Water Filtration Dust Collection?

[Alan Schaffter]

I hate to burst the bubble (pun intended)- it won't work!!

Many prohibitive problems-

First, as a few mentioned whatever type of system- bubbler or centrifugal system- a significant amount of dust, especially fine dust, will not be captured, either because it is in a bubble or just not in contact with water. Hukah, farts in a bathtub, boat exhaust, etc. etc.

You will catch some dust but have a terrible mess- a (big) tank of dirty water to dispose of. It would be absolutely imperative to have a standard cyclone to remove the heavy dust and chips first or you will have a terrible soggy mess that would weigh many times what dust and chips alone would weigh. Picture dumping that vs dumping a dust bin!

Lastly, you are all forgetting how a DC works and principles of air flow. You want to collect dust at the source so you don't breathe it while standing at the source!!! For that you need a lot of CFM - as much as 600 CFM for some woodworking machines. If you add some sort of water filter you will be adding a prohibitive amount of static pressure resistance, and therefore killing CFM!!! Unlike a shopvac which will pull 80"-100" of water (but only 100-200 CFM), typical DC's with their material handling blowers only pull around 10" of water- that means if you try to use a DC with bubbler and a big drum of water, you will kill ALL CFM if it is deeper than 10"!!! If you use a shallow drum less than 10" deep you still limit CFM, plus you would be making one heck of a mess as the bubbles splash everywhere!! - picture a little kid blowing air through a big straw into his glass of milk!!!

Rather than trying to find a way to filter all the dust from the air, find a way to discharge it outside without a filter.

If you don't need CFM and can wait for the air to be cleaned (think ambient air cleaner) AND have decent SP suction (most air cleaners don't) to pull the air though a wetted filter media, it might capture fine dust better than a dry filter. However . . . then you need to figure out how to clean and reuse the filter. Ventilation filters on Navy ships were made with thin metal mesh media (picture Brillo pad) that was sprayed with oil to help it capture the dust. After the air cycled through the filter many times it eventually captured a reasonable amount of dust. They didn't do a good job filtering but any dust caught in the oil stayed there until the filter was removed and cleaned in a bath once a week.

[phil harold]

one word that makes me scared of water filtration of wood dust would be:

MOLD

[Jarrett Vibert]

Any that feel water filtration doesn't work, should do what I suggested in my first reply, and google "wet air scrubber". The tech is in use, and does far greater filtering than possible with a standard dry fiber set up. In fact the advanced systems are in use to pull hazardous vapour from the air, and filter .01 micron without breaking a sweat. So somehow, I think a basic set-up could manage to deal with some .5 micron saw dust.

I won't waste the bandwidth by explaining again how it's done, but there are no bubbles involved, and the mess would be compairable to a couple of tablespoons of dust in a bucket of water for the hobbiest WW. Of course adding anything to a DC system will increase it's operating SP, (ie: pipe, bends, filters, reductions). However an actual "scrubber" only sprays a fine mist into the air path, and doesn't force the air through a body of water. I'd wager a 1 or lesser micron filter would effect your CFM in a more negative manner. Not to mention the complete lack of the needed "seasoning" to achieve optimum performance that dry filters require.

Yes I do believe a well constructed/designed cyclone with a large impeller would be needed to use a "scrubber", but the only real issue is humidity. Pulling an acceptable amount of moisture out of the air before introducing it back into your shop is the real design challenge.

[Alan Schaffter]

Any that feel water filtration doesn't work, should do what I suggested in my first reply, and google "wet air scrubber".

The big difference, most air scrubbers, like you descrive and those in laboratories and secret underground facilities (which I have seen up close) can operate at much less CFM since they aren't trying to keep you from breathing wood dust spewing from a woodworking machine. They can afford to have much higher SP too.

I won't waste the bandwidth by explaining again how it's done, but there are no bubbles involved

That proposal has been made before in this and other threads so thought I'd kill that one too.

The mess would be compairable to a couple of tablespoons of dust in a bucket of water for the hobbiest WW.

Only if an efficient pre-separator were used.

Of course adding anything to a DC system will increase it's operating SP, (ie: pipe, bends, filters, reductions). However an actual "scrubber" only sprays a fine mist into the air path, and doesn't force the air through a body of water. I'd wager a 1 or lesser micron filter would effect your CFM in a more negative manner. Not to mention the complete lack of the needed "seasoning" to achieve optimum performance that dry filters require.

