Anyone have experience with this? Where I work we have alot of dust collector fires. Our collectors are connected to shot peening equipment. Occassionally, I am guessing a spark is sucked into the collector and lighting the filters on fire.
We have sprinklers in the machine but we would like to stop it from happenign all togther. (Every time the sprinkler goes off the fire department is notified). needless to say the fire department is not happy with us.
Is this happening when they're cleaning certain metal items in the peening bays? Many packed powdered metals are highly reactive, especially when mixed - Thermite is ideally ~75% powdered iron and ~25% powdered aluminum, and it burns /really/ good and *very* hot, and it provides it's own oxygen for the reaction...
You need to neutralize the conditions that would set the mixture off, like reaching a critical mass, heat and static charges. I do NOT work in that industry, but that's never stopped me from passing on a decent idea before... ;-P
Silly Wild-ass Guess Idea #1: Try putting a few water misting heads (like they use on outdoor patios) spraying into the inlet airflow? Add just enough moisture to cool off hot bits going in (without making mud) and the moisture should cut the static electricity levels. Link the mist water solenoid to the fan motor contactor, so they run with the fan motor.
Silly Wild-ass Guess Idea #2: A dispenser for metering some powdered limestone or something else that would keep the powder from igniting as easily, into the incoming airflow to the cyclone and bag tower.
A simple screw augur feeder from a bulk hopper, and a variable-speed drive motor on the feed worm to meter it in during the day.
I picked powdered limestone out of my (tuchis) because they spray it around in coal mines to reduce the fire hazards there. One of the chemistry wonks here can probably come up with something much better suited for the purpose of breaking up the thermite reaction that your factory can buy cheap in bulk.
Like bulk sodium bicarbonate (baking soda - Class BC extinguisher powder) or a mix of ammonium phosphate and ammonium sulphate (Class ABC extinguisher powder). Class D extinguisher powder is finely ground sodium chloride - table salt - but that might create rust problems.
Adding a moderator powder to the waste stream would add to the bulk and slightly increase the disposal cost of hauling off what you collect in the bag farm. But if you can stop the fires before they ever start that's a *very* small price to pay.
Could be static electricity igniting the dust initially, once alight its gets the accumulated dust particles smoldering away until you have a full blown fire in the collector system.
Static is often a problem in dusty workplaces - flour mills used to be a classic for static flash fires until they worked out that extracting dust was safer. Do a weblookup on controlling static, easiest way is to earth out collectors, etc. Its made worse if you multiple dust types and varying pipe dimensions, varying pipe materials, also the more disturbance in the air flow the greater the build up of static charges.
Quick and dirty check for static is to go touch part of the system whlist holding an earthed out piece of metal. If you get a zap theres static in the system.
| Silly Wild-ass Guess Idea #1: Try putting a few water misting heads | (like they use on outdoor patios) spraying into the inlet airflow? | Add just enough moisture to cool off hot bits going in (without making | mud) and the moisture should cut the static electricity levels. Link | the mist water solenoid to the fan motor contactor, so they run with | the fan motor.
That seemed like a good idea for a minute until I realized that moisture and metal equals corrosion, and being that there's so much surface area it'll corrode really fast. Piles of damp metal powder corroding quickly gets really hot, and if not cooled down will go into meltdown, then possibly fire, which would be a then be a real mother to put out. Now if you had a non-reactive coolant, that might be another story. Metal damp with anything might not get so much from the scrap yard as dry stuff, though.
We deal with a lot of fine, water-reactive metals in the pyrotechnics business. The common wisdom is to _flood_ the reactants with water, rather than simply misting them.
Creating very fine metal dusts abrasively always invites ignition. Many metals, and some organic compounds and elements will become pyrophoric (ignite upon contact with air) as soon as they are divided into sub-micron sized particles. I've personally witnessed 2-micron magnesium ignite simply by fluffing up the powder in air. Sub-micron titanium is horrific stuff.
Our dust collectors capture particles on filters being continually flooded with a sheet of water. The material is plumbed away and allowed to react in a large volume of water. Then the sludge is sedimented, dried, and disposed of in a suitable manner, if it cannot be reprocessed.