Evaluation and design of in-tank mixing systems 5

[JASR76]

Hi all!!

I have a question about mixing one fluid in a tank. In my case we're working with a big tank (50000 m3) and we're designing jet mixers inside it. Our design involves three nozzles inside the tank that recirculate our fluid inside it. We're using a pump to get this operation.

My problem is that I've found some equations and I dont know where to find the parameters:

H >= P * S/sen^2(delta+5)

H= pressure in our nozzle to mix properly

P = parameter for my fluid = K*(d2-d1)/d2
K= constant depending on our density
d1=density inside the tank
d2=density in the nozzle at the entry

delta = angle of my mixer/nozzle

S = heigth from the nozzle to the surface of the liquid inside the tank


Well, after this mess, does anybody know where to find this parameter P ? I know that is 0.35 for gasoline and 0.86 for the crude, but my case is gasoil...

Thanks in advance

 

[TD2K]

I'm not familar with the equations for jet nozzles (will be interesting to see what others say] but the equation for P looks very odd. The density inside the tank and the density in the nozzle is going to be the same hence the whole equation for P goes to zero.

 

[JASR76]

TD2K thank you very much for your answer

But probably it's not as odd as you think. The density inside the tank and the density in the nozzle is not going to be the same, because when you have fluids like crude, gasoil, etc.. inside the tank the density distributes along its height and for the crude,for example, you would have 0,93 kd/dm3 near the bottom of the tank and 0.86 at the top of the tank. Thats the reason we use a jet mixer, because these kind of fluids tend to stratify.

Anyway, I agree with you, it will be interesting to see what others say....

 

[Shahin71]

Why not using mechanical mixers "Side Entry Mixers"

In jet mixers

1. High fixed cost : Pump cost,piping and valves
2. High operating cost: Pump power
3. Jetting shall create static charges in the tank.

Side entry rotary mixer"Propeler Type" shall be a better option in my opinion.

 

[TrevorP]

I'm sorry, but I disagree with Shahin71.
Liquid jet mixers can be bought off the shelf at relatively low cost from GEA etc. (or made yourself if you know the equations. I'm afraid I don't.).
The pipework is usually already largely there.
The seal is a gasketted flange rather than a packed gland or mechanical seal, and so is much less likely to fail. The pump usually already exists, so there is no need for an additional motor (to drive a side entry mixer). Liquid jet pumps have no moving parts so are less likely to fail in service or require expensive maintenance.
Disadvantages are that they are limited to low viscosity and they don't work at levels below jet entry level. I've not heard of staic issues in vessels due to liquid jet mixers, but static issues can be virtually eliminated by good earthing in metallic tanks and pipework.
Given the large size of the tank, I don't think you'd stand a chance of doing anything very much with side entry agitators.

 

[alaaz]

I understood that you have to mix 3 different kind of liquid : crude,gasoline and ? I'm not sure if you would like to get some lubricants-that's a right way.The density of all 3 products are different.In my experience we mixed 3 dif. products for getting lubricant for some industry.You have to take 3 nozzle on the different level on your tank: 1.a first and lower nozzle use for product with easiest density; 2.a second middle nozzle use for product with heavier density; 3.and the last nozzle use for product with heaviest density. You have to finish first step at all, than finish second step at all, after all use the last step. The heaviest product is going to bottom of the tank (highest density) through middle product to easiest-so,you will mix them.will be better if take the warm products,take the right % of your products(I think you are going to use the 2 kind of lubricants and...some of crude).Give the mixing product to laboratory for testing.

 

[Montemayor]

JASR76:

I've used tank jet mixers. I've used them with success in a variety of high-grade, viscous and slightly viscous liquids. I've employed them in storage tanks 25,000 to 70,000 gallons capacity. I have a profound problem with what you state. Either I don't understand the manner you present the problem or perhaps I understand it correctly and you are working the problem wrong:

1. I always followed the mixer fabricators specific instructions and directions for efficient, in-tank mixing; this has never failed me and yet I fail to understand why you don't do the same.

2. Where is it exactly that you got your "equations" from? And what degree of accuracy, applicability, or plane of reference do you lend to these equations? I wouldn't trust them unless they came from the fabricator or if I derived them myself. Since I can't begin to derive the equations, ...;

3. Even if your equations are applicable, your nomenclature is not: what angle are you referring to? with the horizontal? with the tank wall? with anything else?
What density in the tank are you referring to? The tank density will be different throughout - isn't that why you are mixing in the first place?

What are the units of your equation(s)? If you can't provide units, how can you establish constants or "parameters"? The answer is you can't do this without fixed, identified units throughout.

I can't speak for others, but I just can't trust any parameters anyone would offer without specifically identifying all the units involved and the fabricator as well as the style, model and type of mixer(s).

Engineering never was and never will be comprised of cookbook recipes. Each problem has a solution, but it also requires basic data. I wish I could help, but we don't have the basic data here.

Art Montemayor
Spring, TX

 

[JASR76]

Excuse me for my bad explanations, I’ll try to explain better now:

I’m working with a storage tank 50,000 m3 capacity. The fluid inside is gasoil. I’m trying to design three jetmixers identical to get a good in-tank mixing (avoid stratification). I’m using a pump that already exists (this pump is used to empty our tank) to recirculate the fluid inside the tank sending it to the jet mixers.

Montemayor:

1. I usually follow the mixer fabricators specific instructions and directions for efficient, in-tank mixing too. But in this case I’d like to know how to design this jetmixers, so I found these equations in a book: “Le petrole. Raffinage et genie chimique” of the Institut Francaise du Petrole.
2. “Le petrole. Raffinage et genie chimique” of the Institut Francaise du Petrole. I think they are accuracy but in this book you only have the equation and not how to obtain them.
3. My angle is with the horizontal. The density of the fluid is 0.85 inside the pipe flowing, but I don’t know the density of the fluid once you leave it inside the tank (stratification would increase density in some areas, perhaps 0.90?).

Due to this equation is not theorical (I think is deduced from some experiments), I didn’t give you the units, but here they are:

H >= K*(d2-d1)/d2 * S/sen^2(delta+5)

H= meters of liquid column
K constant that depends on the density
S = position of the jetmixers. Meters under the surface of the liquid
Delta = angle with the horizontal in degrees
_d = density in kg /dm3

I didn’t give all these data because I thought that any of you would recognize these equations and could tell me where I could find more information about this K factor or more information about these equations.

Thank you all

 

[25362]

From the sources I could get my hands on:

The minimum pressures, MN/m[sup]2[/sup] in front of the nozzles of jet mixers for storage tanks are a function of the liquids' viscosities, as follows:

visc. cP of the oils MN/m[sup]2[/sup]

less than 50 0.07-0.14
200-800 0.3-0.45
2000-6000 0.6-0.7