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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 and hearth:
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.