The auger is supposed to be 1 1/2 flights? out of the pipe. The reason being that at 6" from the end of the pipe, you aren't going to pull coal into the pipe from that far away. So the coal is going to grind up at 4-6" away from the end of the pipe and not be pulled into the pipe. Maybe it works with Buck. Maybe it's converting Buck to Rice
Figuring that the coal is going to feed from the top down and be pulled in near the entrance to the pipe, I would go with the 1 1/2 flights.
Another thing with wet coal is that the bin feed worm can rust off at the pipe coupler and then start grinding away inside the coupler. This will also break the shear pins. I've had two large usage users this past week who were breaking pins and one finally broke the worm. The pipe had rusted to the point where pieces of steel broke off and jammed inside the worm drive. Here is one picture of the rusted pipe below. A stainless steel pipe is used when people use wet coal. It's a Schedule 40, 2" Stainless.
Well Stoker man all I can say is that I have 4 flights sticking out of the Tube which is 6" I have Problems and Yes I am bruning buck instead of Rice what happends with less flights sticking out of the tube is when the coal is wet and has
alot of dirt in it It will clump togething and stop feeding coal with more Auger sticking out like 4 flights 6" it will break up
the clumps of dirt allowing the coal to feed .
By the way efm does not recommend 1 1/2 Flights sticking out it is 2 1/2 flights sticking out which is 3 3/4 " look at page three Paragraph three in the Manual I like for 3 or 4 flights it will stop the clumps of dirt and fines from stopping the coal And it will not grind or crush any coal aslong as the Auger end
is above the drum bottom and not touching the bottom of drum free space between the end of the Auger and bottom of drum. The onlytime you will get or hear grinding of coal is when it is coming inside of the tube & once it is inside the tube not on the outside of the tube . Like I said before the wearing of the augers is at the pot end from Either The Pot
bushing wearing out or the Auger bushing wearing out or both . The pot bushing is only .875 O.D. & .750 I.D. Auger
bushing is 7.38 O.D. & 1/2 I.D. When the Pot bushing wear out or Auger bushing then the space between the aguer flights inside the pot is gone causeing the flight to rub against the cast Iron pot wearing the flights and making them sharp this will also effect the mid auger & Bin Auger making then rub against the inside wall of the auger tube You will or should hear the rubbing & grinding of the auger inside the Tube or Pot. When you do stop the furnace and replace the bushing much cheaper then Augers once a Year or earlier when you shut down to clean everything check the Pot bushing & Pot auger bushing . Also check the the inside of the Auger tube coupler if you are using one for build up of fines & dirt . http://www.efmheating.com/manuals/DF520%20Manual.pdf