Building scrubber

[Emryst]

Long post so apologies for that.

I saw this design from one of the fellow members here, you prolly saw the post. My question maybe simple or not I am not sure as I have zero idea in the math to calculate the flow rate needed or maybe even whats to much. My plan is going at it with test runs with basic water when I have it completed. I don't have a fan of any type so I have to buy one. I'm working in my shed that I have retro fitted with plywood walls and put winindow a/c as i had been using it as a work shop of sorts.
Anyway to get to my question this set up would this fan have too much power in flow rate or not enough? I don't want to go wasting money on fans or anything only to have find out it's too much and should have got another one.

As far as the plans go I'm gonna follow it pretty close to plan. Tho I'm having some concerns as to how to solve the air tight system at the bucket with the pipes and hose from pump but not my biggest issue.

I'm sure I have other concerns but at the moment this is my first as I'm wanting to make purchase so I can get building it.

 

[Emryst]

Long post so apologies for that.

I saw this design from one of the fellow members here, you prolly saw the post. My question maybe simple or not I am not sure as I have zero idea in the math to calculate the flow rate needed or maybe even whats to much. My plan is going at it with test runs with basic water when I have it completed. I don't have a fan of any type so I have to buy one. I'm working in my shed that I have retro fitted with plywood walls and put winindow a/c as i had been using it as a work shop of sorts.
Anyway to get to my question this set up would this fan have too much power in flow rate or not enough? I don't want to go wasting money on fans or anything only to have find out it's too much and should have got another one.

As far as the plans go I'm gonna follow it pretty close to plan. Tho I'm having some concerns as to how to solve the air tight system at the bucket with the pipes and hose from pump but not my biggest issue.

I'm sure I have other concerns but at the moment this is my first as I'm wanting to make purchase so I can get building it.

Sorry I forgot to mention in post the fans specs state 700cfm as noted in the Pic attached. It's like 38 bucks from amazon.

 

[Yggdrasil]

Sorry I forgot to mention in post the fans specs state 700cfm as noted in the Pic attached. It's like 38 bucks from amazon.

There are many posts regarding this and one thread that has been going on just now is this one:
https://goldrefiningforum.com/threa...s-and-fume-scrubbers-_hood_.34601/post-372857

Please spend some time searching before you post new threads.

 

[4metals]

The fan is way too large. The fume needs to stay in contact with the solution pumping over the packing for around 8 seconds. Calculating the area of the packing in the design and the CFM listed for the fan, it is 152 times more flow than required. At that rate the exposure of the fumes to the scrubbing chemicals, the system will have little to no effect.

Area of packing = .610 cubic feet
to get the flow time correct multiply by 7.5 (the number of 8 second increments in a minute) This translates into 4.579 cubic feet effective area for proper fume exposure. making 700 CFM 152 times too big.

edit to add calculation.

 

[Emryst]

The fan is way too large. The fume needs to stay in contact with the solution pumping over the packing for around 8 seconds. Calculating the area of the packing in the design and the CFM listed for the fan, it is 152 times more flow than required. At that rate the exposure of the fumes to the scrubbing chemicals, the system will have little to no effect.

Area of packing = .610 cubic feet
to get the flow time correct multiply by 7.5 (the number of 8 second increments in a minute) This translates into 4.579 cubic feet effective area for proper fume exposure. making 700 CFM 152 times too big.

edit to add calculation.

Thanks so much. I don't know the math on how to calculate the flow rate to keep the fumes in solution long enough but with all my reading on this forum and elsewhere I had a feeling it was to much flow. I guess my thinking is always bigger is better and more power is the best. Lol not for this application tho.

 

[Emryst]

There are many posts regarding this and one thread that has been going on just now is this one:
https://goldrefiningforum.com/threa...s-and-fume-scrubbers-_hood_.34601/post-372857

Please spend some time searching before you post new threads.

My bad I saw equipment thread and naturally thought the scrubber fell within that requirement. I mean shouldn't we all be using a scrubber of some sort for our equipment. Is there a way I can move this post or do I have to copy paste it a an new add to the scrubber thread?

