## 43735Re: [new_distillers] Re: calculating heat input

Expand Messages
• Apr 23 9:39 AM
The scrubbers should not be compressed when you are packing your column with them.  They shoudl fill the column but not forced into it.  The column should be operating at atmospheric pressure only - no pressure buildup under the packing or anywhere else.  When the column reaches equilibrium, (by definition) any vapor leaving the boiler should appear at the top of the packing (below the reflux condenser).  I don't know if you have any way to observe or measure any of this, but if you do, it would help to understand what is happening.

There should be vapor coming off of the boiler -- if not, you don't have enough heat going into the boiler (obviously).  It is a good idea to insulate the boiler as well, as heat loss in your big boiler may exceed the heat input and you then have no vapor into the column.  But if you do have vapor going into the column, it must ascend through the packing to be liquified by the condenser(s).  A distillation column will ordinarily store some mass in the packing or plates, but after it reaches equilibrium, this storage is saturated and the column can store no more.  Conservation of mass dictates that what goes in must come out, so there must be vapor to condense.  If there is, but you are getting no product, then (obviously) the reflux ratio is too high (100%) and you can slowly reduce it until you get some product takeoff.  The vapor temperature will tell you the proof of your product.

I would follow Nixon and McCaws procedure:  set the reflux ratio to 100% and allow the column to come into equilibrium, which may take some time (hours).  The temperature of the product vapors will stabilize when the column is in equilibrium.  Then slowly decrease the reflux ratio to obtain product, making sure that the column remains in equilibrium as you do so (by continuing to carefully observe the temperature at the top of the packing).

The only way that you can stop getting vapor at the top of the packing is if you stop putting vapor into the column, or if there is heat loss from the column.  In the latter case, the vapor is condensing in the packing and not reaching the condenser above the packing.  This is why the column must be insulated.   Ideally, the only place that latent heat of vaporization should be removed from the column (to condense vapor back into liquid) is via the condenser(s).

I don't know of ready made insulation to wrap a 2" diameter column, but you can certainly get pipe wrapping insulation or bats of insulation for wrapping water heaters from any hardware store and wrap your column with this stuff.  You don't need to go overboard - the still will (must) work in an imperfect world.  You just need enough to ensure that the column can reach equilibrium and be kept there.

-----Original Message-----
From: totallyanonymousemail18 <totallyanonymousemail18@...>
To: new_distillers <new_distillers@yahoogroups.com>
Sent: Tue, Apr 23, 2013 6:42 am
Subject: [new_distillers] Re: calculating heat input

My column is packed with copper pot scrubbers. They may be to tightly packed; how to know? My column thermo is a Blichmann mechanical, and it read 170, maybe 171. Also, do you have any suggestions on an insulation medium for a 2" column? There doesn't seem to be much ready-made for that diameter. Now the plumb on the column, that may be an issue. It is an open-head SS drum with an ever-so-slight crown when I screw down the ring; the 2" fitting is not smack in the center, but near the rim, so it might not be plumb down the center. That is something I'll check and kludge a solution to. I know that the 4 KW power is too much for my condenser, it gets overwhelmed. at 2.5, the base was as hot as the rest, but the top was cool.

You've given me some things to think on and check. I built my column as a modular system, so that I can lengthen/shorten the column and use different reflux condensers for different applications; I may need to fabricate a more powerful reflux condenser.

Thanks again for the tips.

