12-10-2012, 05:27 PM
OFF DESIGN PERFORMANCE PREDICTION OF STEAM TURBINES
OFF DESIGN PERFORMANCE PREDICTION .ppt (Size: 640 KB / Downloads: 65)
PART-LOAD OPERATION
The demand to utility network is not constant and generating units do not always operate at full load.
A simplest way of varying steam flow rate is by throttling (controlling through A Valve).
Nozzle control governing
The steam consumption rate is much smaller for the nozzle control than for throttle control.
At full load, all the nozzles will be delivering steam at full pressure and the turbine will be operate at maximum efficiency.
At some part load condition one group of nozzles may be shut off while the other nozzles are fully operated.
Where Bi is the static pressure in the outlet of the group (kPa) and pi is the total inlet pressure of this same group.
This relation is only applied for group with a very large number of stages, but is can be applied for at least eight-stage groups with 50% reaction. The proportionality in the former equation can be eliminated as follows:
Variation of Condenser Pressure:
Effect on Pressure of Different Stages
Pressures increase with increase in Condenser pressure (LP last 3-4 stages)
(2) Effect on Temperature of Different Stages
Temperatures increase with increase in Condenser pressure (LP last 3-4 stages)
Effect on Enthalpy Drop of Different Stage
Per stage Enthalpy drop decreases sharply with increase in Condenser pressure (LP last 3-4 stages)
Effect on Losses of Different Stages
Losses increase with increase in Condenser pressure (LP last 3-4 stages)
Effect on Efficiency of Different Stages
Stage Efficiency decreases with increase in Condenser pressure (LP last 3-4 stages)
(6) Effect on Cycle Efficiency & Heat Rate of Different Stages
Cycle Efficiency deteriorates and Heat Rate increased with higher Condenser Pressure