Coalgun- Puff backs & Explosions

Yanche wrote: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?

Still thinking about this one. I don't think the location of the probe is the problem, I think it's the speed the ashing runs at, It pulls the fire down just to satisfy the off setting and that makes the coal grumpy. It just ashes too fast.
Can these AHSs be set to ash within one, two or three degrees? If I was experiencing this problem, I would stop ashing until the fire breaks the surface, about half way up the supply of coal pyramid. Start the asher and reduce the differential a bit, I would guess about 80% of what you had and maybe 60% for something that is seriously booming. Watch the fire for the next few days and make sure that it periodically returns to the surface. That means glowing coals under load and ashed coal when idling. It won't be on the surface all the time, but it needs to pop up every now and then. If the fire starts to disappear in the fresh coal, you'll need to slow it down some more.

coaledsweat wrote:

Yanche wrote: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?

Still thinking about this one. I don't think the location of the probe is the problem, I think it's the speed the ashing runs at, It pulls the fire down just to satisfy the off setting and that makes the coal grumpy. It just ashes too fast.

Do you really mean too fast or too often? The speed at which it pulls the grate is set by the fixed speed ashing gear motor. In my non thermocouple design, how often it ashes is controlled by a percentage timer motor. This motor only runs when the combustion blower runs. It has a 10 minute cycle. Ashing is typically set at 2-1/2 minutes +/- a half minute. This means for 10 minutes of blower run time the grate is moving at a fixed non adjustable speed for 2-1/2 minutes.

coaledsweat wrote:Can these AHSs be set to ash within one, two or three degrees? If I was experiencing this problem, I would stop ashing until the fire breaks the surface, about half way up the supply of coal pyramid. Start the asher and reduce the differential a bit, I would guess about 80% of what you had and maybe 60% for something that is seriously booming. Watch the fire for the next few days and make sure that it periodically returns to the surface. That means glowing coals under load and ashed coal when idling. It won't be on the surface all the time, but it needs to pop up every now and then. If the fire starts to disappear in the fresh coal, you'll need to slow it down some more.

You can raise the glowing coals by just turning off the ashing motor. Of course you have to be careful and not let it rise so high that it burns into the coal supply hopper tube or worst yet into the hopper.

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, The hysterisis setting.


IMAG0089 by ValterBorges, on Flickr

I've run the ashing as low as 95 in summer.
When i was testing at 130 and adjusting the hyst to 5 or 10 it didnt make a difference still boom. As stated earlier this just causes it to ash too much in more steps.
I believe the ashing runs independently from factory. Checking brb

Ok waited for blower to finish cycle and Sv set at 120, Pv was 112. Changed Sv to 122 and ashing begins. Changed Sv back to 120 and once Pv reached 120 it stopped.

Coaledsweat nailed it when he sayd the key is to keep the fire in a pyramid shape and the red glow about 1" from the hooper neck before the blower comes on again. Right after it ashes it will be down about 4" from hooper neck, about 1/4 to 1/2 way of the viewport height.

ValterBorges wrote:Right after it ashes it will be down about 4" from hooper neck.

Yeah, that's a big gulp. No wonder they like to burp.
The way the coal feeds onto the top of the fire in a cone, the amount of fresh coal is exponentially greater as the fire goes deeper into the combustion tube. At 1" below the feed tube, there is probably about a coffee can full of coal on top. If the fire is 3" below the feed tube it may be 4 or more cans. At 6" it may be about 10 cans. Cooking that much coal is going to make a lot of gas.

I'll set the hyst to 5 again and try to measure the height of the fire before and after a few cycles and report back. I think the problem is going to be that it takes the same amount of time to shutoff because it takes a while for the heat to travel to the insulated probe after the blower shutsdown once the heat is rising going another 5 deg doesn't take that long, but the initial time to start heating the probe I suspect is the same, therefore it shakes just as long on 5 as it does on 10 thus introducing the same amount of coal. (time for a test).

Can you go lower than 5?

Although I initially assumed that lowering the differential would be of some benefit, now that I've watched mine ash a few times I realize that this accomplishes little to nothing. When my boiler begins to ash at 120 degrees, the temperature of the ash grate often continues at this juncture to drop well below 120 degrees before it eventually turns the corner and begins to rise again. And when it finally does start to rise, it rises very rapidly and in no time at all it has surpassed 130 degrees (shutting the ash motor off). If instead my ash motor was set to turn on at 120 degrees and shut off at 125 degrees, the amount of time that the ash cycle runs would not be cut in half as I had initially assumed, but rather an ash cycle of perhaps 2-3 minutes overall would be lessened by only perhaps 10 seconds .

ValterBorges wrote:it takes a while for the heat to travel to the insulated probe after the blower shutsdown

On my AHS 130 there is no insulation on the thermo couple probe--it is bare. I have to wonder why the probe would be insulated--does it have something to do with the controller AHS is now using? (my boiler has the Fugi controller)

Think you'll find what you are looking at is a protective sheath. The business end of the thermocouple junction is at the tip and may or may not be quite touching the sheath.

My dad and I recently talked about this issue. He has never seen or operated a Coal Gun, but he has burned his share of coal in hand-fed stoves. His first thought was that too much coal was being added at one time, and covering the existing fire...something that can give you impressive puff backs in a hand-fired stove. I think Axeman Anderson had a good reason for allowing the user to adjust the rate at which the grate moves, as well as the temperature setpoint of the ash probe.

It would be interesting to run the power to the AHS grate motor through a repeat cycle timer, then you could set the timer for 15 seonds on, 15 seconds off, etc...that way you would have an additional means of controlling the grate movement. The object being to add the coal to the firetube in a slower, more uniform fashion. Right now it sounds like the coal is fed to the fire in "slugs" whenever the grate operates.

coaledsweat wrote:Can you go lower than 5?

Yes.

Bob wrote:

ValterBorges wrote:it takes a while for the heat to travel to the insulated probe after the blower shutsdown

On my AHS 130 there is no insulation on the thermo couple probe--it is bare. I have to wonder why the probe would be insulated--does it have something to do with the controller AHS is now using? (my boiler has the Fugi controller)

I didnt mean fiberglass type insulation. I was referring to the ash blanket that acts as insulation from the fire above.

Rob R. wrote:My dad and I recently talked about this issue. He has never seen or operated a Coal Gun, but he has burned his share of coal in hand-fed stoves. His first thought was that too much coal was being added at one time, and covering the existing fire...something that can give you impressive puff backs in a hand-fired stove. I think Axeman Anderson had a good reason for allowing the user to adjust the rate at which the grate moves, as well as the temperature setpoint of the ash probe.

It would be interesting to run the power to the AHS grate motor through a repeat cycle timer, then you could set the timer for 15 seonds on, 15 seconds off, etc...that way you would have an additional means of controlling the grate movement. The object being to add the coal to the firetube in a slower, more uniform fashion. Right now it sounds like the coal is fed to the fire in "slugs" whenever the grate operates.

Thats good maybe even a 2 to 1 on off ratio to give the fire some time to heat up the probe.
Any damage to the motor by doing this? Where would you find one? how much?

If I were spending any money to slow down the ashing, I would spend it on a variable speed control for the ashing gear head motor. Would someone look at the motor and post the make and model number. I'll look for a suitable controller.