The gasification reaction corresponds to the thermochemical transformation of solid combustible biomass (most often wood) into a mixture of several combustible gases. It is in fact an intermediate reaction between pyrolysis and combustion.
Gasification consists of decomposing a carbonaceous solid (biomass) into a mixture of combustible gases by heat and in the presence of reactive gases (oxygen, team). The biomass is, in this case, subjected to complex thermochemical phenomena which follow one another: drying, pyrolysis, partial oxidation and reduction. The gasification reaction takes place under high temperature conditions.
The resulting synthesis gas, called ‘syngas’ (for ‘synthetic gas’), contains hydrogen (H2), carbon monoxide and dioxide (CO and CO2), CnHm, tars and water. H2,CO and CnHm are combustible and their content will determine the calorific value of the gas. Syngas will therefore be used to produce heat, electricity, or both (cogeneration).
Wood is the most common raw material. However, it is possible to gasify all kinds of biomass such as agricultural co-products or green waste, which are generally dry, but also, and increasingly, sludge from sewage treatment plants.
What are the benefits?
The benefit of converting solid biomass into gas is its direct use in an internal combustion engine to generate electricity (alone or in cogeneration), in relatively low power ranges (300 to 1,000 kWel). Beyond that power, vapour turbines are more suitable.
Due to its low energy content, it is not economical to transport it, even when compressed, over long distances.