EFM Coal Uneven in Pot

 
RICHARD2
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Post by RICHARD2 » Sat. Jan. 21, 2023 1:55 am

Rob R. wrote:
Fri. Jan. 20, 2023 6:14 am
I think the coal packs into the pot a bit tighter on the side opposite the auger. With clean coal the air is able to come up through the coal as intended, but when you start getting fines the air takes the path of least resistance.
That idea fits the observed facts; I will try to confirm it.

My auger tube in aluminum.
I increased the air to 4, but no real change in burning. The left side burns to ash, while the stoking pushes the slightly burnt coal on the right side into the ash pan.
KT2 wrote:
Fri. Jan. 20, 2023 9:01 am
I've been having the same issue. I only ever got rice from Direnzo's for 6 years. Had to go to Superior and only could get Buckwheat. It's pretty clean looks good. Problems right away, backside of pot is dead. Only 20 tons since i replaced the auger/pot bushings and made new stainless auger tubes. This boiler only broke a shear pin once in 30 years. I removed auger and checked everything and found nothing wrong. When i cleaned pot out the backside was packed full of fines. The coal sizing I discovered is a good bit bigger than it should be. The nut coal my Dad got last year looked like it had some stove coal in it. This year it looks like everything from rice on up in his nut from Superior.
Sounds like we have a match-- as I mentioned above my so called 'buck' is a mix of pea, buck, rice, barley, and 'grain of sand' fines. The coal was delivered wet, with the fines clinging to the coal. Over the summer the coal dried, and apparently the fines fell off en masse, ready to cause havoc.
The poor alternative sources of coal this year have caused problems for many of us.

 
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Post by lincolnmania » Sat. Jan. 21, 2023 10:02 pm

I'm mixing Superior buck with Blaschak rice and the back of my pot makes less as than the front of the pot, i get more fines with the buck mix. Same deal Superior was out of rice when I went there.

 
Ken C.
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Post by Ken C. » Sun. Jan. 22, 2023 11:50 am

When you emptied the burner pot.. did you empty to the point of fully exposing the auger?
Fines will gather against the lower inside of the burner pot and sort of melt fast and form a crust partially blocking the pathway up to the grates. I have had an EFM-520 for 40yrs. I have cleaned the lower internal fire pot several times using a scraping tool such as a wide blade screwdriver. I clean out the ash and good coal down to the auger. Then use the hand crank and turn the auger backwards pushing the collected fines from the bushings on the auger then scrape off the accumulated coal gunk.

 
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Post by StokerDon » Sun. Jan. 22, 2023 3:56 pm

RICHARD2 wrote:
Sat. Jan. 21, 2023 1:55 am
as I mentioned above my so called 'buck' is a mix of pea, buck, rice, barley, and 'grain of sand' fines.
Well, that is the problem. Underfed stokers are designed to feed and burn 1 very consistent size of coal. Once it starts pushing 2 or more sizes up the auger, they will separate while being pushed upward into the pot. At that point you have to parts of the pot that require different amounts of air to fully burn the coal.

The simplest solution is to just turn the air up to try to burn the smaller sizes. Also, properly sized Pea coal won't fit through an EFM 520 auger. This will make your feeding problems worse.

-Don


 
RICHARD2
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Post by RICHARD2 » Tue. Jan. 24, 2023 1:50 am

On Friday Rob R. suggested that coal on the side opposite the auger packs a bit tighter.
RICHARD2 wrote:
Sat. Jan. 21, 2023 1:55 am
Rob R. wrote: ↑
I think the coal packs into the pot a bit tighter on the side opposite the auger. With clean coal the air is able to come up through the coal as intended, but when you start getting fines the air takes the path of least resistance.

