Do anyone use a carbon filter on the exhaust

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Jan van Oel

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Jan 20, 2020, 10:45:02 AM1/20/20
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Hi All,

At our Makerspace we have a (huge) carbon filter on the Lasersaur exhaust.
We are looking to replace this carbon filter but due to its's size this is very expensive.

Do any of you use a carbon filter to reduce the smell of the fumes before venting them outside?
If so, what size carbon filter have you found to be effective.

Is there maybe an other option to reduce the wood burning smell.

Thanks for all advise.

Regards,

Jan van Oel

Danny Miller

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Jan 20, 2020, 10:59:35 AM1/20/20
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This is very high on my list.  I just brought in a 100W Universal X100 laser we'll probably leave set up as rotary-only.  As such, I expect mostly glass and some anodized aluminum.  But, some wood- I just don't expect a lot of volume.

Hard to run more exhaust.  So I'm thinking about a practical filter  to return air to the room.  This is a tall order.

As a Universal, they have those intake plenums, which are a flow restriction and many blowers really don't draw that sort of static pressure (manual says 6" of static but that's crazy more than it ever would create)

I'm wondering about a washable electrostatic or polyester tackified followed by HEPA and carbon.   I expect the prob being enough cost-effective capacity in the carbon part.

AliExpress had some interesting filter stacks:


Looks too small and special-order replacement filters.  But, I'm not sure.  What caught my eye was a "silver ion filter" as a 4th stage.  Sounds like a catalytic process, but I couldn't find much about it, so it may be a useless gimmick.

Danny 

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jet townsend

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Jan 20, 2020, 2:02:33 PM1/20/20
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This is what I use in my garage studio. It's fine for plywood, but with
acrylic some of the fumes leak from the lasersaur case, just enough to
annoy me. When I cut acrylic I open the garage door for fresh air, you
can't smell anything in the parking pad next to our garage.

why: http://www.flatline.net/journal/?p=333

how: http://www.flatline.net/journal/?p=341

I've had to replace the HEPA filter once every year or so, I mostly cut
baltic birch and paper.

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Danny Miller

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Jan 21, 2020, 11:52:51 AM1/21/20
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What type of filter and how big?  Like that inline HVAC one I saw was 300mm x 180mm filter elements.  I'm guessing that size would clog up almost immediately

Danny

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jet townsend

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Jan 21, 2020, 11:57:23 AM1/21/20
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There are links to the filter build instructions in those posts.
> > <mailto:janv...@gmail.com <mailto:janv...@gmail.com>>> wrote:
> >
> >     Hi All,
> >
> >     At our Makerspace we have a (huge) carbon filter on the Lasersaur
> >     exhaust.
> >     We are looking to replace this carbon filter but due to its's size
> >     this is very expensive.
> >
> >     Do any of you use a carbon filter to reduce the smell of the fumes
> >     before venting them outside?
> >     If so, what size carbon filter have you found to be effective.
> >
> >     Is there maybe an other option to reduce the wood burning smell.
> >
> >     Thanks for all advise.
> >
> >     Regards,
> >
> >     Jan van Oel
> >
> >     --
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> <mailto:lasersaur%2Bunsu...@googlegroups.com>>.
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> >   
>  https://groups.google.com/d/msgid/lasersaur/1c949f4e-a355-4e70-911d-b140829ba999%40googlegroups.com
> >   
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Danny Miller

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Jan 21, 2020, 12:10:44 PM1/21/20
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Help me out here... I'm looking through the flatline links and see a paragraph description, a demo video, but nothing else.

Started to wonder, wouldn't it make more sense to recycle the filter air right back into the laser cutter?  It'll give the filter more chances to scrub.  Like if you're only 90% effective at catching formaldehyde in one pass, instead of constantly dumping the remaining 10% at 600 cfm, you recycle it, formaldehyde levels inside the cutter increase only slightly, and at the end of the project you have the filter running a short while after the cut and only dump the cubic feet of air with a small % of remaining formaldehyde.

jet townsend

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Jan 21, 2020, 9:21:29 PM1/21/20
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https://www.instructables.com/id/Build-a-laser-cutter-fume-extractor/

It's arguably a particle filter, not a fume extractor. I have no idea
how much formaldehyde it pulls from the exhaust.
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Danny Miller

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Jan 22, 2020, 12:14:45 AM1/22/20
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Yeah I know that DIY site.  There is a carbon filter there which is all about adsorbing fume gases, not particulate smoke.

