GAS-L: Re: Re: Pyrolysis vs. Gasification

[Reedtb2@cs.com]

Dear Vern:

I'll be interested in hearing Harry's reply.  Here's mine after 25 years in 
the field.

The first step when air enters the reaction zone is the combustion of 99%+ of 
the volatiles in a process I call "flaming pyrolysis".  This is like flaming 
combustion, (as in a match) but since there is insufficient air, it results 
in a mixture of CO, CO2, H2, H2O, CH4 etc. PLUS 5-25% charcoal, depending on 
the superficial velocity.  "Starved air combustion" is also a good name for 
this stage.  I would also call it pyrolysis fueled by combustion of the 
pyrolysis gases as they form.  

The gas temperatures in flaming pyrolysis can reach 1400C, so there is a lot 
of excess energy which causes the gases then to immediately react further 
with the charcoal, immediately reducing the CO2 and H2O to make more CO and 
H2 until the temperature reaches ~ 800C, at which point the reactions with C 
become too slow.  (See our Handbook of Biomass Gasifier Engine Systems).  

Unfortunately, Nature does not honor our lexicon, so if you really want to 
understand, look at the reactions and don't worry too much about the old 
names.  

Harry?

Yours truly,                        TOM REED

In a message dated 1/22/01 11:06:58 PM Mountain Standard Time, 
VHarris001@aol.com writes:


> Hello Dr. Parker,
>
> Based on the definitions you provided below, can I safely assume that the 
> primary process occurring in a suction air-biomass (not coal) gasifier is 
> "starved-air combustion?"  For instance, since it uses air, the process is 
> not primarily pyrolysis.  Since external energy is not being added, the 
> process is not primarily gasification.  And finally, since oxygen is not 
> being added, it is not primarily autothermic gasification.
>
> By my reckoning, that leaves starved-air combustion as the primary process 
> occurring, producing CO and VOC's.  So, am I safe in assuming that the 
> wood-gas vehicles that were running around Europe during WW2 were, for the 
> most part, running on the products of starved-air combustion (CO and VOC's) 
> and NOT the products of the water-gas reaction (CO + H2)?
>
> Thanks,
> Vernon Harris