429474 Multi-Scale Discrete Element Method-Based Modeling of Biomass Fast Pyrolysis in Dual Auger Reactors

Tuesday, November 10, 2015: 3:36 PM
257B (Salt Palace Convention Center)
Fenglei Qi and Mark Mba Wright, Mechanical Engineering, Iowa State University, Ames, IA

Conversion of biomass into bio-oil by fast pyrolysis is a potential way to produce renewable fuels and chemicals, and provides an alternative to traditional fossil fuels. Auger reactors are often employed as pyrolyzers because of their ability to yield up to 65 wt. % bio-oil. Computational Fluid Dynamics (CFD) simulations have been carried out to investigate granular flow and mixing performance in auger mixers (prototype of auger reactors). However, only a few studies have focused on understanding the thermochemical process of biomass particles in the auger reactors. Besides, in the reported work, the particle-scale thermochemical phenomena are often simplified. Assumptions such as the use of isothermal particles ignores mass and heat transfer behavior with key implications to process performance especially for larger biomass particle sizes.

In this research, a DEM-based method is employed for the modeling of granular flow and heat transfer in auger reactors, and a 1-D single particle model is coupled to simulate biomass intra-particle transport phenomena. Simulations of cold granular flow in auger reactors are validated by comparing to experiment measurements. Furthermore, single particle simulations were conducted and compared to experimental studies. Single particle simulations show that the effects of intra-particle transport phenomena on the pyrolysis process become significant when the particle size is larger than 2 mm. Intra-particle secondary reactions can be ignored when the biomass particle size is less than 4 mm. Single particle simulations indicate the importance of intra-particle transport phenomena and potential simplifications that can be made in DEM-based modeling. 

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