chief
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Electricity (medium scale) from Al OR Fe
In times of monopoly-abuse by the electricity-generating companies, where people have to pay 2000+ % profit-span for electric energy (eg. in Europe),
==> a process would be nice, wherefrom the average person, with some space in the yard, could generate his electricity himself:
==> It would have to be environmentally safe, so the authorities have no (serious) point of intervention.
Galvanic cells using either Al or Fe come into mind ::
===========================================
==> Al: molar weight 26.98 g/mol == 37.06 mol/kg
==> charge after oxidation: 3+
==> -1.66 V electrochemical potential
==> ionization-enegy (3+) : 2.7 MJ/mol == 100 MJ/kg == 27 kWh/kg
==> price: (http://www.lme.com/aluminium.asp) 2500 $/ton (today)
==> electricity-price (100 % conversion) :: 9 ct ($)/kWh
------------------------------------------------------------
of course this is a _very_ raw calculation, after all it's a forum here ...
Scrap-aluminum could be quite much cheaper than the above mentioned stock-exchange-price ...
Some of the otherwise insoluble Al-chemistry is soluble in slightly basic conditions (ph~9) (don't remember exactly what it was: Maybe Al2O3, or some
hydroxide or carbonate), so maybe the electrolyte should contain some hydroxide/soda + some Cl-; ash could be used (K2CO3); end-products all non-toxic
================================================
Iron
==> could be ever-again reduced with coal, having some sort of a galvanic "iron-cycle"
Idea, as maybe obvious:
==> order scrap by the ton (old railroads etc.)
==> Set up maybe 20 (cheap) cells (Al or Fe)
==> get the hidden electric current, thereby bypassing the electro-monopoles
In case of Fe it could be (maybe) an Na2SO4-electrolyte (Na2SO4): below 100 $/ton, yielding some Iron-vitriole (road to H2SO4 by dry destillation at
400 [Celsius])
For Iron the eletrolyte would have to be _not_ basic, since it passivates there.
At the ent it might give a way to buy the cheap siberian water-electricity (put into aluminum-production), by just ordering the aluminum from there
...
[Edited on 21-9-2008 by chief]
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12AX7
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Iron doesn't give much voltage (maybe 0.3-0.4V). Aluminum in lye against an inert metal cathode makes 0.7V or so, not much more impressive than zinc,
in the same conditions in fact (think alkaline battery). You probably need a better solvent to get the full 1.6V from it. If you do, you'll get a
pretty good yield, but it's still a lot more hassle, plus the reagents that aren't recyclable, than commercial electricity.
Tim
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chief
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Yes, low voltage ... But I imagine
==> using maybe 20 pieces of railroad (available at 90/ton), coming directly to my door ...
==> in a not more expensive electrolyte than maybe the ash of my wood-oven
==> or several bags of Na2SO4, or NaCl (25 kg == 7 EUR)
From the large iron-pieces would come a quite high current, and the maybe 10 volts could easily be transformed, output in kW-range and thereby enough
to supply a household.
Maybe the electrolyte should be a re-usable type, that doesn't get consumed, like NaCl: Make the Fe to some hydroxide. If using the potash, in case
FeCO3 could be made, this would have the additional advantage that a low-temperature iron-reduction-process exists, known since the stone-ages, that
gives iron-lumps at temperatures of no more than 1100-1300 [Celsius] (because the slag is thin-flowing, low viscosity, when the carbonates are in;
that also makes FeCO3 a wanted iron-ore).
So the Fe-hydroxide and carbonate could be re-used, just by charcoal-reduction, even in the deepest pampa, behind the forests. At the end this would
turn out to be electricity via fire, but via the electrochemical road instead of the mechanical.
This may be worth exploring, since industry probably preferes the generator-way because it's more simple o the large scale. After-all efficiency might
turn up to be not worse with the electrochemical approach.
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12AX7
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| Quote: | Originally posted by chief
Yes, low voltage ... But I imagine
==> using maybe 20 pieces of railroad (available at 90/ton)
<snip>
From the large iron-pieces would come a quite high current |
No, current is a surface effect, because reaction occurs on the surface. You want sheetmetal. The only thing railroad beams will get you is an
eternal battery life, at a few measly amps.
Tim
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chief
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No sheetmetal (!), because it would last not long enough, and also would have a too high net resistance. "Large" means the somehow big surface of
railroad: 0.3 m^2/(meter length), that would be sufficient; also it's massive, so one does set up such a battery once in a while.
On a more 3D-piece of metal one just has to make 1 heavy-duty-contact (possibly point-welding), that has about 0 Ohm (important at those low
voltages). The low resistance would then allow a high efficiency.
Besides the energy-price is that what industry pays for iron-scrap (mainly), since new ore is cheap and nearly everywhere available ...
What I talk about is: Getting to the industrial price of energy, and bypassing the monopoly; with iron the energy would be even cheaper than with
aluminum.
[Edited on 22-9-2008 by chief]
[Edited on 22-9-2008 by chief]
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not_important
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You want large flat surfaces with the electrodes in very close proximity, else the electrolyte resistance will eat up all the power; plus an uneven
surface will show selective erosion as it attempts to become planar.
Iron-air batteries, using porous carbon electrodes to supply CO2-free air, saw much development effort in the 1970s, mostly in Europe. Large stacks
with 10s of kWh capacity were the target. They were intended to be used as secondary batteries, but obviously could function as primary batteries as
well. Before that I believe the Vanghan-Sherrin Battery back in the 1890s was a iron-based primary, by the end of the 1890s it was out of production.
The energy consumed in making bulk ferrous metals runs from some 35 GJ/mt (China) to 20 GJ/mt (S. Korea & Germany). The iron-air batteries run
about 40% re energy efficiency. Large combined cycle power plants run better than 50%, higher if they can be used in CHP mode. Molten carbonate fuel
cells can be run of coal giving +70% efficiency in combined cycle mode, again higher with CHP.
[Edited on 22-9-2008 by not_important]
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