Coalgun- Puff backs & Explosions

What does it mean in the Axeman-Anderson manual when it says that: "Fire too thick may cause puff-back"

lsayre wrote:What does it mean in the Axeman-Anderson manual when it says that: "Fire too thick may cause puff-back"

I read that as too much burning & unburned coal in the tube. If you ash the fire too aggressively you will end up with a lot of unburned coal on top of the fire.

AA units allow you to adjust the on/off setpoint of the grate ANDthe amount that the grate moves in relation to each rotation of the auger tube. Freddy had some "booms" when he first got his AA130 online, I believe he cured it by changing the grate setting (e.g. 3 clicks to 2).

lsayre wrote:What does it mean in the Axeman-Anderson manual when it says that: "Fire too thick may cause puff-back"

Thick fire = Low Fire
Thin fire = High Fire
Axeman's manual has been around for a long time and uses different terminology than AHS.

There are three sections in the fire-tube basically...the raw coal layer, the fire layer and the ash layer. They are not totally distinct sections, but for adjustment purposes that is how they are described.

When the fire is thick then the ash would be thin and vice versa. In the thick fire case the ashing setting would be too high and need to be lowered.

To take this a step further...(this was mentioned earlier) a thick fire has consumed most of the oxygen deeper in the fire bed plus a quantity of raw coal has just been added on top and is out-gassing volatiles,so with the lack of oxygen in the upper fire bed the stage is now set for a" woomph" when oxygen eventually is allowed to be introduced.

BTW: All boilers have different firing cycles relative to the different loads of the dwelling and of the seasonal demands. Pretty hard to just have one setting and be good all season.

I know AHS boiler owners would just love to have AHS mfgr tell them their magic setting for their boilers, but they can not...you will just have to discover those settings on your own by experimenting.

Thanks McGiever! I just dropped my ashing SV from 120 to 115. Trying to raise the fire some. I noticed that after my huge whomph this evening there was no red flame (no flame at all) to be seen via the flapper port. Only jet black was seen. With Blaschak I always saw an orange glow with dancing blue ladies through the flapper port right after the fan cycled off. With Blaschak my SV was at 130.

Larry,
I burn Blackshak and had all my Baro explosions with Blackshack. I still do not think it is the coal, I think it has to do with fly ash building up somewhere in the funnel in the exhaust chamber.

Mac

AA130 burning buckwheat. Came back from vacation last week to find my baro 5 feet away in peices, cast clean out door blown out of chimney, and another unused pipe blown out of the flue. Figured it was because my son hadn't taken ashes out in a week.

The following day it exploded while I was standing in front of it. Scared the *censored* out of me. Happened about 10 seconds after shutdown of the blower. Did it again an hour later.

Backed asher down to 135°F and no more booms. Don't know if that's all the remedy. It had been fairly warm and a low pressure system. I've felt downdrafts from my chimney with conditions like these. I'd sooner attribute the booms to that but the more ash makes sense as well.

cabinover wrote:AA130 burning buckwheat. Came back from vacation last week to find my baro 5 feet away in peices, cast clean out door blown out of chimney, and another unused pipe blown out of the flue. Figured it was because my son hadn't taken ashes out in a week.

The following day it exploded while I was standing in front of it. Scared the *censored* out of me. Happened about 10 seconds after shutdown of the blower. Did it again an hour later.

Backed asher down to 135°F and no more booms. Don't know if that's all the remedy. It had been fairly warm and a low pressure system. I've felt downdrafts from my chimney with conditions like these. I'd sooner attribute the booms to that but the more ash makes sense as well.

Wow, you gotta ask yourself is this worth it? Do the keystoker and EFM guys blow baro and flues apart? I think it is time for some research and development from the manufacteurs. If not users are going to move on with another product before some one is hurt.
The outdoor boilers are looking better from a safety staindpoint and from what I hear are getting better with extended burn times.

Mac

Yanche wrote: It along withe the A-A boiler is unique in the way it burns coal. Coal is burned in a tube, hence the term "Anthratube". When this method of burning coal was researched in the early 1940's there was nothing like it, in fact some of the experts at the time were surprised by the test results. A report was published in 1945 on the Anthratube. I've uploaded a copy. Much of the development work was done by Anthracite Industries, Inc. A company long gone.

Ya wonder why the company is long gone!!!!!

