Can't get above 90% ABV

[aliveandaware]

I have a offset head (Nixon-Stone) reflux still with a 2” column and 31” packing space below the reflux return tube, and another 10” of packing space (if I chose to use it) above the reflux return and below the T going to the condenser, which could still provide fractioning. I’ve done spirits runs on Uncle Jesse’s recipe twice and a spirit run using an all grain once (all of these were preceded with a number of stripping runs of course), and in all of my spirit runs, I’ve never been able to achieve above 90%. All my spirit runs begin with 40% low wines. If I add feints, I proof it all down to 40% to be safe. All my hydrometer readings are temperature corrected using the calcs on the parent site, and I’ve also chilled a sample to 60F and got the same reading as the temperature corrected value.

The basics:
Heat:
I’m using propane, and I’m using enough heat to where I can run the spirit run all the way to 210F to get all the tails for feints (I stop collecting hearts way before that of course). And I’ve learned that if I turn up the heat just by turning the knob 1/4 inch further, I’ll flood the column and overflow. So I’ve got the heat as high as I can get it, and it’s enough to drive the column all the way to 210F, so that should be plenty of heat.

Takeoff Rate and Reflux:
When I’m in the hearts, I’ve done a throughput test on more than one spirit run. I turn off all reflux and open the product valve all the way. I get 1/2 pint in 2 minutes, so that’s 4 ounces a minute. I let the column re-stabilize and continue. I’ve varied my takeoff rate from 1 pint an hour, to 1 pint in 30 minutes, and the percentage does not change, so that means, to me, that I’m running plenty of reflux. At 1 pint in 30 minutes, the still has actually produced 120 ounces, but I’ve only taken 16, so that’s 87% reflux. On my spirit runs I average 87% reflux, however when I had 1 pint an hour (240oz produced, taking 16 = 93% reflux) I was still only getting about 90% alcohol. So again that tells me my reflux rate is fine.

Column Temp:
I allow the column to stabilize for an hour after reaching a stable temp. The column is double wrapped with foam pipe insulation, and then I wrap that with a towel. My boiler is wrapped in 4 layers of towels. My column stabilizes at around 174F. I’ve put a partial run log below.

Packing:
I’ve tried 25 inches of scrubbers with 6 inches of Raschig rings. I’ve tried 31 inches of scrubbers, and I’ve tried packing the column all the way up to the T heading to the condenser, 41 inches total, nothing makes a difference. Like I mentioned above, I have 31 inches of packing space below the reflux return. And as an experiment, I packed up to that, and above that all the way to the T heading to the condenser (see pictures below for where the T is).

Cooling Water:
My cooling water flows at 1.5 GPM using a diaphragm pump and I run the return through two unused transmission oil coolers cooled with an electric fan. I can do a 12 hour spirit run and my reservoir temperature (a 15 gallon keg) only increases a few degrees. So my cooling water stays below 90F going into the condenser.

I feel I should be getting 94% to 95%. I'm not really shooting for neutral spirits, however I've put so much work into the still and cooling system, I want to understand everything I can about its operation and performance. There are a couple pics below too.

Any advice would be great. Thanks everyone.


