Coalgun- Puff backs & Explosions

larry, have you tried increasing your draft to say .04-,05" to see if this will cleanse the combustion chamber of burnable gasses quicker after the fan shuts down?

The only time I've ever had a puff-back is when starting a fire and having a very thick layer of fresh coal on top of the hot fire.

Greg L

LsFarm wrote:larry, have you tried increasing your draft to say .04-,05" to see if this will cleanse the combustion chamber of burnable gasses quicker after the fan shuts down?

The only time I've ever had a puff-back is when starting a fire and having a very thick layer of fresh coal on top of the hot fire.

Greg L

To do so on a calm day when it is not all that cold outside I would have to add height to my chimney. What brand(s) of anthracite do you generally use Greg?

One thing is certain, and that is that my overall draft situation is no different this season than it was last season, but my conditions are drastically different. My only change has been in my source of anthracite. It is the only variable that has changed.

Following up: I have been in regular email and phone communication with Darren Bricker at AHS (he called me), and he has walked me down to 105 degrees on my SV and 5 degrees on my grate temperature hysteresis. I have also closed my port holes "over the fire air" sliding cover (per Darren this is actually not its originally intended purpose no less) down to only about 1/5 open (from previously having it wide wide open). Darren's actual suggestion was to close it all the way. The changes I have made with Darren's guidance have eliminated any sign of puffs for a few consecutive days running now. It seems that the entire thing is related to how much ash the coal makes. If your coal is not making much ash the SV and the hysteresis must be reduced accordingly to keep the fire high in the tube. I seem to be back to running just fine (no puffs) now that I have it dialed in for UAE Harmony.

Darren is a great guy, and he truly wants to see everyone resolve these issues.

The latest AHS update is that Ben Witmer is no longer an AHS employee. Not sure if he retired, or... (and didn't ask), and also not sure as to how long he has been out of the picture. Therefore they have no one working at AHS who is an active member of this forum at this time. That's why they have not been responding to questions and concerns posted here.

As to how much ash the Harmony is making, I'm changing the ash pan out only at roughly 280 lbs. of coal added, and at that juncture the ashes are weighing only 22 to 25 lbs. Only about half to 2/3 full on the pan. I didn't monitor the ash with Blaschak last season, but I was easily taking the ash pan out for emptying twice as frequently, and I was removing it at visually the same ash pan level.

It seems that the entire thing is related to how much ash the coal makes. If your coal is not making much ash the SV and the hysteresis must be reduced accordingly to keep the fire high in the tube.

If this fault is judged as critical, and it seems to me it should be, then a little learning from ISO 9001 would seems appropriate. Laughing it off just does not make it (sorry whistle). So is the input specification to this issue is no explosions? If so then what are the processes and procedures to arrive at an output spec where this does not happen. Obvious, of course, most quality management is but first we set up IQ/OQ. If I sound like a burned out ex QC manager of an aseptic unit (I needed a job and it paid incredibly well) unit who suffered as a bought in consultant for a customer under a 483 violation (google that) from the FDA and what it took to fix that then I confess that is me. Injectibles most be sterile and coal stoves must not explode in the night - to me it is the same. So qualitative statements like "hysteresis must be reduced accordingly" would mean nothing to an FDA inspector and it means the same to me. Yanche muttering darkly about understanding anthratubes also is a non-sequitur.

A graph correlating ash to hysteresis must be constructed and validated. That even assumes you believe at this point that is the only problem here and I suspect it is multivariate. Given the number of brilliant minds looking at this one a single source fix would have been discovered by now. There needs to be a explosion/no explosion area of the graph and the stove controls need to automatically prevent that from happening. My friends you are light years from that point - sorry these arguments are not convincing. It would be nice to fix this before someone blows themselves up. Never mind the human tragedy, an injury attorney will own AHS after the trial.

For a Coal Newbie, you sure have lot a of coal equipment listed. What is your real history with coal? Let me be the first to say that the 'puff backs' are NOT as terrifying as many make them out to be, however some are worse than others.
The issue is definitely about the height of the fire in the burn chamber, ashing rates, and conditions being just right for a flash back. 544 posts and the beat goes on. AHS equipment is a very good product, and this will be resolved.

whistlenut wrote:The issue is definitely about the height of the fire in the burn chamber, ashing rates, and conditions being just right for a flash back.

Conditions also have to be just right for a safe efficient fire. When those conditions vary which they will with changes in draft and coal and firing rate then the unit has to have designed into it means to compensate for those changing conditions. That it works well most of the time is not good enough. The other alternative is to assume that the dangerous condition will always be there and provide something like a forced draft purge period after every firing period to rapidly exhaust any gasses. Either that or a more measured timed shut down.

franco b wrote:provide something like a forced draft purge period after every firing period to rapidly exhaust any gasses.

37 pages of comments & we come back to my very first post on page one of this discussion: "I built an anti boom device that fingers the door open for 10 seconds each time the fan tries to shut off. That purges the boiler and prevents booms."

I use it in the Fall & in the Spring. During the cold of winter it isn't needed as the fire stays high. As the weather warms & I notice the fire dropping I turn it on. I have never had a puff back when my anti-boom device was turned on, but I've had a few impressive ones when it wasn't! I'd think for about $20 AHS and Axeman Anderson could build a similar gadget. I'd leave it on all the time, but it makes quite a clank when the solenoid slams the door open.

