Sizing of Vessesl/Tank Vents for Powder Services 2

[Proceed]

Is anyone aware of a sizing criteria/procedure for vents in tanks/vessels that handles fine powders?

I am currently reviewing one vendor's proposal for a given conditioning package aimed to inject certain chemical aqueous solution into the main process.

The chemical (fine powder form) comes in bags that are emptied via manholes into one mixing vessel in which water is subsequently ingressed in order to prepare the solution. The vendor drawings shows this vessel's vents ("goose-neck"-type) to be 1" in diameter. I am concerned about long term clogging of such small vents due to progressive accumulation/compaction of powder fines in them (the fact that the vents are open to atmosphere and that water condensation will occur at times -minimum ambient temperature= 15 degrees C- makes the concern stronger).

I have checked vents size against results obtained from equations in the API 2000 RP. Although on these grounds the vents seem to be of adequate size the long-term clogging concern remains as the impact of fine powders is not especifically addressed by API.

From the back of my mind, I remember once reading somewhere about specific guidelines for sizing vents on powder services. Yet memory fails to bring further details.

Is anyone aware of a specific sizing criteria/procedure applicable to vents in powder services?

Thanks for everything.

J.V. Gomez

 

[HEC]

I am not aware of any other guides for vent sizinig. You have mentioned fine powders, is there a chance of explosion of the powder/dust? This would certainlly provide guidence on the vent size. On several applications where dust extraction from a tank has been required a 100mm vent connection has been used. In your post you have referred to API nice to see there is a standard basis for the design however we should not blindly follow standards, especially where they do not apply. API would be dealing with venting fumes or air/vapour mixes, not generally dust or powder.

Mark Hutton

 

[Proceed]

Thanks, Mark, for your comments.

No, no there is not a chance of explosions of the podwer fines in this case. Indeed, for those cases (in which the concern is to have enough area for proper relieving of the released energy) there are a number of articles that provide guidance.

I referred to the API knowing in advance it is aimed to deal with gaseous venting, just to check whether the vents are sized according to it, which they are (or, if greater, to have a reason to "infer" the vendor accounted for powder clogging somehow).

In this particular case, the concern is purely long-term clogging of "goose-neck" vents due to compaction of chemical fines with atmospheric condensed water. I was expecting than, perhaps, there are some rules of thumb out there to deal with cases like this.

So far, I am biased to believe that the 1" vents provided by vendor are too small as to prevent long-term clogging. I say "biased" because I am admitedly basing this opinion on my experience with Portland cement fines, which is Not the actual chemical in the present case (calcium chloride being the actual chemical). I would certainly like not to rely on a "feeling" to issue my opinion to vendor.

Any thoughts?

 

[cub3bead]

Is the tank partially filled when you start adding the powder? If it is it should help minimze the dusting problem.

How big are the outlet and drain connections? I would look to those sizes in determining the proper size of the vent connection.

 

[Proceed]

Yes, the tank is partially filled with water (anything between 30-50% of the tank's volume)prior to the chemical being dumped from the bags into the tank. However, as the mixing system (1,500 RPM propeller)is subsequently turn on, I am concern splashy surface waves might rise fines (eventually building up in the vents).

(Incidentally, it kind of surprise me so a high RPMs for mixing purposes)

Drain and outlet connections are 2" and 3/4", respectively.

Thank you.

 

[proinwv2]

I believe that there are other issues here dealing with transport of solids in a gas stream.

If you would like to discuss this further you can contact me via my website,

http://www.ostand.com

Paul Ostand

http://www.ostand.com

 

[HEC]

Proceed,

IF you are concerned with blocking of a gooseneck, fabricate the gooseneck such that it can be easily dissassembled for inspection/cleaning. A simple design would be to install an elbow from teh tank to horizontal, then to a Tee mounted vertically. The top branch of the tee is to the extraction system, the bottom branch of the tee is capped with a blind flange. This can be removed for cleaning and inspection.

Mark Hutton

 

[Proceed]

Mark: thanks a lot for your comments, as I find them most helpful.

Paul: I shall contact you at your website to obtain further info.

Best regards,

J.V. Gomez