A report presents a numerical-simulation study of pyrolysis of biomass in fluidized-bed reactors, performed by use of the mathematical model described in "Model of Fluidized Bed Containing Reacting Solids and Gases" (NPO-30163), which appears elsewhere in this issue of NASA Tech Briefs. The purpose of the study was to investigate the effect of various operating conditions on the efficiency of production of condensable tar from biomass. The numerical results indicate that for a fixed particle size, the fluidizing-gas temperature is the foremost parameter that affects the tar yield. For the range of fluidizing-gas temperatures investigated, and under the assumption that the pyrolysis rate exceeds the feed rate, the optimum steady-state tar collection was found to occur at 750 K. In cases in which the assumption was not valid, the optimum temperature for tar collection was found to be only slightly higher. Scaling up of the reactor was found to exert a small negative effect on tar collection at the optimal operating temperature. It is also found that slightly better scaling is obtained by use of shallower fluidized beds with greater fluidization velocities.
This work was done by Josette Bellan and Danny Lathouwers of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Physical Sciences category. NPO-30164.
This Brief includes a Technical Support Package (TSP).
Numerical Study of Pyrolysis of Biomass in Fluidized Beds
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Overview
The document presents a study on the pyrolysis of biomass particles in a fluidized bed reactor, focusing on the unique behavior of different particle classes based on their size and physicochemical properties. Conducted at NASA's Jet Propulsion Laboratory, the research aims to optimize the yields of tar, char, and gases produced during the pyrolysis process.
The authors, Josette Bellan and Danny Lathouwers, developed a hydrodynamic model that employs a three-fluid model description. This model is grounded in the kinetic theory of granular flows and utilizes inelastic sphere models to account for collisional transfers in high-density regions. By constructing separate transport equations for each particle class, the model allows for independent acceleration and interaction between different size classes, as well as the exchange of momentum and energy with the carrier gas.
The study emphasizes the importance of understanding the distinct behaviors of biomass particles compared to sand, which is typically used in fluidized bed reactors. The researchers identified that the varying properties of biomass necessitate a tailored modeling approach to accurately predict pyrolysis outcomes. They conducted simulations to evaluate the steady-state operation of the reactor and analyzed the assumptions made by previous studies, demonstrating that some of these assumptions were unrealistic.
Key findings from the research indicate that the optimal fluidizing-gas temperature for maximizing tar yield is around 750 K. Additionally, the study notes that scaling up the reactor size has a minor negative impact on tar yield, suggesting that operational parameters must be carefully managed to achieve desired outcomes.
The document also includes various figures and data representations, illustrating the relationships between temperature, tar yield, and differential reaction efficiency. These visual aids support the findings and provide a clearer understanding of the model's predictions.
In conclusion, this study contributes significantly to the field of biomass processing by providing a comprehensive model that accounts for the complexities of particle behavior in fluidized bed reactors. The insights gained from this research could lead to improved methods for biomass conversion, enhancing the efficiency and effectiveness of renewable energy production from biomass sources.
