Can you help?

Posted in: , on 19. Mar. 2003 - 09:02

Years ago the DSW built 8 dome type storages

40-50,000 t each.

The storages are loaded automatically by

overhead conveyors + trippers, and

unloaded via openings (8m pitch) with

gratings (.25mX.25m) ,hoppers,knife-type

gates to underground conveyors.

Dimensions of the openinggs: 1m w.x2m l.

The problem:

after being couple of weeks in storage, the

material ( bulk potash) sets up bridges above

the openings (the hoppers are empty) and no

access to destroy the bridges.

May be you come across with such or similar

problem and know how to handle it

without significant alterations !


Michael Rivkin

Re: Can You Help?

Posted on 19. Mar. 2003 - 01:34

Dr. Rivkin,

Two possibilities come immediately to mind.

[1] Use air cannons, which can be activated manually or automatically whenever a bridge situation occurs. This should work, if bridging always occurs in the same place.

[2] Cut access ports in the each storage unit wall (requires a good seal system) to allow direct access to clear bridges.

There are other possibilities, including Rema's bladder system; the use of water; mechanical pushers and borers; and interior configuration alterations, but these are all more expensive and, in the case of water, potentially damaging to the product.


Dave Miller ADM Consulting 10668 Newbury Ave., N.W., Uniontown, Ohio 44685 USA Tel: 001 330 265 5881 FAX: 001 330 494 1704 E-mail:

Can You Help?

Posted on 19. Mar. 2003 - 02:17

Dear Mr Miller,

Thank you for the trail, but:

1. Air cannon solution I tried to implement

without any success: the cannon can not be

installed in vertical position constantly no through the

hopper and no through the storage floor

(the height of the pile is 17-18 m).

I tried to install the cannon in inclined

position (about 30 deg ) to destroy the "root" of the bridge, but the grating

shields the "root" from the air blast.

2. No water solution for potash.

3. Practically impossable to cut a port.

4. May be something else?

best regards,

Michael Rivkin

Re: Can You Help?

Posted on 19. Mar. 2003 - 06:15

Dear Dr. Rivkin,

For similar system for fertilizer storage, the hoppers mouth are often covered by steel sheet resting on grid. This prevents solidification of material in hopper, with passage of time.

The feed into hopper is done by partially clearing the material, and removing sheets from hopper mouth. Or storage is done such that hopper mouth portion is kept clear of material storage, and steel sheets are removed, to facilitate material flow by gravity or by pay loader.

Can You Help?

Posted on 20. Mar. 2003 - 07:42

Dear Mr Mulani,

The height of the material pile above

the mouth of the hopper is 17-18 m, so

no way to remove something from the


The first stage of the gravity discharge is OK,

on the second stage the hopper is clean,

but the bridging above the grid stops the

further discharge - this is the problem!

Michael Rivkin

Brian Moore
(not verified)

Re: Can You Help?

Posted on 20. Mar. 2003 - 07:53

Dear Dr Rivkin.

It appears that the original design appears ambitious with regard to reclaim. Is this the same potash material that is effectively stored and reclaimed utilising the Eurosilo concept?

The description of discharge hoppers of 1m x 2m entry dimensions at 8m pitch (both ways) infers a large extent of dead storage between the flow zones of each hopper, and then with periods of 2 weeks of time consolidation at rest for the bulk solid.

Consider the following approaches:

1. By testing the flow properties of the potash, or from site experience determine the maximum time period before the consolidation at rest causes unacceptable bridging. Then develop operational practices such that the material is "exercised" at time intervals less than the maximum. That is withdraw material from each hopper and recirculate the load back into the dome.

This action will disrupt the material stress fields and the formation of stable bridges.

2. Consider installing a false mass flow hopper to extend the existing hoppers, above floor level. This construction can take the form of "witches hats". The geometry of the hopper extensions would be determined on the principles of mass flow/expanded flow design.

This concept could be extended such the flow zones of adjacent hoppers are sized such that adjacent flow zones (ratholes?) combine to reduce the levels of dead storage.

3. Consider forms of mechanical assisted reclaim. For example

- a Tubefeeder set up for either radial or lateral travel for a zone of 8 to 12 meters.

