AHS S130 Coalgun- Puffbacks & Explosions

Rob R. wrote:Maybe I haven't talked to enough AA owners, but my impression is that the Axeman Anderson units don't have nearly the amount of problems with puff-backs as the Coal Guns.

The feed rate is adjustable on the Axeman. It is not on the AHS.

Rob R. wrote:Maybe it's just me, but there is seems to be a lot of variability in the settings required for boom-free operation of the S130 and S260.

I'll comment my thoughts on this...

The Thermocouple probe on both the AHS and the AA's are functioning as a Proximity type heat measuring device.
Since it works some distance from the source of heat that it is required to get it's reading from there comes in some variables.

The pictures that I have seen of the AHS thermocouple and it's mounting configuration look to allow some movement if it were to be inadvertently disturbed. Even during the manufacturing process and shipping and handling there could be slight movements to the proximity location.

I would not have a hard time believing that a Factory Recommended Setting could be somewhat inaccurate.

And as I stated earlier in this thread, Forget any recommended setting and make your own setting based solely on the appearance of the fire's position, then make a note of the findings.

The problem with the AHS Coalgun boiler is: The Dwyer controller and ash monitoring thermocouple constitute an open loop control system. The design really needs to be changed to a closed loop control system; which, continuously monitors and adjusts the ashing SV with a second thermocouple monitoring temperature in the sight tube area---keeping the fire height at its optimum. This needs to be done before an AHS S130/S260 owner's house gets filled with exhaust; and, a whole family dies of CO poisoning---fortunately I've always been home when major KABOOMs have occurred. I'm not sure how my wife and children would respond if a major puff back occurred in my absence. I can only hope they pay attention to the CO alarm; and, get the heck out of the house.

AHS if you're listening: I'll be happy to design the solution for you. I could probably do it on a napkin while at lunch.

lsayre wrote:I was told by my coal supplier that Harmony coal has a bunch more volatiles in it than does Blaschak (and I have no means whereby to verify or refute this), so now that I'm burning straight Harmony I will see if that changes anything. I've been on straight Harmony since September 29th, post my boiler clean-out and re-firing.

I've noticed that the intensity of the mild "whoomps" which I've heard almost immediately after the fan motor cuts off has increased, and I've observed that this is not anything related to poor draft, as the manometer indicated that the draft was holding fairly steady at between 0.03" and 0.04" when I most recently observed the phenomenon from a close proximity. I'm now getting more convinced that the reported higher volatile content of the Harmony pea might indeed be a contributing factor, as this is clearly different from what I experienced all last season with Blaschak pea and/or a blend of Blaschak and Stockton pea.

I just opened the sliding cover on the small "air over the fire" window (the small circular opening that resides within the larger oval flapping fire tube port cover) nearly half way (it having been open only a sliver prior to this change), and I've also set back my ashing SV temp from 130 to 120 degrees F.

lsayre wrote:

lsayre wrote:I was told by my coal supplier that Harmony coal has a bunch more volatiles in it than does Blaschak (and I have no means whereby to verify or refute this), so now that I'm burning straight Harmony I will see if that changes anything. I've been on straight Harmony since September 29th, post my boiler clean-out and re-firing.

I've noticed that the intensity of the mild "whoomps" which I've heard almost immediately after the fan motor cuts off has increased, and I've observed that this is not anything related to poor draft, as the manometer indicated that the draft was holding fairly steady at between 0.03" and 0.04" when I most recently observed the phenomenon from a close proximity. I'm now getting more convinced that the reported higher volatile content of the Harmony pea might indeed be a contributing factor, as this is clearly different from what I experienced all last season with Blaschak pea and/or a blend of Blaschak and Stockton pea.

I just opened the sliding cover on the small "air over the fire" window (the small circular opening that resides within the larger oval flapping fire tube port cover) nearly half way (it having been open only a sliver prior to this change), and I've also set back my ashing SV temp from 130 to 120 degrees F.

I will be experiencing the reverse of what you will be experiencing.
Last year I burned Harmony Buckwheat in the Axeman-Anderson, and this year it will be the Stockton Pea.

As my AA only has a solid blank flapper cover I used a paper binder clip to always allow a good crack for the "over the fire air".

The volatiles in Harmony coal are not too forgiving with improper fire position in burn-pot...but there sure are a lot of fan induced "blue ladies".

McGiever, do keep us informed as to whether the Stockton coal changes anything for you in the puff-back area, as well as how it performs in heating. If I had enough room for a full T/L delivery (my problem being how to get the truck onto and off of the homes lot, and not having room for the coal) I would consider getting a T/L of Lehigh, as it advertises its anthracite as being very low in volatiles. Lehigh will only accept orders for full T/L's.

I stood by and watched this morning as the boiler cycled on due to a thermostat call. After it recovered to 180 degrees and the fan cut off there was no hint of a whoomp! All I heard was the soothing crackling of coal, and there was a nice hot and toasty glowing fire visible through the fire tubes view port flapper (whereas yesterday morning after I observed the whoomp sound under similar circumstances all I could see through the flapper was a scant few glowing coals among a sea of black nuggets). One test does not lead to certainty, but it seems that the changes I made may have tamed the Harmony beast, or are at least changes in the right direction.

The only difference between yesterday mornings observed heat cycle and this mornings observation was that yesterday the boiler ashed throughout most of the firing cycle, whereas this morning it only hit its ashing temp. of 110 degrees (10 degrees below the SV set-point of 120) about 2 seconds before achieving 180 degrees and shutting down, so it did not ash.

