Numerical simulation of biomass fast pyrolysis in fluidized bed and auger reactors

Seeking a clean alternative energy resource is inevitable because of the limited fossil fuel energy resources and greenhouse gas emissions issue. Recently, advances in chemical and fuel processing technologies allow us to convert biomass to energy products with high energy density and value. Fast pyrolysis process is among the promising technologies for converting biomass to bio-oil and combustible gases and has gained substantial attention due to its ability to produce high yields of bio-oil, a valuable liquid which can be further upgraded to transportation fuels. Nonetheless, many obstacles need to be overcome in order to utilize biomass fast pyrolysis effectively and economically. For example, moving to large-scale operations is an important step to lower the capital cost of such processes. However, a detailed understanding of the complex thermo-physical phenomena happening inside the fast pyrolysis reactors is needed for designing and optimizing the process at large scales. In this work, biomass fast pyrolysis is studied in various reactor geometries using a comprehensive numerical framework developed in this study. In this framework, a combination of a flow solver and chemical reaction solver is employed to describe pyrolysis of biomass. A multi-fluid model is used to describe the multiphase hydrodynamics of fast pyrolysis and the kinetic theory of granular flows is used to account for the solid phases. Then, a global pyrolysis reaction mechanism is coupled with the multi-fluid model to build a comprehensive CFD model capable of predicting time-dependent properties of chemically reacting multi-phase flows in pyrolysis process. A time-splitting technique is also employed to couple the flow solver and reaction kinetics. This numerical model is first tested on a bubbling fluidized bed pyrolyzer and validated using experimental data