Dedusting
Dave,
As I see it there are 2 types of dust, jong
1 - Surface dust - this is liberated whenever you shake the product
2 - Trapped dust - which is held within the matrix of pellets
To liberate the most dust you must have a large surface area, and you need a good wind (probably 2 m/s or better).
Then you have large particles of dust >100 um. These are heavy enough to fall out within 1 second of being airborne. And you have fine dust less than 100 micron. this can hang around for an hour or more.
I would imagine you need a trommel with a settling chamber under. This would allow coarse dust to drop through. The oversize is your product as pellets. The fan should pull air through the trommel to pick up the fines.
I would be quite brutal with the air - say 25 - 30 m/s in the duct to allow coarse dust to be drawn into the system. This could jam up your filters real quick. I would pass the stream through a cyclone to act as a prefilter. The bags can then take out the fine and respirable dust.
Try to rig up something in a lab - with a simple screen in a wind box. That will give you some tangile design information. Also a particle size analysis of a dust sample is very helpful to identify where your major problems would be. I have also taken a bulk sample for particle size analysis. That will tell you how much dust you have per kg of pellets.
Take care. Fine plastic dust is explosive. We blew a silo roof 200 m away in Vanderbijl Park. Luckily no one was killed. ■
Re: Dust Removal From Product
Mechanical agitation will not be necessary since you already intend supplying an air current. Copious & well disributed underfloor air will agitate the pellets enough to liberate dust which will then rise to the top of a wide low chamber. A weir at one end will pass the dust over to the collector. Slope the chamber floor towards the bagging station. You then only have to regulate the airflow in sympathy with the dust content.
In quarrying teminology you need a "boiling box" as used to wash dust off concrete ballast so the cement sticks better. ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Dust Removal From Product
Dave,
You require Pelletron's DeDuster that uses a magnetic flux field to break up the electrostatic charge between contaminants viz Dust and pellets, and a innovative air wash floor to separate and remove the contaminants & dust as well. This is in line system below your bagging silo.
We have successfully implemented such systems In Polymer (plastic chips) handing, plants in India, before bagging the product as in your case. If you can give your data as to how much kg/per of material. with approximate dust generation in grams /kg of material handled, Bulk density of material we can device a system for your need to work satisfactorily. ■
Re: Dust Removal From Product
Just make sure you wire it up the right way round or you might blow the silo roof back to Vereeniging. ■
John Gateley johngateley@hotmail.com www.the-credible-bulk.com
Re: Dust Removal From Product
Thanks to eveyone that replied!
My concern is that the surface dust is electrostatically bonded to the pellets. In order to effectively remove the dust, one would have to either destroy this bond, or supply sufficient energy to overcome it. This leads me to the conclusion that I would require either an ionizer and a vibrator with sufficient counter-current air flow.
Although my personal preference is for an elutriator, rather than a vibrating screen, this plant will be erected in China. My information is that a locally made vibrating screen is just so much cheaper than an imported elutriator. I would also use a perforated plate rather than a woven mesh, as my experience with screens in other applications is that they quickly wear through, resulting in metal contamination.
Point taken on the dust explosion hazard - the system will be well earthed. The received product will have a dust content of 100ppm, and the generated dust could be around 250ppm. Product throughput will be 30tph of PP and / or PE.
I welcome any further comments, especially where I am making incorrect statements or comments.
To the two gentlemen that refer to Vereeniging and Vanderbjil Park, I see you are located outside of South Africa. Could you give some further information on the installations, and your companies. You can contact me directly at: dave.meyers@sasol.com
I know of a silo (PP content) in Sasolburg that imploded, and a silo (lime content) in Vanderbjil Park that exploded.
Regards,
Dave. ■
Re: Dust Removal From Product
Dear Forumers
Rightly so.....Yes Explosion Hazards have to be taken care of when handling Such sensitive dusts by doing proper Earthing to eliminate STATICS ■
Dust removal from product
Dear Reader,
I will soon be erecting a conveying and bagging system for PP and PE pelets.
Product will be delivered to site in 20ft ISO containers, decanted, conveyed to blending silos, blended, then conveyed to bagging silos. From the bagging silos, the product will gravity fed into the FFS bagging system.
My concern now is how do I remove dust from the product? There will be some dust in the delivered (raw) product, and some dust generated during the conveying stages.
I am considering installing a simple vibrating screen with perforated plates, with a fan. The idea is to vibrate the product to seperate the dust from the pellets, and then to remove the dust with a counter current of air. This air will then pass through a filter to prevent dust from polluting the atmosphere.
The vibrating screen will be placed between the bagging silo and FFS machine. Will a vibrating system work? Should I rather employ another system such as elutriation?
Regards,
Dave. ■