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API650 Tank with side wall agitator

API650 Tank with side wall agitator

API650 Tank with side wall agitator

I have a customer that has requested a tank designed to AI650 standards with the exception of adding an agitator in the sidewall. Has anyone ever come across this? I'm not really sure how to approach calculating a safe wall thickness. Any recommendations on where to find information to solve this issue would be appreciated.

RE: API650 Tank with side wall agitator

The agitator supplier should provide complete nozzle loads (overturning moment, operating torque, dead weight at a minimum) and you should input that into a nozzle analysis to confirm will be well. Request the mixer vendor's maximum deflection criteria (stiffness) because the flexibility of the nozzle supporting the mixer is the limiting factor, not simple stress in the tank wall. API 650 does not have stiffness criteria but agitator suppliers should have one. API 650 Annex P may be of interest to you but I've heard that tank analytical software is preferred for this.

A couple points of great importance:
1) Tank nozzles are not usually designed with agitators in mind, so it's not a guarantee that it will work.
2) Pay attention to the tank nozzle/manway bolting pattern. There are so many things referred to as '24" manway' or '24" nozzle', that you should double-check the actual bolt pattern being supplied to be certain. I've been involved with a few cases where nobody checked closely until the mixer arrived on site and the tank was pumped down and cleared, and the mixer adapter flange did not line up. That is a sad, expensive day that is perfectly avoidable.
3) Pay attention to in-tank obstructions and clearances. Floor clearance, roof clearance, roof supports (if any), and the minimum liquid level for operating the mixer. Ensure the mixer controls are interlocked against the liquid level to ensure it's never operated where it can damage the roof lining. If the mixer swivels, check clearances at full sweep - this is important because nozzle neck lengths vary.
4) If the mixer has any auxiliary supports, ensure they are constructed to allow the normal tank wall deflection between empty and full. A rigid leg under the mixer that makes the mixer and nozzle into a flying buttress is generally a Very Bad idea for both the mixer and the nozzle.


RE: API650 Tank with side wall agitator

I have a little experience with sidewall agitators (also called side entry) in large diameter tanks..

My experience has been that these agitators usually are applied to large diameter tanks where a somewhat viscous fluid must be kept moving.

(e.g. Crude Oil Storge tank)

They usually are working in groups on large diameter shells

I am curious why he has insisted on a single sidewall agitator .... He only wanted one, right ?

- Do you know more about the tank size, temperature and nature of the fluid ?
- Has he expressed a desire for a certain vendor and a specific model agitator ? If so, I would contact the vendor
- Contact SPX, they make robust side entry mixers and have details that are typically given to tank fabricators
- Bear in mind that some mixers require auxiliary supports and some do not .... they CANNOT be added in the field after the tank is commisioned ... These robust clips must be accurately positioned .... You must know which agitator your customer is selecting !

As stated above ... Location of the agitator manway elevation must consider minimum tank operating level !!

David Geesaman, above, offers solid advice

Sr. Process Engineer

RE: API650 Tank with side wall agitator

Quote (MJCronin)

They usually are working in groups on large diameter shells
I am curious why he has insisted on a single sidewall agitator .... He only wanted one, right ?

Several good points and I'll add to this one. The right quantity and arrangement of side-entry mixers is a balance of having the mixers work together to generate a predictable flow field, and incorporate as much of the tank volume as possible in the bulk flow. However, too much mixing energy can also cause issues and excessive nozzle loads. It definitely makes sense to confirm the process fluid and have the mixers sized and located to produce the best effect (BS&W control and blending do best with different side-entry mixer setups). Asphalt requires special consideration because it may require steam line service to keep the seals from sticking shut.

It is rare to see a single side-entry mixer produce quality mixing. A normal number is two to five for an API 650 floating roof tank.


RE: API650 Tank with side wall agitator

Thank you everyone for your help and suggestions. The tank is a stock tank @ 130°F adn SG 1.0 for a papermill, the agitator brand and model is specified by the engineering firm designing the facility, they provided me the forces and moments from the actuator for design. They just didn't spend the time on the tank design and instead called out "per API650" for shell bottom and side wall. Overall it's a small tank 16' diameter with a sloped bottom. The engineer has located the nozzle in the tank I'm waiting for information from Selzer on the agitator insert the engineering firm specified a "SI-24". I did run a few scenarios using compress to look at nozzle loading (thanks for the idea David!). This looks like it will be a good solution once I get the actual info on the insert.

RE: API650 Tank with side wall agitator

Pulp and paper side entry mixers are a little different machine from petroleum side entry mixers. Much of what I commented on is focused on petroleum side entry mixing, since API 650 is fundamentally an oil storage tank standard.

Paper pulp is really, really hard to mix effectively. It acts as a yield-stress fluid, which is to say the moment it isn't being directly forced to move, it stops moving. To be honest, I've never seen a side entry mixers perform the actual duty of mixing an entire paper pulp vessel. In reality, they keep the pulp moving in a critical area so that the paper pulp doesn't stagnate there.** The bulk product movement comes from something else (e.g. gravity).

The side entry mixers used on oil tanks (such as the Plenty/Lightnin already linked) are best designed for circulating purely-liquid oil products in large, relatively shallow tanks. Paper pulp side entry mixers tend to be simpler and more brutish to withstand the irregular flow of the paper pulp, and tend to have stuffing boxes and lack shutoff devices. Your chosen mixer supplier should be able to assist with these things.

** There are top-entering mixers that have proven highly effective at mixing paper pulp, but the paper industry rarely invests in converting to them. Side-entry mixers remain dominant for reasons other than pure mixing effectiveness. But if you're designing a new tank - perhaps that's worth discussing now.

** Stagnant paper pulp will rot and become a hazard. Ensure that there are no shelves or obstructions that will allow portions of the product to hang up. Unless it's right in front of the mixer, the mixer likely won't stop the stagnation.

RE: API650 Tank with side wall agitator

Most side entry mixers I see are installed in shell manways. API 650 gives guidance on thickening the manway components for such circumstances.

RE: API650 Tank with side wall agitator

Most of the side-entry mixers offered by the major vendors have giant motors with belt or chain drives ....

IMHO, this implies significant nozzle/manway loadings

You should know that the latest atomic whiz-bang in pulp and paper side entry agitation is the SB "SWIVEL MEISTER" .... offered by NOV !!!!

( I do not know if SB stands for "Sum Bitch" or not ..... Hmmmm ????!!!!)

These swivel units give something for the lazy plant operators to do ... although the swivel action must tear up seals ... in my opinion




Philly Mixers have these models: (Note the neato mountings on the tank shell !!!)


Sr. Process Engineer

RE: API650 Tank with side wall agitator

Quote (MJCronin)

These swivel units give something for the lazy plant operators to do ... although the swivel action must tear up seals ... in my opinion

The swivel mixers are used for stopping sedimentation in crude oil tanks. Changing the swivel position every week or so ensures the entire tank floor stays clean.

A well-made mixer swivel seal is a heavy reinforced rubber packing ring that lasts a long time unless it is chemically attacked. The sliding speed and duty cycle are both very low.

I've only ever seen swivel type side entry mixers in crude oil storage, not in a paper pulp application.

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