condensate pump noise

[amar122amar]

we have a LP condensate flash drum. The flashed steam passes through fin fan cooler, and return of fin fan cooler goes back in the drum. The return line is submerged in the tank below the normal level. Pressure in the drum is maintained by venting in the atmosphere or putting nitrogen in the fin fan outlet line (split range control valves).The condensate pump makes a lots of noise. Is it possible that N2 is entrained in the liquid and going to pump. what may be the possible reasons for the pump noise? cavitation, Gas entrainment, recirculation? Is it ok with fin fan outlet line submerged in the liquid?

 

[nickelkid]

What is your NPSHa to NPSHr margin?

 

[amar122amar]

NPSHA=9m
NPSHR=3.5m

 

[dlcgama]

Have you considered a two phase flow?

 

[786392]

Are You sure that NPSH Available is always 9m and never goes below under any operating circumstance?



Best Regards
Qalander(Chem)

 

[rmw]

You probably have vortexing which is bringing entrained gasses into the flash drum and depositing them under the level where the condensate pump is picking them up.

rmw

 

[amar122amar]

Is it ok to have fin fan outlet line submerged in the tank? What purpose does it solve?

 

[786392]

I have doubts on this pipeline's health and integrity over longer life periods and
may be susceptible to leakages;
consequently some leaked steam might agitate the condensate/ get trapped and cause the "Pump in question's vapor/gas locking" thus noise.

Best Regards
Qalander(Chem)

 

[amar122amar]

this is the scheme (please see in the attachment). Can N2 get entrained in the pump suction. Is submerged fin fan outlet line required? or it should be above liquid level?

 

[786392]

Some sort of Vortex arresting system at pump suction may be helpful
Additionally the incoming pipeline may be so positioned below the liquid surface as stirring and agitation gets minimized;
may be a baffle plate slanted 45 degrees to receive the direct inlet material(if installable in earliest opportunity may prove useful).
Other learned colleagues may correct/guide better.

Best Regards
Qalander(Chem)

 

[chemicalengineerthai]

1) It is normal if your fluid contain lighter component than its design.
2) Can you try with following suggestion
-Trottle pump discharge
-Spray water at your drum to gain sub cool liquid.
-check pump vent line already release before pump start. if in doubt, just stop the pump for a while then venting all line to clear vapor lock.
-If pump has minimum flow line try to operate in manual to check if noise still generate in diffrent flow.

 

[Glenfiddich]

I agree that vortexing may be the culprit. Does the vessel have a vortex breaker at the pump nozzle?

 

[amar122amar]

ya pump has a vortex breaker around inlet nozzle.

 

[UNLengineer]

What elevation difference do you have between the pump and tank level? You mention NPSHA of 9 Meters, which would indicate 9 Meters(18 feet) of elevation.

Also, what pressure range do you have for the split range control on N2 and vent? A large pressure swing could cause vapor bubbles to form in the pump suction.

 

[amar122amar]

tank (2.2 meter ID) is at around 4.2 m above ground level. Tank level is maintained around 70%. Pressure at pump suction is 1.25 kg/cm2 (g). Pressure range is 0-1.6 kg/cm2 (g). Pump suction temperature is around 109 deg C.

 

[Glenfiddich]

what is the velocity in the suction pipe? Does the suction pipe have at least 5 diameters of straight run (bigger line size) to the pump and a reducer right at the pump suction nozzle?

 

[amar122amar]

there is one blockvalve and one strainer in the horizontal line to pump suction. can this be a problem? I think valve and strainer should be in vertical line prior to horizontal suction line.

 

[sshep]

What is the velocity and diameter of the suction line? Include any minflow that might be being used in the velocity calc. I think these problems start at the drum outlet nozzle- not neccessarily vortexing in the conventional sense, but this is the critical point in the system where there may be very little liquid head to supress cavitation in the nozzle. Where as the pump may calculate plenty of NPSHa, the calc implies clear liquid all the way to the pump. In reality, the nozzle static pressure drop may be higher than expected (you may have even ignored it in the calculation)- any vapor formation in the nozzle can cavitate the pump and make your NPSHa very much less than calculated.

Try running the drum level as high as possible, and if using a fixed rate minflow (spillback via orifice) try an alternative minflow protection to minimizes suction line velocity.

best wishes,
sshep

 

[ivegotgas]

Can the OP clarify..

Pressure at the Pump Suction is 0-1.6kg/cm2 @ 109oC

0???!!! Definitely an NPSH problem

 

[786392]

That's what the very first response's spirit from me.(3-1-09)

Best Regards
Qalander(Chem)