Let's put the the puff backs in perspective. They can happen in any coal appliance. Just look at all the puff backs reported in the hand fired threads on this forum. Also remember the "Anthrtube" style of boiler was designed in the mid 1940's. The engineers only had the technology of the day for a control system. A simple temperature sensor measuring radiated ash temperature. I'm sure they really would have liked to measure and control the "burn height" in the Anthrature. But they couldn't do that, all they could do is measure the ash temperature. Is it related to burn height? Sure it is but not in a perfect way. It's not a adjust it once control. To many variables, some unknown. For example, let's say you adjust things just right using red ash coal, then switch to white ash coal. The settings are not going to be right. The ashing temperature sensor is going to see a different thermal resistance between it and the burning coal. Why? Because the density of white ash is different than red ash coal. You will need to make adjustments.

How did the engineers deal with this problem long ago? Simple they made the boiler tough, it's built like a tank. No puff back is going to phase the boiler one bit, it's just like a little fart. The inspection flapper door is a different story. It's design has been changed to prevent it from being blown ajar. For the AHS coalgun, first with a bar across the flapper door which limits the door's outward travel and then a further improvement with the "tombstone" cover design. Again a robust, take a puff back, tank like design.

The user many decades ago knew how to burn coal. They grew up with coal, they knew about combustion basics. Maybe not in engineering terms but they certainly knew they had to have a ignition source and air control in their hand fire stove or boiler. Grandpa taught them that. When they moved up to central heat and a stoker they already knew what to look for. Keep the fire high and have good draft. They observed and adjusted the Anthratube accordingly.

Chimney problems? They didn't have any. They had high masonry chimneys with good draft. Not the wimpy metal chimney of today. How about the stove pipe of old? It was thick gauge. Same for the barometric damper, if they had one. Puff back a problem? Not at all. It just blew the fly ash from the stovepipe into the chimney. Just made spring cleaning easier.

Today. The common knowledge of burning coal is gone. What people might know is wood or pellet burning. Different animal. Little other than the starting match applies. Today's chimney and stove pipe. People are cheap. They don't want to spend the money and build it right. Some end up with designs that will not survive a puff back. Why? They didn't learn enough first. I know of no Coal Gun installation with a masonry chimney, heavy gauge stove pipe and barometric damper installed with the concentric stovepipe method that has any problem with puff backs.

Today's control technology. Could I design a better control system. Absolutely. It would have a linear array of thermocouples integral to the anthratube measuring the burn height. I'd have a variable speed combustion blower, boiler water and stack temperature sensors, and a microcontroller with an adaptive software control logic. But why? It would cost a fortune. Just install and operate the Anthrtube like our Grandpa did!

For a Coal Newbie, you sure have lot a of coal equipment listed. What is your real history with coal?

It's no secret for 26 years in England we heated with coal. AGAs, Rayburns, tortoise stoves and the like. The coal was OK bit in the North of England to great Anthracite in Wales to even better Phurnacite (although that product is cr ap now as it is imported). In the South it was coke as coal was used to extract natural gas first post WWII. Not bad heat at all once you got it going and it was dirt cheap as I remember. However, over here it's all different, so I was a non coalie from 1970 to 2008 as I did not burn an ounce of coal but like riding a bike you remember. I am trying to heating about 15000 sq ft of house, barn and related buildings (some unsulated) so one BIG stove can't do it, it's a nightmare. Please come and visit me and consult, I'll even provide free beer. There, now I've come clean.

Now lets' look at you. NH is about 10,000 sq miles. Your heat output from your stove list must be in the millions of BTUs. I know you don't heat Mt Washington as I have seen photos on the TV. So do you heat Concord and all points South?..... HAAHAHHAAHHA. What a tangled web we weave.

Final thought Yanche and whistle, your IQ is, I don't care - fine. I know some on this board that would not agree with you.

Freddie, use should patent you idea and sell them at a profit for yourself I think there is a definate demand.

NWBuilder wrote:Freddie, use should patent you idea and sell them at a profit for yourself

Naaaa.... a patent would involve lawyers & I have little use for lawyers! I gladly give the idea to whomever would like to use it. I'm saving my time with lawyers for a real million dollar idea!

Yanche wrote:Just install and operate the Anthrtube like our Grandpa did!

A lot of those grandpas wound up dead from CO poisoning too. Most smoke pipe was 26 gauge just like now.

Hand fired stoves can easily be operated in a manner that does not result in puff backs. If a unit that bills itself as automatic needs the attention of a hand fired stove then it is not automatic. The cheapest boiler is strong enough to survive a coal gas explosion which proves nothing. A fix does not have to include expensively engineered solutions as Freddy has shown.

franco b wrote: If a unit that bills itself as automatic needs the attention of a hand fired stove then it is not automatic.

I don't think the AHS boiler "bills itself as automatic". Granted it is billed as a stoker and the stoking process is automated but that is a far cry from a fully automatic appliance

Just to note some of the obvious differences from a fully automatic appliance:
1. Coal must be regularly added to the hopper;
2. Ash must be regularly removed; and
3. The ashing control, whether timer operated or controlled by a temperature sensor, must be adjusted for the seasonal conditions, and variations in coal quality as well as the specific installation.

I think the defect, to the extent there is one, is that the manufacturer has failed to fully explain the limitations of the controls installed. While the thermograte control has some advantages over the timer control for ashing and to a limited degree adjusts for some cirumstances it is far from a fully automated control. I think AHS can be fairly criticised for not more clearly informing the buyer of the limitations of the thermograte control and for not more clearing educating the buyer/operator of how to appropriately deal with the limitations.

Maybe AHS should just install a spark plug that fires every few seconds to keep the gasses from accumulating

PRengert wrote:Maybe AHS should just install a spark plug that fires every few seconds to keep the gasses from accumulating

Seems practical! As long as they don't over-design it and leave us with the choices of advancing and retarding the timing in order to have the spark plug firing before the fire reaches top dead center of the draft port door, at top dead center of the draft port door, or after (above) top dead center of the draft port door.