Review on Modelling Approaches Based on Computational Fluid Dynamics for Biomass Pyrolysis Systems

Abstract

Modelling is a complex task combining elements of knowledge in the field of computer science, mathematics and natural sciences (fluid dynamics, mass and heat transfer, chemistry). In order to correctly model the process of biomass thermal degradation, in-depth knowledge of multi-scale unit processes is necessary. A biomass conversion model can be divided into three main submodels depending on the scale of the unit processes: the molecular model, single particle model and reactor model. Molecular models describe the chemical changes in the biomass constituents. Single-particle models correspond to the description of the biomass structure and its influence on the thermo-physical behaviour and the subsequent reactions of the compounds released during decomposition of a single biomass particle. The largest scale submodel and at the same time, the most difficult to describe is the reactor model, which describes the behaviour of a vast number of particles, the flow of the reactor gases as well as the interaction between them and the reactor. This chapter contains a basic explanation about which models are currently available and how they work from a practical point of view.

A meta-analysis of thermo-physical and chemical aspects in CFD modelling of pyrolysis of a single wood particle in the thermally thick regime

“…6) Values of thermo-physical parameters and bio-chemical composition of wood and char used in a specific model (if measured) were used directly from the experimental work or (if not measured or disclosed) matched as close as possible to the wood species from the literature [18]. Within each investigated scenario, models differ with the description of the specific component but not with the parameters.…”

“…Therefore, the gas permeability of poplar char was selected subjectively, taking into consideration the wood anisotropy and correlations in gas permeability between wood and char, which are known for other wood species [18]. The kinetic scheme based on Shafizadeh and Chin (Table S4) was used in the model.…”

“…However, the thermal conductivity of wood in the radial direction was selected to be higher by 20% than the value obtained from the sourced study, with the presumption that such change is in agreement with the literature [31,67,79,80]. Gas permeability in wood was selected from Comstock [22], and gas permeability in char, as in Section 3.1.1., was selected subjectively, taking into consideration the change in gas permeability between wood and char, which are known for certain wood types other than poplar [18]. The initial concentration of the lignins [55] (H-rich, O-rich and C-rich lignin) needed for the detailed kinetic schemes was calculated with split parameters, according to Cobretta et al [31].…”

“…Numerous reviews can be found in the literature about the pyrolysis of single woody particles and its modelling. However, they mostly focus on the assessment of the accuracy of specific models and not on the general impact of the implemented model's components like directional dependency, relationships between parameters and kinetic schemes [7,8,[14][15][16][17][18][19][20][21][22][23].…”

“…In this study, the commonly used practice of calibration of model parameters was not applied to fit the experimental data. Instead, the chemical and thermophysical properties of wood for each step model were selected meticulously and with to highest possible accordance with the real properties of the woods of the experimental research (directly taken from the work or matched to the wood species from the literature [18]). Then, into the step model, the different descriptions of the investigated phenomena was implemented, and their result was compared to find the best possible description.…”