Coalgun- Puff backs & Explosions

markviii wrote:Does the ash controller have a differential setting?

Yes and the AHS directions are to set it at 10 degrees. So if the theromgrate is set for 120 the grate switches on when the sensed temperature drops to 110 and switches off when the sensed temperature rises to 120.

Bob wrote:

markviii wrote:Does the ash controller have a differential setting?

Yes and the AHS directions are to set it at 10 degrees. So if the theromgrate is set for 120 the grate switches on when the sensed temperature drops to 110 and switches off when the sensed temperature rises to 120.

If you reduced the differential to 5 degrees, in theory it would ash more often and for shorter periods of time...admitting less fresh coal at once. Might be worth a try...

markviii wrote:

Bob wrote:

markviii wrote:Does the ash controller have a differential setting?

Yes and the AHS directions are to set it at 10 degrees. So if the theromgrate is set for 120 the grate switches on when the sensed temperature drops to 110 and switches off when the sensed temperature rises to 120.

If you reduced the differential to 5 degrees, in theory it would ash more often and for shorter periods of time...admitting less fresh coal at once. Might be worth a try...

I have experimented a bit with differential but I wasn't successful in resolving the problem.

At the moment--at least until the booms start again--my theory is that keeping the burning level of coal sufficiently high is a more important factor.

But I would be interested to hear if anyone else has experimented with varying the differential and what results were observed.

It would be really great if the AHS rep would join this discussion!

Seems to me what's needed is a different control system. The root cause of puff backs is a unique combination of coal gases, combustion air and an ignition source. Alter significantly any of those and puff back will be gone. What do we have to significantly alter things? Answer, a significant air sucker; the built in combustion blower. So, upon a turn off desire, first open the inspection port door, second allow the blower to run for some timed amount. This will remove the coal gases because you will have over the fire air; significant amounts. Enough to cool the coal if left to run long enough. Third, after the timed duration, shut the combustion blower off. The design right now depends on passive actions to achieve a change one of the three things need for a puff back to occur. Flapper spring door tension just right, coal not outgassing, a good idle chimney draft, maybe a coasting blower fan. It's just not enough for all cases. Opinions?

Yanche, good to have you join this discussion.

I think there is agreement that the puff backs occur when the blower shuts down and the inspection door pops open which results in the inrush of oxygen to mix with coal gases. The boom occurs because there is an ignition source present--the hot coals.

So if my characterization is correct it is not clear to me how good idle chimney draft, or more precisely the lack of good idle chimney draft, causes puff backs.

It seems to me that the cause has to be the accumulation of gases during forced firing--accumulation that exceeds the ability of the fan to draw them off. So my reasoning is that because gases are accumulating during forced draft firing they form an explosive mixture when the inspection door pops open at the end of forced draft firing.

So I keep coming back to my current theory--that the way to reduce the accumulation of gases --with the resulting puff backs--is to move the fire up the coal column. If the fire is sufficiently high, and if the bleed air port is open to admit oxygen above the fire during forced firing, then the accumulated gases should be ignited during force firing. If they are burned off during forced firing then there shouldn't be gasses to explode when the inspection door pops open.
Opinions?

Bob wrote:So I keep coming back to my current theory--that the way to reduce the accumulation of gases --with the resulting puff backs--is to move the fire up the coal column. If the fire is sufficiently high, and if the bleed air port is open to admit oxygen above the fire during forced firing, then the accumulated gases should be ignited during force firing. If they are burned off during forced firing then there shouldn't be gasses to explode when the inspection door pops open.
Opinions?

Bob,

I agree with your theory. We need to figure out a way to keep the fan running until the gasses are ignited or prevent the ash controller from dumping ash without the fan running. I have my fire up the tube column but need to lower my dump temperature to 115. Again, where is AHS help. They should be participating in the forum to help us find a safe solution to the booms.

My AHS S130 Coal Gun's ash grate motor only runs when the blower is running, regardless of the grate temperature. Is this not the case for others Coal Gun's?

lsayre wrote:My AHS S130 Coal Gun's ash grate motor only runs when the blower is running, regardless of the grate temperature. Is this not the case for others Coal Gun's?

My ash grate motor runs whenever the ash temp drops below 120 regardless of whether the fan is running. Can I program my Fuji controller to prevent the grate motor running unless fan is on?

rychw wrote:

lsayre wrote:My AHS S130 Coal Gun's ash grate motor only runs when the blower is running, regardless of the grate temperature. Is this not the case for others Coal Gun's?

My ash grate motor runs whenever the ash temp drops below 120 regardless of whether the fan is running. Can I program my Fuji controller to prevent the grate motor running unless fan is on?

