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Thread: Metal beads in an water slurry

  1. #1

    Metal beads in an water slurry

    I would like some guidance on the design of a thin hopper shaped tank that we will use to feed metallic beads in a slurry, ie a totally wetted system, not dry feeding.

    The hopper will be one meter wide, and 3 meters tall, but only 20 mm deep. We must have mass flow at all times.

    A slurry of beads will enter the top of the tank, slowly descend and exit through a nozzle at the bottom. We are assuming that the bottom should be hopper shaped, with approximately 70 degree sides. We believe that the important design factors are: the slope of the edge walls, the material of the edge and face walls, and the size of the discharge nozzle, both diameter and length.

    Can you provide some guidance on the design?

  2. #2
    Lawrence K. Nordell

    Lawrence K. Nordell

    President and CEO

    Conveyor Dynamics Inc. [eDir]

    Conveyor Dynamics Inc.

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    Dremco:

    Additional information is required to get a better understanding of the problem:

    1. density of beads
    2. density of slurry (pure water or has rheological strength?)
    3. size of beads - frequency of each size if they differ
    4. flow rate of beads
    5. flow rate of slurry
    6. bin dimensions - states 3m high x 1m wide x 20mm tall?
    tall means depth?
    7. nozzle opening shape and other reclaim properties
    8. feed configuration

    My thinking is to model the problem using a Discrete Element Model (DEM) with fluid rheology. This will depend on the bead size(s). A definition of the input and output targets and range of operation are necessary. Is the goal to: maintain mass flow, maximize mixing, FIFO, etc.?

    Lawrence Nordell
    Conveyor Dynamics, Inc.
    1111 West Holly St.
    Bellingham, WA 98225
    USA
    ph 360-671-2200
    fx 360-671-8450
    email: nordell@conveyor-dynamics.com
    web: www.conveyor-dynamics.com

  3. This is a very interesting application. My delay in response is due to vacation in the US, so I was ou of access for a few day. The questions raised by the previous responder are vital to determining the design. It is presumed that mass flow alone is not the only objective and that a uniform velocity is desirable to give an even residence time.

    It would appear that the flow control must be achieved by the outlet system and a positive restraint required to avoid preferential percolation of the fluid.

    On receipt of the details specified it should be possible to put forward some basic recommendations.
    Lyn

  4. #4
    Here are some of the details. The beads are copper, 1-6 mm diameter, and nearly, but not quite spherical. The solution is a copper sulphate/sulfuric acid. The apparent density of the settled slurry, (ie, like sand settled in a beaker) is about 5 gm/cc. The metal density is 8.9, but in the form of these beads, in the liquid, it is about 5. The descending rate for the packed bed of beads is in the range of 1-3 cm/sec, so for the width of 100 cm, a hopper depth/thickness of 2 cm, the mass flowrate is about 200-600 cu cm /sec. To maintain this bed velocity, the nozzle mass flow must clearly be the same, which probably defines the diameter of that nozzle. The nozzle would have to be long enough to include a shut off, or possibly a regulating valve, and a connection to a pipe Tee, so probably 300 mm in length, and the friction in that might require a larger diameter.

    It seems to me that if I knew a linear velocity through a nozzle, a suitable diameter of nozzle could be selected. If oversized, the flow could be controlled with a valve, and it should be a simple matter to get the desired mass flow in the hopper.

    The requirement for perfect mass flow is that the beads will be electrolyzed as they pass through the hopper, and so no beads can be allowed to remain in the hopper. To ensure that none remain, we need only have uniform mass flow.

    In other tests, we have found the hopper angle to be about 70 degrees. The material of one wall will be stainless steel, and we have found that it becomes polished. The other large wall will be a filter cloth type material to serve as a diaphragm. The narrow, sloped sides can be stainless, or a plastic such as frp.

    Am I on the right track, or am I missing something?

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