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Thread: Can you help?

  1. Can you help?

    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 !

    Regards,

    Michael Rivkin

  2. 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.

    Regards,
    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: admconsulting@cs.com

  3. Can you help?

    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

  4. 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.

  5. Can you help?

    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
    grid.
    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

  6. #6
    Brian Moore Guest
    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 www.brightwater.co.nz

    For further discussion email me on www.bcmoore@mpx.com.au

  7. Can you help?

    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
    solution
    with min investment and max efficiency.
    What do you think about vacuum ( crazy
    idea ? )

    Michael Rivkin

  8. 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.

  9. 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.

  10. Can you help?

    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
    problem:
    long loaded storage,
    bridging above a hopper located in the middle
    of the storage,
    no access for a pay loader,
    What would you recommend?

    Regards,
    Michael Rivkin

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