There's 4 parts I question here.  One, that's an expensive shop vac filter, and the carbon looks hard to change.  Two, the thing about fumes bypassing the carbon by simply going over it as it settles is totally going to be a thing.  Three, I have done a lot of long-term laser servicing and smoke tends to build up a lot of concretion on fan blades- so IMHO the fan must be *after* a smoke filter for practical long-term use, which would be a total redesign of the concept.

But what puzzles me more is Universal Lasers specifically have air plenums that require a very significant static pressure to get enough flow, much more so than any other laser.  By spec,"500 CFM @ 6 in static pressure" but that's pretty unrealistic (ok I think 6" is insanely high, you'd need a lot long long, undersized ductwork, but it does need some static).  They show a Fantech FG 6XL, an inline type which in my experience just goes into blade stall when presented with any sort of static pressure on the inlet.  What's weird is HE is showing a Universal Laser in his picture.  

The datasheet for the 6XL does show it can pull *some* flow under static, but that really shouldn't be able to draw sufficiently for a ULS.  Like datasheet says  289 cfm at 1" static, which is impressive for an inline, but still looks on the low side of usable performance, esp if you filter before the inlet.

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jet townsend

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Jan 22, 2020, 7:23:29 PM1/22/20
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On 1/22/2020 12:14 AM, Danny Miller wrote:
> Yeah I know that DIY site. There is a carbon filter there which is all
> about adsorbing fume gases, not particulate smoke.

But it's had no testing and there's no way to insure someone assembled
it correctly, so I wouldn't guarantee that it absorbs fumes. I'm pretty
happy with it for pulling smoke and acrylic fumes at 400CFM. I don't
recirculate the air in the filter because it's "good enough". OTOH, I
don't have students laser cutting all the things you shouldn't laser cut.

Where I work we use an OSHA-rated filtration system, no idea how much
they cost or who takes care of them.

Danny Miller

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Jan 22, 2020, 7:56:30 PM1/22/20
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There is a difficult question of what type of gas we're trying to adsorb.  Because I don't know, not even for common plywood/acrylic, but other plastics and paints.  There's two questions there.  One,  some gases are more adsorbable than others:


Also,  I was browsing a bulk supplier who had a number of granular carbon products that said "this one specifically is what you want for such-and-such gas".  So, I'm being told not all carbon is equal, maybe.  It could just be a vendor trying to push their products by declaring them special-use.
 

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jet townsend

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Jan 22, 2020, 10:57:48 PM1/22/20
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On 1/22/2020 7:56 PM, Danny Miller wrote:
> Also,  I was browsing a bulk supplier who had a number of granular
> carbon products that said "this one specifically is what you want for
> such-and-such gas".  So, I'm being told not all carbon is equal, maybe. 
> It could just be a vendor trying to push their products by declaring
> them special-use.

Probably. I'm using the generic carbon people use for fish tanks. It's
a bit like buying oxygen tanks, the ones we use for o/a welding and
flame work in the glass shop are almost free compared to the oxy tanks
for people to actually breath on a respirator.

Danny Miller

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Jan 23, 2020, 12:14:23 PM1/23/20
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Oh I did notice there are formaldehyde sensors boards (like for Arduino), and also VOCs, TVOC, benzene, CO, and ammonia are mentioned.   

I think formaldehyde would be the most likely toxic gas if you wanted to grade if a carbon filter was actually working, but there's a lot of chemicals which might be in exhaust which the carbon stage might miss and the sensor may not see.  

The VOC sensor might be a wider range of exhaust chemicals, maybe combined with the formaldehyde sensor?

I looked more into the silver ion filter stage- it's only purported to be for killing mold, bacteria, and viruses (of dubious value there).  Not catalyzing VOCs into something else.  Not likely to be useful for this application.


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Danny Miller

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Feb 2, 2020, 2:47:24 PM2/2/20
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Looked more into it, took some readings.  On a similar ULS with "good" airflow, I snaked a tube down the exhaust plenum into the 4" hose and hooked up a static pressure gauge.

I get 2.5" static pressure near the port.  That doesn't tell me what CFM I'm accustomed to, but if you don't reach 2.5" static at the port, it won't pull as much CFM.  I do sort of picture it as 300cfm but I don't know.

Comparing against the Fantech 6XL:


 Well that's not so great.  The static pressure chart shows it drops 60% by 1.5", to 100cfm.  So even without any filter, this can't reach the static pressure that pulls comparable CFM under any scenario.   So, I don't know if this guy removed the ULS plenums or it's a model that never had them, but the Fantech 6XL isn't an option for any of our ULS models.
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