A Partial Run Log

8:11 AM Fire up, dial up to dot
8:53 Col 173.6, heat down to lowest mark
8:57 Col 172.5, heat up to second mark
9:42 Col 173.8
9:50 Col 173.8
9:57 Col 174.0
9:59 Started collecting 1 drop a second, strong acetone smell
10:00 Col 174.0
10:22 Col 174.2 Increased drip rate to 2 drops a second, only about 3 oz so far
10:29 Col 174.3 Still smells like acetone, not as strong, about 5ox so far
10:44 Col 174.5 Smells less like acetone, more like alcohol, 8oz so far
Increased drip rate to 3 drops per second
10:58 Col 174.6 12 oz foreshots collected, no more smell of acetone
11:04 Col 174.7 Put parrot in place, increased to about 4 drops per second
11:06 Start Pint 1, drips started from parrot, 90%
11:30 Col 174.7 90.2%
11:37 Col 174.7 End Pint 1, start pint 2 (31 min)
12:07 PM Col 174.8 End pint 2, start pint 3 (30 min)
12:16 Col 174.7 93% at 89F (31.7C) in parrot (89 % corr)
12:28 Col 174.8 93.3% at 86F (30C) in parrot (89.4% corr)
12:32 Col 174.8 End pint 3, start pint 4 (27 minutes) [.50oz min][85% reflux]
12:53 Col 174.8 End pint 4, start pint 5 (21 minutes) [.76oz min][81% reflux]
With flow rate at 1 TBSP in about 46 seconds, 89%
01:12 Col 174.9 End pint 5, start pint 6 (19 minutes) [.84oz min][79% reflux]
01:38 Col 174.7 End pint 6, start pint 7 (26 minutes) [.62oz min], 88.9% ABV
01:51 Col 174.7
01:57 Col 174.8 92.5% at 80F (26.7C) at parrot
02:05 Col 174.9 End pint 7 (27 minutes)
02:09 Throughput test, 1/2 pint in 2 min 0 sec. [4oz min]
02:15 Col 180.2 Throughput test, 1/2 pint in 2 min 2 sec., 85.6% ABV
Equals 1 pint every 4 minutes
02:17 Allowing column to re-stabilize.
02:20 Col 174.8 Start pint 8, flow set to 1 TBSP every 74 sec
.
.
<snip>
.
.
06:52 Col 175.7 End pint 19, start 20 (23 min) [no smell of tails yet]
07:14 Col 175.9 End pint 20, start 21 (22 min)
07:16 Col 175.9 Possible hint of tails. 87.1% ABV
07:20 Col 176.2
07:35 Col 176.2 End pint 21, start 22 (21 min), (86.9% ABV)
07:58 Col 176.6 End pint 22, start 23 (23 min)
08:16 Col 177.3
08:20 Col 177.4 End pint 23, start 24 (22 min), (85.5% ABV)
08:35 Col 178.4
08:42 Col 178.4 End pint 24, start 25 (22 min), (83.6% ABV)

My still.

My Still

[jholmz]

90% abv is 180 proof what are you wanting? your never going to pull 100% straight spirit, i realize some get 95 sometimes but i would be happy with 90 myself

[aliveandaware]

Correct, I will never pull 100% straight spirit, the azeotrope is 96.5%, and I agree 180 proof is plenty high, and I will end up cutting it down anyway. What I'm trying to understand is that with 31" of packing, with a 2" column, and an 85% reflux, the equipment should perform better. And I'm just wanting to learn what I'm doing wrong.

According to the parent site, with the following figures (my still)
.0508m Column Diameter
.7874m Packing Height
85% Reflux Ratio
1200W Power Input (estimated since I'm using Propane)

Gives 8 Theoretical Plates, which should produce 93.9%, if I add another 10" of packing height (which I have to experiment) , I should reach 94.5%. However, my equipment is only producing about 90%. I designed the still based on designs I found on the web, and according to the numbers it should perform better, I'm just trying to learn.

If someone designs a car to do 130 MPH, and they can only go 100MPH, they will want to know why they cannot achieve what the design said they should, even though 100MPH is plenty fast.
It's a learning process for me.

[woodshed]

Is your abv reading done with temp correction?

[Prairiepiss]

When you are pulling hearts off. You open the takeoff valve all the way and shut off the reflux return valve? How are you going to get a higher ABV if your not refluxing anything?

Generally the packed section needs to be more then what you have. So 90% may be all you can get out of it. Or maybe not.

I would say its a mater of wrong technique.

If you are only using 1200 watts worth of heat. That's not enough. 2000 to 2400 is more like what you need. For a 2" reflux still. 1200 watts won't produce enough vapors to provide enough reflux to get to where you want. And as I said above. If your reflux return valve is shut off. You aren't refluxing anything anyway. Even if it was supplying enough vapors.

Turn the heat up. Let it reflux. And slow your takeoff down to 2 or 3 drips a second. And see what you get.

[aliveandaware]

Yes, my ABV readings are done with temperature corrections from the calcs page in the parent site as mentioned in my original post, and to confirm the temperature corrections I also chilled a sample down to 60F (the calibration temp of the hydro) and it confirmed the readings.

