Multi-fluid modeling biomass fast pryolysis with particle shrinkage model for complex reaction kinetics

Abstract

In the gas-solid fluidized bed reactors for biomass fast pyrolysis, the diameter of particles normally shrink with the process of reaction, which not only affects the hydrodynamics such as segregation/mixing and entrainment behavior, but also influences the yield and composition of the products. Since the particle shrinkage model developed by our previous work (Powder Technology, 2016, 294: 43–54.) could be only applied for the simplified non-competitive single-component single-step reaction kinetics, in order to develop the advanced particle shrinkage model for complex pyrolysis reaction kinetics, three types of pyrolysis reaction kinetics considering the competitive reactions, the secondary cracking of tar, and the intermediate stage between virgin biomass and final products, respectively, were selected as the examples to illustrate the method for developing the relevant particle shrinkage models based on the mass conservation at the particle scale. Consequently, the biomass fast pyrolysis process in a bubbling fluidized bed reactor was simulated combing the particle shrinkage model and relevant pyrolysis reaction kinetics simultaneously. The influences of different particle shrinkage models and reaction kinetics on the flow and reaction behavior were revealed, and the predicted product yields were also compared with the experimental data.