That idea fits the observed facts; I will try to confirm it.
To be able to look at the coal distribution pattern in the pot, I shut the boiler off Saturday so the fire would die out undisturbed. On Sunday I was able to see how the coal in the pot was distributed. Using an artist’s small pallet trowel, I excavated the fire pot in layers about ½” thick, trying not to disturb or mix in the underlying coal. As mentioned above, the demarcation between the uneven height and burning was actually at an angle relative to the door from about 10 o’clock to 4 o’clock; but for simplicity I will refer to it as simply the left and right side.
I removed the ash from the ring, and the top ½” layer of mostly burnt coal. On the right side, which had been lower and poorly burning, I found a layer of very small pieces and fines about ½” thick while on the left side the coal was a mix of full size pieces. In the next lower layer, the right side had some rice and barley pieces mixed in with lots of fines, while the left was again the same mix of full size pieces. At the very bottom on the left where the auger enters, the coal looked the same as it is in the bin, but to the right, between the last blade of the auger and the pot bushing, it was about 80% fines. I cleaned out the bottom of the pot.
I wondered if I could see the separation happening, so I hand cranked the auger, and took photos every few turns. In the sequence below, you can see the coal being ‘sorted’ as it rises in the fire pot. My auger enters from the left, and curiously, from the second photo on, the angled line of the separation is visible.
EFM pot_1.jpg
.JPG | 308.4KB | EFM pot_1.jpg
EFM pot_2r.JPG
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EFM pot_3r.JPG
.JPG | 300.7KB | EFM pot_3r.JPG
EFM pot_4r.JPG
.JPG | 304.7KB | EFM pot_4r.JPG
EFM pot_5.JPG
.JPG | 385.8KB | EFM pot_5.JPG
EFM pot_6.JPG
.JPG | 318.1KB | EFM pot_6.JPG
Later Sunday evening, I saw that earlier in the day [when I had my head the in boiler], Ken C and Stoker Don had posted comments making similar observations. More on their posts below.
I obtained from my silo a coffee can sample of the “unscreened” mish-mash of coal purported to be “buck”, and sorted it. First photo shows the three sizes isolated. To my eye the volume of the pile on the left of the largest pieces is about 1.5 times the amount of mid-size pieces in the center, which in turn is about twice the size of the right side pile of small pieces; and the smaller pile of fines about two-thirds the amount of small pieces.
I used US coins for scale in the close up photos. The diameter of a quarter is 15/16”; a nickel is 13/16”; a dime is 11/16”.
The largest pieces sit on a quarter; the mid-size pieces are on a nickel, with one piece sitting on copper tubing with a ½” i.d., and the smallest pieces are pictured on a dime.
Coal Sorted 001.JPG
.JPG | 323.4KB | Coal Sorted 001.JPG
Coal Sorted 002.JPG

Placed on quarter 15/16"

.JPG | 225.2KB | Coal Sorted 002.JPG
Coal Sorted 003.JPG

placed on nickel 13/16" and on 1/2" i.d. tube

.JPG | 252.8KB | Coal Sorted 003.JPG
Coal Sorted 004.JPG

on dime 11/16"

