[rlonstein]

> I know there are industrial processes where heat is efficiently recycled, but I agree there are serious practical problems, particularly if the molten glass must be cooled quickly.

My experience working with glass is that you _don't_ want it cooled quickly. It will shatter or get internal stresses that cause it to shatter later. You anneal it in a slowly cooling oven over time. Some steels and brass can be annealed slowly and that heat could, I suppose, be captured. Tempering probably not.

> Still, even somewhat lower grade heat can be upgraded back to high grade heat with high temperature heat pumps.

Which requires energy and incurs losses. If you have energy, assuming electricity, that's cheap enough to scavenge low-level waste heat you probably don't need to recapture the heat.