If I set the Fuji controller to 130 and the differential to 10 then when the temp drops below 120 the ash grate runs until the tempurature rises to 130. The power supply that the Fuji controller turns on and off is separate from the power supply for the fan motor.

I think you could change the wiring for the grate motor so that the power source is common with the fan motor rather than common with the power supply for the unit and then the grate motor would only run when the fan is running.

It's my theory that the explosive gases come from heated coal, coal pieces not yet hot enough to burn. When the combustion blower is running it's sucking air up through the ash pit, the burning fire and into the boiler water tubes. If we had a control system that kept the blower running but change where the inlet air came from you would likely exhaust the explosive gases. What would change where the inlet air comes from? Just open the inspection port door. The blower would now suck free air because it's resistance to flow is much less than the suck power needed to pull air up through the ash and coal fire. I believe it might work because if you open the inspection port door while the blower is running you don't get a puff back. Why? Because the combustion gases are easily sucked off and blown out the boiler breach. The ignition source is still there, the burning coals, but the gases are gone.

So, my design would first open the inspection port door with an electromagnet, let the blower run for a few tens of seconds, then turn it off and release the electromagnet.

Yanche wrote:It's my theory that the explosive gases come from heated coal, coal pieces not yet hot enough to burn. When the combustion blower is running it's sucking air up through the ash pit, the burning fire and into the boiler water tubes. If we had a control system that kept the blower running but change where the inlet air came from you would likely exhaust the explosive gases. What would change where the inlet air comes from? Just open the inspection port door. The blower would now suck free air because it's resistance to flow is much less than the suck power needed to pull air up through the ash and coal fire. I believe it might work because if you open the inspection port door while the blower is running you don't get a puff back. Why? Because the combustion gases are easily sucked off and blown out the boiler breach. The ignition source is still there, the burning coals, but the gases are gone.

So, my design would first open the inspection port door with an electromagnet, let the blower run for a few tens of seconds, then turn it off and release the electromagnet.

I think your concept is similar to what Freddy has described he installed on his Axeman Anderson 130

rychw wrote:

lsayre wrote:My AHS S130 Coal Gun's ash grate motor only runs when the blower is running, regardless of the grate temperature. Is this not the case for others Coal Gun's?

My ash grate motor runs whenever the ash temp drops below 120 regardless of whether the fan is running. Can I program my Fuji controller to prevent the grate motor running unless fan is on?

That is interesting. The older Eshland S130 that I have seen had a percentage timer that operated the grate based on run time of the blower. e.g. 2 minutes out of 10, etc. Axeman Anderson boilers have no choice but to ash when the auger is turning...I think that running the grate motor without the blower running is making your boiler more prone to a buildup of gasses from fresh coal.

markviii wrote:That is interesting. The older Eshland S130 that I have seen had a percentage timer that operated the grate based on run time of the blower. e.g. 2 minutes out of 10, etc. Axeman Anderson boilers have no choice but to ash when the auger is turning...I think that running the grate motor without the blower running is making your boiler more prone to a buildup of gasses from fresh coal.

Markviii is correct and I think we need to wire the grate motor to run only when the fan is running. We can wire the grate motor off the fan motor source and that would be the easiest and cheapest short term solution until a permanent solution can be found. Any thoughts?

rychw wrote:

markviii wrote:That is interesting. The older Eshland S130 that I have seen had a percentage timer that operated the grate based on run time of the blower. e.g. 2 minutes out of 10, etc. Axeman Anderson boilers have no choice but to ash when the auger is turning...I think that running the grate motor without the blower running is making your boiler more prone to a buildup of gasses from fresh coal.

Markviii is correct and I think we need to wire the grate motor to run only when the fan is running. We can wire the grate motor off the fan motor source and that would be the easiest and cheapest short term solution until a permanent solution can be found. Any thoughts?

While my grate will continue to run after the fan shuts down it doesn't run very long. When the forced draft of the fan is no longer pulling cooling air in the temperature sensed by the thermocouple rises very rapidly and the control shuts the grate down. So in my application I don't think it would make much of a difference.

Additionally, if the timing of the explosion is when the grate shuts down and the inspection port door pops open then I don't see how changing operation of the grate after that point makes a difference.

I have been looking at purchasing a S-260 and reading all the issues on repeated explosions should I reconsider? I noticed not a lot of feedback from the manufacture on this serious issue . I just went through lack of support from DS with my boiler and do not want to spend money to have something unsafe or undependable. If something like a explosion occured I would not be aware of it for several hours not to mention if your house burns down or fills with smoke and flyash should I be looking at something else?

Jeff