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Thread: Grit removal channel design for industrial drainage (not waste water treatment)

  1. #1
    Associate Engineer
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    Question Grit removal channel design for industrial drainage (not waste water treatment)

    Hi all - I am investigating grit removal options for removing mostly sand from water draining from industrial washing machinery, but need advice specifically regarding grit removal channels used in smaller scale applications.

    Most of the guidelines readily available online pertain to the design of grit removal chambers for large waste water treatment plants, where flow rates of the order of Mega Liters per day are anticipated, compared to the flow rates of approximately 10 l/s in a discharge time of 900 s, once a day, with each discharge containing up to 20 kilograms of sand, specific to the application I am investigating.

    I have considered applying the principles of dimensional analysis to the equations and constants used in the design of channels (longitudinal, or aerated) for larger applications, but am not satisfied with only this approach. It would probably be a good time now to mention that mechanically driven machinery would require too much maintenance and will not be considered, and that I am only considering the aerated type of chamber because air compressors will be readily available on site.

    Can any of you recommend literature, or rules-of-thumb based on experience, about the design of grit separation chambers for smaller drainage applications?

  2. #2
    Administrator Kelly Bramble's Avatar
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    I would think that removing sand or other debris is a low flow/volume application would only require a commercial fluid sand separator.

  3. #3
    Associate Engineer
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    Jun 2012
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    Hi Kelly,

    Your suggestion does seem like the best idea. I did some reading and found several centrifugal solids separators that might work.

    Now to see whether they can work for systems without pumps.

  4. #4
    Associate Engineer
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    These systems typically consist of:
    - Flume that channels the flow away, designed for minimum water speed to prevent settling of solids
    - Settling chamber: that allows heavy particles up to a given size to fall out of solution, may include floctuation chem dosing and oil separation etc.
    - Secondary chamber, typically separated from settling chamber by a weir
    - Filter section w/ backflush (optional if you can allow particles in process water)
    - System pump

    The bigger the primary tank, the smaller the particle is passed through. Technically a large enough tank will remove pretty much all solids, typically not practical though and tanks are often at least 15-20 minutes retention time (at least for steel).

    Steel plants will often exclude the filter and use a trash-pump that can take the abuse of pumping water w/ abrasives.

    Jim.

    Hot rolling mill scale flushing systems, for example, Scale Pits is typically (removed from steel in hot rolling applications) separation chambers are often set at 15-20 minute retention time

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