**1. Lower vacuum**

Turbine
consumes more steam, if vacuum in condenser is maintained on lower side.

Example: Consider a 20 MW Steam Turbine having Inlet
steam parameters 65 kg/cm2 & 490 Deg C & Vacuum maintained in condenser
is -0.9 kg/cm2.

Calculate the
steam consumption of turbine at vacuum -0.9 kg/cm2 & -0.85 kg/cm2

**A-Steam consumption Q at -0.9 kg/cm2
to develop 20 MW power**

P =Steam flow
X( Enthalpy of inlet steam-Enthalpy of exhaust steam)/ 860

Enthalpy of
inlet steam at inlet steam parameters =810 kcal/kg

Exhaust steam
enthalpy at -0.9 kg/cm2 vacuum = 619 kcal/kg

Then, 20 = Q
X (810-619)/860

**Q1 = 90 MT**

**B- Steam consumption Q at -0.85 kg/cm2
to develop 20 MW power**

Exhaust steam
enthalpy at -0.85 kg/cm2 vacuum= 623 kcal/kg

Then, 20 = Q
X (810-623)/860

**Q 2= 90.9 MT**

**It is clear that, Turbine operating at -0.9 kg/cm2 vacuum consumes
lesser steam as compared to turbine operating at vacuum-0.85 kg/cm2**

**2. Lower inlet main stream pressure& temperature**

Turbine
operating at higher main steam pressure consumes lesser steam as compared to turbines
operating at lower pressure

**Example: Consider a 20 MW Steam
Turbine having Inlet steam temperature 490 Deg C & Vacuum maintained in
condenser is -0.9 kg/cm2.**

A-Inlet steam
parameters: Pressure: 65 kg/cm2 & temperature 490 deg C , Enthalpy = 810
kcal/kg

Exhaust steam
parameters P = 0.9 kg/cm2 & Enthalpy = 619 kcal/kg

Steam
consumption of Turbine Q = P X 860 / (Enthalpy of inlet steam-Enthalpy of
exhaust steam)

Q = 20 X 860
/ (810-619)

**Q1 = 90.05 MT**

**B-Inlet steam parameters: Pressure: 87
kg/cm2 & temperature 515 deg C , , Enthalpy = 818 kcal/kg**

Steam
consumption of Turbine Q = P X 860 / (Enthalpy of inlet steam-Enthalpy of
exhaust steam)

Q = 20 X 860
/ (818-619)

**Q2 = 86.43 MT**

**It is clear that, Turbine operating at pressure 65 kg/cm2 &
temperature 490 deg C consumes more steam as compared to turbine operating at 87
kg/cm2 & temperature 515 deg C**

**3. Higher extraction/bleed steam flow**

Steam
turbines consume more steam to develop same power on higher steam extraction as
compared to lower extraction.

**Example: A condensing & extraction
steam turbine having Inlet steam flow 105 TPH at pressure 65 kg/cm2 & 490
Deg C & Vacuum maintained in condenser is -0.9 kg/cm2.**

Here we can cross
check the power generation by steam turbine by increasing the extraction flow
keeping inlet steam constant.

**A-Extraction pressure =
2 Kg/cm2 & Temperature = 150 Deg C, flow = 75 TPH, Exhaust steam to
condenser = 30 TPH**

Enthalpy
of inlet steam, H1 = 810 kcal/kg

Main
steam flow Q1 = 105 TPH

Enthalpy
of extraction steam = H2 =660 kcal/kg

Extraction
steam flow Q2 = 75 TPH

Enthalpy
of exhaust team = 620 kcal/kg

Exhaust
steam flow Q3 = 30 TPH

Power
developed by steam Turbine P = (Q2 X (H1-H2) / 860) + (Q3 X (H1-H3) / 860 )

