Coalgun- Puff backs & Explosions

Re: Help: I Have Repeated Explosions!!

PostBy: McGiever On: Thu Dec 29, 2011 2:49 pm

rychw wrote:I have had two explosions this week thus far so I'm lowering my ash dump temperature to 105 from 110. Both times the ash was being dumped when the fan stopped. My hope is that there will be more hot coal in the fire tube that will consume the coal gas produced during ash dump. Again, for those that haven't been following this thread, I have great draft, short horizontal stove pipe run, ample available air and good qaulity coal. I'll keep everyone posted.



How would you describe your fire bed?

Higher positioned or lower?
Hot coals, thick or thin?

105* setting should get it pretty thin and very high, I think?

I came across this excellent description of how the fire bed responds to adjustments, thanks *mikeandgerry* ;)
It is for the A-A so the ashing linkage adjustment isn't like the AHS, but the theory is all the same.

mikeandgerry wrote:The number of clicks (actually referred to as "teeth taken" in the manual) merely determines how fast the fire builds in the fire pot. Recall that on the AA M-130 the firepot is an 11" diameter open tube filled with coal from the top, burned in the middle and ashed on the bottom. The tube is open on the bottom and the ash is the base of the column. The grate on the bottom reciprocates (called "shake" in the manual), clears the fine ash from the burning coal, and pushes the ash and semi-burnt coal into an ash bin and thus allows coal to feed from the top by gravity. Shake cannot occur without the addition of new coal, whether it's needed or not. Small amounts of coal can and will be fed by gravity as a result of fuel consumption with or without a call for shake.

The fire's "thickness" or depth in the pot (which is not observable) is controlled by the temperature setting on the anthrastat. A lower ash temperature setting (120degF) stops the action of the reciprocating grate sooner resulting in a "thinner" fire yielding less average btu output for summer operation while a higher ash temperature setting (140degF) yields a "thicker" average fire with a greater average btu output for winter operation.

The shake adjuster (a small L shaped slide on the grate lever) can be moved left or right to adjust the rate at which the reciprocating grate is cycled (what you guys are referring to as ashing). Moving this adjustor left or right from one tooth (far left) to three teeth (far right) only changes the speed at which the fire shakes the coal and builds the fire. Only the heaviest loads require three teeth. The anthrastat, along with the load on the boiler, controls the rate of burn and the amount of ash generation. Under low loads, the unit will eject considerable semi-burnt coal because the fire will die down very low and have to be rebuilt via stoking and the addition of coal as a result of a call for shake by the anthrastat at an ash temp lower than 120. In that process, semi-burnt coal will be moved to the ash pan. Under high load conditions, the fire will be often times be stoked and combusted more thoroughly without a call for shake resulting in a more efficient use of coal, burning it more completely because the thicker/hotter fire will stop calls for shake and thus stops the addition of new coal that is not needed.
McGiever
 
Stoker Coal Boiler: AXEMAN-ANDERSON 130 "1959"
Hot Air Coal Stoker Stove: HARMAN MAGNUM
Hand Fed Coal Stove: RADIANT HOME AIR BLAST
Baseburners & Antiques: OUR GLENWOOD 111 BASEBURNER "1908"
Coal Size/Type: PEA / ANTHRACITE, NUT-STOVE / ANTHRACITE
Other Heating: Ground Source Heat Pump
Stove/Furnace Make: Hydro Heat /Mega Tek

Re: Help: I Have Repeated Explosions!!

PostBy: lsayre On: Thu Dec 29, 2011 3:33 pm

I'm beginning to wonder if too wide a differential on the boiler water temperature might in some way contribute to the puff-backs? My differential is only 10 degrees (fan comes on at 170 degrees and shuts off at 180 degrees). Therefore only a minimal amount of coal is required to be added between recovery (firing) cycles. If however my differential was 25 degrees, then on first guess 2.5 times more coal might need to be dumped onto the hot coals during a firing session. 2.5 times as much coal might just be enough to smother the fire underneath the new coal, and not permit any dancing blue ladies to peek through. This might make for the perfect storm of gassing followed by a poof when the first blue lady finally does appear. Your thoughts on this are appreciated.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (It has been fixed!)

