There has been an ongoing discussion about the merits of vacuum or vac-assist drying of WVO (andd also methanol extraction from the waste product). They do the same thing with orange juice to make concentrate without spending too much on heat.
It's not a free lunch though. It takes energy to make a vacuum, or partial vacuum. That may be less energy than just heating, but perhaps a close race with circulation drying with modest heat input. Nobody, so far as I know, has done a carefully documented fair comparison that really compares the numerical data.
Practically, it's a lot easier for me to pump through a pipe with holes to get cheap evaporation, than to produce a pressure vessel that can stand vacuum, plus the vac pump, and a condensor. There's also the problem of of all the contaminants (crunchy bits, etc.) in the used oil. Even with care, it's tricky to keep all the oil vapors and junk out of your vac pump and condensor in the long run.
Some use converted water heaters that would prob. work for vac extraction. I'm waiting for someone else to come up with the cheap, durable, slick efficient vac distillation rig before I jump in.
Finest regards,
Troy
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