Diesel Generator Belly Tanks 1

[Park View House]

Folks,
I am reviewing hazardous area classification for generator belly tanks for diesel (flash point 55C). Now I know diesel is not usually assigned hazardous area classification because it its high flash point. However, I think this might be an exception..
The fuel from the belly tanks is pumped to generator and unburnt fuel is returned to the belly tank. The unburnt fuel is at an elevated temperature (circa 90C) and can be as high as 50% of the fuel flow rate fed to the generator. From a hazardous area classification perspective, the worst case scenario is when the fuel level in belly tank runs low. The residual fuel temperature in the belly tank will be raised and could realistically come within 10C of the flash point of diesel. This is enough to consider the headspace in the belly tank Zone 2 (or Division 2 in USA).
Would anyone have an opinion about this?
I am based in Ireland and using degrees Celsius above.
regards
Richard

 

[Latexman]

Which grade of diesel? Can you share the PFD or P&ID, because it appears the diesel may be heated.

Good Luck,
Latexman

 

[Park View House]

A snip from P&ID attached plus safety data sheet for fuel oil:

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1604936015/tips/SDS_lh4f0j.pdf[/url]
I hope these attachments work. Its my first time on this website.
thanks
Richard

 

[Latexman]

The generator is treated like a "black box", so one cannot see how it is pumped and controlled, or how or why it is heated to ~ 90[sup]o[/sup]C. The diesel appears to be similar to the #2 diesel I am familair with in the U.S. In my experience, generators and pumps do not heat #2 fuel oil that much. But in your case if they do heat it > 55[sup]o[/sup]C, it must be considered flammable, not combustible. Before treating the entire tank as flammable, I'd have to see some heat transfer calcs on the tank, or, better yet, see hard data from the tank temperature transmitter.

Good Luck,
Latexman

 

[Park View House]

Thank you for your comments, very much appreciated.
I agree, I need to get more detail on the generator to see whats going on there!
Thanks

 

[Compositepro]

Diesels often have heaters in fuel pre-conditioners. This for operation in cold weather where waxes may precipitate out. This is low wattage and is only intended to warm the fuel to the engine. You will notice that the return to the tank is very close to the loop inlet. In my F-350 the loop returned fuel to the primary filter/pre-conditioner unit, which was outside of the tank It would be pretty foolish to heat the whole fuel tank to 90C, or anything close to that.

 

[Park View House]

Thank you Composite pro

 

[Hoxton]

Diesel fuel can be returned hot to the tank. This is often 'surplus' fuel from the fuel injection system, and some engines use fuel to cool the injectors.

This is returned to the 'day' tank (baseplate tank on smaller engines), and mixes with the existing fuel. Some engines have a small heat exchanger to cool the return fuel with engine cooling water. This could be a retrofit for you, the engine supplier / agent may be able to help.

Back in 2015 the United Nations re classified diesel fuels as hazardous by changing the flash point limit.

I am in the UK and our Health and Safety Executive took the pragmatic view that as diesel fuel itself had not changed, then there was no need to change the regulations for small amounts of diesel fuel:

“Under the EU CLP Regulation which came in June 2015, there are a number of substances that now meet the criteria for classification as flammable which did not do so in the past. This is partly because the upper flashpoint for classification as a flammable liquid has been increased from 55 °C to 60 °C. The changes mean that for example, diesel, gas oil and light heating oils are now classified as flammable liquids”

and also:

“For the avoidance of any doubt, where diesel fuel is stored in storage tanks with a capacity not exceeding 150,000 litres, designed to recognised and appropriate industry standards such as BS 799 Part 5, OFS T/200, EN 13341 or OFS T/100 and where the vessels were manufactured in a workshop environment to controlled standards and where there is no risk associated with the formation of a flammable oil mist, the requirements of HSG 176 do not need to be applied. Information that could be used to inform this decision would include any historical evidence of an incident due to misting as well as any other relevant guidance”

https://www.oiltanksupplies.co.uk/technical-information/hse-statement/

Your local regulator may have different guidance. (Are you in the Republic of Ireland or Northern Ireland?)

