Dear Tom and Rex
What would you think of the following possibilities:
1: Take the gas products from Tom's first reaction and react with
superheated steam as follows:
6CO + 6 H2O + 5 H2 ==> 6 CO2 + 11 H2
and
2: Take the char resulting from wood pyrolysis, and react with superheated
steam, and sufficient oxygen to maintain an endothermic energy balance as
follows
xC + (x-1)O2 + 2H2O => CO2 + 2H2 + (x-1)CO2
(Neither of these possible reactions are rigorously correct because of the
equilibrium between CO/CO2, and H2/H2O.)
Best wishes,
Kevin
----- Original Message -----
From: "Thomas Reed" <[email protected]>
To: "Discussion of biomass pyrolysis and gasification"
<[email protected]>
Cc: <[email protected]>
Sent: Sunday, December 22, 2013 6:08 PM
Subject: Re: [Gasification] raising H2 concentration in
downdraftgasification
Dear Rex and All
Rex is looking for a higher hydrogen content than producer gas from wood
(below).
Cellulose, C6H10O5, is rich in C, H and O. It is also quite volatile,
vaporizing at ~ 330C and making a good fuel gas
C6H10O5 + 1/2 O2 ===> 6CO + 5 H2
(Plus 2N2 on each side if you use air rather than O2)
This is probably the principle gas burning in the BEF WoodStove,
--------------------------------------------------------------------------------
And the 20% lignin in the wood converts to ~20% 500-600 C charcoal, superior
to commercial charcoals made at 400C.
This is "pyrolysis gas" or "cellulose gas", quite different from the
producer gas made when the charcoal is also gasified, which greatly dilutes
the hydrogen.
Comments?
Thomas B Reed
280 Hardwick Rd
Barre, Ma 01005
508-353-7841
On Dec 20, 2013, at 2:32 AM, "Rex Zietsman" <[email protected]>
wrote:
Hi All,
The deafening silence on this post is quite interesting. At the very least
I
would have thought that someone would have suggested adding steam to the
reduction zone. What about a charcoal gasifier with steam addition?
Any comments on a 1.6MW/2MW thermal gasifier?
Kind regards
Rex
-----Original Message-----
From: Rex Zietsman [mailto:[email protected]]
Sent: 16 December 2013 09:57 AM
Subject: raising H2 concentration in downdraft gasification
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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