energy conservation in steam turbine

7/30/2019 Energy Conservation in Steam Turbine

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ENERGY

CONSERVATION INSTEAM TURBINE CYCLE

Presented ByM.V.Pande

Dy.Director

NPTI, Nagpur


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Costing of Thermal Power Generation

The fuel consumption can bereasonably brought down byconservation techniques

Major cost is fuel cost inthermal power generation


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210 MW KWU Steam Turbine Steam & Water Cycle


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Steam Cycle For 210 Mw Unit


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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 560 0C


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The mean temperature of heat addition inboiler should be as high as possible so as to

approach Carnot cycle process

The temperature of heat rejection should belowest possible to reduce heat rejection to

condenser

The throttling across turbine Stop & ControlValves Should be minimum

Principles Of Cycle Efficiency Improvement


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500 MW Turbine Generator Unit


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210 MW Utility Steam Turbine

HP Turbine

IP Turbine

LP Turbine

Foundation

Gen.EndBearing

Condenser


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Barrel Type HP Turbine

BalancePiston

MovingBlades

Barrel Casing

Inner Casing

Gland

SteamInlet

Steam Exhaust


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Reaction Type KWU HP Turbine Rotor

Impulse-Reaction Type HPT Rotor KWU LP Turbine Rotor


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Thermal Process Losses


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Turbine Cycle Losses


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Controllable Plant Parameters

M.S. & R.H. Steam Temperatures

M.S. Steam Pressure

Condenser Vacuum

Final Feed Water Temperature

DP Across Feed Regulation Station

Auxiliary Power Consumption

Make Up Water Consumption


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Description Effect on Effect onTG HR KW

1% HPT Efficiency 0.16% 0.3%

1% IPT Efficiency 0.16% 0.16%

1% LPT Efficiency 0.5 % 0.5 %

Impact of Turbine Cylinder Efficiency onHR/Output

FOLLOW TEST CODES

ASME PTC - 6 For Steam Turbines


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Effect Of Steam Parameters

Effect of Changing Reheat Pressure Effect of Changing Reheat Temp.

SS

HH


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Comparison of Actual Expansion

with Isentropic Expansion in Turbine

Actual Expansion in HP, IP & LP

Cylinder

ActualProcess

1-2-3-4-5

Turbine Heat Rate & Efficiency Evaluation


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Turbine Cycle Efficiency =860

Heat RateX 100

Turbine Heat Rate = Q1 x (H1 h2) + Q2 X (H3

H2)

Gross Generator Output

Actual Heat DropCylinder Efficiency = ------------------------------ x 100

Isentropic Heat Drop

Turbine Heat Rate & Efficiency Evaluation

kCal/ kWh


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18Heat Rate Characteristics withCondenser Exhaust Pressure

Variation of Heat Rate with Load

Turbine Heat Rate Variation


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Turbine Efficiency Evaluation Data

Kcal/kg/oK


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Turbine Performance Monitoring

Indicators of Reduced Performance - Increase of turbine inlet Steam pressure

- High exhaust steam temperature

- Gland steam supply header leak-off

valve opening increased

- Increase of condenser back pressure

- Higher MS flow at rated load

- Increasing trend of bearing oil temperaturesat outlet

- Axial shift on higher side


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Steam Turbine Heat Consumption Test

These tests are conducted for acceptancepurpose or for routine assessment of turbineperformance

The objective of test is to determine requiredheat input to the turbine for an output on themachine

The heat rate is calculated from the data &compared with optimum

The tests are conducted at 40%,60%,80% &100% load


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Heat Consumption vs Load

7% forthrottle

governed

machines


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Cylinder Efficiency Factors

Cylinder Efficiency depends on

Internal Losses occurring in the steam

flow path inside the turbine + ExternalLosses of steam through Glands &

Mechanical Power Transmission Losses

Cylinder efficiency varies from 85 90%


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Internal Losses of Turbine


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Wetness Loss

This loss is incurred by moisture entrained inthe low pressure steam towards exhauststages of turbine

