Oil storage tank water protection.

[DavidCR]

Good day to you all.

We have two 5000 m3 (31000 barrels) aprox. fixed roof storage tank for diesel (Fuel Oil 2).

We need to specify fire protection based on foam chambers and water cooling to protect the steel walls from heat.

My question is about the water protection system.

We´ve checked the NFPA 15, which includes some criteria about the amount of water needed to delay the heating of the fuel. (The amount of water is huge for a tank like this, 0.25gpm/ft2).

A friend that works for an oil distribution company mentions that the protection of the fuel that they use (fixed systems) is provided by the foam system and it is complemented with water protection considering the steel plate structural resistance in case of fire exposure.

The water system he mentions consist of a pipe at the top that showers the tank with water, and provides protection for the steel in case of fire exposure and use 0.1 gpm/ft2 of exposed area. But he is not able to mention a code or bibliography to support this.

Can somebody please give some recomendations or comments about:

-design objetives and parameters for water systems like this,
-type of nozzles, sprinklers (I mean, is a central "shower" pipe enough?, I´ve seen it but also I´ve seen some photos of sprinkler rings around the tank.
-is NFPA 15 enough for this or other aproaches must be considered?.

Any comment will be appreciated, thanks a lot in advance.

David
Costa Rica.

 

[MJCronin]

DavidCR,

It is my experience that atmospheric tanks, containing #2 distilate do not need foam fire protection as contained under the rules of NFPA-30. NFPA-30 has specific rules about tank design and tank location within a facility ( minimum distances to people, property lines.... etc.)

Tanks and their contents are categoriezed by the "flash point" of the liquid contained. NFPA-30 categorizes liquids as "combustable" (low flash point) and "flammable" (high flash point). Foam systems are required on tanks containing liquids above a certain flash point and/or meeting certain other criteria.

Foam systems will always be found on gasoline and aviation fuel (kerosene) tanks above a certain size.

Something to consider ( maybe you already have!!)

MJC

 

[PAN]

I don't have the latest edition of NFPA 15. But in my understanding the minimal wastage of 2 (l/m)/sq. m should be enough for exposure protection for your storage tank.

The water spray ring should be around and above your fixed roof tank.

 

[lekshmi]

NFPA 30 indicates that tanks located as per Section 2.0 does not need any cooling system. We generally do a heat radiation study considering fuel characteristics, height of tank, location w.r.t other tanks and wind velocity. IP 19 clearly describes the protection (cooling) required for various items based on heat radiation. IP 19 recommends cooling of tank surfaces falling within a heat radiation zone of 8 kw/sqm. Application rate is 2 lpm/sqm. If the tank is having fuel oil and the tanks are located as per NFPA 30 then I do not think these tank need any cooling. Fire water system with hydrants and fixed monitors can be considered for protection of other exposed surfaces. Foam is also not necessary for these tanks as per NFPA.

 

[DavidCR]

Dear fellows.

Thanks a lot for the comments, they have given me a much better perspective for my job, and good points to consider.

To "Lekshmi" (or other who may know): what is the IP19?, is this a standard of the british petroleum institute?, I can´t find a reference of this document (I Supose this document is about recomendations for fire protection on tanks). I´m interested in it and other information with recomendations you may suggest.

Also, I´d like to know what is the base for the recomended value of 2 lpm2.

Thanks a lot again.

DavidCR

 

[farshi]

hi.
pls. see the nfpa-30 or nfpa-15 for calculation fire water requirments for cooling of tank by circule fire water around the tank with many holes in tube with delauge valve system .
yours,
farshi

amir farshi
farshia@nioc-ripi.org

http://www.nioc-ripi.org

 

[rewatson]

You need to review NFPA 11 (foam). You will need 3% foam concentrate. It may be ansulite 3x6 or Kidde 1x3 or 3x6 and an application rate of o.13 gpm/ sq ft. The foam chambers would be one or two as the surface area requires. The application time is 55 minutes. Also, you need a bladder tank and one or two foam monitors with 20 minutes.

