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Electrostatic Charges in Pneumatic Flour

03/17/2021 2:56 PM

I face an issue that some electrostatic charges appears in sight glass on pneumatic flour blow line and when put electric tester screw driver near the glass is lighted.

Also with small hole in the sight glass some charges come the metal out.

Does this dangerous and how to avoid it?

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#1

Re: electrostatic charges in pneumatic flour

03/17/2021 3:08 PM

Yes this can be extremely dangerous, you need a real earth static grounding system in place right away...

https://www.powderbulksolids.com/explosion-protection-safety/how-eliminate-electrostatic-charging-powder-processing-equipment-0

..."In food processing, a range of powder or bulk solid products can combust, including grains, flour and sugar. One of the key factors in determining the risk for dust explosion is the product’s sensitivity to static electricity discharge in specific concentrations and fuel-to-air ratios, as well as its sensitivity to ignition in ambient air or processing conditions.

In general, static electricity can ignite a combustible dust cloud inside a food processing conveyor system if the minimum ignition energy of the dust is very low. Powder and dust conveyed at high speeds through metal pipes or ducting can build up an electrostatic charge in the dust and potentially ignite. Because static charge can accumulate at different points in the system, the equipment should be fully grounded so it does not discharge into the line."...

https://www.processingmagazine.com/material-handling-dry-wet/conveyors/article/21213027/food-processing-selecting-a-conveyor-to-minimize-dust-explosion-risk

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#2
In reply to #1

Re: electrostatic charges in pneumatic flour

03/17/2021 4:22 PM

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#7
In reply to #1

Re: electrostatic charges in pneumatic flour

03/18/2021 8:47 AM

If you are considering igniting of flour or any poweder dust within the conveying pip9ing you have to design the (final) diust bin or conveying air filter with a venting hatch such allowing the pressure and flame relieve from the system in such a manner that there will not be a to high reaction force to the conveying or filter system, but allowing the flame allways to go out from the housing without and restriction .

best regards from Vienna

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#3

Re: Electrostatic Charges in Pneumatic Flour

03/17/2021 4:54 PM

Yes, it is <...dangerous...>. The material <...flour...> has the capacity to explode in air.

An inert atmosphere, such as 100% nitrogen, can prevent catastrophic self-disassembly of equipment, environmental damage, business disruption, injury, and loss of life.

Google "dust explosions" for more information.

There are videos on the topic readily available on YouTube.

The remedy sounds like a job for a specialist.

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#4

Re: Electrostatic Charges in Pneumatic Flour

03/18/2021 7:20 AM

That might become really very dangerous. I have had a pneumatic powder mixture, where the discharge did not happen. And the roof of this facility lifted up.

I have used a copper strip with an adhesive which can discharge electric charges and is then connected to an earthing rod. Similar mkaterials is used at the fuselage tip of earcraft.

regrds from Vienna, Austria Josef

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#5

Re: Electrostatic Charges in Pneumatic Flour

03/18/2021 8:04 AM

I would check your conveying line tube grounding cable (or cables plural if on both sides of the site glass) and make sure you have a good connection to the tube and the ground rod (assuming there is no issue with the rod itself). If you have a single ground strap on only one side of the conveying line, the site glass will act as more of an insulator than conductor. If the site glass is connected to the metal tubing with a Morris style coupling, there is a gasket underneath the coupling that acts as a clamping assist which insulates the metal and prevents continuity if the tube is grounded on only one end. To get grounding continuity to the downstream tube, there is a flat metal strap that runs along the inside of the coupling from end to end and is folded over to contact the coupling and captured tube ends which sometimes goes awol (see pic). The powder will electrostatically cling to the site glass to some degree even with the correct grounding. Also, if you have more than one site glass or multiple clamps, all the tube sections need to be ground connected and any of the couplings should be considered suspect.

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#6

Re: Electrostatic Charges in Pneumatic Flour

03/18/2021 8:05 AM

The problems with static discharge arrangements are:

  • The materials involved in collecting static electricity are not conductive, and
  • Introducing static discharge equipment makes the chances of a spark more likely; it's like putting a lightning conductor on top of a tall structure in that it makes a lightning strike more likely - as evidenced by the original poster's <...electric tester screw driver near the glass is lighted...>.
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#8

Re: Electrostatic Charges in Pneumatic Flour

03/18/2021 9:51 AM

As a mechanical reliability Engineer I work with these folks all the time. We handle yeasts, Sugars, and other nasty go boom stuff that generates dust. These guys go big.

https://www.donaldson.com/en-us/

Even the smallest area, a lab, has a Tigervac explosion proof vacuum as its dust mitigation system.

Please understand, this is not something to screw around with. A mistake not only kills people but destroys your industry. literally.

https://www.bing.com/images/search?q=dust+explosions&form=HDRSC3&first=1&tsc=ImageBasicHover

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