[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:-

• How to find Reactor Heat Transfer Area Theoretically??

• How to Select a Vacuum Pump?

• How To Calculate Volume Occupied by Torispherical Dish??

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 customization's 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 lbs / hr, we will be getting V in Cu.ft/sec and for Air-load we can add 2-5% overall of volumetric flow-rate 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, v = 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

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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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