Unburned Coal

Stoker Coal Boilers automatically feed the coal and have controls and pumps just like any conventions boiler. They are intended to be used as a primary heat and often have domestic hot water coils as an added bonus. They can be set up independently or in dual sytem with your existing oil/gas boiler. They can accommodate both hot water base board or steam plumbing.
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mooseman100
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Posts: 137
Joined: Sat. Mar. 05, 2011 10:31 pm
Stoker Coal Boiler: EFM 520
Stove/Furnace Model: EFM 520
Location: winchester, va

Post Fri. Nov. 15, 2013 6:55 pm

Hey gang,
i have searched and found a few answers to this question. I have a pretty good bit of unburned coal going thru my 520. I would say out of a 5 gal bucket of ash I would have about 1/2 gal of unburned coal.
Here are specifics:
520
Air 4
4 teeth
155 water temp
20 degree differential
2 min/ half hour on timer
Sherman rice coal
My boiler is 120' away from my two exchanger coils 1" thermo pex pipe
I have a plate exchanger for h2O
My circulator runs 24/7
About 1 1/2" of black ring around outside of fire pot

This will be my third winter to use the boiler, or any boiler for that matter. We are very happy with it and the savings, plus awesome heat. My neighbor and I use the same coal, he has a Harman and I see barely any unburned coal in his ashes. So just trying to figure out how to get better. Was going to try to back teeth to 3 and then turn air up to 4.5. Am thinking maybe I am pushing coal out too fast for it all to burn.

Any ideas?

Brent

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Rob R.
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Posts: 11343
Joined: Fri. Dec. 28, 2007 4:26 pm
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Coal Size/Type: Lehigh Rice
Other Heating: Dad's 1953 EFM Highboy
Location: Chazy, NY

Post Fri. Nov. 15, 2013 7:19 pm

Brent, does the fire look uniform? Any chance there is burning coal spilling over one side of the pot?

Are you sure it is set on 4 teeth?

When you looked at the ash ring, how long had the stoker been running?

Perhaps it is just the coal.

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Wiz
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Posts: 926
Joined: Sun. Nov. 27, 2011 8:45 pm
Stoker Coal Boiler: Keystoker Ka 6
Coal Size/Type: Casey Junk Coal :(
Location: Tannersville Pa

Post Fri. Nov. 15, 2013 7:38 pm

Is Harman a handfire or stoker
Randy
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mooseman100
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Posts: 137
Joined: Sat. Mar. 05, 2011 10:31 pm
Stoker Coal Boiler: EFM 520
Stove/Furnace Model: EFM 520
Location: winchester, va

Post Fri. Nov. 15, 2013 9:34 pm

Thanks for the quick response guys.
The unit is level and does not seem to be burning more to one side over the other. I have looked at it while burning throughout a season trying to adjust airflow to get a good ring. So fire burning been going for days or weeks. I also first thought coal, but neighbor burns the same with better efficiency. His is a Harman stoker, maybe it is just a more effcient machine than the efm.

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Rob R.
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Posts: 11343
Joined: Fri. Dec. 28, 2007 4:26 pm
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Coal Size/Type: Lehigh Rice
Other Heating: Dad's 1953 EFM Highboy
Location: Chazy, NY

Post Fri. Nov. 15, 2013 9:37 pm

The Harman stoker is an underfed stoker, similar to your EFM. It should not burn the coal any more or less thoroughly (if the air is adjusted properly).

Please answer my other questions above.

Pacowy
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Posts: 2731
Joined: Tue. Sep. 04, 2007 10:14 pm
Stoker Coal Boiler: H.B. Smith 350 Mills boiler/EFM 85R stoker
Coal Size/Type: Buckwheat/anthracite
Location: Dalton, MA

Post Sat. Nov. 16, 2013 12:06 am

The original manuals for many of the underfeed stokers advise that somewhere around the 10% Brent describes is normal. If it looks like more than it has been in the past, it seems like it might be worth checking the air holes in the grate to make sure they are clear. I'm not familiar with the Sherman rice, but if it has a lot of undersized pieces or is not sized as uniformly as coals used in the past that might contribute to an increase in the unburned percentage, though it wouldn't account for the difference between the EFM and the Harman.

If the ash ring is in the right place, I wouldn't mess with that. In fact,it's possible that the neighbor is running the Harman with excessive air, and that the more complete combustion occurs because the fire is too high on the grate, allowing cooling air to be blown through the dead ash into the combustion chamber, and reducing the actual efficiency of heat extraction by the Harman. I guess it's also possible that the more frequent timer cycles on the Harman contribute to a more complete burn, at the expense of a larger % of time spent running on the timer.

From what I know of the Harman and EFM stokers, I would expect them to produce a similar ash if run at an optimal fuel/air mix with the same coal on the same duty cycles and with unobstructed air holes.

Mike

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mooseman100
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Posts: 137
Joined: Sat. Mar. 05, 2011 10:31 pm
Stoker Coal Boiler: EFM 520
Stove/Furnace Model: EFM 520
Location: winchester, va

Post Sat. Nov. 16, 2013 4:51 am

Rob,
Yes the fire and ring are both uniform. No more coal appears to be coming out of one side over the other.
When holding my finger on the tooth pawl, I count 4 clicks as it drags back for the next grab.

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franpipeman
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Posts: 203
Joined: Fri. Jan. 11, 2008 4:27 pm
Stoker Coal Boiler: efm 520 stoker fitzgibbons pressure vessel
Hand Fed Coal Stove: harman, russo
Coal Size/Type: rice
Other Heating: alpine propane condensing boiler radiant floor
Location: Wernersville pa

Post Sat. Nov. 16, 2013 6:18 am

I always strive for unburnt coal but I never make it. The manual says to expect some unburnt coal. I burn 4 coal and 6 air as I have a long flue with one sloped horizontal run. . I get less unburnt coal with the 6 air, It all burn evenly . I accept it as standard practice. I would love to be told differently. It is mixed with the ash . Also I think longer burn times burn better than a lots of short cycles , that the current weather (mild ) here in pa is having. I have a working barometric draft. Any suggestion would be appreciated.

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Rob R.
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Posts: 11343
Joined: Fri. Dec. 28, 2007 4:26 pm
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Coal Size/Type: Lehigh Rice
Other Heating: Dad's 1953 EFM Highboy
Location: Chazy, NY

Post Sat. Nov. 16, 2013 7:24 am

This issue comes up ALL the time. Unburned coal in the ash does not necessarily indicate inefficient operation, and perfectly burned ash does not indicated efficient operation. The answer is usually somewhere in between.
Pacowy wrote: allowing cooling air to be blown through the dead ash into the combustion chamber, and reducing the actual efficiency of heat extraction
And there it is...if you are blowing combustion air through dead ash in an attempt to reduce unburned coal in the ash, you are sending more heat up the chimney than would be otherwise lost to the ash can.
mooseman100 wrote:Rob,
Yes the fire and ring are both uniform. No more coal appears to be coming out of one side over the other.
When holding my finger on the tooth pawl, I count 4 clicks as it drags back for the next grab.
Good. I didn't mean to imply that you don't know what you are doing, but you would be surprised how many times folks don't have the feed set to what they think.

Any chance you could post a picture of the fire, ash, and the coal? I am curious how the rice coal is sized.

Lastly, when you evaluate the ash ring it is important that the stoker has been running continuously for at least 30 minutes.

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