ABSTRACT
The thermal conversion of biomass requires elevated temperatures and thus heat is required to arrive at the temperature necessary. This heat could be provided by external sources, but we consider the situation that the gasifier is in island operation, where the required heat is generated internally by the partial combustion of the biomass fuel. For accomplishing partial combustion, oxygen is required; the oxygen is supplied through injection of air into the gasifier; this air is often called primary air. After initial ignition of the biomass, the burning process is self-sustainable and the heat, generated by the partial combustion, fuels a number of physical and chemical processes inside the gasifier: • Drying of the freshly fed biomass • Pyrolysis of the biomass-thermal decomposition yielding
noncondensable gases, water, tar, and char • Partial combustion of the pyrolysis products • Gasification of the char • Thermal-catalytic steam cracking as well as gasification of higher gaseous molecules • Homogeneous gas-phase reactions as well as the water shift reaction Assuming that all tar components are fully converted into noncondensable gases and taking 10 wt.% moist cellulose as the feedstock, the resulting overall reaction for the complete gasification
• Biomass and air have to be properly fed into the gasifier and the biomass is to be ignited to start the generation of heat, as required for lifting the temperature up to gasification conditions.
