[Stoves] gasifying sawdust

Crispin Pemberton-Pigott crispinpigott at outlook.com
Sat May 23 14:52:51 CDT 2015


Dear Rob

 

http://cgpl.iisc.ernet.in/site/Portals/0/Publications/ReferedJournal/PartIEx
perimentalstudiesonapulverisedfuelstove.pdf

 

That has the (slow to load) article with a demonstration of how to burn
sawdust with multiple vertical holes instead of the more common (VITA
Handbook) single vertical with single side channel.

 

There are charts of the gasification phase and combustion phase and it seems
to me they ran it in TLUD and BLUD fashion. The burn rate seems to be TLUD
because it is really constant at 0.11 g/s or 1.6 kW.

 

They report the gas phase equivalence ratio but that is such a strange
metric for solid fuel it will be better to try to interpret the gas charts
and make other calculations.

 

There is a very interesting and simple demonstration in Fig 4 of how to tell
where the pyrolysis front moved to during 30 minute runs. I suggest anyone
who is working on gasifiers look at how that was done with three sheets of
paper. 

 

Then conducted pot swapping tests to detect the heat transfer efficiency
under all power conditions (as per CSI-WHT and Indian test 13152).  This
same approach was used on pellet stoves by Penn Taylor using the Burn Out
Test Protocol. See Fig 8.

 

The CO measurement method (sample above the stove) like the PM measurements,
depends on the room and its air turnover to get a number and that does not
translate back to a stove performance metric. They also used a hood to get
O2, NOx and O2. This is dangerous because such an approach means the CO2 has
to be calculated on the assumption that it is not making char. So the
calculated CO/CO2 ratio could be far different from what is assumed. For
anyone who tries this, using a scale under the stove, be aware that
detecting CO and O2 does not tell you what the CO/CO2 ratio is at any time
unless you are burning whole fuel. That is rare in a solid fuel stove.
Unfortunately trying to make an accurate mass balance calculation requires
that one measures the CO2 as well. Done properly you need CO, CO2, O2 and
H2O (vapour). 

 

Regards

Crispin

 

 

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
Robert Lerner
Sent: Saturday, May 23, 2015 14:12
To: Ronal W. Larson
Cc: Discussion of biomass
Subject: Re: [Stoves] gasifying sawdust

 

Thanks Ron. I posted a few photos here:
https://plus.google.com/photos/112929397141178613286/albums/6074575146282561
169.

 

Sorry, I don’t have metrics or performance data. Pressure drop through
sawdust can be considerable, so particle size matters. Planer shavings are
easier than coarse sawdust. Fine sawdust (e.g. from sander or finish work)
is all but impossible. Moisture content was very high (as are most things in
the humid tropics!). I recall running exhaust from my Dodge truck through
the load to heat-dry it to the point where it could sustain a flame. 

 

The big TLUD It was used to dry/prime an even bigger retort kiln (4M³)
filled with damp coarse (up to 30cm dia.) forestry residues, so after
pyrolysis we kept the blower going and oxidized the carbon as well, to wring
all the heat out of it that we could. When the big retort finally took off,
it was pretty amazing. Boys building things and burning stuff


 

We recently looked at reviving the TLUD design to fire ceramic water filters
for CATIS-Mexico (CATIS-Mexico <http://catis-mexico.org/> ), but couldn’t
fit the TLUD into our budget, so we’re going to fire the filters in a
ceramics kiln chamber using a sawdust blower-burner.

 

Rob 

~~~~~~~~~~~~~~~~~~~~~~~
Robert A. Lerner
Mexico cell: 415-101-4591
U.S. direct: 619-618-1248
Skype ID: bajarob
Rob's Biochar TED talk <http://www.youtube.com/watch?v=SgwwV6YrWb0> 

Board member CATIS-Mexico <http://www.catis-mexico.org/> 

~~~~~~~~~~~~~~~~~~~~~~~

 

On May 22, 2015, at 10:16 PM, Ronal W. Larson <rongretlarson at comcast.net
<mailto:rongretlarson at comcast.net> > wrote:

 

Rob and list:

 

            Sounds like an important advance.  Congratulations

 

            I’ll bet most on the list would like to see your pictures.

 

            What weight of sawdust?   The fuel bed height?  Times for the
pyrolysis front to reach the bottom and for total combustion?   Have to
change to lots more “primary” after you had made the char?  Can you
guesstimate the several butterfly ratio settings?  Power for the fan/blower?
Might you have been able to save the sawdust char if the  4 m3 wood was dry?
Any way to describe cleanness of the burns?

 

Ron

 

 

On May 22, 2015, at 6:06 PM, Robert Lerner <bajarob at gmail.com
<mailto:bajarob at gmail.com> > wrote:





We built a big (1M dia.) fan-forced sawdust TLUD gasifier in Costa Rica,
designed by Nikolaus Foidl.

 

Used one blower with two butterfly valves—one to balance primary:secondary
air ratio, and the other to adjust total airflow. 

 

Worked great, though we combusted the char too, because were using the TLUD
to dry & prime a 4M³ retort kiln filled with high MC wood. I have pictures.

 

Rob Lerner

~~~~~~~~~~~~~~~~~~~~~~~
Robert A. Lerner
Mexico cell: 415-101-4591
U.S. direct: 619-618-1248
Skype ID: bajarob
Rob's Biochar TED talk <http://www.youtube.com/watch?v=SgwwV6YrWb0> 

Board member CATIS-Mexico <http://www.catis-mexico.org/> 

~~~~~~~~~~~~~~~~~~~~~~~

 

On May 22, 2015, at 12:00 PM, stoves-request at lists.bioenergylists.org
<mailto:stoves-request at lists.bioenergylists.org>  wrote:

 

Message: 1
Date: Thu, 21 May 2015 11:11:33 -0700
From: Tom Reed < <mailto:tombreed2010 at gmail.com> tombreed2010 at gmail.com>
To: " <mailto:stoves at lists.bioenergylists.org>
stoves at lists.bioenergylists.org"
                < <mailto:stoves at lists.bioenergylists.org>
stoves at lists.bioenergylists.org>
Subject: [Stoves] Sawdust Gasification
Message-ID: < <mailto:3B3D1B5B-91C0-408B-8FBE-38ADAE3896A2 at gmail.com>
3B3D1B5B-91C0-408B-8FBE-38ADAE3896A2 at gmail.com>
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Dear List

One of the benefits of the TLUD stove working on wood chips is that it
produces 20% charcoal, which can be sequestered, removing 38 tons of CO2
from circulation for each           ton of wood gasified (20% due to
formation of charcoal from the lignin and using the gas from the cellulose
(renewable) in place of propane, natural gas of coal gas.  

If we could gasify sawdust, it would bring another, typically dry, source of
fuel into the picture.  However, the particle size of sawdust does not
permit TLUD operation.  Does anyone have a suggestion of how to gasify
sawdust?

TOM REED 

Thomas B Reed 
280 Hardwick Rd
Barre, MA 01005
508 353 7841

 

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