I built a smelter of sorts out of scrap a while back-
I added charcoal and aluminum cans then fired it up. The pipe you see coming out of the bottom is actually a piece of tailpipe obtained for free from a muffler shop. I just went in and asked for a scrap piece and offered to pay them something for it but they just laughed and gave it to me at no cost. It's supposed to be used to push air through holes drilled around where the can sits to make the fire hot enough to melt the aluminum.
According to youtube you're supposed to put a hair dryer on "cold" setting into the pipe for proper air flow. I picked up a cheap hair dryer from Wally World and took it apart, then removed the heating elements because it didn't have a "cold" setting. Only hot and hotter. It refused to work. Upon closer inspection I realized that if the heating element was broken the circuitry refused to power the dryer (which makes sense in the normal use of the thing) but this did nothing for my efforts to have forced air. So I rewired the thing and plugged it in to promptly get a grand display of sparks and a tripped breaker. Screw the hair dryer.... I have better weapons in my arsenal :)
I hooked up the shop-vac on the "blow" side of things and used that instead of the hair dryer. Let me tell you- it worked fabulously! Originally I had the can sitting in the middle of the fire. This is a view after I had poured my first "ingot". The majority of the crap you see left in the can is slag or "dross" (which is a fancy word for stuff that's not pure aluminum.) You're supposed to lift the dross off of the top of the melted aluminum but the melting vessel I used is really too small to get into with the spoon once you take the heat factor into consideration, so I left it there. I just poured the melted aluminum and let it run from below the slag into the ingot mould that I made.
Below you see my efforts at an ingot. I would have done more but I was running out of fire/charcoal so I got what I could with the materials I had on hand. This is two separate pours. I poured the first, re-positioned the can, allowed more aluminum to melt and then made the second pour.
All-in-all it was a fun experience. I'm going to add a stand into the bottom of the smelter to allow the can to sit up off of the steel plate so that the bottom isn't conducting heat away from the aluminum. I'm also going to get wood for fuel instead of charcoal. The charcoal worked fine, but it took an entire bag to do this little bit and at $9 a freakin' bag it would be simpler to buy a couple of pounds of aluminum, ya know? The shop vac on "blow" worked great, but I'm going to use an old vacuum cleaner motor set to blow next time I do this.
Now I just have to figure out a how they make proper moulds so that I can possible create something useful with this new technology :)