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Mixing viscous liquids in storage tanks

Mixing viscous liquids in storage tanks

(OP)
How can you mix a 55 m3 atmospheric storage tank with a viscous liquid (different products are stored) in the range of 200 to 6000 cp without using a mixer with huge motor?

RE: Mixing viscous liquids in storage tanks

Slowly. It's a matter of how long you want to/can wait for it to get mixed.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: Mixing viscous liquids in storage tanks

Does the product thin when heated? can some of it be heated?
Could you sparge with a gas?
At this viscosity an eductor will be of little use.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Mixing viscous liquids in storage tanks

If the product foams (like our products), you do not want to sparge it with gas. Our products will foam up and out the vent! What product is it?

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: Mixing viscous liquids in storage tanks

(OP)
Thanks for the answers. It is resin with solvents. Mixing is required to keep temperature homogenous and make sure solvents are not accumulating at the top of the resin. Temperature is a given and has to stay constant. I dont think there is foaming issue.is it feasible to sparge gases through such viscous liquids? How good can i mix with just a pump recycle flow back to the tank?

RE: Mixing viscous liquids in storage tanks

Drawing-off from the bottom and pumping back to the top is probably adequate for keeping resin and solvent mixed. You do not want to sparge through solvent. Drawing-off or pumping back to several locations would speed mixing. Air-operated double-diaphragm (AODD) pumps work pretty well for this type of operation.

RE: Mixing viscous liquids in storage tanks

Just one recycle loop is likely not enough by the time you get to 1000 cp, I'm picturing a setup where there are multiple pumps drawing from multiple points in the tank to create the recyle loop.

Sparging might just punch holes through the product and not really mix anything...I'm not very familiar with sparging applications though.

Just curious, is there a particular reason you don't want to use an agitator?



RE: Mixing viscous liquids in storage tanks

What do you call "huge"? I would guess what is needed is something in the 5-20 hp range. That is not huge, IMO. If that seems reasonable to you, contact a good mixer company and have them work on a quotation, or give us more information on the tank, it's dimensions, and it's orientation.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: Mixing viscous liquids in storage tanks

(OP)
It is right. I expect sparging to create holes and disturbs mixing. With high mixer speeds in the reactor of the resin we had quality issues.
Pumping from multiple places could be a solution.
Two reasons for not wanting a mixer:1. It is horizontal tank. Due to space and process limitations it is very difficult to fit a vertical tank. Mixing horizontal tank with such volume and using a mixer is not possible.maybe multiple mixers? 2. The available electricity in the plant is very limited.
Btw i expect much higher power such as 100-150 hp.

RE: Mixing viscous liquids in storage tanks

We have similar size vertical tanks in similar duty and viscosity range, but for aqueous emulsions (latex). They have 10-15 hp. Slow RPM with large D/T. 99.9% mixing times < 1 hour. Yes, horizontal is not convenient when mixing. Gravity becomes a hindrance instead of a help.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: Mixing viscous liquids in storage tanks

(OP)
Hello Latexman,
Thanks for the info. Very interesting. Do you mean the time to circulate the liquid in the entire tank is < 1hr ? Do you have recirculation in the tank separately ? Difficult question but can you indicate how good the mixing is ? Is is only to create fine particles in the liquid?

RE: Mixing viscous liquids in storage tanks

Do you mean the time to circulate the liquid in the entire tank is < 1hr? No, the "turn over time" is much less.

Do you have recirculation in the tank separately? Yes we have that capability in some cases, but I am discounting that because it is inferior where we have mixers.

Difficult question but can you indicate how good the mixing is? If we added water to adjust solids or viscosity, it will be 99.9% homogenous in < 1 hour.

Is is only to create fine particles in the liquid? No. Our products are stable emulsions for the most part. Few that sit for long periods of time (weeks) without mixing can have some settlement.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: Mixing viscous liquids in storage tanks

(OP)
Good information. Thanks for the help. I will look reconsider using mixers in that case. 10-15 hp sounds reasonable.

RE: Mixing viscous liquids in storage tanks

Good. If adequate time is given, I think the mixer will be a reasonable size. On our process vessels, reactors and vessels that directly and immediately support the reactors, we have 99% mixing times that are in seconds to a few minutes, because we don't want to keep the reactors waiting. These vessels and tanks have relatively large mixers. But on vessels and tanks that do not directly impact the reactor cycle times, we are more relaxed from a time standpoint. On blend tanks, the 99% mixing time may be minutes to 1 hour. Our operator instructions would say something like, let mix for 1 hour (if 99% mixing time is minutes) or 2 hours (if 99% mixing time is <= 1 hour),and then sample. "Day tanks" and storage tanks have relatively small mixers and would have operator instructions like, mix for a shift (8 or 12 hours) or over night, before sampling or loading the truck, something like that.

Please let us know how it turns out.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: Mixing viscous liquids in storage tanks

I wonder the jet mixer is suitable for your need, cause I saw some jet mixer/pump back design for the storage tank (250 m3) stored the AE3~9 EO or fatty acid chemical which viscosity is less than 200cp, and the pump motor is around 8 kw.

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