How to design a 5000 ton limestone silo ? 4

[Choco2000]

Hello friends I´m new in this forum, I hope we can shere a lot of experience.
I own an engeneering firm and we have the task of desig a 5000 ton limestone silo (steel or concrete), any help on the way to do this, any experience , any tip, any method would be apreciated.

Thanks

 

[dvd]

Is the limestone in one piece?

 

[MikeHalloran]

Method 1:

Hire an engineer for your engeneering[sic] firm.


You need a good secretary, too.



Mike Halloran
Pembroke Pines, FL, USA

 

[JStephen]

Gaylord and Gaylord have some information in the "Structural Engineering Handbook". They also did a whole book on bin and silo design, although it's out of print. I think John Buzek has a book available through SPFA/AISI on bin and hopper design. There are probably some other references out there as well. Refer to ASCE 7 for seismic or wind loading. I believe there is an ACI standard of some sort for concrete silos, and I think there some foreign (non-USA) standards that would be useful if in those countries.

One of the challenges is making a hopper flow. Another problem is that the pressures exerted by the product are not known with great accuracy. You can make assumptions and calculate pressures and drag, but make different, equally reasonable assumptions and the numbers will change entirely. Another issue is that in many cases, there is not a specific design code or standard used for hoppers and silos. Another issue is that the design of leg-supported structures is poorly addressed in the common literature. If the structure is filled and emptied symmetrically, then it is usually assumed to have symmetrical loading inside. But if you fill or withdraw on one side, it complicates the design considerably. In a lot of cases, accurate material properties are not available.

You might also refer to the "Structural Engineering and Other Topics" forum on here.

 

[lilliput1]

Would there be limestone dust and would they be an explosion hazard? Would people that sedign silos for flour also be capable of designing silos for limestone? You must have a registered structural engineer do the design to not be liable & to follow the engineering Code of ethics.

 

[JStephen]

Limestone is not flammable- no explosion hazard. And it need not specifically be a structural engineer.

 

[tomwalz]

Not at all my area of expertise but don't you burn limestone to make lime?

Tom

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

 

[mrMikee]

Bin design is basically a structural engineering problem although the functional aspects such as material flow etc. is very important too. I'd check out the following.

ACI 313 Standard Practice for Design and Construction of Concrete Silos and Stacking Tubes for Storing Granular Materials

http://www.jenike.com/

A 5000 ton bin is a very large bin. I'd suggest getting the help of a consultant experienced in bin and silo design.

Regards,
-Mike

 

[Darken99]

Choco2000,

Just to add onto what mrMikee said, there are other things you need to consider when building bins & silos. One thing people don't look at is an anomaly called bridging. While the material is being emptied and an air pocket is created. This can put a large load on the sidewalls. The worst part is when a large portion of the material drops in the silo causing a vacuum. If the bin/silo’s sidewalls are only designed for outward force, it is possible that bridging could cause a vacuum collapse or sidewall failure. I have no experience with limestone, but it is important to keep any moisture out to prevent it from solidifying.

If you are unsure about how to design this bin, I would take mrMikee's advice and get a consultant with experience with large bulk storage bins & silos.

Regards

 

[JStephen]

I think you heat limestone to make lime, but it takes an external fuel.

From past experience working with hopper cars, I know it varies a lot as to how free-flowing it is. Larger rock without the fines will flow pretty well. Stuff with the fine material, especially when wet, is more of a problem.

 

[Choco2000]

MikeHalloran, we have 2 civil engineers, but like JStephen wrote, there is not enough literature about this, also in civil school don't teach these procedures. Right now we are using the JOHN PIROK method described in the Structural Engineering Handbook, but we just have this chapter of the book. JStephen in this book, you said there are more design methods, Where can I get it?, do you have it?,

I just called limestone for the post, actually is lime in 3" size rocks, lime is what we get after the oxidation (burned limestone).
We have designed several silos in the past for this material, the largest one is 500 tons, and never had any problem, the lime is very dry and the humidity we have is less than 30%, lime does not form bridges inside the silo actually it flows very well. But the thing here is that we are talking about a 5000 ton silo, is a huge silo and its design, from what you may think, is different than grain silos.

