Turbine Cycle Optimisation
By
M.V.PandeDy. Director
N.P.T.I., Nagpur
Costing of Thermal Energy Major cost is fuel
cost in thermal power station
The fuel consumption can be reasonably brought down by conservation techniques
Heat Energy Conversion to Electrical Energy
Inputs Required/Unit of Elect.
Comparison of Various Cycles
Modern Steam Cycle Modern steam cycles are designed
with Reheat & Regenerative Feed Heating arrangement
Cycle is designed with high inlet steam pressure & temperature
Modern Thermal Power Plant
Rankine Cycle with Superheating,Reheating & Feed Heating
210 MW KWU Steam Turbine Cycle
Principles of Cycle Efficiency Improvement
Superheated or dry steam should not enter into condenser
Wetness of steam at turbine exhaust should not exceed 12%
Maximum possible temperatures at SH & RH outlet are used,however, restricted due to metallurgical constraints to5600 C
Principles of Cycle Efficiency Improvement
The mean temperature of heat addition in boiler should be as high as possible so as to approach Carnot cycle process
The temperature of heat rejection should be lowest possible to reduce heat rejection to condenser
The throttling across turbine Stop & Control Valves Should be minimum
Turbine Condition Line
Cylinder Efficiency & Heat Rate
Actual Heat Drop Cylinder Efficiency= ------------------------ Isentropic Heat Drop Heat Input to Turbine Turbine Heat Rate= ----------------------------
Generator Output Power
= @1980 Kcal/Kwhr
Cylinder Efficiency Factors Cylinder Efficiency depends on
Internal Losses occurring in the steam flow path inside the turbine + External Losses of steam through Glands & Bearing Losses
Profile Loss This is due to formation of
boundary layers on the Blade Surfaces
The Viscous Friction reduces the steam velocity & so increases the Entropy
Secondary Loss
This is due to friction on casing wall & blade root & tip
This is also a Boundary Layer Phenomenon between tip & casing + root & shaft
Tip Leakage Loss This loss is due to
steam leakage through the small clearance between moving blade Tip & Casing & also between fixed blade & casing
Inter-stage Labyrinth sealing between them reduces the loss
Disc Windage Loss This loss is due to surface friction
created on the disc or wheel of a turbine as the disc rotates in the atmosphere of steam
This results in loss of shaft power & increase in kinetic & heat energy( temp.) of steam at the exhaust of the turbine
Other Internal Losses Nozzle Loss - Reduction in steam outlet velocity
due to wall friction Partial admission of steam at nozzle
segments in Nozzle Governed Turbine due to opening of respective control valves
Internal Losses of Turbine
Wetness Loss This loss is incurred by moisture
entrained in the low pressure steam towards exhaust stages of turbine
This reduces the efficiency due to absorption of energy by water droplets
The result is the erosion of leading edges of blades particularly at the tip
Erosion cause the inlet blade angle to change & prevents tangential entry of steam
IPT & LPT Blade Erosion Due To Moisture
IPT Last Stage Moving Blades
LPT Last Stage Moving Blades
LPT Exhaust Losses Residual Velocity or Leaving Loss - This loss is due to exhaust velocity of
steam Leaving Loss=Ve2/2 J/Kg - This loss is reduced by increasing the last
stage blade heights Hood Loss - This loss is due to the turning of steam
through 900 to enter the condenser. Loss is reduced by providing Diffusers at the exhaust
KWU Turbine LPT Inner Top-Half
Casing
Diffuser
External Losses of Turbine Shaft & Gland leakage loss -Steam leakage through labyrinth
sealing at the turbine shaft end,which is about 3% of total steam flow. Loss increases in square proportion with increase in labyrinth clearances
Journal & Thrust Bearing losses Governor & oil pump loss
Barrel Type HP Turbine
Balance Piston
Moving Blades
Barrel Casing
Inner Casing
Gland
KWU HP Turbine RotorAdmission Side Sealing