Coalgun- Puff backs & Explosions

I figured out why others couldn't see it. It was an image part of a private message I posted. That post has been deleted, but the image still appears in my control panel "Manage Attachments". A bit strange, that I could see it, but others couldn't even when I gave the fully resolved link.

BTY my installation no longer is as shown. Stove pipe now goes directly to a second chimney and I have a true primary secondary piping system with the coal boiler circulator the return.

Here's the image re-posted and cropped to show the belt motor area.

I had a big puff back last night and this time the house smelled like sulfur. I am heading to the store today to pick up a cailing fan control switch so I can regulate the motor speed of my ash dump motor. I'm running out of options here. I'll keep everyone posted.

rychw wrote:I had a big puff back last night and this time the house smelled like sulfur. I am heading to the store today to pick up a cailing fan control switch so I can regulate the motor speed of my ash dump motor. I'm running out of options here. I'll keep everyone posted.

Look at the amp rating on the motor's data plate, it should be under 2 amps. Get a controller that meets or exceeds that rating.

hope everything works out alright for you rychw, i recently just switched to a mix of nut and pea, and there is some big chunks of nut mixed in. I would say its probably a 60/40 mix, 60 pea 40 nut. I got a deal because it was left over, anyway, i have noticed while coal is being dumped on the fire it is a lot less at a time due to the larger chunks of nut mixed in, pea just isnt flooding the fire like it use to...havent had any puff backs and have also raised my ashing to 130. With burning buckwheat and sv set to 130 i had burps, now with burning the pea nut mix i havent had anything so far

Been a while since I've read the posts. I left a post in regard to me keeping my fire as high up as I can so the fire is about 2" below the funnel outlet. I burn buckwheat and my flapper is the old style with no hole. I also have the grate timer which I adjust in relation to outside temp to keep the fire high. during high demand in cold weather I very seldom have to adjust it to keep the fire where I want it. One thing I have to mention, when the blower turns off and the flapper opens, I can hear and see the blue coal gas burning a nice flame. The key here is to see the blue flames. If I don't, the coal gas is not being burned and can travel into the flue by natural draft then get ignited. BOOM!!!! It's been fine this year with no booms as long as I maintain my fire high and nice blue flames. I hope this may help thanks for listening.

coaledsweat wrote:Look at the amp rating on the motor's data plate, it should be under 2 amps. Get a controller that meets or exceeds that rating.

My grate motor plate says it draws 1.4 amps. I picked up a ceiling fan control rated at 1.5 amps. I wanted a higher rating but that is all they carried. I am going to install the rotary switch tomorrow and see how the boiler reacts with the grate moving at a slower speed. Hopefully there will be less new coal allowed into the burn tube and less chance of booms. I'll keep you posted.

wouldnt it just run twice as long due to temp taking longer to increase and in the end there will be same amount of coal put onto fire just at a slower rate?

dchartt wrote:wouldnt it just run twice as long due to temp taking longer to increase and in the end there will be same amount of coal put onto fire just at a slower rate?

The assumption is that the amount of coal added slower will prevent the fire from being smothered by too much fresh coal added to the tube. I have noticed that if I turn off the ash motor in the middle of dumping, the thermo sensor temperature rises anyway, just not as fast if the motor is running. This is a test like all the other things I've tried. Since AHS isn't trying to help us and solve the problem, we have to do it by trial and error.

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rychw wrote: Since AHS isn't trying to help us and solve the problem, we have to do it by trial and error.

I hear ya on that one....keep us posted

dchartt wrote:wouldnt it just run twice as long due to temp taking longer to increase and in the end there will be same amount of coal put onto fire just at a slower rate?

Yes, of course. But by adding the same amount of coal over twice the period of time, the gases will be dispersed slower reducing the risk of rising to an explosive quantity.

My ideal control system for a stoker boiler would be:

1. Measure delivered BTU
2. Feed it replacement coal equivalent to that required to make up the delivered BTU.
3. Remove ash corresponding to the burnt coal that produced the delivered BTU.
4. Do it all slowly and continuously.

What do we have now.

For #1. A fixed set-point aquastat. Starting at the hi limit you wait until the low limit point is reached.

For #2. You start burning more coal by turning on the combustion blower. This feeds more coal in the column because ash occupies less space allowing the fire and the fresh coal to fall lower.

For #3. At some fixed but adjustable fixed time (ashing timer models) you start removing ash. This also has the effect of disturbing the coal fire and adding more coal. With thermo-ash models you begin ashing a some fixed but adjustable radiated ash temperature.

For #4. None of the above steps are smooth, but are abrupt events which have time constants much, much quicker that a content burning fire would like. The feeding of coal and ash remover are also disjointed.

It all begs for a modern control system.

What can we do with what we have?

1. Make the aquastat differential a minimum. This will get the combustion blower burning sooner, hopefully reducing how much the fire get disturbed because the blower cycles on and off more frequently.

2. Lower the ashing rate by lowering the grate motor speed. "rychw" is trying this.

I all this fails then what's left? Changing the concentration of coal gases so that an explosive mix doesn't exist, i.e. a purge of the boiler firebox. A control method is still to be developed.

Yanche wrote:What can we do with what we have?

1. Make the aquastat differential a minimum. This will get the combustion blower burning sooner, hopefully reducing how much the fire get disturbed because the blower cycles on and off more frequently.

2. Lower the ashing rate by lowering the grate motor speed. "rychw" is trying this.

I all this fails then what's left? Changing the concentration of coal gases so that an explosive mix doesn't exist, i.e. a purge of the boiler firebox. A control method is still to be developed.

I would add one element to the above list:

3. Raise the level of the burning coal in the firebox so that the coal gas is always exposed to an ignition source. To put it another way continuously burn off the volatile gases rather than letting them accumulate.

I intalled the ceiling fan switch today in circuit with the ash grate motor. I've set it at the middle setting since there are three speed options. I have had puffs these last two weeks, some small some quite big. I will monitor the function of the grate motor at the slower speed and hope the puffs are eliminated. I've noticed the there seems to be a correlation between the frequency of the puffs and the boiler running to reheat after domestic hot water call. That is interesting since the fire would not be as strong when reheating from hot water call as it would be from heat call. Again I'll keep everyone posted.

thats very interesting, I dont have a DWH coil, havent had any puffs in awhile had a few here and there awhile ago but nothing consistent