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Fwd: [GreenYes] Fire in pile !
I thought Jim McNelly's answer to the Composting Council listserve below was great on this, for people who are not subscribed to that listserve.

From: Jim McNelly <jim@composter.com>
Subject: Re: [USCC] FIRE IN PILE
Date: Mon, 09 Sep 2002 17:39:21 -0500

At 08:46 PM 9/6/2002 -0300, you wrote:
Does anybody can me help?

I work with composting since 1995 and I use the method of static piles with forced aeration.
The sludge and wood chips proportions are calculated for the total mass to be composting it reaches with humidity of 60% and relationship C/N 30/1.

Greetings Kátia G. Beltrame

I will offer my suggestions point by point, but these are only thoughts as it is hard to be definitive without being at your location. One initial question is how much of your carbon and moisture are "available" vs how much is tied up in the woody mass, not available to the composting reaction. I have seen high moisture piles that are too dry because the moisture is locked in the chip. I have also seen piles that were too wet, even thought though the wood chips were dried leading to a false "available" moisture reading.

The fans are connected the timers that call and they turn off in regular intervals of time in way to supply the amount of necessary air for the maintenance of levels of oxygen enough to maintain conditions aerobics.

It is my understanding that the "on and off" cycles of blowers using Beltsville aeration systems were designed to replace oxygen that was depleted, usually within one half hour. Continuous air can also provide sufficient oxygen without timers. Blowers were turned on and off to save electricity, especially as the blowers were often sized to the mass of the pile being oxygenated. Are you actually measuring oxygen inside the pile or just guessing based upon the mass and the size of the blower? I suspect that you may have an anaerobic pile, if not in all of the pile, in most of it.


One of the piles was with average of very low temperature, for that I interrupted the aeration for 24 hours and then I began again to supply the air inside of the pile (400m3ar/hour/t dry matter).


How did you sample your temperature? Was the sample point representative of the pile? I have seen supposedly cool piles around 40C that were actually overheating inside, up over 70C. Remember, heat is the enemy of composting and a pile over 65C is a pile that is not under control. Heat is a by-product of decomposition, not a cause of it. Heat must be removed to help promote optimum decomposition rates.

One fatal flaw I noticed with forced aeration systems in the 1980s was that the flow of air was based upon the capacity of the blower, not upon the actual flow of air through the pile. I saw odorous piles with plenty of "theoretical" air, but little actual air due to back pressure problems. I first noticed this problem when I put a piece of paper up to the intake duct of a blower and it did not provide even enough suction to hold the paper! No air was moving through the blower. I would look at the aeration system to ensure that the air exhaust ports are not clogged with compost, filled with condensate, or collapsed. Many blowers simply have too little pressure, only around 1 or even two inches of water column. Typically, pressure over four to eight inches is needed to force air through a pile. This often requires a larger blower and consequently an air manifold rather than air to a single pile from a single blower. I suspect that your pile had insufficient air.

After about 20 minutes of aeration the pile caught fire and the aeration tube melted.

There are many causes of a fire in a pile including too high, over 3 meters which causes compaction and the retention of methane, alcohols, and other undesired flammable byproducts. The spark to ignite the fire has been suspected to be pieces of metal such as nails or baling wire, which can act like a battery and spark when they touch other pieces of metal. When agitated or infused with oxygen, the mostly woody pile can begin to burn. Typically a pile that burns is too dry, too high, too hot, and is lacking in oxygen.

We choked the fire of the surface, we began to disassemble the headboard of the pile and we noticed that all your interior had burned and we didn't find the aeration tube that, probably, it melted.
I end that the oxygen inside of the pile provoked the fire, that was favored by the grass bed.
Can anybody explain scientifically because that happened?
I never saw similar in all those years.

I would suggest a more thorough initial mixing to avoid wet and dry areas, and helping to ensure blending of carbon and nitrogen materials. Then keep the piles smaller, around 2 to 2.5 meters. , keeping the base of the windrow to less than 7 meters.

Finally, spread the air more evenly through the pile using more pipe and a 200 cm coarse wood chip base. I believe that air should flow through the mass at locations of at least every .5 meters, often requiring a diffusing manifold to ensure pressure equalization. Get a air velocity tester and actually measure air flow, making sure that you are not experiencing channelling and losing air through only one area of the pile.

In the systems I design, I provide for air sensing in each composting zone and appropriate air flow regulation as well as temperature feedback and high rates of air, typically 10 times that of oxygenation, to keep a pile from overheating.

I hope some of this helps.

Jim~ McNelly
The Compost Man
jim@composter.com
Http://www.composter.com

From: "Moacir Beltrame" <moacir@bioland.com.br>
Date: Fri, 13 Sep 2002 18:44:03 -0300

Does anybody can me help? 
 
I work with composting since 1995 and I use the method of static piles with forced aeration. 
The sludge and wood chips proportions are calculated for the total mass to be composting it reaches with humidity of 60% and relationship C/N 30/1. 
The fans are connected the timers that call and they turn off in regular intervals of time in way to supply the amount of necessary air for the maintenance of levels of oxygen enough to maintain conditions aerobics. 
One of the piles was with average of very low temperature, for that I interrupted the aeration for 24 hours and then I began again to supply the air inside of the pile (400m3ar/hour/t dry matter).  
After about 20 minutes of aeration the pile caught fire and the aeration tube melted. 
We choked the fire of the surface, we began to disassemble the headboard of the pile and we noticed that all your interior had burned and we didn't find the aeration tube that,  probably, it melted. 
I end that the oxygen inside of the pile provoked the fire, that was favored by the grass bed. 
Can anybody explain scientifically because what happened ? 
I never saw similar in all those years. 

I apologize for my English and I thank if somebody to be able to help me.

Katia G. Beltrame
Piracicaba/Brazil
moacir@bioland.com.br      



 

Gary Liss
916-652-7850
Fax: 916-652-0485
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