[Gasification] [biochar] Pine char gasification

Mon Dec 23 17:36:01 CST 2013

Ron,

I didn't mean anything quite so personal. :-/

Most of the biochar research has focused on pyrolitic char and not on
combustion or gasification char. There is a clear bias toward pyrolysis, or
low temperature char. Can anyone really say this is the way that the
Amazonians, or anyone else, created the charcoal that we find in the terra
preta soils? Or was it smoldering combustion, staged combustion (a la Alex
English), or a combination of pyrolysis, gasification and combustion? I know
that I have had a lot of bad slash and straw burns that have left a lot more
char on the ground than ash. Are there "signatures" in the terra preta char
that point specifically to pyrolysis, gasification or combustion?  

I see biochar production growing in stages. For the time being a large
quantity of char that is sold as Biochar is actually char from gasification.
As biochar markets grow we might expect to find more pyrolytic char made
"for purpose" but now we have some pyrolitic char and byproducts of
gasification (including TLUDs) and combustion. 

The "high temperature" gasifier char performs very well and in some
applications better than pyrolytic char. Several studies (and some
commercial producers) have found that conditioning the char through
partially oxidation (to higher temperature) enhances nutrient retention.
These products are for improving soil fertility , not necessarily to replace
activated carbon. So why not consider CO2 gasification as a possible process
step?     

One major producer of char in California uses a downdraft gasifier. In a
downdraft gasifier wood devolatilizes at or above the oxidation zone.
Volatile carbon is oxidized by the air injected from nozzles to make CO2.
The hot CO2 reacts with the char to form CO and H2. This occurs in the
"reduction zone". The reduction zone is often shown as a deep bed of carbon
but in fact it is usually only a couple of inches thick. Large chips reduce
to powdered char in less than 2 inches where gas temperatures are 800-900C.
The resultant producer gas is a mixture of this CO from reducing char and
the devolatilized gas. Taking CO2 and reacting it with charcoal at 800-900C
as Purdue has done is not a lot different so the qualities of the char
should be similar. 

I think we need to explore all avenues of producing char and energy 

1.      Slow pyrolysis - 25%-30% char; 30% oil+gas

2.      Fast pyrolysis - 15% char; 60% oil

3.      Gasification - 5%-25% char; 75%-95% energy

4.      Combustion - 1-5% char; 95% heat

Tom

From: biochar at yahoogroups.com [mailto:biochar at yahoogroups.com] On Behalf Of
Ronal W. Larson
Sent: Monday, December 23, 2013 2:53 PM
To: Biochar; Tom Miles
Cc: Crispin Pemberton-Pigott; Gasification-Request
Subject: Re: [biochar] Pine char gasification

Tom etal:

   1.   I'm not sure I want to accept the "philia" part of this message
("philia" goes with "abnormal" and pedophilia at one google site).  I found
the word agape - but that sounds presumptuous.  But I do admit to being at
the non-sensical end of the char spectrum.  Maybe charphilia is apt.

  2.  I know close to zero about any part of gasification, but I can
understand why one would promote the idea of recycling the CO2 to get more
gas (eventually the Purdue group wants liquid, it seems).  But that has to
result in less char - and apparently leaves much higher temperature char.
Eventually it is almost all CO2, for gasification, but I worry that the char
produced this (high temperature) way might only be suited to replace AC =
activated carbon.

  3.  Since Alex English name came up today, we should note that he also
recycles CO2.

  4.  The dogma of the cult I am in says more char beats more heat, gas or
liquid, so I will look forward to some proof that is not correct. 

 Good luck to the Purdue folk.

Ron

On Dec 23, 2013, at 12:58 PM, Tom Miles <tmiles at trmiles.com> wrote:

Ron,

This work is very important for both the biochar and gasification lists.
Biochar will be produced at the large, or even small, scale as a co-product
of energy (liquid fuels and/or power). The most efficient way to generate
power from the gases and vapors from slow pyrolysis (50% of the energy) is
probably through charcoal gasification (e.g. run the pyrolysis gases through
a charcoal gasifier). There are commercial systems under development to make
char and power in this way. There are also commercial systems under
development to make liquid fuels through combinations of pyrolysis and
gasification. The char products from these and fast pyrolysis processes run
from 0% to about 15% of fuel input. I don't know the fuel or char yield for
Cool Planet.

This particular study prepared the char with high temperature (826 C)
nitrogen.  Wood particles (chips, sawdust) and resultant char particles in
this study are larger than for other char studies. Obs

ervations about BET surface area, particle size and the char morphology are
very interesting. The char morphology looks different than the SEM images
that we typically see. From gasification and pyrolysis we know that pine
carbonizes differently than hardwood so it is interesting to see the
shredded fibrous appearance of the pine char in this study compared to the
neat geometric structures that we often see, which is probably from hardwood
chars. The authors observe that the macropore volume is significantly
greater than the mesopore or micropore volume of the char. They observe
"numerous wide tunnel protruding into the char particles. . . [that] may
provide pathways for bulk transport of CO2 into the particle."

Char conversion numbers are interesting. Only 10-12% of the char was
gasified at 726 C (BET 391 m3/g) while 98-100% was converted at 896 C.
Surface area increased with conversion but not much greater than the 35-47%
conversion at 776 C so CO2 gasification could be used to increase surface
area at the expense of half of char (660 m3/g). Meso and micro pore volume
doubles at the higher rate but stays pretty constant above 776 C.
Researchers conclude that a significant proportion of the pore volume is
within macro pores although the majority of the internal surface area is
within micro pores.  They point out that the mass loss with surface
gasification occurs within the smaller pores leading to pore widening.

Researchers explain that the char gasification process involves three steps:
(1) adsorption of the gas-phase species to the char surface, (2) surface
reactions, and (3) desorption of the gasification products from the surface.
The latter is the rate limiting process.

Recycling CO2 from gasification to gasify the char is an interesting concept
that may apply to modifying char properties (e.g. increase surface area)
from pyrolysis or recovering energy (heat, power, syngas) in an industrial
setting.   

There is very little information about gasification or combustion chars.
Sometimes it helps to step back from our char-philia (and gaso-phobia) to
see what products combined pyrolysis and gasification can produce.  

Tom

RL> don't see any relevance to the biochar list.  (Except if this work shows
that char is more valuable in the ground and/or that an approach like Cool
Planet's is more efficient.)  On the biochar list, we should want BOTH high
value fuels and charcoal.   

     This Purdue work is all about gasification of char - not pyrolysis.   I
am not sure whether the topic is appropriate for "gasification" either,
since that list seems to want gases for engines, not liquids.

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