Vapor management: Difference between revisions

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Liquid Management
Liquid management is a well established reflux design, first popularised with an 'offset head' design (sometimes called a [['Nixon-Stone']]), as seen below:
[[File:Offset head LM.png]]
Offset Head LM


More recently, an inline version has become more popular, this is often called the [[Bokakob]] Inline or Dual Slant Plate design. It looks a lot different but the operation is the same:
Vapor Management (VM)
[[File:Boka LM.png]]
Inline LM


As vapour rises up the column, it passes the takeoff port (in whatever form that may be, slant plates for the boka), and 100% of the vapour is condensed, and the falling distillate collects in a pool at takeoff. A needle valve lets you take off product at a set rate, while the pool overflows back into the column as reflux. This means that you are always taking off quantity X. The amount of reflux is determined by the total amount of distillate produced, less quantity X.
The vapor management column is a relatively new design. While Liquid Management condenses everything and manages the reflux ratio by splitting the liquid, the VM splits the vapour into two streams, and then condenses each separately.


These stills can provide good performance, and have quite a small parts list so are probably one of the cheapest designs to build, don't require too much challenging construction, and are accordingly probably the most built reflux design. The LM has very good heads compression (probably the best of the three main design types). They also allow a reflux ratio of less than 1:1 more easily than a VM. This allows them to operate like a pot still at lower reflux ratios, but (and I'm paraphrasing Husker here, not personal experience) it isn't quite as good as a proper pot still for stripping etc because of the amount of condensation that occurs on the bottom of the slant plates. The LM (assuming a boka type design) is generally regarded as the easiest and cheapest to build.
[[File:Vapor_Management.png|thumb|220px|right|Vapor Management Head]]
[[File:Vapor Management Diagram.jpg|thumb|220px|right|Vapor Management Process]]


A serious drawback of an LM. Lets say (just to make it easy on the math) that the column produces 100ml per minute, and X, your take off, is 50ml/min. this means that at the start of the run, your reflux ratio is about 1:1, which is ok (well, just) for a big tall column taking off hearts. Probably not azeotrope, but close. Now as you're distilling away happily, the amount of ethanol left in the boiler is decreasing. This slows the production down from 100ml per minute to 75ml per minute. However, your valve is still set at 50 mls/min, so your reflux ratio is now .5:1, which is way too low. So, you can think of the valve on a LM as controlling the takeoff rate in isolation of the reflux rate. This results in a slowly decreasing reflux ratio, requiring more operator attention.
Because a VM splits the stream of vapor before [[reflux]] is generated, with the valve set wide open (assuming a full size takeoff port), you're getting roughly 1:1 reflux ratio regardless of the amount of vapor. While with an LM, adjustment would be needed as the production rate decreases, in a VM the reflux ratio will stay constant and output will fall; lets say the valve is still wide open, at the beginning 100mls/min = 50:50 = 1:1, and later 75mls/min = 37.5:37.5 = 1:1. '''The valve on a VM sets the reflux ratio, not the takeoff amount,''' and as the reflux ratio is what you want to set and keep constant over [[hearts]]. Many people see this a one of the key benefits of a VM still.


Design variants and other names:
Also, because of this, the valve settings for VM will remain constant over different charges or the still changes in heat input (which will probably produce at different rates). Anything that varies the rate of production of vapor requires a change in valve settings on an LM. A VM you just leave. Any [[column]] you choose will require some amount of adjustment for [[foreshots]], [[heads]] and [[tails]], but again, the nice thing about the VM is PREDICTABILITY. you can remember what ratio you like to take off heads at, set it, do other things around the shed and change it when you've taken off enough. Instead of having to keep adjusting a valve when tails is looming, you just wait until the thermometer budges, knock back the valve a bit til it goes down, when it budges again open her up and take off the measly liter of tails. Or don't even bother. Tails from a reflux are so gross you won't want them anywhere near your product. The VM is generally acknowledged as the easiest design to run.
Offset Head, Nixon-Stone, Valved Reflux, Bokakob, Boka Inline, Inline LM, Dual Slant Plate.


