Power in the steam Turbines
produces at every stage where the steam is taken out, whether it may be bleed,
extraction or exhaust steam. As the steam out from the turbine increases the
power developed on that particular stage will increase.
Power generation phenomenon.
Power generation in steam
Turbines is calculated based on difference between the heat content of inlet
steam & extracted steam.
Factors affecting the power generation:
 Power generation at particular
stage increases, when there is more steam flow &vice versa
 Power generation at particular
stage increases when there is more difference between inlet & extraction
steam & Vice versa
 Power develop at particular stage
decreases if its extraction pressure increases & vice versa
 Power developed at particular
stage decreases if its extraction temperature increases & vice versa
 Power developed in steam Turbine
decreases if inlet live steam pressure & temperature decrease
 If steam vacuum decreases power
generation reduces or else Turbine will consume more steam to develop same
power
 If exhaust steam temperature
increases then the power power generation reduces or else Turbine will consume
more steam to develop same power
 If wheel chamber pressure
increases, then the power generation capacity of the Turbine decreases
HOW DO YOU CALCULATE POWER GENERATION COST??
In which part of the Turbine higher power can
be produced at lower steam consumption? And why?
It is at the exhaust stage.
Because at the exhaust stage pressure & temperature of the steam is very
lesser than bleed &extraction stages.
In which part of the Turbine lowest power is
produced at higher steam consumption? And why?
It is at the bleed stage. Because
at bleed steam pressure & temperatures are higher than extraction &
exhaust stages
Calculation part:
1Calculate the power generated in a back pressure
steam Turbine, where 50 TPH steam enters the Turbine at 66 kg/cm2 &
temperature 485 Deg C.And steam exhausts to process at pressure 2 kg/cm2 &
temperature 180 Deg C.
For calculation of power we need
to know the enthalpy of inlet & exhaust steam.
Refer steam table
Enthalpy of inlet steam at rated
parameters H1 = 806.5 kcal/kg
Enthalpy of inlet steam at rated
parameters H2 = 677 kcal/kg
Now power developed in steam turbine P = Q X (H1H2) / 860
Where Q is steam flow
P = 50 X (806.5677) / 860
P = 7.52 MW
Note: 860 kcal = 1 KWH
2. Calculate the power developed by a steam turbine by using
following data
Sl No.

Particular

UOM

Value

1

Turbine inlet steam flow

TPH

145

2

Turbine inlet steam pressure

Kg/cm2

88

3

Turbine inlet steam temperature

C^{0}

515

4

Bleed steam flow

TPH

20

5

Bleed steam pressure

Kg/cm2

12

6

Bleed steam temperature

C^{0}

250

7

Extraction flow

TPH

100

8

Extraction steam pressure

Kg/cm2

1.8

9

Extraction steam temperature

C^{0}

145

10

Exhaust flow to condenser

TPH

25

11

Exhaust pressure

Kg/cm2

0.08

12

Exhaust temperature

C^{0}

44

13

Dryness fraction

%

90

Also calculate the
specific steam consumption of this Turbine
Solution:
Note down the enthalpy of steam at various stages
Turbine inlet steam enthalpy H1 = 818 kcal/kg
Bleed steam enthalpy H2 =700 kcal/kg
Extraction steam enthalpy H3 = 657.2 kcal/kg
Exhaust enthalpy =Liquid heat + Dryness fraction X Vapour
enthalpy = 41.77 + 0.9 X 615.5 = 595.72 kcal/kg
Also steam flow is given
Inlet steam flow Q1 = 145 TPH
Bleed steam flow Q2 = 20 TPH
Extraction steam flow Q3 =100 TPH
Exhaust steam flow Q4 = 25 TPH
Power generation at 1st stage (Bleed) P1 = Q2 X (H1H2) /
860
P1 = 20 X (818700) / 860 = 2.74 MW
Power generation at 2^{nd} stage (Extraction) P2 =
Q3 X (H1H3) / 860
P2 = 100 X (818657.2) / 860 = 18.69 MW
Power generation at 3rd stage (Exhaust) P3 = Q4 X (H1H4) /
860
P3 = 25 X (818595.72) / 860 = 6.46 MW
SO total power developed at Turbine shaft P = P1+P2+P3 =
2.74+18.69+6.46 = 27.89 MW
Specific steam consumption SSC = Turbine inlet steam flow /
Power generation = 145 / 27.89 =5.19 MT/MW
3By taking above example, explain how pure
condensing steam Turbines have higher power generation & lower specific
steam consumption (SSC)
Consider the above example, where
Turbine inlet steam flow is 145 TPH & having 25 TPH exhaust steam flow to
condenser.
If we condense 100% steam, then
we will have reduced SSC
Let us see..
Q1=Q4=145 TPH..Where Q4 = Exhaust
steam to condenser
Q2 & Q3 are considered zero
(No flow)
Enthalpy of exhaust steam
increases due to higher exhaust pressure
SO, Consider exhaust pressure =
0.1 kg/cm2 & Dryness fraction 0.9
Then, exhaust enthalpy becomes H1
= 46 + 0.9 X 617 = 601.9 kcal/kg
Total Power developed P= Q1 X
(H1H4) / 860
P =145 X (818601.9) / 860 =
36.43 MW
So SSC = 145 / 36.43 = 3.98 MT/MW
This is very less as compared to
bleed & extraction turbines
4By taking an example No.2 explain how bleed
steam flow will cause reduction in net power consumption
Solution:
We shall take the data of Example No.2
In this, we will increase bleed steam flow, pressure & temperature
& parallel shall decrease extraction flow to match mass flow
Sl No.

