Soot from a propane burner means the air is not set right. There should be an adjustable air gate in the tube going into feed the burner. Adjust that until it cleans the flame up. It likely has a set screw you loosen then turn the outer metal ring, one way for more air to mix in, the other for less. With some trial and error you will find a sweet spot. I suspect the burner needs more air, but experiment to be sure.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.