oxygen depletion?

oxygen depletion?

PostBy: rberq On: Sat Feb 21, 2009 8:13 pm

My brother put a coal/wood furnace in his shop. He had a good bed of coal burning brightly, then he put a wood log on top. It just sat there and would not burn. Only thing we could figure, is that there was no free oxygen left in the air that had passed through the coal. Interesting.
rberq
 
Hand Fed Coal Stove: DS Machine 1300
Coal Size/Type: Nut -- Kimmel/Blaschak/Reading
Other Heating: Oil hot water radiators, propane

Re: oxygen depletion?

PostBy: grizzly2 On: Sat Feb 21, 2009 9:06 pm

I noticed the same thing when I threw some papers in on top of the coals. They slowly blackend, but no flame. I think is is lack of oxygen also. :)
grizzly2
 
Hand Fed Coal Stove: Hitzer 30 - 95
Coal Size/Type: pea and nut/ anthracite
Other Heating: Jotul #3 wood stove in garage. Oil backup in house. Electric backup in house.

Re: oxygen depletion?

PostBy: TimV On: Sat Feb 21, 2009 11:15 pm

My coal dealer gave me some pointers when I started ,one of which was nothing but coal in a coal fire ...not even a cig butt...but i dont smoke :(
TimV
 
Stove/Furnace Make: Energy King Furnace
Stove/Furnace Model: 480 EK

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Re: oxygen depletion?

PostBy: Uglysquirrel On: Sun Feb 22, 2009 10:28 am

My feeble mind suggests wood needs substantially more than than coal, the area above the coal is hot but likely pretty O2 starved for wood (those blue flames do a good job of that) though having a stove with a secondary burn inlet (like the Mark series at the window bottom mayhelp some)...but then who wants to burn wood during the Coalution?
Uglysquirrel
 
Stove/Furnace Model: Pocono

Re: oxygen depletion?

PostBy: Devil505 On: Sun Feb 22, 2009 11:03 am

I have also started to open my secondary air outlets a bit when reloading coal if I don't continue to see flames. The additional oxygen seems to help relight the flames to burn of volatiles. (I then shut the secondary air outlets when done reloading)
Devil505
 
Stove/Furnace Make: Harman
Stove/Furnace Model: TLC-2000

Re: oxygen depletion?

PostBy: VigIIPeaBurner On: Sun Feb 22, 2009 12:17 pm

With the air coming form beneath the coal bed, its oxygen content is mostly consumed. Like the combustion mixture in a gasoline engine, the mix of gas:air has to be in the sweat zone to ignite. Too rich (GAS:air) no ignition and conversely, too lean (gas:AIR) and no ignition. To get the mixtures on either side of the sweet spot to burn, you have to change something else. Like engaging the choke on a carbureted engine or changing the timing curve. I might be restating what Uglysquirrel said using an example I can relate to - maybe others can as well (?). The wood gives off gasses/smoke that don't ignite due to too rich of a mixture in the zone above the coal that is richer in CO & CO2 than O2.

This also might help explain what happens when a new load of coal is placed on top of the fire. It's not just exposure to the flame that sets off the gas above a new load but includes the ratio of gas:air. The side of the fire we keep exposed allows more air up thru and a zone of gas above the fire exists right there that allows the fire to spread smoothly over the new coal that's off-gassing at a higher rate (richer) than the old part of the fire. My stove is a top loader and I don't have secondary air inlets above the fire to use like Devile does. If I'm rushed I'll dump an entire hod and cover the entire old fire. I'll crack the ash door for a better part of a minute to allow more air in then close it. At this point, I'll lift the top lid a few inches and the gas might gently light off with the fresh air drawn into the fire box. If it doesn't, I'll blow into the gap (from a safe distance :roll: ) and it usually lights off, maybe with a gentle POOF! Nothing nearing an explosion like in the discussion started a while ago by Wood'nCoal --->Minor Explosion In Coal Stove
VigIIPeaBurner
 
Hot Air Coal Stoker Furnace: Keystoker Koker
Hand Fed Coal Stove: Vermont Casting Vigilant II 2310
Other Heating: #2 Oil Furnace

Re: oxygen depletion?

PostBy: Devil505 On: Sun Feb 22, 2009 2:14 pm

VigIIPeaBurner wrote:With the air coming form beneath the coal bed, its oxygen content is mostly consumed. Like the combustion mixture in a gasoline engine, the mix of gas:air has to be in the sweat zone to ignite


Yup...I think most modern coal stoves have a mechanism to allow a little secondary air in (above the coal bed) for just that purpose of burning off volatile gases to prevent puff-backs. (small slits near the window, etc) Sometimes, if you fill it with too much fresh coal & smother the flames, most stoves require a little assistance in getting more oxygen to burn the gases. (either open the door a crack like stated above or whatever)
Devil505
 
Stove/Furnace Make: Harman
Stove/Furnace Model: TLC-2000

Re: oxygen depletion?

PostBy: Joe in NH On: Sun Feb 22, 2009 10:48 pm

Can't speak to the wood on coal issue but think the postings in this thread make a lot of sense. I had what I consider to be an oxygen depletion problem this morning with my Harman boiler. I went through my normal routine of shaking and digging out the ashes in the firebox and then load up with about 40 pounds of nut coal. Normally, while I am doing this in the morning, the call for heat and hot water keeps the water temperature where the automatic draft flap stays open and the fire is cooking right along. Most mornings I am off to work and do not have the opportunity to "check" the fire. However, on the weekend I will look at the fire if I happen to be in the basement. Unfortunately, I decided to check the fire this morning shortly after the draft flap had closed and the fire was oxygen depleted. There was a poof and it was pretty obvious that the blue dancers were not happy and were definitely trying to escape. Somewhere in my coal burning past I must have had a similar experience because I have a habit of keeping my head back when I open the loading door. If I had forgotten this morning, I would need to be growing some new eyebrows. Joe
Joe in NH
 
Stove/Furnace Make: Harman
Stove/Furnace Model: Trident SF 260 Boiler

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