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Thread: Stack Height

  1. Stack Height

    Description: Dust collectors include bagfilter, ducting and fan. Usually the outlet duct from fan called stack.

    Question: is there any rule for the height of stack in dust collectors?

  2. #2

    Smile It All Stacks Up

    There is a 'worked example 1.6' in Fluid Flow and Heat Transfer by Axel L Lydersen - Wiley.


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    John Gateley
    johngateley@hotmail.com
    www.the-credible-bulk.com

  3. Stack for dust collector

    Thanks John,

    However my question related to the stack of dust collectors. Centrifugal fan is sized to provide the required pressure drop and we don't expect stack to provide pressure drop.
    Meanwhile the temperature of gas is ambient.
    In this case could be the height of outlet duct(stack) of fan short? I mean it could be finished near ground level?
    Is there any mandatory standard for the height of stack for dust collectors?

  4. #4

    Smile Peering Through the Clouds.

    Any stack, other than flares, has the obligation to provide clean air exit or to ensure that any pollutants are adequately diluted and dispersed. That is what stacks are for. You are obliged to accept that filter bags deteriorate in service and some eventually rupture. Ruptured bags will accelerate exigent airflow and also release pollutants of varying severity into the atmosphere. Releasing exhaust near ground level is therefore unacceptable, in most countries.
    You must calculate the safe stack height in reverse to the example which I quoted. Find the exigent airflow when 2 bags are ruptured during Induced draft fan operation. Apply that airflow through the duct calculation while bearing in mind that airflow through any duct involves pressure drop. You are left with the interaction between the lowest wind speed and the velocity of the exigent dust. Clearly the dust must be able to rise into a prevailing wind for onward transport and dispersion. Dust which can fall back into the stack will adhere to the walls and the build up will eventually collapse into the stack bottom and in extreme cases can cause structural failure. Don't let your stack become a hopper bottom. Although stacks do collapse I have never read of any application of fouling factors. Fouling factors are obligatory in heat exchanger design codes. But first of all you need to determine you wind conditions.

    Along with Lydersen's good example there might be further insight into the design of flare stacks and there is plenty of that in your area. Cheers.
    John Gateley
    johngateley@hotmail.com
    www.the-credible-bulk.com

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