[Terrapreta] Economics of biochar

[Sean K. Barry]

Hi Andrew,

So, what does this do to the stoichiometric lambda (n:m)?  What value of lambda promotes pyrolysis and keeps the oxidant low enough to stay below a full combustion reaction?

n(C5H8O3) + m(O2) <=> ?(CO2) + ?(H2O) + ???

So, with feedstock that has C:H:O at 5:8:3 (1.25 : 2.00 : 0.75) might react like

2(C5H8O3) + 11(O2) <=> 10(CO) + 8(H2) + 9(O2) <=> 10(CO2) + 8(H2O)

But this is the wrong ratio for the "producer gas" composition, which is like ...

{H2:~20-25%, CO:~20-25%, CO2:~10-15%, CH4:~1-3%, H2O~10%, N2:~40-45%, O2:<~5%, other gases, tars:<1%}

Maybe pyrolysis is like 8(CO) + 2(CO2) + 6(H2) + 2(H2O) + 6(O2) ?  There would still be a lot more O2 present then normal "producer gas"?

I think I better look at lambda again ...  it might not be the mole ratio, but rather the weight ratio.

With C:H:O at 1:2:1, mixed ~1:1 by mole with O2, then the weight ratio is 12 + 2 + 16 = 30:32 = 16 + 16, a ratio close also to 1:1 (1.0).

With C:H:O at 5:8:3, then the mole weight of the feedstock is  5*12 + 8*1 + 3*16 = 116.  With a mole ratio of reactants at 2:11, then the weight ratio (the lambda?) would be like (2*116) : (11*16) = 232:176 = ~1.3.  Again, this is close to 1.0

With air as the oxidant (@ ~19% O2 content), then the weight ratio lambda for air is still ~0.25.  This lambda value of ~0.25 for pyrolysis of biomass in air is the number I recall.

More reading is required, again, methinks.

Regards,

SKB
  ----- Original Message ----- 
  From: AJH<mailto:list at sylva.icuklive.co.uk> 
  To: terrapreta at bioenergylists.org<mailto:terrapreta at bioenergylists.org> 
  Sent: Tuesday, January 08, 2008 6:11 PM
  Subject: Re: [Terrapreta] Economics of biochar


  On Tue, 08 Jan 2008 23:22:59 +0000, AJH wrote:

  >not really because you are dealing with mixtures, there's been a
  >recent posting on [stoves] suggesting C3H8O3 is a better model for the
  >global equation.

  Sorry I mistyped that it should be C5H8O3

  AJH


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