- a hydraulic activated "walking floor" similar to that used for the discharge of wood chips from flat bottomed silos.

- hydraulic activated frames that disrupt arches and direct material towards the discharge hoppers. For example the Saxlund Sliding Frames. Refer to the website

For further discussion email me on

Can You Help?

Posted on 20. Mar. 2003 - 01:49

Dear Mr Moore,

1. The recirculation of a bulk material is very

expensive,time & labour-eating process.

The operational team never,practically, uses

this process,taking into account the

dimensions of the storages - 50 m w

and 100 m l each.

2. Shovels which are used to move about

60% of the potash ( 40% - by gravity ) to

the hoppers, have to operate on the

smooth floor of the storage. So, nothing

can protrude above the floor level.

3. Nothing can be changed in the construction

of the storages which were built in 1964-1980.

4. I am looking for some bright idea : the


with min investment and max efficiency.

What do you think about vacuum ( crazy

idea ? )

Michael Rivkin

Re: Can You Help?

Posted on 20. Mar. 2003 - 06:37

Dear Dr. M Rivkin,

Referring to your question, I clarify as below. The method / procedure mentioned by me is often recommended / used in fertilizer plant parabolic silo of say 125 to 250 m length.

The reclaim tunnel conveyor has 5 / 10 reclaim hoppers. The material is stored such that two hoppers mouth are not buried under material (even partial opening to mouth is acceptable). It is designed such that feed from 1 or 2 hoppers meet the conveyor capacity.

During stacking operation, when stockpile extension comes near hopper mouth, it is covered by removable sheets. The feeding to open hopper can be by pay loader or by positioning the tripper discharge on stockpile sloping face, such that gravity flow goes into hopper.

It is to be noted that material is not expected to flow properly / reliably into deeply buried hopper.

This method may allow you to have actual storage as nearly 70% of gross storage.

Please think about revision in style (management) of stacking / reclaiming, and possibly it may be of real help for you. Further suggestion needs stacking / reclaiming arrangement drawing.

Try to keep material relatively live throughout the silo by shortest time interval, in a planned manner.

Re: Can You Help?

Posted on 21. Mar. 2003 - 01:43

Dr M.Rivkin,

Further to my earlier messages, the other expensive (mostly not possible at this stage) solution is to have reclaim conveyor app 3.5m above floor, supported on shelf from one side of silo. The reclaiming is by bi-rail scraper-reclaimer with swiveling – luffing boom. The scraper reclaimer discharge boom always remains attached to reclaim conveyor. The centraly positioned bi-rail remains burred under material, but scraper reclaimer itself clears off material as it advances into stockpile face. The machine reclaims from exposed cross section face and hence it is free from difficulty you are facing.

The present day urea longitudinal silo uses such system instead of hopper arrangement used previously, in view of similar difficulty . The manufacturers budgetary price for above said system may be around USD one million.

Can You Help?

Posted on 23. Mar. 2003 - 07:47

Dear Mr Mulani,

You are right about the optimal management

of storages , we use the method many, many

years.More,we have 12-13 hoppers in one

storage to facilitate the discharge, but..(always

the but!) if you have a number of grades of

the material in one storage and no access

for a pay loader to the hopper located under

the specific grade - this is a real problem we

came across from time to time.

I would like to define more precisely the


long loaded storage,

bridging above a hopper located in the middle

of the storage,

no access for a pay loader,

What would you recommend?


Michael Rivkin

Re: Can You Help?

Posted on 23. Mar. 2003 - 07:12

Mr. Rivlin,

I have not found a full description of the hopper slot configuration( height, dimesions of upper and lower(1x2m) openings with respect to wall angles).

What is the slot lined with? A UHMW plastic like Tivar-88 or glass/ceramic lining is substantially better than any steel surface.

Surface morphology and chemistry of the product can give clues to its behavior and control.

These points would be helpful understanding the nature of the material consolidation and in defining a best option to relieve the arch.

Have you tried suspending the hopper and vibrating its long wall surfaces, resembling an activated bin bottom? It would also seem prudent to articulate the grate above the hopper to break the arch within the small openings.

