[Stoves] [Gasification] gas composition

[AJH]

On Mon, 09 Apr 2007 08:33:19 -0600, Thomas Reed wrote:

>Dear John Bertl and all:
>
>Your list doesn't help much since it doesn't prioritize the components.

That's an ungracious reply Tom, John's post is a concise appreciation
of pyrolysis under different conditions, I'm sure most stovers will
find it informative even though it was initilaly posted in
[gasification] and I don't believ John reads [stoves].

It's up to other to add to the bones of it, with details as you
posted, to give the full story.
  
>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.

Informative post John

AJH