Coalgun- Puff backs & Explosions

Re: Help: I Have Repeated Explosions!!

PostBy: rychw On: Sun Nov 27, 2011 9:43 am

ValterBorges wrote:What temp is your boiler water running between?
How high is the fire in the pot?
How much fresh coal is on top?
What is the draft?
Do you have make up air?
Is the port small hole open?


Boiler temp 165
Fire 3/4 way up tube
Full hopper
Excellent draft (30ft chimney)
Plenty of make up air in this old house
Small port open 100%

lsayre wrote:Does your ash grate motor stop running when your fan shuts off? This seems to be a major key to eliminating the puff-backs.


Yes, I just wired it that way last week.

I'm hoping the lower ash dump temperature will eliminate the explosions. I'll keep you posted.
rychw
 
Stoker Coal Boiler: AHS 130
Coal Size/Type: Pea
Stove/Furnace Make: AHS
Stove/Furnace Model: 130

Re: Help: I Have Repeated Explosions!!

PostBy: lsayre On: Sun Nov 27, 2011 10:02 am

I've just been reading the thread where members are relating their stories of explosions in their hand fed stoves. I currently have a thread running that suggests that the Coal Gun shares many design and function features with hopper equipped hand fed stoves. When viewed in this light the Coal Gun explosions do not seem all that out of line. Perhaps we can learn from the reasoning behind the hand fed stove explosions and relate them to the Coal Gun.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (It has been fixed!)

Re: Help: I Have Repeated Explosions!!

PostBy: McGiever On: Sun Nov 27, 2011 11:50 am

lsayre wrote:I've just been reading the thread where members are relating their stories of explosions in their hand fed stoves. I currently have a thread running that suggests that the Coal Gun shares many design and function features with hopper equipped hand fed stoves. When viewed in this light the Coal Gun explosions do not seem all that out of line. Perhaps we can learn from the reasoning behind the hand fed stove explosions and relate them to the Coal Gun.


There is a "Combustion Triangle"...where all three conditions must all be met to have combustion. It needs a source of fuel, sufficient heat to vaporize that fuel and a source of sufficient oxygen to sustain the combustion...take away at least one piece of the triangle and the combustion process is compromised.

FUEL_HEAT_OXYGEN

It is really quite simple, carbon monoxide gases and other volatile gases that have accumulated [FUEL] and are starved/lacking enough oxygen...and then when suddenly the [OXYGEN] is available you get a...BOOM! The ignition source [HEAT] is a given in any robust fire pot.

The Coal Gun appears to sometimes create a condition of insufficient oxygen and surplus volatiles above the coal-bed after the fan shuts down. Correct this and problem is solved. :)
McGiever
 
Stoker Coal Boiler: AXEMAN-ANDERSON 130 "1959"
Hot Air Coal Stoker Stove: HARMAN MAGNUM
Hand Fed Coal Stove: RADIANT HOME AIR BLAST
Baseburners & Antiques: OUR GLENWOOD 111 BASEBURNER "1908"
Coal Size/Type: PEA / ANTHRACITE, NUT-STOVE / ANTHRACITE
Other Heating: Ground Source Heat Pump
Stove/Furnace Make: Hydro Heat /Mega Tek

Re: Help: I Have Repeated Explosions!!

PostBy: lsayre On: Sun Nov 27, 2011 12:07 pm

McGiever wrote:There is a "Combustion Triangle"...where all three conditions must all be met to have combustion. It needs a source of fuel, sufficient heat to vaporize that fuel and a source of sufficient oxygen to sustain the combustion...take away at least one piece of the triangle and the combustion process is compromised.

FUEL_HEAT_OXYGEN

It is really quite simple, carbon monoxide gases and other volatile gases that have accumulated [FUEL] and are starved/lacking enough oxygen...and then when suddenly the [OXYGEN] is available you get a...BOOM! The ignition source [HEAT]is a given in any robust fire pot.


That would be why many report that in their hand fed stoves if they open the door not long after feeding in fresh coal, they get the poof. In the Coal gun the sight tube door springs open when the fan goes off, and often this opening is preceded by fresh coal being introduced by the action of the ash grate and motor system. Same result - Poof!. It seems to come back to draft. If draft is sufficient, then the CO and other volatiles are being swept away (or alternately are being continuously burned off by air entering through the peep hole, provided that sufficient draft is present) and are thereby not present in sufficient concentration to be greeted by the inrush of air when the sight tube door springs open. In the end it all comes down to good draft and/or low volatiles (good coal). This is pretty much just as Jeff Gingerich has indicated. If this is an accurate way of looking at it then he is vindicated and all that remains is to come up with a solution.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (It has been fixed!)

Re: Help: I Have Repeated Explosions!!

PostBy: ValterBorges On: Sun Nov 27, 2011 12:32 pm

Quote from ahs site.

The draft induction fan will then start, bringing the boiler rapidly to full output. When the heat demand is met, the boiler's induction fan will shut down, and air flow will return to removing gas from the top of the fire, rather than pulling air through (and feeding) the fire.


