3 replies to this topic

[Fakhri]

DearAll,

 

In API 521 page 120, it states that "The volume occupied by the liquid should be based on a release that lasts 20 min to 30 min. Larger hold-up volume may be required if it takes longer to stop the flow. Any accumulation of liquid retained from a prior release (from pressure-relief devices or other sources) should be added to the liquid indicated in items a) and above to determine the available vapour-disengaging space".

 

My question is what is the liquid level in the KO drum of liquid retained from previous release? Is that LZLL, Pump Stop, Pump Start or LZHH levels. What is the justification? In one of client standard they use the LZHH.

 

Appreciate your response.

 

 

Thanks and regards,

 

 

Fakhri

[fallah]

Fakhri,

 

It's not the pump start level nor low low liquid level to keep the required NPSH and pump protection from dry running (if the KOD is equipped with pump); because it hasn't already been considered in calculation of volume available for vapor/liquid disengagement. In fact, it's the volume of the liquid dumps from pressure relief devices from other sources has been retained from prior release and couldn't be removed quickly either by pumping out or by flashing/vaporization...

[Fakhri]

Fallah,

Thanks for your response.

 

My questions is in which space of a KO drum the 20 to 30 minute emergency relief of liquid (condensed vapor or free liquid) shall be stored? Is that above LSLL, above PSL, above PSH or above LSHH?

 

 

Regards,

 

 

Fakhri

[fallah]

Fakhri,

 

In my opinion, between low liquid level and high liquid level. Of course, if there is any accumulation of liquid retained from a prior release, it should be added to condensed vapor plus free liquid...