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Irreversible Flow from Turbine Exit to Condenser
P M V Subbarao
Professor
Mechanical Engineering Department
I I T Delhi
Irreversibilities due to Closed Cycle Policy ..
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The Last Stage of LP Turbine
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First Stage of A Turbine : Governing Stage
A governing stage is the first stage in a turbine with nozzle
steam distribution. The principal design feature of a governing stage is that its
degree of partiality changes with variations of flow rate throughthe turbine.
The nozzles of a governing stages are combined into groups,
each of them being supplied with steam from a separategoverning valve.
A governing stage is separated by a spacious chamber from thesubsequent non-controlled stages.
Governing stages may be of a single-row or two-row type.
Single row impulse governing stage is employed for an enthalpydrop of 80-120 kJ/kg.
Two row governing stages are used when enthalpy drop is high,100 250 kJ/kg.
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Governing Stage
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Selection of Enthalpy Drop & Type of Governing
stage
The enthalpy drop & type of governing stages are selected by
considering the probable effect of the governing stage on the
design and efficiency of the turbine.
Higher the number of governing stages, lower will be the
number of other stages.
A high enthalpy drop in governing stage ensures a lower
temperature of steam in its chamber and permits application of
less expensive materials.
In high capacity steam turbines, a single-row governing stages
are preferred, since the advantages of elevated enthalpy drop
are justified economically.
The efficiency of governing stages,
in
inVustageg
T
p
m
k0002.0
83.0/,
in
inVustagesg
T
p
m
k0002.0
8.0/2,
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Steam Path in Non-Controlled Stages
Estimate approximate mass flow rate of steam by assuming an
overall turbine internal efficiency of 0.85.
Calculate flow through the condenser, using optimum of number
of FWHs. (Using Cycle Calculations).
Calculate Modified Efficiency of Low volume and intermediate
volume stages.
For a group of stages between two successive FWHs.
Z
h
m
lgroup
iso
steam
avgroup
listages
,1
2sin1
2000
6001
5.0925.0
groupegroupiav ..
Average density is calculated as
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The efficiency of groups of very high volume stages:
While designing the steam path, it is essential to consider the
pressure losses in the following:
Pressure loss in reheater: 0.1 prh.
Pressure loss in connecting pipes between turbine
cylinders:0.2ppipe.
group
iso
ev
group
isogegigroup
hvh
hhxx
10000
4001
28.01870.0
,,
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Internal Reheating due to Irreversibilities
3
4s
4IIs
4IIIs
4Is
4Vs
4IVs
4Ia
4IIa
4IIIa
4IVa
4Va
4VIs4VIa
T
s
Governing group
Group 1
Group 2
Group 3
Group 4
Group 5
Macro available enthalpy:
Micro available enthalpy:
shh 43
...444443
sasas IIIIIIIII
hhhhhh
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Macro available enthalpy:
Micro available enthalpy:
s
hh43
N
Ijsas jjI
hhhh 14443
Reheat Factor:
N
Ijsas
sh
jjI hhhh
hhR
14443
43
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Internal Reheating due to Irreversibilities : HP
3
4s
4IIs
4IIIs
4Is
4Vs
4IVs
4Ia
4IIa
4IIIa
4IVa
4Va
4VIs4VIa
T
s
Governing stage
Stage 1
Stage 2
Stage 3
Stage 4
Stage 5
22.33 MPa,3379.0
15.74 MPa,3303.0 k J/kg
13.77 MPa, 3269.0 k J/kg
12.12 MPa, 3236.5.0 k J/kg
10.56 MPa, 3203.8 k J/kg
9.2 MPa, 3171.0 k J/kg
7.94 MPa, 3140.4 k J/kg
4VIIa6.9 MPa, 3104.9 k J/kg
4VIIIa
5.17 MPa, 3036.7 k J/kg4IX
a
5.95 MPa, 3070.9 k J/
Pho=5 %
Pho=19.5%
Pho=21%
Pho=22%
Pho=23.5%
Pho=25%
Pho=30%
Pho=32%
Stage 6
Stage 7
Stage 8
Pho=35%
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0
2
4
6
8
10
12
14
HP1(1s
tSt.)
