Turbine Cycle Optimisation

Turbine Cycle Optimisation By 

M.V.Pande Dy. Director N.P.T.I., Nagpur

Costing of Thermal Energy 

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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 

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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 

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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 

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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 

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 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 

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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 

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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 

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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 

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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 

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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 

Diffuser

KWU Turbine LPT Inner Top-Half Casing

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 Casing Balance Piston Inner Casing

Gland

Moving Blades

Barrel Type HP Turbine

KWU HP Turbine Rotor Admission Side Sealing