Dear Mark and all,
Drying wood is a science for some people, it is for us just a necessity.
We have been making furniture in Indonesia and local cottage industry,
was drying wood under sun. No matter how hot the weather was, wood never
go down below 18%. That was unacceptable, considering we ship furniture
to Denver where relative humidity is very dry. All the furniture was
getting cracked. I introduce a very simple system which was adopted by
the local government as most efficient way of drying wood. Since the
people using the kilns were not educated, our moisture meter was the
walls! When they openned the side door for inspection, if they saw wet
walls, they opened up vents for 15 minutes, or until the walls were dry
again. We simply put a U steel pipe, made with 1 cm thick mild steel, on
the back of the kiln, which was covered with small room built with
bricks. We burned the waste wood in the room, returning air from kiln
enter from bottom of the U and after heated and dried somewhat, pulled
in to the kiln with the pulling force of fans. Because of humidity and
heat, fans lasted about 6 months, they were cheap enough to replace
until we started using special insulated motors, we also solved this
problem. The kilns in my factory worked for almost 12 years with very
little maintenance, since we dried wood under moisture there was not
much warping and cracking.
We now take the same simple principle to dry the wood chips for
gasification or saw dust for briquette production. We use the heat
exchanger for the exhaust gas to lower the heat, to make sure we will
not have fire.
Mark, you are absolutely right, in the big hoppers, chips on the bottom
will dry first, and the moisture will be rising to top. One of our
projects involve drying wood chips from 30-40% down to 10%. The hopper
has capacity of 120 m3. We feed the exhaust heat from the bottom and
installed simple vents on top. When the moisture hits certain level,
the vents open and moisture air pushed out by the force of blowers which
feeds the hopper. Since we feed the boilers and gasifiers, from the
bottom of the hopper ( Hopper supplies wood chips to 2 hot oil burners
and gasifier) it works well for us. Because we dried to wood chips down
to 15%, energy we receive is more from the chips, monthly wood chips
savings are about 300 tons.
For the gasifier feed, we design another system and jacketed screw
feeder for drying wood chips further, since we ad a longer screw feed
and this is an outside installation, we added couple of feeding points
and couple of chimneys to take the moisture air out. I try to apply what
I learned from the list, "The drier the wood is, the less the tar."
On this joyful Holiday season, our best wishes to you and your families.
Regards,
Robert Kana,
Biomass Energy, Indonesia
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