7 replies to this topic

[invssse]

Dear Friends,

 

I have a question regarding to the relief load calculation for a particular case that needs your help.

please find the sketch as attached.

A flash drum's liquid product goes to a steam stripper through a Control Valve(liquid level control for the flash drum). 

The case to study is this CV fails open (total Cv=1100) and liquid level at flash drum loses and the two phase flow from stream S1 will go through CV to the stripper. The relief load from the stripper is to be determined. 

 

the normal flow of S3 is 700 t/hr and at relief case the two phase flow through the CV would be 70 t/hr Vapor plus 1450 t/hr Liquid.

 

My question is that in this case how to determine the relief load required for the Stripper? Would the unbalanced heat method be used in this particular case? 

 

Thank you so much.

 

Regards,

Invssse

Attached Files

•  Column Blow Through Case.jpg   39.55KB   28 downloads

[Bobby Strain]

Some companies insist that the bypass is open to normal flow, too.

 

Bobby

[fallah]

Hi,

 

Where is bottom product line?

 

Is it a gas blowby case? If so, the gas blowby case should be considered among credible scenarios of PSV on the stripper. With such new high incoming flowrate, the stripper is expected to be flooded after a while and the study should be done around this matter:  if the steam can still be injected through the flooded column...?

Edited by fallah, 19 February 2013 - 08:07 AM.

[invssse]

Fallah,

 

thanks for the comment. 

 

Sorry I lost the bottom line for the stripper.

 

yes, basically this is a typical blow-by case for the column. 

it is easy to estimate the relief load for the separator's gas blow-by case such as gas blow by from HHPS to HLPS in hydrocracking unit.

But for column, I have no idea how to analyse it.

As you mentioned, if the stripper is to be flooded, I don't think there will be a proper  steady-state method to estimate the required relief load and a rigorous dynamic simulation seems to be the only choice. 

 

Do you agree on this? thanks.

Edited by invssse, 20 February 2013 - 11:01 PM.

[fallah]

invssse,

 

Agreed. In fact, the key point is finding the column material balance at relieving condition, otherwise as a rough estimation required relief load would be the difference between maximum gas blowby flow in upstream CV failure and normal flashed vapor flow in the steam stripper overhead...

[invssse]

invssse,

 

Agreed. In fact, the key point is finding the column material balance at relieving condition, otherwise as a rough estimation required relief load would be the difference between maximum gas blowby flow in upstream CV failure and normal flashed vapor flow in the steam stripper overhead...

Fallah,

 

What do you mean by "...Normal flashed vapor flow in the steam stripper overhead..."? is it the normal overhead vapor flow to the condenser? thanks.

[fallah]

invssse,

 

Yes, it is the normal overhead vapor flow... 

[CMA010]

Note that the normal overhead vapour rate should be taken at the tirndown ratio of the system. Furthermore, if the gas / vapour (S7) can't be condensed no credit for the normal overhead vapour rate should be taken.