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Still condenser maximum temperature

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Hi fellows,

 

I have a simple question I was not able to find an answer on google.

We run a 600L vodka still. The water flowrate to the condenser of the still is about 8 gallons/minute.

Usually, we use water that is around 50 F for the condenser.

I want to know what is the hottest water temperature we can use in our condenser before we start to lose alcohol vapor that will not condensate?

 

Thank you.

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That's a really high flow rate for such a small still.  Your question is not that simple.  A lot more info is needed to give you a proper answer.  What is the temperature of the coolant leaving the condenser? What is the temp of the condensate leaving the parrot?  Please post a picture or a link to a picture of your still as well as the specs and dimensions of your condenser.

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As mentioned, a lot more information is required to do a purely mathematical calculation.

To simplify it you could slow your water flow rate until you start losing vapour, then speed up a little until the vapour loss just stops.

Measure water flow, the water input and output temperatures. It is reasonably simple maths to calculate an approximate maximum water input temperature at your 8 gpm

I say "approximate" because heat transfer calculations become very complex. At the lower flow rate there is less turbulence and the heat transfer is less efficient.

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On 6/24/2019 at 10:13 AM, Southernhighlander said:

That's a really high flow rate for such a small still.  Your question is not that simple.  A lot more info is needed to give you a proper answer.  What is the temperature of the coolant leaving the condenser? What is the temp of the condensate leaving the parrot?  Please post a picture or a link to a picture of your still as well as the specs and dimensions of your condenser.

Paul,

Are there write ups/ charts on coolant in/out temp, still size, and coolant flow rate?

how do we get to know these stuff?  Can you share some articles/ studies or research about this subject?

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Geoman,

There are a lot of variables here in just this simple process.  The ones listed above plus, the heat exchange surface area, number and size of tubes, shell side or tube side operation, vertical or horizontal, type and location of baffles and on and on. There are some charts on line and there are calculators, formulas and guidance so that you can get very close.  There is even some software that does a great job.

I have been doing this long enough that I know what size and design of condensers are needed for what size stills,  to do the right job.

I based all of my original calcs for condenser sizing on a 2 hr stripping run, for all of my steam fired stills.  Then I increased the heat exchange surface area of the condenser, so that it has 2 to 4 times the knock down that is required to do the 2 hr stripping runs.  This way, if the customer has water that is 15 degrees hotter than the optimum temp or they are running gns really fast, the condenser can handle the job with no issues.  My electric stills are slower so the condensers are smaller on those.

My 300 gallon Ultra Pro Vodka stills have 12" diameter by 40" tube and shell final condensers.  The coolant flow rate for a vodka run is less than 2gpm at 50 F on my stills.  My 150 gallon vodka stills run way less than 1 gallon per minute of coolant during a vodka run.

I  put  8"x40" condensers on our 150 gallon pro series stills.  Also you must have proper baffling.  Our newest baffle design increases the efficiency of our condensers over 600% over the exact same condenser with no baffles. 

The OPs 600 liter still should have at least a 4" x48" condenser that is properly baffled.

 

 

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My admittedly simple understanding of this (partially from my days in construction) is that you need a 40f temp difference to get condensation. 

 

So the short and simple answer is:

- the bigger the condenser the less flow you will need and will allow warmer water. 

- assuming 170f vapor temp and a giant condenser, absolute max theoretical cooling water temp would be ~130f

 

we run 80f cooling water all day and flow maybe 3 gal/min to the RC AND PC combined.  And I’m inputting 9000w and pulling off 80f product. 

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Quote

 

I want to know what is the hottest water temperature we can use in our condenser before we start to lose alcohol vapor that will not condensate?

 

Since you asked.  The hottest temperature you can use is the hottest temperature that will keep the distillate temperature under the closed cup flash point listed in this chart.

Suspect many will be surprised by this, since you get to some fairly cold temperatures as you approach azeo.  Are we talking about large losses if you go over these numbers?  No, but that's not what you asked.

80f input water to a condenser means that in most cases, vapor is going to be generated.

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Wow!  Basically this is observed as evaporation of the spirit? Or is this a  hazard of ignition?

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Oversimplifying, the closed cup temperature represents the minimum amount of vapor to sustain a "flash" burn in a closed container.  It will not burn, but will flash.  The fire point is the temperature at which the distillate will sustain combustion for at least a few seconds.

The initial question, 'what temperature will begin to lose alcohol to vapor' - that's the closed cup point.  It might be a tiny amount of vapor, and not enough to be an issue from a hazard perspective (lots of factors in play there), but it's still losing alcohol as vapor.

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2 hours ago, Silk City Distillers said:

Oversimplifying, the closed cup temperature represents the minimum amount of vapor to sustain a "flash" burn in a closed container.  It will not burn, but will flash.  The fire point is the temperature at which the distillate will sustain combustion for at least a few seconds.

The initial question, 'what temperature will begin to lose alcohol to vapor' - that's the closed cup point.  It might be a tiny amount of vapor, and not enough to be an issue from a hazard perspective (lots of factors in play there), but it's still losing alcohol as vapor.

As @Silk City Distillers makes clear, you will get vapor loss at pretty cool temperatures. And that is of the condensate/distillate, the cooling water needs to be colder than that to get to that temperature. But on the other hand, if you are collecting into an open container (as opposed to a spirit vault), the surface of the collected condensate will equilibrate to room temperature and your evaporation rate at the surface will be that due to about room temperature. Hence, we try to set our coolant temperature and flow rate to get us close to room temperature on the collected condensate/distillate. Anything much more than that will likely mean alcohol loss and reduction in proof. Also, much less than that means condensation on vessels and maybe even drop in proof by extracting water from air in high humidity situations.

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