Electrostatic precipiation of dust

[greybeard]

I've just returned from visiting a wood worker who shows all the symptoms of the problems that fine dust hanging in the air of the workshop produces, both in the shop, and in himself.
He mentioned that he had recently seen in a UK trade fair an electrostatic precipitator for dust removal. We both know that this is an oldish idea, but it seems to have resurfaced in the workshop environment.
Has anyone come across this recently, or has any ideas about the possibilities of using this.
I would emphasise that this would be for the removal of sub-micron sized dust particles, the bits that hang in the air for days and cause most of the problems.
We had a quick brainstorming session, and our two heads managed to come up with an idea for how to produce a diy version, but other input would be welcome.

John

"Like doing jigsaws in the dark."

[HuFlungDung]

I use such a device in the welding area of my machine shop to remove smoke from the air. The technique is effective, but works best if you can position the intake right near the source. Our commercial unit is portable and has an 8" flexible overarm which is self supporting. I think it was about $4000 Cdn, a few years ago when I bought it.

The collection plates must be about 10" x 16" at about 1/2" seperation, stacked 18" high.

The charge plates are only maybe 2.5" wide, and the ionizing wires are about 2" seperation, as are the plates.

The charge plates and the collection plates are built as slide in drawers, so you can pull them out and wash them. I think they are of galvanized construction.

[trilect]

I do contract work on the "BIG" precipitators at paper mills on occation, just be careful about the voltage you use in your unit. I wouldn't want a hot spark inside a chamber full of flamable dust.

Big units have a spark arresting code built in the controller, when a spark is detected it ramps the voltage down to the collection plates until the ionization path disperses then ramps the voltage back up.

I'm sorry, I'm in DIY mode today, I misread your post thinking you where going to build one.

[ViperTX]

Okay....so most air filter...well the woodworking type collect down to 1/2 micron size particles.....if you then replace the air in the workshop...ventilate the shop....you shouldn't have any problems except with airborne allergens....

[greybeard]

HFD - many thanks for the idea of comparing it to smoke precipitators. That's definitely a good analogy to concentrate the ideas on what the problem is like.
We were wanting to cope with these really tiny particles. Even 0.5 - 1 microns may be filtered by the best systems, but it's all the rest downwards in size that are worrying us.
Your details of the set up parallel our initial ideas, so we were heading in the right direction !

[greybeard]

Re the dangers from sparking - obviously a problem to be seriously considered, but I think by keeping the voltages down to the minimum to produce corona disharge, the principle of the device, I would thing the possibility of any sparking could be minimised.
The idea of dropping the voltage immediately a spark is detected sounds great, but I wonder if that is then too late !
Or would the idea be to stop whatever conditions are causing the sparking to collapse, then the normal conditions could resume ? But thanks for raising the issue.

Re air input to the workshop. This was my first thought - to keep recycling the air through a filter as an extra as well as the normal extractors on the individual machines.
Something along the principle of an air conditioning unit, but removing dust insted of moisture.

[Corvus corax]

The workshop type ceiling hanging filters are actually quite effective in my experience, There are quite a few out there for reasonable money. Woodshop particles are rarely under 0.25 micron in size, unless he is working with stone or metal, he is unlikely to see anything smaller. Excepting smoke particles. Electrostatic precipitators are rarely used in workshop environments, because of the ever present danger of ignition. I worked in a medium sized woodshop in St. Petersburg, and one day, when the sanders were first set running, there came a very loud roaring noise, like a pulse jet engine being started. It was a steady drumming and booming noise, punctuated by brief eruptions of yellow flame from the overhead dust collection junctions, leading toward the 20HP collector on the other side of the building. The static electricity created by the air motion was igniting the fine dust created by the belt sander. A series of ground leads was hastily wrapped around the PVC pipes that day, and the problem disappeared. Wood dust ignites easily!

[trilect]

Originally Posted by greybeard Re the dangers from sparking - obviously a problem to be seriously considered, but I think by keeping the voltages down to the minimum to produce corona disharge, the principle of the device, I would thing the possibility of any sparking could be minimised. The idea of dropping the voltage immediately a spark is detected sounds great, but I wonder if that is then too late ! Or would the idea be to stop whatever conditions are causing the sparking to collapse, then the normal conditions could resume ? But thanks for raising the issue.

Thats what we do in large precips, unfortunately over time we get build ups of material on the collector plates even while using mechanical or magnetic rapper systems to dislodge the buildup.

They do the same thing in Wet precipitators, I've never seen the inside of a wet precip though and I'm not exactly sure how they work differently than dry precips.

[Mcgyver]

isn't the issue the time and circulation required to remove the dust? those ceiling mounted filter units supposedly remove the small particles but if it takes 6 hours to do so, there's not much of a health savings. If you don't want to wear a mask, you need dust removal in real time as its coming of the machine, and as per the other thread, home shop set ups (as most don't vent outside) that do so seem to be very rare.

[greybeard]

Mcgyver - good point about the time factor.
More background re the actual setup I'm trying to improve.

He does wear a full face air stream mask during work, and it is the belt sander which is the major problem, which might be in use for several hours at a time.
His isolated location allows him to run a filter all night, so we reckoned that would take care of the real time aspect. I've made several suggestions to him regarding the design of his air ducting system to increase the actual air flow and air speed.
As I've not made any measurements of the particle sizes, I don't want to be pedantic on that score.
But certainly any commercial equipment I've seen in other workshops, is always covered in fine dust, along with all other surfaces in the shop. I've made extensive reading of a site that was set up by someone who devotes himself to this topic, and he makes a good case for more work to be done(sorry I can't find a link).
However his approach is to redesign the cyclone extractor to cope with a wider range of particle sizes. I would be more interested in a secondary system, separate from the main filter.

[greybeard]

Just found the link - www.billpentz.com - click on "dust extractors and cyclones"

[Imagineering]

Just a quick thought on this one - Do you guys remember the Van der Graaf generators from your schooldays? Instead of powering your dust extraction device electrically, it could be feasable to use the VdG system using a perspex Ball/Plate which is charged electrostatically by a friction belt.