Dynamical Modeling Of Biomass Pyrolysis In Fluidized Bed

Thermochemical conversion of biomass offers an efficient and economically process to provide gaseous, liquid and solid fuels and prepare chemicals derived from biomass. The main objective of this study is to develop comprehensive three-dimensional dynamic models capable of describing the biomass gasification or fast pyrolysis process in a fluidized bed and predicting the product and temperature distribution in the reactor. The model results can help to optimize the design and operation of thermochemical reactors. Recent progression in numerical techniques and computing efficacy has advanced Computational fluid dynamic (CFD) as a widely used approach to provide efficient design solutions in biomass thermochemical process. The model results help to show the dynamics process visible and give more insight within the reactor under different operating conditions, which is a benefit to better understanding of the chemical and physical process. In this study, the CFD models on biomass gasification or steam gasification for hydrogen and fast pyrolysis for bio-oil, are developed. Mathematical equations governing the fluid flow, heat and mass transfer and chemical reactions in thermochemical systems are considered and sub-models for turbulence, radiation and other individual processes are included. The product and temperature distributions are studied. The model results are proved to be sensitive and valid.A three-dimensional CFD model of a fluidized bed for sewage sludge gasification is developed. According to the analysis of temperature and product distribution of simulations, the gasifier can be divided into four zones approximately, which are pyrolysis, oxidation, gasification and freeboard zone, respectively. The effects of temperature and Equivalent Ratio (ER) on product and temperature distributions show that the suitable temperatures are 1073-1273K and the suitable ER is 0.15-0.4 for higher content of CO and H₂. The predicted results are in good agreement with the experiment data, which proves the model is sensitive and valid. Simultaneity, with respect to the analysis of simulation data, the model provides possible conditions to get higher quality syngas with more H₂+CO and/or higher H₂/CO ratio according to the application intention.The three-dimensional CFD models for steam gasification of pine waste and air gasification of rice husk in fluidized beds are developed, respectively. The effects of the gasification agency amount and operating temperature on hydrogen content and distribution are studied. The optimization of the reactor design is analyzed.A three-dimensional CFD model of biomass fast pyrolysis for bio-oil in a fluidized bed is developed. The simulations give insight to the producing process of bio-oil. The mechanisms of biomass fast pyrolysis for bio-oil are very complex. The kinetics data of the process are difficult to determine. The accurate kinetics data is needed to optimize the model in the future.The studies show that CFD is a powerful tool for biomass thermochemical process applications including operating conditions analysis, dynamics process visible and product prediction.