# spray nozzles for packed tower



## bigpagoda (Sep 15, 2017)

Hello,
Finally going to build a fume scrubber so I can get back to some recovery. I think I have a good design but can't figure out how to size the spray nozzles inside my towers. I have read lots of posts about making scrubbers and researched commercial ones online but found no real info on the nozzles themselves. I have tested a bunch of different kinds but there are so many options out there I decided I should just ask what kind you guys use? How critical is the droplet size or does it even matter as long as I am getting enough on the surface of the packing to keep it wet but not getting pooling at the bottom. Any advice is appreciated
Paul


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## 4metals (Sep 17, 2017)

Is it your plan to recirculate the same water or mist the packing continually with fresh water? Your question about pooling on the bottom implies misting.


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## bigpagoda (Sep 17, 2017)

yes, I will be recirculating the same solution with an external flojet pump with santoprene seals and gaskets. I am planning to use generic 1 in bioballs for the packing in sections that are twice the diameter of the cylinder. So there will be 3 separate packed areas each with a spray nozzle in each column. I will see if I can post a drawing of my plan so you can see what I am talking about. The nozzle I wanted to use is a spiral cone but I got one that was way too big. I have nozzles that can create a fogging mist and all in between but can't tell what is best. The pumps I am using are capable of 5gpm but the rate will be set according to how well the solution filters back through the packing. (So I can keep a balanced level in the reservoir part of the column.)


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## bigpagoda (Sep 17, 2017)

Here's a drawing of my column. not to scale but showing all the parts.


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## 4metals (Sep 18, 2017)

Nice design, what CFM are you planning to work at? The spiral nozzles will flood this setup, they simply flow too fast. I would start with a simple method by drilling 1/8" holes in a pvc cap to spray a coarse stream over the media. 4 holes on the perimeter to start and one in the center. If you make too fine a mist they will overwhelm the mist eliminator. You can add holes or make less holes depending on the flow rate you hope to achieve. The one thing you want to avoid is the media drying out in any area because it will clog up with caustic salts as the liquid has a high dissolved solids level which, once saturated likes to come out somewhere. (Usually in the hardest place to clean it out from.) Keep in mind you will have to change out the liquid in the scrubber from time to time to prevent this clogging as the solids build up. 

The one thing you will experience is the solution will evaporate from the column and it will be difficult to maintain because you are operating with a small reservoir in the bottom. It is not uncommon for 25% or more of a scrubbers volume to be held up in the packing while the scrubber is operating. With too small a reservoir you end up with pumps running dry or flooding when you are not pumping. A larger reservoir area can fix this. If you had a larger diameter drain into a reservoir that the pump fed from, you would allow the liquid to drain into the reservoir chamber and give yourself a reserve to feed the solution from as well as the ability to add caustic based on a pH measurement or add additional water as the level dictates. 

One nice feature of the entire system working under vacuum is you can shut off the air intake feed where the NOx enters the system and open up a tap in the reservoir where you can suck in more water or caustic or peroxide depending on your application. All using the vacuum pump rather than a dedicated pump for the chemicals.


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## bigpagoda (Sep 18, 2017)

Thank you 4metals,
I believe this is basically your design. My vacuum is 3.5 cfm. The sad little drawing isn't to scale, the reservoir at the bottom will be about 10 in deep. There are 3 sections in the column with 12-14 inches of packing each. I want to assemble the column with all 3 nozzles being driven off the same pump and monitor the reservoir level by using a temporary clear feed tube coming out the bottom going up above the top of the column to see the level while it is running and then set the flow rate off of the results. Hopefully I will get to put it together this weekend and let you know how it works.
Paul


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## nickvc (Sep 19, 2017)

Paul post some pictures once you have it set up or even better as you construct it, this will give other members a starting point for their own systems and I'm sure 4metals will be glad to help and advise as you progress.


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## 4metals (Sep 19, 2017)

> My vacuum is 3.5 cfm.



To effectively scrub NOx the fume needs to be retained in the area of the scrubber where it contacts the chemistry in the circulating liquid for 8 seconds. That is the area where the packing is held. If you can keep the fume in the scrubber long enough the scrubber can do its job effectively. 

With a flow of 3.5 CFM you can get by with a packed section with an area of 0.5 Cubic Feet. (0.4666) There are 7.5 Eight second segments in a minute so the CFM of the vacuum source divided by 7.5 tells you the required volume of the packed section necessary. 

What type of eductor are you using and what type of pump?