They discovered back in the 1940's that unless you stayed on top of a machine with this operating characteristics that it would blow. When I was in the Navy (70-74) I was on a ship loaded with experimental equipment including the boilers. If someone thought something up they would ship it to us with the instructions to install the piece of equipment, run it under real world conditions and record the results. If we couldn't make it run we were to record why we couldn't make it run and put it back in the crate along with our report and notify the Engineering Officer. Our boiler techs were top notch at getting weird pieces of equipment brought to the boiler room with those instructions. If someone behind a desk somewhere wanted something tested in the real word, they sent it to our ship.

The boilers we had on the ship were called Pressure Fired boilers. They operated at 1200 PSI with 1000 degree superheat. Great when they worked correctly under automatic control. Fast response time, unbelievable recovery time after the Machinists Mates spun the main throttle to the full open stops. The fuel we burned was JP-5 commonly known as jet fuel. No bunker C or black oil of any grade for these babies. JP-5 jet fuel only. Combustion air was supplied to the boilers on start up by a turbine spun by an electric motor then switched to a steam turbine when we got steam up then it was switched to operate as a HUGE turbo charger driven by the exhaust gasses from the boiler. All this was on one shaft with a monster 10 row centrifugal wheel air compressor which delivered unbelievable amounts of combustion air. The whole supercharger rig was mounted on what looked like car coil springs only they were 3 feet in diameter.

The boilers were the epitome of it looked good on paper but in the real world, not so good. They were great when the automatic controls were functioning correctly. There were only a couple of other ships that had this technology and we had to go to special schools before we could even go down the ladder into the boiler room. We ended up documenting that it was humanly impossible to operate the boilers in manual control with a normal fire room compliment. Everything happened too fast and it would get away from the best console board operators we had in no time flat.

I learned a term while I was in called " sailor proof. " For a piece of equipment to function properly off the test bench and in the real world the thing had to be sailor proof. If you had a sailor with minimal training and he/she could operate it without blowing it up or breaking it, it was deemed sailor proof.

Reading the 500 plus posts regarding this technology and the problems being experienced would lead one to believe that the consumer is doing the real world R & D for these companies. The posts on this equipment is technically top notch with some of the best engineering concepts I have ever read. The number of people and the spread of knowledge exhibited is phenomenal!!

However all the posts are documenting that if you depend on the automatic control settings, they still go boom. What I have been seeing is the key is the fire height and you need to visually verify it whenever anything changes as it ramps up and down. That kind of defeats the purpose of automatic controls doesn't it. This whole scenario reminds me of my navy days in the boiler room when we tried and tried and tried to get something to work and came to the conclusion that unless you sat right there and watched it and made manual control changes it was going to bite you.

Maybe it's time to read that 1940's post and tell the companies to do their own real world R & D testing.

All it is going to take is for someone to get a big boom, soot up their premises with coal dust, ash, and flying metal. They turn in a claim to their insurance company that pays for the damages and clean up. Then the insurance company will go back to Coal Gun or AA to recover the money they payed out. It's called subrogation when insurance companies go back to the manufacturer for money. You know the phrase "Money talks." Until you can get these companies to start kicking out enough money for damages, nothing will change.

In order to get their attention I recommend every person that has experienced a boom with damages or time spent cleaning up send a bill to the company. If they get enough of these then you will get somewhere with design changes. If you change the design and something happens, then they can blame it on you. Remember this,,,They have already blamed it on the coal your using. Until they get hit in the pocket book, these posts are going to top the 1000 mark and keep going.

Rev. Larry

A new experience for me today. I just observed two back to back (separated by only about 2=3 seconds) flaming puff-backs while the fan was actively running during a heat call. Previous observation had puff-backs only happening very shortly after the fan had shut off (about a minute or two after the puff-backs). Again the manometer is indicating about 0.03" to 0.035" of water column draft. And (crazy as this sounds) about 20 seconds after the fan did finally shut off (and there were no puff-backs) I got up enough nerve to take the tombstone cover off and I saw orange glowing coal with blue ladies through the draft port cover. All of this with my SV at 115 degrees. Very strange!

I don't know enough about these boilers to know whether this is even possible, but has anybody tried using a flame detector (as used on an oil burner to prevent an oil flood if the flame goes out) to control a blower that would introduce overfire air until the blue ladies are visible after fresh coal is added?

If that doesn't make sense I'll go back to sitting quietly.

