Cooling pump recycle

[HDIMR]

Hi,

Pumping Butene from a sphere. The pump has a recycle back to the tank. Recycle stream has gained some heat due to pumping. This heat could increase its vapor pressure or reduce the density. Both conditions could have an influence on the pump performance.

However, what is the dictating value/condition to install a cooler on the recycle or not?

Thanks,

 

[joerd]

As always, the answer is: it depends.
If you have a large pump and expect to run with recycle often, then you should have a cooler.
Butene is stored under its own vapor pressure. The sphere design pressure should be well above the max. vapor pressure expected, i.e. the pressure at the max. expected temperature in the sphere. When you decide on the max. temperature, you take into account max. ambient temperature, max. feed temperature, and the recycle operation. Given the heat capacity of butene and the pump power, you can come up with an adequate temperature rise to be attributed to the pump.

Cheers,
Joerd

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[HDIMR]

Thanks Joerd.

You meant to say that sphere design pressure is dictating the need of cooler or not.

 

[TD2K]

I've rarely seen a cooler on a recycle loop.

In your case, I would send the recycle stream back to the sphere fill line. The pump would have been sized assuming a saturated liquid. The "hot" recycle stream will slightly raise the sphere's pressure (likely, very little) but essentially, you are using the sphere's surface to allow the heat added to the recycle stream to escape to the ambient air. In any event, you still have a saturated liquid and sufficient NPHSA for your pump as that would be driven by the level of the pump, minimum liquid level and line losses to the pump suction.

If you are recyling directly into the pump suction line, then I would do a more detailed analysis since the heat you are adding to the recycle stream is going to raise the fluid's vapor pressure and affect NPHSA. In a system like this, I would not recycle directly to the pump suction even though it's the closest location.

 

[SmartEngineer]

I have seen coolers in some cases as Caustic recycle line to Caustic tank and I think that is due to the heat of mixing of diluted caustic that generates high temperature if kept at continuous circulation. Other cases as those materials having unsaturated HC or diolefins as they tend to promote polymerization if kept at continuous circulation.

In your case you would check the heat of mixing, polymerization events, if applicable, that would result if kept at continuous circulation

Hope this would help

Cheers