Influence of the release and combustion of volatiles on char reactivity of solid fuels

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The current project investigates the influence of volatile release and ignition conditions on the following char burnout of solid fuels, the latter being time-determining for the thermal conversion process. Char combustion has been investigated in many research activities. Experiments, which determine char combustion rate parameters, have been carried out with unprocessed fuels, devolatilizing in the experiment prior to char combustion, or with separately prepared char, leading to comparable char properties for experiments under varying conditions. It is a well-known fact, that the production conditions heating rate, temperature and holding time of the final temperature affect the reactivity of solid fuel chars. As the ignition of volatiles, which is typically not separated from the char combustion process in technical devices, influences the thermal conditions in a particles boundary region, this influence has to be investigated experimentally.This projects aims to investigate the influence of volatile combustion and ignition on the reactivity of solid fuel chars. Typical pulverized fuels (coals and biomass) will be burned in a lab-scale reactor. Characteristic particle sizes of dp= 100 µm are investigated, with varying oxygen content in the applied atmospheres realistic conditions will be simulated. The ignition process will be characterised by optical methods (chemiluminescence, imaging pyrometry with a newly developed camera system) and solid sampling. This enables to determine the time-dependent ignition process and the remaining solid (char). The results from the ignition experiments are used to define positions for char sampling. These samples will be re-fired later on to investigate char samples from different ignition conditions in equal combustion atmospheres. Char reactivity is characterized by measurement of particle temperature and diameter with the newly developed camera system. The temperature and diameter data will be used to calculate char burning kinetics parameters. These parameters will be used to identify the influence of ignition and devolatilization conditions on the subsequent char combustion process.