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