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Packed column, what type of head?

Packed column, what type of head?

Postby Tracker » Mon Jan 14, 2013 1:05 pm

We all know that to get good clean spirit, the column must be stacked, then take-off the product at a rate whick prevents or reduces smearing.
So, with that thought in mind, we must assume that the heat input, column size, refluxing ability and packing holds and separates the fractions, while the head does the job of setting the product take-off speed.
To my way of thinking, VM and the CM (using dephleg) operate on a similar principle of collecting and condensing a set quantity of vapour. LM (as in Bok slant plate) condense all then collect part of the condensate. Pretty similar principle really in that you are collecting part of the product and allowing the remainder to recycle within the column, just a different way of skinning the cat.

Now if we run these different head types at a set take-off speed with all other conditions being identical, why should one type produce a cleaner or better product or in fact be able to also run faster than the other configurations?

I am not looking for the "I run this type and it puts out x times faster than my old one". I am looking for the reasons behind the difference.


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Edited for spelling.
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Re: Packed column, what type of head?

Postby rkr » Mon Jan 14, 2013 5:08 pm

VM and CM and RLM adjust to changes in vapor composition while LM does not. Steam has less liquid in it than ethanol vapor, once vapor composition moves towards more water rich vapor, RLM decreases the take off. Vapor with more water in it is easier to condense and that's why CM decreases the take off rate when ABV of vapor drops. Vapor with more water in it gets also lighter and that's the logic how VM adjusts the take off rate and why it stops between 40-50% ABV.

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Re: Packed column, what type of head?

Postby Tracker » Mon Jan 14, 2013 7:56 pm

Can you explain what you mean about the differences between steam and ethanol vapour? I would have considered them to be the same thing in the context of this discuussion, as in the vapour travelling up the column. Or are you talking about some thing else?


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Re: Packed column, what type of head?

Postby rkr » Mon Jan 14, 2013 8:27 pm

The vapor travelling up the column is always a mix of water (steam) and alcohol vapor. When the concentration of water in this vapor increases the reflux ratio gets increased (ie. less product collected) in RLM, CM and VM which then reduces the concentration of water in the vapor due to increase in column efficiency.

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Re: Packed column, what type of head?

Postby Tracker » Mon Jan 14, 2013 8:42 pm

Thanks for that Rkr but is it not the same thing with the (LM) Bok head. The only difference being that with the Bok, in that you are liquidizing the concentrated vapours within the column then extracting a portion of the product, while returning the remainder back to the column for continued refluxing, while with the others as mentioned you are collecting a portion of the vapour to condense outside the column while returning the remainder of the vapour as a condensed liquid back down the column for continued refluxing. Are not both processes supplying the same end result?
It is this process where I have difficulty in understanding why one method should cause a different result to another.


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Re: Packed column, what type of head?

Postby rkr » Mon Jan 14, 2013 8:51 pm

When using LM and the ABV of the vapor drops, the volume of the condensed liquid will also decrease as water vapor occupies more space than ethanol vapor. This means that you will be removing the same amount of product while returning less back to the column, thus you will have a decreased RR.

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Re: Packed column, what type of head?

Postby Tracker » Mon Jan 14, 2013 8:56 pm

So, are you saying that with a LM head. When you remove product, the abv% drops within the column but with VM/CM heads, the %abv within the column does not drop?


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Re: Packed column, what type of head?

Postby Tracker » Mon Jan 14, 2013 11:27 pm

Ahhh.
So. with some types, you are determining how much is returned for refluxing, while with others you are determining the percentage which will be removed.
Possibly an over simplification but is this what you are meaning?


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Re: Packed column, what type of head?

Postby Tracker » Tue Jan 15, 2013 12:07 am

Righto, I think I am beginning to understand the reasons.
I was assuming that if all perameters were set the same, i.e. column, heat, packing, collection rate etc. then there should be no difference in the resulting product strength or taste.

Not all columns rely on setting the product output rate for optimum performance, so therefore a direct comparison cannot be made.....Yes?


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Re: Packed column, what type of head?

Postby Tracker » Tue Jan 15, 2013 8:26 am

OK, thanks for the info. I will now find another topic to occupy my thoughts.


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Re: Packed column, what type of head?

Postby timmyjane » Sun Jan 27, 2013 1:45 pm

Tracker wrote:OK, thanks for the info. I will now find another topic to occupy my thoughts.


Cheers.


Lol. Glad you thought about it because it helped more than just you.
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Re: Packed column, what type of head?

Postby PaPaBear » Sat Mar 30, 2013 12:44 pm

Yes, thanks for this thread. it has cleared some things up for me.
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Re: Packed column, what type of head?

Postby DrWho » Sun Mar 31, 2013 1:03 am

I agree, very helpful thread. I'd like to add that many folks that build a VM head also include a LM takeoff. I did this with my build (viewtopic.php?f=43&t=1137). The main reason is to take fores & heads via the LM, then the hearts via the VM port.

Using LM for the fores & heads works out better then using the VM for a couple of reasons. First is that the take off rate responds more quickly. A twist of the needle valve and the take off rate changes immediately. The VM port takes some time to react to a change in valve position.

Second is that it is good to not contaminate the VM port with heads. This allows for a smaller portion to be taken as heads, as there is no need to wash the remaining out of the VM side using hearts. So less heads and more hearts, and a sharper cut between heads & hearts. :handgestures-thumbupright:

Then, if desired, can also use the LM side to take tails.

???
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Re: Packed column, what type of head?

Postby Lucky Liqueur » Sun Mar 31, 2013 9:39 am

minime
Let me take a stab at this


How about putting that in the FAQ section?
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