OWB on Bit and chimney fire

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oros35
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Post by oros35 » Fri. Mar. 08, 2019 11:09 am

So I just started using an outdoor boiler in January. Overall I'm surprisingly impressed with it, my house has never been this warm! I've read many horror stories and was leery about trying it, but I picked up a used one for the right price where if I hated it, no big loss.

So my problem:
It seems I'm having fairly regular chimney fires... After a fresh load, 4-5 good coal shovels worth, I will sometimes get dull orange flames out the chimney about a foot or so tall. For the most part it goes out when the forced draft fan goes off and damper closes. Doesn't re-ignite on the next call for heat. Last night it was still going after the fan shut off. As soon as I opened the loading door it stopped. Chimney pipe was almost too hot to touch. Coal bed looked perfect, and burnt great. Still going nice this morning. I've been loading it every 24hrs (about 10pm so smoke is not so visible and not to disturb the neighbors as much with the heavy smoke of a fresh load).

Chimney is about 13 feet tall, 6 inch double wall SS, its a Cozeburn 250 OWB with grates and fire brick, forced draft, water temp set at 165, combustion fan comes on 5 degrees below setpoint.

I'm burning mostly all Bit coal, run of mine from Grove City PA, with a couple of logs tossed in to help with bridging. Coal is large lump to fines, putting it all in.

It seems like it's the soot building on the chimney that is burning off. This coal does put off quite a bit of heavy smoke.

The OWB is 10 years old. Still nice condition. Previous owner used Bit coal and was from WV near Morgantown. Unfortunately he has passed so no asking questions.

Is it something I'm doing? Is it the coal? How can I fix it?

 
LouNY
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Post by LouNY » Fri. Mar. 08, 2019 11:15 am

I don't know but as a guess I could see it as the coal gassing off,
the fire box temp may be to cool to burn it in the combustion chamber and
it's burning in the stack, or the air flow is just carrying the gases out and they are burning in the stack.

 
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corey
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Post by corey » Fri. Mar. 08, 2019 3:46 pm

I agree it could be gasses burning in the chimney bit wood boilers can be a creosote factory with wood. I watched a video were a guy was raking gobs of it off the walls with a hot fire going.

 
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CoalJockey
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Post by CoalJockey » Fri. Mar. 08, 2019 7:43 pm

Once the gasses burn off it should settle down, shouldn’t be anything abnormal. Anything with a forced draft moves plenty of air and the stacks are often short on an outdoor unit.

One of my coal customers had the stack blowing fire pretty regular and he went almost 20 years on the boiler.


 
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McGiever
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Post by McGiever » Fri. Mar. 08, 2019 9:25 pm

Might there be a way to inject some pre-heated secondary air in over the burning coal's surface?
Seen also were a refractory or insulation board was mounted above fire and reflected back the heat to increase surface temps.

Both of these have been discussed here before at one time or another...

 
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oros35
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Post by oros35 » Mon. Mar. 11, 2019 9:27 am

McGiever wrote:
Fri. Mar. 08, 2019 9:25 pm
Might there be a way to inject some pre-heated secondary air in over the burning coal's surface?
Seen also were a refractory or insulation board was mounted above fire and reflected back the heat to increase surface temps.

Both of these have been discussed here before at one time or another...
I've been pondering how to add pre-heat over fire air. Probably going to be a summer project to see if I can come up with a way. I've seen how much that helps get a cleaner fire.
Wish it was just built into these things from the factory. I've only seen a couple that have it factory built and they had other design flaws.

Thanks for the replies!

 
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BigBarney
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Post by BigBarney » Mon. Mar. 11, 2019 1:24 pm

This old design of an outdoor wood boiler has a very inefficient

burn profile and is not easily fixed... The short path of the flame

front is not able to burn the volatiles so most go up the chimney

unburned and lower the burn efficiency to 30-50% maybe...

They burn a large amount of fuel but very little is used to heat

the water and have a large amount of smoke...

A little old but still valid for these era boilers..

http://biomassmagazine.com/articles/10263/epa-lis ... or-boilers

https://www.woodboilers.com/wood-boiler-efficienc ... a-ratings/

It is hard to test wood because of many variables so we have these tests

to rely on with much speculation...

With wood you are trying to burn a fuel with 20+ % water so you will never reach

high efficiency numbers except where they use kiln dried wood to fudge the

numbers up to make it look good , how many wood burners use all kiln dried???

BigBarney

 
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lsayre
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Post by lsayre » Mon. Mar. 11, 2019 1:31 pm

BigBarney wrote:
Mon. Mar. 11, 2019 1:24 pm
how many wood burners use all kiln dried???
I do. And efficiency still stinks vs. my coal boiler. This in a stove touted to be one of the very most efficient. 94% per the EPA (with this information provided by one of our forum members) and 92% efficient per the manufacturer. And right around 61%-63% efficient per my means of measuring what I will refer to as (my experience of) its "real world" efficiency.


 
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Post by LouNY » Mon. Mar. 11, 2019 5:54 pm

Until an outside boiler has a combustion chamber separate from the heating chamber, they will not achieve good efficiencies, with a non-pressurized heating vessel requiring lower water temperatures and the water reservoir in direct contact with the flame and cooling it down so much you can achieve complete combustion.

 
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BigBarney
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Post by BigBarney » Mon. Mar. 11, 2019 7:51 pm

LouNY:::

You hit it out of the ballpark that is the problem with any

heating device , the separation of combustion and heat

extraction .

They both require different conditions and the design

always has to compromise on one or the other.

BigBarney

 
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oros35
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Post by oros35 » Tue. Mar. 12, 2019 9:37 am

LouNY wrote:
Mon. Mar. 11, 2019 5:54 pm
Until an outside boiler has a combustion chamber separate from the heating chamber, they will not achieve good efficiencies, .
This would be the theory behind the gasification boilers?

 
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BigBarney
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Post by BigBarney » Wed. Mar. 13, 2019 5:29 pm

You have to remember that any fuel does not burn until heated

enough to off gas and then the volatile compounds combust and

heat more fuel to gaseous state.

In a gasifier you heat and then direct the gases to be burned in the

combustion chamber usually in a downward path , but in my boiler

the gases and smoke go to the rear outlet above the grate and then

to the heat exchanger for final combustion . With coal the ash would

soon clog a bottom exit so this is the best alternative .

Most of the primary air goes up through the burning coal to the top of the

fuel magazine with the smoke and gases and a measured amount

comes down mixing with the hot gases to make the trip through the

hot fuel again and are completely burned.

That is how you burn any fuel and get no smoke or soot going up

the chimney , I only clean my chimney every 2-3 years and get about

a 5 gallon bucket of fly ash and very little soot.

BigBarney

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