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  • Wednesday, 6 April 2016

    [HOW TO] Calculate required Vapour column Size



    Hello readers.... Good Day!!!
    Today i gonna give you a small brief Introduction about Vapour Column and its necessity and also what effect it can have over regular pharma operations.

    Usually Vapour Column is a part of a reactor , a part of distillation setup whether it is a product concentration distillation or Solvent Recovery Distillation, its secondary, but vapour column always plays a major role, selection of a wrong Vapour Column can lead to unimaginable cases which will have adverse effects over the .....  Hard to Say, but i have to say even it can have effect over distillation rate, recovery rate, and rate of drying also.

    Because if i ask somebody what is the use of Vapour Column / what you know about Vapour Column,
    Mostly the simply reply comes as a Distance piece connected from a Equipment to a condenser or a receiver or a blower/vacuum pump to transfer the vapours that were generated in an operation.

    But this is time to grow up from that kiddo stage and have to know its Importance, what ever Vacuum Pump Capacity or whatever Condenser or whatever Utility or whatever heat transfer area of the equipment you are using doesn't matter, the thing that only matters is whether you selected a right Dia Vapour Column or not, this is the base of Distillation or Drying operations that were done in pharma field. So, right now i think you you gotta brief about importance of vapour column in pharma engineering. So, now i think you are clear, and i'll start my show...


    Do Read:-


    What is a Vapour Column??

    ** Vapour column is a simple line with a 90deg or 45deg elbow bend towards a condenser,

    What is the need of Vapour Column??

    ** A vapour Column used to transfer vapour out of a reactor,

    How Does Vapour Column has an effect over an Distillation or Drying Operation??

    **  Everyone knows how to calculate the flowrate inside a pipeline, so similar calculation need to be applied here, but in a pipe flow we will be taking velocity of fluid, but here our hero is vapour so we need to consider vapour velocity in place of fluid velocity,

    What is the Calculation involved in calculating the Flowrate inside Vapour Column??

    ** Back to Basics again, Flowrate = Fluid Velocity x Cross section area.

    So, i think you are Well Prepared and Can get to point easily,

    For Calculation of Vapour Column Size we need to know, what amount of boilup need to be carried to condenser [ if this is a normal distillation], how much amount of Suction velocity need to be generated towards reactor [ in case of vacuum distillation].

    So, i think now i need to give you some info regarding batch boilup, batch boilup is nothing but the amount of volume that has been generated from the heat transfer equipment where we are adding heat to the batch volume, so this boilup majorly depends upon two operating parameters, 1) Pressure, 2) Temperature.

    * So usually whenever we need to calculate the boilup based on these parameters, we have to stick to basics and start using ideal gas law, right now i dont want to mention the law, but have a look at the derived equation,

    P xV = n x R x T
    so here, P, T are operating parameters, n is number of moles, V is Boilup Volume, R is universal gas constant,

    So in order to calculate the Boilup volume, i'll transform the equation as V = (n x R x T)/P.

    and some more transformation i'll prefer V = ((W/M) x R x T)/P,

    So here right now everything is clear , based on the composition of batch volume you consider, you can generate the data for W, M.
    W- mass of the solvent (volume of solvent x Density of solvent),
    M- molecular weight of solvent.

    In case of binary mixture, you can split that W/M to (W1/M1)+(W2/M2).

    So, Now you got a Clear vision over Boilup,
    Its time to jump to main concept Vapour Column size,
    So first of all we need to know what amount of boilup we need to generate, for that we use the formula,

    V = W x (359/M) x (1/60), by this we will be getting in Cu.ft/sec,
     So, now as usually i'll prefer customizations to make it work for different operating parameters, so i'll be adding some extra functions like, (760/P) for pressure and (T/489.67) for temperature..,

    Finally it will be V = W x (359/M) x (760/P) x (T/489.67) x (1/60),
     here you need to convert T to rankine, for that you need to know,

    T, R= (9/5) x T, K

    So, now integrating all the above,

    V = W x (359/M) x (760/P) x (T/489.67) x (1/60),

    Input W in Kg/hr, we will be getting V in Cu.ft/sec and for Airload we can add 2-5% overall of volumetric flowrate of boilup,

    And after this we need to decide whether its a Normal distillation or Vacuum Distillation,
    if its Normal Distillation we Can have Vapour Velocity, = 100ft/sec, and
    for Vacuum Distillation we can have vapour velocity, v = 170-180ft/sec,

    So, finally for calculating Dia we use optimum pipe diameter,

    D, ft = 0.147 x SQRT( V / v)
    , convert this to inches, 1ft = 12 inch

    For Those who need, we are providing the Excel sheet, Download Here



    About the Author

    Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a techoholic geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
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    Pharma Engineering

    28 comments:

    1. M value to be taken is g/mol or Kg/mol

      ReplyDelete
      Replies
      1. There is not that much to think over the units for molecular weight, anyway for your knowledge the equation above mentioned is in FPS units, so it need to be mentioned in Lb / Mole.

        Delete
    2. Hello ajay.your blogs r very knowledgeable and interesting.I want your help.I want to find out u loop calculation which we found in reflux line of api reactors for traping the vapour from going in condenser . specifically the hight of loop.waiting for your response.

      ReplyDelete
      Replies
      1. Hey Rutika, thanks for your comment,

        Basically there wont be any straight way calculation for that U loop located reflux condensate line, but based on just your approximation you can derive the height, and you may use P = rho x g x H, H is height, P is pressure, based on the temperature of the distillate using antonie equation you can get the vapour pressure, that's it,

        Still any queries feel free to comment

        Regards,
        PHARMA ENGINEERING

        Delete
    3. Hai ajay i'm venkat,

      i didn't got this step. Can you please explain me in detail.
      V = W x (359/M) x (1/60), by this we will be getting in Cu.ft/sec,

      And also what are the units you have considered for W and M like gm/mol or Kg/mol.

