Fires - Smelting Process

First we must be careful to find out if the fires are a result of ignitions by a spark. All these acids mixed with carbon can spontaneously ignite, especially if the precious metals include catalysts, such as vanadium, like they use in catalytic converters. Or, they get fires when they are in the ten hour mode? My calculations indicate that during the ten hour precious metal mode they are basically diluting the exhaust to meet discharge requirements into the atmosphere.  To discharge from the hood at 125 degrees they either need a lot of dilution air or water vapor. For 30 hours a week, they use it as a trash burner. Here again they seem to be trying to hide the true nature of the operation. In the trash burning 30 hours they probably have wild swings in emissions which might ignite poorly combusted components and would be ignited by sparks in the baghouse. I would hate to live downwind during either operation. You need to find out the following.

1.  Do the fires occur while operating?
2. Do fires occur when they are shut down?
3. What are the temperatures in the ducts over a 60 hour period?
4. If they run 8 hours a day do they run 2 hours on smelting mode and six hours trash mode?
5. Do they insulate the duct?
6. What is the charge to the smelter? Coins? scrap gold, scrap silver? perhaps catalytic converters?.
7. It seems like they would have a severe corrosion problem and preheating of ducts should be considered.

We can put out sparks with Quencher^tm spark arrester but we cannot remedy poor control.

The ten hour mode is the ten hours per week when they are smelting. The 30 hour mode is when they are trash burning. Get a piece of bag to examine. It will be obvious if it has been chemically attacked. You should be able to tear or burst a piece with pliers and a vise. 

For more on spark arresters, see  QUENCHER spark arrestor