Particular

UOM

Value

1

Turbine inlet steam flow

TPH

145

2

Turbine inlet steam pressure

Kg/cm2

88

3

Turbine inlet steam temperature

C^{0}

515

4

Bleed steam flow

TPH

30

5

Bleed steam pressure

Kg/cm2

15

6

Bleed steam temperature

C^{0}

285

7

Extraction flow

TPH

90

8

Extraction steam pressure

Kg/cm2

1.8

9

Extraction steam temperature

C^{0}

145

10

Exhaust flow to condenser

TPH

25

11

Exhaust pressure

Kg/cm2

0.08

12

Exhaust temperature

C^{0}

44

13

Dryness fraction

%

90

Solution:
Note down the enthalpy of steam at various stages
Turbine inlet steam enthalpy H1 = 818 kcal/kg
Bleed steam enthalpy
H2 =716.63 kcal/kg
Extraction steam enthalpy H3 = 657.2 kcal/kg
Exhaust enthalpy =Liquid heat + Dryness fraction X Vapour
enthalpy = 41.77 + 0.9 X 615.5 = 595.72 kcal/kg
Also steam flow is given
Inlet steam flow Q1 = 145 TPH
Bleed steam flow Q2 =
30 TPH
Extraction steam flow
Q3 =90 TPH
Exhaust steam flow Q4 = 25 TPH
Power generation at 1st stage (Bleed) P1 = Q2 X (H1H2) /
860
P1 = 30 X (818716.63) / 860 = 3.53 MW
Power generation at 2^{nd} stage (Extraction) P2 =
Q3 X (H1H3) / 860
P2 = 90 X (818657.2) / 860 = 16.82 MW
Power generation at 3rd stage (Exhaust) P3 = Q4 X (H1H4) /
860
P3 = 25 X (818595.72) / 860 = 6.46 MW
SO total power developed at Turbine shaft P = P1+P2+P3 =
3.53+16.82+6.46 = 26.81 MW
Specific steam consumption SSC = Turbine inlet steam flow /
Power generation = 145 / 26.81 =5.41 MT/MW
So by increasing the
bleed steam flow, the work done by the Turbine decreases & hence steam
consumption will increase
5A Turbine’s inlet steam enthalpy is 825 kcal/kg &
Exhaust enthalpy is 590 kcal/kg. Calculate the work done by steam &
specific steam steam consumption
We have,
H1 = 825 kcal/kg, H2 = 590 kcal/kg
Work done per kg of steam = (H1H2) = 825890 =235 kcal/kg
SSC = 860 / Work done = 860 / 235 =3.65 kg/kwh or 3.65 MT/MW
6A steam
Turbine inlet steam pressure & temperatures are 104 kg/cm2 & 540 C^{0
}& exhausts at pressure 0.09 kg/cm2 & temperature 43 Deg C calculate
the
a Work done per kg of steam
b Heat supplied per kg of steam
c Cycle efficiency
Enthalpy of inlet steam = 829 kcal/kg
Exhaust liquid enthalpy = 44 kcal/kg
Exhaust enthalpy by considering 90% dryness fraction = 44
+ 0.9 X 616.44 =598.76 kcal/kg
AWork done per kg of steam = (829598.76) = 230.24
kcal/kg
BHeat supplied per kg of steam = 82944 = 785 kcal/kg
CCycle efficiency = Work done per kg of steam X 100 / Heat
supplied per kg of steam
= 230.24 X 100 / 785 = 29.32%
Note:
Power developed at Generator terminals =
Power developed at Turbine Shaft X Reduction gear box efficiency X Alternator
efficiency
For example:
Calculate the net power developed at Generator
terminal if 100 TPH steam enters the Turbine at 811 kcal/kg enthalpy &
leaves the Turbine at enthalpy 565 kcal/kg .Assume Gear box efficiency as 98%
& Generator efficiency as 95%
Power developed on Turbine shaft = 100 X (811565) / 860 = 28.0 MW
Net power developed at Generator output terminals = 28.0 X 0.98 X 0.95
= 26.06 MW
Also read vacuum troubleshooting in steam Turbines
Power generation phenomenon in STG set
Water balance in power plant
ReplyDeleteWater balance in power plant
ReplyDeleteWhile Calculating SSC of turbine each step you reduces enthalpy of bleed and extraction steam by main stream say H1
ReplyDelete