This reduces the efficiency due to absorptionof 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


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IPT & LPT Blade Erosion Due To Moisture

IPT Last Stage Moving

Blades

LPT Last Stage MovingBlades


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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 laststage blade heights

Exhaust Hood Loss- This loss is due to the turning of steamthrough 900 to enter the condenser. Loss is

reduced by providing Diffusers at the exhaust


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KWU Turbine LPT Inner Top-Half Casing

Diffuser


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Effect of Reheater Spray

Reduction of cycle efficiency due to

fresh steam bypassing the HP turbine

Reduction of power output from HPturbine due to reduction of steam flow

through HP turbine

Higher Silica deposition in IP & LPturbine


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Effects of Silica Deposition on Turbine

Silica deposition causes the passage

areas between blades to progressively

reduce Increases the first stage pressure of

turbine progressively

The Cylinder efficiency is reduced


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Remedies To Reduce Silica Deposition

Do not raise the boiler

pressure until Silica level is

normal

Give Blow down as required

Minimum use of superheater

& reheater spray

Steam washing of turbine by

wet steam at low speeds

Silica in Steam with Boiler Pressure


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Feed Heaters Survey

Feed heaters survey evaluate the performance of heaters & predicts the

deterioration causes

Following parameters are noted down

- Steam pressure at heater

- Steam temperature at heater

- Feed water inlet & outlet temperature- Heater drain temperature

Evaluate the steam flow to each heater by heat balance

Compare the flow values with optimum

Calculate T.T.D. for each heater

The results indicate following problems

- The elevated TTDs on the heater train suggests water side

contamination (oil)

- The high steam flow to particular heater may be due to lower feed

water inlet temperature, suggesting the problem in previous heater


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Turbine Pressure Survey


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Optimum Condenser Back Pressure

It is a misconception that minimum backpressure should be maintained at all loads

The lower back pressure is justified only if the

efficiency gain due to this is greater than

power consumption of CW pumps & coolingtower fans

With the reduction in condenser back pr. the

isentropic heat drop across the last stage

increases & so additional work is done in the

turbine


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Effect of lower exhaust pr.

Volumetric flow rate increases ( high

specific volume of steam),giving rise to

more Leaving Losses

Wetness Loss increases

CW pumping power increases



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36Optimum Back Pressure at

Full Load

Hence to overcome

above problems

optimum vacuum as

shown in graph is

maintained



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External Losses of Turbine

Shaft & Gland leakage loss

-Steam leakage through labyrinth sealing

at the turbine shaft end,which is about3% of total steam flow. Loss increases insquare proportion with increase inlabyrinth clearances

Journal & Thrust Bearing losses

Governor & oil pump loss

KWU HP Turbine Rotor


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KWU HP Turbine RotorAdmission Side Sealing


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Sliding Pressure Operation at Part Loads

In sliding pressure operation,the controlvalves are kept wide open & the pressurebefore the stop valves is varied through boiler

to achieve required part load This reduces throttling losses across control

valves

The initial temperature is maintained atreduced pressure unlike throttling process

The net effect is to improve cycle efficiencyas compared to constant pressure operation


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Heat Saving By Sliding Pressure Operation


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Effect On Heat Rate For ParameterDeviation (500 MW Unit)

DEVIATION IN PARAMETER EFFECT ON HEATRATE (KCAL/KWH)

1. HPT inlet press. by 5.0 ata 6.25

2. HPT inlet temperature by 10.0 deg C 6.0

3. IPT inlet temperature by 10.0 deg C 5.6

4. Condenser pressure by 10.0 mm of

Hg

9.0

5. Re spray water quantity by 1.0% 4.0

6. HPT Cylinder efficiency by 1.0% 3.5

7. IPT Cylinder efficiency by 1.0% 4.0


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energy conservation in steam turbine

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