[Stoves] : Re: Insulation and stove life

Fri Jun 14 03:25:38 CDT 2013

Paul,
I currently use wood ash as  insulating material between the kalan and combustion chamber of the eco-kalan (a rocket stove using wood, charcoal, coconut husk, shell, fronds and other parts of the coconut tree).  The eco-kalan uses 75-85% less firewood and therefore a lot less ash is produced compared to traditional kalans and other traditional cookstoves in Negros Oriental, Philippines.   A shortage in supply of ash is one factor which affects  sales of eco-kalan.    I  have considered making an insulating material  using a  50-50 mix by volume of rice hull & clay in the form of pellets or bricks which would be broken to pieces after firing.  I would fire the pellets or the bricks along with the eco-kalans up to 900 degrees Celsius.  Will there be significant formation of cristobalite under these conditions?  Would handling the fired pellets or the breaking of the bricks be a health hazard?  Thanks,

Rebecca Vermeer

From: Paul Olivier 
Sent: Friday, June 14, 2013 12:07 AM
To: Rebecca A. Vermeer 
Cc: Jon Anderson ; stoves at lists.bioenergylists.org ; larry winiarski 
Subject: Re: Fw: [Stoves] : Re: Insulation and stove life

Rebecca,

If we directly burn river hulls, there should be a lot of cristobalite formed. If we gasify, this problem should be minimized, provided channeling does not occur. Also there might be cristobalite in the particulate matter in the combustion gases. With rice hull pellets in a TLUD  we have a lot less channeling, and a lot less particulate matter. Therefore the rice hull pellet becomes an attractive fuel for these and many other reasons.

Thanks.
Paul Olivier

On Jun 14, 2013 1:44 PM, "Rebecca A. Vermeer" <ravermeer at telus.net> wrote:

  Hello Paul,
  Larry just told me that the silica content of rice hull ash is over 90%.  At the ETHOS 2013 Conference, I saw a TURBO stove developed in the Philippines which used rice hull for fuel.  Given your comment below regarding cristobalite “which is a nasty carcinogen” and severely hazardous to human health (see link below), would you recommend the use of  rice hull as a household fuel for cookstoves? 

  Rebecca Vermeer

  CRISTOBALITE LINK:
  http://nj.gov/health/eoh/rtkweb/documents/fs/1657.pdf
  From: Paul Olivier 
  Sent: Wednesday, June 12, 2013 12:01 AM
  To: Discussion of biomass cooking stoves 
  Subject: Re: [Stoves] : Re: Insulation and stove life

  Paal,

  One thing I look for on my burner is that all burner holes support a flame throughout the process. If channeling occurs during the process or if char is being burned as the process comes to a close, then one can see burner holes that do not support a flame. This means that CO2 is being discharged from the burner holes, and of course CO2 does not burn. When CO2 is formed, this represents a big inefficiency, since combustion takes place far below the pot. When this happens the sides of the reactor can easily turn red hot and melt. I do not know how it is possible to spot the presence of CO2 if the top of the reactor stays open and does not have a lid with burner holes.

  If one turns up the fan a bit too high resulting in channeling, it can happen that only a few holes (among a total of 80 in my case) do not support a flame. If I turn the fan down a bit and shake the reactor, this problem is immediately corrected. Also the effect of the presence of CO2 can be spotted by the cook in another way. The distribution of heat to the pan is not even.

  Also many of the positive characteristics of biochar are lost when biochar is combusted and is reduced to ash. The combustion of biomass and biochar takes place when channeling occurs, and the combustion of biochar takes place if the fan is not turned off at the end of the process. Rice hull ash and rice hill biochar are not at all the same thing when it comes to growing plants. Also rice hull ash can easily contain cristobalite, which is a nasty carcinogen. Under ordinary conditions, no farmer should be handling this stuff.

  Thanks.

  Paul

  On Wed, Jun 12, 2013 at 1:06 PM, Paal Wendelbo <paaw at online.no> wrote:

    Ron

    By end of flame the color of the char is red to yellow, that indicate a temperature of 700 to 800 ˚C and when there is no smoke, complete combustion has taken place. Is that not good for biochar?

    Regards Paal W

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