When I was pulling hearts off I performed a throughput test for 16 ounces only. I wanted to confirm my reflux rate, so I turn off reflux, measure the throughput, then returned to normal reflux (per the book Making Pure Corn Whiskey). Of course I did not run the entire spirit run like that, it was just to measure throughput, and for only about 4 minutes out of the 12 hour spirit run.

The wattage is only an estimate from the calcs page, I mentioned in the original post that I'm using gas. I cannot turn up the heat, if I turn the knob just 1/4 inch more, I flood the column, so I've found the max heat point, it can't get any hotter, not even a little, or I will flood the column. I can provide enough heat to drive the column to 210F when I reach the tails, and I provide enough heat to produce 4oz of product a minute. I had my takeoff set to the point where I was pulling 16oz an hour at one point, so the still produced 240oz in that hour and I only pull off 16oz, so 224oz were being refluxed, or 93% reflux. That's a lot of vapor.

According to the calcs page, my column and packing should provide 8 theoretical plates, which should provide 94% at the least, and up to 94.5% on my last run (with 41 inches of packing). I'm at max heat or I flood the column, and it's a 2 inch column with up to 41 inches of packing. So I'm trying to figure out what part of my technique is incorrect.

[pfshine]

I think there is two things you should try. First is slow the cooling water down to raise the reflux temp. Second is remove the insulation to allow the column to achieve a natural temp gradient. And one more thing maybe move the cooling water lines away from the column or just leave some insulation between them and the column. I think these things should get you a higher abv out the gate.

[Cardinalbags]

For starters, the packing above the reflux return is doing nothing. That part of the column is one way vapour traffic upwards only so packing it is like mounting a sprinkler on the underside of an umbrella..... The length of the packing under the reflux return is what is important. What you have is 31" of packing that is actually doing anything.

You can modify by either routing the reflux return a bit higher in the column and gain some extra effective packing height, but whereas you have such an intricate top end on the still it would be easier to increase packed height by adding at the bottom of the column.

And I would say you are estimating the heat input from the propane on the low side.... 1200W from propane would be just a small flame. As you noted, a 1/4 turn more was flooding out your column. I suspect your heat input is much higher.

In a reflux column, the ABV is dependent on the following things: Height of column, efficiency of packing, total heat input and amount of reflux being returned back down the column compared to how much you are taking off.

The column height I have already discussed above.

Packing: Raschig rings are not that effective. Stick with the copper scrubbers and densely pack them, but not so dense as you can constrict it too much and flood / have pressure build up. I can pull 95% at 3.3L/hr on a 2" column with dense packed copper mesh at moderate heat input and 4.2L per hour when on the hairy edge of flooding. I only have a 36" packed section achieving this.

Takeoff rate: sounds like you are keeping reflux ratios high and taking the product off slowly enough.

Heat input: you are on the hairy edge of flooding or at least within a 1/4 turn on the dial.....

So - the only variables you can play with are packing height and packing efficiency. Add more height or use a higher efficiency packing if you really need to get to producing 95%+

And 12 hrs on a reflux run is a really long run.....

[aliveandaware]

For starters, the packing above the reflux return is doing nothing. That part of the column is one way vapour traffic upwards only so packing it is like mounting a sprinkler on the underside of an umbrella..... The length of the packing under the reflux return is what is important. What you have is 31" of packing that is actually doing anything.

Packing above the reflux return definitely is not as efficient as below, I agree with that. However, it sill provides fractionating. A packed column with zero reflux is called a fractionating column (The Complete Distiller pg 63), a packed column with reflux is called a compound column (pg 64). I'm not relying on that additional packing to provide anything, I was just experimenting. As the high volatile components reach the upper column, they can condense on the packing. As those droplets make their way down, they interact with the hotter vapors of less volatile components on the way up. The heat exchanges into the lower volatile components, re-vaporizing them and giving you multiple micro distillations. Running an unpacked column, measuring your ABV, and then running it packed with zero reflux and measure your ABV, will give you an idea of what fractionating alone can do. It's nowhere near as good as reflux, but it has it's benefits when combined in the mix.

And I would say you are estimating the heat input from the propane on the low side.... 1200W from propane would be just a small flame. As you noted, a 1/4 turn more was flooding out your column. I suspect your heat input is much higher.

