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downdraft gassifer probs????

Started by homeyd, December 07, 2012, 10:20:59 AM

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homeyd

friend of mine built a down draft .works great  ,runs clean 95% smokeless.but several times during the cycles it doesnt want to gas off, or ingnite in the secondary chamber. then you kleen the embers from the two nozzles and it will fire off.but then she may run all night w/out any problems .then subject to not gas off again.any one seen or ever heard of this problem??? heard you can get alot of knowlege from some folks on this site .any advice will be greatly appreicated     thanks in advance

doctorb

homeyd-  Welcome to the Forum.  There are many here with lots of experience with OWB's 

What do you mean, "doesn't want to gas off?"  Do you mean the fans won't shut down, leaving you with a boiling stove?  Or do you mean that it won't re-ignite the fire?
My father once said, "This is my son who wanted to grow up and become a doctor.  So far, he's only become a doctor."

homeyd

doctorb thanks what im meaning to say is .normally in the d. draft position the gasses are forced down thru a couple nozzles in the ceramic.usually when the fans are calling for comb. air beneath the nozzles usually look and sound like a cutting torch.but again the gasses normally ignite ,and all is good.but at times she wont ignite properly..so you gotta clean the nozzles out  close the bypass turn on the fans may have to repeat this step 4-5 x then she ll fire back off    need some help  thanks

doctorb

The opening size from the firebox down into the "reaction chamber" may need to be larger.  Ash from the firebox needs to be able to fall through the opening, or it will clog.  Most Gassers have fans that force the smoke and heat through the coalbed and down into the reaction chamber where more air is forced in, causing the smoke to ignite.  I am a little fuzzy on where the nozzels are that need to be cleaned.  Are they the air intakes for the flow of new air into the reaction chamber, or are they the entryway for the smoke and heat created in the firebox to enter the reaction chamber, where gassification occurrs.
My father once said, "This is my son who wanted to grow up and become a doctor.  So far, he's only become a doctor."

homeyd

they are entry ways for the gasses and heat to go  down into secondary reaction chamber. then hes got another air coming into the reaction area. the openings are aqbout 1.5in. wide x5in.  and there are  three of them"nozzles" thanks again have i got u confused?hope not

homeyd

doc sorry the nozzles are in the btm of the fire box

doctorb

My 2300 does not have "nozzles" to help the heat/smoke travel downward into the reaction chamber. In most gassers, the fans forcing the air into the firebox get "turned up", increasing the air flow downward, so I am not sure why you need nozzles to help with that. I would look for a change in design to prevent this problem.  Good Luck
My father once said, "This is my son who wanted to grow up and become a doctor.  So far, he's only become a doctor."

homeyd

how does yor gasses exit into the reaction chamber

doctorb

Becasue the damper is closed, increased air pressure from forcing air into the firebox only has one way out....down through the coalbed and into the reaction chamber.  There, new air is forced in, creating gassification
My father once said, "This is my son who wanted to grow up and become a doctor.  So far, he's only become a doctor."

WmFritz

Did he just get the boiler running or has it been running fine and just developed the problem? The first thing that comes to my mind is the moisture content of the wood. Gassifiers like dry, seasoned wood.

Could the wood be bridging?  If the splits are too big, they may suspend and die out.
Pictures of the design may help
~Bill

2012 Homebuilt Bandmill
1959 Detroit built Ferguson TO35

doctorb

Quote from: WmFritz on December 07, 2012, 01:52:26 PM
Pictures of the design may help

I agree.  Hard to help on a home manufactured device without some visual input.
My father once said, "This is my son who wanted to grow up and become a doctor.  So far, he's only become a doctor."

homeyd

wmfritz  thanks the boi;er is its second season,he had the prob.a few times last season.the wood is around 20% not bad. the fire box is under pressure oncce the bypass in the top of firebox is  shut. in the btm of the f box has 3 slots  about 1.5 in x 5 in. thats where yhe smoke and heat  go don.then more air is introduced.as said eariler most times it ignites in the lower chamber but sometimes it just smokes instead of igniting. cant figure why it changes??? any ideas greatly appericated

doctorb

Sounds like your coal; bed is not hot enough on some occasions.  It's not just a matter of making smoke and sending it downward and introducing more air.  The coal bed must be hot enough to have the smoke ignite when the added air is introduced.  Now, there are lots of reasons for the coal bed to not be hot enough.  In my experience, it's because the air flow into the firebox is partially blocked by creosote or ash.  I would let the fire burn out, empty the firebox, and clean every air channel into it thoroughly.  Start a new fire with tons of dry kindling, and see if she gassifies.
My father once said, "This is my son who wanted to grow up and become a doctor.  So far, he's only become a doctor."

martyinmi

I'd tell your buddy to try and keep the fine ash to a minimum in his primary burn chamber. It will act as an insulator and won't allow the nozzles and the surrounding refractory material get up to temperature as fast as they should or even at all. That area needs to be in the 700*-800* range for the gas to ignite when the boiler calls for it's next cycle. I like to keep the coal bed 3" to 5" deep. I hoe the ashes/coals over the nozzle once daily to allow fly ash to fall into the secondary burn chamber, then I make sure the nozzle has nothing on top of it before reloading.

If his is running smoke free 95% of the time, he is doing something right. I've owned 2 gassers(Empyre Pro Series 100 and Portage and Main Optimizer 250), and watched a Central Boiler 2300 and 2400, Wood Doctor 5000 and 10000, Empyre Pro Series 400, and a Natures Comfort GT220 in operation, and they all function nearly identical where smoke is concerned. To my knowledge there isn't any manufacturer that guarantees a smoke free burn 100% of the time.

If he has 3 nozzles @ 7.5 sq. in. each it's a wonder it gasifies at all. My Empyre had one nozzle that was approximately 3 cu. in., and my 250's nozzle is about 4 sq. in. Doc B's nozzle is about 5 sq. in. on his 2300. Your buddies boiler would probably function even better if he were to plug at least one nozzle off, maybe even two of them.
No God, No Peace
Know God, Know Peace!

homeyd

i think the reason for 3 nozzles is in case one or two clog or dont fire ,the other ones should take up and keep he fifing ,but as said could be too much of nozzle not allowing it to pressurize the firebox.hes heating about 8500 sq ft ,the tanks about 900 gal,w/ a 4ft x4ft firebox. w/ prob 60 ft of heat exc thru the water.thats alot of water to bring back up to temp. if she fails to ignite and run properly.think thats the reasoning behind the xtra nozzles,ill definetly pass on your thoughts .hopefully this will help.thanks again for yalls comments

WmFritz

Appreciate it if you'd keep us updated on what you guys uncover. ???




Bill
~Bill

2012 Homebuilt Bandmill
1959 Detroit built Ferguson TO35

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