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## Palladium (Sep 19, 2017)

Wouldn't a flooded column be a lot simpler and efficient design for that low a cfm?


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## 4metals (Sep 20, 2017)

Not really. The reaction between the fume and the solution you are scrubbing with happens at the air water interface on the packing. Submerging the packing lowers that area substantially.


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## bigpagoda (Sep 20, 2017)

I was under the impression that the fumes are scrubbed much better when they are not bubbled through a liquid because the surface area of a sphere is the smallest size object. The packing is irregular shaped to maximize surface area in the same volume. My problem is that I don't know how to size my spray nozzles to keep all of that extra surface area completely wetted but not flood the cavities with too much scrubbing solution before it runs out to the reservoir at the bottom.
I started with a spiral nozzle with an orifice that was 1/3 the diameter of the sprayer feed line but it sprayed out like a shower head and would suck my reservoir dry. So I tried several yard sprinkler nozzles (which did seem to be about right) and some very fine mist nozzles we use at work that would take a really long time to reach the bio balls at the bottom. None of them were really any good. I am going to try just drilling out a pvc cap as suggested and see if I can get it right.
I used a excell spreadsheet that I found on the forum for scrubber and blower sizing (sorry, I can't give credit for who posted it-it is a really cool tool!) that confirmed 36inches (3 x 12 in sections) of packing in a 6 in pipe at 3.5cfm has a retention time of 10 sec.- does that sound right?
I do not have an eductor on this system, I will be using it in a semi-closed circuit pulling the fumes out of the hood through a hose and funnel into the scrubber and then exhaust into the vent coming off the blower on the fume hood. I am using an ordinary rotary vane vacuum pump because it's what I have and hopefully my scrubber works really well so I don't fry it in a month. I have seen some posts about building an eductor and have looked at some scary prices for them online but I really don't know enough about how they work. I am spending a fair amount of effort and money to try to build this correctly so If I should really be adding one to this system please let me know.
Thanks,
Paul


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## bigpagoda (Sep 27, 2017)

Well I tested a homemade nozzle with five 1/16 holes in it inside a clear plastic poster cover rolled into a cylinder but didnt seem to get enough of the packing wet. I tried drilling more holes and turning the flow way up but it still looks like the individual bio balls are only holding a few drops of solution at a time and the majority seems to remain dry. I could only get one picture that sort of shows what I am talking about. I am thinking I need to go back to more of a misting size or possibly a hot needle? I was also thinking that maybe this is how they are supposed to look. The professional scrubber I've seen do have similar flow running down the side but there was a little pooling at the bottom of the packing. Any suggestions.
Paul


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## nickvc (Sep 28, 2017)

Paul I don't know if this would work but my thoughts are leaning towards a sprinkler that moves like a lawn sprinkler so it is moving your solution all over your media, it doesn't need to move very fast but I think it would cover move of your media.


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## 4metals (Sep 28, 2017)

The types of tower packing that I have used in commercial fume scrubbing applications are specifically designed to distribute the liquids across their surface and as it flows down it is constantly redistributed. So the trick becomes getting the entire top surface adequately wetted and the spaces below take care of themselves because of the media. 

I do have some experience with bio balls from filtration in reef aquaria. These are also used by some as packing in scrubbers. In reef aquaria they seem to benefit from a rotating spray bar. This indicates to me the liquids may tend to channel through the media if flow was constant from one point. 

A rotating spray-bar may be costly and require considerable CFM to spray effectively, and this may cause problems in a small setup. Another option would be a distribution trough. This is nothing more than a pipe or grid of pipes which sits atop the packing with holes to allow the scrubber liquids to distribute over the packing. If you Google "scrubber internals images" you will see all of the different configurations of packing and packing support and distribution troughs and nozzles used in scrubbers.


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## bigpagoda (Sep 28, 2017)

The one professional scrubber I got to look at up close had packing balls that looked like snowflake crystal leaves that went to very fine hair like ends. I think the bio balls do allow the solution to run through faster because the cavities are much larger. Unfortunately they won't sell me a batch that small and they were fairly expensive. 
I had a wild thought- what if I run a central (or Coiled) tube through the middle of my packing that is perforated regularly with pin holes like a soaker hose. My chemical pumps can be adjusted up to 5gpm so if the holes were very small I think I could put a lot of them in the tube. Just a thought but it would be easy to try.
I have heard of other people on the forum making their own fume scrubbers using all sorts of items for packing- marbles, pvc rings, curlers, hose etc. but haven't heard anything about what they used for the spray nozzle or any flow rates for the solutions or what kind of pump for that matter.


