Closed Cooling Water suction pressure not stable 3

[Michael Sam]

We have a closed cooling water with a fin fan cooling assembly for our gas turbine. it is also equipped with an expansion tank. the cooling water cools the generator radiator, lube oil, turbine legs etc. during normal operation the suction and discharge pressure sometimes increases, so we decrease the pressure by draining at the generator radiator side. when the pressure decreases we top it up by opening a valve connected to the expansion tank. what is the possible causes of this fluctuations or should we modify our system's design.

 

[LittleInch]

A diagram would help plus what sort of pressure increase?

From the description it sounds like normal behaviour or maybe your expansion tank isn't big enough.

Maybe the expansion tank bladder is broken/ leaking

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[curtis2004]

Michael Sam,

I agree with LittleInch, that first expansion tank shall be investigated. What kind of expansion tank is it? Size, and pressures...

Kurt

 

[MJCronin]

Is the expansion tank located on the suction side of the pump ???

MJCronin
Sr. Process Engineer

 

[mk3223]

It's normal that the pressure of the close cooling system is to be changed as the temperature up or down during the operation. So, you need to manually adjust the pressure during the operation. To improve the operation, you may add a pressure control at the cooling system and route the line to the expansion tank for adjust the system pressure automatically.

 

[Michael Sam]

Thank you LittleInch!
During the normal operation the CCCW system the temperature of the cooling water will increase as it passes through the various cooling circuits dissipating the heat that is generated by the various processes. To allow for the expansion of the water, due to this heat pick-up and without causing a significant pressure increase, one (1) expansion tanks is installed.

The top void of the tank is filled with dry air to allow the water to expand as it enters the tank, thus stabilizing the system pressure.

To protect the system from being over pressurized, the tank incorporates a pressure relief valve.

In case of water losses in the closed cooling water system, the pressure in the tank decreases and therefore the system is refilled. For this purpose the system is fed by the Demineralised water.
Nowadays we frequently experience increased suction/discharge pressure and it mostly raptures our generator radiator.
I' am finding the PID from our database. I will post it to you if I get it.
thank you

 

[LittleInch]

So if the air is let out under pressure, but water added is the void in your tank now much smaller than before?

Does the relief valve still work?

A diagram and some more details would be nice.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Michael Sam]

@ MJCronin YES the expansion tank is located on the suction side of the pump.
@ LittleInch We installed new relief valve

 

[LittleInch]

So did that work?

Still looks like your expansion tank is too small.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[lilliput1]

Maybe it is corrosion from using DI water and an open type expansion tank that is rapturing your radiator. Use bladder type expansion tank so the air is not in contact with the DI water. You need to estimate the system total volume and calculate the worst case expansion to properly size the expansion tank. Also you need to make sure the radiator pressure rating is greater than that that will be imposed on it by the system pressure plus the pump head plus the relief valve differential pressure.

 

[Michael Sam]

Thnaks very much:
LittleInch, liliput1
I think our cooling system needs modification. we will schedule it for our next shutdown maintenance.