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Efficient Reheat Cycle Analysis for High Steam Pressures

This analysis by Professor P.M.V. Subbarao explores overcoming hurdles in adopting high live steam pressures in Rankine cycles. Reheating steam improves turbine efficiency, but pressure drops in reheaters must be minimized to optimize cycle performance. The study analyzes the horn cycle, optimal reheat pressures, and the impact of reheating on efficiency, providing insights for implementing high-pressure cycles. Techno-economically viable ranges and cost-to-benefit ratios are considered, along with the effects of various steam parameters.

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Efficient Reheat Cycle Analysis for High Steam Pressures

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  1. Analysis of Reheat Rankine Cycle P M V Subbarao Professor Mechanical Engineering Department Means to Eliminate Hurdles while Adopting high Live Steam Pressures ……

  2. Hurdles in Implementation of High Pressure Cycles Tmax = 546C &Tmin=40 C xturbine-exit Main SteamPressure, MPa

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

  4. Reheaters • The pressure drop inside reheater tubes has an adverse effect on the efficiency of turbine. • Pressure drop through the reheater should be kept as low as possible. • Higher pipe diameter and low steam will velocities can lower the pressure drop, but leads to higher capital cost. • Techno-economically viable Range: Tube diameter : 42 – 60mm.

  5. Cost to Benefit Ratio of Reheat Cycle

  6. 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

  7. Analysis of Horn Cycle Horn Cycle: 4’ – 4 Isentropic Compression. 4 – 5 Isobaric Heat Addition. 5 – 6 Isentropic Expansion 6 – 4’ Isobaric(thermal) cooling. 4’ 6

  8. Condition for Development of Efficient Reheat Cycle

  9. Change in Efficiency due to Reheating Condition for increased efficiency: Select appropriate reheat pressure, pRH, such that left hand side is maximum.

  10. Selection of Reheat Pressure pmax= 15 MPa Tmax= 550 0C Tsat= 342.20C

  11. Effect of Reheat Pressure Dh,% 1.0 0.2 0.4 0.6 0.8 ~0.3 prh/pmax

  12. Optimal Selection of Reheat Point

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

  14. Effect of Reheating on Overall Tm,in

  15. Procedure to Determine Optimum Reheat Pressure • Calculate the efficiency of Rankine cycle, hRankine. • Calculate mean effective temperature of heat addition, Tm,in using • Find out pressure corresponding to Tm,in and entropy at HP turbine exit. • Add reheating at this pressure and calculate efficiency of the Reheat Cycle. • Repeat above steps for few iterations.

  16. pmax= 15 MPa Tmax= 550 0C Tsat= 342.20C

  17. Super Critical Cycle ~ 1990

  18. Effect of Various Steam Parameters on Reheat Cycle

  19. Ultra Supercritical Installations of The World

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