I disagree. If you inject water, you are adding positive back pressure to the system. All the apparatus, and physical design that can inhibit air flow will add much more SP than you think. It must combine the air and water spray so the particles are captured by the water and that likely requires considerable air and water pressure not available in a DC system. The SP resistance of fine filters is not bad if you have enough filter surface area. Seasoning a filter is a joke! With woodshop dust collection, it is a lose-lose situation- you are intentionally clogging the filter so it filters better!!! At the same time you are reducing system CFM so not capturing the dust at the source!!! Don't do it!! This is one reason I (and Bill Pentz and others who understand dust collection) recommend discharging outside if at all possible. Also, there is a reason that these special air scrubber/filtering systems cost thousands and even millions of dollars.

Yes I do believe a well constructed/designed cyclone with a large impeller would be needed to use a "scrubber", but the only real issue is humidity. Pulling an acceptable amount of moisture out of the air before introducing it back into your shop is the real design challenge.

... and cost and complexity. As I said, too many negatives- it just won't work and would be complex and cost prohibitive for a home DC setup.

[Jarrett Vibert]

The big difference, most air scrubbers, like you descrive and those in laboratories and secret underground facilities (which I have seen up close) can operate at much less CFM since they aren't trying to keep you from breathing wood dust spewing from a woodworking machine. They can afford to have much higher SP too.

I've never been in a lab or even know of any secret underground facilities, however we had a scrubber in my old plant that moved a ton of air. It was used to capture fine dust being spewed off of a rice hull drying process. That air was pulled into the scrubber via a hood hung over the dryer, cleaned, and exhausted right back into the plant. Extensive air quality tests were done, and all was within standards for employee exposure without the need of further breathing apparatus.

That proposal has been made before in this and other threads so thought I'd kill that one too.

Shame... It's valid approach to air filtration. But I guess it goes against the norm and ease of thought, so why embrace the possibility.

Only if an efficient pre-separator were used.

Which is exactly what I stated eariler... (re-read or read my first post)

I disagree. If you inject water, you are adding positive back pressure to the system. All the apparatus, and physical design that can inhibit air flow will add much more SP than you think. It must combine the air and water spray so the particles are captured by the water and that likely requires considerable air and water pressure not available in a DC system.

Pretty sure I did say that it would effect SP, but like you, I honestly have no idea how much it would... It would obviously take creating such a beast and applying real world testing to fully understand. However the added SP would be constant, and wouldn't change to due filter life/use. ...Oh and you'd never have to replace a filter.

...snip... This is one reason I (and Bill Pentz and others who understand dust collection) recommend discharging outside if at all possible. Also, there is a reason that these special air scrubber/filtering systems cost thousands and even millions of dollars.

... and cost and complexity. As I said, too many negatives- it just won't work and would be complex and cost prohibitive for a home DC setup.

No disrespect, but it doesn't take a brain surgeon to know blowing the hazardous air away from where you are is the best idea. However when that suggestion isn't a consideration, (again see my first post) and you need to reuse your DC exhaust, compromises must be made. An adequately sized blower (16-1/2 x 4-1/2) can still reach Pentz's recommended 1000cfm at a SP of 18". As far as cost goes, well it certainly wouldn't be cheap, but I can build Pentz's design for the cost of materials or shell out ~$1600 and buy from Clear Vue.

To recap:
Costly...yep
Complex...most likely
Cost prohibitive...considering the potential .vs. retail DC options, which would need additional overhead air cleaning..I'm not sure

So far I haven't seen anything in this thread that would lead me to believe that it wouldn't work. In fact it's a proven method in industry. Mr. Pentz managed to shrink the cyclone down to useable size for hobbiests. So I don't see why at this point the "scrubber" couldn't also be. Again, the only real hurdle to making it a viable concept, is pulling enough moisture out of the exhaust to minimize the humidity the system would cause.

I'll also have to disagree about it's hobbiest's potential. IMHO, this is the only arena were it makes sense. Sure if one was starting from the ground floor, and was being subjected to a continous cycle of design/build/test/scrap/ rinse and repeat, it would be far too cost prohibitive. However I wonder how much time/$$$ Pentz spent perfecting his design.....? ...and if the scrubber design was out there free to use (exactly like B.P. cyclone is), and was simple enough that the average joe could build it himself. Why wouldn't you do it...?

