Sciencemadness Discussion Board

Waterpumps

frogfot - 8-5-2005 at 03:31

Umm, we didn't have a thread on waterpumps until now..

Maby someone can help me to find this specific waterpump that could handle corrosive aqueous solutions (that can also contain org solvents). I'm planning to use it to recirculate water through an air scrubber (a part of my planned filtersystem for the fume hood).

For this purpose it doesn't have to be powerful.. just something like a 30W fountain pump.
Most pumps has either metallic parts or plastic that will be destroyed in mentioned conditions.. Any idea on this?

[Edited on 8-5-2005 by frogfot]

12AX7 - 8-5-2005 at 09:03

I saw a fish tank aerator/pump thing that had a plastic-coated spinning armature to move the water. Think magnetic stirrer with vanes, I guess.

If you can find one where everything is coated and sealed with polypropylene, that ought to work quite well. :)

Tim

Magpie - 8-5-2005 at 09:26

It is quite a challenge to find a material that is corrosion resistant to everything that might be in the absorbed offgases of a home chemist. Teflon or other expensive fluoropolymers probably stand the best chance.

Off the top of my head I will suggest consideration of a peristaltic type (hose)pump for simplicity. Here you just have to pick the best hose material. Nothing else is wetted. I have had good success with polyurethane hose at work. But again you have to look at your material's compatibilty with the fluid being pumped.
Pulsing may be a problem with this type of pump but this may be able to be dampened out with a reservoir of some type. Also these pumps are not cheap.

Or you could just get a cheap sump pump and be prepared to replace as needed. The advantage of a sump pump is that it has no seal to worry about. I'm thinking of the type used for evaporative coolers that go for around US$25.

I am quite interested in your project as I envision that I will want such a scrubber at some point - as my laboratory develops.

unionised - 8-5-2005 at 11:05

I'm not sure how well it would work in this instance but there is a pump with no wetted moving parts to corrode.
If you put tube in a bucket of water and pump air down a thin pipe, the end of which is under the end of first pipe, so it forms bubbles. In the pipe you get a column of mixed air and water, this isn't as dense as water so it rises. A mixture of bubbles and water comes out of the pipe and, if you have it run into a header tank you can let it run down through the scrubber and back to the bucket.
Not a very efficient pump, but relatively robust, you just need an fish tank aerator to run it and those run for years.

A pictures worth a thousand words so here's one
http://www.simplyhydro.com/images/afdrawing.htm

[Edited on 8-5-2005 by unionised]

frogfot - 9-5-2005 at 07:05

Cool, this gave lots of ideas!

I have actually found a peristaltic pump on a recycling station for free (120 ml/min 230V), though its hose has about the same resistance as PVC hoses (particularly org solvents kill them) and there's not many elastic materials for this purpose. Maby it's worth to try making own pipe from silicone sealant :)
Btw, pulsing shouldn't affect the scrubbers efficiency much..

Is sump pump basically an immercible pump that can handle to pump water with big particles? Those usually have too much power.

Whow, unionised, this thing seems to be very promising. Because this gives a broad choise of materials.. though it's a bit hard to beleave that this thing will work.. I'll try this now with my air-mattress pump.

Worth to mention that I used to have an idea to go without any pumps at all, simply by aligning the scrubber tower horisontally in a barrel, half-filled by water. Rotating the tower inside the barrel and letting the air pass through the non immersed part of tower would give good scrubbing efficiency.. But then, the construction gets too complicated..

[Edited on 9-5-2005 by frogfot]

12AX7 - 9-5-2005 at 08:18

How about a waterfall? Pump from a basin to a shower head or three would do it. Still have the problem of reactives though... maybe some washing soda in the water to counter the average acid gas production...

Oh, and works good for cheap evaporation cooling (swamp cooler) and humidification, too ;)

Tim

Magpie - 9-5-2005 at 12:37

Frogfot,

A sump pump can be submersible or not.

I looked at a 5 gpm (20 lpm) aquarium pump (US$46) today. It is submersible and magnetically driven so no seal to worry about. I don't know what pressure it can develop. Chemical compatibility of the plastic housing could be a problem.

I also looked at one of those cheap (US$19) evaporative cooler pumps. They can pump 6 gallons/min (24 lpm) but again I don't know what pressure can be developed. Also the sump they sit in can be no more than 4 inches (10 cm) high.

A small centrifugal pump with a ceramic/carbon mechanical seal, rubber impeller, and metal or plastic housing would definitely provide the flow and pressure needed. But chemical compatilibility would have to be addressed.

As someone has suggested you could keep the water slightly alkaline (say with a buffer salt) and then change it out regularly.

Another option is just to run the sprayed water directly to the sewer.

My rough idea of a gas scrubber is nothing more than a vertically cylindrical tank. It would have a gas inlet above the sump level near the bottom and a gas outlet near the top. There would be a water spray nozzle at the top. The sprayed water collects in the bottom (a sump) and is recycled by a pump. The required sizes of the column and water flow rate will be determined by the flowrate of gas exiting the fume hood.

