low NPSH oil pump

[mil21ochoa]

hi, i´m engineering a pump for drainage of crude storage tank, tha operating conditions are:
1. NPSHa 1 ft
2. flow: 150 gpm
3. discharge pressure: 40 psig
4. crude viscosity: 2000 cP
wich kind of pump its the best for this aplication.

Thanks

 

[25362]

I've a question regarding NPSHA on an atmospheric tank. With a viscosity of 2000 cP, it seems that the vapor pressure of the hydrocarbon would be quite low, resulting in a value much higher than 1 ft. Can you, please, explain how did you estimate this low NPSHA?

 

[JJPellin]

If you verify that your NPSH is actually this low, then you have very few options to pump this stream reliably. Our crude primary pumps have considerably more NPSHa than this and we still have to use vertical turbine pumps in cans to achieve an acceptable NPSH margin for most of our tanks. For one tank, were able to install horizontal, overhung, single-stage pumps with large inducer screws. But, this option would require at least 5 feet or so of NPSHa. Because the flow is so small and the NPSH is so low, I assume you are looking for a heel pump to empty the tank for maintenance. If so, this would normally be done rarely. In our plant, this would be done no more than once per 10 years. I would not install a permanent pump for a service this rare. If you want to drain the tank more often to change crude streams and keep the crudes segregated, then an installed heel pump might be necessary. I would suggest you validate your requirements and then purchase a vertical turbine pump in a can deep enough to give you 10 feet or more NPSHa.

Johnny Pellin

 

[786392]

As mentioned by Johnny Pelin above

a vertical multistage pump with deep sump may work for you

however since the viscosity is on the higher side either some reliable agitating/mixing devices could prove useful in having better fluidity maintained from tank or

some tank suction heater similar to those employed sometimes for highly viscous lube base oil stock storage tanks(subject to safe heating media availability, we used Low Pressure condensing steam at our previous employer lube storage tank yard) may be another viscosity lowering support option!

Best Regards
Qalander(Chem)