Wouldn't a variable speed motor that slows down gradually allow the removing of gas to begin before the door seal is broken and too much oxygen is introduced all at once?

What would be the simplest, cheapest way to move that gas to the flue before the fan shuts off and the door pops open?
ValterBorges
 
Stove/Furnace Make: AHS
Stove/Furnace Model: S260

Re: Help: I Have Repeated Explosions!!

PostBy: lsayre On: Sun Nov 27, 2011 12:39 pm

ValterBorges wrote:Quote from ahs site.

The draft induction fan will then start, bringing the boiler rapidly to full output. When the heat demand is met, the boiler's induction fan will shut down, and air flow will return to removing gas from the top of the fire, rather than pulling air through (and feeding) the fire.


Wouldn't a variable speed motor that slows down gradually allow the removing of gas to begin before the door seal is broken and too much oxygen is introduced all at once?

What would be the simplest, cheapest way to move that gas to the flue before the fan shuts off and the door pops open?


What (besides the draft of the chimney itself) would do this job once the fan winds down and shuts off? Perhaps the ultimate solution is a draft inducer? Has anyone solved their puff-back problem by adding a draft inducer?
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (It has been fixed!)

Re: Help: I Have Repeated Explosions!!

PostBy: Bob On: Sun Nov 27, 2011 2:03 pm

McGiever wrote:FUEL_HEAT_OXYGEN

It is really quite simple, carbon monoxide gases and other volatile gases that have accumulated [FUEL] and are starved/lacking enough oxygen...and then when suddenly the [OXYGEN] is available you get a...BOOM! The ignition source [HEAT] is a given in any robust fire pot.

The Coal Gun appears to sometimes create a condition of insufficient oxygen and surplus volatiles above the coal-bed after the fan shuts down. Correct this and problem is solved. :)


I just want to add the thought that the condition that causes the rapid (large) production of carbon monoxide gases and other volatile gases is the rapid introduction of fresh coal or a large amount of fresh coal atop the fire.

So perhapsl the condition can be controlled or eliminated by reducing the amount of fresh coal atop the fire.
Bob
 
Stoker Coal Boiler: AHS 130
Coal Size/Type: Pea/Anthracite

Re: Help: I Have Repeated Explosions!!

PostBy: rychw On: Sun Nov 27, 2011 5:05 pm

Bob wrote:I just want to add the thought that the condition that causes the rapid (large) production of carbon monoxide gases and other volatile gases is the rapid introduction of fresh coal or a large amount of fresh coal atop the fire.

So perhapsl the condition can be controlled or eliminated by reducing the amount of fresh coal atop the fire.


Bob,

I have attempted to do that by having the grate motor run only when the fan runs, but under low demand I still have explosions. There needs to be some way of controlling the ash dump through the aquastat. The fan should run only when the boiler temperature is low so that the fan can create a good fire on the coal in the tube before too much fresh coal is added. Anyone have any ideas how to use the aquastat to accomplish this function? At this point it is obvious that having the fan running while the grate dumps will not solve my explosion problem.

Again, I have good draft and the same quality coal I've been burning for years without explosions in the past.
rychw
 
Stoker Coal Boiler: AHS 130
Coal Size/Type: Pea
Stove/Furnace Make: AHS
Stove/Furnace Model: 130

Re: Help: I Have Repeated Explosions!!

PostBy: McGiever On: Sun Nov 27, 2011 6:58 pm

So in other words, you say you would want to run the fan only for a period of time prior to starting the grate motor?
McGiever
 
Stoker Coal Boiler: AXEMAN-ANDERSON 130 "1959"
Hot Air Coal Stoker Stove: HARMAN MAGNUM
Hand Fed Coal Stove: RADIANT HOME AIR BLAST
Baseburners & Antiques: OUR GLENWOOD 111 BASEBURNER "1908"
Coal Size/Type: PEA / ANTHRACITE, NUT-STOVE / ANTHRACITE
Other Heating: Ground Source Heat Pump
Stove/Furnace Make: Hydro Heat /Mega Tek

Re: Help: I Have Repeated Explosions!!

PostBy: Bob On: Sun Nov 27, 2011 7:50 pm

rychw wrote:
Bob wrote:I just want to add the thought that the condition that causes the rapid (large) production of carbon monoxide gases and other volatile gases is the rapid introduction of fresh coal or a large amount of fresh coal atop the fire.

So perhapsl the condition can be controlled or eliminated by reducing the amount of fresh coal atop the fire.


Bob,

I have attempted to do that by having the grate motor run only when the fan runs, but under low demand I still have explosions. There needs to be some way of controlling the ash dump through the aquastat. The fan should run only when the boiler temperature is low so that the fan can create a good fire on the coal in the tube before too much fresh coal is added. Anyone have any ideas how to use the aquastat to accomplish this function? At this point it is obvious that having the fan running while the grate dumps will not solve my explosion problem.

