# Study on the Combustion Behavior and Kinetic Characteristics of Semi-Coke from Oil Shale
## 1 Introduction  
With the depletion of conventional fossil energy resources, the development and utilization of unconventional energy sources have gradually become a global research focus in the energy sector. Oil shale, as an unconventional energy resource with abundant reserves and widespread distribution, has attracted considerable attention due to its ability to generate shale oil, semi-coke, and combustible gases during pyrolysis [1]. Among these products, semi-coke is the primary solid residue after oil shale combustion, containing a substantial amount of residual carbon and inorganic mineral components. Given its relatively high calorific value, combustion utilization has become a crucial step in achieving the comprehensive development of oil shale resources. However, the combustion behavior and kinetic characteristics of oil shale semi-coke are significantly influenced by its complex physicochemical composition and structural properties, which differ markedly from conventional coal combustion, necessitating further in-depth investigation [2]. The combustion characteristics of oil shale semi-coke determine its actual performance in energy utilization, including combustion efficiency, energy release rate, and pollutant emission characteristics. The combustion process of semi-coke not only involves the oxidation and decomposition of carbonaceous materials but also includes the thermal decomposition and interactions of inorganic mineral components, leading to complex multiphase and multi-step reaction kinetics [3,4]. Furthermore, due to variations in geological conditions and composition, oil shale from different regions exhibits significant differences in the combustion behavior of its semi-coke, highlighting the importance of region-specific kinetic studies. Currently, the research on the combustion behavior of oil shale semi-coke primarily employs thermogravimetric analysis (TGA) techniques, which monitor mass changes with temperature to reveal combustion characteristics and reaction patterns. Additionally, model-free methods (such as the OFW method and KAS method) [5,6] and model-based methods (such as the Coats-Redfern method based on reaction mechanism functions) have been utilized to fit and calculate kinetic parameters, providing a theoretical foundation for combustion process simulation and optimization. Despite the existing studies on the combustion characteristics of oil shale semi-coke, several issues remain unresolved. Significant discrepancies exist in the fitting performance of different kinetic models on experimental data, making it necessary to further explore suitable models for accurately describing the combustion process of oil shale semi-coke [7]. The combustion process of oil shale semi-coke generally includes stages such as volatile release and oxidation, residual carbon oxidation, and mineral decomposition, yet the reaction mechanisms and kinetic behaviors of each stage have not been systematically analyzed [8]. Moreover, due to regional variations in the physicochemical properties of oil shale semi-coke, studies on the regional characteristics of its combustion behavior and kinetic patterns are of great significance. To address these issues, this study focuses on the semi-coke of a typical oil shale from a specific region. Through thermogravimetric analysis (TGA) experiments, the combustion characteristics of the semi-coke are investigated, and kinetic parameters are determined and compared using both model-free and model-based methods [9,10]. Recent studies have investigated the combustion behavior of oil shale semi-coke using both thermogravimetric analysis (TGA) and pilot-scale combustion systems. For instance, [PERSON] et al. (2011) explored the oxidation characteristics of semi-coke derived from oil shale under various atmospheres, revealing its multi-stage combustion behavior [11]. [PERSON] et al. (2020) used TGA to determine the kinetic parameters of semi-coke combustion and highlighted the complexity of its reaction mechanisms [12].