Re: Help: I Have Repeated Explosions!!

PostBy: macdabs On: Thu Dec 29, 2011 4:40 pm

I have had my new AHS 260 boiler up since Tuesday night without a puffback. The only issue I have had is the boiler temp went from 180* to 115* went down to the shop since the AHS is feeding my oil boiler with 250 ft of pex to the house opened the site cover looked in and saw a small bed of red hot coals. At that moment in time I was almost choking cause the temps were down in the 20s and I thought the boiler burned through 400 lbs of coal. :o Lifted the lid and the hopper was full to the top banged on the side of the hopper and the coal dropped down into the burn pot. I have ton and half of nut coal that I have been burning with chunks that are more on the stove side and the hopper bridged itself. :oops: I know they recommend pea size coal, but I have had zero puff backs at all, could the size of the coal have anything to do with the puff back issue?


Mac
macdabs
 
Stoker Coal Boiler: AHS 260
Coal Size/Type: Pea
Other Heating: Pellet,oil
Stove/Furnace Make: AHS
Stove/Furnace Model: S260

Re: Help: I Have Repeated Explosions!!

PostBy: lsayre On: Fri Dec 30, 2011 3:38 pm

macdabs wrote:I have ton and half of nut coal that I have been burning with chunks that are more on the stove side and the hopper bridged itself. :oops: I know they recommend pea size coal, but I have had zero puff backs at all, could the size of the coal have anything to do with the puff back issue?

Mac


I believe it could. As has been pointed out by others, during the 1953 US Department of the Interior's 'Bureau Of Mines' extensive test of the AA130 they discovered that they needed to drill a 5/8" hole into the sight tube cover in order to properly burn buckwheat coal with no issues. They did not need to do this with pea.

My first guess is that they likely had experienced a puff-back with the buckwheat, and then perhaps AA themselves recommended that they drill the hole in the sight tube cover plate (the precursor to the tiny round hole with the rotating cover plate) to solve the issue. Buckwheat would be more compacted, and the draft of fresh air through the coal bed may have been compromised.

With nut you may never get a puff-back, but as you have noted it apparently tends to bridge up and jam on occasion. I would guess this problem would be even worse with the smaller S130.

It seems that the AA and AHS recommended pea is the best overall choice for most of us.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (It has been fixed!)

Re: Help: I Have Repeated Explosions!!

PostBy: McGiever On: Fri Dec 30, 2011 4:13 pm

It seems that the AA and AHS recommended pea is the best overall choice for most of us.


Yes, for A-A's, bridging at the head leading into fire pot can be bad...jamming up a hollow auger may be even worse. :o
McGiever
 
Stoker Coal Boiler: AXEMAN-ANDERSON 130 "1959"
Hot Air Coal Stoker Stove: HARMAN MAGNUM
Hand Fed Coal Stove: RADIANT HOME AIR BLAST
Baseburners & Antiques: OUR GLENWOOD 111 BASEBURNER "1908"
Coal Size/Type: PEA / ANTHRACITE, NUT-STOVE / ANTHRACITE
Other Heating: Ground Source Heat Pump
Stove/Furnace Make: Hydro Heat /Mega Tek

Re: Help: I Have Repeated Explosions!!

PostBy: rychw On: Fri Dec 30, 2011 7:03 pm

McGiever wrote:How would you describe your fire bed?

Higher positioned or lower?
Hot coals, thick or thin?

105* setting should get it pretty thin and very high, I think?


