[How to] Evaluate filtration feasibility in ANFD

Hiii all......!!!

Its been a gap, since i been posting regularly, 

Recently i've received a query about one of my previous post i.e., about filtration, i've posted about selection of filters, and one guy from a reputed pharma has approached me through mail, as he need in depth about ANFD filtration, and i thought that it can make a separate post as many of us were not upto the mark in this topic, as many a time we cant distinguish which sort of reaction mass can be filtered in ANFD.

For distinguishing the same, we should be possessing enough knowledge about filtration terminology and the commonly used parameters for explaining the filtration.

So, lets startup with some technical terms,





What is Permeation ?

Permeation is type of passage through a resistive medium.

What is Permeative flux ?

Usually flux is defined as amount / quantity of material passing through an area in specified time. Coming to Permeative flux, it can be defined as amout / quantity that is permeated through a material medium of unti area in specified time. 
Usually given units as Liters/min.Sq.m.

What is Specific Cake resistance ?

During filtering slurries, cake will be formed on the filtration barrier, and as on filtration going the cake thickness will increase depending upon the retained volume. The retained cake will add some excess resistance to the slurry which is being filtered along with the filter. The excess added resistance is Specific cake resistance. will hold units as m / Kg.

What is cake Concentration ?

Cake concentration in terms of filtration denotes the solids concentration in slurry. 
will have units like density i.e., Kg/Cu.m.

The above mentioned are the most used terms to describe / distinguish the nature of filtration.

Now lets jump into the topic and based on the preliminary evaluation we can conclude whether the reaction mass can be filtered or not, out of those i can mention some here, 




If reaction mass is Sticky / slimy / free flowing ANFD is not preferred,
If the material nature is Crystalline, ANFD is preferred,
If the reaction mass is acidic in nature, ANFD can be preferred, if its basic then the mass would be sticky, so ANFD is not preferred,
If the nucleation is better i.e., coarser, ANFD is preferred, if its finer ANFD is not preferred.

That's it..!!! This is preliminary evaluation, if i've missed out something just go ahead and comment, i'll add those in the above listing.

Sometimes we cant decide whether we need to select an ANFD or not, and at that time we need to consider a experiment with a buckner filter and performing an experiment is an easy task, but evaluating that and generating a systematic data is vital.

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So, now lemme tell you what sort of input need to be recorded from the performed experiment,

1. Pore Size of the filter cloth,
2. Filter Dia,
3. Reaction mass volume,
4. Applied vacuum,
5. Filtrate volume,
6. Filtration time,
7. Weight of wet cake,
8. Cake height.

So, in a total the above 8 parameters need to recorded perfectly, so in case of any miss recording / wrong recording, it may lead to faltu results.




So now, Lets start the calculation,

Permeation flux = Filtrate volume / ( Filter area x Filtration duration ),

Filter Area = 0.785 x ( Filter Dia ^ 2 ),

Cake Concentration = ( Wet cake wt.  x 0.2 / Reaction mass volume ) x 1000,


                                                 ( 2 x (Filter Area^2) x 133.32 x Filtration time x applied vacuum) 
Specific Cake Resistance = ____________________________________________
                                                 ( Cake Concentration x Rxn. mass viscosity x (Rxn. mass vol.^2))


Its all done now .....!!!
Now lets know about the limits of the above discussed to distinguish the filtration,

If the permeation flux is greater than 45 Lts / mins. Sq.m, then it would be good filtration and you can go ahead with ANFD,
If it is between 15 and 45, it would be moderate filtration and while scaling up we cant assure that the filtration will be good enough and even we cant assure consistent filtration rate, so we have to prefer an trial in pilot plant,
If the rate below 15, its better to move with centrifuge or filter press.





Like Permeation flux we are also having Specific cake resistance, below is the classification to distinguish the filtration nature,

If cake resistance is ,

10 ^ 7 to 10^8           -        Good filtration,
10^8  to  10^10         -        Moderate filtration,
above 10^10              -        Slow filtration


That's it.......!! This post is done here itself,

Lets suppose, now here i'll give one case study / sample calculation with some input data,

Filter cloth size      :  5 µ,

Buckner filter dia  :  5 cms,

Slurry volume        :  1000 ml,

Viscosity                 :  0.3 cP,

Applied Vacuum  : 500 mmHg,

Filtrate volume    :  650 ml,

Filtration time     :   20 minutes,

Wet cake weight :  230 grams,

Cake thickness   :   150 mm,

Also Read:

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Now the result is,




Permeation flux - 16.56 Lt/Sq.m. min,

Cake concentration - 46.00 Kg/Cu.m,

Specific cake resistance  -  4.46 x 10^10 m/Kg.

So as per the above discussion, the filtration is poor, not good enough in ANFD.

I've prepared an automated sheet for you guys and this sheet will do the work for you,

Below is the screenshot of the automated sheet:

Credits: Pharma Engineering

DOWNLOAD HERE

Any queries feel free to comment / reach me through mail ....!!!

Comments are most appreciated ......!!!

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[How to] Calculate NPSH (Net Positive Suction Head) ?

About The Author

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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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