Clinker Question

Clinker Question

PostBy: Ashcat On: Tue Dec 09, 2008 9:09 am

I had my first clinker experience this morning, and I have a question about it. With the cold weather of the night before last, I once again installed my outdoor air supply duct. In an effort to keep the house as warm as possible, I burned the stove fairly hard that night, with stove temperatures of 450-500° on the magnetic stove thermometer. The next morning, I noticed that the area front and center, close to the glass, had burned out the quickest, and at that point was gray. I shook down the grates, reloaded, and last night removed the air supply duct. When I awakened this morning, I noticed the same area was dead. Probing down into this area, I discovered 10 or 12 pieces of apparently fused ash, quite hard and quite light in weight, about 3-4 inches in their longest dimension. The thin layer of fresh coal I had put on top of this area last night had burned. Using my shovel, I dug down to the grates and removed these pieces of fused ash. Then, I filled the hole with fresh coal.

My question relates to why the clinkers formed. It appears obvious that the area of clinker formation, which was closest to the outdoor air supply, suggests that the outdoor air supply had something to do with the formation of those clinkers. After all, there was very cold air (about 17° that night) rushing in through the coalbed right at that area in the front center. Did it have more to do with the coldness of the air, or, because cold air is more dense, was that area of the fire more hot because of increased combustion from the higher air density?

I suspect it has more to do with a hotter fire in that area rather than a colder one, but I would appreciate any insight people here have on this issue. Some background information is necessary: I am burning nut coal, 60 or 70 pounds per day. Filling and loading about every 12 hours.
Hand Fed Coal Stove: Hitzer 983
Coal Size/Type: Nut/Blaschak

Visit Hitzer Stoves

Re: Clinker Question

PostBy: WNY On: Tue Dec 09, 2008 10:14 am

Clinkers form from very hot burning and fusing the coal impurities together. I even get them in my stoker stove when it's really cold (20 or less outside). usually just the smaller "coal Cakes" a small 3-4" diameter chuck that ends up in the ash pan.
Hot Air Coal Stoker Stove: Keystoker 90K, Leisure Line Hyfire I
Coal Size/Type: Rice
Stove/Furnace Make: Keystoker, LL & CoalTrol
Stove/Furnace Model: 90K, Hyfire I, VF3000 Soon

Re: Clinker Question

PostBy: titleist1 On: Tue Dec 09, 2008 10:18 am

I believe it is from the hotter fire at this spot. That is just my guess from what I have observed over the years, although I never made a detailed study of it. My Harman occasionally gets a clinker or two at the front. From what I have noticed it is when I am burning it hard and have "pokered" the front edge of the fire box during the last "ashing". The front edge of the fire box gets a build up of ash since the Harman grates don't shed the ash as well in this area. About every third or fourth day I'll run the poker along the front edge to encourage the ash to get into the pan. This has always bothered me about this stove, although I may rethink my attitude since this may be an ingenious design on their part so clinkers don't form!! :) :)
Hot Air Coal Stoker Stove: Harman Mag Stoker (old style) one in basement, one in workshop
Hand Fed Coal Stove: Harman Mark III on standby for long power outages
Coal Size/Type: Rice/Anthracite; Nut/Anthracite