Mike

macdabs wrote:

cabinover wrote: Wow, you gotta ask yourself is this worth it? Do the keystoker and EFM guys blow baro and flues apart? I think it is time for some research and development from the manufacteurs. If not users are going to move on with another product before some one is hurt.
The outdoor boilers are looking better from a safety staindpoint and from what I hear are getting better with extended burn times.

Mac

It's still worth it to me. It's in my garage and I've been using it for what...four years now with only four of these events. Some of it is a different coal apparently and the rest is operator adjustment. I don't consider these units to be maintenance free. If I wanted that I'd continue using my propane furnace...and I get propane for free basically working for a propane company.

I like the continuous heat and all the hot water I can use. I'll do a little bit of seasonal adjustment to keep that. Beyond these little things, it's simply load every four days, take the ashes out the same time. Done.

Pacowy wrote:I don't know enough about these boilers to know whether this is even possible, but has anybody tried using a flame detector (as used on an oil burner to prevent an oil flood if the flame goes out) to control a blower that would introduce overfire air until the blue ladies are visible after fresh coal is added?

If that doesn't make sense I'll go back to sitting quietly.

Mike

Nothing wrong with thinking outside the box. One could even be so bold as to recommend removing the hopper and installing an EFM conversion stoker in the ash compartment...but we won't go there.

I have had some very "preliminary" but worthy feedback from AHS, and I've combined it with the Axeman Anderson information suggesting that the combustion tube should be nominally half way "ashed up" and I've concluded that if I'm understanding both sources correctly its to a great extent the amount of ashes your coal yields that determines where the fire most often resides within the combustion tube. I'm easily getting less than half the ash volume with my current coal as with the coal I used last season. That in itself means intuitively that for any given SV setting there should be generally far less ash sitting underneath the thin layer of burning coals with my current coal (vs. my previous coal), and that means the coals are burning at well lower than mid-level in the tube, and that means puff-backs. Lowering the ash grate motors trigger temperature is done in an effort to raise the ash level in the lower end of the combustion tube, and that raises the level of the fire, ideally to where the over the fire air from the draft port can have beneficial effect in sweeping away and/or igniting CO and other volatiles. If that means going lower than the minimum manual permitted SV of 120 degrees due to extremely low ash coal, then such might be required (though I say this with due caution and I strongly recommend consultation with AHS or AA before doing so). A coal with very little ash content should require a low to perhaps very low SV set-point (ashing temperature), and at the opposite end of this spectrum an abnormally high ash content coal might need a setting of 140 or perhaps even 150 degrees or more. In a nutshell, less ash content means you will need to adjust your boiler so it ashes less or less often, and greater ash content means you will need to adjust it so it ashes more or more often, all in an effort to keep the fire at or near mid combustion tube level, and also in an effort to achieve and then maintain a proper bed of ash beneath the fire layer. The generally recommended SV of 130 degrees for the AHS models is clearly for your "average" run of the mill percentage of ash content (ash volume) anthracite. What needs to be avoided in all of this is driving the fire too high and potentially into the hopper, or too low and into puff-backs. By this intuitive logic it is not only the draft level driving puff-backs, it is also the coal (or more properly, the percentage of ash content by volume generated by the coal).

As much of this is clearly from intuition, and intuition does not often make for good science, please let me know if this line of intuitive reasoning regarding the ash content of the coal and puff-backs is hogwash.

Makes perfect sense to me Larry. Last year's coal would generally do a full ash pan for every 300# of coal burnt by volume. This year it's looking more like 3/4 of an ash pan per hopper full.

It's entirely possible that my ash wasn't deep enough as anyone with an AA or AHS knows it's nigh impossible to see much of the burn chamber except when you're starting for the season. You can get an eyeful at the flapper door but that's about it.

Maybe we need a see-through window in the old gals?

Rob R. wrote:

Pacowy wrote:I don't know enough about these boilers to know whether this is even possible, but has anybody tried using a flame detector (as used on an oil burner to prevent an oil flood if the flame goes out) to control a blower that would introduce overfire air until the blue ladies are visible after fresh coal is added?

If that doesn't make sense I'll go back to sitting quietly.

Mike

Nothing wrong with thinking outside the box. One could even be so bold as to recommend removing the hopper and installing an EFM conversion stoker in the ash compartment...but we won't go there.

Blasphemy