Pumping Kerosene 2

[TISM]

Dear All,
we are trying to pump 15 lpm odourless kerosene for continuous operation (hours at a time).

We have tried both 17 lpm and 30 lpm vane pumps designed for organic use (diesel, kero, light oils). In both cases the flow rate starts at a reasonably acceptable level (about 14 lpm) and drops over about 10 minutes to 2-5 lpm. It appears that the vanes are softening when pumping the kero, and we cannot get the flows we need.

Has anyone any experience in pumping kerosene
Thanks in advance,

TISM

 

[Jit]

Hi,

Starting with a flow rate of 14 LPM and dropping down to 2 LPM within 10 minutes would suggest that the pump (I am assuming it is centrifugal) is possibly getting starved due to inadequate NPSH. This inadequacy could be a result of any one or a combination of the following factors:

1. Excessive pressure drop in the suction line
2. Inadequate suction head
3. High liquid vapor pressure i.e. kero is hot
4. Pump not adequately primed

On the discharge side, excessive back pressure could have the effect of the flow "backing off" up the pump curve.

I would suggest that you superimpose the system curve on the pump curve to check the equipment's suitability to flow the desired flow rate and the adequacy of the available NPSH. Running the 17 lpm pump at 2 lpm will damage the same in the long run.

Best of luck.

 

[Jit]

Hi,

Just noticed that the pump being used was of the vane type and not centrifugal as assumed by me. Here again, I would check for vapor breakout in the suction - this could casue the pump in losing its prime.

Sorry once again for the error.

 

[25362]

When compared with gas oil, kero, and light lubes, deodorized kero generally contains lighter hydrocarbons which may effectively soften, as you suggest, flexible pump vanes.

This effect, coupled with lower viscosities, would result in a dramatic increase in slip.

In short, your diagnosis seems to be right.

 

[rbcoulter]

Try a gear pump.

 

[tickle]

Sliding vanes pumps could be used. Esbray do them with metal vanes.

Another reason could be the internal relief in the pump. This may open as the back pressure increases causing internal bypass.

I am pretty sure that Jit is along the right lines when talking about NPSH. How does it sound as a theory to you?

Are you noticing any noise with the pump as cavitation occurs? or any chattering as the internal relief opens and closes. Does the pressure change with time? There has been a post on Eng Tips recently regarding cavitation that you should search for.

 

[roker]

hi,
because of the low flow and without knowing the discharge pressure a positive displacement pump is suitable,
of caurse all the above should be checked.
the pump should be according to API standards.
regards,
roker