Maybe I'm just too much of an optimist.

[Alan Schaffter]

I've never been in a lab or even know of any secret underground facilities, however we had a scrubber in my old plant that moved a ton of air. It was used to capture fine dust being spewed off of a rice hull drying process. That air was pulled into the scrubber via a hood hung over the dryer, cleaned, and exhausted right back into the plant. Extensive air quality tests were done, and all was within standards for employee exposure without the need of further breathing apparatus.

And I'll bet it was a beast that cost $$$$$$$$$$$. Were workers standing right in front of the machinery like woodworkers do?

Shame... It's valid approach to air filtration. But I guess it goes against the norm and ease of thought, so why embrace the possibility.

Valid, just not practical for home/hobby shop. Not against any norm, against engineering, performance, and cost. It doesn't take much understanding of the engineering involved to see what is required to ensure consistent and reliable air-water contact such that particulates will be captured before the air is returned to the shop. The size and cost of it would be well beyond what is acceptable to home/hobby woodworkers. The impact on CFM alone would require a relatively massive DC and the size of the scrubber!!!

Pretty sure I did say that it would effect SP, but like you, I honestly have no idea how much it would... It would obviously take creating such a beast and applying real world testing to fully understand. However the added SP would be constant, and wouldn't change to due filter life/use. ...Oh and you'd never have to replace a filter.

We agree here. You can get a very rough idea of the possible SP resistance and impact on CFM if you look at the tables for ducting, fittings, and filters.

One thing we haven't addressed- water. Unless you have special water filters/separators (more complexity and cost) that will allow you to reuse your water, you will be pumping an awful lot of water down the drain- considerable cost again.

No disrespect, but it doesn't take a brain surgeon to know blowing the hazardous air away from where you are is the best idea. However when that suggestion isn't a consideration, (again see my first post) and you need to reuse your DC exhaust, compromises must be made. An adequately sized blower (16-1/2 x 4-1/2) can still reach Pentz's recommended 1000cfm at a SP of 18". As far as cost goes, well it certainly wouldn't be cheap, but I can build Pentz's design for the cost of materials or shell out ~$1600 and buy from Clear Vue.

I would like to see the specs and fan curve for a system with 16.5" blower that moves 1000 CFM at 18" of SP!

If you can find a a big surplus motor/blower, or a big motor and build a blower (carefully dynamically balanced) you can get by for much less than $1600. My last cyclone, a 3D version based on the Pentz design cost me less than $60 to build while my used 3 hp/14" impeller motor/blower unit was less than $250:



(The picture isn't distorted- unlike many cyclones whose cone is 1.64 times the diameter of the cylinder, the length of my cone is 3 times the diameter of the cylinder (hence 3D). It is also configured as a "push-through.")

I've been at this for a long time, almost as long as Bill (and Jim Halbert before him) who I have corresponded with regularly over the years. If you want to see a video tour (slides and video) of my DC system go to this link. It focuses on my autogates but includes info on the whole system.

To recap:
Costly...yep
Complex...most likely
Cost prohibitive...considering the potential .vs. retail DC options, which would need additional overhead air cleaning..I'm not sure

So far I haven't seen anything in this thread that would lead me to believe that it wouldn't work. In fact it's a proven method in industry. . . .So I don't see why at this point the "scrubber" couldn't also be. . . .I'll also have to disagree about it's hobbiest's potential. . . . Sure if one was starting from the ground floor, and was being subjected to a continuous cycle of design/build/test/scrap/ rinse and repeat, it would be far too cost prohibitive. . . . and if the scrubber design was out there free to use . . . and was simple enough that the average joe could build it himself. Why wouldn't you do it...?

Maybe I'm just too much of an optimist.

As proven, the engineering works, but on a large scale, and due to fluid dynamics is not likely to change. The engineering limitations and all those problems, but size and cost being the most important, combined with a limited market, will likely keep an effective scrubber system out of the home workshop.

The most cost effective measure and most effective measure outright is to get a good mask, either filter or supplied air. Next best is a DC with a lot of CFM and discharge outside.

[Jarrett Vibert]

And I'll bet it was a beast that cost $$$$$$$$$$$. Were workers standing right in front of the machinery like woodworkers do?