      ReplyDelete
      Replies
      1. Hey venkat, glad you read my post,

        (1/60) is a time conversion factor,
        359 is standard molecular wt.
        W is the mass flowrate that you want to generate

        Delete
      2. hai ajay again i have one more doubt, in above comment you mentioned standard molecular weight as 359, standard molecular weight of which substance?

        Delete
      3. Hey buddy,

        That 359 includes molecular weight(Mercury) and conversions for converting MKS to FPS.

        Regards,
        AJAY K

        Delete
    4. Hi Ajay

      Every solvents has individual vapour velocity,In above calculation why r we using standard vapour velocity for normal or vaccum distillation...?

      ReplyDelete
      Replies
      1. Under vacuum, there wont be any considerable change in vapour velocity,
        But coming to normal distillation, the velocity depends upon the following factors [Directly & Indirectly],
        1. Vapour density, [Directly]
        2. Heat supply for evaporation, [Directly]
        3. Vapour line sizing, [Directly]
        4. Vapour pressure developed inside reactor, [Directly]
        5. Utility supply to condenser. [Indirectly]

        To make the concept clear, i've given it as constant.

        Regards,
        AJAY K

        Delete
    5. how to caliculate the batch reactor vapour coloumn height and dia meters. Say evaporation is 20 kg/hr

      ReplyDelete
      Replies
      1. Dear,

        W = 20Kg/hr, T(R) = 617.17(Say), P = 200 torr(Say), M.wt. 100 kg/mole(Say),
        Q = 3.89 cu.ft/sec, Pipe dia = 0.02 ft.

        Delete
    6. Hi ajay
      yours work was fabulous. Can u give the vapour column size for methanol distillation?
      here my quantity was 1 kl methanol and also please be say how can we find evaporation rate(w).

      ReplyDelete
      Replies
      1. Hey Venkataramana, thanks for your compliment, W is nothing but our requirement, what amount of boil up / Distillate we want from the reactor. If you want to know the Vapor column size then you need to know the boil up, what are the distillation parameters, and the solvent properties like Mol. wt., Reactor HTA, etc

        Regards,
        AJAY K

        Delete
      2. Here my reactor capacity was 1.5kl and the properties of methanol was boiling temperature 70 degree celcius, molecular weight 32 gm/mol , vapour pressure 13.2 KPsc.

        Delete
      3. you forget mentioning about the reaction mass volume, i'll consider it as around 70% occupancy in reactor and methanol as a pure component in the reaction mass,

        So volume will be 1050 L , Cp = 0.45 KCal/Kg.K, density = 792 Kg/Cu.m, Latent heat = 264KCal,
        Heat transfer area of 1.5KL SS reactor will be around 5.6 sq.m, available heat transfer area = 5.6x0.7 = 3.92 sq.m,
        U = ~200 KCal/hr.Sq.m.K, now lets get into calculation,

        ( m x Cp x dT ) + ( M x lamda ) = U x A x dTln

        ( 1.05 x 792 x 0.45 x 35 ) + ( M x 264 ) = 200 x 3.92 x 23.6

        M = 20.47 Kg/hr

        So boilup =20.47 Kg/hr. = W,

        V = 20.47 x ( 359 / 32 ) x ( 760 / 99 ) x ( 617.67/ 489.67 ) x ( 1 / 60 )

        = 37.06 Cu.ft / Sec.

        D,ft = 0.147 x Sqrt((37.06/100))

        = 0.08 ft = 1.07" ~ 2" vapour line need to be installed.

        Still any queries, feel free to contact me.

        Regards,
        AJAY K

        Delete
    7. hello please suggest me why your taken pressure as 99 mmhg (760/p)

      ReplyDelete
      Replies
      1. Hey, Mr. Anonymous, in the above comment Mr. Venkataramana mentioned the Vapour pressure to be 13.2KPas, which on conversion turns to be 99 mmHg. hope you got the answer,

        Regards,
        AJAY KUMAR

        Delete
    8. Hi Ajay.. This is Ram..Hope u r doing well..Can you please tell me the design of Vacuum pump(Capacity) for Reactor distillation

      ReplyDelete
      Replies
      1. Dear Ram,

        Please follow the link, and use your distillation vapour pressure in place of ΔP,
        http://pharmacalc.blogspot.com/2016/03/how-to-select-required-pump-capacity.html

        If any queries feel free to comment/message.

        Regards,
        AJAY K

        Delete
    9. Hi ajay.. Is there effect of Vapour column height on distillation in Reactors

      ReplyDelete
      Replies
      1. Dear Ram,
        Surely, if the vapour density is higher, then automatically it needs more pressure to reach the condenser, Vapours with lower density needs less pressure, if its atmospheric distillation, then the vapours with low density than air will have some advantage.

        Regards,
        Ajay K

        Delete
      2. Thx ajay..I need one more clarification, if there is a dependency of Vapour column height then what is the optimum Height you suggest for both atmospheric & Vacuum distillation

        Delete
      3. Dear Ram,

        we can only decide height based on vapor density, and if the density is higher its better to arrange vertical condenser setup, so that we can eliminate one 90 degree elbow bend, if its a vacuum distillation, there's no matter of horizontal or vertical condensers. this is what we can do.

        Regards,
        AJAY K

        Delete

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    Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.

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