For a 3 foot wide fume hood 2 foot high and a face velocity of 100 feet/min the gas flow rate would be (3)(2)(100) = 600 cfm (16,848 lpm). Based on this it seems like the column would have to be fairly good sized.

Also for getting a good spray I think there is going to have to be a decent nozzle pressure, say at least 10 psi.

Then there is the matter of disposing of all that effluent air at near 100% humidity. This may be easy when the outside air is hot and dry but what about in the winter. Heating the air before discharge would require calrod heaters or such inserted into the gas effluent pipe.

So, are we sure we want to do this? :o

frogfot - 11-5-2005 at 09:11

Hmm, so theres quite large choise of pumps (the price will limit this..).
Quote:

Another option is just to run the sprayed water directly to the sewer.


Yeah, it would be nice to feed fresh water and drain the contaminated water below the water lock of a sink. Though I don't like the idea of having pipes all over the appartment..
Quote:

As someone has suggested you could keep the water slightly alkaline (say with a buffer salt) and then change it out regularly.


Actually now it seems that having alkaline water is the ultimate solution.. I just realised that I always reuse my org solvents (duh!) and trace amounts that comes from when you're just working with the solvent wouldn't give any problem... this small conc shouldn't affect plastic.
Now I only need a pump that's made of an alkali resistant plastic. Thogh many of plastics can handle (bi)carbonates.
Quote:

Also for getting a good spray I think there is going to have to be a decent nozzle pressure, say at least 10 psi.


IMO good spray is not needed. One could for example pour water on a net with relatively narrow holes (or several nets, one after another). This should form an even shower..
Quote:

Then there is the matter of disposing of all that effluent air at near 100% humidity. This may be easy when the outside air is hot and dry but what about in the winter. Heating the air before discharge would require calrod heaters or such inserted into the gas effluent pipe.


Hmm, I never thoat about the water fumes on winter.. One could always complicate things by cooling the water by a refrigirator compressor :o
I've seen someone were using a compressor from fridge to use for an ice-bath.. so this is doable..

Maby one can even use slightly diluted glycole instead of water..
Quote:

So, are we sure we want to do this? :o


I really don't know.. It seems to be alot of work, but this is doable.. :)

Magpie - 11-5-2005 at 15:10

Frogfot,

This is definitely doable and done all the time in industry. :) If you search "fume scrubber" you can see some commercial designs. They also usually have a demister of some type located near the gas outlet to knock out the droplets. This could just be a layer of plastic scrub pads for us Madscientists.

What I am concerned about in the winter is this big plume of steam issuing from my stack. If one could bleed or force in warm room air to mix with it to lower its humidity it might help.

Have you estimated your fume hood airflow requirement? That is the number that scares me. :o Where are you going to vent your air from the scrubber?

10 psig is nothing for a centrifigal pump. You could probably run one just as easy at 30-50 psig with such a pump. Perry's Chemical Engineer's Handbook gives some spray nozzle flowrates at various pressures from 10 -100 psig. (Sorry for not using Pascals). Spray Systems ( a spray nozzle company) has a website with the same information:
http://service.spray.com/catalog/pdfeng/catalog60b/pdf/050-52_fulljet.pdf

[Edited on 11-5-2005 by Magpie]

[Edited on 12-5-2005 by Magpie]

onga

Ephoton - 27-7-2005 at 02:05

I have an onga pump for distance water transfer.
it has its blade coated in some kind of
resistant material (sorry I dont know what)
and the housing for the blade is plastic
that is resistant to most np solvents
(even DCM)
it has seen halides oxidizing agents
acids and bases and organic chems.
first pump I bought what luck.

bio2 - 27-7-2005 at 12:40

Little Giant makes the pump you need! Many have magnetic drive impellers in all types of plastic and stainless steel.

Readily available and some are dual submersible/in line. The one I use is oil filled, end suction with polypropylene impeller and housing with SS shaft and works great for
just about anything.It also works submersed

For strong acid or base better use a magnetic drive type.

dann2 - 30-3-2009 at 14:44

Hello Folks,

Thought I would stick my 2c onto the end of this thread.
Just wondering where Peristaltic pumps can be picked for nothing!
The Xerox M750 (and friends) have a very small peristaltic pump in them for priming the heads. These may turn up on the dump.
Dishwashers? Have not seen into any of them.
Anyone any suggestions. There always seem to be a demand for Peristaltic pumps on ebay. OK if your sellen I guess.
Thanks, Dann2

Paddywhacker - 30-3-2009 at 16:10

I second Dann2's suggestion. The problem with small peristaltic pumps is the low flow rate, but you coulld accommodate that by packing your scrubber with rockwool or glass fibre and trickling the water through it.

If you are absorbing acidic fumes, and aren't interested in recovering them, then the water can be kept neutralish by a layer of garden lime in the reservoir.

Panache - 1-4-2009 at 21:48

i have like 10 of them a friend scrapped from commercial washers, if you don't mind 240V i'll send you one, they have a programmable delay also but i trash that (useful for timing the caustic flow into the dishwashers). Maximum flow is 4l/hr chokable down to almost nothing.