Fire Protection Strategy: (3) How to estimate the depressurizing rate

Estimate the depressurizing rate 

Depressurizing system design을 위해 depressurizing rate를 산정해야 한다. 이를 위해 필요한 정보나 기준은 아래와 같다 

 

Depressurization requirement 

7 barg or 50% of the vessel's design pressure in 15 minutes [2] 

 

CCPS [3] says that depressurization may not be practical when the vessel design pressure is less than 100 psig because valves and piping can become unreasonably large and costly, or when the vapor depressurizing load governs the size of pressure relief and flare headers. 

 

Required information for estimation of depressurization rate

• System volume:  sectionalization/ Fire zone classification
• External heat load 

System Volume 

Sectionalization of the Process segment with perspective from the fire zone.

https://vegabondsheyla.tistory.com/80 

Fire Zone

 

 

External heat load

Site-specific fire hazard analysis가 필요하나, 업계에서 통용되는 fire heat load가 있으므로 이를 참고할 수 있다. 

https://vegabondsheyla.tistory.com/79

Fire heat intensities

 

 

Process/mechanical information 

• Operating pressure (PAHH) 
• Holding volume (LALL)
• Fluid 
• MDMT of the vessel 

 

Tools for calculation 

Dynamic simulation by HYSYS 

 

 

References

1. Guidelines for the Protection of Pressurized Systems Exposed to Fire, Scandpower
2. API RP 521 
3. CCPS, Guidelines for Engineering Design for Process Safety 7.4