Large Steam

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Large Steam Gas Turbines

• P M V Subbarao
• Professor
• Mechanical Engineering Department

Backbones of Modern Nations
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Advanced 700 8C Pulverised Coal-fired Power Plant
Project
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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 161.
• 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 151.
• 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.
  

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9756 kJ/kWh
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Stage with General Value of Degree of Reaction
Total possible drop in Enthalpy
Exact definition of DoR
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Theory of General Reaction Blading
Vr2 gt Vr1
Ideal reaction blade
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Available power in L Reaction stage
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Stage Sizing
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Selection of Degree of Reaction
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Definition of Isentropic/adiabatic Efficiency

• Relative blade efficiency is calculated as
  

• Internal Relative Efficiency is calculated as

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Typical Distribution of Losses AStages
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Structure of Large HP Turbine
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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

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where
Z No. of stages in group,
a1 Nozzle exit angle
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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

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Axial surface area at the exit from last stage
moving blades, and
Average diameter to blade height ratio is
i No. of flows in LP turbine
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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(a1) 150 to 200

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Stage Loading and Flow Coefficient
Stage Loading Coefficient Ratio of specific
stage work output and square of mean rotor speed.
Flow Coefficient Ratio of the axial velocity
entering to the mean rotor speed.
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Regions of Design
y
Fflow
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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(a1) 150 to 200

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y
F
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Range of turbine Design Parameter

• High Pressure Turbine
• Maximum AN2 2.5107 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

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With known value of U , change enthalpy is
obtained .
For reaction turbine maximum efficiency occurs at
certain loading factor
From change in enthalpy absolute velocity of
steam can be obtained
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Enthalpy Entropy Diagram for Multistage Turbine
Turbine Inlet
Stage 1
h
Stage 2
Stage 3
Stage 4
Stage 5
Turbine Exit
s
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Optimal Variable Reaction 3D Blade Designs