[Stoves] combustion of char -- spontaneous and dangerous

[Kevin]

Dear Crispin

I can think of two possibilities for the possible weight gain:

1: If there was backdraft, as a result of the windy conditions, it might be possible that particles of char or creosote fell from the chimney, or were blown back, to the stove system, creating an increase in weight of the stove system. This material then burned off. Note that the weight at about 2815 is the same as at the very end of the chart, where the red line continues past 6567

2: The oxygen that was picked up would be not only as oxygen, but as CO2. What might have happened is that is that the ash, containing FeO could easily pick up oxygen and become oxidized to Fe3O4, and limestone components in the ash could have been calcined to CaO, which could easily react with CO2 from the atmosphere, to "airslake" back to CaCO3. The "jiggle in the weight" may be a result of "local fire" re-calcining" the lime fraction, or "re-reducing the iron components.

Any likelihood that either of these guesses might be accurate?

Best wishes,

Kevin
  ----- Original Message ----- 
  From: Crispin Pemberton-Pigott 
  To: 'Discussion of biomass cooking stoves' 
  Sent: Monday, February 25, 2013 5:59 PM
  Subject: Re: [Stoves] combustion of char -- spontaneous and dangerous


  Dear Kevin

   

  That is indeed a refuelling. The initial drop is the coal burning. Then it is refuelled (jump up in mass) then it burns down again and eventually goes out completely after some hours. 

   

  The surprises are the shaking of the stove scale by the wind in the night, and then the increase in the system mass. The curve moves up and down in a manner surprisingly similar to the mass change charts of Battacharyya. This was a traditional stove and the burning of coal near the edges of the chamber is not all perfect.  How much O2 can char pick up in a few hours?  Is this real or an artifact of the wind?

   

  Regards

  Crispin

   

   

   

  Dear Crispin

   

  I don't understand the graph...

  1: What are the units of the vertical scale? (Is it Grams weight?)

  2: The weight (?) gain is virtually instantaneous.

   

  Presuming the vertical axis is the weight of the stove system and contents in grams, the instantaneous system weight gain would be 108,400 less 103,800 = 4,600 grams.

   

  What could possibly explain such a large and instantaneous weight gain? Did someone simply put more wood or coal on the fire?

   

  Best wishes,

   

  Kevin

    ----- Original Message ----- 

    From: Crispin Pemberton-Pigott 

    To: 'Discussion of biomass cooking stoves' 

    Sent: Monday, February 25, 2013 2:45 PM

    Subject: Re: [Stoves] combustion of char -- spontaneous and dangerous

     

Dear Friends Here is a mass profile, raw and smoothed with 21 point simple averaging (minus 1000 to pull it down so you can see it). 

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