My fire is higher positioned.
The hot coals extend to @ an inch below the funnel tube.
So I would caracterize my fire as thin and high but, when it is thick and low I have booms daily. Ever since I lowered the ash dump temperature I have had less frequent booms. I have not had one since loweringto 105 so I'll have to wait and see where I go from here. Many of us with AHS boilers are having booms and the common problem is that excess coal gas accumulates if the fire is low so we are trying a higher fire.
rychw
 
Stoker Coal Boiler: AHS 130
Coal Size/Type: Pea
Stove/Furnace Make: AHS
Stove/Furnace Model: 130

Re: Help: I Have Repeated Explosions!!

PostBy: ValterBorges On: Fri Dec 30, 2011 8:11 pm

If you ever forget the ash switch in the off thus ashing less(none), the fire will climb higher potentially reaching your hooper thus ahs has the hooper temp sensor to stop the blower.

I too run at 120sv and find the fire is about 1 inch below the hooper neck and forms a mound. No booms in this configuration.
ValterBorges
 
Stove/Furnace Make: AHS
Stove/Furnace Model: S260

Re: Help: I Have Repeated Explosions!!

PostBy: coaledsweat On: Fri Dec 30, 2011 10:29 pm

Using a high and low temperature at the grate is actually pulling the fire down it the hole and covering it with a big load of fresh coal in one shot with no way to really slow it down except reduce the distance between the two limits to a minimum to get it to ash more often but for less overall time. Yanche, if your still looking for an engineering project, I would recommend a speed control between the ashing mechanism and what drives it. That would be the fine tune missing between these doppelgangers.
coaledsweat
 
Stoker Coal Boiler: Axeman Anderson 260M
Coal Size/Type: Pea

Re: Help: I Have Repeated Explosions!!

PostBy: Yanche On: Fri Dec 30, 2011 11:44 pm

The motor that drives the ashing crank is a small AC motor with an integral gear reduction. It's likely a shaded pole motor. An electronic speed control for it would be a simple design, particularly since there is no need for feedback control.

The various comments about fire height are interesting. Perhaps sensing bottom ash temperature is not the optimum ashing sensor control location. Could absolute fire height be a better indicator? Isn't that what we instinctively look at when decide to shake a hand fired boiler? Coaledsweat, what did you look at when you were running a hand fired boiler? Do you think it's possible to do it with a sensor?
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: Help: I Have Repeated Explosions!!

PostBy: coaledsweat On: Sat Dec 31, 2011 10:29 am

Yanche wrote:The motor that drives the ashing crank is a small AC motor with an integral gear reduction. It's likely a shaded pole motor. An electronic speed control for it would be a simple design, particularly since there is no need for feedback control.

The various comments about fire height are interesting. Perhaps sensing bottom ash temperature is not the optimum ashing sensor control location. Could absolute fire height be a better indicator? Isn't that what we instinctively look at when decide to shake a hand fired boiler? Coaledsweat, what did you look at when you were running a hand fired boiler? Do you think it's possible to do it with a sensor?

It isn't shaking down the hand fired when the problem starts, it's covering the surface of the fire with fresh coal. If the fire is very close to the surface or breaks through, you don't have puffbacks. When you bank the coal, you have a small portion of fire on the surface. I think we have it, AHSs start and stop ashing by temp at two different setpoints. The AA uses the temp probe with a very small differential to trigger the ashing and the rate is adjusted by the sliding stop on the ashing arm. Probably the easiest way to prove this theory is a cheap timer. On that you could adjust the ashing motors run time. 60 seconds on would be AHS's current rate. 30 on 30 off would cut the rate in half.

Edit: If the AHS has a separate motor and controls for the blower and ashing mechanism, they can be operated independently. I would think ashing when the blower is not running would only make a bad situation worse.
coaledsweat
 
Stoker Coal Boiler: Axeman Anderson 260M
Coal Size/Type: Pea

Re: Help: I Have Repeated Explosions!!

