Mixing in tanks 3

[IPGBen]

Hi,

I'm wondering what options there are when improving the mixing of liquids in a tank.
The situation is that we have a couple of tanks, in which we mix several different liquids.
The current design is that we have a pump around with the circulation enters the tank at the top.

Question I have is what other options are available to improve this process?

Greetings
Ben

 

[zerosum]

Probably agitators. What are sizes and relative geometry? Sealed or open to the atmosphere? Tsnk construction mechanically for top or side entering agitator? Lots of information needed for a competant agitator sallesman.

Perhaps just an increase in recirculation rate? Improved baffling and entry direction of the recirculation nozzle?

 

[unclesyd]

Since you state that your are now pumping around your the tank fluids you might want to adding a few eductors in the tank. We use this arrangement on several large storage tanks where we need mixing and prevention of stratification.

http://www.s-k.com/pages/pro_01_04.html

http://www.flowfactor.com/Merchant2...de=FF&Product_Code=1CTEMO&Category_Code=JPCTE

 

[JonHall]

Are your fluids miscible or immiscible? If they're immiscible are you getting phase separation in the main tank? Consider using an agitator system suitable for multi-phase blending, and check the baffles and power input are suitable for your required duty. Without decent agitator/baffle design and insufficient power you'll probably do more separation than mixing in your mixing tank!!

Good reference texts for this sort of thing are "Mixing in the Process Industries" by Harnby, Edwards and Nienow, or "Handbook of Industrial Mixing" by Paul, Atiemo-Obeng and Kresta.

 

[IPGBen]

Thanks for the quick comments and recommendations!
The links helped me in the right direction.

Zerosum:
Adding agitators was the first idea, but the installation was seen as a big problem (cost vs budget), knowing the current design of the tanks. Basically the tanks were not designed for any addition of agitators etc. So the construction would give a relatively high cost.

JonHall:
The fluids are miscible, although highly viscous. Thanks for the reference texts

Grtz
Ben

 

[ash9144]

Another possibility is mixing nozzles on dip pipes inside tank. Or smaller holes along the length of the dip pipe.

 

[tkdhwjd]

If the fluids to be mixed are highly viscous, then eductor type mixers may not work effectively, and you may have to go with a agitator. Eductors are effective if liquid is not highly viscous.

 

[itdepends]

Can you put the fluids you want to mix into the suction nozzle of the pump without any reaction/other consequences? e.g. put the hardest to mix/smaller volume stream directly into the mix pump suction instead of the tank top?

Can you use an inline mixer to blend the fluids before they enter the tank?

Can you use a side entry mixer mounted on a man door?

 

[jmw]

When you say the return is to the top of the tank, does that mean you are sparging the fluid i.e. putting air into it?
If this is a viscous fluid then that air may be difficult to get rid of.

Fuel oils are often blended by what is called "barge mixing" but is in reality batch mixing where residual fuel and then distillate fuel are batched into a tank and then mixed by re-circulating the fuel. How god the mixing is depends on the equipment and the available time.
Some such operations simply rely on the circulation and in one case it was revealed that the return was so close to the pump suction that virtually no mixing took place. Returns are always to a low level to avoid aerating the fuel (though unscrupulous operators can get huge volumes of air into the fuel by other means).

One operator has the return pipe horizontal across the bottom of the tank with a number o holes in the pipe along its length (they claimed this was not just effective but also silent having borrowed the design from submarines for some reason).

JMW

http://www.ViscoAnalyser.com

 

[greenche]

In heavy oil tanks we typically use mixers that bolt up to a ground-level tank manway.

http://www.philamixers.com/index_eng.asp?page=fixed

We have occassionally used a jet mixer that uses a pump around entering below the liquid level.

 

[Wraevyn]

Question: I have a tank that has nitric and hydrofluoric acids mixed together, along with lots DI water. I am trying to pH this to be sent out to the state. I have been adding Sodium Hydroxide to bring it up, but it doesn't seem to be working much at all. I was holding at a pH of 2.5 for the better half of the day. Adding the caustic at a regular rate, but slow enough not to over heat. I got to be around 33C and the pH started to climb. Now I am at a pH of 4.5, but again having the same problem. Every time I add more Sodium Hydroxide, it starts to lower the pH a little, but raise in temp. I had this problem when going from 2.5 to 4.5, but it seem like it took the caustic better at a high temp. So my questions I guess would be, is there a better chemical to neutralize the nitric/hydrofluoric/DI? And is the heat a factor I should be taking into consideration?

 

[ash9144]

Wr
First I'd recommend you make this a new post since you are dealing with a separate issue.
My first question would be is what is the tank made of?