November 14, 2011

Spray Drier - Another view


Hello Friends, I am late again due to shifting to some very interesting industry this time making very useful product Furfural from Bagasse.

The incident of yesterday's interaction forced me to come back to the blog for sharing.

Yesterday I met vice president of a growing mid size company in Gujarat. He told me that spray driers can not be counter current and I should learn this fact. The reason he explained is that dried powder shall be carried away by hot incoming air and therefore you need a cyclone separator at the top for separation of solids & air.

Quite interesting ......This forcefully made me to think about fundamentals of drying......but later on. Before that I thought about creativity of Human mind. its brilliant......it's unlimited......it's really really much much bigger than what we can think of.

Yes dear, all of you should take this as a challenge on this blog itself that how to prove this wrong & how to prove it right.

In the beginning I thought I should re-think on the basics of spray driers and then searched on net also. So I found so many picture / images here.

He may not be fully wrong also, but the word 'Spray driers can not be countercurrent' was not right I am sure.

Really its very difficult for me to write any thing on this topic now. The basic reason he mentioned was that if flow is counter current solid particles will go up with the air & you need a cyclone separator for recovery. Is it really so??

I think it is always so whether it is counter current or co-current. Isn't it?? Most of the pictures on the above link are having cyclone separator. So this argument was also not so good for making spray dries co-current.

In fact, If I see the principle of drying and nature of most of the solids where spray drying is essential or most suitable, it is always better / preferable (Few Exceptions depending on nature of solids) to go for counter current as driving force is always higher and moisture content in dried product from the same size is less.

In fact, those applications where spray drier is generally used, I will not prefer to go for it as it is highly energy intensive & capital intensive compared to thin film drying which I have already done for a very highly hygroscopic material. I will try to put the data for that installation in one of the next articles.

I will prefer spray driers mostly for hygroscopic material with sticky nature in wet condition otherwise its better to go for other options.

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9 comments:

chemind said...

of course their are chances of solid particles carry over along with the dry air when it flow counter currently, but if the spray drier height is increased to such a height where the particle are no more carried but deposit on solid surface of collectors, by changing the design this can be made possible

Erni said...

Nice Blog, I Like it, thank for sharing..
Merry Christmas

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Anonymous said...

Sir where i m working v hv both co- n counter curent with height of 15 meter spray drier n v hv bag filter

profmaster said...

Dear I never said any one type is possible. The point was - someone is saying - 'IT CAN NOT BE'

Anonymous said...

Dear Sir...
as I have seen in pictures ( thanks to the link provided by you) , The air acts as a carrier or transporting medium for solid particles .... and the solid particles have a natural tendency to fall due to gravity which is always down wards, And Applying a carrier force which is upwards....

I agree with you that Let us increase Spray drier Height ( which will increase fixed cost of equipment).. then the actual time of drying ( will it be sufficient or not ).. the location & height of cyclone separator at Top ( which will increase fixed cost due to vertical installation).. sufficient air velocity to carry away particles against their natural fall & power requirement with it.. And Since it's drying ( phase change largely not sensible heat transfer..) Then according to LMTD curve How much beneficial a Counter - Current arrangement will serve.. when th upper line is always horizontal ( phase change)while the same can be achieved with Co-current..
May be I am not much comprehensive, or articulate or I may be wrong but becoz I love your blog.. I just tried to express my view...

With warm Regards,
Your Old IGL Student.. Deepak

Techkasamba Agarwal said...

Thanks Deepak for loving it. Though I could not focus on new topics as I was passing thru rough phase for last one year, I would still try to answer your query.

First of all I cud not understand your point. Let me explain shortly. The point is not to disprove anything neither co-current nor counter-current, both are possible - Yes if I go technically deep I can disprove & discard co-current completely but thats not my intention.

First of all, do not compare cost untill your basic objective is full filled i.e. drying of solids.

1. Why to carry particles till top of the dryer? it is not the basic intention in counter current. Actually if you see the particle distribution of any solid product you will find lot of fines & coarse particles. So those fines will get carried till top (Mind it unintentionally - the intention is to keep the design such that particles should fall at terminal velocity for max drying). Now cyclones are necessity (Majboori in Hindi) to recover those fine particles. It is not by design & not by choice but by compulsion.

2. The size of co-current by your own logic will be much more than counter current due to higher velocity of particles a- own gravity force & b - due to air velocity force (So result is sum of the two velocities while it is opposite in counter current i.e. gravity force - air velocity) and hence, the time of drying available in the same height is much much lesser in co-current. Putting a cyclone is easier than increasing the height of dryer.

3. In terms of mass transfer also its not phase change in actual sense its actually Mass transfer from rich phase to lean phase and hence, the time & contact area is important than heat transfer. Therefore, again the last bit of drying is NEVER possible in co-current and can be achieved only in Counter-Current systems.

4. LMTD is also higher for the entire system in counter current due to a larger gap than co-current in which it continuously goes down from top to bottom. This will also suggest the same thing if you actually do the designing.

I think you are not wrong it comes ultimately with experience and you will learn those things as you grow.

Anonymous said...

Thanks Sir..
Working with you have always been enriching in learning & confidence building up in ourselves.. I regret I did not get much chances to work under you..

And that Experience has always been a benchmark till date.. when working under different bosses came into practice..

And the motivation is clearly obvious.. with you the driving force was .. Learning and gaining knowledge.... and most of the times with other people.. It's just finishing a job..

I take pride in that I have worked under your supervision.. and that helped me to improve myself and my professionalism..

Thanks for your deep & accurate insight in the subject matter..
I also have gone through a hell..

We don't know how strong we are until Being strong is the only option we are left with..

Take care.. & Wish you Luck..
regards..
Deepak

Techkasamba Agarwal said...

Its good that you have understood the importance of time, sincerity & attitude. That's why I told you to improve on those factors & they will decide your future. I dont know what happened to you but Unless you improve it there is no FUTURE.

Anyway wish you Good Luck for new learnings of life.

kelebek vana said...

another nice and informative post from this blog! Keep up the good work!

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