Steam Cycle Theory Reliance)

Steam Cycle Theory Dr. K.C. Yadav, AVP & Head, Noida Technical Training Centre

Learning Agenda    

H2O availability status Energy potential Power generation applications Thermodynamic Properties, Processes & Cycles



Steam temperature and pressure management 2

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H2O Energy Potential    

Potential Energy Kinetic Energy Pressure Energy Flow Energy

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Thermodynamic Properties

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Thermodynamic Processes

Non Flow Processes P=C, V=C T=C Poly Isent H=C

W=mp(v2-v1), Q=H2-H1, U=mCvdT W=0 Q=U2-U1, U=mCvdT W=mpV1ln(v2/v1), Q=W, U=0 W=m(p1v1-p2v2)/(n-1), Q=(r-n)W/n-1 U=mCvdT W=m(p1v1-p2v2)/(r-1), Q=0 U=mCvdT Free Expansion & Throttling (W, Q & U = 0)

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Thermodynamic Processes

Flow Processes P=C, V=C T=C Poly Isent

Ws=0 Q=H2-H1 U=mCvdT W=-vdP Q=U2-U1 U=mCvdT W=RTln(p2/p1) Q=W U=0 W=nm(p1v1-p2v2)/(n-1) Q=(r-n)W/n-1 U=mCvdT 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

Water

Steam

Steam

Ice

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Steam Cycle (Natural) Three Phase Cycles

Steam

Water 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

Isothermal Heat Addition Device

Isentropic Pressure Reducing Device

Isentropic Pressure Raising Device

Isothermal Heat Rejection Device

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Carnot Cycle 

Temperature V/S Entropy

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3

1

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Temp

Entropy

η = 1 – T /T = 1- T /T 1

2

R

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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

Turbine

Boiler Feed Pump

Condenser

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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

Thermal Cycle Efficiency =

Heat added

=

=

He – hb

He – Hf – Wp

He – Hf – Wp

He – Hf – Wp =

= He-ha –(hb-ha)

He – ha – Wp

fun(Ta) – fun(Tr)

He – Hf

=

He – ha

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 Cycle Efficiency

Turbine output =

= Heat added to steam

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Function of (Cp, Cv) Function of (S, L, Cp)

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High steam temperature



W =Fxd =(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 32

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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)

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Behavior in terms absorption, adsorption and solution

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Cohesive and adhesive forces

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Surface tension



Internal energy



Enthalpy



Entropy 35

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Variation in H O Properties 2

No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Ts deg C 0.1 4 15 46 100 165 200 235 250 300 350 355 360 365 370 374.15

Ps Vf Vg bar cubic meteter per Kg 0.0061 0.001 206.31 0.0081 0.001 157.27 0.017 0.001001 77.978 0.1008 0.00101 14.557 1.0133 0.001044 1.675 7.0077 0.001108 2724 15.549 0.001156 0.1272 30.632 0.001219 0.0652 39.776 0.001251 0.05 85.927 0.001404 0.0216 165.35 0.001741 0.0087 175.77 0.001809 0.008 186.75 0.001896 0.0072 198.33 0.002016 0.006 210.54 0.002214 0.005 221.2 0.00317 0.0032 36

Hf KJ/Kg 0 16.8 62.9 188.4 419.1 697.2 852.4 1013.8 1085.8 1345 1671.9 1716.6 1764.2 1818 1890.2 2107.4

Hfg Hg KJ/Kg KJ/Kg 2501.6 2501.6 2492.1 2508.9 2466.1 2529 2394.9 2583.3 2256.9 2676 2064.8 2762 1938.5 2790.9 1788.5 2802.3 1714.6 2800.4 1406 2751 895.8 2567.7 813.8 2530.4 721.2 2485.4 610 2428 452.6 2342.8 0 2107.4 confidentia

Steam Generation 

Heating Surface Phenomenon



Water Surface Phenomenon

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Due to occurrence of vapour pressure

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Due to occurrence of low relative humidity

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Steam Quality Parameters 

Dry Saturated Steam - Either saturation temperature or saturation Pressure

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Wet Steam - Either saturation temperature or saturation Pressure - dryness fraction (DF) = Ms/M(s+w)

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Super Heated Steam - Either saturation temperature or saturation Pressure - Degree of superheat (DS) = T – Ts 38

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Thank you 4th October, 2008