[Stoves] [Gasification] gas composition

[Thomas Reed]

Dear John Bertl and all:

Your list doesn't help much since it doesn't prioritize the components.  
The pyrolysis equations on the other hand do, for instance

CH1.4O0.6 +0.2 H2O (15%, typical) ==> 0.4CO + (0.2CO2 + 0.9H2)       DH 
= 364 kJ/gmole

The hydrogen makes it easy to burn the gas in either a turbulent or 
diffusion flame.  The rest of the cats and dogs are tars and don't add 
much energy to the fire but do contribute to the luminosity.   (The CO, 
CO2 and H2 will equilibrate to some extent and greatly complicate the 
calculations).

Yours truly,

TOM REED              BEF


John Bertl wrote:
> On Friday 06 April 2007 11:59 am, Louis Peltier wrote:
>
>> could some one tell me what the gas composition is
>> when wood is heated in a CLOSED  container to make charcoal.
>> (no air is allowed in the closed container)
>
> The gas composition you are asking for depends on the speed
> of temperature rise (speed of pryralysis), the temperature
> experience by the wood, the time duration of the gas at
> elevated temperatures and if the gas can escape your
> closed container to be cooled.
>
> The possible gases produced are:
>
> H2O               =
> CO2               =   S
> RCOOH           =   L
> CO                 =   O     =
> RCHO              =  W     =
> CH2CO            =          =
> ROH                            =   F
> CH4                             =  A
> C2H6                           =   S
> H2                              =    T
> C2H4                           =
> C2H2                           =
> free radicals:
> CH, CH2, CH3, CHO    2 to 10
> C2
>
> Slow pyrolysis yields charcoal and oxygenated gases
> and vapors of low flammability and releases energy.
>
> Fast pyrolysis yields little of no carbon, forms
> hydrogenated gases and vapors and consumes
> energy
>
> Pyrolysis of wood follows the kinetics of a first
> order reaction. It is diffusion controlled rather
> than rate controlled, the rate being determined
> by the rate of energy transfer within the solid
> rather than by the rate of pyrolysis.
>
> Breakdown of wood components, hemicellulose,
> cellulose and lignin, is not simultaneous.  The
> hemicellulose, particularly its pentosans, are said
> to decompose first largely between 200 and
> 260C followed by the cellulose at 240 to 350 C
> and finally by the lignin at 280 to 500 C.
>
> Hemicellulose evolves more gases, less tar, and
> about as much aqueous distillate as are formed
> from cellulose, but differs from cellulose in that
> hemicellulose yields no levolucosan.  Much of the
> acetic acid formed is attributed to the hemicellulose.
> Scission of a carbon to oxygen bond in a
> pentose leads to further splitting to acetic acid,
> formaldhyde, carbon monoxide and hydrogen.
>
> Cellulose evolves water in the first stage of
> thermal decomposition before any other significant
> changes are observable.
>
> The pyrolytic products first formed from hemicellulose,
> cellulose and lignin promptly undergo
> further reactions, not all of which are pyrolytic.
> Polymerizations and condensations reactions to
> form more comples molecules such as high boiling tars,
> waxes and resinous substances with perhaps
> phenolformaldehyde type linkages are also involved.
>
> Hope this helps
>
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