.JPG | 250.2KB | Coal Sorted 004.JPG
Coal Sorted 005.JPG

fines

.JPG | 310.3KB | Coal Sorted 005.JPG
Using round holes to sort coal:
Rice coal passes through 7/16” and is retained by 3/16” .
Buck passes through 9/16” and is retained by 5/16”.
Pea passes through 13/16” and is retained by 9/16”.
To be “Buck” size every piece should pass through a hole smaller than a dime. And “Pea” should pass through a nickel size hole.
So in round numbers this load of coal is about 25% buck and rice, 10% fines, and 65% pea. An EFM auger cannot successfully transport pea coal; even with buck many on here report ‘sounds’ coming from the auger tube.
The foundational theory of an automatic coal stoker is that proper, and most efficient burning, is achievable by supplying a measured amount of air to burn a measured amount of coal. We set the amount of air with the damper, and the amount of coal by the number of teeth. But to actually work that way, the coal itself must be uniform, both in size and quality. I know this, but until Sunday, when I saw the coal separating as it fed up into the pot, I had thought that the mixture of sizes would rise symmetrically, and the only negative result would be the loss of heat/efficiency resulting from some of the larger pieces being pushed out half-burnt.
Ken C. wrote:
Sun. Jan. 22, 2023 11:50 am
When you emptied the burner pot.. did you empty to the point of fully exposing the auger?
Fines will gather against the lower inside of the burner pot and sort of melt fast and form a crust partially blocking the pathway up to the grates. I have had an EFM-520 for 40yrs. I have cleaned the lower internal fire pot several times using a scraping tool such as a wide blade screwdriver. I clean out the ash and good coal down to the auger. Then use the hand crank and turn the auger backwards pushing the collected fines from the bushings on the auger then scrape off the accumulated coal gunk.
There was an accumulation of fines in the bottom of the pot but they had not yet hardened so I was able to remove them easily.
As you can glean from the quote I use in my profile, I respect your 40 years experience with EFM over 'a lot of theory', but I always thought that the reason the pot auger bushing was made with the groove spiral opposite to the direction of the auger flights, was that while rotating in the same direction, the auger shaft flights pushed coal toward the center and the bushing spiral pushed fines toward the center also.
Auger Bushing.JPG

Auger bushing spiral groove cut opposite to auger flights direction.

.JPG | 11.3KB | Auger Bushing.JPG
StokerDon wrote:
Sun. Jan. 22, 2023 3:56 pm
Well, that is the problem. Underfed stokers are designed to feed and burn 1 very consistent size of coal. Once it starts pushing 2 or more sizes up the auger, they will separate while being pushed upward into the pot. At that point you have to parts of the pot that require different amounts of air to fully burn the coal.
Yes, you are absolutely correct. I just wish I had known about the sizes separating while being pushed up --- I could see the result in the fire, but did not understanding the Why. You have answered the question I posted.
StokerDon wrote:
Sun. Jan. 22, 2023 3:56 pm
The simplest solution is to just turn the air up to try to burn the smaller sizes.
I wish there were a simple solution.The air is supplied to the whole air pot, and enters the coal bed through the holes in the grates. It is the density of the smaller pieces and fines on the right side that causes the air to seek the path of least resistance through the larger pieces on the left side. Increasing the volume of air will not change that dynamic -- the path of least resistance will just get more air. Increasing the volume of air also risks blowing gases out the auger pipe.
For the coal bed to burn evenly, it must have equal resistance to the flow of air. That is the point you made first-- "designed to feed and burn 1 very consistent size of coal." Evening the density within the coal pot is the only way to get the air to flow evenly and hence to burn evenly.

 
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Post by Rob R. » Tue. Jan. 24, 2023 6:26 am

Good analysis. It stinks that you have to work through a bunch of crappy coal. I would go over your findings with your coal supplier and try to work out some sort of resolution.

Is the boiler still able to heat your house and not generate a bunch of unburned coal in the ash?

 
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Post by RICHARD2 » Wed. Jan. 25, 2023 1:21 am

Rob R. wrote:
Tue. Jan. 24, 2023 6:26 am

Is the boiler still able to heat your house and not generate a bunch of unburned coal in the ash?
No. The ash has a lot of partially burned, and some unburnt coal [not shale].
After burning 87 pounds of coal [14.5 hours on 3 teeth at 2 pounds per tooth], the ash tub weighed 23 pounds, minus the tub tare of 4.5 pounds leaves a net weight of 18.5 pounds. That is about 21%.

 
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Post by lzaharis » Wed. Jan. 25, 2023 10:30 am

I am glad that you used a hand sorted sieve analysis of your coal product.

I am sorry you have to go through this with an undersized product as a portion of your fuel loads.
No one is using fine sieve trommel screens to fine screen their coal sadly.

All the coal suppliers/ mines could collectively use a trommel screen their buck, pea and rice coal and take the fines
compact them with a pelleting press to rice size with sugar water and corn starch and have a very dense fuel product.