Original Post by Kiwistiller, edited by Bushman, can be found here: http://homedistiller.org/forum/viewtopic.php?f=60&t=46216
A VM has drawbacks too. The first is that it's quite hard to discover the reflux ratio (here is my experiment to calculate mine). This isn't a major problem, as you don't really need to know. The other drawback is you are limited in how little reflux you can produce (ie the minimum reflux ratio, because the VM cannot (without simple modification) get less than about 1:1 reflux ratio (unless you have a small takeoff port, in which case the minimum ratio will be more like 4:1), it is (imho) unsuited for flavored spirits. I personally consider the VM a one trick pony, neutral and only neutral. But then again, if you want flavor, get a pot still.
 
The other main drawback of a VM is it is less effective for heads extraction when compared to a good LM design. This results in a slightly higher proportion of your total run being heads. To get the advantage of both LM and VM in a single build, many combine them, and have a VM takeoff (for hearts) below a set of slant plates for LM takeoff (for heads extraction). Another option for adding LM functionality to a VM stills is to use a horizontal condenser, like the [[Crossflow Condenser]] or [[Thor's Hammer]].
 
Original Post by Kiwistiller, edited by Bushman, [http://homedistiller.org/forum/viewtopic.php?f=60&t=46216 Can be found here].


[[Category:Equipment]]
[[Category:Equipment]]
[[Category:Glossary]]
[[Category:Glossary]]

Latest revision as of 13:15, 11 December 2022

Vapor Management (VM)

The vapor management column is a relatively new design. While Liquid Management condenses everything and manages the reflux ratio by splitting the liquid, the VM splits the vapour into two streams, and then condenses each separately.

Vapor Management Head
Vapor Management Process

Because a VM splits the stream of vapor before reflux is generated, with the valve set wide open (assuming a full size takeoff port), you're getting roughly 1:1 reflux ratio regardless of the amount of vapor. While with an LM, adjustment would be needed as the production rate decreases, in a VM the reflux ratio will stay constant and output will fall; lets say the valve is still wide open, at the beginning 100mls/min = 50:50 = 1:1, and later 75mls/min = 37.5:37.5 = 1:1. The valve on a VM sets the reflux ratio, not the takeoff amount, and as the reflux ratio is what you want to set and keep constant over hearts. Many people see this a one of the key benefits of a VM still.

Also, because of this, the valve settings for VM will remain constant over different charges or the still changes in heat input (which will probably produce at different rates). Anything that varies the rate of production of vapor requires a change in valve settings on an LM. A VM you just leave. Any column you choose will require some amount of adjustment for foreshots, heads and tails, but again, the nice thing about the VM is PREDICTABILITY. you can remember what ratio you like to take off heads at, set it, do other things around the shed and change it when you've taken off enough. Instead of having to keep adjusting a valve when tails is looming, you just wait until the thermometer budges, knock back the valve a bit til it goes down, when it budges again open her up and take off the measly liter of tails. Or don't even bother. Tails from a reflux are so gross you won't want them anywhere near your product. The VM is generally acknowledged as the easiest design to run.

A VM has drawbacks too. The first is that it's quite hard to discover the reflux ratio (here is my experiment to calculate mine). This isn't a major problem, as you don't really need to know. The other drawback is you are limited in how little reflux you can produce (ie the minimum reflux ratio, because the VM cannot (without simple modification) get less than about 1:1 reflux ratio (unless you have a small takeoff port, in which case the minimum ratio will be more like 4:1), it is (imho) unsuited for flavored spirits. I personally consider the VM a one trick pony, neutral and only neutral. But then again, if you want flavor, get a pot still.

The other main drawback of a VM is it is less effective for heads extraction when compared to a good LM design. This results in a slightly higher proportion of your total run being heads. To get the advantage of both LM and VM in a single build, many combine them, and have a VM takeoff (for hearts) below a set of slant plates for LM takeoff (for heads extraction). Another option for adding LM functionality to a VM stills is to use a horizontal condenser, like the Crossflow Condenser or Thor's Hammer.

Original Post by Kiwistiller, edited by Bushman, Can be found here.

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