Dust explosion design for silo

[DomDunk]

Dear,

I am designing a powdered coal silo, which is subject to explosions. I would like to know if you design these silos taking into account that the relief valve limits the pressures, or if you calculate the silo based on the maximum pressures.

What explosion pressures do you use? I found pressures of 30 psi on internet pages.

 

[spats]

30 psf is way too low. I designed a building in the past where flour was used for making cookies (flour dust is also highly explosive), and the scenario was to provide wall areas that would blow out to provide explosion venting. If I remember correctly, the wall sections were designed to blow out at a pressure of 80 psf. A contained explosion is a lot more than that. Keep looking.

 

[spats]

Oops! I was remembering wrong (been a long time). I think 80 psf was the design pressure on the explosion-resistant walls. It's an old document, but see the attached Factory Mutual document that addresses explosions and explosion venting.

 

[3DDave]

The OP wrote pounds per square inch.

 

[DomDunk]

Thanks,

I'm looking this document.

I'm using 30 psi, pound for square inch. 30 psi = 4320 psf. With respect the pressures that I see in this document it is a big pressure... too big? I will keep looking for information

 

[spats]

Double oops! Of course, the force of the explosion is a function of amount of explosive material,the material's properties, and the size of the confined space. 30 psi could be right in the confined space of a silo. I'll let somebody else answer this question.

 

[DomDunk]

Anyway, thanks for the help spats.

The eurocode says:

During an explosion in the types of solids normally stored in silos, pressures of about 8 to 10 bar (116 to 145 psi) can be attained in a closed space without venting.

I still need to find the reduction given by the venting

 

[WARose]

I don't know that much about dust explosions.....but I've done a lot of blast resistant structures. It's more than just a pressure. Confinement, stiffness of the containment structure, desired level of damage, etc, etc are all important. It's a pretty deep topic.

 

[JStephen]

I've not actually seen a silo that was designed for any pressures other than operating pressures. (Edit: Got to thinking, most of the silos I've seen were not for flammable products.)
Note that petroleum storage tanks are not designed for internal explosions, either. (They may have emergency vents, which are to allow for product boiloff in a fire, not not for internal explosions.)

Reminds me of this commercial.

https://www.youtube.com/watch?v=J-QE80Sn9AE

Edit: Googling up "silo dust explosion overpressure" pulls up some information of interest, one article referencing NFPA 68 and European standards, with a couple of articles where they were specifically trying to calculate the overpressures. "Venting devices are commonly used to try to reduce the damage caused by any dust explosion that may occur in silo systems. In North America and Europe the sizing of these vent areas is governed by standards NFPA 68 and EN 14491, respectively, both of which have recently come into force." (This was a 2009 paper).

 

[DomDunk]

It's very funny that ... I mean, I'm not talking about the video ...

Look at the design standards (eurocode, ACI, NFPA, etc.)...

 

[BrianPetersen]

If the original poster is in north America, nfpa 69 must be considered. Calculations are involved which involve the characteristics of the dust and give the design pressure and the explosion venting requirements.

 

[DomDunk]

I am not in North America, but we use the USA standars, which applies in many countries of the world.

I have also designed using the Eurocode (because I'm european), and also takes into account the explosion.

I am surprised that very often the structural engineers work with more subjects of "mechanical engineering" than the mechanical engineers themselves ... Is not that strange?

(I take the opportunity to apologize for my English ... it's not my language)

 

[Compositepro]

Just for reference, in a completely contained deflagration (a fuel air/explosion where the combustion front is subsonic), the maximum pressure is limited by the amount of oxygen in the air to less than about 150 psi, or ten times the original pressure.

 

[miningman]

Never , ever, underestimate the energy released in a coal dust explosion. I suspect that one cannot guarantee that the combustion front is subsonic, and 150 psi is at the low end of what I might expect. In the 1960s, the NCB in the UK had a research facility at Buxton which probably became the worlds best depository of knowledge on this subject. I know not how much of this knowledgeois available onine today.

 

[miningman]

https://www.youtube.com/watch?v=Vkqj8aLQ8EM

 

[SlideRuleEra]

See "Coal Pulverization System: Explosion Prevention & Process Control":

Also, the current edition of (European) Standard VDI 3673 "Pressure Venting of Dust Explosions"

http://www.SlideRuleEra.net

 

[MGZmechanical]

Hi, I think 50 psi (3,5 bar) explosion pressure it's a typical value for heaters design (coal pulverizing systems,...) where you have air + dust at low pressure (below 50 mbar) and you have an explosión wich usually goes up to 3,5 bar.

There's an EN 14460 to design Explosion resistant equipment
This European Standard specifies requirements for explosion resistant equipment which will be able to withstand an internal explosion without rupturing and will not give rise to dangerous effects to the surroundings. It is applicable to equipment (vessels and systems) where explosions are considered to be an exceptional load case.
There are two types of explosion resistant equipment: explosion pressure resistant and explosion pressure shock-resistant equipment (see Figure 1).

As per silos I don't know of what pressure to consider, sorry.


Don't know if this helps you:

http://publikationen.dguv.de/dguv/pdf/10002/bia-report-13-97.pdf

Best regards

 

[DomDunk]

Thank you all,

I will read the information that you shared.

Thanks,

Daniel

 

[Tmoose]

I interpret silo = Pulverized fuel bin , but that should be verified.

From NFPA 85-01 -

6.4.6 Pulverizer System Component Design Requirements.
6.4.6.1 Strength of Equipment.
6.4.6.1.1 All components of the pulverized fuel system as described below that are designed to be operated at no more than gauge pressure of 2 psi (13.8 kPa) shall be designed to withstand an internal explosion gauge pressure of 50 psi (344 kPa) for containment of possible explosion pressures. For operating
gauge pressures in excess of 2 psi (13.8 kPa), the equipment as described below shall be designed to withstand an internal explosion pressure 3.4 times the absolute operating pressure.


6.4.6.1.9 In a pulverized fuel storage system that is not started and operated with an inert atmosphere in accordance with NFPA 69, Standard on Explosion Prevention Systems, the following equipment shall meet the requirements of 6.4.6.1.1 or shall be equipped with suitable vents. (Refer to NFPA 68, Guide for Venting
of Deflagrations.)
(1) Cyclone
(2) Dust collectors
(3) Pulverized fuel bins

6.4.6.2.5 This requirement shall apply only to new installations.
Brittle materials shall not be used for piping except as
abrasion-resistant linings and where no credit is taken for the
structural strength of the lining. Brittle materials are those
having a plastic elongation of less than 8 percent prior to tensile
rupture.