A consumer gas fractional distiller, producing O2, N2, CO2 and Ar from air.
Why ? Well apart from the obvious, nitrogen can be used to fill car tires and make ice cream, oxygen is a happy gas and barbecue starter, carbon-dioxide to salt the greenhouse a bit and make drinks fizzy, and Argon mostly because having a container of a noble gas laying around needs no excuse, but it can refill tired double-glazed windows too.
The gases are bottled separately of course and, just to make sure, each of the gas dispensers have a unique connector, so you don't get them mixed up.
----- FlyingToaster, Sep 12 2012 What about Neon (18.2 ppm), Helium (5.2 ppm) and Krypton (1.1 ppm)?-- hippo, Sep 12 2012 If purity of gas was not essential, gas separation with permeable membranes or zeolite might be more practical.-- xaviergisz, Sep 12 2012 As I am a routine consumer of all of those gases in light- industrial quantities, I would gladly pay $4,000 for one of these if it kept up with my needs. In fact, I will, in cash, the very minute they hit the tore shelves. Here's a bun, fresh and emitting H2O vapor at an attractive rate.
<note: typo left in place for posterity>-- Alterother, Sep 12 2012 Tore shelves - where the torn things are stored?-- normzone, Sep 12 2012 Where's the hydrogen.-- 2 fries shy of a happy meal, Sep 12 2012 [norm], you're killin' me, man.-- Alterother, Sep 13 2012 [hippo] & [2fries] The idea is for a consumer (ie: cheap and limited featureset) piece of kit: anything that rare would probably be out of its mandate. CO2 at .04% comes in under the wire only because, having such a relatively high freezing temperature, it's so easy to separate out.
[xg] good idea: except for CO2, the other 3 gases are within 15C boiling point of each other, so anything that can help sequester them is welcome.
[bs] "coolth" actually goes back to the 16th century. Was that an idea (or anno chain) where heat for the winter is produced by compressing air, then coolth for the summer is produced by restoring the compressed-air tanks' contents ? I was looking for that earlier.
In that train of thought, CO2 only constitutes .04% of the atmosphere, which is out of proportion to its great usefulness. Therefore the smart thing to do would be to wait until summer and do a "half-cycle", using only enough pressure and cooling to liquefy the CO2. The heat from the process could be piped to an outdoors radiator and disposed of, then the remainder of the gases would be released into the house as very cold air, minus the CO2.-- FlyingToaster, Sep 13 2012 The only windmill ideas I remember were the ones that used friction heating (8th's, and my not-quite-a-complete-ripoff of same). I do recall participating in that thread you mention though (I may have even been the one to suggest the idea). One of [pashute]s ideas ?-- FlyingToaster, Sep 13 2012 Torr shelves - where the compressed gases are stored.-- spidermother, Sep 15 2012 I like this because with it you could keep all the ingredients for air close at hand, and quickly make more if supplies ran low.-- bungston, Sep 15 2012 --Argon's selling for a dollar a cubic foot at the moment; I'd love to have an argon distiller; bring it on!-- Steamboat, Sep 16 2012 random, halfbakery