PostBy: ValterBorges On: Sat Dec 31, 2011 11:46 am

Image
IMAG0019 by ValterBorges, on Flickr

It has separate controls for each.
ValterBorges
 
Stove/Furnace Make: AHS
Stove/Furnace Model: S260

Re: Help: I Have Repeated Explosions!!

PostBy: coaledsweat On: Sat Dec 31, 2011 1:47 pm

ValterBorges wrote:Image
IMAG0019 by ValterBorges, on Flickr

It has separate controls for each.

Wow! Pretty fancy stuff for an anthracite burner! Can you adjust the asher to start and stop really close together or is there a minimum differential? Does it ash without the blower running?
coaledsweat
 
Stoker Coal Boiler: Axeman Anderson 260M
Coal Size/Type: Pea

Re: Help: I Have Repeated Explosions!!

PostBy: lsayre On: Sat Dec 31, 2011 2:10 pm

coaledsweat wrote:Wow! Pretty fancy stuff for an anthracite burner! Can you adjust the asher to start and stop really close together or is there a minimum differential? Does it ash without the blower running?


Yes, no, and a bonus yes !

The differential range of temperatures between ashing start and ashing stop is variable (yes #1), and the ash ash motor starting temperature itself is also variable (bonus yes #2).

As to the "no" answer, the ashing motor will not run unless the fan (blower) is running.

As to yes #1, the factory default differential is 10 degrees.

As to bonus yes #2, the manual recommends that 130 degrees is the ideal overall set point (SV), and at this set point (assuming that the differential is left at the default of 10 degrees) it will begin ashing at 120 degrees and stop ashing at 130 degrees. These temperatures are measured on the ash grates.

The manual goes on to say that in times of low firing demand (warm weather) the set point can be lowered to 120 degrees. This would start the ash grate motor running at 110 degrees, and shut it off at 120 degrees.

My current thinking is that those having the puff-backs should see what happens if they change their differential to 5 degrees, so at a set point (SV) of 130 degrees, it would start ashing at 125 degrees, and stop ashing at 130 degrees on the grates. Or alternately, at an SV of 120 degrees, it would start ashing at 115 degrees, and stop ashing at 120 degrees.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (It has been fixed!)

Re: Help: I Have Repeated Explosions!!

PostBy: coaledsweat On: Sat Dec 31, 2011 5:17 pm

lsayre wrote:My current thinking is that those having the puff-backs should see what happens if they change their differential to 5 degrees, so at a set point (SV) of 130 degrees, it would start ashing at 125 degrees, and stop ashing at 130 degrees on the grates. Or alternately, at an SV of 120 degrees, it would start ashing at 115 degrees, and stop ashing at 120 degrees.

I would agree, run the smallest differential and it will ash more often but for shorter periods and with that load less fresh coal. As Valter stated, his fire broke the surface and no more booms. This would have the same effect as banking a hand fired when reloading.
coaledsweat
 
Stoker Coal Boiler: Axeman Anderson 260M
Coal Size/Type: Pea

Re: Help: I Have Repeated Explosions!!

PostBy: rychw On: Sat Dec 31, 2011 6:16 pm

coaledsweat wrote:I would agree, run the smallest differential and it will ash more often but for shorter periods and with that load less fresh coal. As Valter stated, his fire broke the surface and no more booms. This would have the same effect as banking a hand fired when reloading.


I have shortened my differential to 5 degrees from the factory set 10 degrees. This along with the ash dump temperature of 105, and wiring my ash dump motor to run with the fan only is my latest attempt to prevent the booms. Thanks Coledsweat for the idea, and I'm interested in Yanchee's latest idea concerning the thermo sensor and measuring the ash temperature at the high end of the tube instead of the low end. I'll keep everyone posted.

Happy New Year forum members. Hoping that 2012 is a better year than 2011.
rychw
 
Stoker Coal Boiler: AHS 130
Coal Size/Type: Pea
Stove/Furnace Make: AHS
Stove/Furnace Model: 130

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