H2SO4 mixer options 3

[granny75]

I am looking for a device that will mix 96-92%H2SO4 with water and create a final solution of 5-10% H2SO4. I have found static mixers(on skids) and glass type mixers. Are there any other options? The plant currently has a mixing "pot". The method or type of mixing has to be safe, easy to maintain, and proven. Currently the solution outlet flow rate is about 6gpm. Any help would be appreciated.

 

[Unotec]

How big a tank?
You can have a pump recirculating the tank contents with an acid injection stream and a pH meter downstream from it.
Once the desired pH is achieved, the acid addition stops.

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[EdStainless]

I like the idea of an injection line and a static mixer. materials are the hard part. 96% isn't hard to handle, but the full range sure is. Perhaps a ceramic mixing element.

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Plymouth Tube

 

[granny75]

The day tank is 600 gal.

Unotec - Injection, like the idea, but wouldn't it need some pretty serious materials? Isn't that going through the agressive stage of H2SO4+H2O?

 

[ash9144]

What's the 5-10% solution used for?
This is very difficult application from corrosion and heat of mixing points.
Glass reinforced PTFE will work as long as you can keep it somewhat cool.

 

[EdStainless]

I was thinking of a length of resin lined fiberglass pipe with a ceramic static mixing element in it. There are some resins that can be sued in this acid. Check with Smith on the exact range of concentrations and temperatures.

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Plymouth Tube

 

[Unotec]

What pressures and temperatures do you have?

You can use a PVC piping system into a PVC tank with the static mixer in line.

Or, if money is no issue, go stainless steel.

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[moltenmetal]

Forget that latter suggestion. Stainless steel will be eaten rapidly as you pass through the ~ 25-50% concentration range.

Heat of dilution is not insignificant either. Take heat release into account in your materials selection- and have somewhere for that heat to go.

If you do have a storage tank, a pump-around using a plastic magdrive pump will work. But water and acid are so readily mixed, there's no real need for a static mixer per se unless you want to pump the diluted material continuously at a given concentration (ie. without the storage tank you were discussing). A plastic venturi in the tank will do just fine to mix the contents with the freshly diluted material.

If a mechanical over-the-side tank mixer is required, there are plenty of coating options to choose from.

 

[granny75]

The system will run 24/7 (except plant shut down) and the concentration will vary from 5-10%. So I don't think a pump around would be needed.

A venturi...would the acid be injected/introduce at the throat? Like an inline device? Would there be a potential for "hot" spots, larger concentrations of acid in the line?

Water flow rate could also be monitored with the venturi, sort of dual device and have a pH signal further downstream to verify the mixture concentration for the feed back loop. Am I understanding your venturi suggestion correctly?

 

[Unotec]

Ok, I stand corrected, no 316SS.

granquist, how complex you want the system?

If you do your mass balances correctly and install pH meters before and after the injection you can do it continuoulsy.

The 1st meter will tell the dosing pump how much to add, the second will verify pH.

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[granny75]

K.I.S.S is always the best from my experience.

As long as the system can fluctuate/control the concentration from the feed back loop.

 

[Unotec]

Then I'd add acid in line recirculating the tank until the desired pH is achieved.

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[granny75]

Thank you all for your knowledge. I really appreciate it.

 

[strider6]

granquist

You can find some info on handling of H2SO4 in these ref:

Selection and performance of stainless steels and other nickel-bearing alloys in sulphuric acid

http://www.corrosionsource.com/technicallibrary/nidi/literature/pdf/10057.pdf

http://www2.dupont.com/Clean_Technologies/en_US/assets/downloads/Equipment_FAQs.pdf

http://www.norfalco.com/documents/NorFalco_H2SO4TechBrochure.pdf

hope this help

S

Corrosion Prevention & Corrosion Control

 

[moltenmetal]

A tank mixing venturi is a device you install inside a tank to produce better mixing from a pump-around loop. The pump discharge is directed through the venturi nozzle, and this type of venturi has an open suction- no ported suction nozzle, such that it draws efficiently from the bulk of the tank. It's an efficient way to trade discharge head, which your recirculation pump is producing, for flow which is what you need for mixing. It's a way to turn a cheap plastic magdrive pump into an expensive coated mixer.

You would inject the acid into a section of line on either the discharge or suction side of your pump-around pump. If the flow of recirculation is high enough relative to your acid injection rate, you will be OK.

Check with the pH vendors if you can do 5-10% acid concentration control using pH- I suspect that the pH is too low for this to be an effective method. Conductivity might be a better bet.

 

[granny75]

Moltenmetal - yeah that type of venturi is not what I was thinking of. I was thinking of an external venturi.

Maybe it is the machanical guy in me, but I was thinking of having a venturi made, put a constant acid in the throat and vary the water, via a pump. I did the calculations and it seems I need about .4 gal H2SO4 (98%) to 10.3 gal of H2O to get me in the 7% range.

A machined venturi is simple, robust and can be coated after or made from a product that will not deteriorate under the conditions, i.e. hastelloy. Also, it can be welded...no leaky joints.

Does anyone see a fault in my logic?

 

[EdStainless]

I don't think that a metal alloy exists that will handle the venturi service. Think ceramic internals. Use a piece of alloy 20 pipe for the housing.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[moltenmetal]

I agree with EdStainless- forget about metals- this is an application for non-metallics if there ever was one. Just watch out for the heat of dilution and you have plenty of plastic options for this.

Continuous dilution is feasible but needs to be carefully designed and properly instrumented and controlled. Start-up and shut-down need to be considered carefully. Where do you send the improperly diluted acid etc.? And don't forget about the risk of water creeping up the feed acid line when you're shut down- forgetting about this situation has wrecked more than one acid injection system over the years...

If you're only using 600 gal/day, continuous dilution is swatting this particular fly with a sledgehammer. Batch dilution minimizes waste and reduces the risk that you send improper dilutions to your system- and will be far cheaper to do safely and under control.

 

[ccaissie]

I can't think of a better solution than a static mixer.

They can be made in teflon or high alloy, threaded, flanged, and with inlet ports for the Acid inlet.

Kenics , Chemineer, UET all make this equipment, and there's a wide range of costs.

At 6gpm you're talking a pretty small mixer.

CSC
UET Mixers Inc.

 

[ScottyUK]

Direct injection into a line gives your process little or no chance on the day that the injection control loop goes wild, for example if the sensor providing pH measurement fails and the pump goes to 100% injection rate. The tank provides a buffer where you have time to detect and stop the problem before it kills your process. It's not impossible to engineer the problem out, but to do that first you need to acknowedge that it exists.


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