HP4
HP7
HP10
HP13
HP16 IP
1IP
4IP
7IP
10
IP13
LP2
LP5
Stages
Loss
(kJ/kg) Cumulative loss
Cumulative Losses for All Stages : 500 MW
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Definition of Efficiency
Relative blade efficiency is calculated as:
Internal Relative Efficiency is calculated as:
dropEnthalpyEffective
lossBladeMoving&Nozzle-dropEntalpyEffectiverel
dropEnthalpyEffectivelossprofile-lossleakage-lossesBladeMoving&Nozzle-dropEntalpyEffectiveint, rel
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Blade Efficiency & Internal Relative Efficiency: 800 MW
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Efficiency
Stage No
Relative Blade efficiencyRelative internal efficiency
LP Cylinder
efficiency=78.0
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LP Turbine Exhaust System
In a condensing steam turbine, the low-pressure exhaust hood,consisting of a diffuser and a collector or volute!, connects the last
stage turbine and the condenser. The function of the hood is to transfer the turbine leaving kinetic
energy to potential energy while guiding the flow from the turbineexit plane to the condenser.
Most of exhaust hoods discharge towards the downward condenser.
Flow inside the hood therefore must turn about 90 deg from theaxial direction to the radial direction before exhausting into thecondenser.
The 90-deg turning results in vortical flow in the upper half part ofthe collector and also high losses.
The exhaust hood is one of the few steam turbine components thathas the considerable aerodynamic losses.
It is a challenge for engineers to operate a hood with high pressurerecovery and low total pressure loss in a compact axial length.
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Exhaust Hood
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Exhaust Diffuser For L P Turbine
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Steam Turbine Exhaust Size Selection
The steam leaving the last stage of a
condensing steam turbine can carry
considerably useful power to the
condenser as kinetic energy.
The turbine performance analysis needs to
identify an exhaust area for a particular
load that provides a balance between
exhaust loss and capital investment inturbine equipment.
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Path Lines in Exhaust Hood
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Exhaust Losses
Exhaust losses are losses which occur between last
stage of turbine and condenser.
Exhaust losses made up of four components:
Actual leaving losses Gross hood loss
Annulus restriction loss
Turn up loss
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Residual velocity loss
Steam leaving the last stage of the turbine has certain velocity, which
represent the amount of kinetic energy that cannot be imparted to theturbine shaft and thus it is wasted
Exhaust end loss
1. Exhaust end loss occur between the last stage of low pressure turbineand condenser inlet.
2. Exhaust loss depends on the absolute steam velocity.
Turbine Exhaust end loss
= Expansion-line -end point - Used energy at end point.
T i l h t l h i di t ib ti f t l
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Turn-up loss
Total Exhaust
Loss
Gross hoodloss
Actual leaving
loss
Annulus
restriction loss
Annulus Velocity (m/s)
ExhaustLoss,
kJ/k
gofdryflow
0 120 150 180 240 300 360
10
20
30
40
50Annulus velocity (m/s)
Condenser flow
rateAnnulus area
Percentage of Moisture atthe Expansion line endpoint
Typical exhaust loss curve showing distribution of component loss
SP.Volume
an
steamexan
A
xvmV
3600
01.01.
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Optimal Design of Exhaust Hood
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Performance Analysis of Power Plant
Condensers
P M V Subbarao
Professor
Mechanical Engineering DepartmentI I T Delhi
A Device Which makes Power Plant A True Cycle..
A Device Which set the limit on minimum cycle
pressure..
T S Di R ki C l ith FWH
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T-S Diagram : Rankine Cycle with FWHs.
?,, exitcondincond pp
inCWT ,outCWT ,
?TTD
exhaustturbinep ,
hoodp
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A Device to Convert Dead Steam into Live Water
Water ready to take
Rebirth
Dead Steam
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Steam Condenser
Steam condenser is a closed space into which steam exits the turbine and is forcedto give up its latent heat of vaporization.
It is a necessary component of a steam power plant because of two reasons. It converts dead steam into live feed water.
It lowers the cost of supply of cleaning and treating of working fluid.
It is far easier to pump a liquid than a steam.
It increases the efficiency of the cycle by allowing the plant to operate on largest
possible temperature difference between source and sink.
The steams latent heat of condensation is passed to the water flowing through thetubes of condenser.
After steam condenses, the saturated water continues to transfer heat to coolingwater as it falls to the bottom of the condenser called, hotwell.
The difference between saturation temperature corresponding to condenservaccum and temperature of condensate in hotwellis called condensate depression.
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Two-Pass Surface Condenser
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Layouts of A Condenser
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Layouts of A Condenser
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An Integral Steam Turbine and Condenser System