2 replies to this topic

[Jon K]

Hello,

 

 

I try to calculate and to understand the emergency venting according to NFPA 30.

 

First of all I am familiar with the calculation according to API 2000.

 

The NFPA 30 has this exceptions for tanks > 12000 gallons / 45m³. Unfortunately I don't find this exception in the API 2000. (Or did I miss it?)

That's why I intend to use the NFPA 30.

 

In chapter 22.7.3.3. of the NFPA it says: "The total emergency relief venting capacity for tanks and storage vessels designed to operate at pressures above a gauge pressure of 1.0 psi (6.9 kPa) shall be as follows:"

So what if I have a tank that is operated below the 6.9 kPa/ 69 mbar (or even with open vent)? I am not allowed to use the rest of this calculation?

 

Nevertheless I took the value from the table 22.7.3.2 and compared it to the API 2000. With the equation of 3.3.3.3.2 for required flow capacity q, in normal cubic meter per hour of air I calculate a similar value.

 

But...please explain me the equation 22.7.3.4 from the NFPA.
I use the value from the table (which is free air per hour) and divide by latent heat of vap (of any fluid) and the sqrt of it's molecular weight and at the end I have again free air per hour volume flow? I do not get the logic behind this equation and do not understand what is calculated by this.

 

Any help is appreciated

 

 

Thanks

Jon

 

 

 

 

 

 

Edited by Jon K, 10 February 2021 - 10:55 AM.

[breizh]

Hi,

Consider the document and link attached from Protectoseal : 

https://www.protecto...ressure-vents/#

 

I also add a spreadsheet issued by Ankur ( one of our moderators in this forum)  where you can find pointers , for product different from Hexane .

 

hope this is helping you

 

Note : You should consider to contact the vendor (Protectoseal ) to get confirmation about your calculation .

 

my view .

 

Breizh 

Edited by breizh, 11 February 2021 - 05:53 AM.

[Jon K]

Hi,

thanks for die input.
Actually I still don't think I have the answers to my questions.

Attached is a screenshot from NFPA30, 2018.

Let's consider it is a small tank for naphthalene with 19m² ~ 200ft².

 

For my understanding I use the table (also in the screenshot), lookup 200ft² and get the value CFH.

And then I use the equation 22.7.3.4, put in the CFH from the table and L and M of naphthalene? Is this how it works? The results surprise me a lot...

Furthermore there is no input for the Temperature.

 

[I checked the protectoseal document. You will find the same table as in the NPFA 30 (22.7.3.2) but the rest of the calculation is a different]

 

 

And what about the scope of the NFPA calculation. It says tanks operated at gauge pressure higher 6.9 kPa. What if my tank is operated at atm pressure?

 

 

------------------------------------

 

Thanks for the spreadsheet.

I worked with the API 2000 (7th edition) in the past. My question is why to calculate for hexane and then convert to another fluid?
Chapter 3.3.3.3.2, equation (14) and the table 3 are all that you need for a direct calculation. Or am I wrong with that?


 

 

Again, any comments are appreciated.

 

Jon

 

Attached Files

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