[Stoves] material processing for briquettes few tips ontechnique

Tue Aug 7 22:40:41 CDT 2012

  ----- Original Message ----- 
  From: Richard Stanley 
  To: Discussion of biomass cooking stoves 
  Sent: Tuesday, August 07, 2012 1:50 PM
  Subject: Re: [Stoves] material processing for briquettes few tips ontechnique

  Am all ears 

  # Is that a corn pun? ;-)

  Kevin & Andrew. 

  Clearly its not hydrated lime but rather directly powdered rock lime we are seeing.

  # I don't know the technology involved in corn treatment, , but "lime burning" goes back a long way:
      CaCO3 + Heat ---> CaO + CO2   (Lime Burning)
  Limestone and heat yield Calcium Oxide and CO2.  

  # The CaO can be produced as "Lump Lime", or the "Lump Lime" can be hammer milled or ground to produce "crushed lime", "ground lime", "powdered lime", etc.  This is very different from limestone, ie, Calcium Carbonate, that is crushed, ground, milled, etc., which is commonly known as "ground limestone", agricultural limestone, ag-lime, land lime, etc.

  # If the  lime is dropped in water, it hydrates to produce Hydrated Lime:
      CaO + H20 ---> Ca(OH)2    (Hydrated Lime Production.)
  This is also known as "Slaked Lime", and "Mason's Lime."

  # When dissolved in water, to make "Lime Water", the lime is very reactive, at high pH.

  # Now, there is a problem here... the highly reactive Ca(OH)2 has a big affinity for CO2. It can easily remove CO2 from the air, to "air slake", or, if in a slurry, can remove CO2 from solution. A lump of calcined CaO can "air slake" to produce "powdered limestone."
      CaO + CO2 ---> CaCO3 

  # There can be a two step process involved in "air slaking".... first the CaO can  hydrate to Ca(OH)2, and then it can carbonate to CaCO3:

  How would either variety, Hydrated or not effects the removal of shells off the corn kernels --as done there in large 50 - 75 liter sized vats of hot water is my question.  

  # I don't know the process, but would guess that Hydrated Lime would be employed, and that ground  limestone would not "do the job."  I would guess also that the reactive, high pH hydrated lime would become "spent" in the process of de-hulling. The "spent lime" may be present as part of an organic compound of some sort, or, it may also have been precipitated out as CaCO3, if CO2 was present.

  Best wishes,

  Kevin

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  The efficient management of  the partial decomposition of selected agricultural  residues makes or breaks a production activity from an economic standpoint. In lieu of sophisticated machinery, it often comes down to finding an efficient and locally managed method to accelerate the breakdown of the plant material, preserving its fiber content while dissociating it from the matrix material all left-still -, in a combustible state. 

  Its particularly, the loosened flexible ganglia of fibers, recombined in a water slurry of other plant and granular combustibles, forms  the kind of  tight, well infilled and relatively hot briquette that sells well,  in the local market. 

  If they don't have the fibers at work they can resort to paper if they have it but paper is never going to burn like selected natural plant material which they are familiar with and are best assured to be able to  utilise on a sustainable basis. 

  When it comes to practical briquetting based on traditional skills, there is more collective wisdom in this truck than you can imagine. Its through these incredible folks, and about 300 more, that the production trainers for the region will soon emerge. 

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  Am very busy learning from both ends of the candle here ! 
  Your information could not be more timely: 

  Thanks again, Kevin and Andrew. 

  Richard Stanley
  www.legacyfound.org 
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   On Aug 7, 2012, at 6:42 AM, Kevin wrote:

  Dear Andrew

  Very interesting possible explanation for why "spent agricultural lime" helps with the anaerobic retting process!

  While Ca(OH)2, or "Hydrated lime" can have a pH as high as  about 12.5, and is indeed very caustic, CaCO3 or "Limestone", "agriculture lime, "land lime", has a pH in the range of about 8, which is not very caustic at all

  Is there perhaps another possibility, that being that a marginal change in alkalinity favours growth of different bacteria?

  More specifically, is it perhaps the minor change in pH is "shifting the bug balance", rather than making local chemistry harsher? In other words, are the "retting fungus forms" more favoured with slightly higher pH, while the fungus forms that consume cellulose are repressed?

  Best wishes,

  Kevin

  ----- Original Message ----- From: <ajheggie at gmail.com>
  To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>
  Sent: Saturday, August 04, 2012 2:04 PM
  Subject: Re: [Stoves] material processing for briquettes few tips ontechnique

    On Fri, 3 Aug 2012 10:32:14 -0700, Richard Stanley wrote:

      If processed correctly,  natural fibers will flex and then tend to interlock once blended with other materials in a water slurry.

      One does not  achieve this by simple chopping or even direct use of the fiber without some form of softening (thru partial decompsition, in a hot humid anerobic environment,  (under such as a black plastic bag), or as we are learning from our Mayan colleagues in Guatemala,  use of agricultural lime (which is traditionally discarded after its use in hot water to soften and de-shell their corn kernals).

    As always I find your posts on briquetting educational.

    Alkalis, lime being calcium hydroxide, dissolve lignin and I expect

    this is what the bugs do in retting fibres out of the stem

    (simplistically wood rotting fungi can be classified into brown, white

    and soft rots, the white rots attack lignin and leave the cellulose,

    brown eat the cellulose and soft rots invade all the cells), it's

    lignin that hold all the stringy fibres together. So I can see how

    lime would separate out the fibres.

    Your observation that the bugs work better in anaerobic conditions

    may be that this is what favours a white rot. Flax sheaves where laid

    in a water filled ditch to ret.

    I may have missed something in Rok's post: Rok mentions 16cms diameter

    briquettes with a 5 cms hole, I take it it is the length he is varying

    between 3-12 cms and favouring a length of between 5 and 7cms?

    AJH

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  Am all ears Kevin & Andrew. 