Cold fluidization and kinetic of pyrolysis of wood in a fluidized bed reactor
Biomass pyrolysis is a process in which biomass is converted into gas, liquid and char through a heating process without any air. This process is gaining more attention since it can be used to produce liquid fuel, or tar, which is an alternative for fossil fuels. This thesis focuses on the use of wood shave as the feed stock in an experimental fluidized bed reactor for the pyrolysis process.
The fluidization behavior of wood shave is studied through a series of experiments using a cold fluidized bed, made of a clear plastic container. The wood shave was mixed with ash and sand to improve the fluidization behavior. A mixture of ash-wood in different wood weight fraction was provided and fluidized in the aforementioned plastic container. Increasing the wood weight fraction beyond 13% creates severe channeling, decreasing fluidization behavior. Minimum fluidization for each mixture was measured and the relative Reynolds Number was found respectively. Then the effective particle size and effective density for the different mixtures were calculated and based on these mixture properties the Reynolds Number was found, versus the Archimedes of the mixtures, to predict the minimum fluidization velocity for each. The calculated Reynolds Number is in a good agreement with the experimental data.
During the fluidization, many bubbles were created and the bed shows bubbling bed regime behavior up to a certain gas velocity. Thus a kinetic model based on the bubbling bed regime was developed, and the required temperature and residence time were extracted from the model.
Then an experimental set up, consisting of a stainless steel container and a band heater, was designed and built for high temperature pyrolysis of biomass based on the parameters achieved from the cold fluidization experiments and the kinetic model, suitable for further experiments.