Power Plant Turbines P M V Subbarao Associate Professor Mechanical Engineering Department I I T Delhi A Techno-economically feasible model for large Power Plants…………..
Using the steam to make the Power ! • Rotating the shaft is the ultimate goal of any power plant. • As you have probably noticed, from the text and pictures on Steam Generators, there is no shaft. • Which leads to the question: "now that you have all this super energized steam or Gas, how do you get work from it ? " A boilers / Combustor is only one part of a larger operation, granted, it's a large part but most important part of the operation is it's ability to apply all this steam power.
The Steam Turbine • The more modern method of extracting mechanical energy from thermal energy is the steam turbine. • Steam turbines have been the norm in various land based power plants for many years. • Motive power in a steam turbine is obtained by the rate of change in momentum of a jet of steam impinging on a curved blade which is free to rotate. • The steam is (partially or fully) expanded in a nozzle, resulting in the emission of a high/medium/low velocity jet. • This jet of steam impinges on the moving vanes or blades, mounted on a shaft. • Here it undergoes a change of direction and/or magnitude of motion which gives rise to a change in momentum and therefore a force.
Generation of Motive Power Through Newton’s Second Law Vi U Freaction Ve Work is said to be done by a system iff The sole effect external to the system can be reduced to raising of weight
Ve Vi Analysis of Simple Stationary Impulse Blade • Consider a stationary 180 degree curved blade. • A jet with a velocity Vi incidence on the blade. • The blade deflects the jet along its surface and finally the jet leaves with a velocity Ve. • The magnitude of velocity vector remains unchanged. • However, the direction changes through 180 degrees. • Ve = - Vi • The change in velocity : - 2 Vi. • A jet with a finite mass flow rate will experience a rate of change of momentum, FA: FA FR The force acting on the blade: However, this force cannot develop any motive power.
Analysis of Simple Moving Impulse Blade Vre = -Vri Vae = Vre -U U Vri = Vai - U Vai
Kinetic power lost by the jet : Power lost by jet = Power gained by the Blade Initial Power of the jet : Thermodynamic efficiency of an impulse blade : An efficient impulse blade is bulky …… Suitable for Dense fluids…
Analysis of Simple Reaction Blade U Vai Vri Vre Vae Change in velocity : Motive Power Generated:
Motive Power Generated: Thermodynamic efficiency of a Reaction blade : A compact Reaction blade is inefficient ……Suitable for Thin fluids…
Vre Vae U Vri Vai Simple Impulse-Reaction Blade Jet will lose power both by Impulse and Reaction. One important and essential element in all these cases is a nozzle.
How To Provide A Mass Flow Rate • Area for Flow of Fluid. • Proportional to the Length of the Blade. • More Number of Blade Spacings.
Theory of Turbine Blading BY Dr. P M V Subbarao Mechanical Engineering Department I I T Delhi
U Vri Vai Vai Inlet Velocity Triangle U Vae Vre Exit Velocity Triangle Vri U Vre
U bi ae ai be Vai Vae Vri Vre Vai: Inlet Absolute Velocity Vri: Inlet Relative Velocity Vre: Exit Relative Velocity Vae:Exit Absolute Velocity ai: Inlet Nozzle Angle. bi: Inlet Blade Angle. be: Exit Blade Angle. ai: Exit Nozzle Angle.