There are a variety of systems that can
transform wood into energy for residential,
commercial, and industrial uses. Energy
from wood can be used to generate
electricity, heat buildings, and produce
steam for industrial purposes. In addition,
combustible gas and liquid oil can be
extracted from wood through the process
of heating wood at a high temperature
in the absence of oxygen. This process,
called pyrolysis (pyro means fire and lysis
means decomposition), distills the wood
into three main products: combustible gas,
liquid oil, and char. Pyrolysis is one of the
first chemical reactions that occur when
a biomass material is burned. The flames
that are visible when the material is burning
are not a result of the combustion of the
material itself, but instead flames occur
because of gases released through the process
of pyrolysis. For example, when you build
a campfire, it slowly lights because it takes
time for the wood to be heated to the point
of releasing gas. When the wood becomes
hot, pyrolysis gas is released, and the fire
begins to burn. As more and more gas is
released, the fire grows larger and larger.
Eventually, only ash is left. The fire goes out
because the ash does not release any gas.
This lab activity demonstrates the
process of pyrolysis through the heating
of wood chips and wood pellets (or other
biomass materials) over a Bunsen burner or
portable butane burner in a test tube sealed
with a rubber stopper. Heating biomass
material will create a combustible gas that
burns as it escapes through the glass tube in
the rubber stopper. As the gas continues to
burn, you will see liquid oil begin to form in
the test tube. In addition, the biomass in the
test tube will be converted into char.