Q: Mitigate suction side hydraulic problem?

[hollerg]

Someplace I have read an article on mitigating the effects of suction side cavitation/flashing when there is insufficient NPSHa. I can't halt production to address root causes. I had heard that recycling some of the discharge flow to the suction of the pump may help.

Does anyone have a reference? I cannot recall how to introduce the fluid back to the suction line, the proportion of the discharge flow (10%?) or whether there is a way to predict the performance gain.

Thanks
Gary

 

[Longinthetooth]

Assuming that it is a constant feed centrifugal pump, I thought that recycling part of the product would increase the overall flow through the pump and drive the pump further along it's curve where NPSHR is generaly greater, thus making the problem worse. Maybe if you cooled the recycle flow to lower the vapour pressure of the feed to the pump things could improve.

Regards,

 

[hollerg]

I am trying to avoid cooling the suction line, because the product is molten and only ~ 3-5 C above the melt point.


Googling found research on the recycle (bleed) principle. They claim it can increase pump efficency and reduce NPSHr.

http://www.pumpcavitation.co.nz/Zaher-abstract/Paper8.htm

Seems to be due to entraining the flow, from the source tank, boosting the pressure into the pump. EG a transfer of mechanical energy from the recycle flow to the source tank flow, I guess like an eductor.

This Research was not the article I was thinking of. I think it was in Hydrocarbon Processing or Chemical Process or Chemical Engineering, but I can't find it. The recommendations were only a part of the article on improving pump operation.