[Gasification] Very interesting auto engine powered char maker

[Ken Boak]

Tom, Andrew, Drew & List,

For some reason I failed to receive Tom's first reply email about my 
charcoal making this weekend.  I later found it on the archive.

Whilst the method I described produces a fairly low volumetric yield (25%), 
and a lot of smoke,  it does serve to illustrate to the newcomer the various 
stages of the burn and is a good way of learning a little about the 
practical aspects of charcoal making and the process of gasification.  The 
wood was alder, cut from 6" diameter cordwood which was felled last year, 
but left stacked outside - so still fairly high moisture content.

My own aims are to use the waste heat from my Lister exhaust to at least dry 
then torrefy the woodchip fuel.  I have successfully recovered and measured 
4.2kW heat from the 6hp Lister exhaust when running at rated output.

My next step will be to construct a downdraught gasifier, onto which a 
torrifier stage may be added.

There is also the "pneumatic" power contained in the exhaust of the slow 
speed diesel, which could also be utilised for fuel-handling, grate-shaking, 
de-bridging etc. I like the idea of the metal bellows in the top of the 
Kalle gasifier, that responds to engine demand and is used to provide the 
self cleaning action of the air nozzle.  With the Lister running as slowly 
as 300 rpm, the exhaust beat will be as low as 2.5Hz and could be utilised 
for mechanical agitation of the fuel or reactants in the reaction zone.

The interesting part will be to determine whether there is sufficient 
temperature and excess oxygen in the diesel exhaust to provide an effective 
charcoal initiator.

I have been running the engine very much derated, on waste vegetable oil, 
and this gives rise to much greater quantities of carbon and unburnt fuel 
residues in the exhaust.  When I move to dual fueling on WVO and wood gas, 
my intention is to use the woodchips in the fuel hopper, not only to capture 
these particulates and deliver them to the reaction zone, but to use the 
woodchips as an effective silencer/muffler for the pulsating engine exhaust.

Additionally, with the Lister runnig at 300 rpm,  the powerstroke has a 
duration of  0.1 seconds.  This gives the burning woodgas plenty of time for 
flame propagation. I would be interested in correlating the flame speed of 
the gas mixture to the performance within the slow speed engine - however in 
dual fuel mode, the injected oil will continue to burn well towards the end 
of the powerstroke.

This paper discusses effects of compression ratio on a producer gas fuelled 
engine

http://cgpl.iisc.ernet.in/Biomass%20derived%20producer%20gas%20as%20a%20reciprocating.pdf

It suggests (quite contrary to popular belief) that compression ratios up to 
17:1 can be retained with producer gas fuel, and that the derating is not as 
severe as often thought - conclusions that require further investigation.


regards,


Ken









Dear Ken and All:

I never wanted to be a charcoal maker (Kohlbrenner).  From 100-1900 AD
they lived in the forest, piled up a dozen chords of  wood, covered it
with turf, lit it at the bottom, watched the steam phase, the smoke
phase and finally the blue haze phase, then plugged up the inlet and
outlet holes and let the pile cool for a week or two.  Total time, a
month;  I presume they played cards, drank, etc. as they burned down the
forests of Europe to make the guns and cannon that kept the population
in check.  The resulting desert and the replanting of the forests is
described for those who care in the book "The Man who Planted Trees" by
Jean Giono (available BEF Press, Chelsea Green Press with woodcuts, or
many other publishers, see
http://en.wikipedia.org/wiki/The_Man_Who_Planted_Trees).
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Charcoal is the secret to all good biomass gasification, both in the
production of charcoal (in pyrolytic gasifiers) or the simultaneous
production and consumption of the charcoal in WWII gasifiers.  Depending
on the direction of air through biomass, first or last, the resulting
gasifier will be a "tar-burning, char making" (TBCM) biomass gasifier
(also known as a downdraft, toplit updraft, crossdraft, flaming
pyrolysis etc. gasifier) or a "charburning, tar making" (CBTM) gasifier
(also known as (bottom lit) updraft).  These are all easily illustrated
in the burning cigarette/cigar gasifier discussed here last week.

Thanks for describing the CBTM production method. If you ever run this
experiment again, I hope you will report the moisture content and mass
of the fuel and the final weight of charcoal produced.  I would guess
between 15 and 25 %, depending on the moisture content.  I presume it
would work in a 5 gallon can, and I know it works in a tomato soup can.
However, I hope you didn't have anyone around to object first to the
white smoke, then yellow, then green, mostly incombustible.

Let me describe three more ways of making a drum of charcoal.
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About 1998 Danny Day at a family party connected the tailpipe of his
truck to the bottom of a 55 gallon drum full of peanut pellets.  He ran
the truck (fast idle?) for a while and soon had a combustible gas flare
30 feet tall that entertained the guests.  The charcoal was very dense
and this simple experiment started Danny on making activated charcoal, a
good idea then, not now that the Chinese do it cheaper....

This method relies on using the dephlogisticated (deoxygenated) hot
exhaust (>500C?) produced by consuming the oxygen in the input air with
gasoline.  It differs from the classical method in using higher heat
transfer heating that is fast enough so that the (dry) pellets pyrolyze
and dry simultaneously, so that the flare is combustible from the getgo.
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If you repeat your experiment by packing the fuel tight and lighting the
*top* layer (alcohol or kerosene) of wood or preferably charcoal, air
will be drawn through the mass of fuel to the burning charcoal.  A
combustible gas is formed which can be used for cooking (in the TLUD ND
gasifier) or many other processes.  The charcoal will successively light
lower and lower layers until the flame turns blue when all the biomass
is converted to charcoal and it becomes an updraft charcoal gasifier.
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Finally, if you are brave, you can get a vessel that can maintain a
pressure of 10-20 atmospheres and apply heat (electric or biomass)
around it.  Since the increased pressure keeps the volatiles from
vaporizing at the lower temperature, you can achieve a yield of 35-45%.
This method has been pioneered and patented by Prof. Mike Antal, Coral
Professor at the U. of Hawaii and is nearing commercialization.  His
latest paper on the subject is: M. J. Antal et Al,  "Biocarbon
Production from Hungarian Sunflower Shells", available online at
ScienceDirect (7 references).  It is on my pile to write Mike with comments.

So, charcoal is the key to biomass gasification in many ways, and is
also produced by various processes from gasification.  I've learned to
love it.

Onward, Kohlenbrenners!

TOM REED                          BEF/BEC
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