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Ozone-free electrostatic dust precipitator?

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LAN_403

Dr. Slack

Mon Oct 12 2009, 02:59PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

I'm doing a bit of building work, and my wife is getting fed up with dusting the surfaces daily for a month after a "big dust" event. I have a tendency to asthma as well, and don't get on too well with particulate pollution hanging around for weeks (I use an industrial breathing filter during). I figure a few corona wires in a carboard box with a PC fan ought to be able to reduce the dust load in the air faster than natural fall-out. However, improving the dust levels while creating ozone for a month is not going to do my chest any good.

The main question is, is there a tip radius, and a voltage, which will give good particulate charging while keeping ozone levels negligable? Or is there a cheap and effect way of scrubbing ozone from the exhaust.

I've been Googling, and found lots qualitative information, or expensive solutions, but not yet hard information for what works. Does anybody have any experience, or pointers to relevant sites?

I see that industrial precipitators use the maximum voltage they can, increase until they spark, then back off a bit, so that doesn't help. I understand ozone will react with carbon, even at room temperature, but how fast? Will running the exhaust over a few barBQ briquettes take any appreciable amount of O3 out? I sort of assume that minimum point radius (dress-making pins) to get corona with minium applied volts will result in the least ozone, but is there a voltage threshold? KI reacts with O3, the iodide becoming iodine.

Those boxes on the ceiling that pubs used to use to clear the smoke from the air before the smoking ban rendered them redundant, what balance of voltage and geometry did they use? Did they generate ozone anyway, and assume that exposure was going to be limited to a few hours a day?

3l3ctrici7y

Mon Oct 12 2009, 03:25PM

Registered Member #1806 Joined: Sun Nov 09 2008, 04:58AM
Location: USA
Posts: 136

I think the key is to have the voltage below the threshold at which O3 is produced, but dust precipitation continues; and then do this over a large area.

Take a CRT for example; they get a coating of dust on the face due in large part to the static charge, but produce no ozone (that I aware of).

Perhaps; have a duct or such that has many parallel plates (Al foil clad cardboard?) that are strongly (but not excessively; O3 producing) charged, and a fan to circulate the room air over them.

I think the large collector is usually not done because large==$$.
It may also be necessary to clean it often to maintain cleaning effectiveness.

Proud Mary

Mon Oct 12 2009, 11:09PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

A pleated vacuum cleaner or automobile air filter impregnated with manganese dioxide as a catalyst will turn the ozone back into ordinary oxygen, as well as remove any particulates which have escaped the electrostatic trap.

Ozone will be produced inside the trap in much greater quantities at any points of small radius where coronas form. So keep all edges rounded, avoid roughness, do not use a single wire, and so on.

I believe many electrostatic air scrubbers use vertical plates, so that when the power is momentarily interrupted, all the dust will fall down into a collector at the bottom.

IntraWinding

Mon Oct 12 2009, 11:13PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

I started working on a home made electrostatic precipitator to both improve cooling and prevent dust build up in my PC, but half way through fear of ozone drained my enthusiasm, so I'm also very interested if there's a good solution to this.

I can tell you that the first step is to use the correct dc polarity between your corona wires and your nearby earthed plates as one way makes more ozone than the other.
A less obvious trick they have is to use a thin gold coating on the corona wires. Apparently the gold has a catalytic effect. I think I also remember a design incorporating silver metal in the corona generation area for similar catalytic reasons.

All designs use taught very thin tungsten wires rather than sharp points. Another problem then needs to be solved as the wires start to vibrate which eventually breaks them. There are various patented solutions to this but I believe a simple solution is to to just thread your corona generator with two lengths of corona wire instead of one, although officially they need to have a small gap between them for the vibration damping physics to work. I haven't tried it yet though. I got my gold plated corona wire as a photocopier maintenance product by the way.

Since those pub smoke scrubbers exist I assume the ozone problem was solved but I suspect that relied on having a way to measure the ozone output as they tweaked the design.

I still plan to build the precipitator but I'm not sure I'll ever risk sharing airspace with it for extended periods without some very good reason to believe it's safe.

...

Mon Oct 12 2009, 11:21PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

There is another thread on 4hv about this exact same topic at

, where it was explained that you need to avoid sharp edges, and have a lot of surface area. Check it out.

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