Abstract
Pyrolysis of solid fuels forms a solid carbon-rich fuel, also called char, whose physico-chemical description is rather complex. Heterogeneous oxidation reactions take place during thermochemical conversion of char. The present work proposes a predictive detailed kinetic model, opening a new path for a deeper understanding of the char conversion process. This model considers porosity, surface area, density of surface sites, and their evolution along the conversion process. The chemical aspects of char oxidation are modeled assuming a carbonaceous bulk structure, surrounded by a variety of surface sites which represent the chemical functionalities typically present in such materials. The heterogeneous chemical reactions and their kinetic parameters are defined based on previous studies in the literature and by analogy to homogeneous gas-phase reactions of aromatic species. A mathematical framework is proposed to couple physical and chemical descriptions of the oxidation process. Although the proposed model benefits from experimental information, it is able to comprehensively describe the conversion rate of a broad range of carbonaceous materials such as carbon nanotubes, graphite, and chars only on the basis of their elemental composition. The proposed model represents a first step in exploring the explicit and coupled treatment given to the physical and chemical evolution of the fuel throughout its conversion, allowing us to consistently describe the particle evolution, opening a path for reliable models to manage the chemistry of char conversion.
Highlights
Biomass is increasingly being recognized as a promising carrier for heat, energy, and chemicals production
The most advanced char conversion models available consider a limited degree of complexity in chemical kinetics.[17−23] A more complex chemical description was formulated by Haynes and co-workers,[24,25] defining the concepts of turnover models for char oxidation, and explaining how surface reactions expose unreactive carbon to the gaseous environment
A predictive particle-based model coupling physical and chemical descriptions was developed to describe the heterogeneous oxidation of biochar
Summary
Biomass is increasingly being recognized as a promising carrier for heat, energy, and chemicals production. The most advanced char conversion models available consider a limited degree of complexity in chemical kinetics.[17−23] A more complex chemical description was formulated by Haynes and co-workers,[24,25] defining the concepts of turnover models for char oxidation, and explaining how surface reactions expose unreactive carbon to the gaseous environment. In this case the reactivity of different structures is described by means of a continuous distribution of activation energies. No further information is required, even though the model takes advantage of specific measurements such as intrinsic surface area, density of surface sites, and skeletal density, when available
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