I think you will have problems without recirculation. My MLT is direct fire and if I stop recirulation while heating temps go crazy. I have a full false bottom and the temp at the bottom will jump 20 to 30 degrees higher than what it reads in the grain bed. Keep your flame low it doesn't take much.
I agree with derekm. The mash that is in contact with the directly heated portion of the MLT has to be evacuated almost immediately while the flame is on. My suggestion would be to do your best to insulate the tun so that you don't need to apply heat too often and stir the heck out of it when you do.
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