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## nickvc (Sep 29, 2017)

You could try running your scrubber for some time to allow the media to get wet and then start your reactions or perhaps make a coil from your tubing perforate it and lay that across the top of your media.


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## rickzeien (Dec 18, 2017)

4metals said:


> The types of tower packing that I have used in commercial fume scrubbing applications are specifically designed to distribute the liquids across their surface and as it flows down it is constantly redistributed. So the trick becomes getting the entire top surface adequately wetted and the spaces below take care of themselves because of the media.
> 
> I do have some experience with bio balls from filtration in reef aquaria. These are also used by some as packing in scrubbers. In reef aquaria they seem to benefit from a rotating spray bar. This indicates to me the liquids may tend to channel through the media if flow was constant from one point.
> 
> A rotating spray-bar may be costly and require considerable CFM to spray effectively, and this may cause problems in a small setup. Another option would be a distribution trough. This is nothing more than a pipe or grid of pipes which sits atop the packing with holes to allow the scrubber liquids to distribute over the packing. If you Google "scrubber internals images" you will see all of the different configurations of packing and packing support and distribution troughs and nozzles used in scrubbers.


I found these wiffle type golf balls on ebay. How would these work? 

https://m.ebay.com/itm/Andux-Golf-Hollow-Plastic-Practice-Balls-Golf-Wiffle-Balls-Air-Flow-Ball-Set/252077669806?hash=item3ab0fffdae:m:mEQ5nBWC0dohJyuLBi0HU7g

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## rickzeien (Dec 18, 2017)

rickzeien said:


> 4metals said:
> 
> 
> > The types of tower packing that I have used in commercial fume scrubbing applications are specifically designed to distribute the liquids across their surface and as it flows down it is constantly redistributed. So the trick becomes getting the entire top surface adequately wetted and the spaces below take care of themselves because of the media.
> ...


22.00 for 100

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## 4metals (Dec 18, 2017)

They should work, I do know of one refiner in India who used wiffle balls about the size of baseballs. 

The thing you need to do is allow the airflow and scrubber water flow to "reset" itself by having an open section of tower about every 1 1/2 tower diameters. Just about 6" of space should work fine. Air flow and scrubber liquid tends to channel as it runs through packing, some packing does it more than others. If you were buying expensive, professionally made packing this is taken into consideration but I would assume with these pseudo gold balls. it's not the case.


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## snoman701 (Dec 19, 2017)

Go to the farm store. They've got a wall of sprayer nozzles. Actually, they probably have an appropriate filter as well. 

All kinds of shapes and sizes. 

Although I still think nicks idea of the perforated poly tube is the best. It's simple.


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## rickzeien (Dec 21, 2017)

4metals said:


> They should work, I do know of one refiner in India who used wiffle balls about the size of baseballs.
> 
> The thing you need to do is allow the airflow and scrubber water flow to "reset" itself by having an open section of tower about every 1 1/2 tower diameters. Just about 6" of space should work fine. Air flow and scrubber liquid tends to channel as it runs through packing, some packing does it more than others. If you were buying expensive, professionally made packing this is taken into consideration but I would assume with these pseudo gold balls. it's not the case.


Thank you. I appreciate your advice.

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## bigpagoda (Dec 22, 2017)

I have been working seven days a week for about a month now and haven't been able to get to work on this. I have figured out that using the bio balls requires an extremely high flow rate in order to get all of the surface wet. I used a 750 GPH pump in the test sleeve and got much better results but it caused me another problem. My original plan was to have three 12" sections running off the one pump but when I tested it with three nozzles I don't get even flow to each section and I think I am still getting too coarse of a mist
I think the bio balls are turning into a poor choice for this kind of design but I understand now why the commercial scrubber packing had such fine void spacing. I am interested in trying a coil of perforated poly tube running through the center like nickvc said. I think it is the last hope for this design using the bio balls. I will post results when I do this but I am going to be busy until after New Years.
If this does not work I am going to go with the flooded packing idea. Recently, I had the pleasure to meet with Phildreamer and got to look at his setup closely. We both agreed it was considerably easier than trying to match mist size and flow rates to the bio ball surface area. Phil was extremely nice and he offered much of his afternoon showing me things and answering my questions. Actually, his setup is what encouraged me to think I could build this one myself. So thank you Phil, and I am very much looking forward to showing you my "eye candy" when I am done.
Thank you all and Merry Xmas.


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