Again, I have good draft and the same quality coal I've been burning for years without explosions in the past.


What is the ambient air temperature in the space where your boiler is located? I ask because I think my experience is different than yours if I understand your comments directly. My theory is that the temperature of the water in the boiler and the ambient air temperature both influence the temperature sensed by the thermograte control with the result that it is necessary to use a lower SV in installations with unusually low ambient temperature or boiler aquastat setting. I see you reported an aquastat setting of 165 and if it is an accurate aquastat that is, in my opinion, slightly below the normal range. But do you have a second sensor to confirm the water is actually being maintained at 165?

At the present time the ambient air temp in my out building with the boiler is 60 F and I have the boiler aquastat set to 170. The thermo grate SV is 120. I have never seen the temperature sensed by the thermo grate less than 150 when there has been an extended idle and it drops only slowly when the forced draft begins to operate so it takes a while to drop to the point that the grate begins to operate (110).
Bob
 
Stoker Coal Boiler: AHS 130
Coal Size/Type: Pea/Anthracite

Re: Help: I Have Repeated Explosions!!

PostBy: coaledsweat On: Mon Nov 28, 2011 8:13 am

Bob wrote:So perhapsl the condition can be controlled or eliminated by reducing the amount of fresh coal atop the fire.

Exactly, you should see a ring of burning coal around the outside surface of the firepot at times (depending on where the ashing function is at). If it never breaks the surface, your fire is to low in the combustion tube and you'll get booms.
coaledsweat
 
Stoker Coal Boiler: Axeman Anderson 260M
Coal Size/Type: Pea

Re: Help: I Have Repeated Explosions!!

PostBy: whistlenut On: Mon Nov 28, 2011 8:20 am

...all part of the learning curve.....and thinking we are smarter than some guys who have learned the hard way.......very well stated solution. You can stay at a Holiday Inn someday, also!!!
whistlenut
 
Stoker Coal Boiler: AA130's,260's, AHS130&260's,EFM900,GJ&VanWert
Hand Fed Coal Boiler: Franks Boiler,Itasca415,NYer130,Van Wert
Hot Air Coal Stoker Furnace: Yellow Flame
Hot Air Coal Stoker Stove: Alaska-4,Keystoker-2,
Hand Fed Coal Stove: Alaska,Gibraltor,Keystone,Vc Vigilant 2
Hand Fed Coal Furnace: Van Wert, NYer's, Ford,Jensen.
Coal Size/Type: Rice,Buck,Pea,Nut&Stove
Other Heating: Oil HWBB

Re: Help: I Have Repeated Explosions!!

PostBy: dchartt On: Tue Nov 29, 2011 9:39 am

My draft on a normal day is around .01, .02 if im lucky, no booms here...And thats with the weather here, high 40s low 50s in the day and mid 30s overnight. Aquastat set at 175, water temp usually around 180 to 215 when idling, lots of condensation inside my hopper because boiler is in barn, ashing starts at 110 and stops at 120, peep hole 1/3 of the way open...still putting out a bucket of ash a day with plenty of partial and unburnt coal(cant figure that one out for the life of me)
dchartt
 
Stoker Coal Boiler: AHS 130
Hand Fed Coal Stove: Glacier Bay

Re: Help: I Have Repeated Explosions!!

PostBy: lsayre On: Tue Nov 29, 2011 1:36 pm

dchartt wrote:My draft on a normal day is around .01, .02 if im lucky, no booms here...And thats with the weather here, high 40s low 50s in the day and mid 30s overnight. Aquastat set at 175, water temp usually around 180 to 215 when idling, lots of condensation inside my hopper because boiler is in barn, ashing starts at 110 and stops at 120, peep hole 1/3 of the way open...still putting out a bucket of ash a day with plenty of partial and unburnt coal(cant figure that one out for the life of me)



I'm stil getting plenty of partially burned and unburned in my ashes as well.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (It has been fixed!)

Re: Help: I Have Repeated Explosions!!

PostBy: watkinsdr On: Tue Nov 29, 2011 2:44 pm

I've had no puff-backs (big or small) since:

1. Adding 4" duct which feeds fresh make-up air directly to the "tombstone" intake (bottom). I highly encourage adding fresh make-up air to your system if possible.

2. Left Field Controls type M baro at it's factory setting (0.06" of draft). I highly encourage not touching any of the weights---they are preset/calibrated by Field Controls at their factory.

3. PLC ashing temperature set variable (SV) reduced from 140 degrees Fahrenheit to 130. This setting may change as a function of outdoor temperature; but, I'm hoping 130 is the magic number for my S260 boiler.

4. Sight tube cover "peep hole" 100% open.

5. Significantly loosened the sight tube cover per recommendation from AHS.

BTW: Have you S130 folks complained to AHS about your unburned coal problem yet?
Last edited by watkinsdr on Tue Nov 29, 2011 8:55 pm, edited 1 time in total.
watkinsdr
 
Stoker Coal Boiler: AHS S260 Boiler