- Wood based fuels
- In a gas generating process with wood based fuels the efficiency depends on the
moisture content of the fuel. There are no major differences between the various
kinds of wood. The wood must be dry. The drier the wood is the better it suits the
gas generating process. If the wood is dried to 20% moisture content with natural
methods it must be peeled in stripes when limbed and stored outside in an airy
The size of the wood particles affects the gas generating process. The suitable size
is defined by the dimensions of the generator. The generator can be made to be able
to use either wood chips or chopped wood. A generator designed to use chopped
wood can not be used with wood chips. A generator designed to use wood chips
can be used with wood chips.
The best wood chips can be made from unpeeled limbed wood. The wood can be
either leaf wood or coniferous wood. For reliable operation of the generator big
chips are better than little ones even if the amount of gas generated is not the
greatest possible. The smaller the chips are the more gas is generated but also more
malfunctions occur. So for example cuttings are not suitable fuel if not pelleted. The
best size of the wood chips is 10x20x30 mm and the size of all chips should be as
equal as possible. This kind of fuel produces an airy glowing charcoal layer on the
hearth. The amount of gas generated is constant and no malfunctions occur.
The best possible fuel for gas generating is charcoal which produces very pure gas
with a high heating power. To produce one cubic meter of charcoal 2,5 cubic
meters of wood is needed and a great part of the total heating power of the wood is
lost in the process. One cubic meter of wood is equal to 200 liters of gasoline. One
cubic meter of charcoal is equal to only 80 liters of gasoline.
- Sod is not proper fuel for a gas generator. It produces much ash which melts on the
hearth and clogs it after a while.
- Pelleted straw can be used as a fuel in a gas generator. The properties of straw
vary from crops to crop. The most suitable straw for gas generating is one that
produces ash with a high melting temperature. For example turnip rape produces
this kind of straw.
When generating gas from solid fuel the combustion is incomplete. The gas contains
carbon monoxide and several organic compounds: ethylic acid, formaldehyde, etc. The
gas contains substances that are harmful to personal health. Therefore the gas generator
may not be started or used in a closed space. In addition to this the user must not inhale
the gasses released from the generator and the condensed liquids must be treated
Fuel recommendations: The most recommended fuels for a forward flow gas generator
are wood-based fuels:
- gas with the best quality is produced from charcoal. Charcoal is quite difficult to
manufacture and much energy is lost in the manufacturing process.
- second best gas is produced from chopped wood. The quality of gas generated is
the same all the time and the process is easy to master. Manufacturing chopped
wood takes much time and effort.
- the next best is wood chips. Wood chips require special arrangements to get
continuous gas production: movable hearth to prevent clogging and shaking system
for the generator if used stationary to prevent arch formation. The smaller and
lighter the wood chips are the more difficult it is to master the process.
The wood based fuel must meet the following requirements:
- moisture content about 10%, max 20%
- even size of the particles, no sticks or big particles included
- the wood must not be rotten. Wood species containing tree resin can be included.
The wood need not be peeled but also the peel can be used. On the other hand the
peel itself is not suitable as fuel because it contains much tar and the ash melts in
Translated by Olli.