I'm making a methanol recovery still from a 16 gallon barrel. I will likely process 6-10 gallons of glycerin at a time. I will be installing a water heater element in the barrel but not sure of the size. I don't want to take all day to heat nor do I want to burn the glycerin so...

If you put a 220 element in and run it on 220 without circulation you will burn the glycerin. Try a 3000 220v on 120v.