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Tank compressed air sparging flowrate estimate for moderate agitation
2

Tank compressed air sparging flowrate estimate for moderate agitation

Tank compressed air sparging flowrate estimate for moderate agitation

(OP)
In order to agitate a 10 m3 cylindrical tank (approx. 1900 mm dia & 4000 mm tall) using bubbled compressed air (5 barg) what would be an estimate of the flowrate (scfm) of air needed?

My estimate is 0.45 scfm (0.012 m3/min) based on a correlation I found in Perry's Handbook. Does this rate sound reasonable?

I am trying to verify this or get other estimates or correlations people may have.



RE: Tank compressed air sparging flowrate estimate for moderate agitation

Define what you mean by agitate.
Bubbling a bit of air through it will cause some agitation but what are you trying to achieve. For example if you were trying to keep a heavy powder in suspension it is probably not enough.
What is your process aim?

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

RE: Tank compressed air sparging flowrate estimate for moderate agitation

(OP)
Thanks @ashtree:

Mild to moderate agitation will be good enough. There is no powder or suspension.

The fluid is single phase, hydrocarbon liquid with density & viscosity close to water.

Actually, the process fluid is a food additive waiting to be drummed. Before dispatch it is customary to "mature" it by sparging air for 12 hrs. Apparently this oxidizes away some minor impurities & improves the flavor profile.

Not much info. is available about min. rates but the general wisdom is that if there is visible agitation that's good enough.

RE: Tank compressed air sparging flowrate estimate for moderate agitation

(OP)
A follow up question:

Will a sparger alone be sufficient in such a application or would one typically also provide an impeller / agitator.

RE: Tank compressed air sparging flowrate estimate for moderate agitation

For a food additive, I'd be cautious with compressed air for sparging if this is sourced from a oil lubricated screw compressor, given the likelihood of oil carryover through the dryers / any other inline oil adsorbers that might be fully saturated with oil - unless you're using some oil which is "food grade"??

RE: Tank compressed air sparging flowrate estimate for moderate agitation

(OP)
@george

Thanks. The air source is a "oil free" compressor & it also has an extensive post-filtration system to trap oil, particulates & even reduces the dew point to remove moisture.

So the air is safe for sparging it is just that I am trying to get an approximate estimate of the cfm flow rates I will need. The exact rate isn't critical but I just need an estimate to be able to size the components.

It is established in the lab that "over sparging" does the quality no harm so I can err on the side of abundance (but of course not wanting to overdesign if I can help it)

RE: Tank compressed air sparging flowrate estimate for moderate agitation

I'd suggest asking the food additive manufacturer what air rates are to be used for this oxygen induced oxidation / maturation of the additive.

If you do intend to use compressed air, would suggest getting this off a completely oil free air compressor for this application.





RE: Tank compressed air sparging flowrate estimate for moderate agitation

(OP)
@george

If this was just a mixing / blending application, any idea what rate you'd use?

RE: Tank compressed air sparging flowrate estimate for moderate agitation

In wastewater treatment typical rules of thumb for mixing is 10-25scfm per 1000cuft to maintain suspension of activated sludge. As you have no solids you could get away with 10 or less. It looks like you have about 400 cuft so using the 10/1000 rule would suggest you need 4scfm. But given that you have no solids to keep in suspension i think you could reasonably halve that amount.

A larger bubble size will provide more turbulence than smaller bubbles at the same airflow. A larger bubble will also transfer less oxygen into the solution for the same airflow rate, if that is an issue.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

RE: Tank compressed air sparging flowrate estimate for moderate agitation

(OP)
Thanks @ashtree.

The correlations I'm seeing seem very off from each other. e.g. Perry's Handbook recommends 0.0033 m3/(m2 min) which comes to about 0.01 cfm/ft2. (That'd come to approx. 1.2 cfm per 1000 cuft I estimate)

http://imgur.com/a/hIpHv

On the other hand, some correlations from an electroplating vendor recommend 1.5 cfm per ft2 of cross section. That seems enormously high.

http://www.tsh-technic.com/sites/default/files/doc...

RE: Tank compressed air sparging flowrate estimate for moderate agitation

Electroplating need a great deal of turbulence so that the chemical concentration remains stable across the tank including against the face of the item being plated. Otherwise the concentration reduces as the chemicals are deposited.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

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