(Ta) – fun(Tr)
fun(Ta) – fun(Tr)
Cycle Efficiency is function of heat addition and rejection temperatures (Ta & Tr)
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Thermal Cycle Efficiency
Ratio of isentropic heat drop across the turbine to
the heat supplied to the water in converting it into
steam.
It is directly proportional to the average heat
addition temperature and inversely proportional to
the heat rejection temperature
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Thermal Cycle Efficiency
Average Heat Addition and Rejection temperature can be
suitably changed by
High boiler working pressure
High steam temperature at boiler outlet
High condenser vacuum
Reheating cycle
Regenerative feed heating Cycle
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High Boiler Working Pressure
Variation in water/steam properties (S, L, Cp & Cv) at higher parameters improve Cycle Efficiency
Thermal CycleEfficiency
=Turbine output
Heat added to steam=
Function of (Cp, Cv)
Function of (S, L, Cp)
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High steam temperatureW = F x d
=(F/A) x (A x d)=P x V
Volume of steam is directly proportional to its temperature and hence increases the turbine output and in turn Cycle Efficiency
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High Condenser Vacuum
Reduces the corresponding saturation temperature
at which heat is rejected. Increase the turbine
output and thermal cycle efficiency
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Reheating cycle
High pressure steam cannot be heated beyond the
metallurgical limits and hence reheated after temperature
reduction in some of the high pressure stages. Thus the
average heat addition temperature increases and in turn
increases the cycle efficiency
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Regenerative feed heating Cycle
High Energy and Less Energy Steam is utilized in preheating the boiler feed water, otherwise the energy would have rejected in the condenser
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Thermal Cycle 250 MW Specific
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Thermal Cycle Processes Two stage water pressure raising processes (a-b & c-d) in
condensate extraction pump and boiler feed pump are
represented by very small vertical lines at the left of TS
diagram
Two curved lines above each water pressure raising lines
(b-c & d-e), represent sensible heat addition in Drain
Cooler, Gland Steam Condenser, Low Pressure Heaters,
Deaerator, High Pressure Hearters and Economizer
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Thermal Cycle Processes Two Horizontal lines (e-f & j-a) represent heat addition in
the evaporator and heat rejection in the condenser Two curved lines (f-g & h-i) before the expansion stages,
represent sensible heat addition to steam (i.e. Superheating) in Super Heaters and Re Heater
Two stage steam expansion processes in High Pressure Turbine and Intermediate Pressure / Low Pressure Turbines are represented by two vertical lines (g-h & i-j) at the right of TS diagram
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Properties of H2O Density
Relative density
Specific gravity
Specific heat
Sensible heat
Latent heat
Freezing/melting temperature
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Properties of H2O Boiling/condensing/saturation temperature Critical temperatures Triple point temperature Vapour pressure Saturation pressure Critical pressure Triple point pressure Viscosity Electrical conductivity Thermal conductivity
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Properties of H2O Physical Stability Chemical Reactivity
Non toxic Non corrosive)
Behavior in terms absorption, adsorption and solution Cohesive and adhesive forces Surface tension Internal energy Enthalpy Entropy
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Variation in H2O PropertiesNo Ts Ps Vf Vg Hf Hfg Hg
deg C bar cubic meteter per Kg KJ/Kg KJ/Kg KJ/Kg1 0.1 0.0061 0.001 206.31 0 2501.6 2501.62 4 0.0081 0.001 157.27 16.8 2492.1 2508.93 15 0.017 0.001001 77.978 62.9 2466.1 25294 46 0.1008 0.00101 14.557 188.4 2394.9 2583.35 100 1.0133 0.001044 1.675 419.1 2256.9 26766 165 7.0077 0.001108 2724 697.2 2064.8 27627 200 15.549 0.001156 0.1272 852.4 1938.5 2790.98 235 30.632 0.001219 0.0652 1013.8 1788.5 2802.39 250 39.776 0.001251 0.05 1085.8 1714.6 2800.4
10 300 85.927 0.001404 0.0216 1345 1406 275111 350 165.35 0.001741 0.0087 1671.9 895.8 2567.712 355 175.77 0.001809 0.008 1716.6 813.8 2530.413 360 186.75 0.001896 0.0072 1764.2 721.2 2485.414 365 198.33 0.002016 0.006 1818 610 242815 370 210.54 0.002214 0.005 1890.2 452.6 2342.816 374.15 221.2 0.00317 0.0032 2107.4 0 2107.4
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Steam Generation
Heating Surface Phenomenon
Water Surface Phenomenon
Due to occurrence of vapour pressure
Due to occurrence of low relative humidity
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Steam Quality Parameters Dry Saturated Steam
Either saturation temperature or saturation Pressure
Wet Steam
Either saturation temperature or saturation Pressure
dryness fraction (DF) = Ms/M(s+w)
Super Heated Steam
Either saturation temperature or saturation Pressure
Degree of superheat (DS) = T – Ts
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Thank you4th October, 2008