No, the dryer was quite large, and would quickly fill that particular section of the plant with dust when that scrubber shut down for any short period of time. I couldn't comment on it's cost, but do know we were forced to purchase it because of air quality concerns with the use of standard dry filters.

One thing we haven't addressed- water. Unless you have special water filters/separators (more complexity and cost) that will allow you to reuse your water, you will be pumping an awful lot of water down the drain- considerable cost again.

^^^this goes hand in hand with the separation problem I keep commenting on. Pulling that vapourized water back out of the air stream is the real challenge. Of course if you efficiently could, your wasted water would be minimal.

I would like to see the specs and fan curve for a system with 16.5" blower that moves 1000 CFM at 18" of SP!

I have no curve to post, but can direct you to the same Cincinnati Fan table Mr.Pentz uses in his calculations. The blower in question, is a model I currently have in my possession.

http://www.cincinnatifan.com/catalog...2-internet.pdf

page #9... Model PB-15A... 16-1/2 x 4-3/8 (second from the bottom)

I did take a liberty and rounded up to 1000cfm at 18" from 988....

If you can find a a big surplus motor/blower, or a big motor and build a blower (carefully dynamically balanced) you can get by for much less than $1600. My last cyclone, a 3D version based on the Pentz design cost me less than $60 to build while my used 3 hp/14" impeller motor/blower unit was less than $250:

That was kinda my point in mentioning the diy approach. Yes out of the gate expense for development of the design would be costly. But like you and others, that have benefited from Pentz's leg work the bottom line can be quite minimal after the R&D has been completed.

If you want to see a video tour (slides and video) of my DC system go to this link. It focuses on my autogates but includes info on the whole system.

I actually have sat throguh that video... well done..

[Alan Schaffter]

If I am reading the table correctly, it looks like the specific Cinci fan will pull that CFM/SP through 10" ducting using a 5 hp or larger motor- unless surplus that must be a pretty pricey blower unit.

Fluid dynamics allow you to down-size a cyclone like Oneida, ClearVue, and Dyson have done but the trade-off is you need really high SP provided by a shopvac (60" - 90"!!!) and CFM is severely restricted. When you upsize a cyclone you run into another set of problems- you need to keep the SP low and move a tremendous amount of CFM in order to maintain adequate velocity for cyclonic separation. Throw into that mix some sort of scrubber chamber that will add SP and you can see what may happen.

Without running the numbers, I am firmly convinced it is not feasible (CFM, cost, size, complexity, etc.) to make a filter that uses some sort of enclosure employing water spray, a water curtain, water tank, etc. etc. that will satisfactorily remove dangerous fine, .5 - 10 micron, dust when added to a typical home cyclone based DC (5 hp or less). I wish they were possible.

As I said in another post recently, there are good reasons why almost all factories don't attempt to scrub the DC air so it can be recycled back to the work space.

[Jarrett Vibert]

If I am reading the table correctly, it looks like the specific Cinci fan will pull that CFM/SP through 10" ducting using a 5 hp or larger motor- unless surplus that must be a pretty pricey blower unit.

Close... it's the second from the bottom in the PB-15A section... The blower uses a 8" opening/exhaust, but that really only plays into it's max cfm rating, somewhere around 3800. You can reduce your piping to whatever you chose and take the corresponding hit in SP. In fact, that particular blower came with a blast gate right at the inlet to control the SP/CFM. A SP of 18" at the blower (as noted in that table) is the same regardless of piping size and other design restrictions, whether it's a blast gate or multiple 90 degree bends in your piping...

I have no idea what the retail cost of that unit would be... I was fortunate enough to save it from being scraped. However I don't see any reason why a blower of the same dimensions couldn't be diy'ed. Clearvue offers a steel BC 16" impeller for $245, and the housing could definately be diy.

Mine currently has a 7.5hp 3ph motor attached, and finding a low cost 5hp 1ph solution has been difficult. I actually corresponded with Mr. Pentz about a motor solution, as I was intially having difficulty understanding the Cin Fan table. He suggested I buy a standard 5hp 1ph motor, (as he suggests for his cyclone design), and close the blast gate till I reached the SP of 18" for sake of protecting the undersized motor.

When you upsize a cyclone you run into another set of problems- you need to keep the SP low and move a tremendous amount of CFM in order to maintain adequate velocity for cyclonic separation.

