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Superheating of Steam

Superheating of Steam. P M V Subbarao Professor Mechanical Engineering Department. Recognition and Adaptation of Efficient Mode of Heat Transfer …. Furnace Energy Balance. Enthalpy to be lost by hot gases:. Water walls. Economizer. Furnace. Capacity of Flue Gas.

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Superheating of Steam

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  1. Superheating of Steam P M V Subbarao Professor Mechanical Engineering Department Recognition and Adaptation of Efficient Mode of Heat Transfer …..

  2. Furnace Energy Balance Enthalpy to be lost by hot gases: Water walls Economizer Furnace

  3. Capacity of Flue Gas Total Thermal Power available with flue gas: Rate of steam production:

  4. 3 5 2s 2f 4 2 1 6 s

  5. Paths of Steam and Gas Drum Water walls Economizer

  6. DPNL SH R H T R drum screen tubes Platen SHTR LTSH Economiser stack BCW pump Furnace APH ESP ID Fan Bottom ash Thermal Structure of A Boiler Furnace

  7. S1 S2 Convective Superheater (Pendant) • Convective super heaters are vertical type (Pendant ) or horizontal types. • The Pendant SH is always arranged in the horizontal crossover duct. • Pendant SH tubes are widely spaced due to high temperature and ash is soft. • Transverse pitch : S1/d > 4.5 • Longitudinal pitch : S2/d > 3.5. • The outside tube diameter : 32 – 51mm • Tube thickness : 3 – 7mm

  8. S1 S2 Convective Superheater (Horizontal) • The horizontal SH are located in the back pass. • The tubes are arranged in the in-line configuration. • The outer diameter of the tube is 32 – 51 mm. • The tube thickness of the tube is 3 – 7 mm. • The transverse pitch : S1/d = 2 – 3. • The longitudinal pitch :S2/d = 1.6 – 2.5. • The tubes are arranged in multiple parallel sets. • The desired velocity depends on the type of SH and operating steam pressures. • The outside tube diameter : 32 – 51mm • Tube thickness : 3 – 7mm

  9. Thermal Balance in Convective SH. • The energy absorbed by steam • The convective heat lost by flue gas • Overall Coefficient of Heat Transfer, K

  10. Mean Temperature Difference • The average temperature difference for parallel flow and counter flow is expressed as • It is also called log mean temperature difference • When Dtmax /Dtmin > 1.7, the average temperature may be expressed as: • Generally, the flow direction of the flue gas is perpendicular to the axes of tubes. • If number of bends are more than four, the flow can be treated as counter or parallel flow.

  11. S1 S2 Inline S1 Staggered S2

  12. Effectiveness Factor • The ratio of the heat transfer between fouled and clean tubes.

  13. Thermal Balance in Super Heater. • The energy absorbed by steam • The convective heat lost by flue gas • Overall Coefficient of Heat Transfer, U

  14. Reheater • The pressure drop inside reheater tubes has an important adverse effect on the efficiency of turbine. • Pressure drop through the reheater should be kept as low as possible. • The tube diameter : 42 – 60mm. • The design is similar to convective superheaters. • Overall Heat Transfer Coefficient : 90 – 110 W/m2 K.

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