Lawrence Nordell

Conveyor Dynamics, Inc.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: phone: USA 360-671-2200 fax: USA 360-671-8450

Can You Help?

Posted on 24. Mar. 2003 - 07:29

Mr Nordell,

The additional data:

1.The height of the underground tunnel

is 3m; hopper- upper opening 1x2m, lower

opening .6x.6m, the long wall incl. 48 deg.,

knife gate .6x.6m; conveyor- B=1200,

v=2m/s, capacity 1000 tph.

2.No lining is required: the steel surfice is OK and

no problem into the hopper.

3.The intensive knocking of the hopper

does not help to relieve the bridge.

4.The suspending of the hopper is not

practical ( under load of about 500 t per 1m

of the storage length) and we are looking

for a practical solution.

Michael Rivkin

Re: Can You Help?

Posted on 24. Mar. 2003 - 09:27


Why do you say that a low friction lining is not required?

Part of the reason for bridging is the anchoring of the product on the hopper sides, forming the arch or bridge, on the hopper walls due to friction. Lowering the surface friction of the hopper side walls may reduce the arch strength to a level that inhibits its formation.

The suggestion of using Tivar or porclein or glass like ceramic should lower the friction by 50% as measured in many tests.

You can apply the Jenike Johanson formula, for hopper design, to gain understanding of the likely arch formation and modifications suggested that may yield sufficient improvement to solve your problem.

Or you could give the concept to CDI. We can analyze the behavior of the existing and the proposed change, using DEM, and simulate the problem and benefit I note above.

The 48 deg. long wall angle may be telling but its position is not clear. What is the depth of the hopper? Is the bottom opening symmetrically centered with the top opening?

Lawrence Nordell

Conveyor Dynamics, Inc.

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: phone: USA 360-671-2200 fax: USA 360-671-8450

Re: Can You Help?

Posted on 24. Mar. 2003 - 09:53


I reread the post and appologize for missing your point that the arch or bridge is formed above the grate opening.

The bridge anchor needs to fail. Have you that about trying to break the bridge by sliding the ends of the grate across the narrow slot opening. This would require cutting the concrete floor to facilitate the articulation.

Before any such effort is attempted, you need to characterize the product strength as a function of the consolidation pressure, such as by the Jenike shear cell testing procedure.

This data can then determine the potential arch dimension that may form for the height you noted.

LK Nordell

Lawrence Nordell Conveyor Dynamics, Inc. website, email & phone contacts: phone: USA 360-671-2200 fax: USA 360-671-8450

Re: Can You Help?

Posted on 26. Mar. 2003 - 02:19

Dear Mr. Rivkin,

So small a hopper opening for so great stock - pile height signifies a seriously faulty concept of reclaim-system. Hopper mouth opening certain minimum size is essential in relation to stock - pile height to avoid such problems.

My judgement suggest a ratio around 1:3, steel hopper with UHMW liners and hopper wall vibrators (electro-magnetic or mechanical unbalanced) would have averted the problem. But now it is fait accompli. I suggest two things:

1. Please email me the sketch showing silo, stock - pile, hopper, conveyor and tunnel. I will see if I can be of help to you.

2. I remember one company in Australia who makes mechanical agitator / shaker for material around hopper mouth. It is heavy / sturdy device and they say it works under coal pile of 15m height, to ensure proper flow. Now, whether existing arrangement / civil work can accommodate and take load is a doubtful issue. In the past I had obtain their quotation, but at the moment I do not remember name. However, concerned people may respond from Australia, reading this message.

Clearing Potash Pile

Posted on 27. Mar. 2003 - 10:48

Dear Dr. Rivkin,

It is not clear from the description whether the material is forming an arch on the 250 x 250mm openings of the grating or forming a deep span arch 1 x 2 meter above the grating. The former would appear to be most likely if the hopper beneath empties without a problem. A possible improvement may be given by changing the grid construction to a ‘stepped level’ grill arrangement for the cross rails and dressing the top edges of the bars to a sharp edge to offer less support for the material.