If I understand it correctly... You need to keep the SP low so you can reach the adequate CFM for collection/separation. Smaller comsumer grade DCs need that low SP to function properly. If you have an adequately sized blower/motor that can still maintain medical grade collection at 1000CFM and handle large SP, (note my eariler example), it's a moot point.

Without runninng the numbers, I am firmly convinced it is not feasible (CFM, cost, size, complexity, etc.) to make a filter that uses some sort of enclosure employing water spray, a water curtain, water tank, etc. etc. that will satisfactorily remove dangerous fine, .5 - 10 micron, dust when added to a typical home cyclone based DC (5 hp or less). I wish they were possible.

Well without a design concept I don't see how running numbers is even possible. In my mind I didn't imagine the unit would be much different than Pentz's cyclone. A spray section at the inlet, and then applying cyclonic action to "spin dry" the air before exhausting. Now I have absolutely no formal education in such designs, so I can't say whether or not it's feasible to shrink a scrubber to a useable size and still maintain adequate filtration.

As I said in another post recently, there are good reasons why almost all factories don't attempt to scrub the DC air so it can be recycled back to the work space.

That's simply because they have the option not to.... However "almost all" also means "some do"...

The tech is there, it's just a question of making it practical for the casual user. Considering the quadruple $ figures I see members on this site spending on equipment for their shops. I have no doubt that the potential for medical grade shop air, using a "Pentz's cyclone / Vibert scrubber" combo for under $4k would sell...and definately be considered worth while.

PS: I appreciate your effort in this discussion. It's been some time since I've had a "civil disagreement" on a forum. If nothing else, you've had me brainstorming....

Regards,

Jarrett

[Dick Thomas]

Having worked in industrial plants where clean air discharge was a major part of my job (1 system was 30,000 CFM @ 10" Hg (That's Mercury, not Water)), I can add a few personal experience comments:
1. An efficient DRY cyclone to remove to remove the bulk of the solids is essential!
2. Considering the significant SP losses, and the need for intimate air/water mixing, 'bubbling' the high volume airflow thru a water column isn't practical; rather, standard practice is to pass the air thru a spray nozzle chamber, followed by a second, WET, cyclone (for dust that is not water-soluable).
3. When you start dealing with wet collection, you introduce a whole new level of problems: Corrosion!!! - everything must be stainless or sturdy plastics = $$$$$$; The solids have to be removed from the water, or shortly things clog up, especially spray nozzles, or you re-introduce wet crud (a very technical term) into the exhaust stream; Water must be recycled after separation = pumps, or if not = high water bills;
4. As someone already mentioned, wet removal can be extremely effective (I've used in on toxic gas streams), but it is complicated, high maintenance, and not really practical for a home wood shop.

[Jarrett Vibert]

'bubbling' the high volume airflow thru a water column isn't practical; rather, standard practice is to pass the air thru a spray nozzle chamber, followed by a second, WET, cyclone (for dust that is not water-soluable).

^^That's the type system I was thinking of, but never seen one with a second "wet cyclone".

The solids have to be removed from the water, or shortly things clog up, especially spray nozzles, or you re-introduce wet crud (a very technical term) into the exhaust stream

lol... funny you should mention that. With the system we had at my plant, the reservoir auto make-up float would stick "on". Once the level reached the point where it was in contact with the air stream, everything come blowing out the top like a geiser. Fortunately in our application, we're dealing with a extremely small amount of solids. Regening the sprayed water would be as simple as picking the appropriate location for the pump's feed. The premise is the sprayed water will be removed from the air stream before exhausting. That water needs to be collected, and fortunately gravity is our friend in this case.

As someone already mentioned, wet removal can be extremely effective (I've used in on toxic gas streams), but it is complicated, high maintenance, and not really practical for a home wood shop.

I'm not convinced that a low tech scrubber that would be needed for WW dust would be all that mechanically complicated. I whole heartedly agree that coming up with a functional design would be mentally exhuasting. However the one scrubber I know well really was basic in design, and did exactly what it was meant to do. I'm sure the R&D group that developed it would disagree though.

I know first hand that scrubber maintenance can be a nightmare. In my particular experience, it was a case of it being a "used" unit, staff learning operation on the fly, and being undersized for the volume we dealt with. It did the job, but it's "self cleaning" action couldn't keep up with the amount we threw at it.