Vince Pitelka on tue 30 apr 96
John -
Jim Logan at Amherst Highschool in Amherst MA (call info at 413-555-1212) fires
a raku kiln with a homemade sawdust burner. His system would not be adequate
for a large kiln if you want to be able to go away and leave it.
The homemade systems I am aware of immitate the larger industrial systems.
They require graded sawdust (you could grade your own with a screen), and
involve a large sawdust hopper tapering to an opening at the bottom, with a
shaker (an electric motor with an eccentric weight mounted on the shaft)
mounted on the sheet-metal sides. The sawdust feeds out the opening by
gravity, and falls against a very light-weight spring-loaded flapper attached
to a micro-switch. If the sawdust jams in the hopper, as is prone to happen
frequently, the flapper raises and the micro-switch activates the shaker, which
starts the sawdust flowing again. From the hopper outlet the sawdust falls
into an opening in a pipe with an auger running in it. You can make your own
auger, with a 1" central shaft, a supply of 3/4" x 1/4" flat bar, and a
"rosebud"-tip on an oxy-acetylene outfit to bend the flat bar in a spiral (like
a spiral kid's slide) around the central shaft, with bearings on each end
supporting the shaft. The auger feeds the sawdust down the pipe, and it drops
into a "Y"-branch intersecting the pipe leading from blower to burner port.
The point where the sawdust-branch intersects the blower tube must be designed
in such a way that the air passing by it creates a vacuum, pulling the sawdust
into the airstream. During the firing, the blower speed, and the auger speed
determine the BTU output of the system. If the auger is running slow the
sawdust might back up in the hopper opening, but this doesn't matter. I would
not expect the hopper on a homemade system to supply the burner for more than a
half hour or so. The more sawdust in the hopper, the more weight pushing down,
and the more likely it will jam. If the weight is excessive, even the shaker
might not jar it loose. It seems that frequent refilling of the hopper is
necessary with homemade systems. Also, such systems are apt to need constant
tinkering, and the tendency of the sawdust to flow may depend on the type and
fineness of the sawdust and the amount of humidity in the atmosphere. Maybe
someone out there has experience with a system that runs more trouble-free.
I'd love to hear about it.
- Vince
Vince Pitelka - wkp0067@tntech.edu
Appalachian Center for Crafts - Tennessee Technological University
Smithville, TN
WardBurner@aol.com on tue 30 apr 96
Hey,
Another thing that determines BTU output of sawdust injection burners is the
moisture content of the wood. The water present in green, wet wood, needs to
be turned to steam and driven off. This takes considerable energy that is not
being utilized to raise the temp. of the kiln. If your source of sawdust is
from the furniture industry or like industry that uses kiln dried wood and
then keeps it under cover, your in luck. I think Lowell Baker might be
lurking out there...if he is, he's the person to talk with.
Marc Ward
Ward Burner Systems
PO Box 333
Dandridge, TN 37725
423.397.2914 voice
423.397.1253 fax
wardburner@aol.com
LOWELL BAKER on wed 1 may 96
there are many factors in the performance of the sawdust injection
burner. Moisture is certainly one. I find that small amounts of
moisture are beneficial. I have even fired with sawdust from a
"rough cut" mill. It worked great. One advantage of some moisture
is that it slows the firing some. the sawdust injection burner is
either on or off. you either get no heat at all or you get
hundreds of thousands of btu. It is difficult to regulate at the low
end. I cannot imagine a situation with the exception of a multiple
chambered kiln that would allow you to bisque.
Other problems that you will encounter are sticks, splinters and
blockage. I am currently working on a design change which will (I
hope ) correct this fault. Screening the sawdust helps. Shavings
burn great but are very problematic in smaller systems due to the
clog factor.
I am delighted to see the interest in my burner from this group. I
am in the middle of the end of the year here at the University of
Alabama. I will be firing the sawdust burner here through the first
week in July. I have designed and have 80% complete a new generation
wood kiln which will fire with the sawdust injection burner. It
should be up and running by mid June. It has to work because I have
an exhibition with those wonderful folks at Nanyang Technological
University in Singapore this summer.
I will be happy to walk people throught the process. Phone me at 205-
348-1889 next week. I will also be happy to let you know when we
will be firing as the time approaches if you would like to travel to
hot Alabama to burn sawdust this summer.
Keep in touch
W. Lowell Baker
The University of Alabama
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