Gavin Wiggins's research while affiliated with Oak Ridge National Laboratory and other places

Publications (15)

Data
Source code for the coupling of MFiX with PyTorch Case files
Article
Full-text available
Coupling particle and reactor scale models is as essential as reactor fluid dynamics and particle motion for accurate Computational Fluid Dynamic (CFD) simulations of biomass fast pyrolysis reactors due to intraparticle heat transfer and chemical reactions controlling conversion time and product distributions. Direct online coupling of a particle m...
Article
Full-text available
It is notoriously difficult to build an accurate universal model for biomass pyrolysis due to its sensitivity to a wide number of critical material attributes such as chemical species and physical sizes. In this work, a biomass pyrolysis kinetics with 32 heterogeneous reactions and 59 species was implemented in an open-source multiphase computation...
Article
Accurate prediction of transport phenomena is critical for VPU reactor design, optimization, and scale-up. The current study focused on the validation and application of a multiphase CFD model within an open-source code MFiX for hydrodynamics, temperature field, and residence time distribution (RTD) simulation in a non-reacting circulating fluidize...
Article
We report results from a multiscale computational modeling study of biomass fast pyrolysis in an experimental laboratory reactor that combined the hydrodynamics predicted by a two-fluid model (TFM) with predictions from a finite element model (FEM) of heat and mass transfer and chemical reactions within biomass particles. The experimental pyrolyzer...
Article
We present a computationally efficient, one-dimensional simulation methodology for biomass particle heating under conditions typical of fast pyrolysis. Our methodology is based on identifying the rate limiting geometric and structural factors for conductive heat transport in realistic biomass particles. Comparisons of transient temperature trends p...
Article
We report results from computational simulations of an experimental, lab-scale bubbling bed biomass pyrolysis reactor that include a distributed activation energy model (DAEM) for the kinetics. In this study, we utilized multiphase computational fluid dynamics (CFD) to account for the turbulent hydrodynam-ics, and this was combined with the DAEM ki...
Article
We report results from computational simulations of an experimental, lab-scale bubbling bed biomass pyrolysis reactor that include a distributed activation energy model (DAEM) for the kinetics. In this study, we utilized multiphase computational fluid dynamics (CFD) to account for the turbulent hydrodynamics, and this was combined with the DAEM kin...
Article
Biomass exhibits a complex microstructure of directional pores that impact how heat and mass are transferred within biomass particles during conversion processes. However, models of biomass particles used in simulations of conversion processes typically employ oversimplified geometries such as spheres and cylinders and neglect intraparticle microst...
Conference Paper
Bubbling fluidized bed reactors are widely used for fast pyrolysis of biomass. Whether one is concerned primarily with interpreting laboratory pyrolysis reactor data or evaluating the potential performance of pilot or commercial scale reactors for liquid fuels production, it is important to be able to accurately relate the spatial mixing characteri...
Article
We present an overview of the new 20 MW(t) wood-fired steam plant currently under construction by Johnson Controls, Inc. at the Oak Ridge National Laboratory in Tennessee. The new plant will utilize a low-temperature air-blown gasifier system developed by the Nexterra Systems Corporation to generate low-heating value syngas (producer gas), which wi...

Citations

... The retort/sweep gas/partial autothermal pyrolysis processes all behave differently depending on the proportion of heat conduction from the walls in the bulk, inert gas convection and pyrolysis gas convection. These are the key parameters that could lead to different types of biochar production [45][46][47]. However, these aspects are beyond the aim of the present work and deserve a full, systematic study. ...
... However, its commercialization is limited due to the multiscale challenges in understanding the complex physicochemical phenomena involved in the conversion process. Physics-based multi-scale modeling is used is a tool to investigate these complex multiscale phenomena simultaneously [25][26][27]. By using moderate pyrolysis (temperature 500 °C, ultimate temperature maintained for 10-20 s)-about 20% of biochar can be obtained. ...
... Recently, particle rocketing due to explosive devolatilization along its longitudinal axis has been observed for small particles in benchtop reactor systems with high temperatures (1200°C), which is evidently due to vapors escaping one end of a particle at high velocities (Llamas et al., 2022). Evidently, anisotropic pore structure and porosity evolution play integral roles in the motion of particles inside of a high-temperature fluidized reactor (Ciesielski et al., 2021;Lu et al., 2021;Llamas et al., 2022;Lu et al., 2022). ...
... A few recent FEM studies on biomass have shown that capturing the shape of biomass is key for accurate thermal transport predictions. 134 Even the surface roughness can impact the surface heat transfer coefficient, depending on the scale and fluid properties. 64 Realistic particle shape and porosity have been used in simulations for both solvent extraction 51 and thermochemical conversion. ...
... This sensor had advantages of small size and lightweight with high resistance for temperature variation. Gao et al. validated the multiphase computational fluid dynamics (CFD) model for biomass pyrolysis vapor catalytically upgrading in a pilot-scale phase reactor system ( Fig. 2) by measuring the pressures (Fig. 3a) and temperatures ( Fig. 3b) [49]. The system included a riser, a regenerator, etc. ...
... Armed with external and internal physical descriptors, we then construct model geometries for finite-element simulations. 2D axisymmetric models are selected here based on their advantages of mathematical simplicity and known agreement with more computationally intensive 3D microstructural models, as validated in prior biomass conversion modeling studies performed by some of us (Ciesielski et al., 2015;Pecha et al., 2018;Thornburg et al., 2020). Characteristic particle Feret lengths and widths/thicknesses (i.e., averaged to radii) are gleaned from Table 1; axisymmetry is enforced along the tall axis of the particle with a separate symmetry boundary condition along its short axis. ...
... Daw et al. [631] investigated the biomass particle residence time distribution in fluidized bed reactors. They characterized simple reactor approximations that can be applied to guide, interpret, and correlate lab and pilot-scale pyrolysis experiments. ...
... Finite element method (FEM) software COMSOL Multiphysics 5.6 was utilized to perform numerical time-dependent simulations. A 2D axisymmetric model describes a finite cylinder, which is more accurate than spherical assumptions of biomass particles 41 and allows for morphologically relevant anisotropic transport. The model incorporates simultaneous multispecies reaction, mass transport, and heat transport equations with convection possible within the particle due to pressure gradients resulting from pyrolysis phase changes. ...
... The combination of kinetics and thermodynamics data enhances the knowledge for the process of biomass conversion and gives information concerning the energy required for conversion increase. The values and models for kinetic and thermodynamic parameters can interfere in the CFD results, improving the adjustment between theoretical and experimental data of a pyrolytic reactor [29]. However, the determination of kinetic and thermodynamic parameters for each biomass, using different models is an important step to enable the optimization of pyrolysis reactors. ...
... It requires dedicated software, such as FDS, WFDS, ANSYS Fluent… [16,17]. A coupling between DAEM and CFD tools was used in [18] to simulate the biomass pyrolysis in a fluidized bed. When considering low temperature ramps such as the ones usually considered in thermogravimetric experiments, the temperature may be supposed uniform within the particle and equal to that of the surrounding gas. ...