Flat bottom bins

Matt Stak
(not verified)
Posted in: , on 20. Dec. 2007 - 14:51

I am looking at an installation with 1000 tonne square storage bins for molybdenum ore at a plant in Western Australia. Rather than go for a mass flow design, we are looking at flat bottom bins with a small mass flow chisel shaped hopper section below. The idea being to create some rock boxing effect to protect the bins walls as this ore is extremely abrasive. I have heard an opinion that this will not work, so I seek your opinion on the matter. As I see it, as long as the small hopper section opening exceeds the critical arching diameter (which it does easily) and its mass flow by design, then the large feed bin above should still flow, even with some dead zones in the corners, to give a funnel flow effect. Any thoughts/comments?

Re: Flat Bottom Bins

Posted on 20. Dec. 2007 - 03:20

Mixed flow silos do work and I think you are going in the right direction. You can also consider core flow bin with shallow cone angles and properly size outlet this will have no flow on the walls but will have bigger dead regions if you are willing to live with reduced live bin capacity then I don’t see any problem.

If you want mass flow then ceramic lining is also an option for the hopper section. But this will be an expensive option (Lining costs and structural stiffening).


Re: Flat Bottom Bins

Posted on 20. Dec. 2007 - 03:22

You can reasonably store 1000 tonnes total in a single bay; i.e. 6m beams.

If the live storage is 1000 tonnes then you will need a much larger bin for core flow. Compare the extra steel structure price against linings & see what pops up.

Flow characteristics of moly are, as always, the governing factor.

Gilchrist described molybdenite as being physically similar to graphite. Regardless; if the material wants to mass flow, encourage it & live with the wear. Periodic relining shutdowns are far cheaper than spasmodic dig outs.

John Gateley johngateley@hotmail.com www.the-credible-bulk.com

Re: Flat Bottom Bins

Posted on 20. Dec. 2007 - 11:30


You are talking about expanded flow - it will work if you do it correctly. Check your flow function after several days of storage - it should be in your flow properties report.



Ziggy Gregory www.vibfem.com.au

Flow From Storage Bin

Posted on 21. Dec. 2007 - 10:04

The first question is why consider mass flow if the material does not deteriorarte in any way during time storage and there is not a problem with arching. Ratholes can be overcome with a core flow slot outlet that will self clear when the central region is empty. The cost of dead storage with a time consodidated drained repose angle should be compared with the construction to self clear, rather than mass flow, for inert products.

If the critical arching size for a non-mass flow outlet exceeds the width of the extracting device, presumably a belt feeder providing progressive draw, then a small mass flow section may be justified. With this you may consider an expanded, non-mass flow chisel section that will clear a much wide region of the bin at a much lower slope than that which the material would give. Slip on this face would be intermitent as the mass slides down to refil the central region when the level there falls. A comparatively unexpoited technique that may be useful is to use sequential, non-mass flow chisel shaped construction to avoid the formation of ratholes. Multiple outlets may be an option, although this has obvious complications and costs.

The ultimate economics depends on the value of the ore against constructional geometry but a refined solution would probably offer significant savings, taking into account long term maintenance and a guaranteed performance, which is itself valuable.

The starting point to review options is to know the critical arching dimensions for mass flow and non-mass flow in circular and slot outlets, maximum rathole diameter and wall friction values plus the consolidated, drained repose angle. These details require some expertise and I suggest that TUNRA, based on the University of Newcastle in NSW, may be the best organisation to advise you in Australia.

Matt Stak
(not verified)

Re: Flat Bottom Bins

Posted on 22. Dec. 2007 - 08:32

Thanks. Yes Tunra have already undetaken material testing. I think I'll get the bins modelled by them too. At least I'll get a better handle on how the material will flow. Also will predict the liner life for the mass flow case.

Thanks again for your advice.