Vapor lock 1

[chonglom]

My vertical can pump (centrifugal) cannot pump the light end condensate from the HPKO drum which pressure is ambient to the Condensate Surge Drum (P = 270 psig). Firstly, I think it might occur from lower S.G. from the designed value (S.G. = 0.65) which will effect in insufficient of head due to system curve lift. But yesterday I try to test and found that condensate lever in HPKO durm not decrease. So I take the sample of the condensate to the lab and found that S.G. = 0.66. The discharge pressure gauge is 300 psig which is enough for the condensate to go through the system to CSD. And while testing the pump, there's no cavitation noise. Then I try to bleed the line if there's any gas/vapor on the discharge side, but the condensate came out. I take that condensate to test at the lab and got S.G. = 0.66 which I think is the same one as in the HPKO drum ( not coincedent). Now I'm focusing on vaporlock but I'm not sure if this can be the cause.

Hope anyone can help.

 

[chonglom]

ps. there's a long way to go from the pump discharge to the CSD. The system is about 32 ft up verticaly. I also think if there are any fouling in the pipe which will cause a higher head (but for this, the fouling must make a diameter 20% smaller)

 

[MikeHalloran]

A shot in the dark: Virtually all of the heat that would be rejected from an ordinary pump's motor shell and ventilation, goes into the pumped fluid in a can pump. I.e., maybe the condensate is flashing.



Mike Halloran
Pembroke Pines, FL, USA

 

[chonglom]

If the condensate flashing in the pump, I think it would be a cavitation but I didn't hear any noise. And I also find the condensate came out instead of gas/vapor in the discharge side when I try to bleed the vapor.

If this is my misunderstood please educated me.

 

[BigInch]

vapor lock is when one or a series of up-down pipe runs gathers enough vapor in the down legs and enough liquids in the up legs that the sum of the liquid column heads of all up legs - the near zero sum of heads of all the vapor in all down legs, is greater than the inlet driving pressure (head equivalent).

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[MikeHalloran]

Can you measure the motor current without blowing something up?
Compare it with ... well, what it should be at the OP.



Mike Halloran
Pembroke Pines, FL, USA

 

[Pumpsonly]

Check your CSD working pressure is still 270PSIG or actually higher.

You mention pump discharge pressure gauge is 300 PSI and the pump is not delivering. I would assume this is also equal to shut off condition. The pump will be boiling if you do not have a recirculation line.

You only have about 20PSI difference between pump shut of pressure and the discharge vessel pressure + the static head pressure.

Condensate with 0.66 SG is very unlike to have a VP lower than atmospheric.

 

[SNORGY]

The pump may be cavitating quietly without your hearing it because of the much lower Vg/Vf ratio compared to, say, hot water. The vapour collapse has correspondingly less energy. I faced (as a Mechanical Engineer who specified the pump) a problem like this once in a condensate stabilizer reflux pump (vertical in line) in that the reflux rate could not keep up with the overheads accumulation rate. There were a lot of things in the process (designed by the Process Engineers) that were not right that contributed to the problem, and I was able to identify them by discovering a 20% difference in the inlet feedstock density using flow measurement readings from a Polysonics Doppler Meter and measuring motor current and discharge pressure as suggested by MikeHalloran. That said, I was nonetheless able to get some improvement, even in the off-spec condition, by venting the pump casing back to the vapour space of the reflux accumulator. In that case, the vapour lock appeared to occur in the pump itself.

The real point is that MikeHalloran has an excellent suggestion for your situation.

Regards,

SNORGY.