1-High exhaust temperature:
Vacuum drops or maintains at lower side due to high exhaust
steam temperature flow into steam condenser. This high exhaust temperature is
mainly due to
1-Operation of Turbine at lower loads
2-More clearance in labyrinth seals
3-Not operating exhaust hood sprays
4-More load on condenser
5-Breaking of ejector U loop
2-Low circulating cooling
water flow
Vacuum in condenser reduces due to inadequate cooling water
flow through steam condenser. This is mainly due to;
1-Problems associated with pumps
2-Air pockets in pipe line
3-Leakages in cooling water line
4-Stuck of discharge valve of pump
3-High cooling water
temperature at condenser inlet
Higher cooling water temperature at condenser inlet results into reduction of vacuum due to poor heat transfer from steam to water
4-Poor heat transfer in
condenser
Very less or poor heat transfer in steam condenser reduces
vacuum to very low level resulting into high exhaust temperature &
disturbances in hot well level.
Poor heat transfer is due to;
1-Fouling of condenser tubes due to poor water quality
2-High cooling water temperature
5-Air ingress in condenser
& other vacuum pulling system
This is the most top reason for sudden drop of vacuum in
steam condenser. Air ingress into the condenser is mainly from flange joints,
gaskets, valves etc
Passing of vacuum breaker valve also be the one of the
reason for maintaining low vacuum in condenser
6-Low steam temperature
& pressure at ejector inlet:
7-Poor heat transfer in
steam jet ejectors
This is mainly due to fouling of ejector tubes
steam condenser vacuum & calculations
8-Damages to air ejector nozzles
Increase in nozzle clearances leads to reduction of vacuum
creating efficiency of ejectors
9-Breaking of ejector inter
condenser U seal loop.
This creates escape of hot condensate directly into
condenser leading to increase in exhaust temperature & reduction in vacuum
10-Low gland steam pressure:
Gland steam pressure lesser than design creates ingress of
outside air into condenser through turbine glands.
11-Loading the condenser
more than design
If the condenser steam load is more than design, vacuum
drops slowly
12-High a temperature &
low pressure in the atmosphere reduces vacuum pulling efficiency
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