Generation of Most Eligible Steam for Rankine Cycle

Generation of Most Eligible Steam for Rankine Cycle P M V Subbarao Professor Mechanical Engineering Department Means to Achieve. Qualities of Working Fluid Preferred by Sir Carnot …. .

Reheating : A Means to implement High Live Steam Pressure Improvement in Efficiency, % Supercritical 593/6210 C 593/5930 C 565/5650 C 538/5380 C

Classification of Rankine Cycles

More Bottlenecks to Achieve Supercritical Steam Cycle 3 sup 3 sub 4 sup 4 sub T 2 1 s

Quality and Saturated Liquid-Vapor (Wet) Mixture • Now, let’s review the constant pressure heat addition process for water shown in Figure. • The state 3 is a mixture of saturated liquid and saturated vapor. • How do we locate it on the T-v diagram? • To establish the location of state 3 a new parameter called the quality x is defined as

Adiabatic Expansion of Steam • The liquid in the LP turbine expansion flow field is seen to progressively appear, with lowering pressure, in four forms, namely as: • A fine mist (or fog) suspended in the steam; • As a water stream running in rivulets along the casing (mainly OD); • As a water film moving on the surface of the blades (mainly stator; not particularly evident on the rotor blades owing to centrifugal-flinging action); • As larger droplets created when the water flowing along the surface of the blades reaches the trailing edge.

More Bottlenecks to Achieve Supercritical Steam Cycle 3 sup 3 sub 4 sup 4 sub T 2 1 s

Ill Effects of High Pressure Cycles x Pressure, MPa

Old Last Stage LP Blade

Modified Loss Region

Why should steam condense during Adiabatic Expansion? ? ?

Thermodynamic Characterization of Working Fluid

Philosophical Recognition of Working Fluid Organic Substances must be selected in accordance to the heat source temperature level (Tcr < Tin source)

Progress in Steam Rankine Cycle 1907 1919 1938 1950 1958 1959 1966 1973 1975 MW 5 20 30 60 120 200 500 660 1300 p, MPa 1. 3 1. 4 4. 1 6. 2 10. 3 16. 2 15. 9 24. 1 Th o. C 260 316 454 482 538 566 565 538 T r o. C -- -- 538 566 565 538 FHW -- 2 3 4 6 6 7 8 8 5. 1 4. 5 3. 4 3. 7 4. 4 5. 1 ~17 27. 6 30. 5 35. 6 37. 5 39. 8 39. 5 40 Year Pc, k. Pa 13. 5 h, % --

Reheating of Steam to Enhance Quality at the Turbine Exit Single Turbine drum

Analysis of Reheat Cycle • Consider reheat cycle as a combination of Rankine cycle and horn cycle. • Cycle 1 -2 -3 -4 -5 -6 -1 = Cycle 1 -2 -3 -4 -4’-1 + Cycle 4’-4 -5 -6 -4’. • Therefore, 4’ 6

Analysis of the Reheat Cycle 4’ 6

Clues to Achieve Double Benefit Consider the ratio of Define Increment in efficiency

Selection of Reheat Pressure pmax= 15 MPa Tmax= 550 0 C Tsat= 342. 20 C

Effect of Reheat Pressure on New Tm, in pmax= 15 MPa Tmax= 550 0 C Tsat= 342. 20 C

Dh, % Effect of Reheat Pressure 0. 2 0. 4 ~0. 3 0. 6 prh/pmax 0. 8 1. 0

Optimal Selection of Reheat Point

Reheating : A Means to implement High Live Steam Pressure Improvement in Efficiency, % Supercritical 593/6210 C 593/5930 C 565/5650 C 538/5380 C

Super Critical Cycle ~ 1990

Ultra Supercritical Installations of The World

Double Reheat Ultra Super Critical Cycle 8

Reheater Pressure Optimization for Double Reheat Units 97 bar 69 bar 110 bar

Improvement in Efficiency, % 21 st century Rankine Cycles

Super Critical Cycle of Year 2005

Double Reheat Super Critical Plants Net efficiency on natural gas is expected to reach 49%. Net efficiency on coal is expected to reach 47%.

