hello

There are several reasons for this phenomena discharge not ending in a mass flow. Mass flow can be improved with diffent measures depending on the geometrie of the silo and the discharge openings. ■

Originally Posted by mall

caving, rat holing phenomena for clinker steel silo

hi there

do you have any experince with all these phenomena.......and how to confirm and document it for justification of the stock inside the silo.......

pls advice. tq

One of my least favorite and most favorite subjects from personal experience:

The problem with any aggregates is simply that silos and bins are not designed and implemented with active unloading systems and inadequate sizing of drawdown openings-thats the trouble with 99 percent of the installations that are passive in drawdown.

Quite often the problem is( from my personal experience ) is inattention to detail and installing bin vibrators(as an afterthought) to move material that has a high percentage of fines and that is an absolute negative option and it automatically calls for a small apron feeder.

It is something that is easy very easy to document- if the silo is full and the feeder belt for the silo is stopped and no clinker is being delivered to the out feed belt its a huge problem involving bridging and ratholing.

lzaharis



■

An air blaster in my opinion will only

be effective if the en masse material

has the ability to be physically moved

and have the ability to become free moving.

Thats the nice thing about apron feeders

they move everything at once eliminating

any oportunity to settle, bridge, rathole and

kill people trying to clear it as happened in my

uncles case where two of his men died due to the ore

pass breaking away underneath them 28 years ago.

As long as the material has room to move an apron feeder

of even 36 inch width creates mass flow instantaneosly

and pulls everything through the opening.

An air cannon is ok for material that may be stuck after

the bin is NEARLY EMPTY but the material will most likely have to be

broken up to after a bit of time and the silo cleared to the inside diameter

during a maintenance period to assure proper flow.

We had a 36 inch apron feeder that worked flawlessly for years and

instead of understanding its simplicity with regard to mass flow of granular material they used a pan feeder with a narrow draw point and it constantly plugged with salt and in hindsight again they did not pay attention as they repeated the same reclaim method the second time with the new surge pile

they installed.

After the new surge feeder was completed the old pan feeder was reinstalled under the new drawpoint and I always felt it was rather ghoulish as same feeder was cut open to retrieve the two men who were killed by the blunt trauma injuries they sustained and welded back to together to be reused in the old feeder then installed under the new ore pass in the new mining area.

I do not condone the fact that they were careless in any case but the obvious solutions using a narrow steel reclaim bin with a flood opening wider than the draw point feeding the conveyor would have eliminated any need for bin entry

at any time and no one would have died. Their collective argument of "Its too expensive" still rings hollow 29 years later because they simply did not pay attension to detail by simply using mass flow and gravity and physics to its physical advantage.

Oh an by the way the same feeder is still being used after 28 years and was fully depreciated in 1984 so...........

lzaharis ■

May I suggest you look at our VIBRA-FLOW Activator Feeder. Below is the product description:

VIBRA-FLOW® Activator / Feeder

Vibratory bulk material reclaim has never been so dependable or versatile for rates up to 3,000 tons per hour or more depending on the product. The VIBRA-FLOW activator / feeder combines the material delivery of tandem enclosed feeders with integrated pile activation, all driven by a single, low horsepower vibratory drive. Precise flow control can be adjusted electrically through a VFD, or pneumatically using General Kinematics Variable Force (VF) wheels. Since the unit discharges material vertically to the conveyor below, loading is always centered and symmetrical. This feature helps to eliminate belt tracking problems common to side feeding.

The VIBRA-FLOW also helps eliminate bridging and issues found with other bin or pile activators, using significantly larger hopper openings to the material pile. Standard and specially engineered sizes are available.

3-in-1 Design: The Vibra-Flow combines two feeders and a pile activator into a single, low-headroom unit, significantly reducing both tunnel width and height requirements. This reduction in tunnel size provides considerable cost savings during construction,while maintaining access for inspection and maintenance.

For more information, please contact us at our website, www.generalkinematics.com.

Thomas Musschoot

General Kinematics ■

The way to avoid arching and ratholing is to measure the wall friction and shear st rength of the material to be stored and apply the standard formulae for the size of outlet appropriate to the flow regime selected. This should exceed the critical arching dimension and, in the case of a non-mass flow cone, be greater than the critical rathole size. Note that ratholing cannot occur in a mass flow cone or a plane flow hopper; in the first case, because the wall support is continuouly moving down and in a wedge shape flow channel, because there is no central connection to resist the sides moving together. This is why a catherdral dome and Iglooc an have a hole in the centre and a bridge or railway tunnel would collapse with a gap in the middle.

There is a host of flow aids to counter inadequate design, but they are usually a poor and expensive subsitute. The general situation is 'pay now and benefit later or pay indefinitely over the life of the plant'. ■

Fully understand your problems as we have customers who had exactly the same silo problems – however the solution is simple, efficient and very cost effective – acoustic cleaners I attach an article on how acoustic cleaners can solve both material ratholing and bridging within clinker ash silos. Hope you find it of interest, if so get in touch with me at – don@primasonics.com – and I will be glad to work with you on the best solution.

Kind regards

Donald F Cameron

Primasonics International ■

Apron feeder were mentioned, and I can add: chain conveyors ■

... but it may depend not only from the active discharge, the silo and/or chute could be too small and it makes a bridge or rathole before reaching your discharger ■