However getting back to wood gasification, the process starts with the chipping of the wood into small pieces, which are then conveyed into a heater which is usually fired with the end product gas. Wood has a very high water content, so the heater is used to remove the moisture content of the wood to below 2%.
There are complicated chemical equations which show the gasification of wood process, but I shall endeavor to simplify a really complex process.
Basically from the heater the dry wood chips are conveyed to a gasifier, which is a vertical vessel. There the chips are subjected to high temperature in virtually anaerobic conditions. This is the pyrolysis stage producing tar, char, and volatiles in this first process.
As the char and volatiles rise up the gasifier, they are then subjected to further intensified heating in the combustion stage. In this second stage oxygen is added to the char and the reactions form carbon monoxide, carbon dioxide, and steam which are then combusted. This provides more heat causing the gasification of the char, which is the third stage; it reacts with the carbon dioxide and steam to form the gasses of hydrogen and carbon monoxide, which happens about three quarters way up the gasifier to the top. This gas then exits at the top the gasifier where a portion of it is bled off for use in the drying and processing stages. It then passes through a tar extractor, is cooled, scrubbed and filtered, with the end product being known as producer gas or wood gas.
