[Gasification] raising H2 concentration in downdraft gasification

Thomas Reed tombreed2010 at gmail.com
Fri Dec 20 16:06:38 CST 2013

Dear Rex and All; 

Merry Xmas and happy synthesizing.  

Rex must be a chemical engineer because he has outlined the problem nicely below.
A partial solution is reaction of only the 80% cellulose in the wood to make a synthesis gas:  

C6H10O5 + 1/2 O2 ===> 6 CO + 5 H2 

And leaving the 20% lignin behind as charcoal (Biochar) for soil enrichment and atmospheric CO2 reduction.  

Reaction of part of the CO with water reduces the unbalance to an excellent synthesis gas:

 6 CO + 5 H2 + 3 H2O ===> 3 CO + 8 H2. ||   ==> 3CH2 (oil)  + 3 H2

Leaving enough excess H2 to drive the reaction forward.  Toplit Updraft gasification consumes the cellulose , leaving the lignin as Biochar.


I am an expert in molecular sieves, and have made a quantity of a Fischer Tropsch catalyst with one isolated Fe atom per unit cell.  Should make a low MW diesel.  


If anyone has the means, and would like to pursue this, contact me privately with an offer.  

Tom Reed

Dr. Thomas B Reed 
280 Hardwick Rd
Barre, Ma 01005

> On Dec 16, 2013, at 2:56 AM, "Rex Zietsman" <rex at whitfieldfarm.co.za> wrote:
> Hi All,
> We are looking at a system that will hydrotreat bio oils from pyrolysis,
> catalytic cracking and vegetable oil. For this we need in the region of 30kg
> hydrogen/ton oil. At small scale ie 1 ton oil/hour, this works out at, you
> guessed it, 30kg of hydrogen/hour. As this is a small amount in the overall
> scheme of things, we are looking at gasifying wood chips and to recover the
> hydrogen using pressure swing absorption. What I would like to know is
> whether we can increase the H2 concentration in syngas by tweaking the
> gasifier. Clearly we can look at the water gas shift reaction but, as the
> syngas has to be cooled, washed, pressurised and reheated, it is quite an
> additional investment for the scale we are looking at. If we could simply up
> the H2 content, we would go straight from washing to PSA. Residual gas would
> be piped to a diesel generator where CO and the like will be combusted prior
> to exhaust to atmosphere. 
> For easy mental arithmetic, let us assume a 33% H2 concentration in dry
> syngas. 30kg/hour of H2 is 15kmol/hour or 15/0.33 = 45kmol/hour of syngas. A
> kmol of gas has a volume of 22.4 Nm3. So, to get 30kg/hour requires 22.4 x
> 45 = 1000 Nm3 syngas/hour (mental arithmetic here, go with the flow).
> Assuming an 80% PSA recovery this means that we need 1250Nm3/hour of syngas.
> Not a bad sized downdraft gasifier! Assuming 6MJ/Nm3, this is around a 2MW
> thermal unit. If we can get the H2 concentration up to say 40%, then the
> syngas requirement would be 37.5kmol/hour or 37.5/45 x 1250 = roughly 80% of
> 1250 or roughly 1000 Nm3 syngas/hour. This reduces the size of gasifier to
> 1.6MW thermal and more sensible in size.
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