RDGS,

rewatson

 

[RAJ67]

Any tips on fire protection system for cryogenic domed roof storage tanks ( for ethylene and propylene)?
thanks

 

[DeltaCascade]

Rewatson, you contradicted the others who said that foam was not needed.
RAJ67, you may want to start a fresh thread with your fresh question.
Clear as mud. RAJ67, API codes should help?
Good luck, all.

 

[DavidCR]

Apart from your comments and from RAJ67 little parenthesis, I can add the following:

1. Our local code ask for shorter distances than NFPA 30 and the Oil stored here is quiet important so we think the NFPA requirement is not enough for our needs so as to decide to not to protect the tanks.

2. I still have the doubt about the IP19, what is it?

3. A consultant supported the criteria of the 4.1 l/min/m2 (0.1 gpm/ft2) for water cooling, can anybody comment this value?. Or about the type of nozzle to be used?

4. For the foam system, we´d like to know what foam proportionong system is better, pump skid proportioning system or bladder tank?

5. Can anybody give guidelines or formulas to calculate the radiation from storage tanks like these and the water demand for cooling?

Thanks a lot.

 

[DTR]

Hi all!

In my experience fuel tanks containing hydro carbons which are not polar solvent are protected by foam chambers delivering 4.1 l/min/sq m of 3% foam/water solution, if it is a Type II discharge device the duration of dischage is 30 minutes. The number of Foam Chambers is dictated by the tank diameter all of the above is as per NFPA 11.

To achieve code compliance you may also require supplementry protection by hand held hose lines delivering 200 litres per minute.

With regard to water spray protection I generally apply the exposure protection details within NFPA 15 which gives density of 10.2 l/min/ sq m ,I also apply the 3.7m maximum "run down" deailed in NFPA 15 for protection to Vessels ,for the vertical spacing of the spray rings to the tanks, I know that this rule does not apply to storage tanks, but it is a good guide for vertical spacing.

I think the best nozzle for exposure protection is the medium velocity type with a widespray pattern of 110 deg..

If there are no fire risks local to the Oil Tanks then the exposure protection may not be required and external hydrants may suffice.

I have used variations of the above arrangement on Fuel Oil Storage Areas to Power Plants on many occasions.

 

[lekshmi]

Sorry that this reply is much delayed, I hope you still go through the responses.

IP 19 is a code published by Institule of Petroleum (British). You may be able to get a copy of it through the British Council or a good agent in your area. The 2-lpm/min/m2 is the requirement as per IP 19 typically for storage tanks. Requirement of foam and deluge depends on the product stored, storing and handling temperature, spacing of the tanks, etc. Why don't you refer to NFPA 30, Chapter 2.

About foam (if required by NFPA 30 or IP 19)the details are available in NFPA 11. You can use bladder tank, pelton wheel driven pump or electric (power supply shall be 100% reliable) driven pump with foam proportioner for foam induction. Normally application rate for storage tanks is 4.1 lpm/min/m2. Prefered method of application is us by top pourer. Angus, Chemguard, etc can do the system design and provide you the components as a package.

Details to work our heat radiation are available in the Fire Protection Handbook. I am not able to provide you the details as it is little bit complicated.

 

[DavidCR]

Lekshmi and friends

Thanks a lot. Even time passes. Your comments are quite useful. I hope this thread continues as a good comment place to improove on tank protection.

We are OK with tank spacing with NFPA 30, but not with a local requirement (they ask for D/2 as spacing criteria) and the fuel is vital so we want to protect it. The plant operators (client) wants a huge system so our proposals must be well based, so any comment here is appreciated to improove criteria.

Other aspect I want to consult for is that I´ve been told that roof (fixed cone roof) water cooling protection is not needed since the radiation over the roof is not as significant compared to the heat radiated to the walls. Any comment on this?

Thanks.

 

[lekshmi]

You can consider the application rate of 2lpm/m2 for the surface area of the tank. Cooling requirement for roof will be more crytical. Just imagine that the tank on fire is full with oil and the roof just breaks of (weeak shell to roof design. The roof surface of the neighbouring tanks will be more exposed to the radiation than any other surface since it is at same level as the fire. If the roof is not cooled down it may lead to failure of the neighbouring tanks ultimately. Separate lines are required to cool the shell and the roof surfaces. I hope this reply is of some use.