Using buildings to enclose dry screening processes look like a good idea on the outside, but on the inside, it seems like there is one big mess.
If you are in colder climates where temperatures are well below freezing, the challenge becomes even greater. Attempting to heat the building while a baghouse system is sucking dust and heated air from inside the building and exhausting the heated air outside the building seems insane.
Does anyone have any suggestions, as to how to control dust within dry screening structures?
There are several things you can do. First, examine operations. If there interruptions in process flow or the system is operating under capacity, dust emissions will be aggravated. Keep the equipment running consistently at design capacity.
Second and more importantly, examine engineering practice. if there are a lot of leaks in chute, poor skirt seals, etc. these will allow dust to escape and also cause spillage that causes dust when workers have to clean it up. Button up the system as much as you can by enclosing transfer points, repairing belt skirting and covering the screens. By enclosing the system you can decrease the investment you have to make in more expensive wet suppression or dry collection systems.
Housekeeping is also real important. Dust deposition accumulated on structural members becomes airborne due to vibration caused by production equipment. This will cause dust up in the rafters or dust that has settled on equipment to become re-entrained. I know some plants that washdown the interior or have installed vacuum systems that workers can use.
Once you've done the above. You only have two choices - use a wet suppression system or go to dry collection. There are two types of spray systems that might be useful. The first would be a conventional system designed to add some moisture to the stone to keep dust down. The other would be a fog system installed in the ceiling that would be used to settle dust within the building. Lots of trash transfer stations use fog systems like this. Problem is winter operation and the only way to consistently use a wet suppression system in freezing weather is to heat tape and insulate spray lines and that can ruin $20 to $30 per foot.
I'm surprised that you have problems with using dry collection (baghouses). I would have thought that they would be the best option. I can only quess that you've encountered freeze problems with dust sitting in the hopper making it difficult to unload. Heating the hopper rather than the entire building might be more cost effective. If the building has to be heated, I suppose you could put a heat exchanger in the fan exhaust to recover some of it and return it to the building.
Hope this is helpful.