Advanced 700 8 C Pulverised Coal-fired Power Plant Project

FUTURE ULTRA SUPERCRITICAL PLANT – UNDER DEVELOPMENT EFFICIENCY 55 %

Steam Generation : Explore more Causes for Wastage h x=s

Look for More Opportunities to Reduce Wastage

Follow the Steam Path : Early Stage

Follow the Steam Path : Middle Stage

Follow the Steam Path : End Stage

Follow the Steam Path : The End

Save Wastage thru Recycling !? !?

Regeneration Cycle with Mixer (Open Feed Water Heater)

Synthesis of Rankine Cycle with OFWH 5 T p 2=p 6 4 6’ 3 2 1 7 6

Regeneration Cycle with Mixer (Open Feed Water Heater)

Analysis of mixing in OFWH

Analysis of mixing in OFWH Constant pressure mixing process Consider unit mass flow rate of steam thru the turbine h 6 h 3 Conservation of energy: y h 2 (1 -y)

Analysis of Regeneration through OFWH

Optimal Location of FWH

Performance of OFWH Cycle ~ 12 MPa htotal pbleed, MPa

Gross Workoutput of bleed Steam wbleed ~ 12 MPa pregen, MPa

wbleed Workoutput of bleed Steam y, MPa

wbleed More Work output with more bleed Steams y pregen, MPa

Progress in Rankine Cycle Power Plants Year 1907 1919 1938 1950 1958 1959 1966 1973 1975 MW 5 20 30 60 120 200 500 660 1300 p, MPa 1. 3 1. 4 4. 1 6. 2 10. 3 16. 2 15. 9 24. 1 Th o C 260 316 454 482 538 566 565 538 FHW -- 2 3 4 6 6 7 8 8 Pc, k. Pa 13. 5 5. 1 4. 5 3. 4 3. 7 4. 4 5. 1 h, % -- ~17 27. 6 30. 5 35. 6 37. 5 39. 8 39. 5 40

Open (Direct Contact) Feed Water Heater

An Impractical Efficient Model for Power Plant A Turbine SG yj, hbj Yj-11, hbj-1 B Yj-2, hbj-2 C OF OF C OFW WH WH H 1 y – y 1 - yj – yj-1 - yj-2 1 - yj 1 , hf (j) j j-1 hf (j-2) hf (j-3) hf (j-1) n number of OFWHs require n+1 no of Pumps…. . The presence of more pumps makes the plant unreliable…

Closed Feed Water Heater (Throttled Condensate)

Control of Entropy Generation due to Liquid Heating

Effect of no of feed water heaters on thermal efficiency and work output of a regeneration cycle Thermal Efficiency Specific Work Output

Heater Selection and Final Feedwater Temperature • In order to maximize the heat rate gain possible with ultrasupercritical steam conditions, the feedwater heater arrangement also needs to be optimized. • In general, the selection of higher steam conditions will result in additional feedwater heaters and a economically optimal higher final feedwater temperature. • In many cases the selection of a heater above the reheat point (HARP) will also be warranted. • The use of a separate desuperheater ahead of the top heater for units with a HARP can result in additional gains in unit performance.

Typical Single Reheat Heater Cycle with HARP

Effect of Final Feedwater Temperature and Reheat Pressure on Turbine Net Heat Rate

Double Reheat Cycle with Heater above Reheat Point

More FWHs for a Selected Bleed Points

New Circuits of Desuperheater for Preheating of Feedwater in Steam Power Plants

Efficiency of Danish Coal-Fired Power Plants Continuous development resulted around the mid 80's in an average efficiency of 38% for all power stations, and best values of 43%. In the second half of the 1990’s, a Danish power plant set a world record at 47%.

Average efficiency, specific coal usage, CO 2 emissions h Indian Coal Plants: Efficiency of modern coal power plant = 34 -36% Efficiency of old power plant = 20 -30%

Expectations from Modern Steam Generator for Higher Efficiency • • High Main Steam Pressure. High Main Steam Temperature. Double Reheat & Higher Regeneration. Metal component strength, stress, and distortion are of concern at elevated temperatures in both the steam generator and the steam turbine. • In the steam generator’s heating process, the tube metal temperature is even higher than that of the steam, and concern for accelerated corrosion and oxidation will also influence material selection.