Desperate request for validation of flammable vapour release rate and concentration calculation

[123MB]

Hi All,

I am an electrical engineer who is undertaking hazardous area classification for a dust handling plant.

In performing this classification it has become apparent that there is an area of the plant where a combustible liquid is added to a mix of grains and meals and the mix is heated above the flash point of the liquid.

I have conservatively identified that the area inside the process containment where the mix is heated is a potential gas explosion hazard, however I wanted some calculation to back up this assertion and also to assist with the determination of the concentration of flammable vapour which could be expected to be generated, considering some very conservative bases and assumptions.

I have generated the attached calculation from research and formulae found across the internet, but I would really appreciate it if someone could have a read of it and just, from a common sense point of view, validate the approach I have taken.

Thanks so much

Michael.

 

[MortenA]

I dont know what you will use this for - but if formal QA is needed then i dont think that a site like this is suited. If you are just looking for a little guidance then by all means.

My take that in a closed volume (like a physical box) the vapor pressure is the highest concentration you can get (how long time it takes before it gets there is another story) so that would be 11 kPa or just around 11 % vol/vol assuming 1 atm in the box. So this would be between UEL and LEL and ignition could thus occur given a hot enough source. Following this logic in a uncontrolled environment you could have somewhere where the proprionic acid vapour had the "right concentration" and explosion could occur. If you have sufficient ventilation then i would assume that except very close to the pool then the concentration could not build up. And then close to where a pool could accumulate you could still get ignition and thus you could have something like a unclassified area and a zone 0 or maybe zone I area. The instruments etc in the classified area would then have to follow the rules for this area. Usually there are standards that can help you determining how close close is - often its 3 meters from the source if you have good ventilation (look up this definition yourself i dont have this right here and it may vary based on you country and industry).

Best regards, Mortem

PS: I dont see anything wrong with your calculations i just dont see the point in bringing in a rate expression when the vapor pressure gives you the "ultimate" concentration.

 

[Latexman]

In my safety training over the years I've been taught that a hybrid mixture of a flammable vapor and combustible dust can be a very hazardous situation. A combustible liquid heated above it's flash point generates flammable vapors. One of the controls used for flammable vapors and combustible dust that do not supply their own oxidizer is inerting. Have you considered inerting the operation?

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[123MB]

Thanks very much all for taking the time to provide me some feedback.

 

[Compositepro]

The first place to start is to contact the material supplier. Your concerns must be shared by all users of this material.