P
= (75 X (810-660) / 860) + (30 X (810-620) / 860) =
**19.7 MW**

**B- Extraction pressure =
2 Kg/cm2 & Temperature = 150 Deg C, flow = 65 TPH, Exhaust steam to
condenser = 40 TPH**

Enthalpy
of inlet steam, H1 = 810 kcal/kg

Main
steam flow Q1 = 105 TPH

Enthalpy
of extraction steam = H2 =660 kcal/kg

Extraction
steam flow Q2 = 65 TPH

Enthalpy
of exhaust team = 620 kcal/kg

Exhaust
steam flow Q3 = 40 TPH

Power
developed by steam Turbine P = (Q2 X (H1-H2) / 860) + (Q3 X (H1-H3) / 860 )

P
= (65 X (810-660) / 860) + (40 X (810-620) / 860) = **20.16 MW**

**It is clear that, Turbine power generation at same inlet main
steam flow will increase as extraction flow gets decrease & vice versa**

**Related posts read.......**

**4. Higher pressure/temperature of extraction & bleed steam **

Higher
pressure/temperature of extraction & bleed steam leads to increased steam
consumption to generate same power or power consumption reduces at same inlet
flow.

**Example: A condensing , extraction
& bleed steam turbine having Inlet steam flow 105 TPH at pressure 65 kg/cm2
& 490 Deg C & Vacuum maintained in condenser is -0.9 kg/cm2**

** A-Bleed steam 10 kg/cm2 & Temperature 200 Deg
C, flow =25 TPH, Extraction pressure = 2 Kg/cm2 & Temperature = 150 Deg C,
flow = 60 TPH, Exhaust steam to condenser = 25 TPH**

Enthalpy
of inlet steam, H1 = 810 kcal/kg

Main
steam flow Q1 = 105 TPH

Enthalpy
of bleed steam = H2 =674 kcal/kg

Bleed
steam flow Q2 = 25 TPH

Enthalpy
of extraction steam = H3 =660 kcal/kg

Extraction
steam flow Q3 = 60 TPH

Enthalpy
of exhaust team H4= 620 kcal/kg

Exhaust
steam flow Q4 = 20 TPH

Power
developed by steam Turbine P = (Q2 X (H1-H2) / 860) + (Q3 X (H1-H3) / 860 ) +(Q4
X (H1-H4)/860)

P
= (25 X (810-674) / 860) + (60 X (810-660)/860) + (20 X (810-620)/860)

**P = 18.82
MW**

**B-Bleed steam 14 kg/cm2
& Temperature 260 Deg C, flow =25 TPH, Extraction pressure = 2.5 Kg/cm2
& Temperature = 170 Deg C, flow = 60 TPH, Exhaust steam to condenser = 25
TPH**

Enthalpy
of inlet steam, H1 = 810 kcal/kg

Main
steam flow Q1 = 105 TPH

Enthalpy
of bleed steam = H2 =704 kcal/kg

Bleed
steam flow Q2 = 25 TPH

Enthalpy
of extraction steam = H3 =669 kcal/kg

Extraction
steam flow Q3 = 60 TPH

Enthalpy
of exhaust team H4= 620 kcal/kg

Exhaust
steam flow Q4 = 20 TPH

Power
developed by steam Turbine P = (Q2 X (H1-H2) / 860) + (Q3 X (H1-H3) / 860) + (Q4
X (H1-H4)/860)

P
= (25 X (810-704) / 860) + (60 X (810-669)/860) + (25 X (810-620)/860)

**P = 18.43
MW**

**It is clear that, Turbine power generation reduces at higher
extraction or bleed steam pressure &temperature**

Note:
Steam consumption of turbine increases if,

1-Bleed
steam & extraction steam pressure increases

2-Bleed
steam & extraction steam temperature increases

3-Bleed
steam flow & extraction steam flow increases

**4. Increase of exhaust steam temperature due to more clearance in labyrinth
seals **

Turbine
steam consumption increases if exhaust steam temperature to condenser increases.

**Also read 16-Perfect reasons for increasing the fuel consumption of Boilers**

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kindly explain the reason behind why specific steam consumption increases at lower vacuum

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