spraying/ coating bulk solid while conveying

[13thzodiac]

want to coat solid powder @ around 1500 - 2000 LBS/ hr with liquid material. The amount of the coating is 1% of the solid. i.e. 20 lbs/hr.

How can I start designing the equipment as i feel the amount of coating material is too little compared to the solids for coating the solids evenely.

Is there any way where I can spray the liquid while the solids are conveyed from silo to Hopper.

I did some pilot trials and results show that inside walls get wet when liquid is sprayed while conveying and it forms sticky paste of solids.

can anyone suggest the good spraying/ coating technique for thiis.

thank you

 

[unclesyd]

I've never seen anything done on a conveyor belt other than wash or wet the conveyed material. I've seen a couple of systems where a rotary drum tumbler was incorporated in the conveyor system to lightly coat the conveyed product. This type application has some very severe limits like product has to be non-friable and the carrier for the coating has to be removed quickly.
As you say the coating and solids form a sticky mass then I think you only option is to tumble while coating.

 

[nbog]

As unclesyd said, a rotary tumbler is one of the answers.
I had it in a fertilizer (granular) plant. I added a lance with 2 spray nozzles and never had problems with it. You have to keep in mind that (depending on the properties of your granules) you might have to handle dust. We had cyclones/scrubber so I didn't have to worry about that aspect.

The trick is to create optimal mist droplet size distribution. Heavy mist particles will not provide uniform coating and may cause over-spraying in some spots, leading to the cake formation. If they are too fine, a good portion will get exhausted by dust collection system. Space the nozzles so that their clouds will never get mixed. The tumbler is slightly inclined- granules that escape the first nozzle will most likely get coated by the second one.
Observe the area of the tumbler where the most of the material is (depends on inclination angle, material flowability) and direct the nozzles so that they never spray directly on the walls.

 

[13thzodiac]

Thank you unclesyd and nbog for your replies. I will definately put tumbler as an option.
what i am thinking is can I spray liquid using nozzles if i Blow material with PD blower from one hopper to another. The material will drop thru rotary airlock into the transfer pipes. one end i can have PD blower to blow material through transfer pipes and while the material is flowing i am planning to spray the liquid. This would save me on the investment as i have all the setup

thank you

 

[13thzodiac]

can i do this? what problems will i face?

 

[Compositepro]

The solution to your problem depends entirely on the properties or your materials and exactly what you want to accomplish. If your materials cake or are tacky your process may become difficult or impossible. It makes a difference whether you are spraying corn syrup or salt water.

 

[unclesyd]

I'll have to second the post by Compositepro as I believe you will plug your lines as in your original post you said it made a sticky mess. The mess will get conveyed with your product until it reaches a critical mass that will be virtually impossible to convey by air alone.

 

[NPKresults]

Coating Drums are an option often followed for granular material, you described the material as 'powder'. Can you tell us a little more about the material? particularly size? In addition to rotary coating drums you may consider a mixing screw conveyor or high intensity mixer of some sort especially if dust is a concern. Keep in mind that the finer you can get the coating spray the better, depending on the application you may want to use an air atomizing nozzle, etc.