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Thread: Fluid Bed Dryer Zone Temperatures

  1. Fluid Bed Dryer Zone Temperatures

    G'day,

    My client has a problem reducing the moisture content of a product using a fluid bed dryer.

    The product is a herbicide pellet that is formed by adding water to the powder and then passing it through an extruder. The extruded product is then sent through a fluid bed dryer. The dryer has 2 zones where heated air is introduced.

    The problem is getting the excess moisture out of the pellet.

    At first, the design was to have zone 1 (at the entry of the dryer) at a lower temperature (70 C) with zone 2 having the higher temperature (90 C), but shortly before the equipment was commissioned, head office intervened and switched them around so that zone 1 would have the higher temperature and zone 2 the lower temperature.

    The problem is that the dryer cannot remove the excess moisture now without extending the retention time. Also, with the extended retention time, the temperature in both zones has had to be reduced to 70 C to avoid damaging the product.

    Interestingly, a production line for other similar products has a fluid bed dryer with three zones. Here zone 1 has the lowest temperature (70 C), zone 2 has an intermediate temperature (80 C), and zone 3 the highest temperature (90 C). There are no issues with this.

    I have suggested switching the zones as there is the facility to do this but they are reluctant to try this because it could lose a batch of product. Does anyone have any comments?

    Thanks.
    Ian A. White, MIEAust. CPEng. RPEQ
    WAI Engineering
    www.wai.com.au

  2. #2
    A few things come to mind from my past experience in a salt evaporation plant.


    1 - Is it possible to reduce the water content in the initial mixture?

    2 - We used a FBD to dry evaporated salt after a centrifuge. We heated zone 1 and cooled in zone 2. Too long ago to remember the temps we used. I do remember that it was quite a high temp in zone 1.

    3 - Maintaining a proper bed depth was critical to good drying. We had an adjustable weir at the discharge end of the FBD.

    4 - What is the moisture content of the air being used to dry the pellets?

    5 - If steam is used as the heating source ensure there are no leaks at the heat exchanger - even a fine mist will increase moisture levels in the product.

    6. - Is the FBD a vibrating type or stationary and just moving the product along with the air?

  3. #3

    FBD for herbicide

    It has been my experience that too high or a temperature can "case harden" the extrudate and slow down the water removal.




    Quote Originally Posted by waiwhite View Post
    G'day,

    My client has a problem reducing the moisture content of a product using a fluid bed dryer.

    The product is a herbicide pellet that is formed by adding water to the powder and then passing it through an extruder. The extruded product is then sent through a fluid bed dryer. The dryer has 2 zones where heated air is introduced.

    The problem is getting the excess moisture out of the pellet.

    At first, the design was to have zone 1 (at the entry of the dryer) at a lower temperature (70 C) with zone 2 having the higher temperature (90 C), but shortly before the equipment was commissioned, head office intervened and switched them around so that zone 1 would have the higher temperature and zone 2 the lower temperature.

    The problem is that the dryer cannot remove the excess moisture now without extending the retention time. Also, with the extended retention time, the temperature in both zones has had to be reduced to 70 C to avoid damaging the product.

    Interestingly, a production line for other similar products has a fluid bed dryer with three zones. Here zone 1 has the lowest temperature (70 C), zone 2 has an intermediate temperature (80 C), and zone 3 the highest temperature (90 C). There are no issues with this.

    I have suggested switching the zones as there is the facility to do this but they are reluctant to try this because it could lose a batch of product. Does anyone have any comments?

    Thanks.

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