You could also consider eductors?

JMW
www.ViscoAnalyser.com

We use both types, mechanical and eductors, mixing the same product. The original system of storage tanks were set up with the mechanical mixers The latest series of much, much larger tanks all have a bottom grid of eductors. The motive force comes from a separate pump but the system is setup to use the transfer pumps if necessary.

The majority of our mechanical mixers are of the side entering type. The only real problem we have is seals as the product will crystallize and cause seal problems. There has been some work to mediate this problem.

I think the power requirements are a toss up until you get to a certain size. As our larger tanks are API Type Al it would be a chore to get a side entering mixer to do the job that the eductors are doing.

There are several variables to be considered like, can the tank support the addition of a mixer, the process fluid, turnover, etc. I would get a bunch of information and familiarize myself with what's out there and start doing a  little calling with a list of you specific requirements as to what you are expecting.

Our original eductors.

http://www.s-k.com/pr_jet.htm

A lot of good information.

http://www.vortexventures.com/Literature/Literature.htm

Thank you for the information.

When I said in my original post "jet mixing" I wanted to mean eductors because as far as I know mixing nozzles are not that usual for large tanks mixing in refineries.

Unclesyd, I see that in your new tanks you are using eductors instead of mechanical mixers.Which are the reasons? You mention the seals maintenance and the uncertainty about the required power for a proper agitation. Are eductors much effective in that sense based on your experience, with a much smaller probability to be sized in a wrong way?

Any recommendation about the kind of hydrocarbons for which mechanical agitation/jet mixing are more suitable?

In my case, the tank farm is new so we can decide the mixing method we think is more suitable..

Regards

The new tanks, now a little old, are large Al tanks 45' dia x 42' tall, one is 60' x 60'.  When they were built the dynamics of a mechanical mixers were a cause for concern, so it was decided to go with the eductors. The forces generated by a mechanical mixer were consider too high to be sustained by the MOC 1100 Al.  This was based on previous experience with the smaller Al tanks. Another reason was that the process material has density of 1.35. It was purely a decision based on mechanical considerations.  

The seal problems stemmed from the agitators having to shut off during draw down and the process crystallized at the seal face. This was remedied a change in seal design and using a steam purge at the seal face along with a two speed motor where the agitator could run longer before shutdown.

Power requirements are based on what you are attempting in the way of mixing and you process fluid. It is so much easier to get the basic information now compared to 20 or more year ago. Right now you don't have to get into the mixing kinetics aspect just to what's out there that will do the job.

The second site that I posted had a great deal of very good information and as I said before get you a good handle on what's out there and your process and start talking. These people will have a very good handle on what's being done.   

I have seen in some situations, that a side mixer only mixes a limited amount of fluid - you build up a small pocket of mixing, and do not turn over the entire tank. Something related to viscosity or other.

For large tanks, if you want to thoroughly mix and turn the tank over, try pumping. You pump the stuff out of the bottom and return at the top.

"Do not worry about your problems with mathematics, I assure you mine are far greater."   
Albert Einstein
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Hello again,

I am trying to estimate an initial capacity for the jet mixers of the intermediate and final products of a refinery. I have read in different documents that for homogenization 3 turnovers can be accurate in most cases but for defining the required jet mixers  (size, pressure drop, etc) I should fix the time required for the homogenization. Any suggestion or common practice in order to define such time?

Thank you very much.

You could talk to www.jiskoot.com who supply jet mixers for hydrocarbon mixing, not sure if this is just pipelines though.

JMW
www.ViscoAnalyser.com