When selecting materials for the wood gas equipment a compromise between the
expected life time and price must be made. 3,000 hours can be used as a reasonable life
time before complete overhaul. Highly stressed parts can be constructed to be replaced
easily and this will allow a shorter life time for these parts if highly durable materials
are not available. The materials should be easily weldable and they must keep their
shape when the operating temperature changes.
- Combustion chamber ring, air nozzles, hearth
- The most stressed parts in the gas generator are the combustion chamber ring and
the hearth which are in touch with the glowing coal layer. The operating condition
for these parts is charring. When the generator is not in operation dry distillation
products from the wood can enter the combustion chamber. The most harmful of
these is ethylic acid. The material must be able to withstand temperature changes
between -40 and +900°C. The air nozzles are not quite so highly stressed because
the combustion does not occur with full effect in the coal zone near these and the air
flow cools the nozzles from inside. The nozzles must also stand the effects of
ethylic acid. When the generator is in operation the hearth and the combustion
chamber ring are glowing in red.
- Requirements for the raw materials for the combustion chamber ring, air nozzles
- must withstand temperatures between -40 and +900°C
- must be chemically proof against water, acids, tar and charring
- must withstand mechanical impacts
- must keep its shape and be rigid
- must be easily weldable and machinable
- The combustion chamber ring, the air nozzles and the hearth are critical parts for
the operation of the gas generator. For these parts the best possible materials
available must be used. The combustion chamber ring, the air nozzles and the hearth
must be constructed so that it is easy to replace them when a failure occurs or the
fuel type changes. Because the gas generator must be designed to match the size of
the ICE to be used, this type of construction makes it easier to change the properties
of the generator if the ICE is replaced with a unit of different size.
- Combustion chamber mantle, air channels, tank for condensed liquid, fuel reservoir
(upper and lower part)
- These parts operate at temperatures between -40 and +700°C. The dry distillation
products from the wood are present. When a long life time is required the raw
materials must be chemically durable. Hot water vapor and acids are present. The
raw materials must be easily weldable and they must keep their shape.
- Filter housing inner parts, mixer, cyclone (spark trap)
- The temperature of the gas entering the filter can exceed 400°C. The gas contains
water which condenses on the walls of the filter housing if the filter housing is not
thermally insulated. The condensed liquid is alkalic. The filter element made of
woven glass fabric is installed on supporting steel rods which must keep their
shape in all possible operating temperatures. Normal steel types, for example Fe37,
easily meet these requirements.
- The cooler is surrounded by cool dusty air. Inside the cooler flows hot (up to
300°C) wet gas. This means that the raw material must stand temperatures between
-40 and +300°C and chemical corrosion. The pipes are soldered to the upper and
lower parts of the cooler with brass. The pipes can be equipped with fins to obtain
greater cooling effect. Copper, brass or aluminum are suitable materials for the
pipes. 10 mm is suitable inside diameter for the pipes because the gas is quite pure
and clogging does not occur. The lower part of the cooler must be spacious to
prevent the condensing water to turn into foam. The lower part must be connected to
a gas-tight tank for collecting the condensing water. This tank must stand the effects
of the condensing liquid and a proper volume for it is 10 liter.
- The gas piping is made of easily weldable and tight steel pipe. The inside diameter
must be big enough to ensure free gas flow. The piping must be as short and straight
as possible and sharp curves must be avoided.
Translated by Olli.