Here in México is very difficult to get someone with the expertise for such task, we don have a specialist office like you guys, so we may go with a foreing supplier, but first, we have to see all our options, mrMikee I’m going to check on the aci 313 to see a concrete option.

 

[civilperson]

Put in a cone shaped base at the angle of repose for your lime, (26-40 degrees) or used pneumatic vibrators to ensure flow. Collect in tunnel under tank and use auger transport to outlet. Use aspect ratio greater than 1:1, (height to diameter,60'height to 40' diameter) to minimize equipment for filling. Concrete tanks with post-tensioned wound steel on the exterior are very cost effective for large horizontal loads such as liquids and seismic events.

 

[PeterCharles]

There is plenty of literature available regarding the design of silos (do a Google). The critical start point is the design for flow, either core flow or mass flow. Once you have established your flow regime you can start your structural design as the loads imposed on the bin by the material stored are different according to the flow regime that exists inside the silo.

 

[mrMikee]

Choco2000,

I use the Janssen's equations in ACI 313 to calculate pressures on bin walls which is the only published code in the US that I know of concerning material pressures in bins. However there are a number of other ways to do this but it is interesting how different the results are. There's been recent work in Europe concerning current state of the art in bin design but I don't know if anythings been published. Try a search for Michael Rotter on the internet because he has something to do with the design part of the effort.

As JStephen said the book by Gaylord and Gaylord titled "Design of Steel Bins for Storage of Bulk Solids" is the best text I have seen. I use the plate bending equations for my designs. It is out of print and difficult to find (and expensive) used on the internet. There have been some discussions on bin design in the Structural forum and there are a few people there that I consider to be very knowledgeable.

For very large bins the only literature I've found concerned coal bins. Large bins will generally need cross beams spanning between the sides which can be a difficult problem to design because of the unpredictable but large forces generated by flowing material. Many years ago I was at a presentation of a technical paper by some engineers from Sargent and Lundy that covered a project of theirs for a very large coaol bin. It looked like a state of the art design to me.

But again I'll say that a 5000 ton bin is a very large bin, much bigger than anything I've done myself. Bins for bulk materials is a specialized area of design and there is not much good practical information.

I think you need a consultant or two that can verify the design and flow properties of the limestone and then properly design the bin structurally.

-Mike

 

[prohammy]

Choco,

If you decide that you do need an external vibrator, try this website...

http://www.nettervibration.com/en/home/home.html.

Good guys (european, but as far as I know they supply globally)


Kevin Hammond

Mechanical Design Engineer
Derbyshire, UK

 

[katmar]

I am not a bin designer, but I have project managed their construction. What I learned from the designers confirmed what PeterCharles said - the flow regime can cause enormous vertical downward forces in the shell because of the friction between the solid and the bin wall. Solids do not flow downwards like liquids and they can drag the shell down causing catastrophic failures.

Boiler and power station engineers are the most likely sources of expertise because coal bunkers have the same requirements.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[arto]

There's bin /bunker design info in chapter 7 of Troitsky's "Tubular Steel Structures," available from:

https://ssl.lincolnelectric.com/foundation/item.asp?prodnum=TS&PID=16

 

[Choco2000]

thank you prohammy , we allready use vibrators in some of the customer bins, the first were german made, now we use custome made ones, thanks for the tip¡

arto, I just slip my credit card to get this book, it will be here in 10 to 15 days as they say, thank you for the tip¡
Regards

Adolfo Gómez
Ingeniero de proceso
AIL de la Laguna
Torreón, México

 

[PeterCharles]

The important thing to remember is that if you go for a circular silo with a conical bottom and you end up with mass flow, then there is a heavy pressure 'kick' at the junction between the circular barrel and the bottom cone.

You could do worse than search this specialist storage forum and pick up a lot of current knowledge that may not be in some standards that could do to be updated.

http://www.bulk-online.com/Forum/forumdisplay.php?s=&forumid=38