Large Steam& Gas Turbines P M V Subbarao Professor 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 C, 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 No x production. The dry No x is less than 25 ppm on natural gas. The turbine entry temperature is C and the exhaust temperature is C. 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 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 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

Exact definition of DoR Stage with General Value of Degree of Reaction Total possible drop in Enthalpy:

Theory of General Reaction Blading V r2 > V r1 U V r1 V a1 V a2 11 11 22 11 Ideal reaction blade:

Available power in  % Reaction stage :

Stage Sizing Steam Path

 increasing Selection of Degree of Reaction 11 33 22 44  stage,diagram

Definition of Isentropic/adiabatic Efficiency Relative blade efficiency is calculated as: Internal Relative Efficiency is calculated as:

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

where = average steam flow rate = kg/sec. = Steam flow rate at entry of group in kg/sec, = Steam flow rate at exit of group in kg/see And similarly = m 3 /kg, is the available enthalpy drop of the group is exit velocity loss coefficient = 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 where correction for wetness fraction = 0.8 for peripheral moisture separation design.

Exit velocity loss is given by Axial surface area at the exit from last stage moving blades, and 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 ) : 15 0 to 20 0

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.

 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 ) : 15 0 to 20 0

 

Range of turbine Design Parameter High Pressure Turbine: Maximum AN 2 : 2.5×10 7 – 3.3 ×10 7 m 2.rpm 2. 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/m 2.s Hub/tip ratio: 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