4 replies to this topic

[andybud]

Hi all,

 

I am running a calculation for a pump that is fed from a distillation column. HYSYS states the vapour pressure of the liquid if 4.5 bara. The pressure of the liquid in the system is 7 bara on the suction. Does this mean the liquid is classed as a subcooled liquid, rather than a boiling liquid?

 

Different line sizing criteria apply for each. Thanks

[Bobby Strain]

To get the proper answer, provide a sketch for your system. Along with flow rate and conditions.

 

Bobby

[Sharma Varun]

To get the proper answer, provide a sketch for your system. Along with flow rate and conditions.

 

Bobby

Agreed and please also indicate elevations in the sketch to know the head

[Chemitofreak]

Immediate distillation column bottom is always a boiling liquid. Only after cooling the column bottom can be considered as sub-cooled liquid.

 

The pressure is high because column elevation and liquid level also play part in the suction pressure calculation.

 

As Bobby and Varun suggested post a sketch if you want precise answer.

 

Regards

[Subhendu]

For distillation column, the liquid is in equilibrium with vapor and thus always considered as a boiling liquid. In line with this, pump taking suction directly from the distillation column has to be considered in boiling service and sized accordingly. For boiling liquid, important aspect is that operating pressure does not affect your NPSHa, as vapor pressure is to be considered same as operating pressure. Suction pressure and in effect, NPSHa will be affected only due to column bottom elevation, liquid level and line loss.