Must have Grate to burn coal, or Not?

Must have Grate to burn coal, or Not?

PostBy: RICHARD2 On: Wed Jun 11, 2008 11:25 pm

Do I understand correctly that a pile of coal won't burn on the solid floor of a wood stove --- that it must be supported by a grate so as to receive its primary air from below/through the grate, and not from above; and has the further requirement, that the air flow be up through the entire base area of the firepot, not just a portion of the firepot? ( e.g. posts regarding burning coal in a Royal Crown outdoor boiler topic 4048)

If that is the case, By what combustion principle does the A-A, and AHS, boiler operate? I understand that they use a cycling combustion blower to draw air through the firepot, but their 'grate' is a solid steel plate with limited horizontal, forth and back movement.

Doesn't some thickness of ash always remain on that grate?

How does the primary air flow up through 'the entire base area of the firepot'?
RICHARD2
 
Stoker Coal Boiler: KA2

Re: Must have Grate to burn coal, or Not?

PostBy: LsFarm On: Thu Jun 12, 2008 1:14 am

Actually the grate on the AA and AHS are a solid steel drawer under the round firepot tube.. the combustion air is drawn through the several inches of ash at the base of the firepot.. and up through the coal bed..

See the below photos.

Greg L
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Solid 1/2" thick steel bottom in the 'ash drawer' aka the grate.
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the fire is above the column of ashes you see, the combustion air is pulled through the ashes into the firepot.
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LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: Must have Grate to burn coal, or Not?

PostBy: RICHARD2 On: Thu Jun 12, 2008 11:30 pm

Thanks for posting the photos.

With regard to the second photo --- it appears that the grate motion has caused the ash to form a truncated cone. By that I mean, Isn't the coal in the central area of the firepot being supported directly on compacted ash? [compacted by the weight of the coal in the firepot and in the feed hopper, and also by the grate's shaking motion] Since there appears to be an air gap only at the perimeter of the firepot; Do I understand you to mean, that the requirement of having air flow through the entire base area of the coal bed is being met by the sheer power of the blower, in contrast to natural draft which requires a grate of open design under the entire area of the firepot?

Is the dark, lower half of the firepot a new piece of steel replacing a damaged original, or, Is it a modification of the original design?
RICHARD2
 
Stoker Coal Boiler: KA2

Visit Lehigh Anthracite

Re: Must have Grate to burn coal, or Not?

PostBy: LsFarm On: Fri Jun 13, 2008 6:54 am

You caught me!! That piece of steel was a temporary modification.. Your description is correct, the fire sits on the ashes, the combustion fan pulls air through the perimeter to feed the entire fire.. the fan is very big, and is driven by a 1/2 hp motor.. the fan could suck your toupee off your head.. no worries about getting enough air through the coal bed.. :D

The photo shows a fresh load of ashes added to start a new fire upon... the grate would have about 3-4" of ash in front of the camera if it were a mature fire...

This system works very well,, takes some 'head scratching' to figure it out.. but it does work well.

Greg L

.
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: Must have Grate to burn coal, or Not?

PostBy: Yanche On: Fri Jun 13, 2008 8:54 am

The AHS coalgun boiler is the same design. Some differences in the grate dimensions but the same idea, a powerful internal blower that sucks combustion air in and blows the combustion gases out. When it runs the front damper door is sucked close. This changes the air path that had been a natural draft over the fire, to a forced one through the firebed. I've measured the over the fire draft at a port in the sucked in damper. It varies widely. Anything from pegging the needle to 0.1 inches H2O. Yes, it's 0.1 not 0.01. My theory about the wide range is the resistance to flow through the compacted or not so compacted ash. This might explain why GregL had such a problem burning the low ash UAE coal which would compact well restricting air flow. A perfect example of one flavor of coal does not work with all coal appliances.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: Must have Grate to burn coal, or Not?

PostBy: RICHARD2 On: Fri Jun 13, 2008 11:30 pm

LsFarm wrote: That piece of steel was a temporary modification..


OK. I'll bite. A temporary modification to what purpose? and, With what result?
RICHARD2
 
Stoker Coal Boiler: KA2

Re: Must have Grate to burn coal, or Not?

PostBy: LsFarm On: Sat Jun 14, 2008 7:49 am

Oh man,, don't get me started on reliving my learning experiences with my AA260.. OUCH,, what a frustration for about a month.. Suffice to say,, the directions for starting a fire in the AA boilers is too simple.. the directions work fine for a AA 130 because of the much smaller firepot.. But in the AA 260, the firepot is huge,, and it is possible to get a fire burning in only part of the firepot. And there is NO WAY to see this, or know that it is a partial fire,, except to see lots of unburnt and partially-burnt coal in the ashpan..

So the experiment was an attempt to drop the firebox or fire tube level lower into the ashpan, making for a deeper fire,, in an attempt to burn the coal better... But it was a failure because even after several experiments I still was getting only a partial fire in my firebox...

