9 replies to this topic

[chemks2012]

Dear all,

We have a cylindrical tank containing 40% Nitric Acid used for metal pickling. The tank solution is agitated by air sparge and I want to calculate compressed air flowrate required for air sparger such that there is not vigorous agitation.

I think by tank liquid depth & pipe pressure drop, we know the air pressure requirement but how to know the flow rate etc.

Is there any calculation method/equation please?

Thanks
KS

[breizh]

Consider this resource it may help you.
Breizh

[chemks2012]

Hi Breizh,

Thanks for your reply/literature. In fact, I already got them from internet but there is no much help.

Just to clarify, we do not want any mass transfer between air and tank liquid but we need only uniform mixing and therefore some swirls on the liquid surface would suffice and we do not need vigorous mixing.

I am just wondering, normally, how do we estimate the air flowrate and air pressure required for such application?

Thanks

[breizh]

I don't see other mean than installing a meter to quantify your needs !

Breizh

[DB Shah]

Can you try a circulating pump

[chemks2012]

Hi Breizh,

Thanks but I want to estimate the flowrate first.

Hi DB Shah,

Thanks. Agree, I have that option of using recirc pump but want to install air sparge system.

All,

Any help?

[chemks2012]

All

How do we normally design air sparge agitation system for a tank to ensure uniform mixing (no mass transfer is required)?

Any standard method?

[ankur2061]

chemks2012,

Refer the discusssion and the excel spreadsheet attachement in post #3 in the link provided below. It might help.

http://www.cheresour...-concrete-tank/

Regards,
Ankur.

[Steve Hall]

KS:
The reason you haven't gotten an answer to your specific question is that the fluid dynamics are complex; there's no "standard" method. It's hard enough to model a mechanical agitator for uniform blending and the calculations require knowledge of the Pumping number for the impeller being used. For a sparger, the size and number of the air bubbles will have a big influence on the mixing I think. Your sparger design will control these factors.
One possible approach is to calculate the time for a bubble to travel from the sparge point to the liquid surface -- sorry, I didn't look for an equation or algorithm, but it would be a macroscopic rather than microscopic (diffusional) correlation. Then, you could calculate the hydraulic pressure at the sparge point and from that know the decrease in bubble size as it travels. I then imagine a spreadsheet that provides an input which is the percent of volume occupied by the air at the sparge point (in cross section across the tank) - say, 5% or so. Now you could calculate the total volume of air in the bubbles throughout the tank from sparger to surface. You already know time, so this gives you flow rate in actual volume/time at the pressure condition at the sparger outlet. Convert to mass units. If you assume your sparge pipe is large enough so the pressure drop due to friction is low compared to the hydraulic pressure, you now know the flow and pressure requirement. Finally, since you have no test data, do a range study where you change the volume assumption (5% above) from, say, 0.5% to 15% and see graph the results.
If you could do some kind of pilot test, go for it. Otherwise, use an approach similar to above suggestion and, if the economics are OK size the air pipe and sparger based on your judgement knowing you can turn down the air rate as needed to give you the visual mixing result you desire. You know your upper limit for air is significantly less than 100% of the tank cross-sectional volume as described, so you do have a solid basis for a maximum capacity value

[breizh]

http://www.pulsair.c...mical-mixer.php
Hi ,
You might be interested contacting them .
Hope this helps

Breizh

Edited by breizh, 08 August 2012 - 02:28 AM.