[Gasification] raising H2 concentration in downdraft gasification

Rex Zietsman rex at whitfieldfarm.co.za
Sun Dec 22 00:26:52 CST 2013

Dear Tom and the List,

Happy holidays to all and merry Christmas for the 25th. 

Believe it or not, but we are going via liquefaction and catalytic cracking
aided by in situ hydrotreating and deoxygenation of long chain hydrocarbon
molecules all in one reactor. We produce a decent deoxygenated oil, not
pyrolysis oil. Low yield - only about 250 litres/ton of 15% MC biomass. When
tested via the ASTM tests for diesel, it has a longer tail at both high and
low boilers - easily fixed with fractionation. But, if the starting
feedstock contains sulphur, the residual sulphur is about 10% of the
incoming. This can be as high as 500ppm in the oil which is fine for
"standard" diesel. To make ultralow sulphur diesel we have to hydrotreat.
Hence the hydrogen requirement. 

In one of our projects, we have waste vegetable oil at a good price. The
idea is to deoxygenate this oil to produce a diesel similar to that from
crude oil. Here the hydrogen requirement is high in the range of 30kg/ton.
As it is still relatively small ie 1200 litres/hour, we need 30kg/hour of
H2. Hence the post.

All the best

-----Original Message-----
From: Thomas Reed [mailto:tombreed2010 at gmail.com] 
Sent: 21 December 2013 12:07 AM
To: Discussion of biomass pyrolysis and gasification
Cc: <gasification at lists.bioenergylists.org>; John M. Bradley; Chuck
Subject: Re: [Gasification] raising H2 concentration in downdraft

Dear Rex and All; 

Merry Xmas and happy synthesizing.  

Rex must be a chemical engineer because he has outlined the problem nicely
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>
> 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
> 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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