--- In new_distillers@yahoogroups.com, Bob Glicksman <bobg542492@...> wrote:
>
>
> I am wondering if the 2L product that you are getting are the foreshots and not ethanol. The foreshots have a lower boiling point than ethanol which suggests (but doesn't guarantee) a lower latent heat of vaporization. Question: can you bring the column into equilibrium and get a temperature of the vapors at the top of the still of about 173 deg F (the bp of the 190+ proof ethanol)? Make sure that you have slowly removed the foreshots and heads before going back to 100% reflux and reestablishing equilibrium in the column. This is the main test -- if you can't get the vapor temp up to the bp of high proof ethanol, then you are either not puting in enough heat or have too much loss in your uninsulated column. BTW - I have never heard of anyone actually getting good reflux distillation with an uninsulated column, so I'd strongly recommend that you do this first. Also, check the plumb on the column and make sure that it is absolutely vertical. I know of a number of cases where a few degrees off of vertical causes the reflux liquid to run down the sides of the column and not mix sufficiently with the ascending vapors in the packing, so that the whole fractionating action didn't happen at all. And while you are at it, check your packing. You didn't say what it was, but make sure that it is loose enough to get good vapor flow up the column and good mixing with decending liquid.
>
> Ultimately, you may need to increase the boiler heat but generally speaking, too much heat is worse than too little heat, as long as the still provides the product production rate and proof that you desire. Afterall, whatever heat energy you put in has to be removed by the condenser(s). Also, according the Nixon and McCaw, too much heat means too much vapor which means too much mass flowing into the reflux column which means a higher speed of vapors rizing up a fixed diameter column, all of which means not enough interaction of vapor and liquid in the column leading to low proof and waste of energy.
>
> Hope this helps ...
>
>
> -----Original Message-----
> From: totallyanonymousemail18 <totallyanonymousemail18@...>
> To: new_distillers <new_distillers@yahoogroups.com>
> Sent: Mon, Apr 22, 2013 5:52 pm
> Subject: [new_distillers] Re: calculating heat input
>
>
>
>
>
> On that point, I'm in the same process of heat input calibration. I've got a fairly big boiler (55 gal 304SS) with 3 x 1" FPT fittings at the base: one is a ball valve for flushing, the other has a 4 KW element for heat up, and the last is for simmering/running. At first I had a 750 W element, but when I switched over, the temp in my column plummeted (neither boiler nor column are insulated right now, may be in the future, and I expect this will change my heat calcs). I went to 2 KW, and that was not quite enough to maintain a constant temp at the top of my column. So I thought that 2500 W would do it, and it did for a bit, yielding 5 drops/sec, but after only maybe 2 liters of product, it stopped. So from your response, I either need to dial down further on the reflux, or add some power during the process?
>
> Thanks
>
> --- In new_distillers@yahoogroups.com, Bob Glicksman <bobg542492@> wrote:
> >
> > It is only true at the beginning of a batch distillation. Since the vapors are higher in alcohol than in the liquid, the remaining liquid in the boiler becomes stripped of alcohol as the boiling progresses. That is why you must monitor the temperature of the product vapor and increase the reflux ratio as the main run progresses and then terminate it altogether when you judge that you are at the tails of the run. So yes, you are correct that you could increase the heat input from the absolute minimum as the batch run progresses to prevent the vapor into the column from reducing with time until it is too low for your production purposes. But you don't need to increase the heat to the boiler if you can tolerate the reduction in product takeoff. There is a fairly wide range of vapor volume and speed that works well in any given packed column still and most batch distillers seem OK with this.
> >
> >
> > -----Original Message-----
> > From: chris jude <vegbenz300@>
> > To: new_distillers <new_distillers@yahoogroups.com>
> > Sent: Wed, Apr 17, 2013 11:55 am
> > Subject: Re: [new_distillers] calculating heat input
> >
> >
> >
> >
> >
> >
> > Thanks for that response. With your example of 10% alc. beer, you say the vapors are 54% ethanol and 46% water. Is that a number you could use as a constant for the whole process, or are you having to overcome greater latent heat from the beginning to the end of the batch distillation?
> >
> >
> >
> >
> >
> >
> > On Wed, Apr 17, 2013 at 1:44 PM, Bob Glicksman <bobg542492@> wrote:
> >
> >
> >
> >
> >
> > The minimum heat that you need for distillation is the latent heat of vaporization of your vaporized beer (i.e. the heat energy carried into the distallation column). Thus, if your beer is 10% abv, the vapors are 54% ethanol and 46% water (ignoring all of the other stuff, which is small by comparison). Find the latent heat of vaporization of ethanol and of water, BY VOLUME, and factor these using the 54/46% numbers, above to give the unrecoverable energy of distillation.
> >
> >
> > Note that this calculation is the minimum energy that is needed to distill. In general, you will need to put in more energy due to other factors, e.g.: imperfect insulation in the column, too few plates/low HEPT (necessitating higher than minimum reflux ratio), the "sensible heat" needed to raise the beer to the boiling point to begin with, etc. These other energy needs are, in theory, recoverable and/or avoidable, but the latent heat of vaporization of the beer is neither recoverable nor avoidable (you can recover this heat in the condenser(s) and use it elsewhere, e.g. for cooking the mash, but it cannot be recovered for distillation purposes because the temperature is the temperature of the vapors at the top of the column which is the boiling point of the distilled product and must necessarily be lower than the boiling point of the beer).
> >
> >
> >
> >
> > -----Original Message-----
> > From: chris jude <vegbenz300@>
> > To: new_distillers <new_distillers@yahoogroups.com>
> > Sent: Wed, Apr 17, 2013 7:46 am
> > Subject: [new_distillers] calculating heat input
> >
> >
> >
> >
> >
> >
> >
> >
> > Hi,
> >
> >
> > I'm trying to size a heater for a still. I know the calculation for raising the temperature of the wash up to boiling, but how can I calculate the heat input required for distillation? After the wash is up to the boiling point, is it just the latent heat of vaporization, and losses to atmosphere?
> >
> >
> > Chris
> >
>

• Show all 21 messages in this topic