the relieving load of external fire scenario for distillation collumn 1

[phoenixmoca]

Hi,all,
We all know that the external fire scenario is credible when distillation collumn is located below 25 feet.
But sometimes the distillation collumn is elevated beyond 25 feet with the purpose of avoiding the fire scenario.
So is it needed to consider the relieving load of external fire for the auxiliary pipings of the elevated collumn?
Thank you in advance.

 

[Latexman]

I've seen many, not all, distillation columns whose worst case scenario exceeded the fire scenario, like condenser cooling water failure, reboiler tube rupture, or reboiler steam fails wide open. I don't think I've ever seen a column raised 25 feet above grade for the sole purpose of avoiding fire scenario. There were other reasons I've seen columns raised, like maintenance clearance or low bottoms pump NPSH.

Auxiliary piping is not included in fire scenario of distillation column.

Good Luck,
Latexman

 

[phoenixmoca]

Thank you,Latexman.
I agree with you that the worst overpressure scenario of collumn isn't fire case usually.
But when calculate the relieving load of fire case for distillation collumn it excludes the auxiliary piping no matter what size is the piping?

 

[Latexman]

Auxiliary piping is not included in fire scenario of distillation column.

Also, I’ve worked for 3 chemical companies for 43 years. None of them protected piping from fire with a relief device.

That’s another way of looking at it.

Good Luck,
Latexman

 

[shvet]

So is it needed to consider the relieving load of external fire for the auxiliary pipings of the elevated collumn?

It is user dependent.
API 521-2014
4.4.13.2.2 ... vessel heads protected by support skirts with limited ventilation are normally not included when determining wetted area. The user shall specify whether to include the wetted surface area of connected piping in the wetted-area calculation.

As per my experience piping is not considered in firecase. Note that usually wetted area of piping solely does not contribute enough relief load to exceed max vapor load of distillation column.

 

[phoenixmoca]

Thank you Latexman.
Would you like to share the another way of think about the fire scenario of piping connecting with collumn?

 

[phoenixmoca]

Thank you shvet.
As you mentioned Note that usually wetted area of piping solely does not contribute enough relief load to exceed max vapor load of distillation column.
Is there any standard or best practice refers to this?

 

[shvet]

No, there is not. Again - piping is user dependent. For example:

ExxonMobil
The external surface area (not the heat transfer surface area of the tube bundle) of a tower reboiler and its interconnecting piping should be included in the wetted surface of exposed vessels in a fire risk area. The surface area of piping, other than that for reboilers, is not normally included in the wetted surface area.

JGC
Whether the wetted surface area of connected piping is included in the total wetted-area calculation should be determined by respective project

Shell
The impact of attached piping on the vessel’s fire relief load shall be taken into account. The wetted area of piping connected to the equipment that is in the fire zone should be included in the total wetted area of the equipment.

 

[phoenixmoca]

Hi,shvet,
Thanks a lot for your sharing.
According to the shown company best practices it depends on the user to determine whether the auxiliary piping should be considered.