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NFPA11 problems about foam for oil storage area, Looking forward for reply!

Question asked by Xiaomin Feng on Apr 20, 2016
Latest reply on Jul 21, 2017 by Dennis Miller

Our company building a power plant in Saudi Arabia region, there is a HFO tanks storage area, there are two 5000 m3 HFO tanks, a single tank diameter is24m, height of tanks is 12.5 m, fire dike length 80m, width 40m, center distance between two tanks is 40m.

We want to calculate the foam need for fire extinguishing system. I am puzzled with foam for dike area, according to NFPA 11, 5.7.2 Protection of these areas shall be achieved by either fixed discharge outlets, fixed or portable monitors, or foam hoselines. Is that means we should calculate the foam for dike area and we should also consider the foam for burning tank

Is my calculation is correct or wrong?

1.     Foam solution demand (for burning heavy oil tank):

Calculation basic data: foam solution density: q=4.1L/min.m2, duration time is t=30 minutes.

Hence, foam solution flow rate is:

Q’=q×F=4.1×452.16=1853.86 L/min =30.90 L/s

So, select 2 sets of foam chamber (type: PC16, working pressure: 0.52MPa), the total capacity: Qf=2×934.5=1869.0 L/min.

2. Foam solution demand (for Diked Areas):

Calculation basic data: foam solution density: q1=6.5 L/min.m2, duration time is t1=20 minutes.

Calculated dike area: F1= S-F=80×40-452.16×2=2295.68m2

Hence, foam solution flow rate is:

Q1=q1×F1=6.5×2295.68=14921.92 L/min=248.70 L/s

So, calculated number of foam monitor4 sets (select type FJM-100 foam monitor: working pressure: 0.90 MPa, flow rate: 62.5 L/sK:86.7), the total capacity: Qm=4×62.48 L/s = 249.92 L/s=14995.1 L/min.

   3. Foam solution demand (for Supplementary Protection):

Calculation basic data: minimum number of hose streams required: 2, solution application rate: Q2=189 L/min, duration time is t2=20 minutes.

So, calculated number of foam gun: 2 sets (select type PQ4 foam gun: working pressure: 0.5 MPa, flow rate: 4 L/s), the total capacity: Qn=2×4=8 L/s=480 L/min.

4. Foam concentrate quantity

Calculation basic data: foam concentrate is 3%.

Hence, Foam solution flow rate is:

Qfm=Qf+Qm+Qn =1869.0+14995.1+480=17344.1 L/min=289.1 L/s

Foam concentrate quantity is:

Vf=3%(t×Qf+t1×Qm+t2×Qn)=0.03×(30×1869+20×14997.2+20×480)=10967.2 L=11.0 m3

 

This is the first time we design according to NFPA, and we are not familiar with this standard, we want to learn from experienced engineers, thank you for help us!

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