Still Efficiency

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Still Efficiency

Postby badflash » Mon Jun 04, 2018 8:30 pm

In Alcohol fuel, energy efficiency is money. To be cost effective you need to save every place you can to be able to produce alcohol at below $2 a gallon.

You have to triple distill with a pot still and then use zeolite or other desiccant to get water free alcohol. You can get there with a stripping run and then a run through a reflux still in just 2 steps. It seems like a reflux still is very inefficient as you are re-boiling the alcohol many times and dumping heat out the condenser like crazy.

Which way is most cost effective?
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Re: Still Efficiency

Postby zapata » Mon Jun 04, 2018 11:32 pm

I dont know anything about cost, but you are giving reflux a bad shake on energy efficiency. A reflux still can do many redistillations with power that would have to be used just heating a pot still to boil several times.

A simple way to look at it, if you run a reflux ratio of 1:1 then you will use twice as much energy as a single pot still. However you use less power than 2 pot runs because the pot still requires "wasting" energy to heat it up twice. If the reflux still has 20 plates, you get 10x more distillations with reflux than 2 pot runs, and with less power. 1 pot strip + 1 reflux run? Depending on reflux rate you may end up using about the same power as a triple pot run, but you'll have higher alcohol and need much less dehydrating.

Can you really even use triple pot stilled for fuel? I would guess it would still be too low abv, leaving a lot of water for the dehydrating agent.

Of course the true cost optimization probably comes from a totality of the factors. Can you run a continuous reflux still, using wash as the condenser fluid to preheat it? That's gotta be more efficient by a lot, that way the condenser doesn't waste any power.

What about your heat source? I doubt small distillers have much hope of actually having a positive energy balance, but if it is economical to turn say cheap electricity into a portable fuel than maybe it makes sense. Or can you burn agricultural waste? Then it may make more sense.
I suspect it comes down to using every efficiency trick in the book, and doing a good analysis of the specifics for any setup and location. And even then the economy of scale may not benefit the small producer. $2 a gallon seems a difficult goal for small timers.
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Re: Still Efficiency

Postby shadylane » Tue Jun 05, 2018 9:39 am

If I was going to build an ethanol still, it would definitely be a reflux still.
I'd only distill to 90% ABV and I damned well wouldn't mix it with gasoline.
I'd also recommend not using a steel gas tank :oops:
On a side note, recycling the waste heat really helps on efficiency.
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Re: Still Efficiency

Postby badflash » Tue Jun 05, 2018 7:44 pm

There is not a huge cost in heat to warm water/alcohol mix to 180F. The real cost is in boiling. The latent heat of vaporization is huge compared to heating liquid. Vaporizing alcohol cost you over 400 X as much energy as heating it to boil. If you are doing a 10:1 reflux I'm thinking you are boiling each pound 10 times, vs. 3 times with a pot still. I see all sorts of post that say you can get to 165 proof with a stripping run and a single spirit run. You can run a flex fuel car on 165 proof, you just can mix it with gas without getting to 195+. Triple distilled can get to 190 proof.

How would you recycle heat?
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Re: Still Efficiency

Postby shadylane » Tue Jun 05, 2018 8:15 pm

badflash wrote:Triple distilled can get to 190 proof.

You might get 95% abv at the beginning of the third distillation, but the final product will be lower.

badflash wrote:How would you recycle heat?

Heat is power that you paid for, reuse it as many times as possible before it dissipates :lol:
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Re: Still Efficiency

Postby Reverend Newer » Tue Jun 05, 2018 8:26 pm

If it was efficient, everyone would be doing it. Aim'n fer below $2 per gallon is squeeze'n the turnip IMO
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Re: Still Efficiency

Postby zapata » Tue Jun 05, 2018 8:35 pm

You've probably noticed the relatively low volume of posts in this forum. Most here are booze guys, you'll likely find a lot more info on fuel sites.
If all you want is 82.5% abv, you can get that in a stripping run and a 1:1 reflux ratio in a decent column. You can probably get it from wash with a good reflux still and still use a low enough reflux ratio that you less energy than pot stilling. You certainly dont need a 10:1 reflux ratio for fuel grade 82.5% abv, I dont use that much reflux for that strength beverage grade. I'm not certain it's more efficient, I've never considered a pot still for fuel, everything I've ever looked into was large reflux rigs. Have a play with the pot and reflux calculators on the parent site. They will give you an idea of what to expect, and it's easy enough to extrapolate the total power used.

I haven't run the numbers, but I wouldn't be surprised if making 82.5% abv in triple pot runs, you end up having to leave a fair amount of alcohol in the "tails" at each step, meaning you are recovering less of the total alcohol. A reflux still will be better at that too allowing you to capture more of the alcohol, so I'd look at total power to obtain each unit of 82.5% as well as to make each run.

I have no idea what scale you are looking at. But for example, a 3" CCVM with 4' of lava rock probably exceeds your 82.5% standard from wash, at a 1:1 reflux rate feeding it about 4kw for about a gallon an hour. That is more efficient than pot stilling 3 times for sure. Not really sure, but it's more or less what I'd start looking at for fuel.

The best way to recycle heat is what I mentioned above, use wash as coolant so it is preheated before it enters a continuous still. In a batch setup you do pretty much the same thing, but it's usually a little less efficient unless you get everything dialed perfectly and heat your coolant wash to just below boiling and store it until the current batch is done in a way that doesn't lose much of that heat. Search the forum for preheater, there are several posts, if not entire threads.