 

[Emryst]

The fan is way too large. The fume needs to stay in contact with the solution pumping over the packing for around 8 seconds. Calculating the area of the packing in the design and the CFM listed for the fan, it is 152 times more flow than required. At that rate the exposure of the fumes to the scrubbing chemicals, the system will have little to no effect.

Area of packing = .610 cubic feet
to get the flow time correct multiply by 7.5 (the number of 8 second increments in a minute) This translates into 4.579 cubic feet effective area for proper fume exposure. making 700 CFM 152 times too big.

edit to add calculation.

Question would too low flow rate make it so there is no pull of air at the intake on the hood but rather just suck the air from the tub of solution making it implode?
With that concern is there a flow rate of solution I should be shooting for with the pump. I picked a 400gph with a 6 ft upward lift capacity. But in fairness it's a pump for a pond not a small aquarium. Sadly I already bought this so if I'm over shooting again with too much power I'll have to suck that one up as on the learning curve. My thinking on the pump was it being made of something that will last in 2M NaOH solution so I'm not just throwing good money after bad when it fails in a month. And to have enough power to project the solution upward the 5 ft or so to the 4" pvc pipes and keep everything lubricated for good contain for scrubbing.

 

[Emryst]

I guess I'm also concerned that if the water flow is to high thru the packing it could back up and cause a back up of gas in the hood.

 

[4metals]

Question would too low flow rate make it so there is no pull of air at the intake on the hood but rather just suck the air from the tub of solution making it implode?

Based on the size of the packing a flow of about 5 CFM from an eductor would provide the proper airflow. If you were working in a 5 liter beaker or even a 5 gallon pail with a lid, a small hole in the lid that will direct any fume to the scrubber intake tube will suffice. Too large of a reaction could overpower a 5 CFM scrubber flow but the reaction rate can be controlled with the nitric additions to keep it manageable. Never seal the intake to the scrubber to the reaction vessel. The fumes will rise up naturally on their own and having the pickup tube placed in a way that it allows air from the hood to enter as well will prevent implosion.

 

[4metals]

And to have enough power to project the solution upward the 5 ft or so to the 4" pvc pipes and keep everything lubricated for good contain for scrubbing.

You can flood the packing with too much flow but there is an easy fix. Add a wye in the tubing going from the pump and each discharge leg gets a valve. One side goes to the spray nozzles in the columns and the other returns to the sump. You can play with the balance on the valves to get a good flow that does not hang up too much liquid in the column. (Then remove the handles on the valves so it stays where you set it.).

 

[4metals]

I guess I'm also concerned that if the water flow is to high thru the packing it could back up and cause a back up of gas in the hood.

This is a valid concern but keep in mind the scrubber is to treat the worst of the fumes but the scrubber cannot be the only exhaust. You still want to aim for 100 CFM for every square foot of hood opening. That will remove any leakage and provide for a much nicer work environment for you. A plus of an effective fume scrubber is it will make the exhausted fumes from the hood less corrosive and, as such, less likely to quickly destroy a blower that cannot resist corrosion.

 

[Emryst]

Based on the size of the packing a flow of about 5 CFM from an eductor would provide the proper airflow. If you were working in a 5 liter beaker or even a 5 gallon pail with a lid, a small hole in the lid that will direct any fume to the scrubber intake tube will suffice. Too large of a reaction could overpower a 5 CFM scrubber flow but the reaction rate can be controlled with the nitric additions to keep it manageable. Never seal the intake to the scrubber to the reaction vessel. The fumes will rise up naturally on their own and having the pickup tube placed in a way that it allows air from the hood to enter as well will prevent implosion.

Hood plan is to make from 3/4" plywood I have laying around with 2x4 frame. I have set down plans yet on paper but a quick sketch I attached here.

