When initially pulling vacuum on the condenser, some people insist:
Start the vacuum pump first, then open the isolation valve between the pump to the condenser, others the reverse order of operation.

Was reviewing logic for a combined cycle plant in Europe and saw that the logic first openened the isolation valve between the vacuum pump and the condenser and then started the vacuum pump.
Checked with another plant in England and they assure me it is always done this way.

This is different than my experience with coal fired utility plants in North America, where the logic will typically ensure that the isolation valve is closed, then start the vacuum pump, then open the isolation valve.


Am looking for:
a) others experience about typical operation.
b) reasoning which is used to motivate each choice of operation.

Thanks,
Bob.

 

Dear Bob,

At this CCGT power station in the UK,this subject is under DCS sequential control and is as follows,

Start up
(to open the isol valve there is a permissive to make, and that is "gland steam sealing system healthy"

Then the isolation valve is opened, once the valve open limit switch is made, then the duty vac pump is started.

Shutdown
Duty Vacuum pump (or if running also the 2nd pump)
shutdown.
Then the isolation valve is closed.

We have had the vacuum pump mistakenly start when the isolation valve was not open and within a short time the "excessive vacuum/negative pressure relief valve opened (fitted to each pump) to protect mainly the water ring pump/vac pump.

Hope this helps.

 

Dixie,

This helps. Thanks.

Especially your experience with starting the pump with the isolation valve closed. Could be that this is vacuum pump manufacturer specific.

Thanks again.

Bob.