New fume scrubber design

4metals · Feb 5, 2011

I have been following the thread on building a hood and a scrubber for a long time now and it has gotten pretty long. This scrubber works on a different principle than the one in that thread and was inspired by a client of mine who didn't want to spend the money on a good vacuum system and a good scrubber, but he needed both.

I had posted a thread on building a vacuum system How to build a vacuum filtration system some time ago and it is the type of system required for a strong, commercial operation. Usually refiners processing 100 oz plus lots will benefit from the system.

This scrubber uses a feed similar to the vacuum system and is based on the principle that the eductor pulls air through the venturi and in addition to creating a vacuum, it pumps the air it pulls. By pumping that air into an air tight scrubbing chamber the fume has no place to go but along the airpath and through the scrubber. Plus with a 10 CFM eductor, the time the fumes remains exposed to your scrubber chemistry is exceptionally long for an effective reaction.

As a bonus to this design by using the exhaust over a sealed reactor, 100 ounce digestions are completely handled by the 10 cfm flow. A side bonus is that by shutting off the feed line that pulls air for scrubbing and opening up a line set up to vacuum filter, you can filter and scrub fumes with the same piece of equipment, just not at the same time.

This setup can be pH controlled automatically or for a small shop, daily opening the access port to adjust the pH should suffice. The principles of scrubbing are the same, as is the packing but for someone digesting 100 ounce lots, this system is effective.

Now it's time to have our DIY crowd tear into this design to see what we end up with.

Barren Realms 007 · Feb 5, 2011

A couple of quick question's.

We use to use a corkscrew type spray nozzel are you useing something similar to produce your spray pattern? Or are you useing something home made?

Where your piping from the pump comes down the inside of the tower is it connected where you have it labeled as the inductor(where the piping color changes from red to blue) to force your fumes into the bottom tank and then thru the stack? That is kind of what I am gathering from the picture.

Do you seem to run into any kind of restriction in air flow with the pipeing (red) so far into your solution?

I'm guessing that you have a seperate support system holding up the stack and the tank is not what is supporting the stack but just sealed off where they connect.

I'm guessing where the tank and stack come together is plastic welded or have you used some sort of sealent.

Nice desighn. 8)

4metals · Feb 5, 2011

We use to use a corkscrew type spray nozzel are you useing something similar to produce your spray pattern? Or are you useing something home made?

corkscrews are fine they provide a good distribution and do not clog easily.

Where your piping from the pump comes down the inside of the tower is it connected where you have it labeled as the inductor(where the piping color changes from red to blue) to force your fumes into the bottom tank and then thru the stack? That is kind of what I am gathering from the picture.

The way an eductor works is it compresses the water running down along the column (blue) through a small orifice just before the red line comes in from outside the scrubber. When the water expands after the orifice it draws a vacuum, so the red line going into the liquid level is a mixture of water and air used to pull a vacuum.

Do you seem to run into any kind of restriction in air flow with the pipeing (red) so far into your solution?

The reason the pipe extends beneath the liquid level is so when you are using it in vacuum mode, you will hold a stronger vacuum. If it was not submerged, the vacuum that builds up in the vacuum jug would overpower the suction and the thing would burp. The weight of the water keeps that from happening.

I'm guessing that you have a seperate support system holding up the stack and the tank is not what is supporting the stack but just sealed off where they connect.

The stack is welded to the tank to be airtight, in this case the weight of the column was supported externally in a way not indicated on the drawing, otherwise it would need support by running to the bottom and drilling large holes to allow the airflow to ascend.

Barren Realms 007 · Feb 5, 2011

That was what I figured you did where the stack connectd to the tank. If not I would have set it up like you said with the stack going to the bottom of the tank.

Ok I see what you are doing. I have used a similar system with water to remove sand from pool filters so I know what you are doing now. It's amazing the things you forget as time goes by. Thanks

qst42know · Feb 5, 2011

The blue horizontal line, the arrow isn't indicating the direction of flow is it?

Is this similar to what your drawing depicts?

http://www.nciweb.net/wet_scrubbers.htm

4metals · Feb 5, 2011

No, in fact it is opposite of the flow, it points to the text box saying what is down the line.

The eductors in your link are of the same type but bigger. They work the same.

golddie · Feb 5, 2011

I will be honest with you guys and say that I didnt read in detail what was written here but I will read it when I have the time and the need.
What I would like to ask those who know about my scrubber ,would it be possible to convert my scrubber to one of these
Thanks

shyknee · Feb 5, 2011

4metals
This one is just brilliant.
Great design. I thank you.
The other day I was contemplating using a compressed air venturi vacuum pump and never thought to use the scrub liquid straight from the pump (much quieter too). This is just great !
I think I have a plastic eductor some where I used to suck out the water from my aquarium.

