1. Assume that the 9 hours does NOT include boil up time. If it does, you'd need a massive amount of heat, at least during the boil up phase.

2. At 16% in the mash, which is being generous, 40 gallons of 160 proof is 32 gallons of pure ethanol is 128 liters. So, a wash containing 128 L of pure ethanol, would be about a c.800 L (200 gallon) volume, and so we know what
size the boiler or boilers must be in aggregate. Let's say, 300-400 gallons, I prefer to run a boiler half full, that range covers 50-75% full.

3. Boilup: it takes 1 kWH to bring 10L water to boil, so, we need 80 kWH for boilup. Trade off time vs energy. 1 kWH is 3400 BTU/Hr.

4. Takeoff: OK, 20 L an hour of 80% is 16 L ethanol and 4 L water. The 4 L water will consume 2.5 kWH and the 16 L ethanol, 3 kWH. That's because it takes 1 kW for every 1.6 L water and 1 kW for every 5.4 L ethanol. Latent Heat of Vaporization. Water, 3X that of ethanol.
SO You needed a 5.5 to 6 kW heat source at takeoff. That will boil off 20 L of 160 proof an hour.

Consequences:
If 6 kWH (20,000 BTU) was your max heat input you'd have had a 13 hr boilup time.
So you probably had more, and that's why you had to turn down the heat or face boil over.
A 'slobber box' between boiler and the doubler would have helped prevent mash from reaching the column.
Your condenser needed to handle 6 kWH; your product was coming out hot, so the condenser could have been augmented with an external one and your product would have been at ambient. Much safer when dealing with a high proof ethanol.
A conventional fractionating still (no reflux head) same size as yours, packed with Raschig rings 6x6mm of porcelein, would usually be considered good for 3-4 kW so, you were running at 50% over that, and that is
reasonably explained by the cooling coil through the packing.
Also you didn't insulate the copper column so it is radiating heat like crazy and that would account for some of the difference. The conventional way to go would be:
Dispense with the doubler and the cooling coil in packing -- make condenser bigger (more coils, double coils, cold finger down middle).
Reduce heat to 3-4 kW, or else up the column size (length, diameter, or both)
Measure the temperature at the top - a thermocouple and a digital thermometer is the way to go these days.
The temperature will tell you when the product is all collected, as temperature will sit at 78-79, then start creeping up to 80-82, which means you are taking off isopropyl, and some fusels -- wet socks smell in product.
That's when to quit for liquor.
The virtue of your design, for fuel ethanol, is IMHO, that it runs a bit faster and the predicted lower purity is irrelevant.
For liquor, the column needs to be run slower and the temperature gradient needs to be undisturbed by the intermittent cooling, and the column absolutely needs to be well insulated.
Why dispense with the doubler? Because the double does the job of 1 theoretical plate. The column, to your dimensions, has a good 15-20 theoretical plates depending on what the packing is (NOI marbles) and so dispensing with 1 is ok.
If you keep the doubler, it works better if you have high proof ethanol as the coolant instead of water from the start. Otherwise it takes some time for the doubler to be heated to boiling point and to become saturated with
ethanol vapors, both of which conditions must be met before it does anything.
BTW, the doubler will drive off methanol FASTER than ethanol, as methanol boils only at 60 C. So it won't trap methanol, acetaldehyde or ethyl acetate. BUT, it probably does effectively trap some of the higher boiling
congeners like the fusel oils, acetic acid etc.
well, good for 200
IN short, I find your prediction of 20 L/hr over 8 hours perfectly in line with theory, assuming an adequate mash volume, boiler size commensurate, etc.
NOW: let's look at a 55 gal drum as boiler with maybe 40 gal (160 L) mash in there. This is about what you usually ran at demonstrations, right?
Boilup time @ 6 kW: 2.5 hours. 1.25 hrs @ 12 kW
Takeoff time: 25 liters of 80% will come off in c.1 hour maybe 65-70 minutes @ 6 kW. (This means you turned down the 12 kW heat by half.)
Start to finish 2 hours and 15 minutes.
Is that about what happens? I have to go reread chapter 2 again and see what you said.
The main criticism I would make is, the un-insulated column is just wasting heat. The boiler and the condenser need to be well balanced but, letting so much heat escape is just a waste of energy, and that's a shame in a biofuel
design.
On the other hand, if the 3" pipe was stainless steel and well insulated, I'd recommend testing the thing at 3-4 kW before letting her rip at 6 kW.
And the through-put will drop by 33%. But you will also need 33% less fuel to run your boiler.
Please take these as just friendly critique, which is how they are intended.
Regards, Don