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Sammanfattning

To study biomass pyrolysis processes, a numerical model is developed in this work focusing on the cellulose constituent. A single cellulose particle is supposed to experience pyrolysis at a fairly high heating rate in the case of typical fluidized bed conditions. The model involves the pyrolytic kinetic scheme and the detailed heat and mass transfers caused by radiation, conduction, diffusion and convection with respect to the solid, liquid and gas products from pyrolysis. From the solution of the model, the central role of the reaction heat versus a slow heat supply through the particle is identified. The dynamic characteristic of the pyrolysis and the evolutions of the internal pressure and the flow of the products are analyzed quantitatively. Computation of the model shows the importance of particle permeability, whereas the liquid phase of active cellulose and inter-particle secondary reaction of volatile play a negligible role during the pyrolysis under a typical fluidized bed conditions both for small and large particles. Various predictions by the model provide a good understanding of the complex process of biomass pyrolysis, which can be useful for applications of thermochemical conversions of biomass.

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