4metals · Feb 5, 2011

I think I have a plastic eductor some where I used to suck out the water from my aquarium.

If you have an eductor that can suck 10 CFM out of an aquarium it must be one huge fish tank!

shyknee · Feb 5, 2011

I still think small scale 1oz or less it's still just a hobby for me. The aquarium was a 140gallon tank about 25feet away from the sink .I don't know about the CFM of air but it also emptied my old water bed (25years ago) in about an hour with two feet of head. Do you think this would work ? Thanks 4metals I value your opinion.

4metals · Feb 5, 2011

Shynee,

You could make a trap in glass erlenmeyer flasks filled with glass marbles and caustic liquid. Pull the air through it with your eductor and make sure the bucket on the right side of drawing has a tight fitting lid. You will need to place a hole in the lid which you can plug to allow a slow flow of air in to make up for what you take out. Use a beaker in the pail and you should be fine for a few ounces.

I think you can get plastic erlenmeyer vacuum flasks pretty cheap. I'd still be doing this in an exhaust hood or outdoors.

Barren Realms 007 · Feb 5, 2011

golddie said:
I will be honest with you guys and say that I didnt read in detail what was written here but I will read it when I have the time and the need.
What I would like to ask those who know about my scrubber ,would it be possible to convert my scrubber to one of these
Thanks

Yours is a little different type of tank but it might be possible to get it to work.

shyknee · Feb 6, 2011

Nice thanks

HAuCl4 · Feb 7, 2011

Nice design 4metals!. A variation of the big johnson?. This one does not remake the nitric acid, only vaccums and scrubs right?.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=8619&p=80788&hilit=big+johnson#p80788

rbramsey · Feb 7, 2011

I like this design it seems KISS.

I would like a few more details:
Can someone point me into the right direction for a 10 CFM eductor? Not to be picky, but a part # and website would be great.
What size pump?
What pressure is needed at the eductor?
What size is the pipe from the fume hood and from the pump?

Thanks,
Richard

4metals · Feb 10, 2011

The pipe sizes are dependent on the cfm of the eductor, as are the piping sizes and the pump. This one uses an eductor with a 1 1/2 inch inlet (the line coming down the scrubber into the eductor) and a 2 1/2 inch suction line.

The eductors and the required pump flows can be found here http://www.mcmaster.com/#eductors/=az29d0 look at liquid operated pumps.

Barren Realms 007 · Feb 10, 2011

4metals said:
The pipe sizes are dependent on the cfm of the eductor, as are the piping sizes and the pump. This one uses an eductor with a 1 1/2 inch inlet (the line coming down the scrubber into the eductor) and a 2 1/2 inch suction line.

The eductors and the required pump flows can be found here http://www.mcmaster.com/#eductors/=az29d0 look at liquid operated pumps.

Are you sure about the size being 2-1/2" and not a 2". This is not a regular size pipe. Pipe sizes jump from 2" to 3" in PVC pipe?

4metals · Feb 10, 2011

That particular eductor has a 2 1/2 inch suction port. You could immediately use a fitting to expand that to 3" which is a universally available size. The air will still move through the pipe at 10 cfm (actually 11 with the correct pump) but it's velocity will be a bit slower which is no problem.

This is where some of the machine shop guys should step up to the plate. There has to be a series of standard PVC fittings coupled with a little lathe turning that could turn out an eductor relatively easily. This size from McMaster costs just shy of $800.

THe pump and eductor are the most costly components of the system.

Barren Realms 007 · Feb 10, 2011

4metals said:
That particular eductor has a 2 1/2 inch suction port. You could immediately use a fitting to expand that to 3" which is a universally available size. The air will still move through the pipe at 10 cfm (actually 11 with the correct pump) but it's velocity will be a bit slower which is no problem.

This is where some of the machine shop guys should step up to the plate. There has to be a series of standard PVC fittings coupled with a little lathe turning that could turn out an eductor relatively easily. This size from McMaster costs just shy of $800.

THe pump and eductor are the most costly components of the system.

Yea I agree. It would be better to make it out of SCH80 grey pipe because of the thicknes ofthe walls. Only trick is you have to put a bushing inside the pipe you keep it from deforming when you turn it. This is what has to be done when you thread it or the pipe will deflect inwards during the threading process and crack and break.

qst42know · Feb 10, 2011

Schedule 40 or 80 PVC in 2-1/2" is available through USPlastics.

http://www.usplastic.com/catalog/item.aspx?itemid=23979&clickid=redirect

New fume scrubber design

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