4 replies to this topic

[victortheone]

Hi, I want to calculate the surface area for a blowdown system between shutdown valves (containing many equipment including finned air coolers). I need the surface area and volume to model the blowdown  segment in unisim EO BD utility. I need to calculate the surface area for both fire case and cold blowdown cases.

 

I know for Pool fire case scenario, based on API 521 we only have to calculate wetted surface area for bare tubes of air coolers. But for Jet fire scenario considering jet fire occuring in nearby separator, do we need to calculate the surface area of finned air cooler or just bare tubes area?

 

I guess we need to calculate total surface area of bare tubes (including wetted + non wetted areas) for jet fire case.

 

Kindly if anyone can provide input on whether we need to include the total finned area of air coolers for blowdown area estimation?

 

[breizh]

Hi,

Share a PId or PFD for us to understand and support your query.

breizh

[victortheone]

 Screenshot 2026-02-17 134531.png   282.68KB   0 downloadsHi,

Share a PId or PFD for us to understand and support your query.

breizh

Hi Sure, from the attached PFD we can see the two blowdown valves (EBV) for 1st stage and 2nd stage compressor. The segmentation valves are shown as EV and the sizing of EBV is jet fire case, and common heat load of 100 kW/m² will be applied to entire blowdown area and 2 EBVs open simultaneously. So my question is do we consider finned surface for air coolers or just only the outside bare tube area? Finned area is considerably larger than bare tube area. Volume of the system between segmentation valves are already calculated, the query is only for surface area. 

Edited by victortheone, 17 February 2026 - 07:39 AM.

[breizh]

Hi,

Consider this resource to support your work:

Fundamental of process safety engineering by S. K Biswas, U.Mathur and S.K.Hazra , CRC press.

Should be area exposed to fire. I would say bare tube area.

Wait for comments from others.

 

edit: See attached document, point 15 related to air cooler.

another reference:

Fires,explosionsand toxic gas dispersions by Marc A J Assael

KonstantinosE Kakosinos 

CRC Press

Breizh

Attached Files

•  Safety BP Pressure relief system.pdf   89.87KB   1 downloads

[victortheone]

Hi,

Thank you for the attachment and answers. The attachment didn't specify anything about the surface area calculation (whether do we consider the fins or not), We will consider only bare tube area as of now and I will wait if anyone has some good explanation

Hi,

Consider this resource to support your work:

Fundamental of process safety engineering by S. K Biswas, U.Mathur and S.K.Hazra , CRC press.

Should be area exposed to fire. I would say bare tube area.

Wait for comments from others.

 

edit: See attached document, point 15 related to air cooler.

another reference:

Fires,explosionsand toxic gas dispersions by Marc A J Assael

KonstantinosE Kakosinos 

CRC Press

Breizh