Coal Types for Stokers?

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ChinaClipper
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Post Thu. May. 24, 2012 6:06 pm

Can anyone give me the quick explanation of the differences between a stoker used with Bituminous vs Anthracite? Are they interchangeable between Coal types? Air flows? Feed rates? I am wondering about the Axeman Anderson 130/60 and EFM's/Iron Firemans in particular. I am sure there are some easy answers out there, anyone wanna make it clear to a simpleton like me? :idea: Thanks!

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Richard S.
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Post Fri. May. 25, 2012 3:52 am

There is two issues with the soft coal, firstly the sizing and secondly clinkers. Soft coal AFAIK isn't sized like anthracite at least to the same degree and consistency. The other issue becomes many soft coals easily clinker and with design like EFM that doesn't work that well.

Specifically with the EFM they recommend rice which is about the size of pencil eraser. EFM did have stoker they modified for soft coal but I don't know what came of it.



Spspecifically with the Axeman Andersons the auger mechanism has issues with dirty coal and I'd imagine the soft coal is just asking for trouble.

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LsFarm
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Post Fri. May. 25, 2012 4:47 am

You cannot use Bituminous coal in an Axeman Anderson stoker boiler.
The only Bit-burning stokers are SOME of the larger EFM boilers, Some Gentlman Janitor models.

Bit coal varies greatly from mine to mine.. Anthracite varies only slightly.
Most Bit coals will burn more like wood, the fire will spread through a hopper full of coal. anthracite waits to burn until after it leaves the hopper,
and is in the burn chamber/on the grate.

Anthracite burning stokers burn either rice [pencil eraser size], Buckwheat [navy bean to green olive size] and AxemanAnderson's burn Pea, [ripe olive to thumb size].

Bituminous 'stoker' size varies from breaker to breaker, but mostly it is around golf ball size, but Bituminous is soft, and breaks up and grinds to
fines [sand-like or powder] when run through an auger feed system,,
And because most Bituminous coal will clinker, which is melting of the ash into large clumps, most stoker systems can't handle the clinkers. So the
Bituminous stoker stoves require the owner/operator to use tools to physically remove the clinkers every day. Most Bit burning stokers do NOT have
and ashpan, but count on clinker formation so that the ash can be removed as solid chunks.

Most anthracite stokers have an ashpan, and anthracite coal only clinkers ocassionally, when burnt very hot..

If you want a stoker boiler, and have access to anthracite coal, then you have lots of choices of boiler brand, coal size etc.

If you want to burn only Bit coal, then you will have limited boiler/stoker makes and choices.

Greg L


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Post Fri. May. 25, 2012 2:49 pm

Richard S. wrote:There is two issues with the soft coal, firstly the sizing and secondly clinkers. Soft coal AFAIK isn't sized like anthracite at least to the same degree and consistency. The other issue becomes many soft coals easily clinker and with design like EFM that doesn't work that well.

Specifically with the EFM they recommend rice which is about the size of pencil eraser. EFM did have stoker they modified for soft coal but I don't know what came of it.

Spspecifically with the Axeman Andersons the auger mechanism has issues with dirty coal and I'd imagine the soft coal is just asking for trouble.
IIRC, EFM conducted tests with a variety of bit and sub-bit coals, and achieved surprisingly successful results. Maybe stoker-man can chip in on that. The sizing of the coal seems to be the biggest issue - some of the older units with the larger diameter feed tubes probably have greater sizing flexibility.

Mike

ChinaClipper
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Post Sun. May. 27, 2012 2:23 am

WOW ! Ask and you shall receive! Thanks for the informed responses, good answers only beget more questions~! Mainly, what role does the high volatiles associated with Bit. play in Stoker design? IIRC those are dealt with by secondary airflow. Thanks again for the input! Scott :idea:

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LsFarm
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Post Sun. May. 27, 2012 3:15 pm

In a Bit-burning stoker, the coal is fed into the bottom of a burn pot, like the one you see in the video posted above.
As the coal is heated, but not burning yet, the volitiles are boiled or cooked out of the coal, they escape through the burning coal above and there is extra combustion air added at the top of the burn pot.. so the volitiles burn off just above the coal bed.

Since this burning of volitiles is pretty constant, and there is not a huge batch of additional fresh coal being added, the amount of soot or unburnt volitiles is minimal,

Greg L.

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