5 replies to this topic

[122]

We have condensate recovery system with steam vent condenser. Due to tube leakage in vent condenser its cooling water was isolated. After isolation CW we have observed severe cavitation in condensate export pump. From pump discharge there is a stream which is used as heating media elsewhere in the process and this cooled stream returns back to condensate flash tank. When ever we line up this stream cavitation stops, isolating it starts cavitation problem again. My question is whether non functioning of steam vent condenser is the root cause behind cavitation or something else is going wrong which is increasing the condensate temperature.

[PingPong]

My question is whether non functioning of steam vent condenser is the root cause behind cavitation

Seems likely, but to know for sure, you could look up the documentation of the pump.

 

The vendor will have provided a curve of Required NPSH (NPSHR) versus volumetric flow.

 

The specification sheet of the pump (if available) will give the pumping temperature and vapor pressure that the design engineer originally specified (including a working vent condensor). Also the originally calculated Available NPSH (NPSHA) is on that sheet.

 

If you can measure the current pumping temperature and flowrate, and read the actual vapor pressure from a steam table, you can see the difference in vapor pressure and therewith estimate the current NPSHA. If you know how you can determine the NPSHA more accurately using the current vapor pressure, calculating the pressure drop over the suction piping of the pump, and determining the elevation difference between liquid level and pump impeller eye. If the NPSHA is close to, or less than, the NPSHR for the current flowrate then you can expect cavitation.

[gegio1960]

122,

your description is not very clear (you could improve it with a drawing....).

anyway, it seems you've mentioned two factors that cause loss of cooling to the system, then decrease of NPSHA (by decrease of density and increase of vapor pressure), then cavitation

[aroon]

Please elaborate diagrammatically. Following input may also be sufficient to cross check:

 

Loss of cooling to vent condenser will result in your trapped condensate to be collected at saturation temperature. If your condensate pot elevation and suction line size is not sufficient to provide required NPSH at the pump suction then pump will obviously cavitate.

[122]

Dear PingPong,

 

I had same thought in mind as suggested by u but there is no TT/TG in pump suction or flash drum bottom. I tried to measure temperature externally on bare pipe surface, with the help of a temperature gun but it does not give representative value.  Can u suggest any other method of measurement?

[PingPong]

From pump discharge there is a stream which is used as heating media elsewhere in the process .....

Usually there are TT/TG at heat exchangers, so look at one of those that use the condensate as heating medium.