Well, since it just missed ashing on the previous thermostat heat call, it ashed hard and long on this last one. Results at the end of the firing cycle when the fan shut off: Success, only crackling coal and no flaming 'whoomp' sound.

Last year I started burning the Harmony Buckwheat in a FHA furnace w/ an inclined/flat grate stoker...nice tall blue flame, but never a "whoomph". By design, there is never a pile of fresh coal added on top of an intense fire with these type stokers, so... no drama there.
One of the reasons I got buckwheat was due to knowing I would be changing out the FHA furnace to the boiler during mid heating season and knew the buckwheat would work in them both.

About your observation yesterday and today,just as with any hand fed coal unit,(which is really the same as w/ these boilers) you need a little exposed open flame ( your "crackling") to consume the volatiles as they are produced, instead of accumulating throughout the boiler cavity and part way up the flue/chimney and then get the delayed source of ignition.

Now you are seeing that the recommended setting number is less important than is the actual fire position.
A good setting is whatever setting that will get the fire high enough to keep burning off the volatiles at the time the fan turns off.

I just picked up the Stockton Pea yesterday and also I have not yet lit up the AA for the season...so I'm yet to see how that coal works out for me.

lsayre wrote:I stood by and watched this morning as the boiler cycled on due to a thermostat call. After it recovered to 180 degrees and the fan cut off there was no hint of a whoomp! All I heard was the soothing crackling of coal, and there was a nice hot and toasty glowing fire visible through the fire tubes view port flapper (whereas yesterday morning after I observed the whoomp sound under similar circumstances all I could see through the flapper was a scant few glowing coals among a sea of black nuggets). One test does not lead to certainty, but it seems that the changes I made may have tamed the Harmony beast, or are at least changes in the right direction.

The only difference between yesterday mornings observed heat cycle and this mornings observation was that yesterday the boiler ashed throughout most of the firing cycle, whereas this morning it only hit its ashing temp. of 110 degrees (10 degrees below the SV set-point of 120) about 2 seconds before achieving 180 degrees and shutting down, so it did not ash.

Larry, your observations and experience are perfectly consistent with what would be expected. If you look at the "Antratube" portion of the document 1945 Housing and Heating Conference posted by "steamup" there is a terse explanation of burning coal in a slender column. The important combustion physics are this, "it was found that Anthracite burns approximately 4 to 5 pieces deep. In other works, the oxygen in the air for combustion will pass a given fuel amount of fuel surface before it is completely completely consumed." This quote gives a key to understanding what's happening. As the Anthracite is burned not all the oxygen in the fan induced air is used up. This means if the burning Anthracite is low in the tube the coal above the burning portion is being pre-heated by the combustion gases, expelling volatiles and creating carbon monoxide. This gas is sucked up by the combustion blower and the heat in it transferred to the boiler water as it passes through the 2 pass boiler tubes. All is well and good. But the carbon monoxide gas is combustion-able. When the level of the fire in the column is high the carbon monoxide is burned, when it is low, all of it is not burned. What is not burned also travels through the boiler and out the chimney. If there is a lot of it you get the rotten eggs smell. When the fire is low, more carbon monoxide gas is produced because there is more raw coal, being heated. Now when the combustion blower stops, so does the movement of the carbon monoxide. It's lighter than air so, some of it must mix with the air from the now open flapper door. You have all the ingredients for combustion (fuel, heat and oxygen) so boom it goes. The important operational characteristic is to have the fire high enough to burn all or most of the carbon monoxide while the combustion fan is running.

I believe additional controls for adjusting the fire high would be helpful to establish it in the right position. Stopping the grate motor would raise the height, operating it more would lower it. I also believe this control should be independent of the ashing set point temperature and hysteresis. Right now all of us are suggesting different set point temperatures, temperatures that have worked for us, but it's likely just a method for moving the position of the fire.

I agree with much of what you say. Do you see any correlation between the level of volatiles present within the coal itself and the post fan ignitions, or is it strictly a CO phenomenon?

I don't have many data points, on the volatility of coal. I've only burned from three sources Superior, Blaschak and UAE Harmony mine. The Superior was red ash, burned hot and I had lots of puff backs. The other two are white ash and few or no puff backs.

My Harmony ash is pronouncedly red throughout. My Blaschak and Stockton only had occasional red spots interspersed amongst the gray ash.

Would this type/brand of boiler have less puff backs if it were running hard vs idling? Maybe these boilers operate best when under load and are not suited for light loads and moderate temperatures.

Dewey, did you have as many puff backs when you had the S130, I know that unit was too small and you replaced it with the S260?

Based on my observations from reading these posts and others over the course of several years, and maybe being unbiased since I have no boiler, it seems that I would take the following preventative actions, as a minimum, if I were to buy one.

A). Have a custom one-piece exhaust made from the same alloy-steel tubing used for heavy-duty vehicle exhaust systems welded into place. This way, it would be impossible that a puff back could blow apart the boilers exhaust resulting in spilled and deadly CO build-up in a home.

B). Install a Photohelic that would activate a fan and an alarm system, drawing in fresh outside air, if the draft were to fall below a set point. This could prevent CO poisoning which we all value far more than saving money on heating our homes.

I actually believe that the Whoomps come after long and hard runs combined with heavy ashing cycles. In my opinion both are required. But then again, I did not have this issue with Blaschak, so I believe that the 3 requisites for a puff-back are volatile coal, a hard run of the fan cycle, and heavy ashing.