ONce I discovered the partial fire situation, by digging out the unburnt and partially burnt coal from around the central column of burning coal in the firebox,[by reaching in from below and over the ashgrate and ashpan], I had one of those head-slapping moments,, AH-HA !! and knew then what to do, and that I needed to assure I had the ENTIRE firebox burning.. ONce burning completely,, the AA has run flawlessly for 5-6 months..

My above problems seem to only exist in the bigger AA260, not in the 130 size boilers.. the difference is the size of the firebox and the amount of coal burning in it.. There are numerous 130 boilers, both AA and AHS on the forum with ZERO issues mine was the only one with this problem... mostly created by myself, and by my instalation in my odd-ball setup.

Read my story in the 'Axeman Anderson 260 Disection' thread... do a search for the topic,, it is about 15 pages long,, from this time last year..

Greg L..
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: Must have Grate to burn coal, or Not?

PostBy: RICHARD2 On: Sun Jun 15, 2008 12:39 am

Hi Greg,
I did read about your acquisition and setup of the AA260; the problem you had with unburnt coal in the ash; and your investigation and conquering of that problem. That, and the Royal Crown Wood Boiler post cited above, influenced my posting the question herein.

The Royal had a blower pushing air up through its open grates, but the fire wouldn't spread laterally. Given the hugh size of the Royal firebox I understand the recomendation to block off part of the length of the grate, and form a smaller firepot by installing a removable 'back wall'. But, not clear is why the Royal would also need firebrick to confine the coal bed to the width of the grate. Given the fact that both use fan propelled air up through the coal bed, it is curious that the fire spreads laterally in the AA but not in the Royal.

I have never seen an AA, Is the ash drawer movement slow or fast ? Put another way, Is it akin to vigorous hand shaking, as if sifting sand through a fine screen, or more of a deliberate, slothful forth and back motion?
Richard
RICHARD2
 
Stoker Coal Boiler: KA2

Re: Must have Grate to burn coal, or Not?

PostBy: LsFarm On: Sun Jun 15, 2008 1:05 am

The ash drawer movement is slow,, about 2 minutes for a full fore and aft motion..

The fire box or pot in the AA has vertical sides.. the Royal boiler has tapered or round sides.. the shallow wide coal bed won't burn well or long..

The best design for a coal bed is DEEP, with vertical sides.. with the entire bottom of the coal bed a grate... a shallow bed of coal, with tapering-to-shallow sides just won't burn well, even with a fan forcing combustion air..

Greg L
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: Must have Grate to burn coal, or Not?

PostBy: RICHARD2 On: Sun Jun 15, 2008 2:26 pm

LsFarm wrote:The best design for a coal bed is DEEP, with vertical sides.. with the entire bottom of the coal bed a grate... a shallow bed of coal, with tapering-to-shallow sides just won't burn well, even with a fan forcing combustion air..


Other than the distinction that the sides are vertical vs tapering, Is a carpet bed type stoker considered "shallow"? I did notice that Keystoker and others use a down-sloping grate, whereas Harman pushes the coal up a slope which forms a thicker resevoir of coal; but the actual burn area appears to be rather thin --- No?

Do the carpet bed stokers perform poorly? Inefficiently? Is that why AA is so well thought of?
RICHARD2
 
Stoker Coal Boiler: KA2

Re: Must have Grate to burn coal, or Not?

PostBy: LsFarm On: Sun Jun 15, 2008 5:12 pm

Carpet bed stokers work well, the reason being that the pieces of coal are small,, they burn hot and fast and are pushed off the end of the bed as fresh coal is added...larger pieces of coal in the AA or in a hand feed, or a 'Royal OWB' require a much longer burn time,, a deep firebed to burn completely, and a good supply of air..

All of the stokers are pretty sophisticated and advanced for buring the coal they are designed to burn, and they burn it well.. the compromise wood/coal units like OWBs,, Us Stove furnaces, are marginal and require a lot of 'fine tuning' and are often frustrating to get to burn right.. They are a comprmixe..

The only stoker that is slightly inefficient is the older 'Triburner stoker',, and it just needs an additional fan added to be as good as the new designs..

So no, the bed stokers do very well, Leisureline, Keystoker and Harman are all very good quality bed type stokers..

The under feed stokers are also very good,, an older design, from the early 1900's,, perfected over the years..

Then there is the AA/Eshland/AHS design.. yet another 'animal'' different but works well.. sort of a stoker-fed firebox with self ashing [shaking] but with hand feed characteristics too..

Greg L

.
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: Must have Grate to burn coal, or Not?

PostBy: RICHARD2 On: Mon Jun 16, 2008 5:52 pm

Thank you Greg.

Richard
RICHARD2
 
Stoker Coal Boiler: KA2

Visit Lehigh Anthracite