Computational fluid dynamics/Discrete element method investigation on the biomass fast pyrolysis

Significance 

Presently, climate change and the need to reduce greenhouse gas emissions have become a global concern among stakeholders and policymakers. Therefore, development and use of alternatives sources of energy other than fossils fuels have attracted significant attention of researchers. Among the available non-fossil energy sources, biomass stands out due to its abundance and environmentally friendly nature. Recent studies indicate that different methods have been developed to enable efficient utilization of biomass by converting it into liquid fuel. For instance, a fluidized bed reactor is widely used for fast pyrolysis of biomass. Alternatively, several numerical simulation models such as the computational fluid dynamics have been developed to investigate biomass pyrolysis in a fluidized bed under different condition. Unfortunately, the effects of the varying conditions and model parameters have not been fully explored thus leading to unreliable results. Therefore, researchers have been looking for alternatives and have identified computational fluid dynamics/discrete element method as a promising solution.

To this note, Zhejiang University scientists: Chenshu Hu (PhD student), Professor. Kun Luo, Shuai Wang (PhD student), Dr. Liyan Sun and Professor Jianren Fan from State Key Laboratory of Clean Energy Utilization investigated biomass fast pyrolysis in a fluidized bed. Additionally, they further investigated the effects of the gas velocity and particle shrinkage on the behaviors of the gas-solid phases. In particular, they developed a computational fluid dynamics/ discrete element method for simulation purposes. Their research work is currently published in the research journal, Industrial and Engineering Chemistry Research.

Briefly, the research team commenced their work by cross-examining the computational fluid dynamics/discrete element method coupling method. Next, temporal and spatial characteristics of the biomass particles were analyzed taking into consideration different conditions involving heat transfer, entrainments behavior, chemical reactions, and movements. Additionally, experimental data from literature was used to validate the simulations results.

From the simulations and experiments, the authors observed that the shrinkage patterns exhibited significant effects on the entrainment behaviors and minor effects on the product yields. The analysis also showed that after shrinkage, the entrainment velocity increased with the increase in the particle size. As a result, the constant size and constant density shrinkage patterns lead to shortest and longest residence time, respectively. Furthermore, it was worth noting that the temporal characteristics of the biomass pyrolysis were hardly affected by the superficial gas velocity specifically in terms of chemical conversion and heat transfer. However, it significantly affected the spatial properties of the pyrolysis process.

In summary, the study by Zhejiang University researchers successfully presented the use of computational fluid dynamics/discrete element methods in the analysis of the biomass pyrolysis processes thus overcoming challenges witnessed in the previous techniques like two-fluid models. Generally, the influence of model parameters and different fluidized bed conditions are uncovered. Altogether, the proposed framework offers a promising solution in enhancing the use of biomass energy as a way of reducing the dependence on fossils fuels, which is a key environment pollutant.

About the author

Chenshu Hu received his bachelor degree from Zhejiang University in June 2014. Currently, he is a doctoral candidate in the State Key Laboratory of Clean Energy Utilization at Zhejiang University under the guidance of Prof. Kun Luo and Prof. Jianren Fan. As a visiting student, he worked with Prof. Ahmed F. Ghoniem to study the particle clustering in the non-cohesive particulate system in Massachusetts Institute of Technology in 2018.

His work focused on the simulation of reactive dense gas-solid flows and the model development in different methods (i.e., PR-DNS, CFD-DEM, TFM, coarse-grained CFD-DEM and MP-PIC). He has written over 15 refereed publications. His research has contributed to a better understanding on the meso-scale structures, mixing behaviors, and interplays among hydrodynamics, heat transfer and chemical reactions in a variety of fluidized bed applications.

About the author

Kun Luo is a full professor in the State Key Laboratory of Clean Energy Utilization at Zhejiang University, China since 2010. He received his B.S.E. from Wuhan University in 2000, and his Ph.D. from Zhejiang University in 2005. From 2007 to 2009, he worked at the Center for Turbulence Research, Stanford University as a postdoctoral fellow.

Prof. Luo’s research centers on Computational Energy Sciences with high-fidelity simulations on complex multiphase flows and combustion in energy and power system. He and his students have developed a number of algorithms, codes, and multi-physics simulation platforms for studying reacting/non-reacting two-phase flows towards efficient and clean energy utilization. In these endeavors, Prof. Luo has undertaken over 10 projects as the principal investigator, and authored or co-authored more than 150 technical papers in international peer-review journals. Prof. Luo has won the Distinguished Paper Award from the 33rd International Symposium on Combustion and the Wu Zhonghua Excellent Young Scholar Award from Chinese Association of Engineering Thermal Physics in 2011.

He is an Associate Editor of the Canadian Journal of Chemical Engineering, an Editorial Board member of International Journal of Spray and Combustion Dynamics, and an Editorial Advisory Board member of International Journal of Multiphase Flow.

About the author

Shuai Wang obtained his Bachelor degree in Zhejiang University China, and now he is a PhD student in Zhejiang University China. His research area was around multi-scale modeling of biomass gasification in dense reactive fluid-particle systems.

His research has yielded drastic improvements to CFD-DEM methods, which enable scientists to predict flow dynamics, heat transfer, and chemical reactions of gasification processes in fluidized bed reactors. He has over 15 publications, spanning across a wide range of challenges facing fluidization, pyrolysis, gasification, combustion and data-driven algorithms.

About the author

Liyan Sun obtained his Master degree and PhD degree in Thermal Engineering in Harbin Institute Technology and worked at Zhejiang University. His research area was around the multi-phase flow behavior and reactive characteristics of the chemical engineering reactor and make good understanding and insight of the operation process.

Dr. Sun further expanded his research expertise to the numerical simulation and the development of numerical model. More than 16 relating papers has been published about this research area. Dr. Sun is currently a main international project member for developing novel combustion technology and controlling the emission.

About the author

Jianren Fan is a Cheung Kong Scholar Professor in the Department of Energy, Zhejiang University. He received his B. S. degree from Xi’an Jiaotong University of China in 1981 and PhD degree from the Department of Mechanical Engineering, Technical University of Vienna, Austria in 1984. His current research includes numerical simulation and experimental studies on gas-solid two-phase flows and combustion. Direct numerical simulation (DNS), large eddy simulation (LES) and PIV techniques are developed to investigate turbulent coherent structures, particle dispersion, spray atomization, turbulence modulation, particle-particle interactions, heat/mass transfer and chemical reaction in turbulent flows. Theoretical and experimental investigations of nano-fluid and fuel cell have also been performed.

He is a Member of Board of Directors of the Chinese Society of Thermophysics, a Member of Editorial Board of Frontiers of Energy and Power Engineering in China, Journal of Hydrodynamics, Journal of Engineering Thermophysics, and Journal of Zhejiang University (Science). He was awarded the Second-classs Prize of the National Natural Science of China in 2005.

Reference

Hu, C., Luo, K., Wang, S., Sun, L., & Fan, J. (2018). Computational Fluid Dynamics/Discrete Element Method Investigation on the Biomass Fast Pyrolysis: The Influences of Shrinkage Patterns and Operating Parameters. Industrial & Engineering Chemistry Research, 58(3), 1404-1416.

Go To Industrial & Engineering Chemistry Research

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