I am wondering out loud here if using carboard egg crates filled with a mix of undersized coal and fines mixed with molasses and allowed to dry would help with the fire as you could break up each carboard egg carton into 12 pieces and add them to the fire occasionally through the viewing door and use the fire on the top of the Tuyere/Burn pot to dispose of them?

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

The folks at All Canadian Heaters use a heavy cast cap on thier tuyere burn pots with a hole in the center that forces all the coal that is burning to the center and out of the tuyere where everything is burned and falls away on the sloped tuyere cap and the flue gas then passes through the secondary burn fire tubes and the turbolator spirals and burns even more to extract more heat from the coal fire.
The tuyere cap is also spun by the arm attached to the auger drive like the older prill, iron fireman and the new stokers used
in the Dakotas, Montana and Wyoming using the rotating ash ring.


 
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Rob R.
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Post by Rob R. » Wed. Jan. 25, 2023 10:44 am

RICHARD2 wrote:
Wed. Jan. 25, 2023 1:21 am
No. The ash has a lot of partially burned, and some unburnt coal [not shale].
After burning 87 pounds of coal [14.5 hours on 3 teeth at 2 pounds per tooth], the ash tub weighed 23 pounds, minus the tub tare of 4.5 pounds leaves a net weight of 18.5 pounds. That is about 21%.
I am sorry to hear that your coal is poor quality. Have you discussed this with your supplier?

 
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Post by KT2 » Wed. Jan. 25, 2023 5:59 pm

I originally thought my coal looked pretty clean until tonight I shoveled it around in the bin and there is large amounts of small fines that settled down. Like way too much small stuff. So I thought I should check on this thread! My coal looks identical to yours. After it rains on my ash piles you can see tons of unburnt coal. I guess I'll pay more next time and not go to Superior. Direnzo's was such a clean first class operation. No mud or junk sitting everywhere.

 
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Post by Idlorah » Wed. Jan. 25, 2023 6:32 pm

KT2 wrote:
Wed. Jan. 25, 2023 5:59 pm
Direnzo's was such a clean first class operation. No mud or junk sitting everywhere.
That they were I miss their coal.

 
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Post by RICHARD2 » Thu. Jan. 26, 2023 12:56 am

lzaharis wrote:
Wed. Jan. 25, 2023 10:30 am


I am wondering out loud here if using carboard egg crates filled with a mix of undersized coal and fines mixed with molasses and allowed to dry would help with the fire as you could break up each carboard egg carton into 12 pieces and add them to the fire occasionally through the viewing door and use the fire on the top of the Tuyere/Burn pot to dispose of them?
Wouldn't the cost of the molasses exceed the value of the coal fines? Anyway, my coal is stored in a 12 foot high silo; with about 8 feet of coal above the doghouse---I have no way to sift out the fines.
lzaharis wrote:
Wed. Jan. 25, 2023 10:30 am
The folks at All Canadian Heaters use
Thanks for that reference, it is an interesting design. The description states that their augers "feature a section of reverse directional flighting for smooth coal feed". Do you know how that works? I assume it is related to the sub-b coal they use, but I am not familiar with the theory of operating an auger that has flighting in both directions. Wouldn't the two sections be pushing against each other?
KT2 wrote:
Wed. Jan. 25, 2023 5:59 pm
I originally thought my coal looked pretty clean until tonight I shoveled it around in the bin and there is large amounts of small fines that settled down. Like way too much small stuff. . . . . After it rains on my ash piles you can see tons of unburnt coal. I guess I'll pay more next time . . .
I see unburnt and partially burnt coal when I dump the ash, but the real scope of the issue is made plain by the rain. I wound up with this stuff from another mine only because my supplier couldn't get any loads from the mine he normally uses.
Rob R. wrote:
Wed. Jan. 25, 2023 10:44 am

I am sorry to hear that your coal is poor quality. Have you discussed this with your supplier?
I have not yet talked to my supplier. I think he tried to get the best coal he could. Apparently, the 'normal source' mine had sold out their production; something about contracts to ship to Europe. ? ? ?

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