Off gassing causing pump efficiency issues! 1

[carltogr]

Currently I am having problems with inadequate pump priming, and low pressure before and during operation of Centrifugal Magnetic Drive Sealless type pumps. I am pretty sure it's because of the entrained vapor and off-gassing of O2 from the ammonia stream being pumped. Can anyone help me out with finding the right type of pump and manufacturer for this type of application?

Characteristics:

Trace amounts of: NH4OH and H2O2
pH ~10-12
Temp. ~80-140
S.G. ~1.04

 

[hacksaw]

have you provided adequate suction head for the pump you are working with?

 

[jalvarez]

Independently of the fact that your pump is a Centrifugal Magnetic Drive Sealless one, you need to check the issue of NPSH, available and required by the pump. There are a miriad of threads and articles on this issue.
If you checked the NPSH and it seems OK, maybe it's very close to the limits, or the pump doesn't work as it was offered/promised (check with the supplier!) or the NPSH issue was originally not well taken into account.
Again, if everything looks OK and you still have problems, e.g. due to some gases in the pump inlet, ask the supplier if it is possible to accomodate an inducer in your pump. It will be easier than elevating (!) the suction drum, or lower/change the pump, or increase the suction line diameter.
Obviously, check the drum for correct gas disangagement, existence of an antivortex baffle, etc.
Hope this helps, have a safe day

 

[rmw]

Can you put a bleed back, or a vent line, back to the suction source?

What J alvarez has said about the preventive measures of getting the NPSH right, if it is really an off gassing problem, and not a saurated vapor flashing problem due to insufficient NPSH, then you are just going to have to accept the fact that the gasses are there and deal with them, which means getting them out of the pump, so the pump can pump liquid.

A vent line should help with that.

rmw