 

[Park View House]

Thank you , very helpful!

 

[LittleInch]

I don't think the diesel is being "heated" specifically to 90C, but it's probably pressurised then pressure let down and all in small quantities very close to the engine jacket so inevitably it warms up.

Also if you've got a dirty great radiator blowing hot air all around the place then everything heats up to 90C...

The real thing here is so what? Your tank instruments for me should be zone 2 rated regardless. what other impact does it make?

This is quite informative

https://www.hse.gov.uk/comah/sragtech/techmeasareaclas.htm

Diesel is also a bit notorious for generating large electrical static potential if your inlet velocities get high and you don't allow the fuel to dissipate this to earth properly.

If it's just the tank that makes it to zone 2, which is after all for non normal operation and only for a short time I can't see what the issue is. IMHO.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Park View House]

Yes that's the bottom line for me. I'm assigning Zone 2 for headspace of belly tank. Client is pushing back a little on this!

 

[georgeverghese]

From memory, I dont recall us ever having to deal with belly tanks for diesel in DEGs'. We always had a remotely located day tank feeding the DEG with a pump local to the day tank, and a pressure recycle back to tank. It does look very risky having a DEG sitting right on top of this large inventory of diesel, which will no doubt get hot through conduction through the DEG frame wall and radiation from the DEG also.

 

[Park View House]

Thanks georgeverghese!

 

[LittleInch]

Is it 20 m3?

Depending on your generator this might classify as literally a "day" tank , i.e. 24 hrs running.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Hoxton]

Belly tanks (aka baseplate tanks) are very common on smaller sets, due to trying to make use of all the space.

It also enables any spills to be collected in the base of the enclosure.

From memory, oi tanks of less than 1000 litres do not need to be bundled if the tank is a day tank and it is literally intended to use up the fuel in a day. Unless the tank is near water etc.

You still get fined if you leak oil! So most of us bund anyway!

I
Think that a belly tank oil fire would be difficult to establish unless there was a source of sufficient oxygen.

 

[bimr]

When you refer to the headspace, is that internal space in the belly tank?

 

[Latexman]

the worst case scenario is when the fuel level in belly tank runs low.

Can you estimate that? Is it below an existing low-low level the tank won't run at anyway? Can that estimated level be used to set order points for fuel oil such that the tank will not normally get that low? This may be worth some effort.

Good Luck,
Latexman

 

[Hoxton]

My reference to '1000 litres above was incorrect, it is a little off topic, but I thought that I would correct it. The requirement for a bund or drip tray comes in at 201 litres. I'm thinking of the older regulations..

I think that this is a common sense link to the capacity of a standard oil drum.

Remember that you must include the engine lube oil...

https://www.gov.uk/guidance/storing-oil-at-a-home-or-business

 

[PersonalProfile]

If interested, I note:

ENQUIRY 1
Should installations where diesel fuel with a flashpoint above 60°C is stored or handled for
normal use as a fuel be classified as a hazardous area?
RULING:
No. However:
(a) If the bulk mass of the fuel is being heated by other than solar radiation or is involved
in any process that may reduce the flash point below 60°C then hazardous areas need
to be assessed.
and
(b) The vapour space in a diesel tank that has previously contained flammable liquids or
shares a vent line with other tanks with lower flash point fuels needs to be considered
for hazardous area classification due to the potential for vapour from other sources.

Australian Standard, 2017, AS/NZS 60079.10.1:2009 Rul 1:2017, Explosive atmospheres Part 10.1: Classification of areas—Explosive gas atmospheres (IEC 60079-10-1, Ed.1.0 (2008) MOD)(Ruling 1 to AS/NZS 60079.10.1), Australia.

And:

http://www.iceweb.com.au/Ex-web/IDC2015/CaseStudyBianchini.pdf