The ‘Stepped level’ grill system is to removed the square opening grid and fit two levels of cross rail grills that are at 90 degrees to each other, and has clearance between the two grills in the vertical direction. Sticking to the same plan size of open spacing, this means that the top layer offers longitudinal slots 250mm wide x 1000mm long. The lower layer will be 2000mm long, but is shielded from direct overpressures by the upper layer. The immediate benefit of such an arrangement is that the flow characteristics of the top slotted openings would be equivalent to square openings almost 500mm across. However, the lower layer is dealing with product that is subjected to less compacting pressure and is looser by virtue of flowing through the upper grill. It may therefore be a better option to increase the spacing of the top grill, to say 400mm, and reduce the spacing of the lower grill, to say 200mm, to give a somewhat similar protection as the 250 square grid against the passage of lumps. Together with the sharp top edges, this type of grid will offer far less support for arches to form on the grill bars.

If the material clears from immediately above the grill, but forms a deep arch over the 1 x 2 Metre opening, there is a more difficult problem. Even if the arch can be collapsed, it is probable that a ‘pipe’ would develop to the surface of the pipe. The divergence of a pipe from the outlet hole may be expected to be negligible with a condition of product that has formed an arch. It would therefore still be difficult to clear the remaining bulk by means of power shovels because of the deep and nom. 8 metre wide bed of material left between the outside of the pile and the openings. Before attempting to address this problem I suggest the above situation be considered first, to establish whether it offers a viable solution.

with b est regards,

Lyn Bates

Can You Help?

Posted on 30. Mar. 2003 - 08:29

Dear Mr Bates,


2. We have more than 100 hoppers (!). The bridges

are set up above different hoppers and from time

to time,so, we are looking for a simple, cheap,

effective and stand-by bridge ''terminator''.

3. I afraid we 'll never find our dream-device.

Michael Rivkin

Bridging Of Potash

Posted on 1. Apr. 2003 - 10:40

Just a thought, and this may not be relevant, but is it at all possible to stretch a steel cable across the main diameter of the floor of the silo in such a manner that it can rotate through 180 degrees. This movement should undercut the footings of the bridges from my understanding of the description.

Implementation might require some thought but it might be a cheap option if this addresses the root of the problem.


Steve Davis

Hatch Associates

Can You Help?

Posted on 1. Apr. 2003 - 11:12

Mr Davis,

Thank you for the reply.

Sorry, I did not catch the details of your proposal:

it's possible to put a rope under a pile (50 m width

and 18 m height ), BUT HOW TO ROTATE IT?

In addition, the first pay loader will pull the

rope out.

Michael Rivkin

Brian Moore
(not verified)

Re: Can You Help?

Posted on 1. Apr. 2003 - 11:36

Dr Rivkin,

Further to your brainstorming problem,

1. Do you have any flow properties of the potash (Instantaneous YL, Time Consolidated YL, Bulk Density x consolidation pressure)

2. Are you able to forward an drawing/sketch of the floor plan and cross section of hopper/belt interface for the forum readers to gain a better insight?

Could I suggest evaluating two devices nominated previously on this thread.


Air cannons. The arrangement however utilising a horizontal fan jet nozzle such that the air blast projects a sheet of compressed air along the concrete floor surface, towards the free edge of the hopper. The nozzles would be located some half metre from the concrete edge with the 2m hopper side.

The air supply pipe would require concrete hole coring.

Air bladders. In a similar fashion, air bladders arranged along the 2m concrete/ hopper edge to upset the bridged potash at the base of the arch.

As a further comment, the 2m x 1m entry to the hopper would be classed as an axisymmetric flow channel. Reduction of the arching dimension would be achieved by conversion to a 2D plane flow channel. This would involve increasing the 2m to at least 3, 3.5m.

Re: Can You Help?

Posted on 9. Apr. 2003 - 07:28

Dear Mr. Michael Rivkin,

In my earlier message, I had mentioned that some companies manufacture vibrating device on the feed inlet / hopper mouth.

Please refer the message by Silexport inter in the thread - Bulk Coal Discharge - in the New Projects, Tenders, Inquiries Forum.

Possibly, this may be of interest & help to you.


Ishwar G Mulani

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Email :

Re: Can You Help?

Posted on 11. Apr. 2003 - 03:01

Bridging Problem

Potash being of similar characteristics to that of salt (which I am more familiar with) is very hygrosopic.

