I'm burning Wyoming bituminous coal in my homemade hand-fed. I have three grates made of rebar, patterned after the Harman Mark III. When I first burnt the stove this fall, I started with all 3 grates. I noticed two things. First, the house got too warm with that much grate area. Second, the walls of the stove and glass quickly were covered with a tarry, oily, black, sticky substance. Also, after a few weeks, the walls of the stove and stovepipe were quickly getting a "fuzzy" buildup that reduced my draft, heat transfer, etc.
I decided after a few weeks that I should check my stovepipe for buildup, so I shut the stove down. I cleaned the chimney and stovepipe, which were both getting pretty heavy buildup. While I was at it, I took one of the grates out of service by stacking firebrick on the back grate and removing the rear connector pin from the shaking mechanism (see photo of grate connector). I was hoping that would reduce the BTU output of the stove.
For the past 2 months I have been burning this way with 2 grates in service. The result was that my chimney, stovepipe, and firebox have been staying much cleaner. I inspected the stovepipe after 1 month, and it was very clean. I have not cleaned the chimney, and it looks clean as well. The fuzz has burnt off the firebox and I don't have the oily glass and walls.
So now the weather has turned colder. I had a few changes I wanted to make to the stove, like adding some sheet metal under the grates to better funnel the ash to the pan, preheated secondary air, etc. I also thought I should "unreduce" my firebox to get more BTUs back. I did that last night. Today, I am back to burning 3 grates, but the oily tar is back and the firebox is growing "fuzz" again. It also seems like even 6-8 hours after I load coal, not all of the coal has ignited completely, some still as black as when I added it.
Here's my question: I'm wondering if this has something to do with my draft. My 6" SS chimney is marginal, but sufficient to keep the stove going and keep the house at 80*+ if I want to. I have read some threads that claim that regardless of the burn rate, the soot shouldn't change (unlike wood fires where smoldering causes creosote). However, I'm thinking that my setup is causing the soot to form worse if I burn a big firebox at a low rate. I'm thinking of going to a single grate and see what happens. Any thoughts?
One more question: If I do things just right, have a nice deep tight bed, and burn the volatiles off hard and fast, say within an hour or two, I can get many hours of dancing blue flames from the bit. coal. It's a sweet sight. I just about can't quit looking at the dancing blue ladies. They elude my camera pretty well even without a flash though.
Of course anthracite can and should give blue flames. But are others burning bit. coal getting blue flames? Or only yellow flames and then just glowing coal? I can't get much blue flame when I run all 3 grates, maybe because there's not enough airflow through the bed.
Thanks for your thoughts. I've posted several times on different issues. Everyone is helpful. Just hoping to get some answers and leave a trail for others to solve future problems too.