 

[Emryst]

You can flood the packing with too much flow but there is an easy fix. Add a wye in the tubing going from the pump and each discharge leg gets a valve. One side goes to the spray nozzles in the columns and the other returns to the sump. You can play with the balance on the valves to get a good flow that does not hang up too much liquid in the column. (Then remove the handles on the valves so it stays where you set it.).

OK like a flow control valve inline so not to flood packing pipe. If I'm understanding you.

 

[4metals]

With that size opening and hood size have you considered using a modified IBC? They are available used for reasonable prices and if you factor in the price of plywood today plus the cost of a corrosion resistant coating it may be cheaper. Use of IBC's for this purpose has been discussed on the forum.

 

[Emryst]

Based on the size of the packing a flow of about 5 CFM from an eductor would provide the proper airflow. If you were working in a 5 liter beaker or even a 5 gallon pail with a lid, a small hole in the lid that will direct any fume to the scrubber intake tube will suffice. Too large of a reaction could overpower a 5 CFM scrubber flow but the reaction rate can be controlled with the nitric additions to keep it manageable. Never seal the intake to the scrubber to the reaction vessel. The fumes will rise up naturally on their own and having the pickup tube placed in a way that it allows air from the hood to enter as well will prevent implosion.

I'm using small batch I only got 600ml beakers so I can't do large processing.

I did find a fan with 23 cfm and also found a fan speed control with h m l settings h being max cfm. So that give me so adjustment capability. It doesn't give enough info on specs to say what the cfm is for each setting tho as they don't know the fan it will be used for.

 

[4metals]

Using a water induced vacuum produced by an eductor (venturi) will give a low flow and last a very long time, in line fans for scrubbers can be a crap shoot. May work and may last......or not.

 

[Emryst]

Using a water induced vacuum produced by an eductor (venturi) will give a low flow and last a very long time, in line fans for scrubbers can be a crap shoot. May work and may last......or not.

Yeah I hear u on that but I have already started down this road to go back and redesign I'm just chucking any time effort and money I'm invested out the window.

 

[Emryst]

This is a valid concern but keep in mind the scrubber is to treat the worst of the fumes but the scrubber cannot be the only exhaust. You still want to aim for 100 CFM for every square foot of hood opening. That will remove any leakage and provide for a much nicer work environment for you. A plus of an effective fume scrubber is it will make the exhausted fumes from the hood less corrosive and, as such, less likely to quickly destroy a blower that cannot resist corrosion.

Since suction increases with the reduction of pipe size. Maybe a 2" pipe at hood going into the 4" pipe with packing with a flex pvc hanging closer to beaker would be better.

With that size opening and hood size have you considered using a modified IBC? They are available used for reasonable prices and if you factor in the price of plywood today plus the cost of a corrosion resistant coating it may be cheaper. Use of IBC's for this purpose has been discussed on the forum.

The IBC sounds like a good idea but I have the 2x4 and ply already so it's a 0 cost factor.

 

[Yggdrasil]

Since suction increases with the reduction of pipe size. Maybe a 2" pipe at hood going into the 4" pipe with packing with a flex pvc hanging closer to beaker would be better.

The IBC sounds like a good idea but I have the 2x4 and ply already so it's a 0 cost factor.

This will work only if the fan is able to create strong enough suction.
The best solution for you I think, will be a vacuum system by water-jet venturi and a slight suction in the hood.
That can be scrubbed by misting in a 200L plastic barrel or similar.

 

[Emryst]

This will work only if the fan is able to create strong enough suction.
The best solution for you I think, will be a vacuum system by water-jet venturi and a slight suction in the hood.
That can be scrubbed by misting in a 200L plastic barrel or similar.

I have been researching principles of a venturi system. I consider myself a fair mygyver type. But I am at a lost on how I can make the venturi shell as well as what the flow of solution injection should be and if this 400gph pump I got be enough? Any way you could point me in the right direction. Prior post of another members ideas I can play off of or something like that.
I want to see if I can still use most of the things I have gotten for the scrubber I was intent on building. But if I'm gonna make a switch better do it before I even start any construction.