Large Steam& Gas Turbines
P M V SubbaraoProfessor
Mechanical Engineering Department
Backbones of Modern Nations ……
Advanced 700 8C Pulverised Coal-fired Power Plant Project
The state-of-the-art Gas Turbines
• The newer large industrial gas turbines size have increased and capable of generating as much as 200 MW at 50 Hz.
• The turbine entry temperature has increased to 12600C, and the pressure ratio is 16:1.
• Typical simple cycle efficiencies on natural gas are 35%. • The ABB GT 13 E2 is rated at 164 MW gross output on natural
gas, with an efficiency of 35.7%. • The pressure ratio is 15:1. • The combustion system is designed for low Nox production.
• The dry Nox is less than 25 ppm on natural gas. • The turbine entry temperature is 11000C and the exhaust
temperature is 5250C. • The turbine has five stages, and the first two rotor stages and
the first three stator stages are cooled; • the roots of the last two stages are also cooled.
Fuel Natural gas
Frequency 60 Hz
Gross Electrical output 187.7 MW*
Gross Electrical efficiency 36.9 %
Gross Heat rate 9251 Btu/kWh
Turbine speed 3600 rpm
Compressor pressure ratio 32:1
Exhaust gas flow 445 kg/s
Exhaust gas temperature 612 °C
NOx emissions (corr. to 15% O2,dry) < 25 vppm
GT24 (ISO 2314 : 1989)
Fuel Natural gas
Frequency 60 Hz
Gross Electrical output 187.7 MW*
Gross Electrical efficiency 36.9 %
Gross Heat rate 9251 Btu/kWh
Turbine speed 3600 rpm
Compressor pressure ratio 32:1
Exhaust gas flow 445 kg/s
Exhaust gas temperature 612 °C
NOx emissions (corr. to 15% O2,dry) < 25 vppm
9756 kJ/kWh
0200
21
hh
hh
21
22
22
21
21
22
rraa
rr
VVVV
VV
22
21
22
22
21
2000rraa VVVV
hh
22
21
21
22 1 aarr VVVV
Exact definition of DoR
1021
22 1
hhVV rr
Stage with General Value of Degree of Reaction
Total possible drop in Enthalpy:
Theory of General Reaction Blading
Vr2 > Vr1
U
Vr1Va1
Va1Va2
112 1
1122 coscos rrstage VVUmP
22
21
21
22 1 aarr VVVV
Ideal reaction blade:
1
111 cos
cos
UV
V ar
2
221
2
1
1122 1cos
cosaa
ar VV
UVV
Available power in % Reaction stage :
21
22
21%, 2 rraavialble VVV
mP
22
21
21%, 12 aaaavialble VVV
mP
Stage Sizing
2
cos 1max,
stage
12
cos 1
1max
aV
U
Steam Path
increasing
Selection of Degree of Reaction
132
4
jetV
U
stage,diagram
Definition of Isentropic/adiabatic Efficiency
• Relative blade efficiency is calculated as:
• Internal Relative Efficiency is calculated as:
dropEnthalpy Effective
loss Blade Moving & Nozzle-dropEntalpy Effectiverel
dropEnthalpy Effective
loss profile - loss lakage-loss Blade Moving & Nozzle-dropEntalpy Effectiveint, rel
Typical Distribution of Losses AStages
Structure of Large HP Turbine
Calculations of HP and IP Turbine Efficiencies
• The efficiency of a joined group of turbine stages between two successive bleed points is defined.
• Full loss of the exit velocity in the last stage, for operation on superheated steam is also accounted.
• The statistically generalized expression is
av
gr
avav
gstri
h
vm
120000
6001
5.0925.0 0
where .
avm = average steam flow rate = . .
1 2m m kg/sec.
.
1m = Steam flow rate at entry of group in kg/sec,
.
2m= Steam flow rate at exit of group in
kg/see And similarly
avv = 1 2v vm3/
kg,
0grh is the available enthalpy drop of the group
ev is exit velocity loss coefficient = 2
1
1sin
z
Z = No. of stages in group,
= Nozzle exit angle
Calculations of Last LP & Last Stage Turbine Efficiency
• To calculate the internal relative efficiency for the low pressure cylinder, proper consideration to be given to incorporate losses due to exit velocity and the losses due to moisture.
• The statistically generalized expression is
0
0 0
4000.87 1 1 1
10000
wfLPCLPC ev
ri wf LPC LPC
h hhk
h h
where correction for wetness fraction 1 21
2wf wf
y yk a
= 0.8 for peripheral moisture separation design.wfa
Exit velocity loss is given by
2.310 0.1
12 1
c cev
m vh
i
2 2d l 2m
Axial surface area at the exit from last stage moving blades, and
2
2
d
l
i = No. of flows in LP turbine
Average diameter to blade height ratio is
General Rules for Steam Path Design
• For HP Axial (flow) velocity at the inlet is 40 m/sec and at the outlet 65 m/sec.
• For IP axial velocity of steam at the inlet is 60 m/sec and at the outlet 80 m/sec
• For LP axial velocity of steam at the inlet is 75 m/sec and at the outlet of last front stage is 130 m/sec.
• Maximum mean blade speed used so far: 450 m/s
• Generally acceptable range of inlet flow angle(1) : 150 to 200
Stage Loading and Flow Coefficient
Stage Loading Coefficient: Ratio of specific stage work output and square of mean rotor speed.
2,0
2
,0
m
stagestage
r
h
U
h
Flow Coefficient: Ratio of the axial velocity entering to the mean rotor speed.
m
exitstagefexitstagefflow r
V
U
V , ,
flow
Regions of Design
General Rules for Efficient & Economic Flow Path Design
• For HP Axial (flow) velocity at the inlet is 40 m/sec and at the outlet 65 m/sec.
• For IP axial velocity of steam at the inlet is 60 m/sec and at the outlet 80 m/sec
• For LP axial velocity of steam at the inlet is 75 m/sec and at the outlet of last front stage is 130 m/sec.
• Maximum mean blade speed used so far: 450 m/s
• Generally acceptable range of inlet flow angle(1) : 150 to 200
Range of turbine Design Parameter
• High Pressure Turbine:
• Maximum AN2 : 2.5×107 – 3.3 ×107 m2.rpm2.
• Stage loading coefficient: 1.4 – 2.0
• Stage Exit Mach Number: 0.4 – 0.5
• Low Pressure Turbine:
• Inlet mass flow rate: 195 – 215 kg/m2.s
• Hub/tip ratio: .35-.5
• Max. Stage loading (based on hub): 2.4
• Exit Mach Number: 0.4 – 0.5
For reaction turbine maximum efficiency occurs at certain loading factor
With known value of U , change enthalpy is obtained .
From change in enthalpy absolute velocity of steam can be obtained
Enthalpy Entropy Diagram for Multistage Turbine
h
s
Turbine Inlet
Turbine Exit
Stage 1
Stage 2
Stage 3
Stage 4
Stage 5
Optimal Variable Reaction 3D Blade Designs