yeah, definiteley, heat will have to be put to copper! On the fuel group, people seem to have successfully (or to their satisfaction) converted the C803 to continuos operation, although for beverage use a few more things need to be considered.
The first things to look at are feed control, boiler heating methods and control, bottoms extraction..
With the continuous stuff, there are especially issues with reboiler overflow control/non siphoning/side-stream extraction etc, heating without caking or burning if direct heated, steam generation/control if indirect, and constant feed flow/pressure/control etc to look at. Once a working model for these is developed, work can proceed on stripping and rectification columns, reflux mechanisms etc.
Thought's I've had the other day related to racing cars may help I think. They have a fuel cell (fermentor), a lifting pump (mash pump), swirl-pot (beer-well), and then a regulated pressure pump plus injector rail/s (feed pump, feed injector and control valve). Maybe overcomplicating it, or it may be adding complexity to make other "things" easier - don't know yet! Finding food grade stainless pumps may be the issue, although there seem to be such suitable pumps in the wine and beer industry. "Thin" mash may not be an issue, but thick mash, although it can be stripped (and is stripped commercially) has a few more things to deal with.
Having a gravity fed output from the "beer-well" would simplify matters though, just using a mash pump to lift to a height that gives enough head for the maximum flow desired, and a constant pressure/head for a simple valve to control flow rate. If a float switch used to keep beer-well head constant, feed rate can be fairly contsant. Saves on another feed pump too.
So with continuous still, there is another mechanism for control besides cm, lm, vm, and pm (power control), and that is fm - feed management. For a given power/steam input, there will be a range (hopefully reasonably broad in a favourable design) over which the feed rate is optimum. Not enough, and the reboiler wil be running dry, and yield % goes down in stripped vapor, too much and the other obvious things happen such as boiler being cooled too much, bottoms not being stripped enough etc, column being overloaded etc. The "nose" should be reasonably broad though - again it's a matter of putting torch to metal..
A 2" packed column would be a useful small scale to play with, although 2.5" gives that much more room for varibility and vapor handling. You may be looking at around 1-1.5kW (may be a bit less with full insulation and feed pre-warming) in the reboiler for these. More power would allow higher feed rate, but off course everthing needs to be proportionally sized.
Plated in these sizes (2") can be fiddly, although quite a few have done it now - not sure of the "power" handling capability for this size. Packed columns though, are not reccommended for continuous feed except for very well filtered, low-foaming washes. "Channeling" can be a problem in packed columns too, so a "feed spreader", or high-pressure "misting" jet would be important.
A 4" bubble cap plate column for thin mash stripping, or a 4" weir dam perforated plate stripper should be handy sizes, the lack of "dumping" and ability to turndown feed and power rates being advantages of the bubble cap, and thick mash handling being being one advantage for the perf plate. For both, the ability to handle foaming volume in the direct mash fed stripper (hence the large size, maybe even 5-6" may be required, despite the possible vapor imbalance, if mash is really foamy) will be important. Dont' know how well an antifoaming agent would work here, but no doubt there is information out there, and it may help improve the size balance.
Above the feed stripper, another plated stripper (how many plates I wonder.. 4?) could be used to account for foaming, proteins etc, and to strip the bulk of water and fuesls, and to simplify things after that, a packed column would be ideal as a rectifier. A 2.5" here should be fine, and in these diameters, enough rectification should be available in a reasonable height to allow a single column setup, without the further difficulties of "split" columns, despite their convenience.
Two ways to deal with heads - take the stripped/rectified spirit and redistil in a batch still making desired cuts, and the other way is to regard the "continuous" still as a batch continuous (which it would be anyway unless 24/7 automated!), and collect enough runs to use it as a de-methyliser column, and the bottoms draw would be pure ethanol, assuming that full rectification had already been performed, otherwise it would be a profile of water, fusels, congeners etc. There would be opportunity for draw off at various plates to investigate profiles if "flavoured" washes used, getting a bit technical though compared to simple distilling! Mind you, that's the kind of thing plated columns allow....
While calcs may be nice to verify certain things, like with many builds, it's a matter of mocking up some prototypes and seeing how they go, checking the parameters in real situations etc. With easy and smooth control of feed rate, relfux, and boiler energy etc, a few calcs to help put one in the right ball-park, it's down to real-life results then. One almost needs to be a fairly experienced engineer, chem engineer, and existing practitioner etc to be able to account for everything of importance without building, and even they still prototype....
For testing, one doesn't even need to ferment, as suggested cheap beer or wine could be used, another thing that could be done is mix industrial alcohol/meths with water, add a little iso-propyl, dash of acetone say, and one has a medium that the composition is very well known, and can be used over and over again. A "cleaner" mix may be desired for a beverage still though, although same principle can apply for prototyping withouts lots of fermenting.
I need to start building too, it's still all conjecture until one finds practical ways to build the kit... ! Not going to have the chance for a while though, so I would be keen to see anyone else get into it
Rads right about the scale of fuel type production being a problem in an urban environment - it can be done, but takes a bit (lot!) of planning, plus regulatory, safety and stillage disposal matters to attend to. This is where visiting fuel forums woud be worthwhile if thinking about making more "fuel" than required for a lawnmower, and why co-op, rural/industrial and more business like ventures are used.
Especially matching feedstock sources and volume, production volume capability etc to desired demand. Some of the best feedstocks are sugary wastes from soft drink companies (for cost), this reduces processing energy, stages and effort (compared to starch), and the stillage is "thin", but full of yeast for backslop nutrients, and the balance useful for feediing veggie gardens, lawns etc. Other local food-wastes could be good, such as fruit, bread etc.
Corn/starchy type feedstock wastes/stillage also good for the compost and veggie gardens, and apparently, ddgs, and dwgs are really good for corn growing (and maybe sweetcorn??!) too, so their are possibilities for handling larger amounts of organinc waste in smallinsh environments if plants, compost, soil or possibly hydroponics can be involved. Cattails make good water remediation plants and can be grown in split drums etc, so another possibility.
However, I'm going off-topic a bit here, and this is more towards the fuel section.....
One thing of interest to look at is industrial and ecological symbiois, perhaps a bit of a fancy name for common sense integration ideas, but a good model to use when thinking about efficiencies, and ways of re-using energy and effort,
http://en.wikipedia.org/wiki/Industrial_symbiosis, plenty more exmaples/info on the net.
Good luck, best thing to do on here is take any practical advice on board, try different ideas, even against practical advice is fine, but unlike others who come and go on a fairly regular basis without building anything or without previous applied and/or closely enough related knowledge, but argue ad-infinitem, report back some results, everyone loves results! Quite often things can be made to work, sometimes it's an easy matter, other times it's a complicated contrivement only suitable for the those suitably interested! Room for all here, traditional, and leading edge both.
