Alternate Fuel

[Opsa]

I'd love for us to do the sugar cane thing, but it is a tropical plant and wouldn't grow north of Tennessee. Still, I can't help but think that some of those bellyaching tobacco growers should give sugar cane a try. Might make them rich.

[Sibling Zono (anon1mat0)]

The way things are going it will grow up in Canada soon...

[Aggie]

Still wonderin' about sugar beets for ethanol.

[Bob in a quantum-state-of-faith]

Still wonderin' about sugar beets for ethanol.

Anything with sugar in it, can be fermented.  Just ask the Russian's. 

Of course, to make a fuel suitable for burning, you must distill it, and that takes heat.

From whence the heat comes, is the real sticky-wicket.

I don't think that leftover pulp from crushed sugarbeets would provided enough, though.

So the heat must come from somewhere else.  The usual "solution" is fossil fuel.... kinda defeats the whole point, yes?

I can visualize a solar still, but you'd need a really low-cloud place, like Arizona or West Texas.   I don't imagine the sugar beets would grow there.   So, you'd have to ship them.  By truck or by rail, and you'd be using..... fossil fuel again.

[Opsa]

I just found this article, which also mentions sorghum. Hadn't heard that one before.

http://journeytoforever.org/biofuel_library/ethanol_motherearth/meCh2.html

[Swatopluk]

Downriver (and that would be the case in the US) the transport would not use up that much fuel (sail, drift etc. for most of the time, motor only for close maneuvering).

[Aggie]

http://www.autobloggreen.com/2007/11/23/first-sugar-beet-ethanol-plant-opens-in-the-uk/

Apparently someone thinks beets'll work....  but I do agree on the distillation issues.

Then again, we have lots of sugar beets and wind turbines in the same neck of the woods here, could use electric distillation units I suppose.

[Sibling Zono (anon1mat0)]

How high temperature is required for distillation? Solar thermal to replace water heaters works quite well above 50C even in cloudy places.

[Aggie]

Between 78 and 100 C for ethanol/water solutions.  Not sure what the other components of the mixture (fermentation leftovers and byproducts) would do to it, though.

[Bob in a quantum-state-of-faith]

How high temperature is required for distillation? Solar thermal to replace water heaters works quite well above 50C even in cloudy places.

Between 78 and 100 C for ethanol/water solutions.  Not sure what the other components of the mixture (fermentation leftovers and byproducts) would do to it, though.

Depends on how much water you want to extract.

The initial solution is roughly 12% or so, the max concentration you get to before the yeast is poisoned by it's own processes.  But, that solution is not just water/ethanol.  It also usually contains still more starch/sugars that could be processed, if the alcohol were removed.

So, heat it enough to "boil" off the alcohol, but not the water.  Capture the vapors in a distillation apparatus.  The heat from that (the distillation thingy) could be used to warm the fermentation vats, as a bit of heat above ambient will speed things up there, but it's not strictly needed.   Or, the distillation heat could be sent to pre-heat the incoming liquid, before it actually gets to the boiler.  Why dump it into the atmosphere?

Anyway, if you want to get all the alcohol, you'll need heat up to just shy of 100C/212F.  You need to closely monitor the amount of heat you put in, and the temperature of the liquid.  It will have a couple of plateaus as the alcohol is driven off.  When you pass the last one, it should stabilize just at or below 100C for a time-- the latent heat of vaporization of the water will be starting, then.  You stop there, as you've removed nearly all the alcohol.  Send the liquid back to the fermentation vats, after cooling.  Use it's hot temperatures to help pre-heat incoming liquid.  Again.   

If you do elect to recycle the liquid back to the fermentation vat, you'll need to monitor it's sugar content, too.  If the liquid, after evaporation of alcohol, contains little or no starch/sugar, it may be discarded.  It ought to contain little, by this time.  Just trace minerals and chemicals leftover from the plant material that did not ferment, or boil off.  If cooled, it should be safe enough to use for plant watering.

Back to the vaporized alcohol.  It won't be 90% after the first distillation-- quite a bit of water will vaporize, too, even though the temperatures are well below boiling.

So, you'll need to re-distill it a second time.  This time, it becomes tricky.   It's now concentrated enough to sustain a fire, but not enough to be useful as a fuel.  So, heating it must be done in completely enclosed containers.   And the temps must be monitored even more carefully than with the initial run.   Watching for plateaus, again-- only these will be more subtle, not as sharp or distinct. 

.............

Obviously, the above is for a max-fuel output.  If the operator is willing to drop the efficiency, and just vent or waste part of the yield,  a single distillation cycle is enough.  You stop collecting the vapors after the first temperature plateau, to reduce the percentage of water vapor.  But, you must continue to heat it (voiding the vapors) to drive off the excess alcohol, if you wish to re-introduce the liquid for more fermentation.

Again, if you want to drop even more efficiency, you could just discard the liquid, or use it as plant fertilizer or hog-feed.

It would all depend on the quantity and quality of your final product, of course.

A very small operator, say a single small farm, might elect to just extract the minimums-- pretty simple to do, and the cost benifits of ignoring the waste is offset by the tiny overall yields anyway.

But, if you are processing 1,000's of gallons monthly?  You really would have to look at a more involved processor.

........

I see no reason why a solar collector for heat could not work-- unless the system is setup in a mostly-cloudy area (like Seattle, WA).  You really need 3 of 4 days of the year sunny or more, to make solar only viable.

.......

If the plant were large enough, there's absolutely no reason why they couldn't just utilize their own product to produce the required heat, though.

.......

If the plant were a single farm?  I'd suggest adding a manure processor, to produce methane gas.  Utilize the methane to heat your fermentation and distillerys.  What small farm doesn't have more than enough manure....!  

[pieces o nine]

Unscientific reply:  there's a sugar beet processing plant in the townlet where I spent part of my childhood. It's on the route to visit mom, and in passing through there now one runs the risk of passing out...

Please return to your scientific discussion.

And if you can plan for the bacteria that thrive in the waste water, that would be cool, too...

[Swatopluk]

Distillation for alcohol is an old hat. Membrane separation is the thing to do (and effectively needs far less energy because the soup has not to be boiled*)

*thermodynamically it needs of course the same amount but the heat loss is far greater for the distillation process.

[Bob in a quantum-state-of-faith]

Distillation for alcohol is an old hat. Membrane separation is the thing to do (and effectively needs far less energy because the soup has not to be boiled*)

*thermodynamically it needs of course the same amount but the heat loss is far greater for the distillation process.

I didn't realize they had a membrane that could separate water and alcohol.  Neat trick, if true.

[Aggie]

Swato would know, I think. 



Is pressurization necessary for separation?  Do you think the current membranes are selective and efficient enough to do continuous separation (i.e. have part of the fermentation mixture diverted for separation on a continuous basis and then returned, to prevent alcohol poisoning of the fermenting organisms)?

[Swatopluk]

To my knowledge the membranes are used by now as the almost exclusive means to produce absolute alcohol. Normal distillation can only achieve about 98% due to the formation of an azeotrope. See pervaporation. Whether it works well/economically on mixtures with more than about 5% of the component to be extracted, I don't know.