Keep an eye on the pot. With that much air, you could be burning deep into the pot. After a long stead burn, you want to see a dark spot in the middle of the pot. You could also have air leaks at the gaskets that are requiring extra air.
Assuming the stoker was running for 20-30 minutes before you took that picture, I would back the air down and watch for a thinner ash ring. I don't think you are too far from the mark, but UAE is potent coal and you need to make sure the air is not set too high.
Here are two videos that some crazy guy posted on youtube. The first one is 4 teeth and 4 air, the second is 5 teeth and 4.5 air. I have it on good report that the stoker was burning Kimmel's rice. Notice how the orange area is larger, the ash ring is thinner, and the center of the fire is slightly darker. The dark spot in the second video is a little larger than I usually see with those settings...possibily because the stoker hadn't been running continuously for very long.
I am no EFM expert, but if you can get away with less air, and have a good ash ring without excessive amounts of unburned coal in the ashes...you will have a more efficient boiler with a lower stack temperature.
Edit: Fixed spelling.
Last edited by Rob R. on Tue Oct 18, 2011 1:36 pm, edited 2 times in total.
x2 on less air (or more coal) and a smaller ash ring.
I wouldn't obsess about a small amount of unburned coal in the the ash. Even in a good fire, all pieces don't get burned to ash at exactly the same rate, and pieces that aren't completely burned can get "marooned". If you try to feed enough air to minimize/eliminate that, the boiler won't run efficiently. It's kind of like trying to run your car engine so zero gas vapors escape the combustion chamber unburned. If you have a lot of unburned coal in the ash, you might want to look more closely at the quality or uniformity of the sizing of the coal you're using. In general, I'd focus mainly on fine-tuning the fire, rather than the ash.
Mike brings up a good point. Just because you have unburned coal in the ashes doesn't mean the fire is not adjusted properly...your coal supply may be the culprit and contain exessive amounts of slate/bone. In that case, adjust for a nice burn and the ashes are what they are.
What works good for one person may not work for the next. Even if you are happy with the way your stoker is running, it is a good idea to keep an eye on it when you get a fresh load of coal...especially if it is from a different supplier.
It would be great if EFM had a series of pictures for reference at the same firing time with different settings to help us all learn what is a good fire.
I kept hearing of the elusive dark spot of fresh coal in the middle and didn't see it for the first year I burned. It wasn't until we came home from a winter vacation where the house was jacked up immediately from 50 F, five showers in a row and a weeks worth of laundry going that I finally saw the dark spot.