Re: flash carbonization of biomass

[AJH <andrew.heggie@dtn.ntl.com>]

On Tue, 25 Dec 2001 23:10:17 -0700, "Ron Larson"
<ronallarson@qwest.net> wrote:


>
>    I looked at your site
>(http://www.soest.hawaii.edu./HNEI/R3proj.html#Anchor-High-Yield-47747) and
>found a little more than in your note.  Thanks for sending us this
>information and congratulations at finding a fast new means of pyrolysis.  I
>am afraid I still haven't understood the process - and I understand the need
>for doing more development work - and for protecting patents, etc.  I am
>sure we all wish you great success for pursuing your new,  higher pressure,
>lower energy approach - and of hearing more as you make further progress.


I am not familiar with Mike's work other than that which he has posted
to this list. I thought the major achievement of his process was the
high yield of carbon as opposed to high volatiles charcoal. This
should have good implications for low ash charcoal for use in high
grade metal refining.

>    However, I presume that your announcing this does allow you also to
>suggest whether there is a possible small-scale approach possible for
>home-based simple cook-stoves.  Higher pressure would usually equate to
>higher cost, but perhaps not.  

High pressure is very limiting as the vessel size increases, which has
implications for mechanised loading. What a lot of people seem to fail
to appreciate is that charring even at low pressures can be a quick
process.

> Certainly producing large amounts of
>charcoal quickly should eventually suggest also lower cost charcoal
>briquettes for home use.  But I am also asking whether you think charcoal
>making stoves (two outputs:  cooking and charcoal) are possible that employ
>your new discoveries?  Are there fundamental reasons to recommend persons on
>this list interested in small cook-stoves to stay away from high-pressure
>approaches ?  (I am thinking of something like a pressure cooker - which is
>not an outrageous complexity or price.)  You still must have a good bit of
>"waste" energy.  Do you think it is still possible to use that for rural
>bakeries, brick kilns, etc?

Ronal, I wish I had had time to comment on your posts with regard to
ceramic kilns, I consider them to be a good prospect for "cascaded"
use of heat as they reject their heat at such high temperatures and it
is often wasted. Use of pyrolysis offgas for a tile or brick kiln has
always been a dream of mine. Remember those posts all those years ago
of the school kid's method of making "drawing" charcoal in a cocoa tin
with a small pinprick to allow offgas to escape? The jet from this is
impressive and patently is driven by pressure in the can trying to
escape. The pressure arises because the wood has broken down to a char
residue and a vapour/gas mix. The same concept is used (from an
original idea by Yuri?) in the Karves' retort to char cane leaves. The
drawback of this retort heated from outside approach is that the heat
transfer can only take place through the walls of the vessel and
thence from char particle to unreacted biomass, but it does make use
of the offgas being flared in a supporting fire. There is likely to be
gradation of the extent of charring from outside to middle.

Traditionally char was made in kilns, basically an air starved fire in
a container, I believe the idd stove is a kiln in this respect. The
kiln has a heat transfer advantage in that the offgas and combustion
products circulate around as yet unreacted biomass. The disadvantage
is that valuable char is consumed preferentially to offgas to achieve
this.

So one needs to combine the attributes of a kiln's good heat transfer,
with those of a retort's high char yield. This is the approach Lurgi
used in coal retorts and I believe the Simcoa plant. Mike appears to
be taking the same route and it is also my preferred approach.
Unfortunately despite being on the starting blocks since 1997 I have
got no further than preliminary tests and a long winded research
project with a UK academic establishment.

This is why I am not keen on promoting IDD as a means of making
charcoal, though I am happy to accept its by product is charcoal that
is produced with little pollution and as such is better than much
charcoal making. I think Tom Reed agrees with me the IDD pyrolysis
front is powered by charcoal burning, plainly this detracts from
charcoal yield. With the advanced clean charcoal making I, and Mike
Antal, are playing with any heat necessary for maintaining pyrolysis
comes from burning some of the offgas and recirculating this hot gas
stream through the char. There are a number of ways of configuring
this, none patentable IMO but nonetheless the actual designs will be
proprietary and subject to confidentiality.

The implementation I am looking at uses quite basic technology and
should be possible to deploy in the sort of situations envisaged by
the Karves' project. A benefit to my mind is that this method can
control the temperature and cook time of the biomass to vary the
resulting char from post torrefied wood through Tom's seasweep and up
to metallurgical grades. My interest is in high volatiles charcoal and
I have made material which is friable like charcoal but retains 45% of
the mass of the original dry matter.

AJH


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