Gasification is a high temperature thermochemical degradation process that, in a low-oxygen environment (partial oxidation), turns carbonaceous solid feedstock into a flammable synthesis gas (syngas) with a determined heating value, which varies depending on the feedstock. For example, using woody biomass and air as oxidant agent, the resulting syngas is mostly a mixture of hydrogen (H2), methane (CH4), carbon monoxide (CO), carbon dioxide (CO2) and nitrogen (CO2).
The goal in gasification is to take control of the discrete thermal processes, usually mixed together in combustion, and reorganize them: drying, pyrolysis, combustion, cracking and reduction. These processes are naturally present in the flame that we see in a fireplace where wood logs are burning, or the flame burning off a simple match, although they mix in such a way that the human eye cannot distinguish them. Through gasification we can isolate these processes and interrupt them before gas combustion happens, in order to pipe it away and burn elsewhere.
Gasification was originally introduced in the XIX century, when coal was gasified to produce town gas for public lightning and cooking stoves; gradually, natural gas and electricity distribution networks replaced it, but still gasification has been widely used from early XX century not only for making a combustible gas, but also in the production of synthetic chemicals such ammonia, liquid fuels, tar, char, hydrogen… Wood gas and gasifiers were widely used in Europe also on vehicles during World War II, as gasoline and diesel were rationed or unavailable: in fact, the gasification of 3 kg of beechwood could supply the equivalent of 1 liter of gasoline.