diesel stoarge tank needs inert gas?

[Leclerc]

I don't think that No2 diesel,of a specification fine enough for an emergency electrical generator, requires an inert blanket when stored at ambient temperature.

However, I would like other peoples views on this, and some information on custom and practice.

My reasoning:
From typical data sheet,
LFL is GT 0.7%v/v, UFL is LT 5.0%v/v.
vapour pressure at 20 deg.C is 0.4 mmHg.
B Pt is 160 deg.C, i.e. vap. press. at 160 deg.C is 760 mmHg.
If I had 3 points I could work out 3 Antoine constants.With only two points, assume ln(vp)vs 1/T is linear.

Average temperature during hottest month is 27.8 deg.C. Assume highest temperature of 150 m3 tank is 30 deg.C.

Interpolating, vapour pressure at 30 deg.C is 3.1 mmHg, which is 0.41 %v/v in air. This is below 0.7%v/v, and therefore vapour is not flammable and inert gas blanket not required.

thanks in anticipation.
Leclerc.

 

[Leclerc]

er, I made a mistake with arithmetic: vap press. by interpolation is 1.24 mmHg, not 3.1 mmHg. Conclusion still stands. Sorry!
Leclerc

 

[25362]

Safety considerations are often site-specific. You are mentioning "stagnant" conditions; I'd like to consider, for example, the chance of having a static electricity buildup and sudden discharge which are common ignition sources. Besides, No.2 diesel may have a flash point as low as 38^oC.

Static sparks can be incendiary. Thus tanks should be duely grounded. Even if tanks are earthed and the liquid is not conducting, when filling the tanks not all of the static charge will drain away, and some will remain in the liquid. A spark may pass between the tank roof and the surface of the liquid, with energies above 0.25 mJ, igniting vapors or mists present in the vapor space.

To prevent this from happening one may:

-make the liquid conducting with suitable additives
-keep the pumping-in rates below 7 m/s when dry, and below 1 m/s when water may be present. Note that when leaving the refinery the fuel will inevitably come in contact with water and air, and if it contains cracked products, this may lead to the formation of gums and sediments which may cause filter plugging, etc., not to forget static buildup
-avoid mists with large drops, that if present, can have less than 1/10 of the normal LEL
-keep sufficiently long pipe portions after flow restrictions such as valves or filters for static relaxation
-prevent the formation of flammable mixtures by inert gas blanketing.

To avoid possibilities such as these in an unknown location, yes, I'd go for having inert gas blanketing for a 150 m³ No.2 diesel storage tank.

Kindly comment.

 

[MJCronin]

Leclerc,

Well, if you decide to put a nitrogen blanket on a No2 diesel fuel storage tank based on the fuel characteristics....it may be a first. This is the type of decision that can end jobs and reputations.

The governing rules for the placement, construction, materials, inspection and fireprotection for diesel fuel and the storage of almost all other similar liquids is the NFPA Standard #30.

Within this NFPA standard are precise definitions and classes of "flammable" and "combustable" liquids. These are based upon the measured flashpoint of the liquid stored. NFPA 30 also specifies minimum distances between tanks ( of various classes) and distances to buildings and property lines. The type of fire protection (if any) is dictated based on the volume stored, liquid category and tank location.

Almost all of the No2 diesel stored in the USA requires no active fire protection devices or systems. Many tanks have "grandfathered" acceptance. Some "newer" No2 diesel tanks, based upon thier unique placement, capacity etc., have AFFF foam injection systems installed.

25362, your comments are valid, but I disagree with your approach. You do not have to go back to "first principals" to establish rules for one of the most commonly stored fuels on earth......follow NFPA 30.

In my opinion, if the diesel fuel is to be stored for emergency use, your primary design concerns should be:

1) Diesel fuel clogging (or waxing-out)in low temperature climates and,

2) Periodic Fuel recirculation (to prevent eventual degradation) and periodic fuel testing (to an ASTM or other accredited Standard)

Let is know more about your facility, placement of this tank and other details.....

MJC

 

[25362]

to MJCronin, please consider that NFPA 30 as well as OSHA Standards 29 CFR 1910. 106 and 1910.1200 are all american (not world-wide) standards, codes or rules.

 

[MJCronin]

25362 (Chemical),

I realize and understand the scope and limits of USA codes, standards and statutes.

My primary point is, that unless there ar some very unusual circumstances, there is no need to put an inert blanket on a No2 diesel fuel storage tank. There are many, many of these tanks in the USA with simple vents.

My secondary point is that, unlike many "merchant" tanks, storage of emergency diesel fuel requires some other design, operation and maintenance considerations that I suspect Leclerc is not aware of.....


MJC

 

[Leclerc]

More information:
150 m3 Tank will be located in Shanghai coastal region (PRC).Facility is a petrochem complex, making plastics intermediates.

Temperatures:average temperature for coldest month is +3.3 deg.C, average temp for hottest month, 27.8 deg.C
Coldest temperature, -10 deg.C. I don't suppose tank temperature will drop below 0 deg.C, neither rise above 30 deg.C.

Filling rate is 30 m3/h via a 3" dip pipe. Lowish velocity.
Consumption is very low (only used as fuel for emergency generator), therefore not much filling activity after initial fill.

I intend to specify highish spec. material. (flash point 50.0 deg.C, pour point less than -12 deg.C)I don't want the clients to find themselves with a tank of waxy rubbish when they most need it.

Tank will not be heated(or lagged or traced) and neither will the transfer line from tank to generator.
I have access to NFPA Codes via internet. Difficulty is trying to read them and identify relevant chapter/ para.

I suspect that chapt.4 is relevant and chapt3.3.25.1 for fuel definitions (Class II I think I have), but would be grateful if someone with a paper copy could identify table on whether I would need to inert gas blanket.

 

[25362]

I wonder whether "breathing" the humid (salty?) air in coastal areas would be considered "healthy" for the storage tank. I'll be glad to learn what codes say about this.
Thanks.

 

[jsummerfield]

Offshore platforms have Diesel firewater pumps, standby generators and cranes. We do not inert the Diesel on offshore production or processing platforms in the Gulf of Mexico.

Nitrogen is available and we use a nitrogen blanket on some other fluids.


John

 

[abcmex]

Leclerc,
consult with the chinese Ex-Protection code; if you are planing with a Design Institute they can provide additional information for the requirements (by law) in Shanghai.
Consult with the diesel supplier regarding the properties of the Diesel, its a monopoly so there will not be so many types! I think the flash point may be higher than what you can get in Shanghai. On the practical view I have seen some Diesel tanks and they were not with N2-layer
kind regards

 

[Leclerc]

gentlemen,
thank you for your comments and yor insight into diesel storage.

I am minded not to inert the diesel tank, but I see that that I need to find further info re actual diesel to be stored, and lay down a few specifications for the detailed design team so that the final design justifies this decision.

thank you, Leclerc.

 

[abcmex]

Leclerc,
Ex protection code GB 50058-92

kind regards