Again, not my world at all, but if I really wanted to make a go the first thing that comes to mind to sketchup would be a 6' tall 3" column. 4kw reboiler and auto drain at the bottom, mid column wash feed. Wash pumped through the RC to preheat. Run clear wash continuously, maybe filtered wash if fouling on the packing is a problem. That could be an order of magnitude off, and I imagine the fuel guys have a better design already sorted somewhere.

Good luck.
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Re: Still Efficiency

Postby Saltbush Bill » Tue Jun 05, 2018 8:40 pm

Reverend Newer wrote:If it was efficient, everyone would be doing it.
:thumbup:
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Re: Still Efficiency

Postby The Baker » Wed Jun 06, 2018 8:25 am

badflash said 'How would you recycle heat?"

Simple answer, a pre-heater.

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Re: Still Efficiency

Postby bluefish_dist » Wed Jun 06, 2018 8:37 am

My column will do azeo from a 10% wash. It might take 20-30% longer than a stripping run. Far less energy than a strip and finish. For fuel it would be plenty pure enough.

The trick for a column is make it really tall. 8 to 10 ft on a 4", 6-8 ft on a 2" That way you can run less reflux and get a higher output while maintaining azeo.
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Re: Still Efficiency

Postby badflash » Wed Jun 06, 2018 7:18 pm

If I can get a gallon for 4KW-Hr of electricity, that is under 50 cents a gallon for what I pay. My feed stock is free, and the enzymes and yeast nutrients run about 20 cents. Cost out of pocket is under $1 a gallon, just labor.
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Re: Still Efficiency

Postby zapata » Wed Jun 06, 2018 8:07 pm

Free feedstock helps a lot. Of course water costs something, for both mashes and cooling. Should you amortize your equipment over some volume? If you arent already setup, $500+ for a still could buy a good bit of fuel.

And all the little things you buy. I know I tend to think only in terms of major equipment being a 1 time expense, and major ingredients being the only ongoing expense. But then you decide you want a different valve. Or you need a new funnel. Or damn, maybe some more teflon tape, or wouldn't it be better if that hose was on a quick disconnect. More jars, buckets, fermenters on and on. It adds up.
But yeah, under a $1 / gallon for major ongoing expenses is pretty good. And maybe for utilitarian fuel the little bits are less attractive or just cheaper. No need for jars if you're just collecting in a fuel can, you can use your plastic shop funnel etc.
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Re: Still Efficiency

Postby badflash » Thu Jun 07, 2018 3:34 am

I've been a brewer since early 1980 doing whole grain mashes for more than 15 years and am in the process of building a legal farm beer brewery. I have most of the small stuff already. I also make bio-diesel and there is some overlap in the equipment. I am just really looking at ways to use all the byproducts to my best advantage. The pigs get just about everything once I'm done fermenting.

I want to get as energy independent as I can. I still remember waiting overnight in gas station so I could get gas during the oil crisis and even-odd gas rationing. One of my cars is a diesel, the other is a flex fuel truck. That was no accident.
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Re: Still Efficiency

Postby Saltbush Bill » Thu Jun 07, 2018 5:37 am

Build a digester to turn pig shit to methane, heat the still with methane and ya might start getting some where, free heat for the still is a big bonus.
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Re: Still Efficiency

Postby The Baker » Thu Jun 07, 2018 8:21 am

Saltbush Bill wrote:Build a digester to turn pig shit to methane, heat the still with methane and ya might start getting some where, free heat for the still is a big bonus.


And for a bonus direct the (carbon dioxide I think) given off by the fermenter into your greenhouse IN THE DAYTIME. Feed it into a big plastic bag at night....?
And I think the flue gas from the methane has the same effect; but check it for safety. A local tomato grower has acres of them under glass; he heats water, by gas, in the daytime and directs the gas from the fire to the tomatoes, storing the hot water in a HUGE insulated tank (he had THREE cranes lifting the curved metal sheets to build it) and heats the glasshouses at night with the water.

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Re: Still Efficiency

Postby badflash » Thu Jun 07, 2018 12:59 pm

My pigs live in a pasture setting, they are not penned up, otherwise I'd be doing that. I remember the stuff in the Mother Earth News on that years back A guy named Frye had it all worked out.
Saltbush Bill wrote:Build a digester to turn pig shit to methane, heat the still with methane and ya might start getting some where, free heat for the still is a big bonus.
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Re: Still Efficiency

Postby Saltbush Bill » Thu Jun 07, 2018 3:24 pm

Never heard of Mother Earth News, digesters are not all that uncommon on pig farms in many counties.
Maybe you will have to shovel the pig shit out of the pasture then do it.
But then maybe shoveling pig shit to heat a still is a bit like making your own ethanol to power your own truck...just a wee bit inefficient.
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Re: Still Efficiency

Postby badflash » Thu Jun 07, 2018 7:49 pm

Mother Earth News is a very cool publication and was huge in the 1970's for DIY and off grid folks.

I suggest you go shovel pig shit and compare that to running a still. I do it all the time, I think you are the type of person that would enjoy it.

Saltbush Bill wrote:Never heard of Mother Earth News, digesters are not all that uncommon on pig farms in many counties.
Maybe you will have to shovel the pig shit out of the pasture then do it.
But then maybe shoveling pig shit to heat a still is a bit like making your own ethanol to power your own truck...just a wee bit inefficient.
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