Do you notice the problem more during high humidity periods?

The bridging is most likely caused by the level of moisture in your product causing binding of the crystals to eventually form a bridge.

We experience similar problems with salt and found that the ventilation of the buildings by means of simple agricultural style fans to reduce humidity in the dome buildings works quite well. You would need to size the fans to move enough air to change the air in the building over a 10-12 hour period.

Hope this helps.

Gary Blenkhorn

Gary Blenkhorn
President - Bulk Handlng Technology Inc.
Linkedin Profile:

Offering Conveyor Design Services, Conveyor Transfer Design Services and SolidWorks Design Services for equipment layouts.

Bridging In The Dome Typr Silo Above The Reclaim Hopper.

Posted on 13. Apr. 2003 - 08:42

Dear Dr. Rivkin,

Hope you have found a solution. In case, yes fine otherwise i think i have got a solution. in the meantime, i just want to be sure of your problem and the amount of trouble it is creating for you.

Apart from the above, I just want to know how much money you have budgeted in mind to solve this problem. As the solution I have in mind is simple, practical. But one need to know that is your silo roof is strong enought to withstand a load of 30 kN approximate at each point where the bridging formation is taking place.

In my opinion, the air canons / blasters function very nice in case these are installed at the periphery of the silo or the hopper. In such case, the effectiveness of the aircannon is most as it minimises the adhessive forces acting between the material and the walls of the silo or hopper or chute.

In a case like yours, you have to use mechanical means.

I am sure i have a solution in my mind.

What Reward do you offer, in case the solution is a real solution. LOL.

In the mean time please send me a sketch showing the overall height of the bridge chimney. You have mentioned that the base of the bridge is 1 m x 2 m am I right ? Yes, then let me know the maximum and the minimum height of the chimney ( what ever you call this space under this bridge.) . On the basis of this information, I will send you a sketch showing the arrangement to break in this problem.

It is in a very preliminar stage, but I am sure it will meet your purpose.

In the mean time, please be informed that in the storage silos of Cement, Rawmeal for Cement Plants, Fly ash and Grould Slag this kind of phenomenon do take place and we take care of the same.

Apartt from the above, in the above menetioned silos, the material cakes formation take place on the silo walls and we have mechanism to clean those.

On the same pricipal, i will devise a mechanism for breaking the bridging formation in your dome type silo.

In case, you are interested and the reward which you are gonna offer me are attractive, the 100% effective solution is yours.

Please donot hesitate to contact me over phone.

You may find me a little blunt but "me is what I is." a straight person.

Looking forward to hear from your end.

Wishing you Good Luck.


HN CHhabra

Can You Help?

Posted on 13. Apr. 2003 - 01:39

Dear Colleagues,

Thank you for your help, but I afraid we have to live

with the bridges.


1.Let's imagine you are the Operation Manager

of the huge storage capacity,discharge pits,

shiploaders, etc.

You know everything ( or almost everything ) about

each grade of the material ( internal friction angle,

friction coefficients, so on ), but (thank to segregation)

you know nothing about PSD of material stored

above the concrete opening.

You know that the potash is a hydroscopic material,

but the bridges happen in the Sdom ( RH about 20%)

and in Ashdod ( RH about 90%).

You can't spend time and money using trial & error


We hoped that somebody came across with a

similar problem and the solution was found, but...

2.I want to remind some details:

we have a number of rectangular dome-type

storages ( no silo!),each 50 m wide and 100 m long.

The row of openings (1mx2m), 12-13 openings/storage.

Max height of a pile above openings 17-18 m.

Discharge capacity is about 1000 tph.

3.I'm not the Operational Manager.

Michael Rivkin

Bridging In Potash Hopper.

Posted on 14. Apr. 2003 - 10:31

Dear Dr. Rivkin,

It is sad to note the way, you intend to close the matter.

You are not the Operating Manager !!!!

You don't want to use the trial and error method, Fine.

Now give 2 minutes to the thought mentioned below. Analyse it. In case it appeals to you please let me know. I may refine the solution.

You and all our colleagues who posted their advice or soltions on the net are capable and smart engineers. But the fact remains, no solution is found so far.

