7 replies to this topic

[james.corrobro@gmail.com]

i have an automatic blowdown on a separator vessel (gas-liquid-water-three phase sep)

 

Also i have a psv on the vessel

 

psv blocked flow load < psv fire case load

 

should psv be size for fire case? since blowdown will take care of depressurization...what should the sizing case be considered for psv

 

if psv is for fire case then would blowdown and psv open together in fire?

[fallah]

i have an automatic blowdown on a separator vessel (gas-liquid-water-three phase sep)

 

Also i have a psv on the vessel

 

psv blocked flow load < psv fire case load

 

should psv be size for fire case? since blowdown will take care of depressurization...what should the sizing case be considered for psv

 

if psv is for fire case then would blowdown and psv open together in fire?

 

The PSV should be sized for fire case...

 

You cannot take credit for Automatic Blow Down as it's an instrument system...

[james.corrobro@gmail.com]

 

i have an automatic blowdown on a separator vessel (gas-liquid-water-three phase sep)

 

Also i have a psv on the vessel

 

psv blocked flow load < psv fire case load

 

should psv be size for fire case? since blowdown will take care of depressurization...what should the sizing case be considered for psv

 

if psv is for fire case then would blowdown and psv open together in fire?

 

The PSV should be sized for fire case...

 

You cannot take credit for Automatic Blow Down as it's an instrument system...

 

Thanks fallah..just one more ques...in case of fire, psv and blowdown will both open. For flare load then we have to consider psv relieving capacity + blowdown flow? wouldnt that be very high flow

[fallah]

 

 

 

 

The PSV should be sized for fire case...

 

You cannot take credit for Automatic Blow Down as it's an instrument system...

 

Thanks fallah..just one more ques...in case of fire, psv and blowdown will both open. For flare load then we have to consider psv relieving capacity + blowdown flow? wouldnt that be very high flow

 

 

In general, the above statement isn't correct. In fire case BDV will be opened manually but the PSV will be opened just when the pressure inside the separator reaches to the design/set pressure.

[sonu19921103]

Hi James,

 

As already responded in the previous posts; you need to size the PSV for both cases and made selection accordingly(do take care of valve trim should be certified for both vapor and liquid).

 

In real world the PSV is no final solution to fire case (vessel will fail due to decrease in mechanical strength at high temperatures).

 

In order to cover the same automatic blowdown are necessary; automatic blowdown will lower the system pressure allowing more time. It Also helps by deescalating the event by flaring the potential fuel for fire.

 

For flare sizing two separate cases "blowdown & Fire" need to be considered (based on fire circles); load to be considered accordingly.

[james.corrobro@gmail.com]

Hi James,

 

As already responded in the previous posts; you need to size the PSV for both cases and made selection accordingly(do take care of valve trim should be certified for both vapor and liquid).

 

In real world the PSV is no final solution to fire case (vessel will fail due to decrease in mechanical strength at high temperatures).

 

In order to cover the same automatic blowdown are necessary; automatic blowdown will lower the system pressure allowing more time. It Also helps by deescalating the event by flaring the potential fuel for fire.

 

For flare sizing two separate cases "blowdown & Fire" need to be considered (based on fire circles); load to be considered accordingly.

sonu19921103 so let say we have 3 vessel in the same fire zone, and all have psv sized for fire case and all have blowdown as well (Automatic)....so for flare sizing we take 2 cases, one is when all psv open in fire case, and one when all blowdown open, we will take maximum flow from both case and do sizing for header
 

[james.corrobro@gmail.com]

 

 

 

 

 

The PSV should be sized for fire case...

 

You cannot take credit for Automatic Blow Down as it's an instrument system...

 

Thanks fallah..just one more ques...in case of fire, psv and blowdown will both open. For flare load then we have to consider psv relieving capacity + blowdown flow? wouldnt that be very high flow

 

 

In general, the above statement isn't correct. In fire case BDV will be opened manually but the PSV will be opened just when the pressure inside the separator reaches to the design/set pressure.

thanks fallah, for fire case since we have automatic blowdown...wont the blowdown open automatic when fire is detected
for flare sizing, do we take psv loads plus blowdown or take psv load separate and blowdown separate and then take governing
 

[sonu19921103]

 

Hi James,

 

As already responded in the previous posts; you need to size the PSV for both cases and made selection accordingly(do take care of valve trim should be certified for both vapor and liquid).

 

In real world the PSV is no final solution to fire case (vessel will fail due to decrease in mechanical strength at high temperatures).

 

In order to cover the same automatic blowdown are necessary; automatic blowdown will lower the system pressure allowing more time. It Also helps by deescalating the event by flaring the potential fuel for fire.

 

For flare sizing two separate cases "blowdown & Fire" need to be considered (based on fire circles); load to be considered accordingly.

sonu19921103 so let say we have 3 vessel in the same fire zone, and all have psv sized for fire case and all have blowdown as well (Automatic)....so for flare sizing we take 2 cases, one is when all psv open in fire case, and one when all blowdown open, we will take maximum flow from both case and do sizing for header
 

Hi James,

 

your understanding is correct.

 

Best Regards

Sonu Singh