Why does vacuum in steam condenser reduce or drop??

 

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:

Parameters lesser than rec recommended leads to reduction of vacuum pulling

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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