How does corona discharge affect the performance of electrostatic precipitators?

[rollcast]

Though EE was the best section but if not I'll repost or get a mod to move it.

We were learning about Electrostatic precipitators that are used in power stations and the like to remove dust particles from the smoke they release.

However in the diagram that our teacher had it just showed the metal grid and then the plates above them.

And he said that the grid is positively charged and the plates are negatively charged and as the dust particles pass through the grid they become positively charges and are then attracted to the negative plates where they lose their charge and fall down.

Now I've seen these things before at a trade show my dad took me to and at the trade show the demonstrator was talking about positive corona discharge around the plates and the effect it has of ionizing the air and dust and then its attracted to the negative corona around the plates.

So I said to the teacher and he basically said that no corona discharge should occur as there should be no arcing between the grid and the plates?

 

[Mike_In_Plano]

It's best not to correct your teachers, but I think he's probably wrong on this.

Just because there is a corona discharge, that doesn't mean an arc will start. A surface that experiences a sudden change in field strength is subject to corona discharge. For example, a needle point, or a thin piece of wire when charged with a high voltage will start a corona. You can see it by turning out the lights and looking for a faint blue glow. Typically, you can smell a bit of ozone as well.

With the corona will come prodigious quantities of ions that will attach to particles which are in turn attracted to surfaces (not necessarily charged surfaces).

If you look at air cleaners / ionizers in stores, you can often see needle points or bristles that accomplish this function. In a copy machine, it is a thin piece of wire.

There's more under heaven and Earth than encompassed in your prof's philosophy :-)

- Mike