Pump selection help needed for tank circulation...

[STENCH999]

I have a 50 gallon tank containing a Black Oxide chemical solution for blackening metal.

Tank operating temp is 200 deg F.

the MSDS for this solution shows:
Sodium Hydroxide <30%
Sodium Nitrate <10%
Sodium Nitrate <1%

This concentrated basic solution gets mixed 50-50 with water.


I would like some help on selecting a suitable pump (or maybe something else?) for circulating this tank for even temperature dispersal.

Right now all i have in the tank is water, and there is a huge temp difference between the top and bottom of the tank, I was thinking of an external pump that would take the hot fluid from the top of the tank and pumping it down to the bottom.

This pump would be in continious operation pretty much all of the time, so something reliable with a long life span would be what I'm after.

Any help would be greatly appreciated.

 

[Scipio]

Have you considered a small mixing agitator inside the tank instead of a pump?

 

[TZellers]

Scipio has a great idea if you just looking to keep things at even temps. sodium Hydroxide is troublesome when it comes to mechanical seals and even magnetic coupled pumps, although I would have to give the edge to the mag-drives (unless double mech seals are involved).

 

[STENCH999]

I have considered an agitator setup, but space is of a concern.

There is not much room in the tank when the chainsaw bars get dipped in.

 

[TZellers]

Well, you may want to consider a duplex positive displacement pump, but I'm not what temperature limitations they have.

If you do go for a centrifugal pump, I would recommend a low speed pump for several reasons, namely the lower PV values on the mechanical seal (sealed pump) or plain bearings (mag drive). The cheaper neo magnets used are temperature sensitive, so you may need to compensate for them (they lose strength and higher temps, but if the pump was designed appropriately, you shouldn't have much of a problem at 200. Get above 250, and SamCo magnets are much better. Also, low speed pumps last longer as the bearings don't have near as much load (assuming sotck motors, etc) on them.

All things considered, in a sealled pump the only wear item is the seal. The pump should last a long time, but you may have to spend $200 or so every 6 months or so on a seal.

 

[STENCH999]

After talking to a local distributor, he suggested a Little Giant model TE-3-MD-HC:

http://www.littlegiant.com/littlegiant/specsheet.nsf/SpecSheets/581604/$File/995779_TE-3-MDHC.pdf

Can somebody concur with what was suggested?.

many thanks

 

[Scipio]

The pump itself looks like it would do the trick, assuming it's piped up properly and that Ryton, which I'm not familiar with, can handle the NaOH solution. Usually I've seen teflon lined mag drives running that stuff, or simple stainless steel if there's no chlorides in the water. I don't know if anything like that's out there in your flow/pressure range though. One thing to check with the manufacturer, however, is the NPSH requirements of the pump - since your solution is so hot you might have problems with cavitation if the pump needs more than a foot or two of suction head.

 

[TZellers]

I don't have my LG book handy, but in support of what Scipio said, just about all of the March or LG mag-drives spin at 3450. These mag drives usually have stationary shafts with impeller/magnet assemblies that rotate around them. This setup requires a spider/thrust bearing located at the front hub of the impeller (for axial thrust). This spider/thrust bearing is a necessary obstruction to support the stationary shaft, but increases NPSHr, especially with the relatively small eye of the impeller in these size pumps. Definately check the NPSHr curves and do some basic calcs to see if it will be a problem. You may have to spin at 1750rpm to reduce the NPSHr (better idea anyway). I don't know if the bearings are sized to run at low speed however, so ask. I'll check in my LG book by this afternoon and post what I find.

 

[HEC]

May I suggets a ducted agitator in the tank to "pump" the tank contents around. Or I note that the tank is heated, where are the heaters mounted, the high temperature may provide an opportunity to use convection to do the mixing. You should try thinking out side the square, rather than installing a pump and external pipework that will become a maintenance cost, leak hazard etc.
In relation to the Mag Drive pump these pumps are quite sensitive to the bearings running dry. Cavitation is also a problem. You may be getting more problems than you are solving.
HEC

 

[Scipio]

You know, since HEC is suggesting agitators again, there is another option getting back to agitators - you can get magnetically coupled, bottom-mounted agitators for this size of tank. Bottom mounting, with a low profile impeller, might solve the problem of the agitator getting in they way of dipping your blades. You could put a grill of expanded steel or something over the impeller to keep from dipping the blades right into the agitator itself. Might be overkill for what you're looking for, but I figured it was worth throwing out. Check out this site,

http://biotechniconline.com/magagitators.html.

 

[TZellers]

Sorry for the delay. My LG book is low on engineering inof, no max temps, no speed limits indicated. The curves only show 2 pole 50 and 60Hz performances.

 

[ChickenSoop]

I'd also recommend a mixer. A pump with mechanical seal - the seal would have to be a double. Not too many little pumps have this option. Also - won't there be little metal filings after a while? If so, a seal won't hold up long.

 

[MikeHalloran]

If the solution is not subject to foaming, you could use a sparger pump, easily constructed from PVC and driven by a small flow of compressed air.

Primary component is a big PVC sweep ell, of the kind they sell for plastic conduit, 2" size or bigger. This is suspended in the tank with one leg horizontal and one leg pointed down, flush against a side or an end.

Second major component is a little porous plastic throwaway air line muffler, 1/4"NPT or so, suspended just inside the distal end of the vertical leg of the big ell and supplied with compressed air at ~<3 psi. An air line regulator with 1/4" npt ports is plenty big enough.

Set the regulator so there is just enough pressure to offset the static head at the muffler. The muffler emits a fine cloud of bubbles, which travel upward within the big elbow, then emerge in a stream from the horizontal leg, inducing a nice circulation around the tank, while drawing dense liquid from the bottom.

You'll be amazed at how effective it is, and how strong a circulation it can induce.

The ones I made for our acid pickling and passivation tanks were actually supported by the air feed, an inverted 'J' constructed of 1/4" sch80 PVC pipe and fittings, with the vertical leg stuck through a milled hole in the outer radius of the big PVC ell. Next time I'd use a bigger, stronger air feed or put the whole thing in a sturdy box; our guys managed to destroy all of them in less than a month by dropping heavy workpieces on them. Maybe your gorillas are more gentle. ;-)




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[STENCH999]

Mike,

I wish there was room in these tanks for some of the ideas you guys mentioned.

http://www.myfilestash.com/userfiles/STENCH999/BLACK OXIDE1.JPG

http://www.myfilestash.com/userfiles/STENCH999/BLACK OXIDE2.JPG

the only room i can use inside these POS tanks is pretty much just below these heaters.

Thanks for all your help guys!.

 

[sreid]

Let me suggest pumps from Sethco. Excellent Technical Staff. Qualty, reasonable prices.

http://www.sethco.com/html/mag_3.htm