Author Options:

Reclaiming Wasted heat to make electricity Answered

I work in an aluminum casting facility and we're looking for ways to save energy etc...

one thing that we've got no shortage of is heat (during the summer the temp near the ceiling above the furnaces is over 230F)

i've looked into stuff like they do in steel mills in Germany where they run pipes through the furnace linings and then use the heat from the furnace to make steam and run steam generators.

but i was thinking of something else today. would you be able to just mount a bunch (or one huge) peltier exchanger (or whatever they're called) on the ceiling above the furnaces and use that to make electricity? i'm aware that they create electricity because of temperature differences (and not specifically from being hot or cold in general) so would we have to cool one side of the unit for maximum efficiency?

are there any other ways that anyone knows of to turn waste heat directly or indirectly into electricity?


The mental image of steam powered stuff inside an aluminum foundry is simply awesome...

Do you use hot water there, for washing yourselves? You could replace your boiler with a heat-recovery system.


we do, but since we're in TVA territory and they're going to be doing some ridiculous rate hikes next year, we're looking for a way to offset that (i know not using electricity to heat our water would help that, but i think that we could in theory actually generate juice here see my math correction)

Maybe the company should save money & energy by adding more insulation..?


500,000 square foot building. only so much insulation can be accomplished (though i'm sure you're talking about our heat sources and not the whole building)

Yes, it's possibly old, from when energy wasn't so expensive?


slight math correction. i talked with our environmental safety guy and we don't want to focus on the "wash heat" (his words) that just floats around the building... apparently the sweet spot would be the flue gas that comes directly out of each of the 4 furnaces at around 1800 degrees F. i'd imagine we'd be able to do a lot more with that kind of heat

.  If your exit gases are at 1800°, I'd look into steam generation. You can use the steam to drive turbines to generate electricity, pump combustion air, &c.

that's my first idea and seems like the smartest option as far as a quick(ish) solution.

however, water near molten aluminum is not a good thing (think of superheated steam explosions in several tons of molten metal) so "they" are wary of it.

. Duct the outlet gasses away from the molten metal before allowing water near anything.

Sterling-cycle engines.

If there's not enough heat to make steam the hot air could be chanelled through large diameter to a place with cold air, damsel placed in the pipes could be used to run generators.

The conversion efficiency is TERRIBLE, (<5%) , you're making DC, you'll have to chop up into AC, and the cells are terribly hard to mount. effectively.

Thermal recovery is probably best. ;-)