My proposal is a little crude but I am sure it will work.

The solution is as hereunder:

Please install a wire rope of 60 / 63 mm diameter ( twisted Steel Wire rope from the top of the silo roof). The length of the rope shall be such that it always remain in the area where the cavity forms after the bridging formation. The one end of the rope is connected to the output shaft of a vertically down output shaft type gearbox. The gearbox is connected to a motor of may be 11 kw variable speed type AC motor having maximum rpm as 3000.

At the other end of the shaft connect a cross or star. The length of each arm from the center of star or cross is 500 mm approximately. Connect a rope of 22 mm ( twisted Wire rope) of length approximate 1000 mm. At the free end of this rope attach 10-15 kgs steel ball or any jarred edge ball / box size 300 mm dia or face width. Whenever the bridging formation is likely to take place or have taken place, Run the 11 kW motor, increase the speed of motor from 300 rpm to 3000 rpm slowly say in 3 minutes time.

Because of the high speed of the star, the wire ropes attached at the end of the star or cross will try to straighten due to the centrifugal forces.

Now, the starightened ropes and the ball will hit the material and break the material.

Of course, the solution suggested is not based on a study. But I am sure it will work.

In case, you can let me know the plant address, I don't mind contacting the plant operating manager and would like to have the feed back from him on this issue.

If it appeals to you also wonderful.

With Kind Regards.

Chhabra HN

PS : Youcan send me a reply on my personal email

My Telephone numbers are 00 91 9810390819 or 01 91 124 2306370 after 20.00 hours and before 08.00 as per Indian Standard Time.

Re: Can You Help?

Posted on 14. Apr. 2003 - 10:52

Hi all,

I wasn't going to add more to this, but after Mr Chhabra's interesting suggestion and Mr Rivkin's note that the silo is in fact rectangular, I note that to drag a rope, cable or beam attached to rails at the toes of the long sides of the silo along the length of the silo to undercut the bridges would be relatively easy. This feature would of course be parked at one end to allow access for payloaders during normal operation, or could be removed or lifted clear.

Again, basic engineering, no proof available, but it could not take much force to undercut a pile of potash that has compacted under it's own weight.

Potash Bridging

Posted on 23. Apr. 2004 - 08:04

Dear Michael,

So, One year or so on, how have U gone and solved the sever bridging problem.??

We would be interested to learn


James Morrish

Bridging Problem With Fertilizer/Potash

Posted on 27. Apr. 2004 - 06:14

Dear Sir your problem has an easy fix, in this miners opinion.

what you need to do is purchase a small slusher hoist from a mining equipment supplier and purchase a large slusher bucket to go along with it.

The beauty of it is you could set up the small slusher in one or more spots inside the dome and then have a huge radius of points to anchor the sheave wheel which allows the cable to run back and forth with forward and reverse motion of the wire rope alternately riding over the piles of material and scooping them up and dragging them toward the draw point.

A very small double drum slusher with over-under cable set up with fairlead rollers will solve your problem very nicely with little set up time and no major rebuilding of systems. Also the slusher/tugger hoists are designed to be portable as well so you could use one slusher for your entire operation/ I would buy an electric powered unit rather than an air powered unit due to the corrosive atmospere in the dome itself. these machines work very efficiently and quickly moving material as well.

The big thing you must always keep in mind is that you do not want people near those draw points as they will fail without any notice-I will testify to this because I lost a very close friend due to this same type of situation 22 years ago in a salt mine where I used to work.

Putting your problem in algebraic terms using the X-Y plane

the slusher itself could be set up on 0, -12 and the sheave for the cable could be mounted any where from -12,-5 to 12,-5

with almost complete coverage inside each storage dome.


"Semper Excellsior"

Re: Can You Help?

Posted on 28. Apr. 2004 - 12:55

Dear Mr. Izaharis,

Thank you for your reply,but I can hardly imagine a slusher

system working at 1000-1200 tph capacity especially in our

case then piles of various grades of potash stored in row.

The solution found is to install an air blaster to build a small

positive pressure under a "bridge" ( the knife gate is shut).

The instant opening of the knife-gate creates so called "flush

effect" destroying the bridge.

Michael Rivkin