I agree, that was just the number on the HETP calcs page on the parent site, and since I didn't have a value for that field, I just left it with the default value. 1 kW heater will produce about 1,600 grams of distilled water every hour, or about 30ml every minute. 1kw will produce 5.3 liters of ethanol per hour, or 89 ml every minute. With 40% low wines 1kW should produce about 54ml per minute. I was producing 118ml every minute, so that means I was providing about 1325kw of energy?


I agree about the Rachig rings. After some research I found that the surface area to packing volume of Rachig rings is 14.4 where copper scrubbers it's 38.4, so I don't use the rings anymore.

So - the only variables you can play with are packing height and packing efficiency. Add more height or use a higher efficiency packing if you really need to get to producing 95%+

I will try packing the column tighter, I know it wasn't very tight the last couple of times, so I can add more volume of scrubbers. And I can raise my reflux return up a bit too, I've been thinking about doing that anyway.

And 12 hrs on a reflux run is a really long run.....

In "Making Pure Corn Whiskey" page 80, it took him 9 hours on a 5 gallon wash. I'm running 7 1/2 gallons of low wines. So I figured 12 hours was about right. I'd LOVE to cut that down, 12 hours per spirit run is a long time, and I've done it a number of times.

Second is remove the insulation to allow the column to achieve a natural temp gradient.

Every book I've read, and there's been about 6 or 7 of them so far, state that during your spirit run, you want to insulate the column very, very well. Otherwise the slightest breeze will through off your equilibrium. I can see my column temp drop just when the wind blows the flame of my burner. Also, that's also why they say don't use a hot plate because of the on/off method of temp control. You want your column very stable. The insulation is between my column and my water supply lines, so they don't affect the column temp. I've tried various water flow rates, from about 8oz a minute to about 400oz a minute and haven't noticed an affect on the ABV.


Ethanol has a boiling point of 173.1F, so the fact that my column temp is 174F, does that indicate a problem, or is that a normal column temp for a spirit run?

[TDS]

I got a little bit of a boost when I switched to Lava Rocks, 2-3 %. I'm a big fan now.
Or else add column length, as was previously suggested, from the bottom.
If it's triclamp to the keg you can buy a foot of preflared ss, teflon gaskets, clamp it in.

[rad14701]

Wow...!!! All over the radar here... Let's see if we can get you straightened out...

First, I think you're running too much heat and too much cooling... You're just smearing the entire reflux run... Too much heat is just as bad as not enough... And you're countering that with too much cooling... And having that reflux return down the column instead of as high up as possible isn't helping... But you should still have the entire column packed with only one type of structured packing, and I'd recommend scrubbers...

There is a great tutorial by Husker in the New Distiller Reading Lounge that explains how to run this very still in full detail... Essentially, you only need enough reflux to keep the column will stabilized at equilibrium... And just enough coolant flow to avoid vapor escaping from the reflux condenser chamber... Throttle things back and I can assure you that you'll have far better results... Use finesse instead of attempting to brute force that reflux column into submission...

[Cardinalbags]

A packed column with zero reflux is no more than a pot still unless you are getting passive cooling on a massive scale..... been tested and documented over and over again.... unless you got a condenser coil on the outside of that upper packed section..... it is one example of where the compleat distiller is a bit out of date...

And as far as spirit runs go... I do 25l of low wines in 5 hours total from start of heat up to breaking the still back down on spirit runs and half that time is spent stabilizing and drawing off fores and heads and then getting the next 20 of 500ml jars is the remainder of the time.... that is a testimony of packing efficiency to be able to draw off that fast. Those old texts were full of examples of folks doing 12-20 hour marathon runs on 1-1/4" dia rigs with water heater boilers..... Don't get me wrong... those guys writing those texts were the forefathers of our modern distilling gear, and their scientific principles are still valid today. We have just made better advances since then....

[TDS]

I ran an offset nixon stone for my first rig,
I still think you should give lava rocks a go.
Running in 100% reflux is definitely a plus initially,
after warmup before you start takeoff...
let the vapor stack, like a parfait....
takeoff should be slow enough to keep the layers stable.
mash rookies thread on column packing is most excellent.
Cheers!

http://homedistiller.org/forum/viewtopi ... =1&t=30727